Surface potentials of monomolecular films of n-long chain alkoxy ethanols

Abstract

Surface potentials (ΔV) of monomolecular films of n-long chain alkoxy ethanols CH₂(CH₂)_n-1-OCH₂CH₂OH designated as C_n-OC₂H₄OH (n = 16, 18, 20 and 22) were measured by the ionizing electrode method at three temperatures (around 15, 20 and 25°C) as a function of surface pressure (π) and area/molecule (A). The results have been represented as ΔV-π, ΔV-A, µ⊥-A andπ-A isotherms, where µ⊥ is the normal component of the apparent dipole moment per molecule. The data provide valuable information as regards molecular interaction and orientation of various films at different pressures. The transition pressures for different phase changes such as gas → liquid condensed (G → L_e) and L_e → S (solid state) observed in ΔV-π curves agree well with the π-A curves. In all the films studied ΔV increases as π increases or A decreases. It also increases as the chain length increases from C₁₆ to C₂₂ at all the temperatures. The surface dipole moment (µ⊥) generally decreases as area/molecule decreases except in C₂₂-OC₂H₄OH at 14.4°C in the highly condensed region. Diffused first order change has been observed for C₁₈-OC₂H₄OH at 14.7 and 19.4°C, for C₂O-OC₂H₄OH at 24.4°C and for C₂₂-OC₂H₄OH at 14.4 and 19.2°C. The superior behavior in reducing the water evaporation loss by alkoxy ethanol films compared to that of the corresponding alcohols has been discussed.