In situ observation of precipitation or phase separation induced by solvent addition is important in studying its dynamics. Combined with optical and fluorescence microscopy, microfluidic devices have been leveraged in studying the phase separation in various materials including biominerals, nanoparticles, and inorganic crystals. However, strong scattering from the subphases in the mixture is problematic for in situ study of phase separation with high temporal and spatial resolution. In this work, we present a quasi-2D microfluidic device combined with total internal reflection microscopy as an approach for in situ observation of phase separation. The quasi-2D microfluidic device comprises of a shallow main channel and a deep side channel. Mixing between a solution in the main channel (solution A) and another solution (solution B) in the side channel is predominantly driven by diffusion due to high fluid resistance from the shallow height of the main channel, which is confirmed using fluorescence microscopy. Moreover, relying on diffusive mixing, we can control the composition of the mixture in the main channel by tuning the composition of solution B. We demonstrate the application of our method for in situ observation of asphaltene precipitation and \(\beta \)-alanine crystallization.

原位观察由添加溶剂引起的沉淀或相分离对于研究其动力学很重要。结合光学和荧光显微镜，微流体装置已被用于研究各种材料的相分离，包括生物矿物、纳米颗粒和无机晶体。然而，混合物中亚相的强散射对于具有高时间和空间分辨率的相分离的原位研究是​​有问题的。在这项工作中，我们提出了一种准二维微流体装置与全内反射显微镜相结合，作为原位观察相分离的方法。准二维微流体装置由浅主通道和深侧通道组成。主通道中的溶液（溶液 A）和侧通道中的另一种溶液（溶液 B）之间的混合主要由扩散驱动，这是由于主通道浅层的高流体阻力，这是使用荧光显微镜证实的。此外，依靠扩散混合，我们可以通过调整溶液 B 的成分来控制主通道中混合物的成分。我们展示了我们的方法在原位观察沥青质沉淀和\(\beta \) -丙氨酸结晶。