Molecular dynamics simulation study on the structure and the dynamic properties of nano-confined alcohols between graphene surfaces

- Confined alcohol molecules orient themselves with the hydrophobic methyl groups exposing to the two plates.
- Polar hydroxyl groups stand away from surface to preserve a hydrogen-bonding with adjacent layer.
- The diffusion coefficient decrease by increasing the size of alkyl group in alcohol molecules.
- Increasing the relaxation time occur by increasing the size of alkyl group in alcohol molecules.

Molecular dynamics simulation was conducted to study the structure and dynamics of hydrogen bonds in alcohols (methanol, ethanol, and 1-propanol) confined within graphene nanopores at a constant parallel component of pressure, 101.3 kPa, and at constant temperatures, ranging from 260 to 340 K. The results indicated that, while confined alcohol molecules orient themselves with the hydrophobic methyl groups exposing to the two plates, the polar hydroxyl groups stand away from surface to preserve a hydrogen-bonding with adjacent layer. Contrary to confined water, the average of hydrogen-bond values of confined alcohol molecules is found to be the same as bulk. Decreasing diffusion coefficient, increasing the relaxation time and, accordingly, decreasing hydrogen bond exchange dynamics occur by increasing the size of alkyl group in alcohol molecules in bulk and confined fluids. Our findings in this work indicate that the effect of confining surfaces on the confined fluid increase at lower temperatures compared to the higher temperatures.