Shear thickening effect of the suspensions of silica nanoparticles in PEG with different particle size, concentration, and shear

Construction of nano-silica particle clusters and their effects on the shear thickening properties of liquids

It is of great research significance to prepare a new shear thickening fluid (STF) with a simple process, remarkable thickening effect and excellent impact resistance from the properties of the particles. Inspired by the shear thickening mechanism, nano-silica particle clusters (SPC) with different morphological structures were prepared by the reaction of amino-modified silica with polyethylene glycol diglycidyl ether (PEGDGE), and the structure models of particle clusters were designed through theoretical analysis. The structure of SPC was affected by the degree of amination modification and the molecular weight of PEGDGE, which was analyzed by DLS and TEM. The shear thickening behavior of the fluid was evaluated by steady-state rheology and dynamic-state rheology analysis. The shear thickening behavior of the fluid composed of SPC also changed greatly with the influence of the degree of amination modification and the molecular weight of PEGDGE. In addition, compared with the STF contained original silica, the STF contained SPC could produce a faster and stronger shear thickening response. Therefore, silica particle clusters are not only a promising candidate for the preparation of high-performance shear thickening fluids, but can also be better applied to industrial and scientific fields such as impact protection and shock absorption.

Rheological behavior of xanthan gum suspensions with Fe-based nanoparticles: the effect of nanoparticles and the mechanism

The rheological behavior of a xanthan gum (XG) suspension with Fe-based nanoparticles (Fe-NPs), e.g., nanoparticles of zerovalent iron (nZVI) and Fe3O4 (nFe3O4), needs to be understood for better injection of Fe-NPs for groundwater remediation. In this study, the rheological behavior of a XG suspension of nZVI and nFe3O4 was investigated at different particle concentrations. The Ostwald, Sisko, Williamson, and Cross models were employed to fit the rheological behavior of the suspensions for quantitatively describing the effect of the particles. The results showed that the viscosity of the XG solutions decreased with increasing particle concentrations and they maintained shear thinning properties. The Cross model was the best among the four models to describe the shear thinning behavior of the XG solution in the presence of the particles. According to Cross model analysis, increasing particle concentrations increased the degree of shear thinning behavior, as indicated by the increase of the power index (n). Also, the relaxation time (λ) decreased with increasing particle concentrations, which indicated an increase of molecule movement of XG. Compared with nFe3O4, nZVI resulted in a larger decrease in viscosity and a larger increase in the degree of shear thinning behavior. There was a good linear relation between n and λ for the suspensions (R2 = 0.85), which indicated that increasing molecule movement of XG was an important mechanism for the particles to intensify the shear thinning rheological behavior of the XG suspension of Fe-NPs. This study added insight into the knowledge of the rheological properties of the XG suspension of Fe-NPs, which is of importance for the field injection effort.

Polyethylene Oxide (PEO) Provides Bridges to Silica Nanoparticles to Form a Shear Thickening Electrolyte for High Performance Impact Resistant Lithium-ion Batteries

The development of shear thickening electrolytes is proving to be pivotal in the quest for impact resistant lithium-ion batteries (LIBs). However, the high viscosity and poor stability associated with the need for high filler content has to date impeded progress. Here, this work reports a new type of polymer-bridged shear thickening electrolyte that overcomes these shortcomings, by utilizing the interaction between polymer chains and silica nanoparticles. The incorporation of polyethylene oxide (PEO) facilitates hydrocluster formation providing impact resistance with a filler content as low as 2.2 wt%. This low viscosity electrolyte has a high ionic conductivity of ≈5.1 mS cm-1 with excellent long-term stability, over 30 days. The effectiveness of this electrolyte in LIBs is demonstrated by excellent electrochemical performance and high impact resistance.

Effect of Solvent on Convectively Driven Silica Particle Assembly: Decoupling Surface Tension, Viscosity, and Evaporation Rate

The process of convectively self-assembling particles in films suffers from low reproducibility due to its high dependency on particle concentration, as well as a variety of interactions and physical parameters. Inhomogeneities in flow rates and instabilities at the air-liquid interface are mostly responsible for reproducibility issues. These problems are aggravated by adding multiple components to the dispersion, such as binary solvent mixtures or surfactant/polymer additives, both common approaches to control stick-slip behavior. When an additive is used, not only does it change the surface tension, but also the viscosity and the evaporation rate. Worse yet, gradients in these three properties can form, which then lead to Marangoni currents. Here, we use a series of alcohols to study the role of viscosity independently of other solvent properties, to show its impact on stick-slip behavior and interband distances. We show that mixtures of glycerol and alcohol or poly(acrylic acid) and alcohol lead to more complex patterning. Marangoni currents are not always observed in co-solvent systems, being dependent on the rate of solvent evaporation. To produce homogeneous particle assemblies and control stick-slip behavior, gradients must be avoided, and the surface tension and viscosity need both be carefully controlled.

Synthesis and properties of SiO2/SiO2@Ag two-phase STFs

Soft body armor with a strain-sensing function using conductive shear thickening fluids (STFs) has gradually gained research interest. In this study, conductive SiO₂@Ag core-shell microspheres were synthesized and the influence of process parameters on their properties was evaluated. Subsequently, SiO₂ and SiO₂@Ag were used as dispersed phases to prepare two-phase STFs, the effect of the core-shell microspheres' proportion on the rheological properties of the STFs was investigated, and its mechanism was discussed. The results indicated that SiO₂@Ag core-shell microspheres were coated with elemental silver and when the concentration of sodium hydroxide and glucose were 0.07 and 0.09 mol L^-1, respectively, the coating surface was the most uniform and compact, and the conductivity reached the minimum value of 0.56 Ω cm. The two-phase STFs exhibited good and reversible shear thickening behaviors and the critical shear rate decreased with increasing core-shell microsphere concentration. Additionally, when the mass fraction of SiO₂ and SiO₂@Ag core-shell microspheres was 45% and 20%, respectively, the thickening rate was 325%, and the resistance of two-phase STFs decreased simultaneously with the emergence of shear thickening that reached the lowest value of 795.16 kΩ. This study provides a novel strategy for synthesizing conductive STFs for strain-sensing flexible stab-resistant composites.

Microscopic mechanism study of the rheological behavior of non-Newtonian fluids based on dissipative particle dynamics

Non-Newtonian fluid rheological properties are a hot research topic for realizing intelligent applications. In order to investigate the microscopic mechanism and structural evolution process of the nonlinear rheological behavior of non-Newtonian fluids, this paper systematically investigates two continuous nonlinear rheological behaviors of non-Newtonian fluids, namely shear-thickening and shear-thinning rheological properties, using a non-Newtonian fluid system composed of polyethylene glycol (PEG) mixed with nano-silica (Nano-SiO₂) by a dissipative particle dynamics (DPD) method. It is shown that at low shear rates, the molecular chains of PEG in the fluid are stretched due to shear flow and the molecular structure is transformed into an ordered state; and the effective hydrodynamic radius of Nano-SiO₂ beads decreases, which makes the translational friction coefficient of the beads decrease and the system mobility increases, exhibiting shear-thinning behavior. When the shear rate exceeds the critical value, the contact and collision probability between Nano-SiO₂ beads in the non-Newtonian fluid increases; a large number of silicon hydroxyl groups exist on the surface of Nano-SiO₂, which form a large number of hydrogen bonds when they are close to each other and constrain the particle separation, resulting in a large aggregation of Nano-SiO₂ beads, leading to an increase in the effective kinetic radius of Nano-SiO₂ beads and an increase in the coefficient of translational friction, forming a blockage of the fluid system and exhibiting a shear-thickening behavior. Our study provides insights for understanding the rheological behavior of non-Newtonian fluids from a microscopic perspective, and contributes to the intelligent application of non-Newtonian fluids.

Fumed Silica-Based Suspensions for Shear Thickening Applications: A Full-Scale Rheological Study

Understanding shear thickening fluids (STFs) is critically important in a broad spectrum of fields ranging from biology to military. STFs are referred to the suspension of solid particles in an inert carrier liquid. Customizing the thickening behavior is vital for obtaining desired properties. Hence, comprehending shear thickening mechanisms is necessary to fully understand the factors affecting the shear thickening response of the STFs. Herein, we systematically investigate the effects of a wide range of parameters, from inherent properties of the constituents, including size and surface chemistry of the suspended particles, to practical conditions such as temperature and shear history, on the shear thickening behavior of fumed silica nanoparticles (NPs)-based suspensions in a polyethylene glycol (PEG) medium. Accordingly, increasing the hydrophobicity of the silica NPs or decreasing the NP size transforms the suspensions from sol to gel. The sol systems exhibit a strong shear thickening response, while shear thinning behavior is prominent in the strong gel systems. Hybridization of different silica NPs is also leveraged to tune the shear thickening behavior. In addition, we showcase the decisive role of operating temperature or shear history on the shear thickening behavior of suspensions. For instance, in terms of the shear history, above a critical value of preshear, the shear thickening behavior occurs at lower shear rates for STFs containing hydrophilic NPs. It is believed that the provided insights in this study can pave the way for developing advanced STFs with prescribed features.