Effect of temperature on the surface viscosity of monolayers of n-alkoxy propanols and n-alkoxy butanols

Abstract

The surface viscosities (μ) of monomolecular films of four n-alkoxy propanols (C 16, C 18, C 20, and C 22) and two n-alkoxy butanols (C 16 and C 18) were measured as a function of surface pressure (π) and shear rate ( g) at two different temperatures viz. 20 and 30°C, using a rotational viscometer. In addition to μ-π curves, π- A (area) isotherms were also drawn for all the monolayers studied. In the case of C 16- and C 18-alkoxy propanols and alkoxy butanols, μ increases with increase in temperature whereas μ decreases with increase in temperature in the case of C 20 and C 22 alkoxy propanols especially after the L c → I transition. A similar type of behavior was also observed for the n-alcohols [Patil et al., J. Colloid Interface Sci. 25, 462 (1967)] and n-alkoxyl ethanols [Katti and Patil, J. Colloid Interface Sci. 28, 227 (1968)]. It seems that the hydrocarbon chain plays a more prominent role than the polar group so far as the effect of temperature on these monolayers is concerned. The activation energy of viscous flow ( ΔF), relaxation time (τ), and the intermolecular interaction energy W i− k (0.94 r i ) have been calculated. Almost similar values were obtained for ΔF and also for W i− k (0.94 r i ) indicating that kindred relaxation phenomena are involved in all these monolayers at different temperatures. The interaction energy is however found to increase slowly with temperature.