关键词: 红外光谱, 水, 曲线拟合, 微乳液, NaDEHP

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