Price Hannah C, Mattsson Johan, Murray Benjamin J
School of Earth and Environment, University of Leeds, Leeds, UK.
Phys Chem Chem Phys. 2016 Jul 28;18(28):19207-16. doi: 10.1039/c6cp03238a. Epub 2016 Jul 1.
The diffusion of sugar in aqueous solution is important both in nature and in technological applications, yet measurements of diffusion coefficients at low water content are scarce. We report directly measured sucrose diffusion coefficients in aqueous solution. Our technique utilises a Raman isotope tracer method to monitor the diffusion of non-deuterated and deuterated sucrose across a boundary between the two aqueous solutions. At a water activity of 0.4 (equivalent to 90 wt% sucrose) at room temperature, the diffusion coefficient of sucrose was determined to be approximately four orders of magnitude smaller than that of water in the same material. Using literature viscosity data, we show that, although inappropriate for the prediction of water diffusion, the Stokes-Einstein equation works well for predicting sucrose diffusion under the conditions studied. As well as providing information of importance to the fundamental understanding of diffusion in binary solutions, these data have technological, pharmaceutical and medical implications, for example in cryopreservation. Moreover, in the atmosphere, slow organic diffusion may have important implications for aerosol growth, chemistry and evaporation, where processes may be limited by the inability of a molecule to diffuse between the bulk and the surface of a particle.
糖在水溶液中的扩散在自然和技术应用中都很重要，但低含水量时扩散系数的测量却很少。我们报告了直接测量的蔗糖在水溶液中的扩散系数。我们的技术利用拉曼同位素示踪法来监测非氘代和氘代蔗糖在两种水溶液之间边界处的扩散。在室温下，水活度为0.4（相当于90 wt%蔗糖）时，蔗糖的扩散系数被确定为比同一物质中水的扩散系数小约四个数量级。利用文献中的粘度数据，我们表明，虽然斯托克斯 - 爱因斯坦方程不适用于预测水的扩散，但在所研究的条件下，它能很好地预测蔗糖的扩散。这些数据不仅为深入理解二元溶液中的扩散提供了重要信息，还具有技术、制药和医学方面的意义，例如在冷冻保存中。此外，在大气中，缓慢的有机扩散可能对气溶胶的生长、化学和蒸发有重要影响，在这些过程中，分子在颗粒主体和表面之间扩散的能力可能会限制这些过程。
