Surface wave studies at air/liquid interfaces.
Item
-
Title
-
Surface wave studies at air/liquid interfaces.
-
Identifier
-
AAI9510641
-
identifier
-
9510641
-
Creator
-
Cao, Beihua.
-
Contributor
-
Co-Advisers: Mahn Won Kim | Herman Z. Cummins
-
Date
-
1995
-
Language
-
English
-
Publisher
-
City University of New York.
-
Subject
-
Physics, Fluid and Plasma | Physics, Optics
-
Abstract
-
We use surface heterodyne light scattering to study the thermally excited surface waves at the interface between air and a polymer solution. Three specific polymer waves at the solutions are chosen to vary the degree of surface adsorption from a depletion layer to an adsorption layer. The first solution is polyisobutylene (PIB) in decane, which exhibits no depletion or adsorption at the interface; the second one is polybromostyrene (PBrS) in toluene which exhibits a depletion layer; and the third one is polyethyleneoxide (PEO) in water, which exhibits an adsorption layer since the polymer is surface active. Since the thicknesses of the depletion and adsorption layers depend on the molecular weight, we also study the interfacial properties of PBrS in toluene and PEO in water using polymers with both low and high molecular weights.;We measure the power spectra at several scattering vectors, and as the bulk polymer concentration and molecular weight are varied. Two theoretical models are used to analyze the experimental data. The first model uses the theory for capillary waves at a simple liquid interface. The second model uses the theory for viscoelastic polymer solutions at an air/solution interface.;For PIB in decane, we find that the theory for viscoelastic polymer solutions is a more suitable model for relatively high polymer concentrations; it also gives better results for the surface tensions and viscosities.;For PBrS in toluene, we find that, for low molecular weight (90K), the surface waves lie in the capillary wave regime over the entire concentration range accessible to our experiments. By contrast, for high molecular weight (900K) at high polymer concentrations, the surface waves are strongly affected by the viscoelastic behavior of the bulk. In all cases, the depletion layers have no effect on the surface waves. This result is consistent with the small thickness of the depletion layers.;For PEO in water, we find that, for low molecular weight (85K), the surface wave motion is strongly modified by the presence of the adsorption layers. By contrast, for high molecular weight (1000K), the adsorption layers appear to have no effect on the surface waves. This is consistent with the results of surface tension and ellipsometry measurements, which show that 85K PEO forms very dense and thick adsorption layers at the solution interface while 1000K PEO can not form this type of adsorption layer. We also show experimentally that the surface waves of PEO/water solutions with {dollar}M\sb{lcub}\rm W{rcub}{dollar} = 1000K cross over from capillary waves to elastic waves as the polymer concentration is increased.;Finally, we study the interfacial properties of graft copolymers at the air/water interface using a surface balance, ellipsometry, surface light scattering and atomic force microscopy (AFM). This combination of techniques enables us to determine the surface structure of monolayers of graft copolymers at the air/water interface.
-
Type
-
dissertation
-
Source
-
PQT Legacy CUNY.xlsx
-
degree
-
Ph.D.
