Experimental optical retrieval of the Thermal Boundary Resistance of carbon nanotubes in water

Carbon-based nanostructures are extensively employed as solid additives in nanofluids or polymer matrices for applications in light harvesting, energy conversion and storage. To predict heat transfer in carbon-based nanostructures, a quantitative comprehension of thermal energy exchanges at the interface with their external environment is crucial. The Thermal Boundary Resistance (TBR) stands out as a key parameter hindering efficient thermal energy exchanges between nano-objects and their surroundings. In this work we experimentally determine the TBR for the archetypal case of an interface between multi-wall carbon nanotubes (CNTs) and water. Ultrafast energy exchanges are investigated using femtosecond time-resolved optical spectroscopy. Data rationalization via a thermo-optical model allows retrieval of a CNT/water interface TBR of (4.6 ± 2.2)×10−8 m2K/W. This value constitutes a benchmark for theories aimed at understanding energy transfer between a CNT and water. Notably, the functionalization of the surface of CNTs with covalent groups has been demonstrated to reduce the TBR and facilitate solid–liquid heat exchanges. The measurement and analysis protocol developed in this study is versatile and can be applied to any nanofluid and nanocomposite material.