|Budget Amount *help
¥16,400,000 (Direct Cost : ¥16,400,000)
Fiscal Year 1991 : ¥700,000 (Direct Cost : ¥700,000)
Fiscal Year 1990 : ¥15,700,000 (Direct Cost : ¥15,700,000)
Not only Mechanical properties, which give macroscopic features of gels, but also light scattering, which gives features of gels on molecular level, were measured in order to analyze the critical phenomena near the sol-gel transition point.
dynamic light scattering method was carried out to determine the sol-gel transition point. From the fluctuations of scattered light intensity in the course of time, auto-correlation function was measured, and then by using Stokes-Einstein equation, cluster radius was calculated from the diffusion constant which was obtained from the correlation function. Results suggested that first, primary clusters were formed, and then the primary clusters polymerized with each other to form larger secondary clusters. The size of secondary clusters showed a tendency to diverge when the concentration approached the gelation point. By fitting the data with scaling law, the critical exponent was determined to be 0.84, which is not so far off from the critical exponen
t of correlation length in percolation theory, which is said to be 0.9.
In the case of agarose, which forms clusters by non-covalent bonds, it was also possible to determine the cluster radius of agarose sol by using the dynamic light scattering method. Average cluster radius showed a tendency to diverge when the concentration increased and approached the sol-gel transition point. It was also possible to fit the data with scaling law, and the gelation concentration and the critical exponent were determined to be 4.5*10^<-3>(wt%) and 0.98 at the temperature of 27ﾟC.When the temperature was lowered and approsched the gelation temperature, the cluster radius became larger. By fitting the data, the gelation temperature and the critical exponent were determined to be 32.7ﾟC,and 1.36, for 0.15(wt%) agarose sol. The critical exponent thus obtained was larger than the theoretical value.
From the above results, it was suggested that by measuring the cluster radius distribution, concepts of percolation and scaling were shown to be effective when determining the physical property changes near the sol-gel transition point. Less