Modification of Surface Properties Through Polymer Adsorption. Kinetics, Interaction, Degradation and Stability
Sammanfattning: The interfacial behaviour of polymers in relation to surface modification and polymer degradation was studied. In the first part the interfacial behaviour of amphiphilic poly(ethylene oxide)–poly(D,L-lactide) (EmLn) diblock copolymers at hydrophilic and hydrophobic substrates from aquous solution was studied. All copolymers showed a much higher saturation adsorption compared to that of the poly(ethylene oxide) homopolymers, displaying only a weak dependence on the copolymer composition. At hydrophilic substrates, the layer thickness was significantly higher than expected for unperturbed copolymer dimensions. A cooperative increase of the intial adsorption rate and the saturation adsorbed amount with increasing bulk concentration suggested the formation of surface-aggregates at hydrophilic silica, which was also supported by AFM. At methylated silica, the layer thickness and interfacial density correlated with highly extended poly(ethylene oxide) chains assembled in a dense brush-layer. Inhibition of fibrinogen adsorption was enhanced with increasing surface coverage of preadsorbed copolymer, and was largely independent of the copolymer composition. After extensive degradation of the copolymers, there was little inhibition of fibrinogen adsorption. An increasing degree of degradation also resulted in a decreased copolymer adsorption. The adsorption at silica initially increased with the degree of degradation due to deposition of aggregates onto the surface. At extensive hydrolysis of the L block the copolymer adsorbed amount at hydrophilic silica and hydrophobic silica approached that of the poly(ethylene oxide) homopolymer. This also resulted in degradation-induced flocculation of polystyrene dispersions in the presence of Na2SO4. In the second part of the work, exchange, surfactant interaction, and degradation of adsorbed proteins, notably gelatin, was investigated. The adsorption of gelatin was significantly different above and below the helix formation temperature (T-helix). Additions of SDBS after gelatin preadsorption resulted in a pH-dependent total adsorbed amount increase and a swelling of the adsorbed layer, which was followed at higher surfactant concentration by a decrease in both the total adsorbed amount and the amount of adsorbed gelatin. Interaction between the proteolytic enzymes krillase or trypsin and preadsorbed gelatin resulted in the transition to a thinner and denser layer. At silica, gelatin was essentially removed, whereas at hydrophobic silica, both residual gelatin and proteolytic enzymes were present even after longer exposure. The effects of krillase addition was quantitatively similar above and below T-helix, whereas the effect of trypsin addition to preadsorbed gelatin was enhanced at below T-helix. A faster and more extensive degradation of gelatin at hydrophobic silica is observed for higher enzyme concentrations. The exposure of preadsorbed gelatin to inactivated krillase showed a nearly complete elimination in the effects observed upon addition of intact krillase. This indicated that the enzymatic activity of krillase in its native form plays a major role for the interaction between krillase and pre-adsorbed gelatin.
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