Laser light-scattering measurements of viscoelastic monomolecular films

• Published in: Journal of colloid and interface science Vol. 83; no. 2; pp. 315 - 334
• Main Authors: Hard, Sverker, Neuman, Ronald D
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 1981
• ISSN: 0021-9797; 1095-7103
• DOI: 10.1016/0021-9797(81)90328-3

Laser light-scattering measurements of the capillary wave motion of aqueous surfaces covered with fatty acid and lecithin monomolecular films are reported. An improved measuring technique allowed quantitative determination of both film dilational elasticity and film dilational viscosity. Fluctuating capillary wave properties were observed with surface films in the gaseous—liquid two-phase region. For monolayers in the liquid-expanded state, the elasticity determined by light-scattering measurements is the same as that obtained by film-balance measurements at higher surface concentrations but not at lower concentrations. The well-known transition between liquid-expanded and liquid-condensed films does not show up in the measured elasticity. This result can be expected from reported observations of finite speed, stepwise barrier-compressed pentadecanoic acid films. The viscosities measured by the light-scattering technique are smaller than one surface millipoise and are comparable in magnitude to surface viscosity values obtained with mechanical surface (shear) viscometers.