Simultaneous, Non-Contact Measurement of Liquid and Interfacial Thermal Properties via a Differential Square-Pulsed Source Method

Accurate characterization of heat transport across solid-liquid interfaces is essential for thermal management in micro- and nanoscale systems. Yet existing techniques often require prior knowledge of liquid properties, which complicates the simultaneous resolution of interfacial and bulk behaviors, and lose sensitivity once interfacial conductance exceeds 100 MW m^-2 K^-1. Here we present a differential square-pulsed source (DSPS) method that provides simultaneous, noncontact measurement of liquid thermal conductivity, volumetric heat capacity, and solid-liquid interfacial conductance without any predefined liquid parameters. Dual-frequency excitation combined with in situ substrate referencing enables property extraction from multilayer structures, and numerical simulations show a typical uncertainty of about 8% in interfacial conductance, confirming robustness. The protocol is validated for a wide spectrum of liquids, including oils, lubricants, aqueous electrolytes, and pure water, with excellent agreement with literature values for bulk properties. Analysis of the data set clarifies how vibrational-spectrum mismatch, ionic layering, and related interfacial phenomena govern heat transfer, and demonstrates that oleophilic hexadecyl silane modification of aluminum increases interfacial conductance by a factor of 16. The results reveal that conductance can be strongly tuned through surface wettability and chemical functionalization, offering direct guidelines for interface engineering. Because the approach is readily extendable to soft materials such as thermal-interface gels, it promises broad applicability in emerging interface-dominated thermal technologies.