Modification of the wettability of polymer surfaces using nanoparticles

The effects of nanoparticles, embedded into the matrices of polymer films, on the wettabilities of the surfaces of the composite films are investigated following a two-fold procedure. First, five particles such as silica (of two sizes), tin oxide, alumina and zinc oxide ranged from 7 to 100 nm are mixed with a poly(methyl siloxane). Second, silica nanoparticles (7 nm) are embedded in five different polymers such as poly(methyl methacrylate), polystyrene and three poly (alkyl siloxane) products. Nanocomposite films are produced by adding nanoparticles in the polymer solutions which are then sprayed on silicon substrates. In the first study, which includes the use of different nanoparticles, the contact angle hysteresis is monitored as a function of particle concentration. It is shown that similar water repellency that corresponds to hysteresis <5 is achieved using any of the five tested particles when these are mixed with the siloxane at elevated concentrations. However, the wettability of film surfaces prepared using dispersions of low particle concentration, is highly affected by the particle size and concentration: (i) water repellency of the modified polymer surfaces is enhanced when nanoparticles of small sizes are used i.e. films prepared using particles of small sizes correspond to lower hystereses compared to films produced using bigger particles. (ii) As the particle concentration increases, we first notice an increase in hysteresis, which then decreases. This result is explained with respect to the surface morphologies of the films which are revealed using Scanning Electron Microscopy (SEM). In the second study, which includes the use of different polymers, it is shown that superhydrophobicity can be achieved using any of the previously mentioned organic materials. According to SEM images, similar continuous rough structures are formed on the surfaces of the films, prepared using different polymers and (the same) silica nanoparticles. This is supported by the Cassie-Baxter equation which suggests that comparable surface porosity factors correspond to the different composite films. (C) 2013 Elsevier B.V. All rights reserved.