Second-harmonic scattering in aqueous urea solutions: evidence for solute clusters?
Second-harmonic scattering in aqueous urea solutions: evidence for solute clusters?
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DOI：
10.1039/c3fd00089c
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发表时间：
2013-06
影响因子：
3.4
通讯作者：
M. R. Ward;S. Botchway;A. Ward;A. Alexander
中科院分区：
文献类型：
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作者：
M. R. Ward;S. Botchway;A. Ward;A. Alexander
本文首次报道了用扫描显微镜测量尿素浓水溶液的二次谐波散射。在从欠饱和（S = 0.15）到过饱和（S = 1.86）的饱和条件范围内测量SHS信号作为溶液浓度（C）的函数，其中S = C/C（sat），C（sat）是饱和浓度。结果显示SHS信号随浓度呈非线性增加，在S = 0.95和1.75附近具有局部最大值，表明这些点附近溶液结构发生变化。瑞利散射图像表明，在近饱和（S = 0.95）尿素溶液中的颗粒的存在。随时间变化的SHS测量表明，信号起源于在通过溶液扫描焦点体积期间遇到的单个事件，与来自粒子的二次谐波产生（SHG）一致。来自直径<200 nm的钛酸钡（BaTiO 3）纳米颗粒的水性分散体的SHG显示出比尿素溶液大约20倍的信号。结果表明，存在一个人口的半有序簇的尿素溶液浓度的变化。
Measurements of second-harmonic scattering (SHS) from concentrated aqueous solutions of urea are reported for the first time using scanning microscopy. SHS signal was measured as a function of solution concentration (C) over a range of saturation conditions from undersaturated (S = 0.15) to supersaturated (5 = 1.86), where S = C/C(sat) and C(sat) is the saturation concentration. The results show a non-linear increase in SHS signal against concentration, with local maxima near S = 0.95 and 1.75 suggesting a change in solution structure near these points. Rayleigh scattering images indicate the presence of particles in nearly saturated (S = 0.95) urea solutions. Time-dependent SHS measurements indicate that signals originate from individual events encountered during scanning of the focal volume through the solution, consistent with second harmonic generation (SHG) from particles. SHG from aqueous dispersions of barium titanate (BaTiO3) nanoparticles with diameters <200 nm, showed signals approximately 20 times larger than urea solutions. The results suggest the existence of a population of semi-ordered clusters of urea that changes with solution concentration.