Abstract
Thermoresponsive polymer layers on silica surfaces have been obtained by utilizing electrostatically driven adsorption of a cationic-nonionic diblock copolymer. The cationic block provides strong anchoring to the surface for the nonionic block of poly(2-isopropyl-2-oxazoline), referred to as PIPOZ. The PIPOZ chain interacts favorably with water at low temperatures, but above 46 °C aqueous solutions of PIPOZ phase separate as water becomes a poor solvent for the polymer. We explore how a change in solvent condition affects interactions between such adsorbed layers and report temperature effects on both normal forces and friction forces. To gain further insight, we utilize self-consistent lattice mean-field theory to follow how changes in temperature affect the polymer segment density distributions and to calculate surface force curves. We find that with worsening of the solvent condition an attraction develops between the adsorbed PIPOZ layers, and this observation is in good agreement with predictions of the mean-field theory. The modeling also demonstrates that the segment density profile and the degree of chain interpenetration under a given load between two PIPOZ-coated surfaces rise significantly with increasing temperature.
Highlights
Temperature-responsive polymers constitute a subgroup of stimuli-responsive polymers distinguished by significant change in state in response to temperature variations.[1]
This is the case for polymers like poly(N-isopropylacrylamide) (PNIPAAM),[1,3] poly(ethylene oxide) (PEO),[4,5] poly(propylene oxide) (PPO),[6,7] poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA),[8,9] and poly(2-alkyl-2-oxazoline).[10,11]
Normal and friction forces acting between thermoresponsive polymer layers formed on silica surfaces have been investigated as a function of temperature
Summary
Temperature-responsive polymers constitute a subgroup of stimuli-responsive polymers distinguished by significant change in state in response to temperature variations.[1]. The LCST of PNIPAAM is dependent on molecular weight, polymer concentration, and the presence of end-group functionalities.[18,19] Surfaces bearing PNIPAAM chains have been widely investigated[13,20−22] for their temperaturedependent surface properties
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