| Abstract
| - We report the results of atomic force microscopy (AFM) based nanoscale probing of thermal andnanomechanical properties of relatively thick (50−90 nm) polymer brush layers from poly(styrene-co-2,3,4,5,6-pentafluorostyrene) (PSF) and polymethylacrylate (PMA). These layers, with a high density ofgrafting, are synthesized according to a “grafting-from” approach on a silicon surface modified with areactive self-assembled monolayer. In the dry state, glassy and rubbery brush layers are found to behomogeneous matters with no signs of lateral chain segregation, which is observed for polymer layers withlow to moderate grafting densities. We observed that thermal, mechanical, and thermoelastic propertiesof these polymer brush layers are virtually identical to that for unconfined polymers obtained concurrentlyvia bulk polymerization. Direct measurement of heat dissipation and the thermoelastic response withinthe PSF brush layer confirms that the glass−rubber transition occurs between 100 and 110 °C as expectedfor the high-molecular weight polymer. Surface nanomechanical mapping reveals much lower adhesionof the PSF layer, which is glassy at room temperature and contains fluorine-enriched segments, in comparisonwith the sticky PMA layer containing polar segments. At room temperature, the PSF layer shows acompression elastic modulus of approximately 1 GPa whereas the rubbery PMA layer has an elasticmodulus of 50 MPa, typical for the rubbery state. Heating the glassy PSF layer results in a gradualdecrease of the elastic modulus caused by the glass transition, and conversion to the rubbery state iscompleted above 110 °C with an elastic modulus of 15 MPa.
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