An amino acid surfactant, monosodium N-stearoyl-L-glutamate (MSSG), was assumed to associate with higher alcohols (HAs) in 1: 1 molar ratio in an aqueous phase, and the packing parameters of the 1/1 MSSG/HA associates, P-alpha, were calculated by molecular dynamics (MD). P-alpha is defined as A(t1) (l(t1) + l(t2))/a(h)l(t1), where A(t1) stands for the cross-sectional area of the MSSG tail, l(t1) for the length of the MSSG tail, l(t2) for the length of the HA tail, and alpha(h) for the area of the MSSG head group. The P-alpha value increased from 0.83 to 1.02 as the HA tail length (l(t2)) increased from C-14 to C-22. Associates of HAs having longer tails with MSSG are likely to fit better into bilayers because P-alpha is closer to l when l(t2) is longer. In the graphical results of the MD simulation for the association, however, a steric hindrance was found between the head groups of MSSG/HA when l(t2) was greater than or equal toC(19). Based on this result, HA was classified into short-chain HA (SCHA, l(t2) < C-19) and tong-chain HA (LCHA, l(t2) greater than or equal to C-19), and several possible packing units, composed of compositional combinations of MSSG, SCHA, and LCHA, were proposed. The packing unit is a building block which could constitute bilayers, and it is composed of variable compositional combinations of MSSG/HA. Assuming that SCHA associates with MSSG, the packing parameter, P-unit, was calculated in a water box by MD for each packing unit. P-unit is the packing parameter of a packing unit and it is defined as V-u/l(u)alpha(u), where V-u is the tail volume of the packing unit, l(u) is the chain length, and alpha(u) is the head area. For the calculation, stearyl alcohol (C-18-OH, SA) was chosen as a SCHA and behenyl alcohol (C-22-OH, BA) as a LCHA. When the compositional ratio MSSG:SCHA:LCHA was 1: 1: 1, Punit was around 1. The packing unit having Punit of around I formed a colloidally stable suspension for 30 days and its aggegate was a lamellar structure. However, the other packing units, for which P-unit deviates significantly from 1, precipitated out in their suspensions and showed no evidence of a lamellar structure. According to the graphical MD simulations for the compositional MSSG/SCHA/LCHA associations in bilayers, vertical steric hindrance was found between LCHAs when P-unit deviated significantly from 1. The steric hindrance would prevent the packing units from forming a stable bilayer and induce precipitation in the suspensions. Therefore, a proper combinational ratio of MSSG:LCHA:SCHA:LCHA:SCHA would play a major role in forming a lamellar structure. (C) 2004 Elsevier Inc. All rights reserved.