title: Wrinkling Measurement of the Mechanical Properties of Drying Salt Thin Films.
abstract: We report a time-resolved approach to probe the mechanical properties of thin films during drying and solidification based on surface wrinkling. The approach is demonstrated by measuring the modulus of a ternary system comprising an inorganic salt (aluminum chlorohydrate), a humectant (glycerol), and water across the glassy film formation pathway. The topography of mechanically induced wrinkling of supported films on polydimethylsiloxane (PDMS) is experimentally monitored during mechanical extension and relaxation cycles. Nontrivial aspects of our method include the need to oxidize the (hydrophobic) PDMS surface prior to solution deposition to enable surface wetting, which simultaneously creates a glassy-layer skin, whose wrinkling can contribute to the overall topography. Film drying is studied as a function of solution concentration and time, and a range of pattern morphologies are found: sinusoidal wrinkling, transient double-wavelength wrinkling accompanying film "crust" formation, ridging associated with stress localization, and cracking. We quantify the evolution of the elastic modulus during the sinusoidal wrinkling stage, employing bi- and trilayer models, which are independently confirmed by nanoindentation. The method provides thus a simple and robust approach for the mechanical characterization of out-of-equilibrium thin films.
authors.affiliation: Department of Chemical Engineering, Imperial College London , London SW7 2AZ, United Kingdom.
authors.forename: Giulia L
authors.initials: GL
authors.lastname: Ferretti
authors.affiliation: Department of Chemical Engineering, Imperial College London , London SW7 2AZ, United Kingdom.
authors.forename: Manuela
authors.initials: M
authors.lastname: Nania
authors.affiliation: Department of Chemical Engineering, Imperial College London , London SW7 2AZ, United Kingdom.
authors.forename: Omar K
authors.initials: OK
authors.lastname: Matar
authors.affiliation: Department of Chemical Engineering, Imperial College London , London SW7 2AZ, United Kingdom.
authors.forename: João T
authors.initials: JT
authors.lastname: Cabral
mesh_terms: D000536:Aluminum Hydroxide / Q000737:chemistry*; D055119:Elastic Modulus; D057927:Hydrophobic and Hydrophilic Interactions; D008567:Membranes, Artificial; D012828:Silicones / Q000737:chemistry*
chemical_list: D008567:Membranes, Artificial; D012828:Silicones; C078211:polymethylsiloxane; D000536:Aluminum Hydroxide; C016976:aluminum chlorhydrate