Can Ice-Like Structures Form on Non-Ice-Like Substrates? The Example of the K-feldspar Microcline

Abstract

Feldspar minerals are the most common rock formers in Earth’s crust. As such they play an important role in subjects ranging from geology to climate science. An atomistic understanding of the feldspar structure and its interaction with water is therefore desirable, not least because feldspar has been shown to dominate ice nucleation by mineral dusts in Earth’s atmosphere. The complexity of the ice/feldspar interface arising from the numerous chemical motifs expressed on the surface makes it a challenging system. Here we report a comprehensive study of this challenging system with ab initio density functional theory calculations. We show that the distribution of Al atoms, which is crucial for the dissolution kinetics of tectosilicate minerals, differs significantly between the bulk environment and on the surface. Furthermore, we demonstrate that water does not form ice-like overlayers in the contact layer on the most easily cleaved (001) surface of K-feldspar. We do, however, identify contact layer structures of water that induce ice-like ordering in the second overlayer. This suggests that even substrates without an apparent match with the ice structure may still act as excellent ice nucleating agents.

Heterogeneous seeded molecular dynamics as a tool to probe the ice nucleating ability of crystalline surfaces

“…More often than not, the structure of the ice nuclei at the interface with a particular crystalline substrate has very little in common with the topology of the ice bulk phase. For instance, density functional theory calculations have shown that the layer of water molecules mediating the interaction between ice nuclei and the (001) surface of the mineral feldspar does not resemble an ice-like structure 50 . Similar results were obtained by means of classical force fields 51 and coarse-grained potentials 43,44 as well.…”

Perspectives on the Future of Ice Nucleation Research: Research Needs and Unanswered Questions Identified from Two International Workshops

“…Ice nucleation activity is influenced by several independent molecular properties, including surface hydrophobicity [32,36,37], surface morphology [38], and local electric fields [39][40][41]. The widespread notion that ice nucleation agents have surfaces similar to the surfaces of ice has recently been challenged [42], and even amorphous surfaces may act as good ice nuclei [43]. A comparison of experimental observations and computer simulation of nucleation of ice on feldspar showed that ice has higher nucleation rates at the surface regions with a larger number of defects [44].…”

Refreeze experiments with water droplets containing different types of ice nuclei interpreted by classical nucleation theory

“…Even if the temperature has dropped low enough to overcome the energy barrier to form a critical ice embryo at the nucleation sites of Hoggar Mountain dust and ATD, embryos of a critical size might form only infrequently. Pedevilla et al (2016) investigated the most easily cleaved (001) surface of the microcline with ab initio density functional calculations. They demonstrated that water does not form ice-like overlayers in the contact layer; however, they identified contact layer structures of water that induce ice-like ordering in the second overlayer.…”