Preparation of silane-terminated polystyrene and polymethylmethacrylate self-assembled films on silicon wafer

Covalent Grafting of Tethered Homopolymer Film on p-Si(100)

Covalent grafting of a homopolymer film onto a p-Si(100) surface was performed by use of surface electroinitiated emulsion polymerization. This polymerization method was one-step and cost-effective, and worked in the aqueous dispersed media containing both nitrobenzenediazonium (NBD) tetrafluoroborate and methyl methacrylate (MMA) monomer. NBD was reduced in the vicinity of substrate at the cut-on voltage of the pulsed voltage and was successively grafted on a Si surface, leading to a polynitrophenyl (PNP) layer. The reduction of NBD simultaneously initiated the polymerization of MMA. The resulting PMMA macroradicals in the solution can react with the previously grafted PNP at the cutoff voltage of the pulsed voltage for thickening the polymer film. The prepared polymer layer completely covered the Si surface, as investigated by the scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques. Importantly, chemical components and the thickness of the grafted polymer film were well controlled by the applied voltage and the charge flow passing through the Si electrode. X-ray photoelectron spectroscopy (XPS) measurement further confirmed the Si-C bond between the polymer layer and the Si substrate. The homopolymer film was extremely effective in protecting the underlying Si from atmospheric oxidation.

Surface modification of a biodegradable magnesium alloy with phosphorylcholine (PC) and sulfobetaine (SB) functional macromolecules for reduced thrombogenicity and acute corrosion resistance

Siloxane functionalized phosphorylcholine (PC) or sulfobetaine (SB) macromolecules (PCSSi or SBSSi) were synthesized to act as surface modifying agents for degradable metallic surfaces to improve acute blood compatibility and slow initial corrosion rates. The macromolecules were synthesized using a thiol-ene radical photopolymerization technique and then utilized to modify magnesium (Mg) alloy (AZ31) surfaces via an anhydrous phase deposition of the silane functional groups. X-ray photoelectron spectroscopy surface analysis results indicated successful surface modification based on increased nitrogen and phosphorus or sulfur composition on the modified surfaces relative to unmodified AZ31. In vitro acute thrombogenicity assessment after ovine blood contact with the PCSSi and SBSSi modified surfaces showed a significant decrease in platelet deposition and bulk phase platelet activation compared with the control alloy surfaces. Potentiodynamic polarization and electrochemical impedance spectroscopy data obtained from electrochemical corrosion testing demonstrated increased corrosion resistance for PCSSi- and SBSSi-modified AZ31 versus unmodified surfaces. The developed coating technique using PCSSi or SBSSi showed promise in acutely reducing both the corrosion and thrombotic processes, which would be attractive for application to blood contacting devices, such as vascular stents, made from degradable Mg alloys.

Direct passivation of hydride-terminated silicon (100) surfaces by free-radically tethered polymer brushes

A simple and effective means for passivating crystalline silicon is reported by the use of free-radical polymerization (FRP) to directly graft polymer chains to a hydride-terminated surface (Si-H). Complete surface coverage and passivation was achieved in approximately 24 h at 60 degrees C or 30 min at 90 degrees C. Mechanistic studies determined that chain attachment followed a hydride-transfer-based grafting-to mechanism. The grafting process is compatible with a variety of monomers and was used to assemble polymer brush layers (2-12 nm thick), with grafting densities ranging from 0.02 to 0.65 chains/nm2 rivaling densities typically obtained by grafting-from scenarios. This new passivation route provides a uniquely accessible means to covalently anchor dense polymer brushes to silicon surfaces without the need for functionalization of the polymer chain ends or the substrate.