Force modulation microscopy study of phase separation on blend polymer films

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Abstract
We report force modulation microscopy study of phase separation on blend polymer films of ether-type phenylene vinylene based copolymer and cyano-substituted poly(2,5-didecyloxy- p-phenylene vinylene). Three different tips with spring constants of 0.6, 3, and 60 N/m, and various modulation frequencies between 5 and 10 kHz have been employed. It is found that consistent and correct image contrast can be obtained only with the stiffest tip. Theoretical calculation based on Sneddon mechanics also predicts a tip-sample stiffness close to that of the preferred tip. These results suggest strongly that the tip spring constant used in force modulation microscopy should be comparable to (or greater than) the interaction stiffness.