A molecular dynamics study of the effect of functional groups and side chain on adsorption of alcoholic surfactant and interfacial thermal transport

YT Guo and D Surblys and H Matsubara and T Ohara, JOURNAL OF MOLECULAR LIQUIDS, 335, 116243 (2021).

DOI: 10.1016/j.molliq.2021.116243

In the present study, we investigated the effect of the number and position of functional groups, and the length of the main chain and side chain in organic surfactant on adsorption behavior and interfacial heat transfer between silica surface and alkane solvent by non-equilibrium molecular dynamics simulation, where the surfactants were primary/secondary alcohol, monohydric/dihydric alcohol, and linear/ branched alcohol. The results showed a similar adsorption behavior for all the surfactant types, where hydroxyl functional (AOH) groups adsorbed onto the silica surface and alkyl chain was in contact with the solvent, which produced a heat path from silica via surfactant to solvent. The number of adsorbed AOH groups did not directly translate to significantly decreased thermal boundary resistance due to the adsorption structure. Coulomb interaction enabled the closer distance between primary terminal AOH groups in surfactant and silica surface, which enhanced the solid-surfactant intermolecular heat transfer. However, Coulomb interaction contributed less to shorten the molecular distances between secondary AOH groups in surfactant and silica surface, which was connected to less efficient heat transfer from silica to surfactant and thereby did not enhance the interfacial heat transfer as much as surfactants with terminal AOH. The increase in terminal AOH groups in the surfactant molecules could not significantly reduce thermal boundary resistance, although the adsorption amount of AOH was distinctly greater than that of surfactants with single AOH. The side chain in surfactant enabled the efficient surfactant-solvent intermolecular heat transfer but related to the desorption of surfactant when decreasing the temperature. Thus branched-chain dihydric alcohol performed better than other surfactants on reducing thermal boundary resistance when the interfacial temperature was high enough to maintain the sufficient adsorption amount. We considered such reverse temperature-sensitive surfactant has a great potential application to fulfill multiple needs for heat dissipation of electronic devices, especially the high temperature operation. The new insights obtained in the present study were a step towards a molecular structure design of surfactant enhancing solid-liquid interfacial heat transfer. (C) 2021 The Author(s). Published by Elsevier B.V.

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