Rheology of silica dispersions stabilized by polymers

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.

Visual assessment and rheological characterization of shape retention of products on a surface

A device to measure the height loss of a sample extruded from a syringe on a surface is described thus emulating toothpaste extrusion from a tube with the goal to predict shape retention of the extruded ribbon. Correlations with rheological tests are considered with a special focus on experiments more likely to be implementable in an industrial environment. In agreement with previous studies, the instantaneous viscosity maximum measured in a stress ramp test is a good predictor of ribbon height loss. Up- and down-shear flow curves of the thixotropic loop were fitted with a generalized Casson equation and the correlations of the fitting parameters with the height loss were also considered. Yield stress extracted from the up-shear flow curve as well as the shape of the curve is found to define the ribbon height loss as well as the degree of thixotropy which may be quantified by the width of the loop or simply as the ratio of viscosities at low shear rate.

Adsorption of the Xanthan Gum Polymer and Sodium Dodecylbenzenesulfonate Surfactant in Sandstone Reservoirs: Experimental and Density Function Theory Studies

Chemical flooding using a polymer and/or surfactant has been widely applied in oilfields worldwide for enhanced oil recovery. Chemical adsorption in reservoirs has a significant effect on the rock permeability and wettability and hence can affect the overall oil production. In this work, two chemicals, namely, the xanthan gum (XG) biopolymer and sodium dodecylbenzenesulfonate (SDBS) anionic surfactant, were used individually as displacement fluids. The amount of chemical adsorption on the rock surface and the residual resistance factor (permeability reduction) were calculated throughout the flooding experiments using an unconsolidated sandstone (SS) pack model. The effects of the injected chemicals' concentration and reservoir salinity on adsorption capacity have been examined. Additionally, the effect of the addition of nanosilica particles (NSPs) to the injected fluid on the rock adsorption was also investigated. The results showed that the amount of XG and SDBS adsorption on the rock surface increased, albeit to a different extent, by increasing the chemical concentration at the applied salinities (0, 3.5, 5, and 10%) of the displacement fluids. Also, the permeability reduction increased with the increase in XG and SDBS concentrations; however, permeability reduction due to SDBS flooding was lower than that of XG in SS. The use of NSPs as a coinjectant to the XG and SDBS displacement fluids increased the adsorption on the SS rock. A plausible mechanism for the adsorption of the XG/NSP and SDBS/NSP blends on the SS surface was proposed. A density function theory calculation was employed to establish a relation between the adsorptivity of NSPs on SDBS and XG and the total energy and dipole moment of the molecules.

Linking intermolecular interactions and rheological behaviour in capillary suspensions

HYPOTHESIS

Capillary suspensions feature networks of particles connected by liquid bridges, which are obtained by adding a small amount of a second immiscible liquid to a suspension. It is possible to link the network formation as well as the rheological behaviour of capillary suspensions to the intermolecular interactions of their constituents.

EXPERIMENTS AND SIMULATIONS

Through a combination of experimental and numerical methods, we present a novel approach, based on Hansen solubility parameters computed from Molecular Dynamics (MD) simulations, to rationalize and predict the rheological behaviour of capillary suspensions. We investigated the formation of capillary suspensions for various combinations of bulk and secondary liquids mixed with hydrophilic silica particles. The predictions were confirmed experimentally by rheological analysis, interfacial tension measurements and microscopy (CLSM) imaging.

FINDINGS

Numerical and experimental results show that the Hansen solubility parameters theory allows to predict the formation of capillary suspensions, whose strength exponentially decays with decreasing intermolecular interactions between the secondary liquids and the dispersed particles. High immiscibility between the bulk and secondary liquid strengthens the gel up to a critical immiscibility point, above which the strength of the gel remains mostly affected by the affinity between the secondary liquids and the dispersed particles. Furthermore, we find that hydrogen-bonding and polar interactions control the formation of capillary suspensions. This simple approach can guide the selection of adequate solvents and immiscible secondary liquids, allowing an easy formulation of new particulate-based gels.

Two step yielding in soft materials

A review is presented on the topic of two-step yielding observed in complex fluids that cover a broad variety of materials ranging from colloidal gels, attractive glasses, emulsions, suspensions, and several commercial paste-like materials. The common features in various systems displaying two-step yielding behavior are the presence of two characteristic forces between the interacting particles or two varying representative length or time scales. This focused review aims to provide physical insights, mechanistic understanding of the two-step yielding and other associated rheological consequences of this nonlinear behavior. A discussion is provided on the microstructural details with an overview of different experimental systems exhibiting double-yielding studied so far highlighting the similarities and differences among them. Particularly, the effects of continuous phase properties, dispersed particle phase factors (size, shape, softness and surface charge) and external force field (electric, magnetic, thermal and shear flows) on two-step yielding are considered.

Filament Extrusion and Its 3D Printing of Poly(Lactic Acid)/Poly(Styrene-co-Methyl Methacrylate) Blends

Herein, we report the melt blending of amorphous poly(lactide acid) (PLA) with poly(styrene-co-methyl methacrylate) (poly(S-co-MMA)). The PLAx/poly(S-co-MMA)y blends were made using amorphous PLA compositions from 50, 75, and 90wt.%, namely PLA50/poly(S-co-MMA)50, PLA75/poly(S-co-MMA)25, and PLA90/poly(S-co-MMA)10, respectively. The PLAx/poly(S-co-MMA)y blend pellets were extruded into filaments through a prototype extruder at 195 °C. The 3D printing was done via fused deposition modeling (FDM) at the same temperature and a 40 mm/s feed rate. Furthermore, thermogravimetric curves of the PLAx/poly(S-co-MMA)y blends showed slight thermal decomposition with less than 0.2% mass loss during filament extrusion and 3D printing. However, the thermal decomposition of the blends is lower when compared to amorphous PLA and poly(S-co-MMA). On the contrary, the PLAx/poly(S-co-MMA)y blend has a higher Young’s modulus (E) than amorphous PLA, and is closer to poly(S-co-MMA), in particular, PLA90/poly(S-co-MMA)10. The PLAx/poly(S-co-MMA)y blends proved improved properties concerning amorphous PLA through mechanical and rheological characterization.