Surface freezing

A snowflake is made up of ice crystals that are stuck together. Snowflakes form high in Earths atmosphere. Hail is a frozen mass of water that often forms inside thunderstorms. Sleet is made up of drops of rain that freeze as they fall to Earths surface. Freezing rain is precipitation that falls as liquid but freezes when it hits the cold ground. Together, these different forms of frozen precipitation move drops of liquid water out of the atmosphere and onto Earths surface where they can melt and seep into oceans and groundwater or freeze and build up to create glaciers and ice sheets. 

Heni, M., and Ldwen, H., Surface freezing on patterned substrates, Phys. Rev. Lett, 85, 3668, 2000. 

The oxygen isotopic composition of seawater (5 0 ) is controlled by fractionation effects due to evaporation and precipitation at the sea surface, freezing of ice in polar regions, the admixing... 

In Scandinavia, the constant of integration is used to reflect any initial maltreatment that can lead to initial carbonation. For instance an average quality concrete that was deshuttered too early and may have had slight surface freezing can give ko = 10 mm. A properly treated concrete has ko 1 mm (Miller, 1995). 

Prasad, S., Hanne, L., Dhinojwala, A. Surface segregation in polymer blends driven by surface freezing. Macromolecules 39, 7467-7470 (2006)... 

M Kramer, B Sennhenn, G Lee. Freeze-drying using vacuum-induced surface freezing. Journal of Pharmaceutical Sciences 91 433-443, 2002. 

Tl 3 s - Moulding surfaces freeze, but gate is still live Low pressure, to avoid flashing before skin is frozen. 

In some cases, screw cooling is used to improve the pressure-generating capability of the screw. The screw is cooled all the way into the metering section. The colder screw surface freezes the polymer close to the screw or, at least, significantly increases the viscosity of the polymer melt close to the screw surface. This reduces the effective channel depth of the extruder screw and can result in improved pressure-generating capacity if the screw was cut too deep to begin with. Therefore, if... 

Kramer, M., Sennhenn, B., Lee, G., 2002. Ereeze-drying using vacuum-induced surface freezing. J. Pharm. Sci. 91 (2) 433-443. 

In the case of a thermoplastic, which is already fully polymerized, the curing of a heated liquid or semisolid to a complete solid is the heat removal during phase change. The heat sink consists of the upper and lower mold surfaces so that the resin layers in the vicinity of these surfaces freeze first. The process is complete when the core solidifies. 

Microstructures that are typically observed in molded parts and extrudates include anisotropic textures. The higher orientation in extrusion can result in highly oriented rods or strands, at high draw ratios and/or small diameters, or in structures with an oriented skin and a less oriented central core in thicker strands. This skin-core texture is due to a combination of temperature variations between the surface and the bulk and the flow field in both extrusion and molding processes. For instance, the flow fields in a molded part are shown schematically in Fig. 1.7 [46]. Extensional flow along the melt front causes orientation. Solidification of the polymer on the cold mold surface freezes in this orientation. Flow between the solid layers is affected by the temperature gradient in the mold, and the resulting flow effects [57, 58] result in a rapidly cooled and well oriented skin... 

V.P. Modak, H. Pathak, M. Thayer, S.J. Singer, B.E. Wyslouzil, Experimental evidence for surface freezing in supercooled n-alkane nanodroplets. Phys. Chem. Chem. Phys. 15(18), 6783-6795 (2013)... 

The effect of a structured surface on the crystallization of hard-sphere colloids has been extensively studied in experiments [87, 88, 89, 90], These experiments indicate that crystallization on a template is induced at densities below freezing. This finding is supported by computer simulations of hard spheres in contact with a patterned substrate, by Heni and Lowen [91], These simulations indicate that surface freezing already sets in 29% below the coexistence pressure. Furthermore the effect of a surface on crystallization has also been studied in mixtures of binary hard-spheres [92, 93] and colloid-polymer mixtures [94, 95, 96], In both systems surface crystallization was found to take place before bulk fluid-solid coexistence. In the systems studied in Refs. [92, 93, 94, 95, 96], depletion forces favor the accumulation of the larger component on the wall, and this should facilitate surface crystallization [97]. 

The accordance between experimental and calculated data in Figure 9.2 is rather satisfactory. At the same time. Figure 9.2 clearly shows the tendency of ATj values, calculated on the basis of Equation 9.24, to overestimate the experimentally measured shifts of surface freezing temperature. Evidently, this results from using the values of n, evaluated for the bulk solid (rotator phase) and liquid states, instead of the unavailable corresponding characteristics for surface monolayers. 

---