Refractive Index of Liquid Mixtures: Theory and Experiment

被引:193
作者
Reis, Joao Carlos R. [1 ]
Lampreia, Isabel M. S. [1 ]
Santos, Angela F. S. [1 ]
Moita, Maria Luisa C. J. [2 ]
Douheret, Gerard [3 ]
机构
[1] Univ Lisbon, Dept Quim & Bioquim, Ctr Ciencias Mol & Mat, Fac Ciencias, P-1749016 Lisbon, Portugal
[2] Univ Lisbon, Dept Quim & Bioquim, Ctr Quim & Bioquim, Fac Ciencias, P-1749016 Lisbon, Portugal
[3] Univ Clermont Ferrand, F-63177 Aubiere, France
关键词
amphiphiles; excess properties; liquids; refractive index; thermodynamics; GLYCOL DIMETHYL ETHER; EXCESS MOLAR VOLUMES; BINARY-MIXTURES; 298.15; K; THERMODYNAMIC PROPERTIES; CYCLIC-KETONES; IONIC LIQUIDS; ISENTROPIC COMPRESSIBILITIES; CHEMICAL THERMODYNAMICS; DIFFERENT TEMPERATURES;
D O I
10.1002/cphc.201000566
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
An innovative approach is presented to interpret the refractive index of binary liquid mixtures. The concept of refractive index "before mixing" is introduced and shown to be given by the volume-fraction mixing rule of the pure-component refractive indices (Arago-Biot formula). The refractive index of thermodynamically ideal liquid mixtures is demonstrated to be given by the volume-fraction mixing rule of the pure-component squared refractive indices (Newton formula). This theoretical formulation entails a positive change of refractive index upon ideal mixing, which is interpreted in terms of dissimilar London dispersion forces centred in the dissimilar molecules making up the mixture. For real liquid mixtures, the refractive index of mixing and the excess refractive index are introduced in a thermodynamic manner. Examples of mixtures are cited for which excess refractive indices and excess molar volumes show all of the four possible sign combinations, a fact that jeopardises the finding of a general equation linking these two excess proper-ties. Refractive indices of 69 mixtures of water with the amphiphile (R, S)-1-propoxypropan-2-ol are reported at five temperatures in the range 283-303 K. The ideal and real refractive properties of this binary system are discussed. Pear-shaped plots of excess refractive indices against excess molar volumes show that extreme positive values of excess refractive index occur at a substantially lower mole fraction of the amphiphile than extreme negative values of excess molar volume. Analysis of these plots provides insights into the mixing schemes that occur in different composition segments. A nearly linear variation is found when Balankina's ratios between excess and ideal values of refractive indices are plotted against ratios between excess and ideal values of molar volumes. It is concluded that, when coupled with volumetric properties, the new thermodynamic functions defined for the analysis of refractive indices of liquid mixtures give important complementary information on the mixing process over the whole composition range.
引用
收藏
页码:3722 / 3733
页数:12
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