Interfacial Thermal Transport over Solid-Liquid Interfaces Mediated by Heterogeneous Self-Assembled Monolayers: A Molecular Dynamics Study

QY Luo and D Surblys and G Kikugawa and T Ohara, JOURNAL OF PHYSICAL CHEMISTRY B, 129, 8888-8901 (2025).

DOI: 10.1021/acs.jpcb.5c01889

Interfacial thermal management plays a pivotal role in ensuring efficient heat dissipation in nanodevices with solid-liquid interfaces. Although sandwiching self-assembled monolayers (SAMs) that have heterogeneous chain lengths between solids and liquids is considered a promising strategy for enhancing interfacial thermal transport, it has received limited attention in the current research landscape. In this study, we systematically examine the effects of liquid-induced SAM stiffness and pattern densities of heterogeneous SAMs on interfacial thermal resistance (ITR) over SAM-mediated Au-polymer liquid interfaces with various SAM-liquid affinities using nonequilibrium molecular dynamics simulations. Our findings confirm that hydrophobic alkanethiol SAMs exhibit higher induced stiffness, while hydrophilic poly(ethylene glycol) (PEG)-COOH-functionalized SAMs are comparatively softer, thereby influencing the equilibrium structures of the patterned SAM surfaces. The structured arrangement of stiff heterogeneous alkanethiol SAMs is well-preserved, which increases the contact area utilized by liquids compared to that of nonpatterned systems, thereby resulting in smaller ITR. Thus, a dense arrangement of alternating SAM lengths is recommended for minimizing ITR. The softness of hydrophilic SAMs limits the potential increase in the contact area, making it challenging to further reduce ITR compared to that of nonpatterned systems, particularly under very high SAM-liquid affinity, where ITR can exceed that of nonpatterned configurations. The liquid adsorption density on SAM surfaces is a key factor governing the ITR in varying affinity cases. The hydrogen bond number density plays an additional role when hydrogen bonds form between the SAMs and liquid molecules. These insights highlight the importance of prioritizing induced stiffness in the molecular design of patterned SAM surfaces for efficient thermal management in nanodevices with multiple solid-liquid interfaces.

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