Characterizing penetration of a contaminant into block copolymer coatings

Polymer coatings are critical as protective barriers and it would be beneficial to understand how the polymer properties relate to small molecule penetration into coatings. Towards this goal, we investigate how a model dye molecule penetrates into block copolymer coatings. In a typical experiment, a drop of fluorescent Rhodamine B dye solution of known concentration is placed on a coating of micron-order thickness, while confocal microscopy is used to visualize the resultant fluorescence inside the coating over time. As a starting point, block copolymers are synthesized with polystyrene (PS) blocks and modifiable polydimethylsiloxane (PDMS) blocks. Using image analysis methods, we track the temporal and spatial fluorescence distribution in the coating. A model based on first principles is developed to determine the rate of penetration; we find that the rate of dye penetration into the coating is a function of the initial dye concentration and the PDMS content in the block copolymers. Ultimately, we expect that a better understanding of how small molecules penetrate into polymers will help guide the design of more effective coatings for a wide range of applications.