Dynamics of low anisotropy morphologies in directional solidification

Area of Science:

• Materials Science
• Crystallization Dynamics
• Complex Morphogenesis

Background:

• Directional solidification is crucial for controlling material properties.
• Understanding diffusion-limited growth and resulting morphologies is key in materials science.
• Seaweed or dense branching morphology (DBM) is a complex pattern observed in directional solidification.

Purpose of the Study:

• To experimentally investigate quasi-two-dimensional diffusion-limited growth in directionally solidified succinonitrile.
• To analyze the influence of solutes (poly(ethylene oxide), acetone, camphor) on seaweed growth morphology.
• To examine the effect of surface tension anisotropy on the observed growth patterns.

Main Methods:

• Directional solidification of succinonitrile with varying solutes.
• Controlled growth near the [111] crystallographic plane to achieve near-isotropic in-plane surface tension.
• Microscopic observation and analysis of resulting seaweed morphologies under different conditions and misorientations.

Main Results:

• Seaweed growth is favored near the [111] plane due to near-isotropic in-plane surface tension.
• Growth morphologies are highly sensitive to minor surface tension anisotropies from misorientations.
• Observed morphologies include degenerate, stabilized, and strongly tilted seaweeds, with degenerate forms showing fractal-to-compact transitions.
• Strongly tilted seaweeds exhibit twofold anisotropy, and transitions between seaweed and dendrite growth occur at low anisotropy.

Conclusions:

• In-plane surface tension anisotropy significantly dictates seaweed morphology in directional solidification.
• The [111] plane offers a unique condition for studying isotropic growth, but deviations lead to complex anisotropic patterns.
• Observed morphological transitions provide insights into the fundamental mechanisms governing diffusion-limited growth and pattern selection.