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This paper focuses on the origin and implications of particle pressure and discontinuous shear thickening in concentrated suspensions. These properties are both related to the tendency of a flowing suspension to exert normal forces on the confining boundaries, thus providing a conceptual relation of the two seemingly distinct issues through a consideration of the pressure-volume relation of a flowing suspension. An overview of basic elements of suspension mechanics related to these topics is presented, including microstructure and continuum formulations based on single-phase and two-phase perspectives. The historical development of understanding of particle pressure and its influence on particle migration and that of discontinuous shear thickening are described. The mechanistic basis for the particle pressure in terms of suspension microstructure and the role of frictional contact interactions in shear thickening are described. A few open questions related to these topics are presented in conclusion. 

Phase change materials (PCMs) are latent heat storage materials that can store or release thermal energy while undergoing thermodynamic phase transitions. Organic PCMs can be emulsified in water in the presence of surfactants to enhance thermal conductivity and enable applications as heat transfer fluids. However, PCM nanoemulsions often become unstable during thermal cycling. To better understand the molecular origins of phase stability in PCM nanoemulsions, we designed a model PCM nanoemulsion system and studied how the molecular-level environments and dynamics of the surfactants and oil phase changed upon thermal cycling using liquid-state nuclear magnetic resonance (NMR) spectroscopy. The model system used octadecane as the oil phase, stearic acid as the surfactant, and aqueous NaOH as the continuous phase. The liquid fraction of octadecane within the nanoemulsions was quantified noninvasively during thermal cycling by liquid-state 1H single-pulse NMR measurements, revealing the extent of octadecane supercooling as a function of temperature. The mean droplet size of the PCM nanoemulsions, measured by dynamic light scattering (DLS), was correlated with the liquid content of octadecane to explain phase instability in the solid−liquid coexistence region. Quantitative 13C single-pulse NMR experiments established that the carbonyl surfactant head groups were present in multiple distinct environments during thermal cycling. After repeated thermal cycling, the 13C signal intensity of the carbonyl surfactant head groups decreased, indicating that the surfactant head groups lost molecular mobility. The results explain, in part, the origin of phase instability of PCM nanoemulsions upon thermal cycling. 

We use the conservative phase-field lattice Boltzmann method to investigate the dynamics when a Newtonian droplet comes in contact with an immiscible viscoelastic liquid film. The dynamics of the three liquid phases are explored through numerical simulations, with a focus on illustrating the contact line dynamics and the viscoelastic effects described by the Oldroyd-B model. The droplet dynamics are contrasted with the case of a Newtonian fluid film. The simulations demonstrate that when the film is viscoelastic, the droplet dynamics become insensitive to the film thickness when the polymer viscosity and relaxation time are large. A viscoelastic ridge forms at the moving contact line, which evolves with a power-law dependence on time. By rescaling the interface profile of the ridge using its height and width, it appears to collapse onto a similar shape. Our findings reveal a strong correlation between the viscoelastic stress and the interface shape near the contact line. 

Asphaltenes can cause operational challenges in petroleum production facilities and adverselyaffect production by adsorption on mineral surfaces and alteration of the oil wettability of reservoirs.Therefore, understanding asphaltene adsorption mechanisms and their effects is crucial toimproving the effi ciency of oil production and reducing costs. In this study, we focus onunderstanding the impact of asphaltene concentration and the depositing environment ofasphaltene adsorption on solid surfaces using the quartz crystal microbalance with dissipation(QCM-D) technique. The initial and long-term kinetics of adsorption at different concentrations wereexamined on three different solid surfaces including silicon dioxide to represent quartz mineral,stainless steel, and gold. The frequency–dissipation data showed evidence of monolayer adsorptioninitially, followed by multilayer formation. At short times, the adsorbed mass increased linearly withtime, suggesting that the process was kinetically controlled rather than diffusion-controlled. Theresults were reproducible and did not depend on convection velocity but did depend on the surfacematerial. At later stages, the monolayer development appeared to follow the random sequentialadsorption (RSA) theory. Once multilayer adsorption commenced, the rates agreed well with thetwo-layer model of Zhu and Gu, 1990. The impact of asphaltene adsorption on the wettability of thesurface was examined using contact angle studies, which showed decreasing water wettability withan increase in the adsorbed mass. The contact angle of water after 12 h of adsorption leveled off ataround 100° on all three surfaces. Contact angle measurements were also used to evaluate if brinesalinity causes the wettability alteration of surfaces with the adsorbed asphaltene. The resultsindicate that at 3% NaCl solution, the contact angle decreased only slightly by less than 2°. 

Controlling the downhole pressure is an important parameter for successful and safe drilling operations. Several types of weighting agents (i.e., high-density particles), traditionally barite particles, are added to maintain the desired density of the drilling fluid (DF). The DF density is an important design parameter for preventing multiple drilling complications. These issues are caused by the settling of the dense particles, an undesired phenomenon also referred to as sagging. Therefore, there is a need to understand the settling characteristics of heavy particles in such scenarios. To this end, simultaneous measurements of liquid phase flow patterns and particle settling velocities have been conducted in a Taylor-Couette (TC) cell with a rotating inner cylinder and stationary outer cylinder separated by an annular gap of 9.0 mm. Liquid flow patterns and particle settling velocities have been measured using particle image velocimetry (PIV) and particle tracking velocimetry (PTV) techniques, respectively. Experiments have been performed by varying the rotational speed of the inner cylinder up to 200 rev/min, which is used in normal drilling operations. Spherical particles with diameters of 3.0 mm or 4.0 mm and densities between 1.2 g/cm3 and 3.95 g/cm3 were used. The liquid phases studied included deionized (DI) water and mineral oil, which are the basic components of a non-Newtonian DF with a shear-thinning viscosity. The DF is a mud-like emulsion of opaque appearance, which impedes the ability to observe the liquid flow field and particle settling in the TC cell. To address this issue, a solution of carboxymethyl cellulose (CMC) with a 6% weight concentration in DI water was used. This non-Newtonian solution displays shear-thinning rheological behavior and was used as a transparent alternative to the opaque DF. For water, PIV results have shown wavy vortex flow (WVF) to turbulent Taylor vortex flow (TTVF), which agrees with the flow patterns reported in the literature. For mineral oil, circular Couette flow (CCF) was observed at up to 100 rev/min and vortex formation at 200 rev/min. For CMC, no vortex formation was observed up to 200 rev/min, only CCF. The settling velocities for all particles in water matched with the particle settling velocities predicted using the Basset-Boussinesq-Oseen (BBO) equation of motion. For mineral oil and CMC, the results did not match well with the predicted settling velocities, especially for heavy particles due possibly to the radial particle migration and interactions with the outer cylinder wall. 

We studied the evolution of capillary bridges between nominally flat plates undergoing multiple cycles of compression and stretching in experiments and simulations. We varied the distance between the plates in small increments to study the full evolution of the bridge shape. Experiments show that contact angle hysteresis determines the shape of the bridge. In sliding drops, hysteresis can be modeled using a contact angle-dependent resistive force F̃R applied at the contact line. We developed a model that accurately captures the evolution of the bridge shape by combining F̃R and constrained energy minimization. Unlike previous work, this allows for both complete and partial contact line pinning. We also explored the effect of using nonparallel plates. The asymmetry in the bridge shape causes the movement of the center of mass of the bridge and can be explained by contact angle hysteresis. We find that even a slight misalignment between the flat plates can have a measurable effect. 

When an aqueous drop contacts an immiscible oil film, it displays complex interfacial dynamics. When the spreading factor is positive, upon contact, the oil spreads onto the drop's liquid–air interface, first forming a liquid bridge whose curvature drives an apparent drop spreading motion and later engulfs the drop. We study this flow using both three-phase lattice Boltzmann simulations based on the conservative phase field model, and experiments. Inertially and viscously limited dynamics are explored using the Ohnesorge number $Oh$ and the ratio between the film height $$H$$ and the initial drop radius $$R$$ . Both regimes show that the radial growth of the liquid bridge $$r$$ is fairly insensitive to the film height $$H$$ , and scales with time $$T$$ as $$r\sim T^{1/2}$$ for $$Oh\ll 1$$ , and as $$r\sim T^{2/5}$$ for $$Oh\gg 1$$ . For $$Oh\gg 1$$ , we show experimentally that this immiscible liquid bridge growth is analogous with the miscible drop–film coalescence case. Contrary to the growth of the liquid bridge, however, we find that the late-time engulfment dynamics and final interface profiles are significantly affected by the ratio $H/R$ .