Polymer suspension based shear inspissating fluid-fabric for protective applications was a new thought. Shear inspissating fluid was besides known as STF. Generally STF contains liquid medium and solid atoms which can be inorganic or organic based. Basically, the viscousness of the Shear Thickening Fluid ( STF ) will be increased when shear emphasis increasing. By working this unstable distortion from STF, for the cloth itself, the clash between yarn-yarn and fiber-fiber will be increased drastically when force applied over the fabric complex. Then, the cloth itself will be holding higher energy soaking up when STF impregnated with the cloth itself compared with un-impregnated fabric complex.
The ground for this choice was motivated by old plants in this country, every bit good as the good features provided by these two stuffs. US Patents 5599290 and 5545128 have developed Bone break bar garment and method ” . In these two plants, carried out by the same writers, the patent outlines a design used to decide the issue of the harmful effects of impacts on the castanetss of aged persons. This design was described as being composed of the followers: “ the constituent includes a dilatant stuff that was comparatively stiff near the clip of impact and comparatively fluid at other times. In a preferable incarnation, the innovation provides a hip tablet, possessing a thickness little plenty to be compatible with wearer acceptableness, that conforms to the form of the organic structure during mundane activities such as walking, sitting, and sleeping, and was therefore comfy to the wearer ” ( 5-14 ) .
In order to pattern the rheological behaviour of these fluids, it has been proposed to utilize a power jurisprudence analysis with the relationship between the viscousness and shear rate represented by
I· = K yn-1
Where K is the fluid ‘s consistence and N is the power jurisprudence advocate particular to the part of high or low viscousness. Harmonizing to Barnes, the shear-thinning and shear-thickening parts can be accounted for by, “ utilizing the amount of two power Torahs, with one value of N less than integrity and one greater ” . ( 8 )
The rheology studied will be focused on colloidal suspension instead than difficult atom suspension. Hard atom suspension like silicon oxide atom, was extensively studied by many researched over the universe like Wagner and Lee Barnes ( 5 – 8 ) .They claimed, the difficult atom suspended in the polythene ethanediol ( bearer fluid ) will exhibit shear inspissating behaviour by changing the volume fraction of the atom over bearer fluid from, above 40 % to 55 % . 30 % by volume fraction will non exhibit shear inspissating behaviour but in Ragvahan experiments showed ( 10 ) , by utilizing 10 % volume fraction of fumed silicon oxide suspended in the Polypropylene ethanediol ( PPG ) , shear inspissating behaviour had occurred but probably referred to particle agglomeration ( flocculated gel ) instead than “ hydrocluster ” because fumed silicon oxide, of course have low surface country and larger atom size. In the experiment, the oncoming passage called critical shear rate seems holding two points, the higher and the lower shear strain, due to the original construction of the bearer fluid itself ( polypropylene ethanediol ) . The formation of vinyl group and heterosexual concatenation in PPG gave two formations of bunchs ( 10 ) .
Colloidal suspension survey was non emphasized and exhaustively studied because of the complexness of the colloidal system itself, which usually involved many factors such as steric and electrostatic stabilize, stableness of the suspension and the formation of the hydrocluster via alteration of the interaction atom of the colloidal suspension. In chapter 2, theoretical treatment about colloidal suspension which contributed to the new phenomenon of Shear Thickening Fluid ( STF ) such as structure-relationship of the colloidal suspension in polymer solution and Solid/Liquid passage ( SLT ) and besides liquid/Solid passage ( LST ) [ 17 ] . Harmonizing to the DVLO theory, stabilisation of atom in the suspension with steric and electrostatic ( will be hold detailed account in the chapter 2 ) charges are of import parametric quantities to be investigated. The colloid atoms were besides known as surface charge atom. It involved the attractive force and abhorrent force for every individual atom in the colloid scattering or suspension, which contributed to the shear inspissating behaviour of the STF.
In this paper, colloidal suspension rheology will be chief subjects, by associating it with the structure-relationship and LST theory. In the chapter 2, more elaborate oncoming passage of STF will be extensively discussed. Conventionally, the onset passage involved Order-Disorder passage ( ODT ) and hydrocluster.
The chief standards in Shear Thickening Fluid ( STF ) were to foretell critical shear rate which was the critical point when the atoms were suspended in the STF. It started to constellate with each other, exhibiting shear inspissating behavior upon addition in shear rate. There were many factors in STF, some of them were, volume fraction dependance ( between atom and bearer fluid ) , atom form and size dependance ( porousness ) and particle interaction dependance. The atoms can be normal charge ( difficult atom such as fumed silicon oxide, clay and any metal oxide atom ) or colloidal atom ( with charge ) .
In this paper, fumed silicon oxide will be used as a chief stuff for difficult atom every bit good as and colloid scattering. Fumed silicon oxide will be turned into colloidal suspension by environing the charging over its surface atom. The chief principal of colloidal suspension for this survey was based on DVLO theory. Therefore, by analyzing the electrokinetic for each suspension, relation between this survey with mensural rheology through the power jurisprudence index and output emphasis value, there are possibilities to associate the structure- relationship in colloidal suspension of STF with onset passage ( SLT & A ; LST ) evaluated. There were two basic demands for exhibiting shear inspissating behaviour from colloidal suspension [ raghavan, Wagner, barnes ] , foremost, the volume fraction of the solid in the suspension must be really high and secondly, suspension must be nonflocculated or deflocculated
STF Fabric complex will be impregnated with STF has great possible in slug cogent evidence application particularly for soft armour. The waistcoat will be holding higher flexibleness and less heavy than conventional soft armour. Wagner and his squad claimed, STF will increase the clash between yarn-yarn and fiber-fiber by 500 % utilizing pull out yarn trial. Besides, by utilizing NIJ as mention stabbed and puncture opposition trial ( NIJ 115.00 ) for STF Fabric complex, it easy passed degree 1 protection. For the slug trial, besides NIJ as mention, it showed interesting consequences. Alternatively of higher incursion from the slug ( 9mm ) to the conventional fabric complex, for STF-Fabric composite, slug was deflected off ( recoil ) and had less important grade over the top of the clay in tried frame panel. Basically, fabric complex will be placed over the top of the clay. The grade of the clay will be used as mention for the debauched energy ( energy soaking up ) from the trial. A bigger diameter of the grade and the deepness for the grade was deeper bespeaking the cloth complex has a low dissipated energy system. Smaller diameter of the grade and less deepness of the indented clay, showed, a higher dissipated energy system for the fabric complex.
1.2 Problem Statement
Wagner found that STF had rheological feature of dilatant but studied on the usage of difficult atom in suspension. Colloidal suspension of smoke silicon oxide in polymeric aqueous media was performed by other research worker but they studied merely ionic strength and critical shear rate consequence. In deepness survey on formation of hydroclusters in colloid demand to measure to associate construction relationship between shear inspissating behaviour of polymer suspension with respect to composing ( volume fraction ) , atom porousness, size and form of atom. Hence, viscousness measurings were evaluated for different polymer systems to find the consequence of these systems on critical shear rate and shear inspissating phenomena. Stabbed and puncture immune fabric composite using STF with high spike and knife impact public presentation can be affected by the preparation of STF and adhesion between STF suspension and cloth narration. Hence, this survey is hoped to work out the jobs faced by indepth understanding on rheological and public presentation facets in the development of STF fabric complex for protective applications.
1.3 Significant
1.4 Aims Of Study
The specific aims of the undertaking include: –
To find physical colloid belongingss of colloidal suspension from difficult sphere atoms and colloidal scattering via zeta possible surveies.
To find the rheological behaviours of the colloidal suspension from the effects of repulsive force system present during steady shear experiments.
To manufacture STF fabric composite utilizing assorted beds of Kevlar 49 and cotton cloth and find pang and puncture opposition of STF cloth complex harmonizing to standard NIJ 115.00 trials.
Mentions
Bazhenov, S. ( 1997 ) . Dissipation of Energy by Bulletproof Aramid Fabric. ” Journal of Materials. Science, 32, 4167-4173.
Cunniff, P. ( 1992An Analysis of the System Effects in Woven Fabrics Under Ballistic Impact, Textile Research Journal, 62, 495-509
3. Egres Jr. , R. ( 2005 ) . Stab public presentation of shear inspissating fluid ( STF ) -fabric compositesfor organic structure armour applications. International SAMPE Symposium and Exhibition, 50, 2369-2380.
4. Lee, Y. ( 2003 ) . The ballistic impact features of Kevlar woven cloths impregnated with a colloidal shear inspissating fluid. Journal of stuffs scientific discipline, 38 ( 13 ) , 2825-2833
Maranzano, B.J. and Wagner, N.J. , ( 2001 ) The effects of interparticle interactions and atom size on reversible shear thickener: hard-sphere colloidal scatterings, Journal of Rheology, 45 ( 5 ) , 1205-1222, 2001
Maranzano, B.J. , Wagner, N.J. , Fritz, G. , Glatter, O. , ( 2000 ) Surface charge of 3- ( trimethoxysilyl ) propyl methacrylate ( TPM ) coated Stober silica colloids by zeta-phase analysis visible radiation dispersing and little angle neutron sprinkling, Lagmuir 16, 10556-10558.
Maranzano, B.J. , Wagner, N.J. ( 2001 ) , the effects of atom size on reversible shear thickener of concentrated colloidal scatterings, J. Chem. Phys. 114 10514-10527.
Barnes HA ( 1989 ) Shear-thickening ( ”dilatancy ” ) in suspensions of
nonaggregating solid atoms dispersed in Newtonian liquids. J Rheology, 33, 329-366
I.F.Efremov, The Dilatancy of Colloidal Structures and Polymer Solutions Translated from Uspekhi Khimii, 51 285-310 ( 1982 ) , Russia Chemical Reviews, 51 ( 2 ) , 1982
SRINIVASA R. RAGHAVAN AND SAAD A. KHAN Department of Chemical Engineering, North Carolina State University, Raleigh, North Carolina 27695-7905
G. Fritz, B. J. Maranzano, N. J. Wagner, N. Willenbacher 2002, High frequence rheology of difficult sphere colloidal scatterings measured with a torsional resonating chamber, Journal of Non-Newtonian Fluid Mechanics, 102, 2, pp 149-156
J. Schuster, D. Heider, K. Sharp, M. Glowania, 2008, Thermal conductions of three-dimensionally woven cloth complexs Composites Science and Technology, 68, 9, pp 2085-2091
Young Sil Lee Norman J. Wagner Dynamic belongingss of shear inspissating colloidal suspensions Rheol Acta ( 2003 ) 42: 199-208
Hoffman RL ( 1974 ) Discontinuous and dilatant viscousness behaviour in concentrated suspensions. II. Theory and experimental trials. J Colloid Interface Sci 46:491-506
Hoffman RL ( 1997 ) Explanations for the cause of shear thickener in concentrated colloidal suspensions. J Rheology 42:111-123
Egres, R.G. , Lee, Y.S. , Kirkwood, J.E. , Kirkwood, K.M. , Wetzel, E.D. , and Wagner, N.J. 2003. “ Novel flexible organic structure armor utilizing shear-thickening fluid ( STF ) composites. ” Proceedings of 14th International Conference on Composite Materials. San Diego, CA.July 14 – 18, 2003.
Horst Henning Winter et. Al: Rheology of Polymers near Liquid-Solid Passages
Chapter TWO
LITERATURE REVIEW
2.1 Shear Thickening Fluid ( STF ) : Introduction & A ; Review
Shear inspissating fluid, fundamentally have two different types of fluid behaviour shear cutting and shear thickener. There are two types of shear inspissating behaviour in the fluid behaviour. First, Shear thickener is a non-Newtonian flow behaviour ( dilatant ) observed as an addition in viscousness with increasing shear rate or applied emphasis besides known as clip independent stuff ( Barnes, 1989 ; Maranzano and Wagner, 2001 ; Lee and Wagner, 2003 ) . Non-Newtonian flow behaviour ( rheopectics ) observed as an addition in viscousness with increasing continuance of emphasis ( shear rate invariable ) known as the clip dependent stuffs which have a memory to deform over period of clip ( figure 1 ) .
FIGURE 1
Show the Various Types of Flow
Concentrated colloidal suspensions dwelling of solid/hard domains atoms dispersed in a bearer liquid have been shown to exhibit rheological shear inspissating behavior ensuing in big, sometimes discontinuous additions in viscousness above a critical shear rate. This passage from a fluxing liquid to a solid-like stuff is due to the formation of shear induced transient sums, or “ hydroclusters, ” that dramatically increase the viscousness of the fluid ( Barnes, 1989 ; Maranzano and Wagner, 2001 ; Lee and Wagner, 2003 ) . For stabilise the STF and avoiding agglomeration behaviour, co-solvent is added and it must be done because STF has a really strong molecule interaction between atoms and bearer fluid ( attraction force ) instead than abhorrent force when force is applied at specific clip ( critical shear rate and critical shear emphasis ) [ Barnes, 1989 ; Maranzano and Wagner, 2001 ; Lee and Wagner, 2003 ] .
FIGURE 2
Shows the Curve of The Shear Thickening Fluid when the Shear Stress Applied on the Material
The Shear Thickening Fluid ( STF ) is the combination of the atoms suspended in the bearer fluid. Figure 2 showed the STF curve when shear emphasis applied on the stuff. The atoms used can be made of assorted stuffs, such as Silica Dioxide or other oxides, or polymers such as Polystyrene ( PS ) or Polymethyl methacrylate ( PMMA ) , or other polymers from emulsion polymerisation. Generally, atoms can be in assorted forms like spherical, egg-shaped, disk-like or clay atoms ( Barnes, 1989 ) .
The atoms can be stabilized in solution or dispersed by charge, Brownian gesture, grafted polymers and others. Then, pH value of a suspension besides contributed to the stableness of suspension via colloidal status such as steric repulsive force and electrostatic system. The effects of pH value, concentration of the wetting agent, and ionic strength of the wetting agent are major factors for the colloidal suspension. This influence parametric quantity is due to the agglomeration atom size ( F. Rey, M.A. Ferreira et Al. 1995 ) .These are basic parametric quantities in the rheological suspension and colloidal suspension system. Many surveies of shear inspissating fluid system ( Barnes 1989, Hoffman 1998, Wagner 2004 ) , focal point on the colloidal particles merely such as nanoparticles colloidal silicon oxide and monodisperse silicon oxide, which is it is good known as a really stable single atom interaction in the suspension [ Brownian suspension ] .
In this paper, electrostatic stabilize and steric repulsive force system is used to command the interparticles interaction in the rheological suspension. Electrostatic stabilize is less surveies due to the complexness in the rheological suspension. Concentration and ionic strength of the wetting agent are the chief parametric quantity of this paper and the concluding pH value is critical measured in order to exhibit rheological shear inspissating. F. Rey, and M.A. Ferreira in their paper “ Effect of concentration, pH, and ionic strength on the viscousness of solutions of a dirt fulvic acid ” claims, all the parametric quantity in this surveies showed the dramatic instant consequence of the suspension due to the gel point of the suspension or good known as isoelectric point ( iep ) by seting H+ nowadays in the rheological suspension. in add-on of steric repulsive force system, doing a barriers for the single surface atom is a purpose in this paper. The dual beds of the barriers ( thickness ) due to the zeta potency and electrokinetic theories are independent from the shear emphasis during rheological experiments. Because of the chief purpose of this paper are to find the factors affecting onset passage of the STF due to the interparticle interaction dependance which are closely related to the colloidal suspension rheology and the effects of the onset passage ( rheological behaviour ) for the pang and puncture opposition trial of fabric complex.
Then, the co-solvent that are used, it can be aqueous in nature and non-aqueous which can be chosen to stabilise suspension system The co-solvent should be environmentally stable like ethyl alcohol and methyl alcohol, so that, they remain built-in to the cloth and suspended during service. Another map of co-solvent is to take down the viscousness of the STF, so that impregnation procedure of fabric composite becomes efficient and easy. By seting the viscousness of the STF, areal denseness of concluding cloth complex can be alter and besides monitored. The atoms must acquire through and suspended in the fiber-fiber and yarn-yarn [ Lee Wagner et Al 2003 ] . The consequence from the good impregnation procedure is the clash force between yarn-yarn and fiber-fiber will be increased [ Lee Wagner et Al 2003 ] .
But in this paper, by utilizing information from Wagner and other research workers, a fluctuation of the drying temperature for the STF and STF- cloth complex will be designed and tested via thermic debasement technique ( pre-degradation ) and swelling behaviour of the STF-fabric complex after at the different drying temperature. The thought are to avoid pre-degradation part and swelling behaviour of the STF in the drying procedure which is believed will cut down the public presentation of the cloth complex due to the undermentioned factors, debasement of the STF and STF-fabric composite due to the drying temperature and swelling behaviour of STF. By combination those factors, believed, the internal clash between fiber-fiber and yarn-yarn will be reduced which is doing inefficiency of energy absorbtion or dissipated energy for fabric complex ( Wagner 2004 ) .
2.2 Mechanism of Shear Thickening Fluid ( STF )
The mechanism of STF usually can be described via hydrocluster theory and order-disorder theory. The similiarity of these theories is a thought of a new macrostructure formation occurred, moreover, it are closely related to rheological experiments such as temperature and clip factors. A few research workers like Barnes ( 1989 ) , Hoffman ( 1998 ) and Wagner ( 2004 ) , claimed colloidal factors such as different types of bearer fluid, particles porousness, and volume fraction of atom suspended. But, these two theories still ca n’t explicate in item about the mechanism of STF. Wagner and his squad claimed the formation of hydrocluster must be a deflocculated suspension and major parmaters of STF are volume fraction, interparticle interaction, and atom porousness. A new theoretical passage will be proposed for STF behaviour. Liquid-Solid passage ( LST ) or semi-solid passage affecting the relaxation province of the fluid during passage which is usually include the alterations of loss and storage modulus during passage and believed new formation of a new macrostructure are formed during rheological experiment. This a new macrostructure formed due to the formation of the attractive force force and repulsive force force in the STF, which is believed closely related with dual bed theories in zeta possible theory. LST theories is based on the passage of the stuff due to the changing of the complex modulus which are can be translated into the formation of gel ( stiffness ) and relaxation province of the stuff during near transiton and at the onset passage.
2.2.1 Hydrocluster
The most related theories to the shear thickener behaviour are the hydrocluster theory. Basically, the hydrocluster will be occurred when the balance force from shearing flow in the concentrated suspension and the force lifting from atom – atom ( interparticles ) interaction ( Bender and Wagner 1995 ) .There are two conditions, foremost via colloidal factors ( steric and electrostatic repulsive force ) and atom interactions between particle-particle and particle-carrier fluid ( Bender and Wagner 1995 ) . Figure 3 showed the formation of hydrocluster, when the applied shear emphasis on the STF.
The formations of hydrocluster are still extensively investigated by research worker in the full universe. The chief involvement of this alone behaviour is the onset passage ( critical shear rate ) from liquid province to solid or gel province. This phenomenon affecting the rapid alterations of fluid viscousness in a 2nd whether applied it with shear emphasis, applied electric field ( mention to the ER fluid ) , and applied magnetic field ( mention to the MR fluid ) . There are specific equipments for sensing of this phenomenon such as optical rheometer, little angle neutron sprinkling ( SANS ) , and two beam light laser dispersing. But with all this equipments, still the formation of hydrocluster is unknown phenomena.
Harmonizing to this theory, at the lower emphasis ( below critical emphasis, maximal volume packing fraction ) interparticle interaction either Brownian gesture or electrostatic, doing the concentrated suspension is easy flow ( shear thinning behaviour and viscousness of the suspension go lower ) due to the atoms slippage in the bearer fluid. As the emphasis is increased, the attractive force forces is somewhat additions than repulsive force force in between atoms of the concentrated suspension ( particles collection become larger and the viscousness of the suspension go higher ) . When the magnitudes of the shearing force are equilibrium to the interparticle interaction, the atoms in the concentrated suspension become “ bunch ” besides known as hydrocluster.
FIGURE 3
Showed the Detailed Formation of Hydrocluster when Applied Shear Stress on the STF. Above Experiment, utilizing Two Different Volume Fractions ( % ) 0.50 and 0.52 with a same Colloidal Particle which is has been suspended in the Ethylene Glycol.
This theory is foremost suggested by Brady ( Bossis and Brady 1989 ) as a consequence from stokesian Dynamics simulation and so, supported by optical rheological experiment by Wagner ( Bender and Wagner 1995 ) . Basically, these phenomenons are closely related with phenomenon of “ Resonance ” in physic. In natural philosophies, resonance is the inclination of a system to hover at greater amplitude at some frequences than at others. These are known as the system ‘s resonating frequences ( or resonance frequences ) . At these frequences, even little periodic drive forces can bring forth big amplitude oscillations, because the system shops vibration energy [ the fundamental of physic 1999 ] .
2.2.2 Order-Disorder Theory
The order-Disorder mechanism is foremost suggested by Hoffman ( Hoffman 1972 ) which obeserved the monodispersed supension under shear generate different forms at critical shear rate ( before and after ) . Harmonizing to this theory, when the suspension is sheared, atoms is ordered in the specific formation ( hexangular or pentangular ) of jammed beds parallel to the plane of shear. After a crtical emphasis is reached, the instabilities in the formation of jammed beds become greater and atoms are out of the formation. Then, these atoms collide and jammed to each other and bring forth in the rise of viscousness.
FIGURE 4
Showed the Diffraction Patterns from Monodisperse Suspension under Shear. ( A ) sample Shear Below Critical Shear Stress. ( B ) Sample Shear above Critical Shear Stress
( Hoffman 1972 )
An illustration of these form can be seen in figure 4 Hoffman monitored the monodispersed suspension under shear and showed that figure 4 ( A ) corresponds to the order formation of the jammed beds while figure 4 ( B ) is disorder or random formation of the jammed beds after critical shear emphasis is reached.
FIGURE 5
Showed the Formation of Packed Layer at earlier and after Critical Shear Stress. Picture ( A ) the Order Formation of the Packed Layersin below Critical Shea Stress. Picture ( B ) the Disorder Formation of the Packed Layers after Critical Shear Stress.
The illustration of the phenomenon for the order- upset formation of the jammed beds that suggested by Hoffman can be seen in figure 5. those formation is captured by the Hoffman by utilizing a simple shear in figure 4 ( A ) is same formation in the figure 5 ( A ) . Hoffman predicted that, those formation occur due to the strong surface bonding in the monodisperse suspension which usually reffered to the H and new wave der waals bond. In figure 5 ( B ) , the upset formation occurs when sample shear above critical shear emphasis. Atom are collide and jam-packed each other and bring forth in rise of viscousness due to the agglomeration of the atoms.
2.2.3 Introduction Liquid-Solid Transition ( LST )
In this paper, a new construct theoretical onset passage of STF will be proposed. The chief thoughts of this theoretical construct are the macrostructure of the fluid are alterations during onset passage from liquid province to the solid or gel province, and liquid- solid passage province which is usually affecting the relaxation province ( ? ? ? ? ? ) . The passage besides can be province as semi-solid passage at the critical shear rate. This paper, besides will be investigated the formation of the passage by utilizing colloidal atoms which are stabilize by utilizing two system, steric and electrostatic repulsive force system.
LST involves many such of factors, such as theory of gelation, ramifying theories, and infiltration theories. All the theory in LST are closely related to the formation of the macrostructure, whether consequence on the temperature environing or over clip.
2.2.3.1 Theory of Gelation
The LST of polymers is besides technically of import since it occurs in about all of the common fiction procedures. Examples are injection casting of semi-crystalline polymers ( where the surface quality of the finished parts may be affected by gelation shear inspissating fluid ( STF ) and processing of crosslinking polymers. Therefore, the oncoming passage for STF can be detected by utilizing LST.
There are several theories in gelation are usually used in LST. First is ramifying theories and 2nd is infiltration theory. The onset passage are really of import to the STF for comparing with the hydrocluster formation theories and order – upset theory and proposed new theoretical thought for the rheological behaviour due to the factors impacting the public presentation of STF such as molecular weight dependance, volume fraction dependance and atom – atom interaction dependance. Those all factors which impacting the public presentation of STF had been discussed in old sub-chapter.
2.2.4 Description of the Phenomena for Shear Thickening Fluid ( STF )
Basically, the phenomenon of STF is investigated by utilizing a batch of parametric quantity in the last two decennaries. Volume fraction, atom porousness and interparticle interaction dependance is a major parametric quantities for STF. In this paper, molecular weight of bearer fluid is added in the STF ‘s parametric quantity, in order to increase the possible parametric quantity for the STF ‘s phenomenon.
2.2.4.1 Volume Fraction Dependence
Volume fraction factor is the chief parametric quantity in the shear thickener fluid [ STF ] . In general, a solid or difficult atom which is suspended in the bearer fluid such as ethene ethanediol, polythene ethanediol or other bearer fluid which are aqueous in nature or non-aqueous in nature can exhibit shear inspissating behaviour at the minimum scope of volume fraction in between 30 % to 49 % . Above 50 % of volume fraction, the rheological shear inspissating behaviour can be measured at lower shear rate but it depending on the complex viscousness of the suspension which is it is related to another parametric quantities like atom size and porousness. Meaning, surface country and aspect ratio of the atom are greater influenced on the concluding viscousness of the STF.
One parametric quantity that has a immense consequence on the critical shear rate is the volume fraction. At low volume fractions ( below 0.5 ) , shear thickener is either less dramatic or non important [ Word picture of Shear-Thickening Fluid-Filled Foam system for Use in Energy Absorption Devices, Jose 2004 ] .
Wagner and his squad besides claims, colloidal silicon oxide ( 14nm ) which is suspended in the polythene ethanediol, less than or 30 % volume fraction of STF will bring forthing less or no important of inspissating behaviour either at low shear rate or higher. Raghavan and khan which analyzing the rheological behaviour of fumed silicon oxide suspended in low molecular weight polypropene ethanediol claim, non-flocculated suspension exhibit shear thickener at 10 % [ w/w ] under steady flow and strain-thickening under oscillating shear. Strain-thickening refer to the disconnected addition in the complex modulus [ complex viscousness ] .
Fumed silica by and large known has higher agglomeration size up to 140 micrometer. Therefore, volume fraction has less important affected on the shear thickener behaviour. The agglomeration size is the chief factor in the Raghavan and Khan surveies ( figure 2.2.4 ) .
The consequences of Barnes demonstrate that at volume fractions in the scope of 50 % , the shear thickener behaviour is expected and predictable. In add-on, theoretical analysis of the maximal volume fraction of monodispersed suspensions predicts this value is Omax=0.605, where this value corresponds to, “ the volume fraction for a cubically stacked hexangular wadding ” ( Boersma et al. 1989 ) .
2.2.4.2 Molecular Weight of the Carrier Fluid Dependence
Molecular weight of the bearer fluid is a new parametric quantity in the STF. Wagner and his squad reported that the viscousness of the bearer fluid is of import to foretell the oncoming passage from shear thinning to the shear inspissating behaviour in the STF. A trouble occurs from acquiring exacts experimental measuring of the consequence of bearer fluids due to the world that altering the bearer fluid affects the interparticles interaction. In this paper, by supervising the zeta potency of the bearer fluid, those two effects ( molecular weight dependance and Particle-Particle Interaction Dependence ) can be separated.
The onset passage of STF will be a chief index for this parametric quantity neither the suspension are flocculated or deflocculated. The thought of used difference molecular weight is cames from colloidal suspension which prepared by raghvan, in his experiment polypropene ethanediol ( PPG ) as a chief bearer fluid. He are experimental the consequence of the rheological behaviour for fumed silicon oxide suspended in PPG at lower concentration ( aggregate fraction ) , and showed the STF behaviour at low output emphasis ( figure 6 ) . The experiment by raghvan is difference from Wagner and barnes, which used colloidal atom from Nissan Chemicals ( MP4540 ) and suspended in PEG 200 at high concentration for exhibit shear thicknening behaviour ( figure 6 ) .
FIGURE 6
Viscosity as a Function of Shear Rate for Colloidal Silica Stf ( A ) and Fumed Silica Stf ( B ) at Assorted Particle Loadings.
Therefore, when turnable fumed silica atom into colloidal fumed silica via steric and electrostatic repulsive force system, suspended it in the different molecular weight of bearer fluid at assorted atom burdens, believed, the suspension will exhibited shear inspissating behaviour at low output emphasis.
2.2.4.3 Particle-Particle Interaction Dependence
Interparticles interactions are really of import in finding the shear inspissating behaviour of a suspension. Flocculated suspension will non exhibit shear thickener ( Barnes 1989 ) , but alternatively they will demo shear cutting, as shown in figure 7.
FIGURE 7
Represented the Effect of Particle-Particle Interaction on the Flow Behavior of a Suspension.
Basically, the flow behaviour of a suspension is highly affected by interparticle interaction. These phenomenons besides refer to the concluding status which refers to the pH value of a suspension. Therefore in table 1, the Floc sizes are monitored due to the consequence of pH value, electrolytes, and polymer on a china clay suspension. Because of flocculation is expected to get down at lower pH values, viz. border to face that china clay is positively charged and de-flocculation at higher pH values it carries a net negative charge on the surface. ( Nongkhran Chaiwong 2008 ) .
Table 1
Floc Size of Kaolin Flocculation as Function of pH, Electrolytes and Polymers.
The flocculation of china clay depended on pH, electrolytes and polymers flocculants. Floc size and floc strength increased with increasing of cation valency in the electrolytes and increasing of molecular weight in the polymers ( Nongkhran Chaiwong 2008 ) .
The information that gathered from table 1 is of import for the colloidal suspension and STF. The shear inspissating behaviour of a suspension must non hold flocculation, from that ground, supervising a suspension by avoiding flocculation is necessary.
2.3 Colloidal Suspension Rheology
In this paper, the rheological surveies of Shear inspissating Fluid ( STF ) are concentrating on the colloidal particles. The Scopess of surveies are focused on the non-Newtonian fluid behaviour such as viscousness, power jurisprudence index, tangent teta, and modulus of the STF.
2.3.1 Viscosity
There are a tonss of definition of viscousness, mensurating the internal clash of fluid is a simple account. The clash becomes evident when a bed of fluid is made to travel in relation to another bed. The greater the clash, the higher sum of force required doing this motion, and it is called “ shear ” .
Isaac Newton defined viscousness by sing the two parallel flat a distance “ dx ” and are traveling in the same way at different speeds. The premise by Isaac Newton, required force in order to stabilise or keep is relative to the difference in velocity through the liquid, or the speed gradient ( dv/dx ) . To show this, Newton wrote in equation and besides can be illustrated in figure 8:
( 1 )
Where viscousness is a changeless for a given stuff and is called its “ Viscosity ” . The speed gradient is a step of the alteration in velocity at which the intermediate beds move with regard to each other. It describes the shearing the liquid experiences and is therefore called “ shear rate ” . This will be symbolized as “ Y
“ and its unit of step is called the “ mutual second ” ( sec-1 ) .
Brookfield viscosimeter is used to find the viscousness ‘s value of the STF. By utilizing particular little sample arranger from BROOKFIELD and helped from Brookfield ‘s agent in Malaysia, finding value of the shear rate, shear emphasis, power jurisprudence index, tangent teta, and loss & A ; storage modulus of STF become world. Those theoretical mathematical equations will be used for finding of new theoretical relationship of STF besides known as liquid-solid passage ( LST ) .
FIGURE 8
The Term F/A Represent the Force per Unit Area Required Producing the Shearing Action. it is Referred to as “ Shear Stress ” and will be Symbolized By “ I¤ ” . Its unit of Measurement is “ Dynes per Square Centimeter ” ( Dynes/cm2 ) or Newton per Square Meter ( N/m2 ) .
Viscosity can be determined mathematically by this expression:
( 2 )
. LST researched usually are focused on the passage of the storage modulus to the loss modulus in the crosslinking polymers such as natural and synthetics latex. In this paper, particular little arranger ( 21/13R ) is used to find the value of STF ‘s viscousness. The HB theoretical account of viscosimeter is used because the high concentration of the silica atom suspended in the bearer fluid, resulted the STF ‘s viscousness is high.
2.3.1.1 Cylindrical Spindles
The undermentioned equations apply to cylindrical spindles merely, on any Brookfield
Viscometer/Rheometer.
Shear RATE ( sec-1 ) = = 0.93N
SHEAR STRESS ( Dynes/cm2 ) I„ =
Viscosity ( Poise ) I· =
Definitions: = angular speed of spindle ( rad/sec )
, N = RPM
RC = radius of container ( centimeter )
Rb = radius of spindle ( centimeter )
Ten = radius at which shear rate is being calculated ( centimeter )
M = torsion input by instrument ( dyne – centimeter )
L = effectual length of spindle ( centimeter )
( Refer APPENDIX )
2.3.2 Power Law Index & A ; Tangent Teta
Harmonizing to the technology section of BROOKFIELD, there is sort direct relationship between power jurisprudence index and tangent teta which can be reviewed in the equation 3 and 4. The equation is the mathematical developed by Ostwald ( ? ? ) . Basically, power jurisprudence index indicates the flow behaviour such as when “ N ” is equal to 1, the stuff is Newtonian fluid, but “ n ” is less than 1, the stuff is shear cutting and “ n ” is more than 1, the stuff is shear inspissating fluid.
( 3 )
( 4 )
The standard standardization for BROOKFIELD viscosimeter has been developed in this paper by utilizing the Newtonian fluid such as H2O and Si oil. The standard standardization process is designed to minimise mistake reading from torque spring during experiment. The thought comes from the basic inactiveness forces of the unwinding and weaving spring during experiment. Therefore, by utilizing Newtonian fluid as standardization fluid, intending the value of power jurisprudence index will be precisely 1.
The relationship between power jurisprudence index and tangent teta for little sample arranger can be reviewed in equation. When the value of ” N ” is 1, intending the tangent teta is 45 grades. Therefore, when the tangent teta is 45 grades, graduated process for that viscosimeter is good. The standard standardization process can be reviewed in the chapter 3.
FIGURE 9
Illustration for the Onset Transition of the Tangent Teta. The Calibration Procedure to Minimize Error Reading of the Viscometer causes from Inertia Forces by making Phase Correction.
Furthermore, the thought of locking tangent teta to 90 grades in individual caput rheometer is bad thought because the onset passage is from 0 grades to 180 grades as shown in figure 9. Normally, x-axis is represents strain, the applied distortion, and the pointers represent the end point emphasis, or torsion, vectors.
The emphasis response for a strictly elastic stuff will be in stage with the strain giving a tangent teta of 0A° . For a strictly syrupy stuff, the emphasis response will be in stage with the strain rate bring forthing a tangent teta of 90A° . [ Brookfield ‘s technology section ]
The inactiveness torsion part from motor and geometry can be 180A° in tangent teta.A The instrument measures the altogether or entire tangent teta.A The tangent teta of the sample needed to cipher the viscoelastic belongingss is determined by deducting the inertial part from the entire tangent teta. As the natural stage signal is straight measured by the rheometer, it is an easy accessible signal that should be reported. The benefit of sing the natural stage is it allows one to measure the sum of stage rectification being applied to the measuring [ Brookfield ‘s technology section ] .
Furthermore, tangent teta besides will be used for determine the onset passage for the STF by associating it with LST theories. Figure 10 showed the relationship between construction belongings relationships with tangent teta. This onset passage is closely related with complex modulus which will be discussed subsequently in the loss & A ; storage modulus.
The researched for the onset passage between tangent teta and complex modulus is lacked because of the complexness for the determine factors impacting the onset passage. Example, researched on the STF, widely focused on the effects of the atoms suspended in the bearer fluid such as, the formation of the hydrocluster due to the different ionic strength of the wetting agent [ ? ? ? ? ? ] , and the effects of the shear inspissating behaviour of the STF on the cloth complex for the pang and slug opposition applications [ ? ? ? ? ? ? ] .
FIGURE 10
Simple Relationship between Complex Modulus and Tangent Teta.
In this paper, believed, tangent teta is a major factor for the shear thickener behaviour, whether in hydrocluster theories or in order – upset theory. Proposing the Liquid – solid passage is major subscriber in this paper. The ground is simple, the ability of the STF altering from liquid province ( gel formation ) into solid province are closely related to the LST behaviour, which had been discussed earlier. That onset passage neither, due to the Brownian gesture ( atoms moved indiscriminately and clash each others ) or the effects of the surface possible energy or the combination both factors.
Last but non least, a batch of the rheological behaviour particularly for STF will be discussed in this paper. For the relationship between tangent teta and complex modulus will be discussed in the following sub-chapter. The new theoretical relationship for viscoelastic belongingss between tangent teta and complex modulus will be revealed in this paper.
2.3.3 Storage & A ; loss modulus of the snap
Normally, appraisal for viscoelasticity are done by making proving such as weirdo and recovery trials and straight off shows the fluid ‘s behaviour is more solid- or liquid-like in its response. Normally, for this trial, controlled shear emphasis and strain ( CS ) , where an oscillatory strain, I? , with an amplitude, I?a, and angular speed, .
But in this paper, by utilizing a BROOKFIELD viscosimeter as a basic instrument proving equipment for rheological surveies of STF, and acquiring all the information every bit good as advice from BROOKFIELD ‘s technology section in Malaysia for theoretical storage and loss modulus. The troubles of this theoretical is comes from to find the shear strain of the STF by utilizing normal viscosimeter. There is a impossible to find shear strain in normal viscosimeter because of the losing detector which is related to the fluid distortion ( amplitude ) via applied shear emphasis and [ Brookfield ‘s technology section ] .
The complex modulus of snap, G* , is defined as
( 5 )
and denotes to the entire opposition of the fluid to the response strain. The complex modulus of the snap can be broken down to its existent and fanciful parts as
( 6 )
There is a basic relationship in complex modulus of snap. But in this paper, the angular speed is different because the instrument for the testing is viscometer and non rheometer. By utilizing particular little arranger ( mention appendix ) from BROOKFIELD ‘s, happening the value of the shear rate, and shear emphasis become realistic.
An angular speed of the spindles ( rad/sec ) utilizing BROOKFIELD ‘s viscosimeter, , is defined as
( 7 )
For oscillating strain rule, an angular speed is defined as
, ( 8 )
Because of much different rules in controlled shear rate, which viscosimeter is utilizing a rule of changing the motor velocity to acquire shear response from the distortion ( shear strain ) fluid, while, the fluctuation of the frequences is used by rheometer ( an oscillatory ) .There is basic apprehension of viscoselasticity which had been translated into figure 11 below.
FIGURE 11
The Basic Relations between Shear Stress, Viscous Stress, and Elastic Stress ( Resulting from the Changing the Stress ) in footings of a Complex Number ( a?s-1 = I ) where Syrupy Stress is In-Phase and the Elastic emphasis is Out-Of-Phase and Oppositely-Directed.
The fluid distortion ( shear strain ) which, it is translated to the tangent teta, have simple relation with elastic and syrupy emphasis. The relation is defined in equation
( 9 )
, ( 10 )
Equation shows the relationship between complex viscousness with viscousness and snap. While from figure showed the relation between elastic and syrupy emphasis, which it can be besides defined as
( 11 )
The purpose is to acquire the value of the snap from the equation. Because of the complex modulus which it can be reviewed in equation, besides have dealingss with snap and an angular speed. The dealingss can be defined in equation.
( 12 )
Therefore, by associating complex modulus with tangent teta, storage and loss modulus can be determined. Those two equations can be reviewed in equations13 and 14
, ( 13 )
( 14 )
All the equations for the determined storage & A ; loss modulus are guided and advices from the BROOKFIELD ‘s technology section.
2.3.4 Newtonian fluid
The type of flow behaviour which Newton assumed for all fluids is called “ Newtonian ” . A Newtonian fluid is represented diagrammatically in figure 12. Graph A shows that the relationship between shear emphasis and shear rate is a consecutive line. Graph B shows that the fluid ‘s viscousness remains changeless as the shear rate is varied. Water and thin motor oils are illustration of Newtonian fluid.
FIGURE 12
Flow Behavior of Newtonian Fluid. Graph A Represent the Relationship between Shear Stress and Shear Rate While Graph B, the Relationship between Viscosity and Shear Rate.
So, at a given temperature the viscousness of a Newtonian fluid remains changeless regardless of which viscosimeter theoretical account, spindle or velocity is used to mensurate it.
The behaviour of Newtonian liquids in experiments conducted at changeless temperature and force per unit area has the undermentioned characteristics:
the lone emphasis generated in simple shear flow is the shear emphasis S, the two normal emphasis differences are zero
the shear viscousness does n’t change with shear rate
the viscousness is changeless with regard to the clip of shearing and the emphasis in liquid falls to zero instantly the shearing is stopped
The viscousnesss measured in different types of distortion are ever in simple proportion to one another.
2.3.5 Non-Newtonian fluid
Non-Newtonian fluid can be clip -dependent or time-independent fluid. Mention to the tabular array show two major bunchs of non-Newtonian fluid, shear cutting and shear thickener behavior.There are several types of non-Newtonian flow behaviour, characterized by alterations fluid ‘s viscousness to fluctuations in shear rate.
Pseudoplastic
Dilatants
Bingham plastic
Thixotropy
Rheopexy
Table 2.2 showed the categorization of the Non-Newtonian fluids. Non-Newtonian fluids can be classified into two types, clip dependent behaviour ( T.D.B ) and clip independent behaviour ( T.I.B ) .
Table 2
Classs of Nonlinear Fluids in Non-Newtonian Fluids
Behaviors
Shear Cutting
Shear Thickening
Time dependant
( memory stuffs )
Thixotropics
Rheopectics
Time independent
( non-memory stuffs )
pseudoplastic
Dilatants
With output emphasis
Bingham plastic
–
2.3.5.1 Non-Newtonian fluids – clip independent
Pseudoplastic:
fluid displayed a decreasing viscousness with an increasing shear rate, some illustrations include pigments and emulsions. This type of behaviour is called shear-thinning.
Dilatant:
is characterized by an increasing viscousness with an addition in shear rate, some illustrations include clay slurries, confect compounds, maize amylum in H2O, and sand/water mixtures. Dilatancy is besides reffered to as shear-thickening liquids.
Bingham
Liquid behaves like solid under inactive conditions. A certain sum of force must be applied to the fluid before any flow is induced. This force is called output value. Tomato ketchup is an illustration of such fluid. Once the output value is exceeded and flow Begins, fictile fluids may expose Newtonian, pseudoplastic or dilatant flow features.
2.3.5.2 Non-Newtonian fluids – clip dependent
Some fluids display a alteration in viscousness with clip under conditions of changeless shear rate.
Tixotropic:
fluid undergoes a lessening in viscousness with clip, while it is subjected to constant shearing ( lubricating oils ) .
Rheopectic:
fluid ‘s viscousness increases with clip as it is sheared at a changeless rate.
2.3.6 Particular Characteristics ( Rheology ) of Dispersions, Suspension and Emulsions
Dispersions, suspension and emulsions, which are polyphase stuffs dwelling of one or more solid stages dispersed in a liquid medium, can be affected to rheological by figure factors.
In this paper, the atom collection or scattering stableness is a chief concern during rheological experiment. In chapter 3, a method process is developed to minimise all those factors which are affected during experiment. The stableness of scattering system is peculiarly of import when mensurating viscousness. If the scattering system has a inclination to settle, bring forthing a non-homogeneous fluid, the rheological behaviour of the system will be alteration and the incompatibility viscousness value of the scattering system.
All the possibility is included in the computation particularly for Liquid – Solid Transition ( LST ) , to bring forth really dependable result subsequently. All the procedures or processs for supervising all those possibilities are used zeta possible theories ( DVLO ) .
2.4 Colloidal Suspension
Colloidal suspension is defined as scattering of the solid atoms in a liquid medium. Examples pigments, claies, and slurries. The chief thought of utilizing colloidal suspension for STF are to heighten the electrokinetic mobility of silica atom in STF and to cut down swelling behaviour of silicon oxide atom after impregnated into cloth during drying procedure. Basically, colloidal suspension is referred to the stableness of the suspension, and zeta potency will be used to supervise the suspension stableness by mentioning DVLO theory.
In the colloid engineering, flocculation, de-flocculation, and curdling footings wa really of import during designed the suspension or emulsion system. Wordss flocculation is refer to the atoms aggregate ( floc ) during collection procedure. The floc may or may non sediment or phase separate ( Zetasizer Nano series proficient note ) . Normally, those province is refer to the stableness of the colloidal system. This flocculation procedure is reversible procedure, sometimes besides called as de-flocculation. If the sum alteration to new signifier of formation ( particle size increased ) and much denser, and this state of affairs called curdling. Natural gum elastic latex is a closed illustration of the stuff that undergoes curdling procedure and this curdling procedure is irreversible procedure. The procedure of colloidal system which is related with flocculation and curdling can be seen in figure 18.
FIGURE 18
The Schematic Diagram of the Flocculation and Coagulation Process of Colloidal System ( Zetasizer Nano Series Technical Note )
In this paper, the colloidal atoms will be used in STF. Therefore, zeta possible via pH titration method ( acid-base method ) will be used for supervising stable system for colloidal suspension in the STF. Colloid stableness is non a chief issue in this paper, but the involvements are come from the consequence of the pH value and the strength of electrolytes on the electrokinetic mobility of the STF. The chief thought is to change the zeta possible belongings and supervising the consequence of it on the STF ‘s rheology which is focused on the critical shear rate at a changeless volume fraction.
2.4.1 Zeta potency
In 1940, Derjaguin, Verway, Landau, Oberbeek developed a theory which dealt with colloidal stableness known as DVLO theory. There are tonss of techniques to mensurate zeta potency such as titration, and Electrophoretic visible radiation dispersing ( ELS ) . In this paper, titration technique is used to find zeta possible belongings and isoelectric point ( iep ) of uncharged and colloidal atoms. DVLO theory is used as chief guidelines for determine uncharged and colloidal atoms consequence on the STF ‘s suspension.
2.4.2 DVLO theory
DVLO theory related to the stableness of scattering system by supervising the electrical dual bed repulsive and Van de Waals attractive forces. The thought of the good suspension or emulsion in stableness is to make a abhorrent barrier forces for forestalling two atoms nearing one another and adhering together. But if the collide atom ‘s with sufficient energy in overcome abhorrent barrier, the attractive force will draw them.
There are tonss of factors that affect the stableness of the scattering such as different atoms has a different unique stable system that will be designed depends on the undermentioned standards:
Types of atoms such as mineral or non-mineral stuffs, monodisperse or polydispersed and etc.
Types of scattering or suspension technique that will be used such as high velocity and shearing disperser, and utilizing supersonic intervention. All the technique fundamentally has a alone consequence on the atoms such as the consequence of charges from supersonic intervention on the scattering system which is related to the consequence of electrostatic system on the quiver of atom in scattering or suspension systems.
Atoms concentration in the scattering or suspension system. Low atoms concentration in the system has higher or stable system than high atoms concentration.
Water or dissolver system. Normally, that type of system affecting primary and secondary system for stabilising the suspension such as NR latex have a chief system for stabilising its ain system, protein, and ammonia solution for secondary system.
The attractive and abhorrent force must be equal or abhorrent force is greater than attractive force, the stable system for scattering, suspension or emulsion will be achieved.
Controling those stable systems usually is complicated, affecting tonss of parametric quantity and factors. Anand Yethiraj surveies showed, there are seven factors which are to command and acquire stable colloidal scattering system. The chief involvement of his surveies is to find the stage passage dynamicss ( thermodynamic ) consequence on the spherical colloidal scattering system based on these seven factors.
All this seven factors can be summarized in figure 19. When the stable scattering is achieved, isoelectric point of the normal and colloidal charged is determined by utilizing pH titration technique, besides known as acid- base titration method utilizing pH metre. The elaborate about this titration is presented in the chapter 3.
FIGURE 19
Seven Factors that Affecting the Stable Dispersion System by Anand Yethiraj.
Therefore to keep the stableness of the scattering system, the abhorrent force must be dominant. There are two basic mechanisms that affected scattering stableness ( figure 20 ) : –
Steric repulsive force – this involves the debut of polymer into the system absorbing on the atom surface and forestalling the atom surface coming into close contact. The barrier that created from the atom surfaces chiefly designed for primary stabilizing system in the suspension system. The good steric system related to the thickness of the barrier. The surface potency and molecular weight of the absorbing polymer affected the public presentation of the steric system in scattering system particularly for colloidal stableness ( Ion steric effects on cataphoresis of a colloidal atom by By Aditya S. Khair and Todd M. Squires ) .
Electrostatic repulsive force – this is consequence of the atom interaction due to the part charged to the colloidal scattering. The designing of the electrostatic system involved surfactant such as ionic or cationic wetting agent and besides non-ionic wetting agents. By making interfacial beds called diffused bed, atom separation can be controlled by seting the electrolytes ionic strength and type Doctor of Optometry wetting agent besides affected the atom separation and scattering stableness ( Zetasizer Nano series proficient note ) .
FIGURE 20
The Illustration of the Steric Repulsion ( A ) System and Electrostatic Repulsion System ( B ) in the Colloidal System.
The colloidal particles fundamentally are environing by two barriers: the interior part ( austere bed ) when the ions strongly bound and an outer part ( diffuse bed ) where they are less associated. When particles moves ( eg. due to the gravitation ) , ions within barrier move it. Those ions beyond the barrier stay in majority dispersant ( Zetasizer Nano series proficient note ) . The potency at this barrier is the zeta potency ( figure 21 ) .
FIGURE 21
Conventional Representation of Zeta Potential
Each mechanism has its benefits for peculiar system. Steric repulsive force system is simple, necessitating merely the add-on of a polymer such as polythene ethanediol and polyvinyl intoxicant. However, polymer is expensive and in some instances the polymer is unwanted eg. Application at high temperature such as ceramic and Ti casting procedure affecting dramatis personae and sintered procedure at high temperature, doing polymer has to be burn out due to the debasement temperature of polymer itself. This causes shrinking and can take to desert [ ? ? ? ] .
Electrostatic repulsive force system has the benefits to stabilising the scattering by changing concentration of the ions in the system. Besides, by changing pH value which is closely related to the electrostatic repulsive force system, the rheological behaviour of the system besides altering such as the formation of macrosturcutre of the atoms dispersed or suspended will be lessenings or additions due to the neutering of the attractive force force in the scattering or suspension. Nongkhran Chaiwong claimed by changing the stochiometric behaviour of the clay suspension ( table 2.1 ) , the floc size besides gave different consequences during experiment utilizing different electrolytes and polymers. The formation of floc size are closely related with viscousness of the scattering or suspension, whether its tends to flocculated ( shear cutting ) or deflocculated ( shear thickener )
Therefore, by supervising that chief parametric quantity in colloid engineering such as steric and electrostatic repulsive force system, the formation of the floc size can be control via polymer or stochiometric which is closely related to the concluding rheological behaviour of the Shear Thickening Fluid ( STF ) .
2.4.3 Isoelectric point ( iep )
Isoelectric point is a atom whereas the surface potency is normal or uncharged. At the isoelectric point of solid atoms is zero, zeta potency is zero. This is found by seting the value of pH to allow value during pH titration experiment ( acid-base ) . The oxide surface responds by going more positive as the pH is loader by undergoing the undermentioned reaction:
If the pH is raised it becomes more negative:
Normal ( uncharged ) and colloidal atoms are really of import to the STF, hence, find the value of isoelectric point is a critical. Table below shows the exact value for some common oxides.
2.5 Applications
2.5.1 Personal organic structure armour
In conventional organic structure armour, in order to accomplish those superior belongingss, many facets must non be neglected like the cost of system, the entire weight of the system, and the flexibleness of the system. Normally, the conventional system consists of difficult and soft organic structure armour used ceramic complex as an insert, which is it are really heavy and bulky, and besides stiff in order to accomplish specific detailed of coveted belongingss. In norm, entire weight of conventional system is about 30 kgs per waistcoat. Other disadvantages of the conventional system are the mechanical belongingss of ceramic complex, which is usually brickle in the nature.
Other disadvantages of the conventional system are the entire protective country and the consequence of slug injury after the slug impact. First, entire protective countries in the conventional system are limited because of the rigidness and entire mass of the organic structure armour system. Not all the organic structure of individual wear it is protected ; ceramic home base merely covered the critical and the chief variety meats like bosom. The slug injury consequence after all is the chief key of all the armour system and all interior decorator should undertake down these chief factors. Ceramic will halt the slug incursion from through the system but ceramic has hapless impact soaking up of force from slug to the all system expeditiously. The effects of this failure are the soldier ‘s life will be in hazard because of the concealed force from the impact between slug and ceramic home base ( Lee et.al 2003 ) .
Normally stab and puncture opposition are neglected because the maker of organic structure armour system ever assumed that, Kevlar itself are good in ballistic impact belongingss hence, Kevlar should hold no job at all with the pang and puncture opposition.
But all that premises is non every bit expected because neat Kevlar has critical failing for pang and puncture opposition. Neat Kevlar are combination of Kevlar fibres at different orientation. Because of the different orientation, orderly Kevlar have a spread ( interphase ) between the Kevlar fibres ( pennant and woof ) . Therefore, the spike or knife can easy perforate through the spread between the fibres by forcing off the fibres. At the terminal, spike and stab easy perforate Kevlar cloth.
2.5.2 Material development for personal organic structure armour
Body armour is indispensable equipment for constabulary and protection system. Presently, organic structure armour is fielded merely in specific bad scenarios, and is typical limited to chest and head protection. However, a important per centum of battleground hurts occur to the appendages, including weaponries, legs, custodies, and cervix. Armor for these appendages must offer protection from fragment and ballistic menaces, without significantly restricting soldier mobility and sleight ( G. Fritz, B. J. Maranzano et. Al ) .
Conventional organic structure armor stuff is typically comprised of many beds of polyaramide cloths with optional ceramic tile inserts. These stuffs are excessively bulky and stiff for application in appendages protection. A stuff is needed which can offer the tantamount ballistic public presentation of bing organic structure armor stuffs, but with significantly more concentration and flexibleness.
The general characteristics of containment fibres for usage in energy dissipating cloths are high doggedness and high tensile modulus. These stuffs illustration Kevlar and spectra are besides considered ballistic stuffs. At the same clip, in more application, it may be desirable the utilize cloths holding the benefits of comparative low majority and flexibleness. To accomplish such belongingss, polymeric fibres may be used. The fibres which may be preferred include aramide fibres, ultra-high molecular weight polymers like polythene and polypropene.
Typically, polymer fibres holding high tensile strength and a high modulus are extremely oriented, thereby ensuing in really smooth fibre surfaces exhibiting a low coefficient of clash.
