Mechanical and Thermodynamic Properties of Chlorophyll-a Surfactants at Air-Water Interface

Abstract

Self-assembly of surfactants at air-water interfaces are widely used in the process of forming thin films for various applications. However, methods of determining fundamental properties of molecular scale interactions of these floating monolayers involve complicated processes. In this study, Langmuir-Blodgett method was used to generate surface pressure-area isotherms, which were manipulated to determine various mechanical and thermodynamic properties of Chlorophyll-a surfactants crucial in understanding molecular level interactions crucial in bottom-up design architectures. Results demonstrated optimum Chlorophyll-a concentration at 2.0 mg/ml of giving proper molecular area at zero surface pressure at 86.7 Å2/molecule. Using the elastic modulus profile, deposition pressure for close-packed phase is calculated as 26 mN/m. Young’s modulus meanwhile was measured as 0.04 GPa corresponding to about 6000 psi of pressure, which is between the values exhibited by rubber (0.01 to 0.1 GPa). Close-packed Chl-a monolayer was observed to have properties similar to rubber, with its Poisson’s ratio calculated at about 0.55. The results measured illustrates that the method could be employed to scrutinize deposition conditions and film characteristics for Chl-a molecules and other amphiphilic materials in the fabrication of bio-devices.