title: Effect of Aluminum Substrate Surface Modification on Wettability and Freezing Delay of Water Droplet at Subzero Temperatures.
abstract: In this study, we have investigated the freezing delay of a water droplet on precooled substrates of an aluminum alloy that is commonly used for heat-exchanger fins. The surfaces of the substrates were modified to obtain surfaces with different hydrophilicity/hydrophobicity and different surface chemistry but without significantly modifying the surface topography. The freezing delays and water contact angles were measured as a function of the substrate temperature and the results were compared to the predictions of the heterogeneous ice nucleation theory. Although the trends for each sample followed the trend in this theory, the differences in the extents of freezing delays were in apparent disagreement with the predictions. Concretely, a slightly hydrophilic substrate modified by (3-aminopropyl) triethoxysilane (APTES) showed longer freezing delays than both more hydrophilic and more hydrophobic substrates. We suggest that this is because this particular surface chemistry prevents ice formation at the interface of the substrate, prior to the deposition of the water droplet. On the basis of our results, we suggest that not only wettability and topography but also the concrete surface chemistry plays a significant role in the kinetics of the ice formation process when a water droplet is placed on a precooled substrate.
authors.affiliation: Department of Energy and Environment, Danish Building Research Institute, Aalborg University , A.C. Meyers Vænge 15, 2450 København SV, Denmark.
authors.forename: Maral
authors.initials: M
authors.lastname: Rahimi
authors.affiliation: Department of Energy and Environment, Danish Building Research Institute, Aalborg University , A.C. Meyers Vænge 15, 2450 København SV, Denmark.
authors.forename: Alireza
authors.initials: A
authors.lastname: Afshari
authors.affiliation: Department of Chemistry, Technical University of Denmark , Kemitorvet 207, DK-2800 Kgs Lyngby, Denmark.
authors.forename: Esben
authors.initials: E
authors.lastname: Thormann
keywords: aluminum; freezing delay; ice nucleation; surface chemistry; surface modification; wettability