Effect of Evaporation Rate

The wavelength dispersion of out-of-plane birefringence of the samples is shown in Fig. 9.16. All films show positive birefringence with extraordinary wavelength dispersion irrespective of the evaporation rate. However, the magnitude of the birefringence Increases with increasing the evaporation rate. Therefore, a similar situation with a thick film occurs for the film evaporated slowly. 

The decrease in the birefringence for a film obtained by the prolonged evaporation process suggests that stress, i.e., molecular orientation, is relaxed. It is reasonable because the polymer chains are able to move randomly during the cast process. 

Wavelength dispersion of out-of-plane birefringence for films obtained at various evaporation rates standard (o], slow (0], and very slow (A). Reproduced with permission from K. Songsurang, A. Miyagawa, M. E. A. Manaf, R Phulkerd, S. Nobukawa, and M. Yamaguchi, Cellulose, 2013, 20, 83. 2013, Springer Link [11]. 

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It can be concluded from Figs. 9.11-9.13 that the achievable anisotropy is found to be a function of the evaporation rate. Therefore, further study is performed focusing the effect of evaporation rate. 

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