Langmuir film behavior of a series of triphenylsilylether-terminated alcohols

This dissertation investigates the quasi-two-dimensional phase behavior of monolayer films at the air/water interface (Langmuir film) formed by a series of triphenylsilylether-terminated alcohols. These particular surface-active molecules are members of the class termed bulge amphiphiles, due to the general lollipop-like shape of the surfactants. Langmuir film isotherms, the plot of surface pressure (π) against surface area (A), are the primary method used to describe the monolayer films. The phase transition points and monolayer compressibilities for each amphiphile were obtained from the isotherm curves. Isotherms were taken at several temperatures (14--26°C) in order to determine the Langmuir film phase diagram for the triphenylsilylether (TPSE) series, and to calculate the change in entropy over the phase transition. Brewster angle microscopy (BAM) was used to image the monolayer films during isotherm experiments. The results for the TPSE series amphiphiles confirm the behavior demonstrated by another bulge amphiphile, with the addition of observations specific to the TPSE series. With compression, these monolayers collapse reversibly and with a large increase in entropy. A reversible monolayer collapse mechanism for bulge amphiphiles is proposed. This mechanism focuses on the relatively weak intermolecular forces exhibited by the TPSE series due to their molecular structure. The collapse mechanism is compared to the smectic-nematic transition (cybotactic clusters) observed in liquid crystals