Dynamics of low anisotropy morphologies in directional solidification

Abstract

We report experimental results on quasi-two-dimensional diffusion limited growth in directionally solidified succinonitrile with small amounts of poly(ethylene oxide), acetone, or camphor as a solute. Seaweed growth, or dense branching morphology, is selected by growing grains close to the [111] plane, where the in-plane surface tension is nearly isotropic. The observed growth morphologies are very sensitive to small anisotropies in surface tension caused by misorientations from the [111] plane. Different seaweed morphologies are found, including the degenerate, the stabilized, and the strongly tilted seaweeds. The degenerate seaweeds show a limited fractal scaling range and, with increased undercooling, suggests a transition from "fractal" to "compact" seaweed. Strongly tilted seaweeds demonstrate a significant twofold anisotropy. In addition, seaweed-dendrite transitions are observed in low anisotropy growth.

Experimental apparatus and sample preparation techniques for directional solidification

“…Rotations of 360°m ake it possible to determine additional symmetries (e.g., twofold) which are often overlooked, yet can have important effects. [11][12][13] Using this technique, it is possible to select a particular orientation or study the growth over a range of orientations as shown here. Note that the large aspect ratio cells are valuable in these studies since there must be a sufficient area for the sample to grow and rotate without encountering the boundaries of the cell.…”

“…In this case, a rotation beyond 90°is not necessary. It is known, however, that there can be nonfourfold symmetries [11][12][13] in 2D interfacial growth. Incorporating the ability to rotate a full 360°allows for the determination of sample orientation and all in-plane crystal symmetries.…”

Phase Field Modeling on Polymer Crystallization and Phase Separation in Crystalline Polymer Blends

“…For a certain crystallographic direction, for example, the <100> direction for a cubic crystal, the surface energy is anisotropic [17], and the morphology develops with cellular or dendritic patterns. Meanwhile, for crystalline axes along <111> direction, the surface energy is isotropic [18]; the interface development has been dominated by seaweed growth [2]. There have been several suggestions as to how to incorporate anisotropy into the phase field description.…”

“…It appears that the main branch and the secondary arm are locally symmetric about the axis of temperature gradient. Such interface morphology with a slight degeneracy is called degenerate seaweed according to Utter and Bodenschatz [18].…”

“…18 Emerged final crystalline morphologies of PEO/DA blends following thermal quenching to various indicated temperatures, showing (a-f) the coexistence of spherulitic crystals in the continuum of isotropic melt. The impinged spherulites inFigure 4.18g represent the single phase PEO crystal region, as the quenching was performed just below the solidus line.…”