Spontaneous cracking of amorphous solid water films and the dependence on microporous structure

Vapor-deposited, porous,amorphous, water-icefilms, also calledamorphous solid water (ASW),crack spontaneously duringgrowth when thefilm thickness exceeds a critical value (Lc). We measured theLc duringgrowth of ASWfilms as a function ofgrowth temperature (Tg = 10 K, 30 K, and 50 K) and deposition angle (θ = 0°, 45°, and 55°) using a quartz crystal microbalance, an optical interferometer, and an infrared spectrometer. The critical thickness, 1–5 μm under our experimental conditions, increases withTg andθ, an indication offilm porosity. We suggest that ASWfilms undergo tensile stress due to the mismatch between substrate adhesion and contracting forces derived from the incompletely coordinated molecules on the surfaces of the pores. We provide a model to explain the observed dependences ofLc on theTg andθ in the context of Griffith theory and estimate the tensile strength of low-temperature ASW to be ∼25–40 MPa. Our model can be applied more generally to describe fracture of othersolids with microporous structures, such as metallic or ceramic materials with voids.

Source: Applied Physics Letters - November 14, 2016 Category: Physics Authors: Caixia Bu, Catherine A. Dukes and Ra úl A. Baragiola Source Type: research