| Summary: | 碩士 === 國立臺灣科技大學 === 高分子系 === 97 === In this study, the effects of altering different volume ratio of two solvents and sPS gel on the structure and gelation mechanisms are discussed. The solvent used in this work, prepared at the volume ration of 3/7, 5/5, and 7/3, are o-Xylene (oxy) and Cyclohexanone (cho), respectively. The phase diagrams of sPS/oxy and sPS/cho gels reveal the melting and gelation temperature and the junction points, however, were δ form crystals according to the results obtained via FTIR and WAXD. The melting temperatures appeared different due to the larger thickness of the crystals in sPS/oxy gel .The structures of three-dimensional fibril network in sPS/oxy gel and spherulites packing in sPS/cho gel were also observed from POM and SEM owing to the variant
volumes in the solvents.
The gelation rates of sPS gels were measured by test tube tilting in five solvents at different polymer concentrations at 30oC. The gelation rate is expressed as concentration-dependent function: tgel-1= [(c-c*)/c*]n. The value of exponent n depends on the mechanisms of gelation. Exponent n=0.44 in sPS/oxy gel is close to percolation exponent β=0.45, which indicates that three-dimensional percolation is a suitable model for gelation process of sPS/oxy solution. Exponent n=2.54 in sPS/cho gel is close to chain aggregation exponent n=2, indicating that the gelation process is chain aggregating in sPS/cho solution. The n values of the mixture solutions between 0.44 and 2.54 indicate the competition of percolation and aggregation. According to the physical meaning of the [η]c value, it can divide concentration into four regions by chain aggregation. In sPS/oxy solution gelation occurs in infinite dilution limit ([η]c<1) since the strong interaction between PS monomers and o-Xylene observed
from Huggins content (k).
X-type patterns were observed from Hv mode SALS in three mixture solutions at low concentration. The characteristic length (ξ) of gel was analyzed through Debye-Bueche theory. The characteristic length is close to the mesh size of gel network from SEM picture. Therefore, the intensity of Hv scattering contains the orientation fluctuation of forming gel structure.
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