Maitra Tanmoy, Antonini Carlo, Mauer Matthias Auf Der, Stamatopoulos Christos, Tiwari Manish K., Poulikakos Dimos (2014), Hierarchically nanotextured surfaces maintaining superhydrophobicity under severely adverse conditions, in NANOSCALE
, 6(15), 8710-8719.
Asthana Ashish, Maitra Tanmoy, Buechel Robert, Tiwari Manish K., Poulikakos Dimos (2014), Multifunctional Superhydrophobic Polymer/Carbon Nanocomposites: Graphene, Carbon Nanotubes, or Carbon Black?, in ACS APPLIED MATERIALS & INTERFACES
, 6(11), 8859-8867.
Maitra Tanmoy, Tiwari Manish K., Antonini Carlo, Schoch Philippe, Jung Stefan, Eberle Patric, Poulikakos Dimos (2014), On the Nanoengineering of Superhydrophobic and Impalement Resistant Surface Textures below the Freezing Temperature, in NANO LETTERS
, 14(1), 172-182.
Eberle Patric, Tiwari Manish K., Maitra Tanmoy, Poulikakos Dimos (2014), Rational nanostructuring of surfaces for extraordinary icephobicity, in NANOSCALE
, 6(9), 4874-4881.
Maitra Tanmoy, Antonini Carlo, Tiwari Manish K., Mularczyk Adrian, Imeri Zulkufli, Schoch Philippe, Poulikakos Dimos (2014), Supercooled Water Drops Impacting Superhydrophobic Textures, in LANGMUIR
, 30(36), 10855-10861.
We propose to investigate the open fundamental questions related to ice formation and adhesion on a sub-cooled surface through experiments and theoretical considerations. The problem is relevant to many scientific and practical applications such as telecommunication and electrical networks, bridges, hydrological and highway structures, aircraft wings, etc. Icephobic coatings are a promising means to address this problem. The aim of this approach is to engineer coatings, which prevent formation of ice by providing unfavorable thermodynamic conditions for ice nucleation, growth and reduction of the bonding forces between the coating and ice, thereby reducing the ice adhesion on to the substrate. Additional decrease of ice adhesion on the icephobic coatings is achieved by imparting roughness to the surface or by chemically altering the surface layers. Since the physical principles of reduction in ice adhesion are not well understood, a number of previous works have focused on using textured superhydrophobic surfaces with an intuitive assumption of proportionality between hydrophobicity and icephobicity. Typically, air trapped underneath a water droplet on superhydrophobic surfaces minimizes the water/substrate contact area and can lead to severe reduction of wetting, delay of ice formation, reduction of ice adhesion and easier droplet roll-off. However, inconclusive results have been obtained in recent studies, especially with respect to a direct correlation between delayed icing and hydrophobicity of the surfaces. Our preliminary results presented herein are counterintuitive, in that they point to a markedly improved icephobic behavior (large delay in ice nucleation and growth) of ultra-smooth, moderately hydrophobic to hydrophilic surfaces, compared to rougher superhydrophobic surfaces. Clearly, systematic research involving separate and controlled tuning of surface roughness and energy is needed in order to describe the dependence of the freezing process on them. The influence of hierarchical morphology ? consisting of micro-to-nanoscale roughness, which promises to capture both ultra low (liquid) droplet adhesion combined with severely icephobic behavior remains to be investigated and is focal point of the proposed research. The multiscale features in hierarchical morphologies have two advantages. Firstly, they limit the water to the nanoscale feature, thereby suppressing the ice nucleation. Secondly, they trap air at the liquid/solid interface of the water droplet, thus should also be more efficient at reducing the adhesion of the ice formed by freezing the droplet. The current proposal is aimed at addressing these open fundamental questions related to ice formation and adhesion on a sub-cooled surface through experiments and theoretical considerations. The proposed task plan can be divided into two parts:1.A series of experiments on freezing of microdroplets on sub-cooled surfaces with hierarchical micro-to-nanoscale patterns will be carried. The hierarchical morphology will be created via several microfabrication techniques while surface functional groups will be applied in the form of self assembled monolayers of progressively changing surface energy and icephobicity. The nanoscale features in hierarchical morphology will be kept below few nm, i.e. below critical ice nucleation radius. The surface morphology will be characterized by electron and atomic force microscopy.2.Optical visualization of the water (ice)/substrate interface will be employed to interpret the measured dynamics of ice formation and adhesion on surfaces with roughness patterns ranging from smooth to hierarchical with various sizes. The predictions of heterogeneous ice nucleation theory will be compared with the experimental findings and possible theoretical extensions will be proposed, for example by accounting for the structure of the water layer adjacent to a sub-cooled surface. The effect of recalescent ice formation on the solid surface surrounding the ice region, through possible formation of a condensation halo (as our feasibility experiments have indicated) and its influence on subsequent ice nucleation will be thoroughly investigated. The overall goal of this study is to advance the fundamentals underlying the dependence of icing process on substrate morphology (smooth to hierarchical) and wettability (hydrophobicity or icephobicity). Systematic tuning of the hierarchical texture along with functionalization will be used to retard the ice crystallization and minimize the ice adhesion on such surfaces under both stationary and dynamic (flow) conditions of the surrounding gas. In addition to their fundamental value, the results of the study will also help the future designs of supericephobic surfaces with significantly delayed icing and low ice adhesion.