Water Storage in Thin Films Maintaining the Total Film Thickness as Probed with in situ Neutron Reflectivity

We investigate a new type of thin film material which allows for water storage without an increase in film thickness, whereas typically water storage in polymers and polymer films is accompanied with a strong swelling of the film, i.e., a strong increase in the film thickness. So these films will avoid problems related to strains which are caused by swelling. The basic key for the preparation of such thin films is the installation of a glassy network by the use of an asymmetric diblock copolymer polystyrene-block-poly(N-isopropylacrylamide) [P(S-b-NIPAM)] with a long PS and short PNIPAM block in combination with a solvent which is more equal in interaction with both the blocks as compared to water. With in situ neutron reflectivity the water storage and removal are probed. The total film thickness increases only by 2.5% by allowing for a total water storage of 17.4%. Thus the material can be used for coatings to reduce humidity in nano-applications, which might suffer from changes in the water content of the surrounding environment.