title: Novel method for visualizing water transport through phase-separated polymer films.
abstract: Drug release from oral pharmaceutical formulations can be modified by applying a polymeric coating film with controlled mass transport properties. Interaction of the coating film with water may crucially influence its composition and permeability to both water and drug. Understanding this interaction between film microstructure, wetting, and mass transport is important for the development of new coatings. We present a novel method for controlled wetting of polymer coating films in an environmental scanning electron microscope, providing direct visual information about the processes occurring as the film goes from dry to wet. Free films made of phase-separated blends of water-insoluble ethyl cellulose (EC) and water-soluble hydroxypropyl cellulose (HPC) were used as a model system, and the blend ratio was varied to study the effect on the water transport properties. Local variations in water transport through the EC/HPC films were directly observed, enabling the immediate analysis of the structure-mass transport relationships. The leaching of HPC could be studied by evaporating water from the films in situ. Significant differences were observed between films of varying composition. The method provides a valuable complement to the current approach of making distinct diffusion and microscopy experiments for studying the dynamic interaction of polymer films with water.
authors.affiliation: 1 Department of Applied Physics, Chalmers University of Technology, SE-41296 Gothenburg, Sweden.
authors.forename: Anna
authors.initials: A
authors.lastname: Jansson
authors.affiliation: 2 AstraZeneca R&D Mölndal, SE-43183 Mölndal, Sweden.
authors.forename: Catherine
authors.initials: C
authors.lastname: Boissier
authors.affiliation: 2 AstraZeneca R&D Mölndal, SE-43183 Mölndal, Sweden.
authors.forename: Mariagrazia
authors.initials: M
authors.lastname: Marucci
authors.affiliation: 2 AstraZeneca R&D Mölndal, SE-43183 Mölndal, Sweden.
authors.forename: Mark
authors.initials: M
authors.lastname: Nicholas
authors.affiliation: 1 Department of Applied Physics, Chalmers University of Technology, SE-41296 Gothenburg, Sweden.
authors.forename: Stefan
authors.initials: S
authors.lastname: Gustafsson
authors.affiliation: 3 Department of Chemical and Biological Engineering, Chalmers University of Technology, SE-41296 Gothenburg, Sweden.
authors.forename: Anne-Marie
authors.initials: AM
authors.lastname: Hermansson
authors.affiliation: 1 Department of Applied Physics, Chalmers University of Technology, SE-41296 Gothenburg, Sweden.
authors.forename: Eva
authors.initials: E
authors.lastname: Olsson
mesh_terms: D002482:Cellulose / Q000031:analogs & derivatives* / Q000737:chemistry; D008855:Microscopy, Electron, Scanning / Q000379:methods*; D014867:Water / Q000032:analysis*
chemical_list: D014867:Water; C013517:ethyl cellulose; D002482:Cellulose; C008079:hydroxypropylcellulose