E f ? n Y a n analysis by the free volume theory of diffusion, a study of the diffusion coefficients, Dz, the distribution coefficients, KZ, and the permeability coefficients, P, of NaCl in various hydrophilic polymers was made with the assumptions that the free volume of a polymer/diluent system is linearly proportional to the volume fraction of diluent (H), and that NaCl permeates only through polymer/diluent systems in which the diluent of polymers is also a good solvent of the solute (NaCl).The values of Dz (over five orders of magnitude) were found to vary exponentially with changes in 1/H, as expected from the free volume theory of diffusion, in a wide range of H-values and converge to the value of the diffusion constant of NaCl in pure water.The values of kz defined by g NaCl per cm3 polymer/g NaCl per cm3 solution were found to be more characteristic to the type of polymers particularly a t a lower range of H-values. At higher ranges of H-values, kz is nearly equal to H, however, at lower H, kz values deviate significantly from the value of H and its extent was found to be greatly dependent on the chemical nature of polymers, whereas the diffusion coefficient follows the normal pattern predicted by the free volume theory.The values of P which are given by the product of Dz and kz also were found to vary exponentially with changes in 1/H a t higher range of H, however, a t lower range of H it deviates from the relationship due t o the varying dependence of factor kz on 1/H. ZUSAMMENFASSUNG:Unter Bezugnahme auf die freie Volumentheorie der Diffusion wurden die Diffusions-(Dz), Verteilungs-(kz), und Permeabilititskoefhienten (P) von NaCl in verschiedenen hydrophilen Polymersystemen untersucht. Es wurden die Annahmen gemacht, daR das freie Volumen eines gequollenen Polymersystems linear proportional zum Volumenbruchteil des Quellungsmittels (H) ist, und weiterhin, daR NaCl nur durch solche Polymersysteme permeiert, deren Quellungsmittel ein gutes Losungsmittel fiir NaCl darstellt.Wie aus der freien Volumentheorie der Diffusion z u envarten, wurde fiir die Werte von Dz iiber einen weiten Bereich (5 GroDenordnungen) eine exponentielle Abh-igkeit von 1/H gefunden sowie ein Konvergieren der Dz-Werte mit der Diffusionskonstante des NaCl in reinem HzO fiir hohe Werte der Polymeren.Die Werte von kz (g NaCl pro ml Polymeres/g NaCl pro ml Losung) erwiesen sich, besonders im Bereich niederer H-Werte, fiir die Art des Polymeren charakteristisch. I m Bereich hoher H-Werte ist kz beinahe gleich dem Wert von H ; im Bereich niederer H-Werte weicht kz jedoch von H ab, wobei die GroRe der Abweichung stark vom cheniischen Aufbau des Polymeren beeinflu& ist. In diesem Bereich entspricht der Wert von D dem aus der freien Volurnentheorie folgenden.Die Werte von P, gegeben durch kzDz, anderten sich ebenfalls exponentiell rnit 1/H im Bereich hoher H-Werte, wichen jedoch von dieser Beziehung im Bereich niederer H-Werte infolge des Einflusses von kz ab.
The contact angle of a water droplet on the surface of a solid polymer or hydrogel (water‐swollen three‐dimensional network) depends on whether a hydrophilic moiety of the polymer molecule is oriented towards the air interface or towards the bulk of the solid, but not on the hydrophilicity of the molecule. Therefore, the short‐range rotational mobility of a polymer molecule has a major influence on the apparent hydrophilicity of a polymer surface as measured by the contact angle of water. By the came principle, the abnormally large hysteresis effect observed in advancing and receding contact angles of water on some polymer surfaces can be attributed to the reorientation of hydrophilic moieties of polymer molecules at the surface. These factors are demonstrated by selected polymer surfaces with different degrees of mobility at the polymer‐air interface.
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