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Contribution of Surface Chemistry to the Shear Thickening of Silica Nanoparticle Suspensions Wufang Yang, Yang Wu, Xiaowei Pei, Feng Zhou, and Qunji Xue Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.6b04060 • Publication Date (Web): 04 Jan 2017 Downloaded from http://pubs.acs.org on January 10, 2017

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Contribution of Surface Chemistry to the Shear Thickening of Silica Nanoparticle Suspensions Wufang Yang†,‡, Yang Wu†, Xiaowei Pei†, Feng Zhou*,†,Qunji Xue† †

State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics,

Chinese Academy of Sciences, Tianshui middle Rd, 730000 Lanzhou, China ‡

University of Chinese Academy of Sciences, 100049 Beijing, China

ABSTRACT: Shear thickening is a general process crucial for many processed products ranging from food and care to pharmaceuticals. Theoretical calculation and mathematical simulations of hydrodynamic interactions and granular-like contacts have proved that contact forces between suspended particles dominate the rheological characteristic of colloidal suspensions. However, relevant experimental studies are very rare. This study was conducted to reveal the influence of nanoparticle (NP) interaction on the rheological behavior of shear-thickening fluids (STFs) by changing the colloidal surface chemistries. Silica NPs with various surface chemical compositions are fabricated and used to prepare dense suspensions. Rheological experiments are conducted to determine the influence of NP interaction on corresponding dense suspension systems. Results suggest that the surface chemistries of silica NPs determine the rheological behavior of dense suspensions, including shear thickening behavior, onset stress, critical volume fraction, and jamming volume

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fraction. This study provides useful reference for designing effective STFs and regulating their characteristics.

1. INTRODUCTION “Shear-thickening fluids” (STFs) have been increasingly investigated because of their vast applications in shampoos, paints, cements, damper, soft body, bullet-proof material, and energy fields, among others.1, 2 Dispersed particles in these solutions can be spherical, worm-like micellar, and plate-like.3,4 Especially in the context of a body bullet-proof material, STF displays outstanding absorption of a high amount of energy when impacted with a high-velocity bullet.5, 6 However, the granulation process in suspension rheology has not been elucidated.7 In 1972, Hoffman suggested that the granulation might be a consequence of an order-to-disorder transition(ODT).8,9 Subsequent studies have shown that shear thickening could be induced by “hydrodynamic clustering” rather than an ODT,10–14 and shear thickening is a phenomenon controlled by hydrodynamic lubrication force. The measured viscosity of a concentrated colloidal suspension can be resolved into two components, namely, thermodynamic and hydrodynamic components.11 Additionally, Wagner et al. used hard-sphere colloidal model (a toy-model) and fluctuation-dissipation theorem to argue that flow-induced density fluctuations can be ascribed to the formation of hydroclusters.3 Kaldasch et al. used activation model of shear thickening to investigate the impact of non-DLVO force on the onset of shear thickening. They suggested that shear stress stimulates the formation of percolated jammed clusters, also known as hydroclusters.15 Then, based on a time-dependent Ginzbrug-Landau model, they


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implied that this shear jamming is due to a stress-induced critical slowing down of the density mode along the compression axis of sheared suspensions.16 Based on these simulations and calculations, shear thickening that occurs between γ c (critical shear rate, above which the viscosity increases sharply) and γ max (the maximum shear rate, where shear thickening transition is complete) is apparently the result of microstructure transfer (hydrocluster, sol-gel, and jamming) during flow or stress. Such structural change from ordered nanoparticles (NPs) to chaotic large clusters is induced mainly by hydrodynamic force and strongly affected by the delicate balance among interparticle forces, Brownian motion, and hydrodynamic interactions.17 However, several numerical simulations have also indicated that, compared with the experimental results, hydrodynamic interactions agree well with experimental results only in the shear thinning regime but fail in simulating the shear thickening effect, which contrastingly increases as the volume fraction increases.18–20 Wyart, Mari and Lin performed simulation studies and have also argued that shear thickening in many systems is a stress-induced transition from a flow of lubricated near-contacting particles to a flow of a frictionally contacting network of particles. They further stated frictional colloidal suspensions can reproduce continuous shear thickening (CST) and discontinuous shear thickening (DST).21–24 For example, Mari et al.24 explicitly elucidated the link between frictional contacts and shear stress by investigating the fraction of frictional contacts using simulation including the hydrodynamic force, a repulsive interaction, and frictional contacts,. Additionally, this study also showed that jamming volume fraction (ϕJ) is very sensitive to the interparticle friction


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coefficient. Royer et al. detected the rheological signature of frictional interactions in shear thickening suspensions and suggested a scenario in which shear thickening is driven primarily by the formation of frictional contacts. In this scenario, the hydrodynamic force played a supporting role at lower concentration.25 Lin et al. used shear reversal experiments to measure directly the contribution of hydrodynamic and contact forces to shear thickening. The results shown that CST does not originate from hydrodynamic interactions but from the formation of particle contacts.26 In this case, the frictional contact between colloids is essential for the shear thickening effect. The effect of temperature, charge, pH, and solvent on the behavior of STFs has been investigated.27–30 However, only a few experimental studies have determined the effect of particle surface properties on suspension rheology, illustrating the need for robust measurements of particle friction.26

In this study, interactions between silica NPs mimicking frictional contact are tailored by surface chemical modifications of NPs to understand the impact of frictional contact of dispersed phase on the rheological behavior of dense suspensions. First, silica NPs containing different functional groups of Si-O-Si bond, −OH, benzyl, alkyl, −NH2, and oligoethyleneglycol methacrylate (OEGMA) polymer brushes are fabricated separately (see Supporting Information). These surface modifications could change the interparticle interaction or frictional contact by altering the surface interactions, namely, hydrogen bond interaction, van der Waals interaction, and π-π stacking effect. Then, variations in the rheological behavior [including onset stress, critical volume fraction (ϕc), and ϕJ] of silica NP dense suspensions under dynamic


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shear conditions are experimentally investigated. This work elucidates the effect of interparticle interaction/frictional contact in shear thickening suspensions with complex rheological behavior. This study also provides guidance on the preparation of high-performance dense suspensions.

2. RESULTS AND DISCUSSION

Dense suspensions typically involve CST and DST, depending on the volume fraction. DST will be observed for a volume fraction above a threshold value (ϕc). The impact of chemical modifications/frictional contacts on the two shear thickening effects are investigated separately, because the rheological behavior of CST and DST significantly differ.

2.1 Effect of chemical modifications on the CST

CST is achieved by preparing low-volume fraction (39%) dense suspension via the dispersal of silica NPs into polyethylene glycol (PEG, Mw400 g/mol). The effect of Si-OH group content on the CST was considered first, because the interparticle interactions between NPs depend on the surface functional group density. FT-IR results (Figure S1) showed that many Si-OH groups exist on the surfaces of fresh silica NPs. However, heat treatment at 600 °C for 4 h results in the reaction between the surface adjacent Si-OH groups and production of numerous Si-O-Si bonds, leading to the decrease in the amount of Si-OH groups. Additionally, the Si-O-Si bonds can also be broken, and Si-OH groups are regenerated after piranha solution treatment. This result indicates that the content of Si-OH group on fresh SiO2 NP


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surface can be reduced by calcination and regenerated by piranha solution treatment. Figures 1b–d depict the variation in the shear viscosity of the three kinds of suspension samples with increasing shear rate. For fresh silica NP dense suspension (Figure 1b), shear thinning is observed first, in which shear viscosity decreases as shear rate increases. Then, the shear viscosity increases from 1.75Pa·s to 2.5Pa·s when the shear rate reaches the threshold γ c. However, the rheological curve of thermal-treated silica NP dense suspension differs considerably from that of fresh silica NP suspension. Figure 1c shows hardly any shear thickening with the increase in shear rate after the general shear thinning stage. In addition, the apparent dynamic shear viscosity of thermal-treated silica suspension is much lower than that of fresh silica suspension within the entire test. However, for the piranha-solution-treated silica NP dense suspension, the obvious shear thickening property recovers, and the apparent viscosity increases from 1Pa·s to 1.8Pa·s (Figure 1d). Moreover, the apparent dynamic shear viscosity of piranha-solution-treated silica NP dense suspension is in-between the apparent viscosity of thermal-treated and fresh silica suspensions.

These rheological experimental results are consistent with the numerical simulation and experimental results by Mari and Wyart et al.21–24, 26 It is proved that stress-induced frictional contacts are not only dependent on hydrodynamic interactions but also on surface forces, in particular repulsive interparticle forces. Thus, shear thickening is a transition from a flow state in which particles remain well separated by lubrication layers to a flow of a frictionally contacting network of


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particles. Moreover, attractive forces between the particles produce high viscosities.22 The most remarkable difference among these dense suspensions is the surface functional group density of the silica NPs. Thus, the attractive forces among fresh silica are stronger than those of the thermal-treated silica system. Moreover, the existential attraction between fresh NP phases, such as hydrogen bonds, is an important element in granulation that results in the shear thickening phenomenon. Figure 1a illustrates that granulation results from a change in microstructure during the shear thickening stage. This shift is due to the combined effect of frictional contact induced by hydrodynamic force and intermolecular attraction. However, for thermal-treated silica NPs, the absence of hydroxyl groups leads to the very weak attractive force between NPs to overcome the thermal Brownian motion and zeta potential (ζ, which will be discussed later in the paper). Hence, colloidal particles remain separated and randomly dispersed in the dispersion medium. Consequently, a low-viscosity and contactless (hence, frictionless) state is speculated. Thus, the clusters or granules cannot effectively form by the action of hydrodynamic shear force such that shear thickening phenomenon is hardly observed. This case is consistent with the simulated rheological behavior in which frictional contact force is neglected by dynamic particle-scale numerical simulations.21 Figure 1d shows that, although the shear thickening property of piranha-solution-treated silica NP colloidal suspension does not meet that of the fresh silica NP colloidal suspension, obvious shear thickening characteristic is again achieved by regenerating Si-OH groups. Compared with the fresh ones, the weakened shear thickening characteristic in the


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piranha-solution-treated silica NP colloidal suspension can be attributed to the decreased density of Si-OH groups which may lead to low attractive force (or a low friction coefficient). Consequently, low apparent viscosity and weak shear thickening property are exhibited. These experimental and analytical results illustrate that the chemical components of silica NPs are essential to the shear thickening effect. Shear thickening for fresh silica NP suspension is substantially stronger than the thermal-treated ones, which suggests the transition from contact dominated rheology to contactless rheology by decreasing the OH group density.

Figure 1. (a) Mechanism of shear thickening effect and rheological characterization of SiO2 nanoparticle (NP) colloid suspensions. (b) Fresh, (c) Thermal-treated, and (d) Piranha-solution-treated SiO2 NP colloidal suspensions. The disperse phase in the third type of suspension was thermally treated first. Volume fractions of colloid particles for all samples are 39%.


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The argument is further proved using other dense suspensions in which the silica NPs were modified with amino, benzyl, and alkyl groups. These suspensions were characterized by IR and TG to confirm the modification (Figures S2 andS3). Figure 2b–d show the dependence of the apparent viscosity of the three kinds of dense suspension on shear rate. The apparent shear viscosity of amino-modified SiO2 NP dense suspensions can increase from 1.1 Pa·s to 1.5Pa·s when the shear rate increases (Figure 2b). For benzyl-modified SiO2 NP colloidal suspensions, the apparent shear viscosity can also be elevated from 1.1 Pa·s to 1.5Pa·s when the shear rate increases (Figure 2c). However, for alkyl-modified SiO2 NP colloid suspensions, varying the suspending medium changes not only the viscosity but also the solvency for the stabilizer layer.31 Despite the strong hydrodynamic shear forces and high apparent viscosity as shown in Figure 2d, no shear thickening behavior could be found, but shear thinning is measured in the whole shear range. For various rheological curves, this phenomenon might be due to the interparticle attraction by hydrogen bonding and π-π stacking interactions among amine and benzyl groups, respectively (Figure 2a). Thus, obvious shear thickening phenomena appear for both suspensions. The absence of shear thickening effect in alkyl-modified SiO2 NP colloid suspensions can be ascribed to ineffective frictional contacts among alkyl-modified SiO2 NPs to form the granules.


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Figure 2. (a) Mechanism of shear thickening effects induced by hydrogen bonding and π-π stacking. Rheological curves of colloidal suspensions: Disperse-phase SiO2 NPs assembled by (b) APTES, (c) benzyltrichlorosilane, and (d) OTS. The silica NP surface groups changed from hydroxyl to benzyl, amino, and alkyl group, respectively. Volume fractions of colloid particles for all samples are 39%.

Grafting hydrophilic polymer brushes on silica NP surface is another approach to obstruct

frictional

contact

between

SiO2

NPs.

The

poly(ethylene

glycol)methacrylate(p-OEGMA) brushes were grafted onto silica NP surface via surface initiator atom transfer radical polymerization (Figures S4 and S5). The rheological behavior of p-OEGMA-SiO2 NP dense suspensions is shown in the Figures S6a and 6b. In spite of the similar chemical structures between p-OEGMA and dispersed medium (PEG-400), shear thickening is not observed in either


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p-OEGMA-SiO2 NP colloid suspension (Figure S6a) or the very sparse p-OEGMA brush attached case (Figure S6b).

The intermolecular force between silica NPs mainly depends on the physiochemical properties of the different functional groups attached to the silica NPs. Given that the chemical modifications of silica NPs were conducted at the nanoscale, the effect of the physical properties (such as rigidity) of those functional groups on the intermolecular forces might be ignored. Hydrogen bonding forms in both hydroxyl- and amino-modified silica NPs, and π-π stacking occurs for benzyl-modified silica NPs. However, no strong interaction force exists between silica particles modified by alkyl and OEGMA polymer brushes (van der Waals interaction for alkyl-silica and repulsive interaction between brush-silica). Therefore, the occurrence of shear thickening above γ c is associated with interparticle interactions (frictional contacts) among silica NPs and hydrodynamic shear force. The attractive force has significant impact, because it might contribute to the turbulence near the surface of particles and the momentum of the fluid mass. The strength of the interaction force/frictional contact determines the stronger granulation and thus higher shear viscosity. Hence, the combined factors of hydrodynamic force and frictional contacts should be considered together when elucidating the shear thickening performance of colloid suspensions.

2.2 Effect of chemical compositions on the DST


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Recent theoretical treatment on shear jamming has proved that, for dense suspensions, a DST appears above that ϕ (a critical point in which d γ ⁄dσ = 0 appears). This parameter depends on the nature of the suspended particles. That is, increasing nonsphericity or surface roughness decreases ϕc,23 and the short-range interactions can alter the onset density of shear thickening as well.32 Here, we infer that chemical modification could impact the critical points as well. Thus, the effect of surface modification on ϕc and ϕJ were systematically investigated. The relation between the shear rate γ and the shear stress σ in dense suspension is depicted in the Figure 3. The results show a series of flow curves for suspensions with increasing particle volume fraction ϕ, and the results are very similar with the typical numerical result calculated by the single parameter theory.22 A transition from CST to DST is observed upon increase in ϕ for the three kinds of silica NP dense suspensions. Considering the fresh silica NP dense suspension (Figure 3a), at moderate density ϕ < 46%, γ (σ) is a strictly monotonic function of γ , and the shear thickening is continuous (Figure S7a). As ϕ increases to 46% a critical point appears at which the slope is horizontal. If ϕ > 46%, DST appears, and γ (σ) is no longer a monotonic function of γ . The whole curve assumes an S-shape. Moreover, suspension rheological experiments at high-volume fractions often stop at a certain volume fraction (ϕJ), beyond which sample preparation becomes impossible as the sample fractures under normal handling stresses. In the present system, ϕJ for fresh silica NPs was estimated at ϕJ ≥ 51%. The experimental results agree with the prediction that DST should begin at an onset packing fraction, ϕc < ϕJ, below the jamming point.22


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Similarly, ϕc and ϕJ for the thermal-treated and amino group-modified silica NP-based dense suspensions were also determined. The ϕc values for the thermal-treated and amino-modified silica NPs are 54% and 48%, respectively (Figures 3b and 3c, S7b and 7c), and their corresponding ϕJ values are ϕJ≥ 59% and ϕJ≥ 52%. Thus, ϕc decreases as follows: thermal-treated silica system > amino-modified silica system > fresh silica system. ϕJ also shows the same order.

ϕJ has been proved to be strongly sensitive to the nature of contact forces between suspended particles by dynamic simulation.21At small γ , the thermal motion keeps particles separated and hampers contact. As γ increases, the Brownian forces are not strong enough to overcome the frictional forces bringing particles together, leading to a transition from a frictionless to a mostly frictional rheology. Consequently, ϕc and ϕJ are reduced if particles are frictional. In our experiments, fresh silica is characteristic of strong frictional contacts (or larger friction coefficient) among silica NPs by hydrogen-bond interaction, lower ϕc and ϕJ are observed. However, for the thermal-treated silica NPs, the effective attractive interaction is reduced greatly, very little resistance is provided to relative motion, and higher ϕc and ϕJ are exhibited. By contrast, for the amino-modified silica system, the frictional contacts are induced by amino groups. ϕc and ϕJ are within those of thermal-treated system and fresh silica ones. Moreover, the crucial importance of friction can also be speculated using Figure S7. For a certain volume fraction silica NP dense suspension, the thickening for thermal-treated silica NPs is substantially weaker than that for fresh silica NPs ones. This rheological behavior agrees well with reported result that shear


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thickening is more pronounced with high friction particles than low ones.23 Finally, the DST transition calculated by single parameter theory occurs at 55% and the jamming volume is 58%,22 which substantially agree with the values for thermal-treated silica NP system.

Figure 3. Relation between the shear rate γ and the shear stress σ in dense suspensions with increasing volume fraction (ϕ) from top to bottom. (a) Fresh silica NP dense suspensions, with0.35 ϕ 0.50; (b) thermal-treated silica NP colloidal suspensions, with 0.35 ϕ 0.58; and (c) amino-modified silica NP suspensions, with 0.38 ϕ 0.48.

2.3 Effect of chemical compositions on onset stress of STF and its stability analysis

Two states exist, namely, a low-viscosity frictionless state and a high-viscosity frictional shear jammed state, above a ϕc. The two states are separated by a critical shear stress set by finite interparticle repulsions or steric interaction potential, at which repulsive force among particles are not sufficient to prevent the proliferation of contacts.22, 33 Thus, the effect of surface chemical modifications on silica NP on the onset (σonset) of shear thickening was investigated, and the experimental results are


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shown in the Figure4. Theoretical23, 25 and experimental26 results show that σonset is roughly independent of the volume fraction.Figure4 displays that, for fixed particles type, although γ at the onset of thickening decreases with increasing ϕ (Figure S7), σonset varies only weakly with ϕ. However, the σonset values for various particle types significant differ. The σonset values for fresh, thermal-treated, and amino-modified silica NP dense suspensions are 110, 15, and 60 Pa, respectively. Compared with the experimental data21, 34, 35 and simulation result,36 the critical onset stresses presented in this study are typically of the same order of σ ≈ 100k T/a (a is the particle radius).

Considering that σonset is apparently the point at which repulsive forces between particles are not sufficient to prevent the proliferation of contacts, the short-range repulsive force that are expected to prevent a colloidal dispersion from aggregation, such as van der Waals forces and electrostatic interaction, should be considered. Therefore, ζ as an indicator of the repulsive force of actual suspensions were also measured. The higher the absolute value of ζ, the stronger the repulsion forces, thus a higher shear stress is needed to overcome the force bringing particles together. For fresh silica NPs, the ζfresh was −57 mV. While for the hydroxyl group density reduced greatly after calcination, the corresponding ζthermal-treated decreased to −18.5mV. Moreover, ζamino was 31.6mV for the amino-modified silica NPs. The experimental result shows that σonset values for fresh silica NPs (110 Pa), amino-modified silica NPs (60 Pa), and thermal-treated silica NPs (15 Pa) decrease sequentially. These results are consistent with the results from previous simulations.21, 35, 37 Previous simulations


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showed that shear thickening can not only be masked by a yield stress and can be recovered when the yield stress is decreased below a threshold but can also be increased by increasing the magnitude and range of the repulsive forces the shear stress. Moreover, the ζ values can also be used to illustrate the stabilization of actual suspensions. The measured ζ indicates that the as-prepared dense suspensions are stable against perturbations of the velocity field at low stresses by the short-range stabilizing repulsive force, such as electrostatic interactions.

Figure 4.Shear stress dependence of the shear viscosity η. Volume fractions are shown in the graphs. The frictional contact (interparticle interaction) is expected to be tailored

by

chemical

modification.

(a)fresh,

(b)thermal-treated,

and

(c)

amino-modified silica NP dense suspensions.

3. CONCLUSION

The effects of the interparticle interaction on shear thickening behavior, including σonset, ϕc, and ϕJ, of surface-modified silica NPs are described. Three major conclusions can be drawn. First, existential frictional contact (or attractive force) induced by attraction among NPs is prerequisite to the achievement of shear thickening. The attraction could be induced by hydrogen bond, electrostatic


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interaction, and π-π stacking. Additionally, the switch from the contact-dominated frictional rheology for fresh silica NPs to the contactless (hence frictionless) rheology for thermal-treated silica NPs can be achieved. Second, ϕc for the transition from CST to DST decreases as follows: thermal-treated, amino group-modified, and fresh NPs. This phenomenon indicates that ϕc decreases with increasing frictional contact. Third, onset stress and the repulsive force among silica NPs are negatively correlated. These experimental results quantitatively match previous mathematical calculation and theoretical simulation. This work is beneficial in the design of high-performance dense suspension systems by clarifying and understanding the interaction between colloid particles.

Supporting Information Synthesis and characterization of the silica NPs modified with different functional groups, rheological curves of dense suspensions with different volume fraction. This material is available free of charge via the Internet at http://pubs.acs.org.

Corresponding Author *E-mail: [email protected]. Tel: 0086-931-4968466. Fax: 0086-931-8277088.

Notes The authors declare no competing financial interest.

ACKNOWLEDGMENTS This research was finally supported by NSFC (51335010, 21434009)


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References (1) Wagner, N. J.; Brady, J. F. Shear Thickening in Colloidal Dispersions.

Phys.Today 2009, 62, 27-32.

(2) Ding, J.; Tian, T.; Meng, Q.; Guo, Z.; Li, W.; Zhang, P.; Ciacchi, F. T.; Huang, J.; Yang, W. Smart Multifunctional Fluids for Lithium Ion Batteries: Enhanced Rate Performance and Intrinsic Mechanical Protection. Sci. Rep. 2013, 3,1-12.

(3) Hu, Y. T.; Boltenhagen, P.; Pine, D. J. Shear Thickening in Low Concentration Solutions of Wormlike Micelles. I. Direct Visualization of Transient Behavior and Phase Transitions. J. Rheol. 1998, 42, 1185-1208.

(4) White, K. L.; Hawkins, S.; Miyamoto, M.; Takahara, A.; Sue, H. J. Effects of Aspect Ratio and Concentration on Rheology of Epoxy Suspensions Containing Model Plate-like Nanoparticles. Phys. Fluids 2015, 27,123306.

(5) Waitukaitis, S. R.; Jaeger, H. M. Impact-activated Solidification of Dense Suspensions via Dynamic Jamming Fronts. Nature 2012, 487, 205-209.

(6) Feng, X.; Li, S.; Wang, Y.; Wang, Y.; Liu, J. Effects of Different Silica Particles on Quasi-static Stab Resistant Properties of Fabrics Impregnated with Shear Thickening Fluids. Mater. Des.2014, 64, 456-461.

(7) Mewis, J. Colloidal Suspension Rheology: Introduction to Colloid Science and

Rheology. Cambridge 2012.


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(8) Hoffman, R. L. Discontinuous and Dilatant Viscosity Behavior in Concentrated

Suspensions. I. Observation of a Flow Instability. J. Rheol. 1972, 16, 155-173.

(9) Hoffman, R. L. Discontinuous and Dilatant Viscosity Behavior in Concentrated Suspensions. II. Theory and Experimental Tests. J. Colloid Interface Sci. 1974, 46, 491-506.

(10) Bossis, G.; Brady, J. F. The Rheology of Brownian Suspensions. J. Chem. Phys. 1989, 91, 1866-1874.

(11) Bender, J.; Wagner, N. J. Reversible Shear Thickening in Mono disperse and Bidisperse Colloidal Dispersions. J. Rheol. 1996, 40, 899-916.

(12) Maranzano, B. J.; Wagner, N. J. The Effects of Interparticle Interactions and Particle Size on Reversible Shear Thickening: Hard-sphere Colloidal Dispersions. J. Rheol. 2001, 45, 1205-1222.

(13) Maranzano, B. J.; Wagner, N. J. The Effects of Particle Size on Reversible Shear Thickening of Concentrated Colloidal Dispersions. J. Chem. Phys. 2001, 114, 10514-10527.

(14) Lee, Y. S.; Wagner, N. J. Dynamic Properties of Shear Thickening Colloidal Suspensions. Rheol. Acta. 2003, 42, 199-208.

(15) Kaldasch, J.; Senge, B.; Laven, J. The Impact of non-DLVO Forces on the Onset

of

Shear

Thickening

of

Concentrated

Suspensions. Rheol. Acta. 2009, 48, 665-672.


Electrically

Stabilized

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(16) Kaldasch, J.; Senge, B.; Laven, J. Time Dependent Ginzburg-Landau Approach to Shear Thickening in Electrically Stabilized Colloidal Suspensions. Journal

of Thermodynamics 2013, 3, 319-323.

(17) Vermant, J.; Solomon, M. J. Flow-induced Structure in Colloidal Suspensions.

J. Phys.: Condens. Matter. 2005, 17, R187-R216.

(18) Brady, J. F.; Morris, J. F. Microstructure of Strongly Sheared Suspensions and its Impact on Rheology and Diffusion. J. Fluid Mech. 1997, 348, 103-139.

(19) David, R.; Brady, J. F. Structure, Diffusion and Rheology of Brownian Suspensions by Stokesian Dynamics Simulation. J. Fluid Mech. 2000, 407, 167-200.

(20) Phung, T.; Brady, J. F.; Bossis, G. Stokesian Dynamics Simulation of Brownian suspensions. J. Fluid Mech. 1996, 313, 181-207.

(21) Mari, R.; Seto, R.; Morris, J. F.; Denn, M. M. Discontinuous Shear Thickening in Brownian Suspensions by Dynamic Simulation. Proc. Natl. Acad, Sci, U.S.A. 2015, 112, 15326-15330.

(22) Wyart, M.; Cates, M. E. Discontinuous Shear Thickening without Inertia in Dense Non-Brownian Suspensions. Phys. Rev. Lett.2014, 112, 098302.

(23) Seto, R.; Mari, R.; Morris, J. F.; Denn, M. M. Discontinuous Shear Thickening of Frictional Hard-sphere Suspensions. Phys. Rev. Lett. 2013, 111, 218301.


Page 20 of 23

Page 21 of 23

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Langmuir

(24) Mari, R.; Seto, R.; Morris, J. F.; Denn, M. M. Shear Thickening, Frictionless and Frictional Rheologies in Non-Brownian Suspensions. J. Rheol.2014, 58, 1693-1724.

(25) Royer, J. R.; Blair, D. L.; Hudson, S. D. Rheological Signature of Frictional Interactions in Shear Thickening Suspensions. Phys. Rev. Lett.2016, 116, 188301.

(26) Lin, N. Y.; Guy, B. M.; Hermes, M.; Ness, C.; Sun, J.; Poon, W. C.; Cohen, I. Hydrodynamic and Contact Contributions to Continuous Shear Thickening in Colloidal Suspensions. Phys. Rev. Lett.2015, 115, 228304.

(27) Warren, J.; Offenberger, S.; Toghiani, H.; Pittman, C. U., Jr.; Lacy, T. E.; Kundu, S. Effect of Temperature on the Shear-thickening Behavior of Fumed Silica Suspensions. ACS Appl. Mater. Interfaces.2015, 7, 18650-19661.

(28) Shan, L.; Tian, Y.; Jiang, J.; Zhang, X.; Meng, Y. Effects of pH on Shear Thinning and Thickening Behaviors of Fumed Silica Suspensions. Colloids

Surf. A, 2015, 464, 1-7.

(29) Zhang, H.; Yuan, G.; Zhao, C.; Han, C. C. Liquid-gel-liquid Transition and Shear Thickening in Mixed Suspensions of Silica Colloid and Hyperbranched Polyethyleneimine. Langmuir 2013, 29, 12110-12117.

(30) Zhang, H.; Yuan, G.; Luo, J.; Han, C. C. Shear-thickening in Mixed Suspensions of Silica Colloid and Oppositely Charged Polyethyleneimine.

Langmuir 2014, 30, 11011-11018.


Langmuir

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Page 22 of 23

(31) Frith, W. J.; D’Haene, P.; Buscall, R.; Mewis, J. Shear Thickening in Model Suspensions of Sterically Stabilized Particles. J. Rheol.1996, 40, 531-548.

(32)Fernandez,

N.;

Mani,

R.;

Rinaldi,

D.;

Kadau,

D.;

Mosquet,

M.;

Lombois-Burger, H.; Cayer-Barrioz, J.; Herrmann, H. J.; Spencer, N. D.; Isa, L. Microscopic Mechanism for Shear Thickening of Non-Brownian Suspensions.

Phys. Rev. Lett.2013, 111, 108301.

(33) Kaldasch, J.; Senge, B. Shear Thickening in Polymer Stabilized Colloidal Suspensions. Colloid Polym. Sci. 2009, 287, 1481-1485.

(34) Zhou, Z.; Scales, P. J.; Boger, D. V. Chemical and Physical Control of the Rheology of Concentrated Metal Oxide Suspensions. Chem. Eng. Sci.2001, 56, 2901-2920.

(35) Franks, G. V.; Zhou, Z.; Duin, N. J.; Boger, D. V. Effect of Interparticle Forces on Shear Thickening of Oxide Suspensions. J. Rheol.2000, 44, 759-779.

(36) Kaldasch, J.; Senge, B.; Laven, J. Shear Thickening in Electrically-stabilized Colloidal Suspensions. Rheol. Acta.2008, 47, 319-323.

(37) Brown, E.; Forman, N. A.; Orellana, C. S.; Zhang, H.; Maynor, B. W.; Betts, D. E.; Desimone, J. M.; Jaeger, H. M. Generality of Shear Thickening in Dense Suspensions. Nature Mater. 2010, 9, 220-224.


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