《玉面》风流玉扇

15、第 15 章

　　Number 3, the van derWaals–London force is by far the predominant
　　one of the three; see Fowkes [8]. Nonetheless, the fact
　　that especially van derWaals–Keesom forces seemed decidedly
　　polar to most workers continued to make it difficult to discern
　　a clear distinction between apolar and polar forces. However,
　　a firm distinction between apolar and polar forces became possible
　　at last through the work of Chaudhury [23], who in his dissertation on: “Short-range and long-range forces in colloidal and macroscopic systems”, in his surface-thermodynamic analysis of apolar and polar interactions based on Lifshitz’ theory[24], proved that on a macroscopic scale, all three van derWaals forces are apolar and all three decay at the same rate as a function of distance (which for van der Waals–London forces has to be smaller than about 10 nm, on account of retardation phenomena setting in beyond that distance (see, e.g., Refs. [25,26]). Thus at a macroscopic- as well as at a microscopic-scale, all three van der Waals forces can and should be treated together, as apolar interactions. This at last opened the door to developing the combining rules for polar interactions, as entirely separate from those of the macroscopic- as well as the microscopic-scale Lifshitz–van der Waals interactions.

　　In order to identify these polar combining rules it was important to remember that whilst Lifshitz–van derWaals (LW) forces occurring in apolar liquids between identical apolar molecules or particles can never be repulsive, LW forces in apolar liquids between two apolar molecules or particles of different compositions can repel one another under precisely definable conditions
　　[27–31,16,17].

　　In contrast with apolar (i.e., purely LW) systems, in polar systems, identical polar [e.g., poly(ethylene oxide)] macromolecules, immersed in water, repel each other to an amply sufficient degree to dissolve in water. This fundamental difference with apolar (LW) systems furnished an important clue leading to the solution of the problem of the treatment of polar interactions.