Temperature-dependent domain growth in 9-hydroxypalmitic acid monolayers

The surface pressure—molecular area isotherms and the texture features of 9-hydroxyhexa-decanoic acid monolayers are studied using the film-balance technique and Brewster-angle microscopy. In the two-phase coexistence region, homogeneously reflecting condensed-phase domains of a regular shape are formed. The 9-hydroxy-hexadecanoic acid monolayers show an unusual low, but linear, increase in the transition pressure with temperature and striking shape changes of the condensed-phase domains at different temperatures. The features of the monolayer are drastically changed by alkyl chain substitution by an OH group at the 9-position. The morphological features indicate molecular packing of nontilted alkyl chains in an orthorhombic and hexagonal lattice, respectively. OH substitution at different positions of the alkyl chain affects strongly and in a different way both the phase behaviour and the domain texture of the nonsubstituted palmitic acid monolayers.