Conventional wisdom tells us that interfacial thermal transport is more efficient when the interface adhesion energy is enhanced. In this study, it is demonstrated that molecular bridges consisting of small molecules chemically absorbed on solid surfaces can enhance the thermal transport across hard-soft material interfaces by as much as 7-fold despite a significant decrease in the interface adhesion energy. This work provides an unconventional strategy to improve thermal transport across material interfaces.

The nature of the bond is a dominant factor in determining the thermal transport across interfaces. In this paper, we study the role of the hydrogen bond in thermal transport across interfaces between hard and soft materials with different surface functionalizations around room temperature using molecular dynamics simulations. Gold (Au) is studied as the hard material, and four different types of organic liquids with different polarizations, including hexane (CHCH), hexanamine (CHNH), hexanol (CHOH), and hexanoic acid (CHCOOH), are used to represent the soft materials. To study the hydrogen bonds at the Au/organic liquid interface, three types of thiol-terminated self-assembled monolayer (SAM) molecules, including 1-hexanethiol [HS(CH)CH], 6-mercapto-1-hexanol [HS(CH)OH], and 6-mercaptohexanoic acid [HS(CH)COOH], are used to functionalize the Au surface. These SAM molecules form hydrogen bonds with the studied organic liquids with varying strengths, which are found to significantly improve efficient interfacial thermal transport. Detailed analyses on the molecular-level details reveal that such efficient thermal transport originates from the collaborative effects of the electrostatic and van der Waals portions in the hydrogen bonds. It is found that stronger hydrogen bonds will pull the organic molecules closer to the interface. This shorter intermolecular distance leads to increased interatomic forces across the interfaces, which result in larger interfacial heat flux and thus higher thermal conductance. These results can provide important insight into the design of hard/soft materials or structures for a wide range of applications.