Conventional analysis and characterization of polymer brush formation relies on laborious methods that use a quartz crystal microbalance, atomic force microscope, microcantilever, or other tools that measure the concentration change of solutions. Herein we develop a simple and easy method that utilizes intrinsically flat two-dimensional (2D) plasmonic nanoparticles as sensors for unveiling the mechanism of polymer brush formation on surfaces. Via ultraviolet-visible spectroscopy, the plasmonic nanoparticles can be used to determine the amount of polymers near the surface in situ. As the amount of polymers increases near the surface, the nanoparticle characteristic localized surface plasmon resonance wavelength redshifts, and the shift amount corresponds linearly to the polymer density near the surface. By functionalizing the nanoparticles in solutions of thiolated polyethylene glycol (PEG-SH) with or without PEG disulfide (PEG-S-S-PEG), the three-regime kinetics of the polymer brush formation is confirmed. The fast adsorption and slow chain rearrangement in the first regime are found to be the causes of the latent regime. In the latent regime, the adsorbed polymer chains rearrange to anchor their ends onto the surface and contract to liberate space so that other polymer chains can graft onto the surface until saturation. The fundamental understanding gained herein enables the design of surfaces with complex chemistries and properties, which can find broad applications in responsive sensors, films, and coatings. Moreover, the novel analytical method of using 2D plasmonic nanoparticle as a sensor to understand the polymer brush formation is applicable to investigating the grafting of other molecules such as self-assembled monolayers, protein, and DNA.

The use of electrospun polystyrene (PS) fibers to create continuous long range ordered multi-scale porous structures in titanium diboride (TiB 2 ) is investigated in this work. The introduction of electrospun PS fibers as a sacrificial filler into a colloidal suspension of TiB 2 allows for easy control over the pore size, porosity, and long range ordering of the porous structures of the sintered ceramics. Green bodies were formed by vacuum infiltrating an electrospun-fiber-filled mold with the colloidal TiB 2 suspension.The size, volume, distribution, and dispersion of the pores were optimized by carefully selecting the sacrificial polymer, the fiber diameter, the solvent, and the solid content of TiB 2 . The green bodies were partially sintered at 2000°C to form a multi-scale porous structure via the removal of the PS fibers. Aligned continuous cylindrical pores homogeneously distributed across the samples were derived from the PS fibers in a range of~5-20 μm and partial sintering produced inter-particle porosity with sizes of 0.3-1 μm. TiB 2 near-net-shaped parts with the multi-scale porosities (~50-70%) were successfully cast and sintered. This low-cost processing technique can be used in the production of thermally and mechanically anisotropic structures into near-net shape parts, for extreme environment applications, such as high temperature insulation. K E Y W O R D Saligned continuous porosity, multi-scale porosity, processing, titanium diboride

No abstract

No abstract

No abstract