Abstract:Interface undercooling is one of the most significant parameters in the solidification of colloidal suspensions. However, quantitative measurement of interface undercooling of colloidal suspensions is still a challenge. Here, a new experimental facility and gauging method are designed to directly reveal the interface undercooling on both static and dynamic cases. The interface undercooling is visualized through the discrepancy of solid/liquid interface positions between the suspensions and its solvent in a thermal gradient apparatus. The resolutions of the experimental facility and gauging method are proved to be 0.01K. The high precision of the method comes from the principle of converting temperature measurement into distance measurement in the thermal gradient platform. Moreover, both static and dynamic interface undercooling can be quantitatively measured.

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Ice growth has attracted great attention for its capability of fabricating hierarchically porous microstructure. However, the formation of tilted lamellar microstructure during freezing needs to be reconsidered due to the limited control of ice orientation with respect to thermal gradient during in-situ observations, which can greatly enrich our insight into architectural control of porous biomaterials. This paper provides an in-situ study of solid/liquid interface morphology evolution of directionally solidified single crystal ice with its C-axis (optical axis) perpendicular to directions of both thermal gradient and incident light in poly (vinyl alcohol, PVA) solutions. Misty morphology and V-shaped lamellar morphology were clearly observed in-situ for the first time. Quantitative characterizations on lamellar spacing, tilt angle and tip undercooling of lamellar ice platelets provide a clearer insight into the inherent ice growth habit in polymeric aqueous systems and are suggested exert significant impact on future design and optimization in porous biomaterials.

Abstract:In the field of freezing colloidal suspensions, it is important to understand the particle-scale behavior of particle packing. Here, we reveal the dynamics of particle packing by identifying the behavior of each single particle in situ. The typical pattern consists of locally ordered clusters and amorphous defects. The microscopic mechanism of pattern formation is ascribed to the non-equilibrium particle-packing process on the particle scale, described with the Pé clet number. The macroscopic migration of a particle layer is also revealed by an analytical model involving parameters of freezing speed and initial volume fraction of particles.Key words: colloidal suspensions, freezing, particle self-assembly, in-situ revealing [9], etc. In all of these cases, the segregation of particles from the growing ice and the consequent increase of particle concentration in the fluid regions are vital. In particular, the arrangement of segregated particles on the scale of single particles is important, because the particle-scale structure is the key to understanding the rejection of particles and hence predicting the large-scale structure [10].During freezing of a suspension, particles are expelled from ice [11,12], forming a close-packed layer in front of the freezing interface. This process can cause self-assembly of the particles [13] similar to that caused by drying [14,15] or sedimentation [16] of colloidal suspensions. Similarities between these patterns suggest that the physics underlying the colloidal behavior may be similar, though the driving forces in each case differ. Therefore, knowledge gained from studying particle packing in freezing colloidal suspensions may be applicable to colloidal

A review is given in the paper for solidification researches with transparent model materials. The effective experimental method was first proposed by Jackson and Hunt in 1965. The transparent model materials for solidification researches are a kind of non-faceted crystals known as "plastic crystals" or "globular molecules", which have very low entropy of melting as that of metals. According to Jackson's theory proposed in 1958, entropy of phase transformation will determine whether the phase interface morphology is smooth or rough in atomic scale, which will lead to faceted or nonfacted phase interface in microscopic and macroscopic scales. Succinonitrile (SCN) and its alloys with water, ethanol, acetone, and NH 4 Cl-H 2 O solution are most commonly used as transparent model materials for solidification researches of dendritic growth, anisotropy of solid-liquid interfacial energy, crystal nucleation, crystal grain formation, directional solidification, eutectic and peritectic solidification, solidification defects formation such as bubble, hot tearing, etc. Among these researches, the most impressive work was the critical test of dendritic growth theories with high purity succinonitrile by Glicksman et al., which gave positive answer to the Ivantsov's analysis and negative answer to the ad hoc condition of the maximum velocity hypothesis. The future researches with transparent model materials could be suggested in three aspects: 1) accurate measurement of material properties and alloy phase diagrams in more plastic crystals, especially to find more transparent eutectic and peritectic alloys; 2) accurate measurement of the grain boundary groove shape to obtain precise data of the anisotropy parameters of the interfacial free energy in transparent model materials; 3) to get clear pictures of solidification processes with morphology details in a relatively large area, with continuous movement of liquid and particles, in order to give experimental support to numerical simulations aimming at accurate description of microstructure formation during solidification of multicomponent alloys under complex conditions of real casting and welding processes. transparent model materials, solidification, plastic crystal, dendritic growth Citation:Huang W D, Wang L L. Solidification researches using transparent model materials -A review.