Abstract
An efficient way to apply coatings on complex surfaces is electrospraying. We report on coating of porous model surfaces with well-defined properties using a multiple nozzle electrospraying system to spray sunflower oil and butter-based coating materials. Selected model surfaces were nickel membranes with large rectangular straight-through pores (13 mu m width), polyether sulfone membranes (PES) with small, interconnected pores (0.2 mu m) and dense cellulose membranes. The coating materials penetrated the pores of PES and nickel membranes, filling them up and thereby significantly decreasing the water vapour permeation flux through the substrate. Once the pores were (partially) filled, application of additional coating material caused only minor further flux reduction. For the cellulose membrane, the materials accumulated on the membrane surface; the resulting reduction in water vapour permeation rate was much lower as for the other membranes. Surface coverage during deposition was simulated using a Monte Carlo approach and appeared in agreement with experimental values at lower amounts of applied coating material (< 0.03 kg/m(2)). After deposition of larger amounts, using repeated electrospraying, the water vapour permeation flux reduction was larger than expected from the simulations. This was explained by re-melting and fusion of droplets, which indicated that repeated electrospraying of lipids could be an attractive method to create thin coatings with excellent barrier properties for, e.g. foods and pharmaceuticals that typically have such complex, porous surfaces.