Molecular dynamics simulations of surfactant adsorption at oil/water interface under shear flow--颗粒学报PARTICUOLOGY

Ren, Y., Zhang, Q., Yang, N., Xu, J., Liu, J., Yang, R., . . . Sachweh, B. (2019). Molecular dynamics simulations of surfactant adsorption at oil/water interface under shear flow. Particuology, 44, 36-43. https://doi.org/10.1016/j.partic.2018.09.002

Molecular dynamics simulations of surfactant adsorption at oil/water interface under shear flow

Ying Ren ^{a b *}, Qiang Zhang ^{a c}, Ning Yang^{a b}, Ji Xu ^{a b}, Jialin Liu ^{a d}, Ruixin Yang ^{a c}, Christian Kunkelmann ^e, Eduard Schreiner ^e, Christian Holtze ^e, Kerstin Mülheims ^e, Bernd Sachweh ^f

a State Key Laboratory of Multiphase Complex Systems, Institute of Process Engineering, Chinese Academy of Sciences, P.O. Box 353, Beijing 100190, China
b Center for Mesoscience (COM), Institute of Process Engineering, Chinese Academy of Sciences, P.O. Box 353, Beijing 100190, China
c China University of Petroleum-Beijing, Beijing 102249, China
d University of Shanghai for Science and Technology, Shanghai 200093, China
e BASF SE, 67056 Ludwigshafen am Rhein, Germany
f BASF Advanced Chemicals Co., Ltd., Shanghai 200137, China

10.1016/j.partic.2018.09.002

Volume 44, June 2019, Pages 36-43

Received 11 June 2018, Revised 12 September 2018, Accepted 13 September 2018, Available online 26 January 2019, Version of Record 30 April 2019.

E-mail: yren@ipe.ac.cn

Highlights

• Adsorption kinetics of surfactants under shear were studied via non-equilibrium MD simulations.

• Mechanisms of emulsion droplets with dynamic interfacial structure in mixing devices were discussed.

• Structures of emulsion droplets in high-shear mixers are jointly determined by both the interfacial level and the device level.

• Coupling between two mesoscale phenomena were implemented in computer simulations with promising results.

Abstract

Surfactants are extensively used in many chemical products to improve their stability, appearance, texture, and rheology. Precise control of the emulsion droplet size distribution, which depends on the characteristics of the surfactant used, is important for target-oriented product design. A complete understanding of the structures and dynamics of emulsion droplets at the reactor level requires coupling of two mesoscale physical constraints, that at the interfacial level, i.e., smaller than a single droplet (Mesoscale-1), and that at the device level, i.e., larger than a single droplet (Mesoscale-2). In this work, the structures and adsorption kinetics of Mesoscale-1 surfactant molecules were studied via coarse-grained molecular dynamics. A non-equilibrium model that could introduce stable shear flow into the simulation box was used to investigate the interfacial structures at the droplet interface under different shear rates. The configurations of the surfactant molecules and adsorption amounts were compared with those obtained without flow. The adsorption kinetics for different shear rates were compared to determine the effects of hydrodynamic interactions. The dominant mechanisms governing the dynamic structures can thus be summarized as maximization of the adsorption density at the interface and minimization of flow resistance in the bulk phase (water and/or oil molecules). A scheme for coupling between Mesoscale-1 and Mesoscale-2 is proposed. This method is promising for the incorporation of interfacial structure effects into the hydrodynamics at the reactor device level for the manipulation of chemical products.

Graphical abstract

Keywords

Surfactant adsorption; Molecular dynamics simulation; Mesoscale modeling; Shear flow

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