Photochemically Prepared, Two-Component Polymer-Concentration Gradients

Abstract

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.

Impact of chain morphology on the lubricity of surface-grafted polysaccharides

“…The success of this method in achieving the desired system has previously been conrmed with XPS, ToF-SIMS and VASE. 20,21 Subsequent UV illumination in ambient air or in air with 100% relative humidity, with the aim of activating any remaining azides, was found to inuence neither the thickness nor the friction measurements, within experimental error. Samples produced using lower molecular weights of dextran were found to yield signicantly lower chain densities in addition to lower overall layer thickness, presumably due to less efficient covalent attachment related to the conformation of the spin-coated chains; the same trend has also been observed for other polymers.…”

“…Following this, the wafers were placed on a spin coater, covered in a solution of 25 g L À1 dextran (dextran T200, 2 MDa, Pharmacosmos A/S, Denmark) in water, and then spun at 4000 rpm for 40 s, then 5000 rpm for 10 s. The wafers were allowed to dry for 15 minutes, then exposed to UV light (Philips TUV 11 W, peak wavelength 254 nm) at a distance of 10 cm. Dextran gradients were produced by varying the UV exposure time (from 3.5 s to 240 s) along the wafer using a moving shutter, 21 programmed to evenly space the desired exposure durations in discrete steps along the wafer. Following the UV exposure, the wafers were immersed overnight in ultrapure water to remove excess non-attached or physisorbed polymer, then rinsed with water, dried with nitrogen, measured by ellipsometry, and then stored in a dark prior to friction measurements.…”

Tailoring SU-8 Surfaces: Covalent Attachment of Polymers by Means of Nitrene Insertion

“…The conditions for spincoating and the UV irradiation time have been chosen according to previously published results. 20 A nonspecific photochemical reaction initiated at the PFPA moieties covalently links the SU-8 surface with the polymeric chains of the top layer that are directly in contact with the linker layer. Finally, the sample was thoroughly rinsed with water to remove the unbound polymer, leaving the SU-8 surface with a covalently bound layer of PDDA or PSS.…”

Unraveling the Mechanism and Kinetics of Binding of an LCI‐eGFP‐Polymer for Antifouling Coatings

“…To date, only a limited number of works have demonstrated initiator‐coupling strategies that address the broad range of surface chemistries of different materials, such as the use of plasma sputtered polymers, [ 64 ] formation of a priming film of polydopamine, [ 65–67 ] and the use of C−H insertion reactions. [ 68,69 ] Moreover, the stringent polymerization conditions necessary for controlled polymerization are often too complex or expensive to translate into an industrial process. Other approaches to circumvent these difficulties include physisorption of polymers and grafting‐onto via end groups or blocks.…”