Lo Nostro Pierandrea, Fratoni Laura, Ninham Barry W, Baglioni Piero
Department of Chemistry and CSGI, University of Florence, via della Lastruccia 3-Sesto Fiorentino, 50019 Florence, Italy.
Biomacromolecules. 2002 Nov-Dec;3(6):1217-24. doi: 10.1021/bm0255692.
Wool is a complex material, composed of cuticle and epicuticle cells, surrounded by a cell membrane complex. Wool fibers absorb moisture from air, and, once immersed in water, they take up considerable amounts of liquid. The water absorbency parameter can be determined from weight gain, according to a standard method, and used to quantify this phenomenon. In this paper we report a study on the water absorbency (or retention) of untreated wool fibers in the presence of aqueous 1 M salt solutions at 29 degrees C and a relative humidity of either 33% or 56%. The effect of anions was determined by selecting a wide range of different sodium salts, while the effect of cations was checked through some chlorides and nitrates. Our results show a significant specific ion and ion pair "Hofmeister" effects, that change the amount of water absorbed by the fibers. To understand this phenomenon, the water absorbency parameter (A(w)) is compared to different physicochemical parameters such as the lyotropic number, free energy of hydration of ions, molar surface tension increment, polarizability, refractive index increment, and molar refractivity. The data indicate that this Hofmeister phenomenon is controlled by dispersion forces that depend on the polarizability of ionic species, their adsorption frequencies, the solvent, and the substrate. These dispersion forces dominate the behavior in concentrated solutions. They are in accord with new developing theories of solutions and molecular interactions in colloidal systems that account for Hofmeister effects.
羊毛是一种复杂的材料，由角质层和表皮层细胞组成，周围环绕着细胞膜复合物。羊毛纤维从空气中吸收水分，一旦浸入水中，它们会吸收大量液体。根据标准方法，可以通过重量增加来确定吸水性参数，并用于量化这种现象。在本文中，我们报告了一项关于在29摄氏度、相对湿度为33%或56%的情况下，未处理的羊毛纤维在1 M盐水溶液存在下的吸水性（或保水性）的研究。通过选择多种不同的钠盐来确定阴离子的影响，同时通过一些氯化物和硝酸盐来检查阳离子的影响。我们的结果显示出显著的特定离子和离子对“霍夫迈斯特”效应，这些效应会改变纤维吸收的水量。为了理解这一现象，将吸水性参数（A(w)）与不同的物理化学参数进行比较，如离液序列数、离子水化自由能、摩尔表面张力增量、极化率、折射率增量和摩尔折射度。数据表明，这种霍夫迈斯特现象受色散力控制，色散力取决于离子物种的极化率、它们的吸附频率、溶剂和底物。这些色散力在浓溶液中主导行为。它们与解释霍夫迈斯特效应的胶体系统中溶液和分子相互作用的新发展理论一致。
