原位干涉法监测琼脂糖凝胶的干燥
Drying of agarose gels monitored by in-situ interferometry
摘要：
水凝胶表现为粘弹性软固体，并显示出充满水的多孔微观结构，水的典型量为90%w/w或更多。因此，这些材料对通过蒸发的水分损失高度敏感，这会影响其机械性能。然而，除了分散的经验观察，鲜为人知的是凝胶干燥动力学，缺乏时间和空间分辨的测量。在这里，我们报告了一个基准研究的缓慢干燥的琼脂糖凝胶在圆柱形培养皿。凝胶对培养皿侧壁的弱粘附性保证了凝胶直径在干燥过程中保持恒定，并且凝胶收缩完全是垂直的。通过使用迈克耳孙干涉仪的原位干涉测量法监测变薄速率。利用一种新颖的时空滤波方法分析了干涉条纹的位移，使我们能够高精度地测量约10 nm/s的局部细化率。在沿凝胶半径的不同位置进行的实验表明，在干燥过程结束时经历突然坍塌之前，凝胶以恒定的速度局部变薄。我们进一步使用在干燥过程的早期阶段在盘的中心处测量的稀化速率作为稳健的可观察量，以量化添加剂对凝胶干燥动力学的作用，并比较不同组成的凝胶。我们的工作证明了干涉测量法是一种强大的工具，可以量化微量添加剂对生物聚合物凝胶干燥的影响。
英文摘要：
Hydrogels behave as viscoelastic soft solids and display a porous microstructure filled with water with typical amounts of 90\%~w/w or more. As such, these materials are highly sensitive to water loss through evaporation, which impacts their mechanical properties. Yet, aside from scattered empirical observations, little is known about the gel drying kinetics for which there is a lack of temporally and spatially resolved measurements. Here we report a benchmark study of the slow drying of agarose gels cast in cylindrical Petri dishes. The weak adhesion of the gel to the lateral wall of the dish guarantees that the gel diameter remains constant during the drying process and that the gel shrinkage is purely vertical. The thinning rate is monitored by in-situ interferometry using a Michelson interferometer. The displacement of interference fringes are analyzed using an original spatiotemporal filtering method, which allows us to measure local thinning rates of about 10~nm/s with high accuracy. Experiments conducted at different positions along the gel radius show that the gel thins locally with a constant velocity before experiencing a sudden collapse at the end of the drying process. We further use the thinning rate measured at the center of the dish during the early stage of the drying process as a robust observable to quantify the role of additives on the gel drying kinetics and compare gels of different compositions. Our work exemplifies interferometry as a powerful tool to quantify the impact of minute amounts of additives on the drying of biopolymer gels.
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