Memory effect in the collapse process of isolated polymer chains in a solution

The effect of a temperature perturbation at T ₂ on the chain collapse process at T ₁ < θ was studied for poly(methyl methacrylate)(M _w) = 1.1 × 10 ⁷) in the mixed solvent of tert-butyl alcohol + water(2.5vol%). The solution was quenched from θ to T ₁ and preserved at the temperature for a period of t ₁=300 min. Then the temperature was rapidly changed to T ₂ and kept for t ₂=1440 min. Finally the temperature was changed back to T ₁. The chain collapse/expansion process was described by time evolution of expansion factor α ², which was determined by static light scattering measurements. For T ₂ < T ₁, the collapse process at T ₁ seemed not disturbed by the temperature perturbation at T ₂ (memory effect). For T ₂ > T ₁, the collapse process at T ₁ was accelerated or decelerated depending on T ₂.