Structure and Dynamics of n-Alkanol Monolayers on a Mica Surface
D Bhandary and S Khan and JK Singh, JOURNAL OF PHYSICAL CHEMISTRY C, 118, 6809-6819 (2014).
All-atom molecular dynamics simulations are conducted to understand the structural and dynamical behavior of self-assembled monolayer of n-alkanols on a mica surface. In particular, we report the effect of increasing carbon chain length (C-1-C-10) on the self-assembly, surface diffusion, and preferential tilting of n-alkanol monolayer, for monolayer surface coverage ranging from 6 X 10(-5) to 3.54 X 10(-3) mol/m(2). The adsorption phenomena typically follow the Langmuir adsorption isotherm. However, the maximum adsorption is observed for n-hexanol, and it drops with further increase in the chain length. The surface diffusion coefficient, D within monolayer, is nonmonotonic in nature. The maximum value of D, decreases with increasing carbon chain length, with an exception of methanol owing to its preferential attachment with the cage of mica due to the presence of Kt The behavior of D, is clearly explained using instantaneous autocorrelation function of hydrogen bonds with the surface. Further, D-s, is found to vary inversely proportional to the lifetime of hydrogen bond of alkanols with the surface. Most probable tilt angle of molecules with increasing alkyl group (C-1, C-2, C-4, and C-6) is in the order 71 degrees > 38 degrees > 29 degrees > 19 degrees. However, for octanol we observed molecules to attain a preferential tilt angle of 80 degrees. The self-assembly behavior of lower alkanols, i.e., C-1, C-6 is contrary to that seen for higher alkanols.
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