Dynamic Formation Mechanism and Aging of Physical Gels Revealed Using Luminescent Probe Method

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1. In order to get microscopic information of thermoreversible agarose and gelatin hydrogels, we added 8-anilino-1-naphtalene sulfonic acid (ANS) whose fluorescence behavior strongly depends on polarity of its microenvironment. We measured the dependence of both fluorescence and fluorescence anisotropy of ANS on concentration and molecular weight of biopolymers, and temperature. Spectral analysis has clarified that there are two types of 3_1 helix form taking part in gelation of agarose. The temperature dependence of ANS fluorescence properties suggest that at the gel melting temperature the helical form does not break down to random coil form but rather the aggregation of helix rods just becomes untied and one or some isolated helix rods.2. Whether syndiotactic polystyrene (sPS) forms gel or not is dependent on solvent. Our fluorescence probe technique clarified that in the case of solvents such as chloroform, benzene, and toluene there are some free volume for them to stay among sPS chains because of the formation of polymer-solvent compounds. Conversely , in the case of solvents such as trans-decalin that are too large to stay among sPS chains, sPS cannot form polymer-solvent compounds, and consequently it never forms a gel.3. To clarify the primary driving force in the formation and stabilization of gels of the derivatives of 1, 3 : 2, 4-di-O-benzylidene-D-sorbitol (DBS) in various solvents, the effects of derivative concentrations on the thermal, viscoelastic, and structural properties of the gels were examined in detail. In conclusion, a DBS molecule is so bulky and so highly oriented to one dimension that it cannot readily form a three-dimensional crystal ; as such, DBS molecules are assumed to not easily form a crystal but rather to form a fiber structure, which would promote the gel network.