We have discovered unusual behavior of polymer coils in a binary solvent (

) near the critical temperature of demixing. The exceptionally close refractive indices of the solvent components make the critical opalescence relatively weak, thus enabling us to simultaneously observe the Brownian motion of the polymer coils and the diverging correlation length of the critical fluctuations. The polymer coils exhibit a collapse-reswelling-expansion-reshrinking transition upon approaching the critical temperature. While the first stage (collapse) can be explained by the theory of Brochard and de Gennes, the subsequent expansion-reshrinking transition is a new unexpected phenomenon that has not been observed so far. We believe that this effect is generic and attribute it to microphase separation of the solvent inside the polymer coil.

我们发现二元溶剂中聚合物线圈的异常行为（

）在混合的临界温度附近。溶剂组分的异常接近的折射率使临界乳光性相对较弱，因此使我们能够同时观察聚合物线圈的布朗运动和临界波动的不同相关长度。当接近临界温度时，聚合物线圈表现出塌陷-膨胀-膨胀-收缩的转变。虽然第一阶段（崩溃）可以用Brochard和de Gennes的理论来解释，但随后的膨胀-收缩转变是一种新的未曾预料到的现象，至今尚未观察到。我们认为，这种影响是普遍的，并将其归因于聚合物线圈内部溶剂的微相分离。