Investigations Of Nanoscale Thermal Transport Mechanism And Modulation At Solid-liquid Interfaces

With the increasing maturity of microelectronic technology,electronic equipment is developing towards miniaturization.When the device size is reduced to the length scales on the order of the mean free path of the energy carrier,the overall thermal performance of nanoscale devices is determined mostly by the interfacial thermal resistance of the constituent materials,rather than the intrinsic thermal properties of the materials.Compared with the solid-solid interface,the two-phase difference between solid and liquid leads to extreme thermal resistance at the interface.Reducing thermal resistance is of great significance to improve the energy conversion efficiency and the heat dissipation performance of microelectronic devices and microfludic technologies.Previous studies have found many factors affecting interfacial thermal conductance at solid-liquid interface,while the dominant factors of nanoscale thermal transport at different interfaces still lack systematic investigation due to the diversity of interfaces and the complexity of mechanisms of thermal conduction and thermal convection.With the development of device miniaturization,the decreased time and space scale makes it difficult to deeply analyze the nanoscale thermal transport mechanism by macroscopic experiments.Aiming at the above issues,this paper is conducted by molecular dynamics simulation and thermal transport theory.The influence of atomic lattice structure is considered by introducing three kinds of palladium crystal faces of(100),(110)and(111),and the important role of water layer structure near the metal surface in thermal transport across solid-liquid interface is discovered.The ordered water layer can act as a "phonon bridge" to strengthen the interfacial phonon coupling and thus improve the thermal transport.When the order degree is partially destroyed,the increased interfacial friction will promote the phonon transfer in shear direction,which further strengthens interfacial thermal transport.The general law of interfacial thermal conductance changing with the order degree is discovered: the interfacial thermal conductance will show a trend of first increasing and then decreasing with the water layer varying from highly ordered to completely disordered.Multilayer graphene oxide is established to consider the effect of surface modification by functional groups,and the dominate role of interfacial hydrogen bond in thermal transport between graphene oxide and water is found.The hydroxyl concentration not only affects the thickness and surface structure of graphene oxide,but also affects the number of interfacial hydrogen bond and interaction strength.The interfacial thermal conductance is proportional to the hydrogen bond density,and tends to converge with the increased oxidation concentration due to the saturation of hydrogen bond density.Compared with the cluster distribution,the uniformly distributed hydroxyl groups are more conducive to form hydrogen bonds and promote thermal transport.Considering the influence of elastic modulus difference at interface,the graphene and substrate with different stiffness are established,and the stiffness shows a significant influence on the thermal conductivity of two-dimensional materials and the thermal transport of the interface with water.When the stiffness is distributed in a gradient,the thermal rectification effect is generated,where heat flux prefers to transfer from the softer end to the harder end.The increased stiffness of materials will reduce the interfacial thermal conductance.Since the interlayer thermal transfer is mainly dominated by phonons in out-of-plane direction,the suppression of low frequency phonon leads to its decrease of one order of magnitude.Based on the phonon vibration spectra,thermal excitation method and thermal relaxation time constant,the thermal transport difference is attributed to the suppression of low frequency phonon and the asymmetric phonon scattering.Considering the influences of microchannel geometry and fluid flow,the model of thermal transport across solid-fluid interface is proposed,and the important effects of flow field on microchannel heat dissipation is found.The differences of different methods for controlling temperature are discussed based on the viscous temperature rise caused by external force,and the quantitative relationships between viscous heat and flow velocity under the influence of multiple factors are established.The flow velocity shows little effects on the thermal transport in the smooth channel.But in the rough channel,the surface morphology will interfere with the flow field of the nearby fluid,and the acceleration of the fluid velocity in the center will limit the thermal motion of the fluid at the morphology bottom,which leads to the decrease of the thermal conductance.Nevertheless,the overall energy exchange of the rough channel is higher than that of the smooth channel,which indicates its better heat dissipation effect.According to the differences in the microstructure of the solid surface,this paper adopts molecular dynamics simulation and various thermal transport calculation methods to construct multiple sets of thermal transport models at solid-liquid interface,and taking into account factors such as atomic lattice structure and defects,surface local functional groups,material hardness differences,and microchannel geometries.The effects of interfacial water structure,interfacial hydrogen bond,interfacial contact and flow field on interfacial heat transport at nanoscale are discussed.The results will provide theoretical support and guidance for the thermal design of micro-nano devices and microfluidic technology.