We investigated the evolution of concentration and phase structure of colloidal suspensions in a twoends-open tube during drying process. the volume fraction and crystal structure of suspension in the capillary tube were determined by reflection spectrometer during drying process. Our experimental results show: (a) evaporation takes place in two directions of the tube, though much stronger in one direction than the other; (b) during drying process, colloidal suspension column along the tube can be divided into four regions, namely, the close packed region, concentrated region, initial concentration region and dilution region. A new model describing the evolution of concentration profile was proposed and the calculated results based on the model are in good agreement with the experimental ones. According to solute conservation, we also present a simple way to estimate the concentration of close packed region. Drying, as a common process in nature, has been widely utilized in many research and industry fields, such as printing, coating and ceramics 1-3. In colloidal suspension, the drying process can also be used to induce self-assembly and form three-dimensional organized colloidal structures (colloidal crystals) through drying of droplets 4-6 , of films 7-10 or in capillary tubes 11,12. Among most of the methods above, a high concentration of colloids is reached locally (e.g., close to the drying interface of capillary tube) due to the interplay of evaporation and capillarity, forming the three-dimensional colloidal crystals. Especially, the drying colloidal suspension confined in capillary tube with two ends open offers an alternative approach to investigate drying process and evaporation phenomena 13,14. Drying process in capillary tube is of certain importance in many fields 15-19. Through drying colloidal suspension in the tube, the acquired patterned surface can be used as a model for molding regular micro-/nanostructure and the rough surface can capture cells more efficient than blank glass surface which can provide promising application for biomedical areas 20. Formation of basalt columns during cooling of lava can be modeled by the drying of colloidal suspension confined in capillary tube which shed new light on the basalt column formations 21,22. Macroscopic soft colloidal crystals with fiber symmetry can be fabricated by drying colloidal suspension inside two end open tube with potential applications in photonic band gap materials, optical filters, sensors, and so forth 11. Since the drying process in capillary tube is vital, the model for the concentration distribution inside the tube during this one-dimensional drying has also garnered attention 23,24. For drying the colloidal suspension in capillary tube, the movement of suspension is normally in one direction and relevant models were developed to analyze the volume fractions of close packed structures or dense states 25. By our understanding, the temporal concentration distribution should be essential experimental data for modeling because the proce...
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