Rheology of concentrated dispersions

Flow Behavior of Entangled Polymer Nanoparticle Composites in a Nanotube: Insights into Jamming State

Using molecular dynamics simulations, this study investigates the equilibrium properties and flow behaviors of entangled polymer nanoparticle composites (PNCs) within a nanotube. The results show that the density distribution of nanoparticles (NPs), displacement of polymer chains and NPs, and the moduli of PNCs remain relatively unaffected when NP volume fractions (ΦN) ≤0.10. However, the flow behavior of entangled PNCs deviates from the ideal parabolic profile seen in unentangled PNCs, displaying plug-like flow characteristics with a significant platform region, indicating the presence of shear bands. Interestingly, entangled PNCs at intermediate ΦN values undergo a significant alteration in NP distribution under steady flow, resulting in notable NP aggregation. At ΦN = 0.30, a distinct change in the static structure of PNCs occurs, reducing the equilibrium distance between neighboring NPs. Consequently, the motion of both polymer chains and NPs becomes restricted, leading to an increase in the moduli of PNCs resembling solid-like behavior. Additionally, the entangled PNCs experience a complete absence of flow, indicating the entry into a jamming state. This study contributes to the understanding of PNCs flow behavior and provides insights into fundamental aspects and practical implications of PNCs.

On the Response of a Herschel-Bulkley Fluid Due to a Moving Plate

In this paper, we study the boundary-layer flow of a Herschel-Bulkley fluid due to a moving plate; this problem has been experimentally investigated by others, where the fluid was assumed to be Carbopol, which has similar properties to cement. The computational fluid dynamics finite volume method from the open-source toolbox/library OpenFOAM is used on structured quad grids to solve the mass and the linear momentum conservation equations using the solver "overInterDyMFoam" customized with non-Newtonian viscosity libraries. The governing equations are solved numerically by using regularization methods in the context of the overset meshing technique. The results indicate that there is a good comparison between the experimental data and the simulations. The boundary layer thicknesses are predicted within the uncertainties of the measurements. The simulations indicate strong sensitivities to the rheological properties of the fluid.

Rheological characterization of CNC-CTAB network below and above critical micelle concentration (CMC)

The network of Cellulose Nanocrystal (CNC) suspension is explored below and above the critical micelle concentration (CMC), in the presence of cetyltrimethylammonium bromide (CTAB) with a positively charged head using TEM imaging and rheological characterization. CNC-CTAB gels show shear thinning behavior, complex relationship between strain amplitudes and CTAB concentration, diminishing thixotropic behavior as a function of CTAB and single and two yielding stress maxima as a function of CTAB, resulting from different microstructure below and above the critical Micelle Concentration (CMC) of CTAB. Comparing the flow curves of CNC-CTAB suspension/gel revealed the role played by CTAB content, CNC concentration and sonication energy in strengthening of the network. We analyzed and obtained yield stress from steady shear, creep testing and oscillatory experiments and compared them.

Graphene networks and their influence on free-volume properties of graphene–epoxidized natural rubber composites with a segregated structure: rheological and positron annihilation studies

The motion of ENR chains is retarded by the geometric confinement of “GE networks”, producing a high-density interfacial region in the vicinity of GE nanoplatelets.

Factors Affecting the Rheology and Processability of Highly Filled Suspensions

Suspensions filled with rigid particles at volume-loading levels that approach their maximum packing fraction are widely encountered, especially in the energetics, ceramics, pharmaceutical, magnetics, composites, food, and personal care industries. Highly filled suspensions, regardless of industrial application, exhibit a number of common rheological and processability traits, including viscoplasticity and wall slip, that necessitate special rheometers and appropriate characterization and numerical simulation methods. Furthermore, various factors, including the dispersion and distribution of the particles and their agglomerates, the entrainment of air, the filtration-based migration of the binder phase, and the shear-induced migration of particles, play important roles and must be considered in the design and optimization of manufacturing operations for processing of highly filled suspensions.

Coexistence of liquid and solid phases in flowing soft-glassy materials

Magnetic-resonance-imaging rheometrical experiments show that concentrated suspensions or emulsions cannot flow steadily at a uniform rate smaller than a critical value (gamma(c)). As a result, a "liquid" region (sheared rapidly, i.e., at a rate larger than gamma(c)) and a "solid" region (static) coexist. The behavior of the fluid in the liquid region follows a simple power-law model, while the extent of the solid region increases with the degree of jamming of the material.