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

The effect of temperature perturbation on a single-chain-collapse process was studied for poly(methyl methacrylate) with the molecular weight M _w=1.05×10⁷ in the mixed solvent of tert-butyl alcohol+water (2.5 vol%). In the chain-collapse process after a quench from the θ temperature to a temperature T₁, the temperature was changed from T₁ to T₂ at the time t₁ after the quench and returned to T₁ at the time t₁+t₂. In the three stages at T₁, T₂, and T₁, 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 (T₁>T₂), 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 T₁. 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 T₁ without being affected by the temperature perturbation of T ₂ during t₂. The memory effect was observed irrespective of the time period of t₂. The positive temperature perturbation (T₁<T₂) showed an acceleration of the chain-collapse process.