The phase behavior and kinetics of selected amphiphilic Langmuir monolayers

Langmuir monolayers of pure compounds and mixtures of various acids, acetates, esters, thioic esters, and alcohols were studied. In general, the phase diagram of each compound or mixture can be classified as one of two types or an intermediate of those two types. The acids and acetates have a similar phase diagram, Type I, due to a large effective head group. The alcohols and most esters have a similar diagram, Type II, due to an effectively smaller head group. The thioic esters studied and methyl hexadecanoate have intermediate behavior. To first approximation, the two types of diagrams represent the extremes in effective head group size and differ primarily in the presence or absence of the L2 phase, a phase with a large unit cell. The effective size of the head group was shown to have a strong dependence upon the degree of hydrogen bonding with the water subphase.;New image processing methods were developed to study the kinetics of monolayer textures. In preliminary experiments over short times with n-nonadecanol at room temperature, we find that the average growth in length of azimuthal tilt domains scales as tn where n = 0.246 ≈ 1/4. The preliminary result of n = 1/4 is consistent with late-time Rayleigh-Benard coarsening or a system with a non-conserved order parameter coarsening from a disordered phase to a striped phase. The image processing methods developed are general and suitable for analysis of other systems.