Memory effect in the chain-collapse process in a dilute polymer solution

摘要

The effect of temperature perturbation on a single-chain-collapse process was studied for poly(methyl methacrylate) with the molecular weight M-w=1.05x10(7) in the mixed solvent of tert-butyl alcohol+water (2.5 vol %). In the chain-collapse process after a quench from the theta temperature to a temperature T-1, the temperature was changed from T-1 to T-2 at the time t(1) after the quench and returned to T-1 at the time t(1)+t(2). In the three stages at T-1, T-2, and T-1, measurements of the mean-square radius of gyration of polymer chains were carried out by static light scattering and the chain-collapse process was represented by the expansion factor as a function of time. An effect of chain aggregation on the measurements was negligibly small because of the very slow phase separation. For the negative temperature perturbation (T-1>T-2), the chain-collapse processes observed in the first and third stages were connected smoothly and agreed with the collapse process due to a single-stage quench to T-1. A memory of the chain collapse in the first stage at T-1 was found to persist into the third stage at the same temperature T-1 without being affected by the temperature perturbation of T-2 during t(2). The memory effect was observed irrespective of the time period of t(2). The positive temperature perturbation (T-1