# Solvent fluctuations around solvophobic, solvophilic and patchy nanostructures and the accompanying solvent mediated interactions

## TL;DR

This study uses classical density functional theory to analyze how solvent density fluctuations influence the forces between nanostructures with different surface affinities, revealing capillary evaporation effects and interface structures.

## Contribution

It introduces a detailed DFT-based approach to connect solvent fluctuations with mediated forces between solvophobic, solvophilic, and patchy nanostructures.

## Key findings

- Strongly attractive forces occur at small separations for solvophobic blocks.
- Enhanced density fluctuations correlate with incipient gas-liquid interfaces.
- Capillary evaporation leads to low-density intrusions between nanostructures.

## Abstract

Using classical density functional theory (DFT) we calculate the density profile $\rho({\mathbf r})$ and local compressibility $\chi({\mathbf r})$ of a simple liquid solvent in which a pair of blocks with (microscopic) rectangular cross-section are immersed. We consider blocks that are solvophobic, solvophilic and also ones that have both solvophobic and solvophilic patches. Large values of $\chi({\mathbf r})$ correspond to regions in space where the liquid density is fluctuating most strongly. We seek to elucidate how enhanced density fluctuations correlate with the solvent mediated force between the blocks, as the distance between the blocks and the chemical potential of the liquid reservoir vary. For sufficiently solvophobic blocks, at small block separations and small deviations from bulk gas-liquid coexistence, we observe a strongly attractive (near constant) force, stemming from capillary evaporation to form a low density gas-like intrusion between the blocks. The accompanying $\chi({\mathbf r})$ exhibits structure which reflects the incipient gas-liquid interfaces that develop. We argue that our model system provides a means to understanding the basic physics of solvent mediated interactions between nanostructures, and between objects such as proteins in water, that possess hydrophobic and hydrophilic patches.