(408i) Monte Carlo Simulations Of Binary Amphiphile Mixtures

The self-assembly of amphiphilic molecules is a widespread phenomenon. Lipids dissolved in aqueous solution spontaneously form vesicles, and other surfactants form spherical or cylindrical micelles depending upon the size of the hydrophilic head group relative to the volume and length of the hydrophobic tails [1]. The addition of surfactant to a solution containing lipid bilayers causes the vesicles to rupture and break apart into smaller aggregates. Mixtures of silica nanopartcles and block copolymers have also been studied recently for use in the fabrication of nanoelectronic devices [2]. We examine the behavior of dilute solutions containing a binary mixture of amphiphilic particles. Each model particle consists of a rigid solvophobic head group and one or more flexible solvophobic chains. The results of multiple simulations in the grand canonical ensemble are combined via histogram reweighting to determine whether these solutions undergo macroscopic phase separation or micellization. The critical micellar concentration is determined from the dependence of osmotic pressure on the density of each component [3,4]. In prior work with a single amphiphile species, we found that the morphology of the aggregates depends on the number and length of the chain segments. Here, we examine the effect of amphiphile structure on the range of densities over which two types of aggregates coexist.

[1] Israelachvili, J.N., Mitchell, D.J., Ninham, B.W., J. Chem. Soc. Faraday Trans. II 72, 1525-1568 (1976).

[2] Warren, S.C., Disalvo, F.J., Wiesner, U., Nature Mater. 6, 156-161 (2007).

[3] Floriano, M.A., Caponetti, E., Panagiotopoulos, A.Z., Langmuir 15, 3143-3151 (1999).

[4] Panagiotopoulos, A.Z., Floriano, M.A., Kumar, S.K., Langmuir 18, 2940-2948 (2002).