Surface viscosity of monomolecular films of n-alkoxy ethanols at various temperatures and pressures

Abstract

Abstract The surface viscosities of monomolecular films of n-alkoxy ethanols CH3(CH3)n−1OCH2CH2OH designated as CnOC2H4OH (n = 16, 18, 20, 22) were studied as a function of surface pressure (2–40 dynes/cm), temperature (15°–30°C), and shear rate (0.12–1.8 sec−1) using a rotational viscometer. The transition pressures observed for two-dimensional phase changes, i.e., from a liquid condensed (Lc) to an intermediate (I) or to a liquid-solid (LS) state agree fairly well with those found in π-A isotherms. For the C2OC2H4OH film the LS → S transformation has been obtained at 34 dynes/cm; this is higher by 2 dynes/cm than that observed by Deo et al. in π-A isotherms. The LS phase is found to be stable for a particular compound and at a particular temperature. The supermobile character of the film may be attributed to the strong hydrogen bonding between the film molecules themselves and a weaker interaction with the water subphase. Activation energy for viscous flow and relaxation time have been determined for all alkoxy ethanols at Lc → I or Lc → LS transition pressures and at different temperatures.