Spontaneous surface flattening via layer-by-layer assembly of interdiffusing polyelectrolyte multilayers

We report a facile means to achieve planarization of nonflat or patterned surfaces by utilizing the layer-by-layer (LbL) assembly of highly diffusive polyelectrolytes. The polyelectrolyte pair of linear polyethylenimine (LPEI) and poly(acrylic acid) (PAA) is known to maintain intrinsic diffusive mobility atop or even inside ionically complexed films prepared by LbL deposition. Under highly hydrated and swollen conditions during the sequential film buildup process, the LbL-assembled film of LPEI/PAA undergoes a topological self-deformation for minimizing surface area to satisfy the minimum-energy state of the surface, which eventually induces surface planarization along with spontaneous filling of surface textures or nonflat structures. This result is clearly different from other cases of applying nondiffusive polyelectrolytes onto patterned surfaces or confined structures, wherein surface roughening or incomplete filling is developed with the LbL assembly. Therefore, the approach proposed in this study can readily allow for surface planarization with the deposition of a relatively thin layer of polyelectrolyte multilayers. In addition, this strategy of planarization was extended to the surface modification of an indium tin oxide (ITO) substrate, where surface smoothing and enhanced optical transmittance were obtained without sacrificing the electronic conductivity. Furthermore, we investigated the potential applicability of surface-treated ITO substrates as photoelectrodes of dye-sensitized solar cells prepared at room temperature. As a result, an enhanced photoconversion efficiency and improved device characteristics were obtained because of the synergistic role of polyelectrolyte deposition in improving the optical properties and acting as a blocking layer to prevent electron recombination with the electrolytes.     

Bonding structure analysis of carbon nitride films by Raman spectroscopy and X-ray photoelectron spectroscopy (XPS)

Carbon nitride films were prepared by an opposed-target DC reactive sputtering system and the bonding behaviors were investigated according to the nitrogen content and annealing temperature. Annealing leads to a loss of nitrogen from the films and the CN is totally removed at 600 °C. Due to annealing at 600 °C, the C---C out-of-plane vibrational band intensity at 700 cm⁻¹ becomes very low and also the CN band at 2200 cm⁻¹ disappears completely. The sp² bonding in a CN compound is the most stable phase. Due to carbon's atypical nature in having its p orbital more compact and tightly bound compared to s states, the C=N sp² phase is more stable than the C---C sp³ phase. As the C=N sp² phase dominates the structure, the film is mainly graphite-like with some proportion of C---C, CN and N=N bonds.     

Optical spectra of aqueous solutions of glutamine-tryptophan associates

The optical density and luminescence ability of aqueous solutions of glutamine-tryptophan depend on the degree of oxidation of the initial dry substances of dipeptide. Glutamine-tryptophan has a high associating ability, which increases if stored. The general form of the optical absorption and luminescence spectra of the associates differs little from the spectra of monomers. Among the spectral-optical symptoms of association of a substance in a solution for glutamine-tryptophan, we discovered the hypochromism and narrowing of the absorption spectra and shortening of the fluorescence lifetime. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 4, pp. 436–439, July–August, 2000.     

Preparation of YSZ Coated AISI-Type 316L Stainless Steel by the Sol-Gel Coating Method and Its Corrosion Behavior in Molten Carbonate

The effect of heat-treatment conditions on the corrosion behavior of yttria stabilized zirconia (YSZ) coated AISI-type 316L stainless steels in molten carbonate are investigated. YSZ films on stainless steel were prepared by the sol-gel method. While the sample heat-treated at 800°C for 2 hours in air has an uneven surface microstructure with macrocracks, a YSZ coated sample heat-treated in argon has an even microstructure. The polarization resistance and corrosion rate of YSZ coated sample heat-treated in air were deteriorated from 6.948 cm² and 364.7 mpy (millimeter per year) to 3.291 cm² and 769.8 mpy, respectively, by the corrosion for 100 hours due to its poor surface microstructures. At the same experimental condition, meanwhile, those corrosion parameters of YSZ coated sample heat-treated in argon were 15.43 cm² and 164.2 mpy, respectively, and those were improved to 18.83 cm² and 134.6 mpy after the corrosion for 100 hours. This is attributed to the YSZ film with well developed surface microstructures. The concentration profiles of elements and X-ray diffractograms indicate that the oxide layer of YSZ coated sample heat-treated in argon had a triple layer structure composed of outer YSZ film, in between Fe₂O₃ layer, and inner chromium rich layer during corrosion.     

Dendritic macromers as in situ polymerizing biomaterials for securing cataract incisions

Dendritic macromers are attractive macromolecules for hydrogel formation since high cross-linking densities at low polymer concentration can be obtained, varied physical properties can be observed based on the macromer structure, and low viscous aqueous solutions can be injected in an in vivo site of irregular shaped to form a well-integrated polymer network. A peptide dendron possessing terminal cysteine residues was synthesized and characterized. When this peptide dendron was mixed with poly(ethylene glycol dialdehyde) in aqueous solution at pH = 7.4, a hydrogel spontaneously formed as a consequence of thiazolidine linkages between the macromers. Such in situ polymerized hydrogels are of interest for tissue engineering and wound-repair applications. To evaluate the potential use of this hydrogel sealant in ophthalmic surgeries, a 3-mm clear corneal incision (i.e., the wounds created during a typical cataract surgery) was successfully sealed.