No abstract

Volume phase transitions of a DNA gel and a single giant DNA chain caused by spermidine 3+ ͑SPD 3+ ͒ were investigated. The change in volume for the single DNA ͑V / V 0 ϳ 10 −5 ͒ was four orders of magnitude greater than that for the DNA gel ͑ϳ10 −1 ͒, while the critical SPD 3+ concentration for the gel ͑1.8 mM͒ was one order of magnitude greater than that of the single DNA ͑0.12-0.25 mM͒ at the same pH 6.86. We tried to describe mean-field theories with virial expansion, which is valid for the coil-globule transition of a single polymer chain, for the volume phase transitions to explain the reason why such marked differences appeared. Considering the degree of the ordering of Kuhn segments arising from the gel network structure together with the chain length of cross-linked polymer chains, the volume phase transitions were described and then the significant differences were reproduced quantitatively. We concluded that the network structure plays a significant role in the volume phase transition of the gel.

No abstract

Simultaneous measurements of weight, volume and mechanical properties have been performed during the gel-to-glasslike transition of heat-treated egg-white gel. Change in the elastic stiffness occurred in three steps: in the initial stage, it remained almost constant, then increased exponentially, and lastly, saturation was attained. The saturation point almost coincided with the characteristic time at which the rates of decrease of the weight and volume changed. In addition, from the time dependence of the differentiated values, the close correlation between the elastic stiffness and weight was revealed. It was also found that the loss of free water induces an increase of about a thousardfold in elastic stiffness of gels during transition.