Title

Monte Carlo Simulation of a Film Growth With Reactive Hydrophobic, Polar, and Aqueous Components By a Covalent Bond Fluctuating Model

Document Type

Article

Publication Date

4-28-2007

Department

Physics and Astronomy

Abstract

Using a bond fluctuating model (BFM), Monte Carlo simulations are performed to study the film growth in a mixture of reactive hydrophobic (H) and hydrophilic (P) groups in a simultaneous reactive and evaporating aqueous (A) solution on a simple three dimensional lattice. In addition to the excluded volume, short range phenomenological interactions among each constituents and kinetic functionalities are used to capture their major characteristics. The simulation involves thermodynamic equilibration via stochastic movement of each constituent by Metropolis algorithm as well as cross-linking reaction among constituents with evaporating aqueous component. The film thickness (h) and its interface width (W) are examined with a reactive aqueous solvent for a range of temperatures (T). Results are compared with a previous study [Yang Macromol. Theory Simul. 15, 263 (2006)] with an effective bond fluctuation model (EBFM). Simulation data show a much slower power-law growth for h and W with BFM than that with EBFM. With BFM, growth of the film thickness can be described by h proportional to t(gamma), with a typical value gamma(1)approximate to 0.97 in initial time regime followed by gamma(2)approximate to 0.77 at T=5, for example. Growth of the interface width can also be described by a power law, W proportional to t(beta), with beta(1)approximate to 0.40 initially and beta(2)approximate to 0.25 in later stage. Corresponding values of the exponents with EBFM are much higher, i.e., gamma(1)approximate to 1.84, gamma(2)approximate to 1.34 and beta(1)approximate to 1.05, beta(2)approximate to 0.60 at T=5. Correct restrictions on the bond length with the excluded volume used with BFM are found to have a greater effect on steady-state film thickness (h(s)) and the interface width (W-s) at low temperatures than that at high temperatures. The relaxation patterns of the interface width with BFM seem to change noticeably from those with EBFM. A better relaxed film with a smoother surface is thus achieved by the improved cross-linking covalent bond fluctuation model which is more realistic in capturing appropriate details of systems such as polyurethane film. The steady-state film thickness increases monotonically with the temperature possibly with two logarithmic dependences. The equilibrium interface width shows a nonmonotonic dependence: on increasing the temperature, W-s seems to increase slowly before it begins to decay W-s=4.12-1.39 ln(T). (c) 2007 American Institute of Physics.

Publication Title

Journal of Chemical Physics

Volume

126

Issue

16

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