Evolution of concentration and phase structure of colloidal suspensions in a two-ends-open tube during drying process

Abstract

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...

Novel <i>operando</i> observation technique based on combined optical coherence tomography–thermogravimetry for monitoring internal structural changes of drying ceramic slurries

“…It was also observed that agglomeration progressed inhomogeneously in the thickness direction. A similar inhomogeneity was observed in a drying process in a capillary tube 22) and was predicted through simulations on drying suspensions. 23) However, those cases are different from drying in the production process of actual ceramics.…”

Is Unidirectional Drying in a Round Capillary Always Diffusive?

“…It can be also noticed that the consideration of tubes or channels with two open ends is classical in the studies of drying of colloidal suspensions. 14,21,22 Here we show that the classical description of unidirectional drying in capillaries used as model pores depends on the closing condition of the capillary. While drying in cylindrical capillaries closed by a solid plug follows a classical diffusiondriven behavior, a faster capillary-drying regime, characterized by a constant-rate period, 23,24 can be induced when the capillary end is in contact with a liquid plug.…”

“…Stefan in 1871 was the first to describe the diffusion-driven drying in a vertical capillary tube: he showed that the evaporation of a liquid in a circular tube slows down as the air–liquid interface is receding inside the tube . Since then, round capillaries have been used in several studies to understand the flow and transport processes with different fluids such as ionic solutions , or colloidal suspensions . Unidirectional drying in capillaries has also been extensively studied by changing different parameters including geometry and wettability properties of capillaries. − Generally, capillaries of polygonal cross section are considered to be closer to the geometry of real pores due to the presence of corners and angles where thick capillary films can form and strongly influence the drying kinetics ,, or imbibition process .…”

Directional motion of charged particles near filter membrane

“…定为 L = 0 mm, 测量范围为 L = 0.5-15.5 mm). 反射光谱反射峰波长的变化可以 转变为粒子体积分数 𝛷 和数密度 n 的变化 [17,18] 纯水 + 滤膜 3.06×10 -6 1.49×10 -7 3.59×10 -7 3.21×10 -5 2.04×10 -6 1.12×10 -6…”