278.15-313.15 K下糖-水二元体系的介电常数

测定了D-(-)-果糖、D-(+)-葡萄糖、D-(+)-半乳糖、D-(+)-木糖和D-(-)-核糖五种糖的水溶液在不同质量摩尔浓度和不同温度下的介电常数(D). 结果表明, 在一定温度下, 这些糖的水溶液介电常数对数值都随糖浓度的增大而减小; 在一定糖浓度时, 介电常数值随温度升高而减小. 果糖、葡萄糖、半乳糖和木糖水溶液的介电常数(D)随温度的变化均满足关系式: lgD=A1-B1(T-298.15), 而核糖水溶液则符合: lgD=A2-B2(T-298.15)+C2(T-298.15)2. 此外, 这五种糖的水溶液的介电常数与摩尔分数(x)满足关系式: lg(D/D0)=-B3x. 在相同温度和浓度时, 介电常数的大小顺序通常为: 水>半乳糖-水>果糖-水>葡萄糖-水≥木糖-水(而核糖较特殊).

Dielectric Constants for Binary Saccharide-Water Solutions at 278.15-313.15 K

The dielectric constants (D) for aqueous solutions of D-(-)-fructose, D-(+)-glucose, D-(+)-galactose, D-(+)-xylose, and D-(-)-ribose were measured at 278.15, 283.15, 288.15, 293.15, 298.15, 303.15, 308.15, and 313.15 K. Molalities of saccharides are at 0.2, 0.4, 0.6, 0.8, 1.0, and 1.2 mol·kg -1. The results indicated that the logarithmic values of dielectric constants for these saccharide-water solutions decreased with increasing molalities of saccharides and decreased also as the temperature rising. At given molalities, the relationship between dielectric constants and temperatures can be expressed by lgD=A1-B1(T-298.15) for fructose-water, glucose-water, galactose-water, and xylose-water solutions, and by lgD=A2-B2(T-298.15)+C2(T-298.15)2 for ribose-water solution. At given temperatures, dependence of the dielectric constants on the mole fraction (x) can be described by lg(D/D0)=-B3x for all five saccharide-water solutions. At given temperatures and molalities, the dielectric constants are mostly in the order: water>galactose-water>fructose-water>glucose-water≥xylose-water (there is not the order for ribose).