高分子线性柔性链在超滤过程中第一类突变现象的观察

THE OBSERVATION OF FIRST ORDER TRANSITION IN ULTRA-FILTRATION OF FLEXIBLE LINEAR POLYMER CHAINS

利用一种双层结构的膜屏蔽了每个微孔所产生的流场之间的相互作用,从而首次观测到理论上预计的高分子线性柔性链在超滤过程中的第一类突变现象,即仅当宏观流速高于一宏观阈值时,高分子长链方可通过尺寸远小于链无扰半径的微孔,且该宏观阈值与高分子链的长短无关.另外,实验中的过滤膜含有多个微孔,实验结果显示,当一给定的宏观流速低于宏观阈值时,部分微孔会被无法通过的较长的高分子链堵塞,造成未堵塞微孔中的微观流速大于微观阈值.因此,较短的高分子链可从未堵塞的微孔通过滤膜.

By using a special double-layer membrane to avoid interaction among flowing fields in different pores, the theoretically predicted discontinues transition in ultra-filtration of flexible linear polymer chains was observed for the first time. Namely, the chains could pass through pores with sizes much smaller than the chain＇s unperturbed radius when the flow rate is higher than a threshold. In theory, such a threshold is independent of both the chain length and the pore size. However, we found that when the macroscopic flow rate was lower than the threshold, some of the pores were blocked by a fraction of longer polymer chains. Therefore, the microscopic flow rate in the non-blocked pores became higher than the threshold so that the rest of the chains could pass through these non-blocked pores. This leads to an apparent separation of the chains with different lengths