Nanomechanical Thermal Analysis of Photosensitive Polymers

A few nanograms of poly(methyl methacrylate) (PMMA) or poly(vinyl cinnamate) (PVCN) was coated onto one side of a silicon cantilever, and the photodegradation of PMMA or photo-cross-linking of PVCN was investigated as a function of UV irradiation time. After UV irradiation, the resonance frequency and deflection of the polymer-coated silicon cantilevers were measured as a function of temperature, and these properties were found to be related to changes in the modulus and surface stress of the coated polymers, respectively. A decrease in the modulus and tensile surface stress was observed for PMMA under UV exposure due to photodegradation, whereas an increase in the modulus of PVCN was observed due to photo-cross-linking. In addition, the influence of UV exposure on the glass transition of the PMMA and PVCN was investigated using deflection measurements. Whereas a single glass transition was observed for PMMA, two distinctive glass transitions were observed for PVCN due to the copresence of cross-linked and un-cross-linked of PVCN. Variations in the polymer structures were also investigated as a function of UV irradiation time using Fourier transform infrared spectroscopy and compared with the results obtained using the cantilever measurements.