Use of Moiré Fringes in Investigating Surface Wave Propagation in Monolayers of Soluble Polymers

Abstract

The moird fringe wave visualization technique produces instantaneous records of the wave field, from which the propagation characteristics of the surface may be deduced. This is particularly useful for surfaces whose properties are time variant. Although the wave damping properties of the polymer monolayers examined were considerably more complicated than those of monolayers of simpler surface active agents, existing theory was shown to be adequate in explaining the observed effects on the basis of the surface tension and surface dilational elasticity of the monolayer. This agreement of theoretical prediction with observation supports the evidence for the existence of longitudinal surface waves. Using the moird technique to investigate the time variation of solution-adsorbed monolayers of poly(ethylene oxide) on water, it was found that this polymer produces from solution the same type of stable monolayer as is produced by spreading the material in a monolayer on a pure water substrate.

Dynamic Surface Properties of Solutions of Poly(ethylene oxide) and Polyethylene Glycols

“…However, such determination is beyond the scope of this work. Even the reliable estimation of the main relaxation times in the surface films of PEG and PEO is still lacking and the data of different authors are not always in agreement. − ,,, In this work, eq 4 is used only for qualitative comparison with the results of the methods of transversal and longitudinal surface waves.…”

“…It was shown also in ref that the conventional dispersion relation, which connects the characteristics of surface waves with the surface properties, holds at least for dilute polymer solutions. Different forms of this equation have been presented in the literature. ,,,− ,− In this work we will use thedispersion relation for surface waves in the liquid of finite depth where k = 2π/λ + iα is the complex wavenumber, α is the damping coefficient, λ is the wavelength, g is the gravitational acceleration, m 2 = k 2 − iωρ/μ, σ is the surface tension, μ is the viscosity, ρ is the density, and h is the depth of the liquid in the trough (in our work h = 15 mm).…”

“…Low-frequency surface waves have been used until now mainly in studies of spread polymer films. − Only Scott and Stephens have presented results of measurements of the characteristics of capillary waves for PEO solution at a single concentration …”

Spreading characteristics of an insoluble surfactant film on a thin liquid layer: comparison between theory and experiment

“…This additional light source had no discernible effect on the Moiré pattern. There are many excellent references describing the geometric optics that govern the Moiré technique in the refracted image configuration (Theocaris & Koutsabessis 1965;Scott 1972;Scott & Stephens 1972;Kheshgi & Scriven 1983;Kafri & Glatt 1989). We therefore simply list the relevant equations used to reconstruct the time-variant surface profile in the Appendix and turn our attention to the experimental results.…”

“…This sensitive technique, which maps the time variant surface slope, is ideally suited to surface deformations occurring over an extended region. The technique has been successfully used previously to measure the acoustical properties of adsorbed polymer monolayers at an air-water interface (Scott & Stephens 1972), the wavelength and damping coefficient of propagating surface waves in the presence of surfactant (Scott 1972) and the surface profile of a falling liquid curtain (Kheshgi & Scriven 1983). Note that our experimental set-up does not involve use of a restraining ring for surfactant delivery, which may be disruptive to the spreading dynamics at early times, particularly for the thin films investigated.…”