title: Thermosensitive copolymer coatings with enhanced wettability switching.
abstract: Expanded cross-linked copolymers of poly(N-isopropylacrylamide) (PNiPAAm) and poly(acrylic acid) (PAAc) of varying monomer ratios were grafted from a crystalline silicon surface. Surface-tethered polymerization was performed at a slightly basic pH, where electrostatic repulsion among acrylic acid monomer units forces the network into an expanded polymer conformation. The influence of this expanded conformation on switchability between a hydrophilic and a hydrophobic state was investigated. Characterization of the copolymer coating was carried out by means of X-ray photoelectron spectroscopy (XPS) ellipsometry, and diffuse reflectance IR. Lower critical solution temperatures (LCSTs) of the copolymer grafts on the silicon surfaces were determined by spectrophotometry. Temperature-induced wettability changes were studied using sessile drop contact angle measurements. The surface topography was investigated by atomic force microscopy (AFM) in Milli-Q water at 25 and 40 degrees C. The reversible attachment of a fluorescently labeled model protein was studied as a function of temperature using a fluorescence microscope and a fluorescence spectrometer. Maximum switching in terms of the contact angle change around the LCST was observed at a ratio of 36:1 PNiPAAm to PAAc. The enhanced control of biointerfaces achieved by these coatings may find applications in biomaterials, biochips, drug delivery, and microfluidics.
authors.affiliation: School of Chemistry, Physics and Earth Sciences, Flinders University, Bedford Park, South Australia 5042, Australia.
authors.forename: Mahaveer D
authors.initials: MD
authors.lastname: Kurkuri
authors.forename: Matthew R
authors.initials: MR
authors.lastname: Nussio
authors.forename: Alec
authors.initials: A
authors.lastname: Deslandes
authors.forename: Nicolas H
authors.initials: NH
authors.lastname: Voelcker
mesh_terms: D018625:Microscopy, Atomic Force; D008856:Microscopy, Fluorescence; D011108:Polymers / Q000737:chemistry*; D012996:Solutions; D013057:Spectrum Analysis; D013696:Temperature; D017155:Wettability
chemical_list: D011108:Polymers; D012996:Solutions