R. N. King

Contact angles at the solid—water interface

Abstract The study of polymer—water interfaces by contact angle methods can be accomplished directly at the polymer—water interface. Using two water-immiscible liquids or a liquid and a vapor, one can deduce the dispersion and polar components of the hydrated solid surface free energy and the solid—water interfacial free energy. The theory is presented and a numerical analysis procedure is developed to solve the equations in the general case. The special case of n -octane and air is also presented. Data and results are given for poly(hydroxyethyl methacrylate-methoxyethyl methacrylate) copolymers of varying composition and equilibrium water contents. The results show that the hydrophilic component dominates the polymer—water interfacial properties, even at relatively low hydrophilic component compositions. The method presented should be useful for the study of polymer—water interfaces, particularly for hydratable or mobile polymers which can reorient to equilibrate differently with a water environment than with the air or vapor environment commonly used in contact angle studies.

Fibroblast cell proliferation on charged hydroxyethyl methacrylate copolymers

Abstract Two fibroblastic cell lines, 3T3 and 3T12, were grown on hydrophilic hydrogel substrates containing various amounts of positive or negative charge. The materials were copolymers of hydroxyethyl methacrylate (HEMA) and methacrylic acid (MAA), N,N -dimethylaminoethyl methacrylate hydrochloride (DMAEMA-HCl), or trimethylaminoethyl methacrylate chloride (TMAEMA-Cl). The samples were prepared as spun cast films on ultraclean glass microscope slides. The cells were grown in 10% fetal bovine serum supplemented Dulbeccos modified medium (DMM). Both cell lines survived and proliferated on the positively charged DMAEMA-HCl or TMAEMA-Cl copolymers with HEMA. Cells did not survive on the negative MAA-HEMA copolymers nor on the neutral HEMA homopolymers. Proliferation did not correlate with water content of the gel materials. Attachment as well as proliferation did correlate well with zeta potential and mole percentage positive charge as determined by bulk titration data.

Interfacial tensions at acrylic hydrogel-water interfaces

Abstract The hydrogel-water interface is a highly mobile transition region, perhaps on the order of 100 A in depth, which interfaces the bulk gel network with the surrounding aqueous solution. Consideration of the adsorption characteristics at such an interface requires information on the interfacial free energy or interfacial tension. Such information is generally difficult to obtain by most conventional methods. In this paper, we have applied underwater contact angle techniques (sessile bubbles) as probes of fully hydrated interfaces. Utilizing work of adhesion and contact angle assumptions, and contact angle data using captive air, octane, and dodecane at the gel-water interface, we have obtained the hydrated gel surface free energy and the gel-water interfacial free energy. The interfacial free energy drops rapidly to near zero as the equilibrium water content of the gel network approaches 30 wt%. Apparently, the surface, even with relatively low water contents, has sufficient mobility to achieve a molecular orientation which minimizes the interfacial tension. Data are presented on copolymers of methyl methacrylate-hydroxyethyl methacrylate, ethyl methacrylate-hydroxyethyl methacrylate, methoxyethyl methacrylate-hydroxyethyl methacrylate, methacrylic acid-hydroxyethyl methacrylate, and dimethylaminoethyl methacrylate-hydroxyethyl methacrylate, all prepared in our laboratories, and a commercially prepared polyacrylamide gel with varying crosslink density. These systems cover the equilibrium water content range from roughly zero to in excess of 90% wt%. Brief discussions of the possible effects of surface and interfacial tension-induced deformation of the gel substrate and the effects of charge density at the interface are also included.

Streaming potential investigations: Polymer thin films

Abstract Streaming potential evaluations were carried out on a wide variety of biopolymer and synthetic polymer thin films supported on glass microscope slides. The film-forming and streaming evaluation techniques are sufficiently accurate to provide reproducible results between different investigators. Films evaluated to date include various silanes, albumins, agarose, and synthetic polymers based on hydroxyethyl methacryle (HEMA), n -butyl methacrylate ( n -BMA), and methylacrmethylate (MMA). The effect of negative and positive charge incorporation upon the streaming potential and thus the ζ potential was studied via incorporation of methacrylic acid (MAA) and both HC1 and CH 3 C1 salts of dimethylaminoethyl methacrylate (DMAEMA) into the neutral polymer chains of HEMA, n -BMA, and MMA via copolymerization. Thin films of polystyrene, polydimethyl siloxane, polyvinyl chloride, and avcothane were also evaluated successfully.

Photoelectron mean free paths in barium stearate layers

Abstract Barium stearate monolayers were deposited on polished clean germanium and copper substrates using the Blodget technique. Film thicknesses were determined by ellipsometry by assuming the films were optically isotropic with a refractive index of 1.5 and an absorption coefficient of zero. X-ray photoelectron spectroscopy intensity ratios, obtained at 223 K to minimize vaporization, were used to determine electron inelastic mean free paths (IMFP) in the barium stearate layers. The substrate photoelectron lines cover a binding energy range of 1200 eV. IMFP values range from approximately 27 ± 5 A at about 230 eV to 65 ± 12 A at about 1480 eV kinetic energy. The approximately linear shape of this function, together with the throughput function of the instrument, suggests that over the binding energy range of 0–600 eV, the photoelectron mean free paths and throughput effects in the Hewlett-Packard instrument approximately cancel.