Investigation of particle size effect on film formation of polystyrene latexes using fluorescence technique
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This study reports the particle size effects on the film formation behavior of pyrene labeled polystyrene (PS) latexes by a combination of steady state fluorescence (SSF), UV-vis (UVV) and atomic force microscopy (AFM) techniques. For this purpose, PS latex dispersions of same molecular weight but different particle size were used. Four different latex films were prepared from dispersions of 203,320, 400 and 900 nm PS particles by drop casting at room temperature and annealed at elevated temperatures in the range of 100-250 degrees C for 10 min time intervals above the glass transition (T-g) temperature of PS. Scattered light intensity (6) and fluorescence intensity (I-p) from P were measured after each annealing step to monitor the stages of film formation. Evolution of transparency of latex films were monitored using photon transmission intensity, In.. Atomic force microscopy (AFM) was used to detect variation in the physical structure of annealed films. Onset temperatures for minimum film formation (T-0), void closure (T-v), and healing (T-h) processes were determined. The film formation stages (void closure and interdiffusion) were modeled and related activation energies were determined. It is found that both T-v and T-h) shifted to lower temperatures as PS particle size decreases. In addition, void closure (Delta H) and interdiffusion (Delta E) energy values also decreased with decreasing the particle size. These results showed that the PS particles undergo complete film formation at much lower temperatures and requiring less energy as the particle size decreases. AFM images were also verified these results produced from optical data. (C) 2016 Elsevier B.V. All rights reserved.