Photochemically prepared, two-component polymer-concentration gradients.
A versatile, photochemical surface-modification approach using nitrene-insertion reactions has been employed to develop an ultrathin, two-component, polymer-gradient coating. Perfluorophenyl azide (PFPA) acted as the photosensitive moiety, forming a nitrene radical upon 254 nm UV exposure. Cationic poly(allyl amine) was grafted with PFPA and surface-anchored onto silicon wafers by means of electrostatic self-assembly. After spin-coating of polystyrene (PS), the substrate was illuminated from behind a moving shutter, thereby controlling the azide-to-nitrene conversion degree across the substrate, and leading to a gradually varying PS density after rinsing. Backfilling with poly(vinyl pyrrolidone) (PVP) and re-exposing to UV light formed a two-component polymer-density gradient. The composition varied linearly following exposure to a linear UV exposure profile, as determined with spectroscopic ellipsometry (ELM) and X-ray photoelectron spectroscopy (XPS). High-spatial-resolution, time-of-flight secondary ion mass spectrometry (ToF-SIMS) revealed a high degree of mixing between the two incompatible polymers on the micrometer scale. The dynamic water-contact angle (dCA) was found to depend strongly on the sample history, suggesting adaptive properties of the coating, which was further confirmed by angle-resolved XPS (ARXPS). To confirm the applicability of the system for biological investigations, gradients were exposed to zoospores of the macrofouling alga Ulva linza , and a critical PS composition of 70% was identified, above which settlement started to increase. It has been shown that a two-component polymer-density gradient can provide a high-throughput platform for determining critical surface properties of polymer blend materials.
Laboratory for Surface Science and Technology, Department of Materials, ETH Zurich , Wolfgang-Pauli-Str. 10, CH-8093 Zurich, Switzerland.
Olof
O
Sterner
Ângela
Â
Serrano
Sophie
S
Mieszkin
Stefan
S
Zürcher
Samuele
S
Tosatti
Maureen E
ME
Callow
James A
JA
Callow
Nicholas D
ND
Spencer
D001386:Azides / Q000737:chemistry; D006845:Hydrocarbons, Fluorinated / Q000737:chemistry; D015394:Molecular Structure; D055668:Photochemical Processes; D011073:Polyamines / Q000737:chemistry*; D011137:Polystyrenes / Q000737:chemistry*; D011205:Povidone / Q000737:chemistry*; D012825:Silicon / Q000737:chemistry; D055672:Static Electricity; D013499:Surface Properties; D014466:Ultraviolet Rays
D001386:Azides; D006845:Hydrocarbons, Fluorinated; D011073:Polyamines; D011137:Polystyrenes; C556136:perfluorophenyl azide; C063994:polyallylamine; D011205:Povidone; D012825:Silicon