论文标题
微流体无界面扩散：扩散系数的测量和界面驱动转运现象的证据
Microfluidic free interface diffusion: measurement of diffusion coefficients and evidence of interfacial-driven transport phenomena
论文作者
论文摘要
我们已经开发了一种微流体工具，可以通过遵循微通道中最初陡峭的浓度梯度的时间松弛来测量水溶液中溶质的扩散系数$ d $。我们的芯片利用了多层柔软的光刻和气动微丙烯酸的打开，以触发纯水的互连和最初通过阀门在通道中分离的溶液，这是所谓的自由界面扩散技术。在距扩散区距离的另一个微丙娃娃率关闭通道，从而抑制对流。使用此芯片，我们已经测量了从小分子到聚合物和聚合物的较大尺寸范围内溶质的扩散系数，其值在$ d \ in [10^{ - 13} - 10^{ - 9} { - 9}] $ 〜m $ $^2 $/s。相同的实验，但随着添加的胶体示踪剂的增加，还显示了由于存在溶质浓度梯度而导致的延伸性斑点和扩张 - 渗透现象。但是，我们表明，这些界面驱动的转运现象不会影响探索浓度范围内溶质扩散系数的测量。
We have developed a microfluidic tool to measure the diffusion coefficient $D$ of solutes in an aqueous solution, by following the temporal relaxation of an initially steep concentration gradient in a microchannel. Our chip exploits multilayer soft lithography and the opening of a pneumatic microvalve to trigger the interdiffusion of pure water and the solution initially separated in the channel by the valve, the so-called free interface diffusion technique. Another microvalve at a distance from the diffusion zone closes the channel and thus suppresses convection. Using this chip, we have measured diffusion coefficients of solutes in water with a broad size range, from small molecules to polymers and colloids, with values in the range $D \in [10^{-13}- 10^{-9}]$~m$^2$/s. The same experiments but with added colloidal tracers also revealed diffusio-phoresis and diffusio-osmosis phenomena due to the presence of the solute concentration gradient. We nevertheless show that these interfacial-driven transport phenomena do not affect the measurements of the solute diffusion coefficients in the explored concentration range.
