Effect of processing conditions on the quality, stability, and permeability of thin organic films
Abstract
Thin organic films are used in a wide variety of applications, from membranes to microelectronics. While coating processes have been studied extensively, little work has been done in the quantitative characterization of the produced films. In this Thesis, spin coated polymer films are characterized using ellipsometry and Fourier Transform Infrared Spectroscopy-Attenuated Total Reflection (FTIR-ATR) for film quality. A new two-angle ellipsometric method for determining the thickness, refractive index, and film quality of a transparent film was developed, and was found to be better than conventional methods. Atactic poly(methyl methacrylate) (PMMA) films spin coated from toluene solutions at 23°C, and subsequently annealed at 140°C, were found with ellipsometry to be thinner, more uniform, and of higher quality than films spin coated from chloroform solutions. This represents the first quantitative study of the quality of spin coated polymer films using two-angle ellipsometry. ‘Quality’ films imply close to normal bulk density, few defects or pores, and little surface roughness. FTIR-ATR spectroscopy was used as an additional method for assessing film quality by placing films in direct contact with liquid water and aqueous solutions of electrolytes and surfactants, and measuring the uptake of water in situ. Spin coated films absorbed non-bulklike water only. Poor quality films, produced by casting, absorbed bulklike water also. The highest quality films absorbed the least water overall at equilibrium. Results from dynamic mass transport experiments suggested that after water initially penetrated the films, pores and defects were filled on a longer timescale, from several minutes to hours. PMMA films, such as the ones produced here, have potential uses as semi-permeable membranes for the separation of electrolytes or surfactants from water. The selectivity may be controlled with the control of the film quality. The use of ellipsometry was expanded to the direct probing of the surface density of cationic surfactant monolayers at the air/water interface. The surface density results were robust and fairly reliable for the three algorithms tested. Ellipsometry results compared favorably to results from reflection absorption infrared Spectroscopy.
Degree
Ph.D.
Advisors
Franses, Purdue University.
Subject Area
Chemical engineering
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