Characterization of ice nucleation at mineral surfaces.
Graziano, Zachary A.
Slough, Diana P.
Lin, Yu-Shan
2016
- The crystallization of ice from liquid water occurs both homogeneously and heterogeneously. Most atmospheric ice nucleation occurs heterogeneously, at the surface of atmospheric aerosols. These atmospheric aerosols can include organic compounds, some bacteria, mineral dusts, pollens, and soot particles. While homogeneous ice nucleation requires temperatures as low as –37 °C, heterogeneous ice ... read morenucleation can occur at much higher temperatures. While experiments have been successful in both identifying active ice nucleating agents and determining the temperatures at which they can cause the onset of freezing, it remains difficult to predict whether a surface will be an ice nucleating agent and equally challenging to design surfaces with ice nucleating ability. Knowledge of how these surfaces template the formation of ice on the molecular level would greatly enhance our ability to design surfaces with hyperactive ice nucleating ability. We consider three commonly growing faces of the ice Ih crystal: primary prism, secondary prism (fastest growing), and basal (slowest growing). Silver iodide (AgI) is known to be an excellent promoter of ice nucleation. Its ability to cause freezing at temperatures as high as –4 °C and relative safety have made its industrial use important as a cloud seed. Kaolinite is commonly found in atmospheric mineral dusts and is known to nucleate ice at temperatures as warm as –10 °C. It is a layered mineral, with each layer consisting of repeating alumina tetrahedra stacked atop repeating silica tetrahedra. Each layer is neutrally charged. The aluminum surface of the kaolinite layer is hydroxylated and has the ability to act as both a hydrogen bond donor and acceptor. The silicon surface only acts as a hydrogen bond acceptor. Submitted in partial fulfillment of the grant requirement of the Tufts Summer Scholars Program.read less
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