Surface viscosity of monomolecular films of n-alkoxy propanols and n-alkoxy butanols at 25°C

Abstract

The surface viscosities (μ) of a series of n-alkoxy propanols and oxy butanols having the general formula C n OC 3H 6OH and C n OC 4H 8OH where n = 16, 18, 20, and 22 have been measured at 25°C as a function of surface pressure (π) at different shear rates ( g). All the monomolecular films studied exhibited non-Newtonian character. π- A isotherms for the above compounds were also reported at 25°C. The transition pressures observed for two-dimensional phase transformation, i.e., liquid condensed ( L c ) to an intermediate state ( I) or solid state ( S) are in good agreement with those found in μ-π curves. The extrapolated values of viscosity at zero shear rate and infinite shear rate have been taken for calculating the free energies of activation for viscous flow and relaxation times (τ). It is observed that the intermolecular interaction energies and free energy changes of activation for viscous flow were found to be more or less the same for all monolayers studied, thereby indicating that the relaxation phenomenon remains almost unchanged irrespective of transition pressure and viscosity observed in these monolayers. Viscosity data of these compounds have been compared with those of n-alcohols and n-alkoxy ethanols.