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

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.