Solvent dependent friction force response of polystyrene brushes prepared by surface initiated polymerization.
ABSTRACT Polystyrene (PS) brushes were prepared on oxide passivated silicon by the surface initiated polymerization (SIP) technique. From an AIBN-type free radical initiator, which was silanized and immobilized on silicon wafers, styrene brushes were directly polymerized and grafted from the surface. The formation of the initiator monolayer and, subsequently, the polymer brush on the surface were monitored by X-ray photoelectron spectroscopy (XPS) and ellipsometry. Friction force measurements were performed by atomic force microscopy (AFM), using a 5 microm SiO2 colloidal sphere tip and under systematically varied solvent environments (nonpolar to polar), to demonstrate the dependence of brush lubricity on solvation. The relative uptake of solvents in the PS brush was determined by quartz crystal microbalance (QCM), and it correlates well with friction data. It is surmised that, in poor solvent environments, the polymer brush exists in a collapsed conformation, giving rise to the higher observed friction response.
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ABSTRACT: We directly monitor in parallel and in real time the temporal profiles of polymer brushes simultaneously grown via multiple ATRP reaction conditions on a single substrate using arrays of silicon photonic microring resonators. In addition to probing relative polymerization rates, we show the ability to evaluate the dynamic properties of the in situ grown polymers. This presents a powerful new platform for studying modified interfaces that may allow for the combinatorial optimization of surface-initiated polymerization conditions.Journal of the American Chemical Society 09/2011; 133(38):14864-7. · 10.68 Impact Factor
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ABSTRACT: Implant medical research and tissue engineering both target the design of novel biomaterials for the improvement of human health and clinical applications. In order to develop improved surface coatings for hard tissue (bone) replacement materials and implant devices, we are developing micropatterned coatings consisting of polymer brushes. These are used as organic templates for the mineralization of calcium phosphate in order to improve adhesion of bone cells. First, we give a short account of the current state-of-the-art in this particular field of biomaterial development, while in the second part the preliminary results of cell culture experiments are presented, in which the biocompatibility of polymer brushes are tested on human mesenchymal stem cells.Frontiers of Materials Science in China 04/2012; 3(2):132-144.
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ABSTRACT: With the advent of regulated, surface initiated polymerizations, specifically using controlled radical approaches, the choice of polymerizable compounds and the control over grafting chemistry have seen tremendous advancement. New analysis techniques and approaches are now needed to characterize these brushes with molecular precision. In addition, spatial structure control at the nanoscale, and tuning of thickness as well as composition of the brushes, have become feasible by utilizing recently developed enabling molecular nanofabrication approaches. Atomic force microscopy (AFM) is a powerful analytical tool for the characterization of polymer brushes, as well as for the fabrication of brush structures across the length scales. AFM has been used to investigate polymer brushes in a number of ways including imaging surface morphologies, measuring brush thickness, estimating the value of number average molar mass, observing stimulus responsive behavior and probing surface mechanical properties. In addition, AFM based methods such as nanoscratching, dip-pen nanolithography (DPN) and scanning probeoxidation (SPO) have been also employed for the nanofabrication of patterned polymer brushes. This feature article gives a short account of this field and highlights recent advances.Journal of Materials Chemistry 01/2010; 20(24):4981-4993. · 5.97 Impact Factor