Pressure dependence of Kapitza resistance at gold/water and silicon/water interfaces

Abstract

We conducted non-equilibrium molecular dynamics simulations to investigate Kapitza length at solid/liquid interfaces under the effects of bulk liquid pressures. Gold and silicon were utilized as hydrophilic and hydrophobic solid walls with different wetting surface behaviors, while the number of confined liquid water molecules was adjusted to obtain different pressures inside the channels. The interactions of solid/liquid couples were reparameterized accurately by measuring the water contact angle of solid substrates. In this paper, we present a thorough analysis of the structure, normal stress, and temperature distribution of liquid water to elucidate thermal energy transport across interfaces. Our results demonstrate excellent agreement between the pressures of liquid water in nano-channels and published thermodynamics data. The pressures measured as normal stress components were characterized using a long cut-off distance reinforced by a long-range van der Waals tail correction term. To clarify the effects of bulk liquid pressures on water structure at hydrophilic and hydrophobic solid surfaces, we defined solid/liquid interface spacing as the distance between the surface and the peak value of the first water density layer. Near the gold surface, we found that interface spacing and peak value of first water density layer were constant and did not depend on bulk liquid pressure; near the silicon surface, those values depended directly upon bulk liquid. Our results reveal that the pressure dependence of Kapitza length strongly depends on the wettability of the solid surface. In the case of the hydrophilic gold surface, Kapitza length was stable despite increasing bulk liquid pressure, while it varied significantly at the hydrophobic silicon surface.

Atomic density effects on temperature characteristics and thermal transport at grain boundaries through a proper bin size selection

“…Recently, the ITR has been computationally measured between two media. [26][27][28][29][30][31] These reports suggest that density is one of the key factors affecting the thermal resistance at the interface. For instance, an increase of the atomic density at the interface improves the probability of intermolecular interactions, resulting in an enhanced phonon transmission and, consequently, a reduced ITR.…”

Spectral mapping of heat transfer mechanisms at liquid-solid interfaces

“…Here the absolute value accounts for the fact that at the left interface, heat flows from the solid to the liquid. Temperature jump ∆T s at the surface is determined by extrapolating linearly fitted temperature profiles in the solid and the liquid to the interface and calculating the difference [18]. Note that the precise values of ∆T s are not critically important in our analysis, because we focus on the spectral distribution of conductance instead of absolute values.…”

“…The calculation of Fig. 7(a) has been performed for intermediate coupling ε ls , and we expect that the effect of pressure is even stronger for smaller ε ls [18].…”

“…Exerting pressure on the solid-liquid system is known to boost the interfacial conductance at hydrophilic interfaces [18], because the increasing pressure enables closer S-L interface 1st-2nd bulk u.c. 2nd-3rd bulk u.c.…”

“…Molecular dynamics (MD) simulations have been used to investigate the effects of, e.g., liquid-solid bonding strength [13][14][15][16], temperature [17], pressure [18], surface roughness [19,20], surface patterning [21], and surface functionalization [22][23][24][25] on the interfacial conductance. Detailed analysis of heat transfer mechanisms at solid-liquid interfaces is, however, still lacking, mostly due to the nonexistence of simplifying small-displacement approximations allowing for extracting frequency-dependent mode transmission functions as in stiff solid-solid surfaces (see, e.g., Refs.…”