数字全息干涉法测量二元溶液互扩散系数

Determination of mutual diffusion coefficient for binary solution using digital holographic interferometry

由一维无限长扩散模型入手,建立了探测光相位与液体互扩散系数之间的数学模型,进而在现有数字全息干涉法的基础上,提出了一种新型的二元液体互扩散系数测量方法。由于该方法直接利用探测光相位求取互扩散系数,因此可有效避免外界噪声信号对实验结果的影响,从而降低了数字全息干涉法对外界光学环境的要求。该方法的互扩散系数测量相对合成不确定度为0.7%。测量了25℃下、0.33 mol/L KCl水溶液的互扩散系数,实验结果与文献值符合良好,验证了该测量方法的可行性。利用该方法,测量了甲醇/环己烷二元系在其不互溶区附近的互扩散系数,揭示了其在该区域的变化规律。依据实验数据,预测了该二元系的热力学亚稳定和非稳定区域的分界线——Spinodal曲线。

The mathematic model between the phase distribution of object beam and the mutual diffusion coefficient of binary solution was established based on the one-dimensional and infinite model.A novel experimental method for measuring the mutual diffusion coefficient of binary liquid mixtures was proposed based the existing digital holographic interferometry.For the presented method,the mutual diffusion coefficient is determined directly through the phase distribution curve of object beam,which can obviously avoid the influence of ambient noise on the experimental result.The requirement of the optical condition in the lab was considerably reduced.The relative combined uncertainty of mutual diffusion coefficient is around 0.7%.The mutual diffusion coefficient of KCl aqueous solution at 0.33 mol/L and 25℃was measured.The result is in good agreement with literature data,which proves that the new measuring principle is feasible and correct.With the new method and experimental apparatus,the mutual diffusion coefficient of methanol/cyclohexane binary mixture was measured and analyzed near the immiscible concentration region.Based on the experimental result,the Spinodal line,which is used to describe the boundary between the thermodynamic instable region and the metastable region,was predicted for methanol/cyclohexane binary system.