Polymer Crystallization Dynamics Investigated by Synchronous Scanning Spectrum
LUO Wei-ang1,2, CHENG Ling1, DAI Li-zong1, CHEN Xu-dong2, MAI Kan-cheng2, CHEN Yu-jie3*, LIAO Zheng-fu4*
1. Fujian Provincial Key Laboratory of Fire Retardant Materials, College of Materials, Xiamen University, Xiamen 361005, China 2. School of Chemistry and Chemical Engineering, Sun Yat-sen University, Guangzhou 510275, China 3. Laboratory of Optoelectronic Materials and Technologies, School of Physics and Engineering, Sun Yat-sen University, Guangzhou 510275, China 4. Faculty of Materials and Energy, Guangdong University of Technology, Guangzhou 510006, China
Abstract：There is a cosine function between the reflected light intensity of a solid surface and its refractive index. And the mean squared fluctuation of refractive index is related to fluctuation of density and concentration. So some internal structures changes of materials can be reflected by changes in reflected light. Based on this theory, the synchronous scanning spectrum (SSS) technique was successfully applied to monitor melting and nonisothermal melt-crystallization of poly(ε-caprolactone) (PCL) film on a copper substrate. SSS can be implemented on a spectrofluorimeter by simultaneously scanning the excitation and emission monochromators (i.e. Δλ=λex-λem=0 nm). In SSS of PCL films, two dominant peaks correlated to the light source spectrum of the spectrofluorimeter (at 467 and 473 nm) were used to characterize the macromolecular structure evolution during the melting and nonisothermal melt-crystallization processes. Detailed thermodynamic and crystallization kinetics parameters obtained by SSS method. The Avrami exponent n obtained by SSS method is in the range of 2.8～3.2 with an average of 3.13, illustrating a heterogeneous nucleation process followed by a three-dimensional spherulitic crystal growth mechanism. The crystallization activation energy is -158.2 kJ·mol-1. These results are in agreement with values determined from differential scanning calorimetry (DSC) method. It indicates that SSS technique is a simple, effective in situ method for measuring the dynamic melting and crystallization process of polymers. Moreover, the SSS method is a universal spectroscopic technique based on a spectrofluorimeter for monitoring both luminescent and non-luminous solid polymers.
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