Deposition Types and Final Structures for LB Films of Homologous Series of Long Chain Acids, Alcohols, and Esters

Abstract

Langmuir-Blodgett (LB) films of homologous series of simple amphiphilic compounds such as long chain fatty acids, alcohols, and esters have been investigated in order to clarify the factors governing the deposition type (X or Y) and their final structure (single or double layer, i. e., head-to-tail or head-to-head). These compounds play important roles as matrix materials to control molecular arrangement in constructing functional monolayer assemblies. From the measurement of transfer ratios in downward and upward trips, the X- and Y-types of film deposition were examined. While only Y-type deposition occurs with long chain acids and alcohols, both X- and Y-type depositions can be achieved with various long chain esters depending on physical conditions such as surface pressure, temperature, and dipping speed. X-ray diffraction patterns of the LB films were obtained by Weissenberg camera method. From the long-spacing values, single or double layered structure was determined. It has been found that LB films of long chain methyl esters take the head-to-head structure while long chain ethyl esters and acrylates have the headtotail structure, irrespective of deposition types. Thus, the final stable structure of a LB film seems to be determinedb y the hydrophilicityof. polar head groups. Theser esults provide a criterion for the selection of an appropriate matrix material to control the arrangements of functional molecules in the LB films.