Abstract: Microstructure of water in water/NaDEHP/n-heptane microemulsion system has been studied by means of Fourier transform infrared spectroscopy (FT-IR). The intensity and peak position of H₂O bands in the system was found to vary with water content W₀, (the molar ratio of water to NaDEHP). The frequency of O-H stretching band of water shifted from 3385 to 3417 cm^-1 in the system when the W₀ value increased from 1 to 25. The O-H stretching bands were resolved by using resolution enhanced technique of second derivative and curve fitting. Four peaks located at (3610+-10),(3512+-10),(3420+-10) and (3250+-20)cm^-1 in the system were obtained. These four peaks were assigned to free water, phosphate-bonded water, bulk water and Na⁺-bonded water, coexisting in the same microemulsion solutions. Area fraction of the four types of water molecules were estimated quantitatively after O-H stretching bands were resolved by curve fitting. When the water content was increased, the area fraction of bulk water increased. Meanwhile area fractions of phosphate-bonded water and free water in the system decreased with water content. For Na⁺-bonded water, the area fraction increased with W₀ up to the value of 11, after that, it decreased gradually. All these variations are due to the interactions of water molecules with both phosphate and Na⁺ in the microemulsion system.

Key words: FT-IR, water, curve-fitting, microemulsion solutions, NaDEHP

摘要： 运用傅立叶变换红外光谱(FT-IR)对水/NaDEHP/正庚烷微乳体系中水的微结构进行了研究。结果表明，随着体系中加水量的增大，水分子OH伸缩振动红外吸收峰的频率由3385cm^-1向高频移动至3417cm^-1(与AOT形成的微乳体系的变化趋势相反)。进一步对3050cm^-1至3750cm^-1范围内的水分子OH伸缩振动吸收峰进行曲线拟合，得到4个子峰，说明微乳体系中的水分子存在有4种不同的配位环境。4个子峰的频率为(3610±10)cm^-1，(3512±10)cm^-1，(3420±10)cm^-1和(3250±20)cm^-1，分别与自由水、磷酸根的结合水、本体水及Na⁺的结合水相对应。根据各拟合峰的峰面积与总的峰面积之比，可以得知微乳液中处于不同环境的水分子所占的百分含量。本体水的百分含量随着体系中加水量的增大而增大，磷酸根的结合水及自由水所占的百分含量随着加水量的增大而减小，Na⁺离子的结合水所占的百分比随着水与NaDEHP的摩尔比W₀的增大而增大，W₀等于11时达到最大值，而后这一百分比随着W₀的增大而减小。不同配位环境中的水分子所占百分数的变化导致了微乳体系中水分子OH伸缩振动吸收峰向高频方向移动。

关键词: 红外光谱, 水, 曲线拟合, 微乳液, NaDEHP