Rheological behavior of concentrated silica suspension and its application to soft armor

The objective of this study is to develop an advanced stab and/or ballistic proof material composed of shear thickening fluid (STF) and Kevlar composite fabric. In this study, we prepared STF using sphere silica and fumed silica as silica particles and ethylene glycol and polyethylene glycol (PEG 200) as medium fluid, respectively. And the rheological properties of the STF were investigated under different conditions. Also, we impregnated Kevlar fabrics with the STF, and investigated the stab and ballistic resistances of the targets layered by the STF impregnated Kevlar fabrics. From the results, we observed that the STF significantly showed the reversible liquid–solid transition at a certain shear rate, and the STF treatment significantly improved the stab and ballistic resistance of Kevlar fabric. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Preparation of body armour material of Kevlar fabric treated with colloidal silica nanocomposite

Abstract

To safeguard bodies of soldiers better, including their necks and joints, a novel armour material was exploited using nanocomposite. Compared with traditional armour materials, this new material possessed superior barrier property and more comfortable characteristics. The new armour material was made of Kevlar cloth and shear thickening fluid (STF). Colloidal silica particles were first synthesised via the Stöber synthesis method and then they were used to prepare a suspension with solvent of polyethylene glycol 200. At last, Kevlar cloth was treated with the suspension and the resultant was named as STF–Kevlar nanocomposite. In this process, the particle sizes were characterised with scanning electron microscopy. The rheological properties were measured with a Physica MCR301 stress controlled rheometer. The results showed that the silica particles could be determined to be monodispersed spherical particles. The suspension, named the shear thickening fluid, had shear thickening characteristic. The property of multilayer STF–Kevlar nanocomposite targets was compared to that of the neat Kevlar cloth and the results indicated that the STF–Kevlar nanocomposite had an improvement in barrier property and was more flexible and comfortable. The mechanism that could improve the barrier property of STF–Kevlar was briefly explained.     

不同体系剪切增稠液体的流变行为研究

剪切增稠液体是指其表观粘度随剪切速率增加而变大的一类流体。工业生产中,剪切增稠的出现会阻碍输送管道,破坏生产设备。针对这种情况,人们对如何降低流体粘度造成的不利影响进行了大量研究。另一方面,剪切增稠液体是“液体防弹材料”的关键组成部分,并且在减震、控制方面也具有可观的应用潜力。该文采用原生粒径为50 nm 的SiO2和80～100 nm 的 CaCO3分别作为分散相,聚乙二醇（PEG）200为分散介质,采用超声分散法制备得到不同固含量的剪切增稠液。并通过纳米粒度仪和扫描电镜对分散相粒子团聚情况进行分析;通过应力控制流变仪分别对 SiO2/PEG200和 CaCO3/PEG200悬浮分散体系的稳态流变性能进行分析。结果表明,两种体系试样在测试中均出现剪切增稠现象,并且分散相质量分数越高,剪切增稠效果越明显;而高质量分数的 SiO2/PEG200体系的粘度变化范围更大,增稠现象更为明显。     

The rheological properties of shear thickening fluid reinforced with ZnO of different friction characteristics

The viscosity of shear thickening fluid (STF) changes significantly with low concentrations of additives. However, existing research has suggested that there has not been any consistent enhancement mechanism of additives. The possible reason for this research gap is that existing research has focused on the effect of the shape and content of additives on shear thickening (ST) performance, whereas the friction characteristics of additives on ST performance have not been considered. Accordingly, nanoparticle-enhanced STF with various friction characteristics of ZnO was synthesized in this study to investigate the enhancement mechanism of additives. The aspect ratio of ZnO with different shapes was obtained through SEM analysis. The friction characteristics of ZnO were examined. Lastly, the rheological behavior of reinforced STFs was evaluated. The results indicated that ST performance was enhanced compared with that of neat STF, which was significantly dependent on the friction characteristics of ZnO.     

Shear thickening fluids in protective applications: A review

A thorough and critical review on Shear Thickening Fluids (STFs) is presented based on a literature survey. The rheological properties of STFs are discussed considering many factors affecting shear thickening behavior and the use of STFs in protective systems is reviewed. The main focus of this review is multi-phase STFs, relatively new to the literature (in the last five years). Multi-phase STFs include a second phase in suspensions and the influences of this additional phase on rheological behavior and protective applications are discussed extensively. Based on this extended review, STF do benefit protective applications, but the major contribution is not driven by the shear thickening behavior. Rather, STFs are responsible for the increase in friction along fabrics and enhanced fiber/yarn coupling in fabric based protective systems. As a result, of these effects, the load transfer is spread over a wider area and penetration depth is lowered in an impacted structure.     

Application of shear thickening fluid in ultra high molecular weight polyethylene fabric

An advanced stab‐resistant material composed of shear thickening fluid (STF) and ultra high molecular weight polyethylene (UHMWPE) fabric was investigated. STF was prepared by dispersing nanosilica (SiO₂) into ethylene glycol. The shear thickening behavior of STF with the increase of the shear rate was observed by PhysicaMCR301. STF/UHMWPE composite fabric was synthesized by impregnating UHMWPE fabric in STF dilution. Stab resistant experiment was conducted on a self‐made stab test machine with knife and spike as stab tool. The results demonstrate that the stab resistant property of the UHMWPE fabric is greatly improved by impregnating STF. The stab resistant property is greatly increased with the increase of mass fraction of silica in STF. Especially, when the mass fraction of SiO₂ in STF is 38%, the stab resistance force and energy absorption of STF/UHMWPE are optimal for knife and spike threats. With the same stab resistant properties, the flexibility of UHMWPE fabric impregnated with STF is higher than that of the neat fabric. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Impact behavior of aminosilane functionalized nanosilica based shear thickening fluid impregnated Kevlar fabrics

In the present work, two types of shear thickening fluids have been synthesized by using neat and aminosilane functionalized silica nanoparticles and their viscosity curves have been obtained by the rheometer. Based on the values of peak viscosity of synthesized shear thickening fluids, the surface functionalized nanosilica based shear thickening fluid has been chosen as a best candidate due to the high viscosity for impregnation into the neat Kevlar of different layers viz. four (04) and eight (08) layers for velocity impact study. The experimental investigations reveal high energy absorption of shear thickening fluid impregnated Kevlar as compared to the neat Kevlar. The maximum energy absorption 62 J is achieved corresponding to the initial velocity 154 m∙s⁻¹ for 08 layers shear thickening fluid impregnated Kevlar specimen. The data have also been analytically determined and validated with the experimental data. The experimental data have good agreement with the analytical data within the accuracy of around 15 to 20%. The present findings can have significant inferences towards the fabrication of shear thickening fluids using nanomaterials for numerous applications such as soft armors, dampers, nanofinishing and so forth.     

Rheological properties of bitumen in water emulsions with added solids

Experimental work was carried out to investigate the rheological properties of bitumen in water emulsions containing solids of different shape and size. The bitumen volumetric concentration was varied up to 60%, solids free basis, and the solids volume fraction (total volume basis) was varied up to 0.2. Irregular-shaped silica sand (average diameter: 9 and 33 μm) and smooth spherical glass beads (average diameter: 27 and 44 μm) were used as the added solids. In the low shear stress range, shear thinning behavior was observed for bitumen in water emulsions. At high shear stress, the viscosity of the emulsions became fairly independent of the shear stress. The addition of solids to the bitumen emulsions increased the mixture viscosity. The addition of irregular-shaped silica sand gave a higher viscosity than a similar addition of the spherical glass beads. The viscosity of the emulsion/solids mixtures was influenced by the solids size as well; the smaller size particles gave a higher viscosity. The addition of solids to the bitumen emulsions also induced shear thickening (dilatancy) behavior at high solids volume fraction. The degree of the shear thickening increased with the oil concentration.     

剪切增稠液体的制备及其性能和应用

综述了以纳米二氧化硅/聚乙二醇(SiO2/PEG)分散体系为代表的剪切增稠液体的制备及其表征和应用情况。表明这些体系在低剪切速率下出现剪切变稀现象,而在高剪切速率下会出现剪切增稠现象,适用于防弹、减震等应用方面材料,特别在个体防护方面有很重要的应用。指出剪切增稠液体与芳纶织物复合的防弹材料在保持穿着舒适性和灵活性的前提下,比纯芳纶织物有更好的防护效果。此外还有纳米碳酸钙/聚乙二醇(CaCO3/PEG)分散体系等也是剪切增稠液体。     

Influence of carrier fluid on the electrokinetic and rheological properties of shear thickening fluids

This paper presents a study on the influence of hydroxyl groups and oxygen atoms together with chain length and branching of carrier fluid on the rheological and electrokinetic properties of shear thickening fluid (STF). An STF is non-Newtonian fluid behaviour in which the increase of viscosity increases with the applied shear rate. Ethylene glycol, triethylene glycol, 1,3-propanediol, glycerin, poly(propylene glycol) of different molecular weight and poly(propylene glycol) triol were used as the carrier fluids (dispersants). Silica powder with an average particle size of 100 nm was used as the solid phase. Zeta potential, particle size distribution (by DLS technique), steady-state and dynamic rheological measurements were conducted. Experimental results indicate that a different amount of hydroxyl groups and oxygen atoms together with chain length and branching of carrier fluids have a significant influence on the intermolecular interactions thereby and on the rheological properties of suspensions. Depending on the composition, it is possible to control rheological properties. The use of a suitable carrier fluid allows the required pattern flow to be obtained, from Newtonian through shear thinning to shear thickening, given specific shear conditions.     

The importance of surface hydration and particle shape on the rheological property of silica-based suspensions

Two types of ball milling methods, wet planetary ball milling and dry tumbling ball milling, were used to grind fused silica powders for the preparation of silica-based suspensions in this experiment. The effect of surface hydration and particle shape caused by the two milling methods on the slurry rheology was investigated. The results showed that, with similar particle size distribution, the viscosity of the suspensions prepared from the powders milled by wet ball milling ranged from 275 mPa s to 311 mPa s within 20 min and the suspension exhibited a continuous shear thickening behaviour whereas the viscosity of the suspensions prepared from the powders milled by dry ball milling ranged from 69 mPa s to 74 mPa s and the suspension exhibited a shear thinning behaviour first, and then exhibited a slightly shear thickening behaviour. The reasons were attributed to the differences in surface hydration and particle shape. It was postulated that the two factors affected the slurry rheology through the modification of particle interactions during the flow of high concentration suspensions.     

单分散氧化硅浓缩悬浮液浸渍Kevlar复合材料的防刺性能

以St(O)ber和离心交换法制备了不同浓度的单分散SiO_2/PEG浓缩悬浮液,并研究了其流变性能和用其浸渍Kevlar编织布所得复合材料的防刺性能.研究发现,所制备浓缩悬浮液在质量浓度低于50%时,具有微弱的剪切增稠效应,增稠所能达到的粘度值随浓度增加缓慢升高,而临界剪切速率降低;当浓度在55%左右时,先是剪切增稠,随后出现轻微的剪切减稀现象;当浓度达到65%时,出现较为显著的剪切增稠效应.所制备复合材料的防刺性能比纯Kevlar编织布有一定的提高,当SiO_2质量百分比浓度在40%～45%区间时,抗刺力可提高到1.66倍左右.     

Studying the mechanical properties of composites made of Kenaf‐Nylon 66 fabric,silica nanoparticles,and epoxy resin

In this study, the effect of the relationship between yarn material and yarn count tex on the mechanical behavior of plainly woven hybrid fabrics impregnated with silica nanoparticles and epoxy resin has been investigated. First, various types of bicomponent and single‐component fabrics with plain weaves are prepared using kenaf and nylon‐66 yarns with yarn tex count of 334 and 427. To prepare the composite, silica nanoparticles with a particle size of 200 nm are mechanically mixed into glycol polyethylene with a molecular weight of 200 along with ethanol in proportions of 6:1. The weight percent of silica particles in the suspension has been selected as 60%. Using a round edge indenter, the concentrated indentation force test has been performed based on the 6264D standard to determine the strength of each fabric sample. Then, by impregnating the mentioned fabrics with polymer materials (silica nanoparticles and epoxy resin) and performing the concentrated force tests again, it is found that the hybrid fabrics with a yarn tex count of 427 and impregnated with polymer material enjoy the highest shear thickening properties. POLYM. COMPOS., 37:674–683, 2016. © 2014 Society of Plastics Engineers     

Preparation and characterization of imidazolyl ionic liquid-based shear thickening dispersion system

Shear thickening liquid (STF) is a new nonNewtonian fluid widely used in industrial production. In this paper, a novel shear thickening and dispersing system, namely poly methyl methacrylate (PMMA)/1-butyl-3-methylimidazole hexa-fluorophosphate ([BMIM]PF₆), was prepared using ultrasonic with PMMA as the dispersing phase and [BMIM]PF₆ as the dispersing medium. The stability, thixotropic, reversibility, rheology, and viscoelasticity of the dispersion system was studied, respectively. The dispersed system has good stability. The dispersed system shows high response sensitivity to shear rate, as well as good reversibility to shear thickening. Compared with traditional silicon dioxide/polyethylene glycol dispersion system, PMMA/[BMIM]PF₆ dispersion system displays a significantly enhanced shear thickening effect. Nonionic surfactant triton X-100 of 4 wt% can greatly improve PMMA/[BMIM]PF₆ dispersion system's shear thickening behavior. This paper provides a new idea for the further development of protective materials by using STF.     

SiO_2/PEG分散体系的流变学性能研究

随着剪切增稠液体在防护领域的应用,其流变学性能的研究显得尤为重要。本实验制备了一系列SiO2/PEG分散体系,并解释了制备过程中所出现的实验现象;采用高压毛细管流变仪测试了SiO2/PEG分散体系的流变性能。研究结果表明,随着剪切速率的变化,分散体系的表观粘度先减小后增大,并且剪切增稠现象具有可逆性;分散介质相对分子量的增大,不利于分散体系的剪切增稠;SiO2固含量越大,剪切增稠现象越明显。     

Viscometric properties of poly(dimethylsiloxane) filled with spherical silica particles

The shear viscosity and primary normal stress coefficient were measured for colloidal dispersions of monodisperse silica spheres in poly(dimethylsiloxane). The viscometric properties of the dispersions were a function of the shear rate, particle diameter, and the volume fraction of particles. Dimensional analysis of rheological properties of colloidal dispersions of spherical particles in a second-order fluid was performed, and the experimental data were analyzed in terms of the appropriate dimensionless groups. The reduced shear viscosity of the colloidal dispersions was a function of the volume fraction of particles and the reduced shear stress (or reduced shear rate). The reduced primary normal stress coefficient was a function of the volume fraction of particles, the reduced shear rate, and the Weissenberg number.     

Rheological property and curing behavior of poly(amide-co-imide)/multi-walled carbon nanotube composites

Poly(amide-co-imide) (PAI)/multi-walled carbon nanotube (MWCNTs) composites were prepared by using solution mixing with ultrasonication excitation in order to investigate effects of MWCNTs on rheological properties and thermal curing behavior. Steady shear viscosity of the composite showed bell shaped curves with three characteristic patterns: shear thickening, shear thinning, and Newtonian plateau behavior. Both storage modulus and complex viscosity were increased due to higher molecular interaction than that of the pure PAI resin. Especially, hydrogen peroxide treated MWCNT/PAI composites had the highest storage modulus and complex viscosity. Glass transition temperature of the PAI/MWCNT composite was increased with increasing MWCNT content and thermal curing time since the mobility of PAI molecules was reduced as more constraints were generated in PAI molecular chains. It was found that thermal curing conditions of PAI/MWCNT composites are determined by considering effects of weight fraction and surface modification of MWCNTs on internal structure and thermal properties.     

Preparation of Monodisperse ZrO2 by the Microwave Heating of Zirconyl Chloride Solutions

Based on the principle that the solubility of a salt decreases as the dielectric constant of the solvent decreases, zirconia powders were prepared by heating a zirconyl chloride solution with a 2-PrOH-water mixture as the solvent. The morphology, size, and size distribution of the resulting particles were highly sensitive to the heating method used on the starting solution. Particles formed under conventional heating methods were polydisperse, agglomerated spherical, or irregularly shaped because of inhomogeneous precipitation through the temperature gradient, the shear force induced by stirring, compositional nonuniformity, and the low heating rate. The present study demonstrated that microwaves provide an excellent means of heating uniformly and rapidly without stirring. The particles resulting from microwave treatment were monodisperse and spherical, with a mean diameter of 0.28 μm.     

Rheology of UV curable colloidal silica dispersions for rapid prototyping applications

Silica is a very promising material for micro-devices produced by rapid prototyping techniques due to its high transparency, thermal and chemical resistance. UV curable dispersions for rapid prototyping methods such as stereolithography should posses specific rheological properties which are crucial for such applications. We developed highly filled, low viscosity silica dispersions (up to 60 vol%) in UV curable, acrylate based systems. The influence of silica particle size, solid loading, temperature and shear rate on the viscosity of dispersions was investigated. The dispersions exhibited different types of shear thickening depending mainly on the size of particles. The critical shear rate defined as the onset of shear thickening, was found to be dependent on temperature, particle size, solid loading of the dispersions. The understanding of these rheological properties enables the design of new dispersions that meet rapid prototyping process requirements.     

A Model for Removal of Compact,Rough, Irregularly Shaped Particles from Surfaces in Turbulent Flows

A model for removal of compact, rough, irregularly shaped particles from surfaces in turbulent flow was developed. Following the approach of our previous bumpy particle model, irregularly shaped particles were modeled as spherical particles with a number of bumps on them. To improve the model, the effect of surface roughness was added to the bumps. Each bump was modeled with large number of asperities and the Johnson-Kendall-Roberts (JKR) adhesion theory was used to model the adhesion and detachment of each bump and asperity in contact with the surface. The total adhesion force for each bump was obtained as the summation of each asperity force in contact with the substrate. To account for the variability observed in the removal of particles, the number of bumps and roughness values of particles are assumed to be random, respectively, with Poisson and log-normal distributions. For particle separation from the surface, the theory of critical moment was used, and the orientation of bumps on the surface was considered when determining the range of shear velocity needed for removal of the irregularly, shaped particles. The effects of particle size, turbulent flow, particle irregularity, and particle surface roughness on detachment and resuspension were studied for different particles and surfaces. Model prediction for removal of rough, irregularly shaped graphite particles from steel substrate was compared with the available experimental data and earlier numerical models, and good agreement was obtained. This study may find application in adhesion and detachment of irregular particles from flooring in indoor and outdoor environments.