Polymer chain interdiffusion in gel/gel adhesion
Abstract
In this research, the effect of the degree of crosslinking, polymer hydrophilicity, surface chemistry, and bulk diffusion on the adhesion and cohesion of hydrogels was investigated. Gel/Gel adhesion is important since it may be used to improve the design of bioadhesive controlled drug release devices. Hydrogels were prepared by free radical, solution polymerization of acrylic acid, 2-hydroxyethyl methacrylate, and ethylene glycol dimethacrylate. The surface chemistry of selected polymers was modified by grafting poly(ethylene glycol) of varying molecular weight onto the network's surface. Polymer networks were also prepared which were loaded with monodisperse poly(ethylene glycol). The surface and bulk properties of the polymers were characterized by dynamic and equilibrium swelling studies, contact angle measurements, GC, GPC, DSC, TGA, and FTIR spectroscopy. The adhesion between hydrated polymer gels was investigated as a function of polymer composition, swelling media pH and ionic strength, contact time, and surface chemistry by using tensiometry. It was found that the fracture energy decays rapidly when the volume fraction of the polymer increases. The role of diffusion in gel/gel adhesion was examined by near-field FTIR microscopy. A device was designed and built to modify a standard FTIR microscope for these experiments; compositional maps can now be obtained with improved spatial resolution and enhanced signal to noise. The resolution was enhanced by about a factor of five with this technique. Polymer diffusion across a gel/gel interface was a substantial mechanism of adhesion. The diffusivity of poly(ethylene glycol) was on the order of 10$\sp{-8}$ to 10$\sp{-9}$ cm$\sp2$/s for these swollen polymer gels. The diffusivity of poly(ethylene glycol) in poly(acrylic acid) gels scaled as M$\sp{-0.41}$. This is similar to values which have been reported for poly(ethylene glycol) diffusion in aqueous solution. The fracture energy required to fracture the gel/gel interface increased by a factor of 100 when poly(ethylene glycol) was incorporated into the network. These studies also suggest that the wetting characteristics do not control adhesion when bulk polymer diffusion is occurring within the system.
Degree
Ph.D.
Advisors
Peppas, Purdue University.
Subject Area
Chemical engineering|Polymers
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