Higher-order structure formation in adsorbed monolayers at aqueous solution surfaces studied by Brewster angle microscopy

The first-order phase transitions in adsorbed monolayers of 2-hydroxyethyl laurate have been studied by film balance and Brewster angle microscopy (BA M). A cusp point in the surface pressure-time (pi-t) curves indicates the c ommencemnet of phase transition. The critical surface pressure necessary fo r the phase transition increases with increasing temperature. Large size ci rcular domains having characterishtic internal stripes are observed up to 1 0 degrees C. The width of the stripes increases with increasing termperatur e. The separate stripes in a domain undergo continuous narrowing into a cor e defect which lies on the domain peripheral line at 2 degrees C. The core defect seems to be also present at higher temperatures but remains far out of the doman boundary at 10 degrees C. Two surface phases observed after th e cusp points by BAM are pseudo equilibrium state and the global equilibriu m is attained with the formation of one condensed surface phase after a lon g time.