Diffusion in solutions

化学家和许多其他科学家使用磁共振波谱等技术来研究均匀组成的溶液中的分子运动。提出的扩散研究是不同的。我们研究了由化学成分变化驱动的梯度扩散过程。这种扩散在广泛的实际应用中是重要的，因为它提供了分子水平上的质量传输和混合，因此控制了许多物理和化学过程的速率，如化学反应、晶体生长和溶解、气体吸收、清洁、化学信号和污染物的扩散。我们通过监测注入到不同组成的流动载体溶液中的溶液样品的分散来测量扩散。这项经过验证的技术将用于研究聚合物、电解质、蛋白质、洗涤剂、微乳液和其他科学技术感兴趣的材料的多组分溶液。这些系统中的扩散是强耦合的。例如，一个扩散的蛋白质分子可以运输数百甚至数千个盐离子。蛋白质扩散将在不同的pH值下测量，以提供关于生物系统中传输的新信息，例如质子耦合传输。为了帮助理解为什么扩散是强耦合的，渗透压测量将被用来确定扩散的基本热力学驱动力。另一个目标是通过包括由不同迁移率离子的输运产生的电场中的迁移，准确地描述传播的化学波。激光散射经常被用来通过分析扩散产生的微观浓度波动来表征聚合物、蛋白质和其他胶体。我们的工作将通过比较一系列定义良好的多组分溶液的光散射和梯度扩散数据，建立对流行光散射测量的正确解释。为了解决在多组分系统中测量梯度扩散的长期问题，红外光谱将用于跨扩散剖面的溶质特异性检测，这比传统的体折射率剖面具有相当大的优势。

Chemists and many other scientists use techniques such as magnetic resonance spectroscopy to investigate molecular motions in solutions at uniform composition. The proposed diffusion research is different. We study gradient diffusion processes driven by changes in chemical composition. This kind of diffusion is important in a wide range of practical applications because it provides mass transport and mixing on the molecular level, and therefore controls the rates of many physical and chemical processes, such as chemical reactions, crystal growth and dissolution, gas absorption, detergency, chemical signaling, and the spread of pollutants. We measure diffusion by monitoring the dispersion of solution samples injected into flowing carrier solutions of different composition. This proven technique will be used to study multicomponent solutions of polymers, electrolytes, proteins, detergents, microemulsions and other materials of scientific and technological interest. Diffusion in these systems is strongly coupled. A diffusing protein molecule, for example, can transport hundreds or even thousands of salt ions. Protein diffusion will be measured at different pH values to provide new information about transport in biological systems, such as proton-coupled transport. To help understand why diffusion is strongly coupled, osmotic pressure measurements will be used to determine the fundamental thermodynamic driving forces for diffusion. Another goal is to accurately describe propagating chemical waves by including migration in the electric field generated by the transport of ions of different mobilities. Laser light scattering is frequently used to characterize polymers, proteins and other colloids by analyzing microscopic concentration fluctuations produced by diffusion. Our work will establish the correct interpretation of popular light-scattering measurements by comparing light-scattering and gradient diffusion data for a series of well defined multicomponent solutions. To solve the longstanding problem of measuring gradient diffusion in many-component systems, infrared spectroscopy will be used for solute-specific detection across diffusion profiles, which has considerable advantages over conventional bulk refractive-index profiling.