Study on interface thermodynamic mechanism of membrane fouling in flat sheet ceramic membrane treating oilfield produced water.

In this study, a flat sheet ceramic membrane experimental device was constructed, and the thermodynamics of membrane fouling interface was studied for oilfield produced water. The flux of ceramic membrane in three kinds of model solutions were measured with time, as well as the surface tension, contact Angle and Zeta potential of solid. The thermodynamic mechanism of membrane fouling interface combined with XDLVO theory were explored for three kinds of model solutions. The thermodynamic study of the interface of ceramic plate membrane shows that the total interaction energy between membrane and oil droplets decreases with the increase of the distance between two interfaces at initial stage of membrane fouling, and finally transforms from the mutual attraction to the mutual repulsion. The total interaction energy between reservoir and oil droplet is shown as mutual attraction, and the total interaction energy decreases with the increase of the distance between reservoir and oil droplet interface. The zeta potential of crude oil was affected by salinity to some extent. The electrostatic shielding effect of the salt ions leads to a decrease in the ζ-potential of the three solutions. They are in the order: model solution A > model solution B > model solution C. This leads to a decrease in the electrostatic interaction (EL). And since the oil layer has the same composition as the oil droplets, the EL interactions in the three solutions can behave as mutual repulsion.

Elastocapillary interactions of thermoresponsive microgels across the volume phase transition temperatures.

HYPOTHESIS: Effective interactions of thermoresponsive microgels are known to be influenced by their volume phase transition. These soft colloids behave as repulsive spheres in the swollen state but show strong attraction in the collapsed state. We hypothesize that this transition in microgel interactions is governed by the interplay between surface tension and bulk elasticity. EXPERIMENTS: Using dissipative particle dynamics, we modeled the interactions between two coarse-grained microgel particles having a lower critical solution temperature around 32 °C, which are suspended in an explicit solvent. The potentials of mean force between microgels with different crosslinking densities were systematically characterized in the temperature range of 12-58 °C across the volume phase transition from steered molecular dynamics simulation trajectories. FINDINGS: The detailed dynamics of interaction is uncovered for microgels in different states. The simulations reveal the formation of capillary bridges between collapsed microgels at high temperatures, which contributes to strong attraction at contact. An elastocapillary model based on interface thermodynamics is proposed to describe microgel interactions and accurately predicts simulation data in a wide range of temperatures and overlapping distances. The results provide important physical insights into effective interactions between soft colloids that underpin broad applications of stimuli-responsive microgels.

Janus Segregation at the Carbon Nanotube-Catalyst Interface.

The contact between a carbon nanotube (CNT) edge and a catalyst is a curvilinear interface of fundamental and practical importance. Here, the first-principles evidence shows that on a rigid/solid catalyst the faceted CNT edge is significantly lower in energy compared to the minimal-length circle, with the interface energy difference decreasing on more compliant surfaces. This universal trend, found for typical monometallic (Ni, Co), bimetallic (Co7W6), and metal carbide (WC) catalysts, results in a peculiar edge segregation into one-dimensional Janus (armchair-zigzag) interface. Its lowered energy greatly enhances the nucleation probability of chiral tubes, dramatically affecting their growth kinetics. This offers a richer basis for understanding, modeling, and control of catalytic CNT synthesis.