Spectrophotometric investigation of the copolymerization of styrene or methyl methacrylate with 1,8‐naphthalimide dyes

The copolymerization of styrene or methyl methacrylate with 1,8‐naphthalimide dyes to yield fluorescent side‐group copolymers was investigated. During copolymerization, no changes occurred in the chromophoric systems of the dyes. Colorimetrically, it was found that more that 0.90% of the dyes were chemically bonded to the polymer chain. The effect of polymer coloration was proven by appropriate coloristic characterization. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2463–2470, 2001     

Graphoepitaxy of High‐Quality GaN Layers on Graphene/6H–SiC

The implementation of graphene layers in gallium nitride (GaN) heterostructure growth can solve self‐heating problems in nitride‐based high‐power electronic and light‐emitting optoelectronic devices. In the present study, high‐quality GaN layers are grown on patterned graphene layers and 6H–SiC by metalorganic chemical vapor deposition. A periodic pattern of graphene layers is fabricated on 6H–SiC by using polymethyl methacrylate deposition and electron beam lithography, followed by etching using an Ar/O₂ gas atmosphere. Prior to GaN growth, an AlN buffer layer and an Al_0.2Ga_0.8N transition layer are deposited. The atomic structures of the interfaces between the 6H–SiC and graphene, as well as between the graphene and AlN, are studied using scanning transmission electron microscopy. Phase separation of the Al_0.2Ga_0.8N transition layer into an AlN and GaN superlattice is observed. Above the continuous graphene layers, polycrystalline defective GaN is rapidly overgrown by better quality single‐crystalline GaN from the etched regions. The lateral overgrowth of GaN results in the presence of a low density of dislocations (≈10⁹ cm⁻²) and inversion domains and the formation of a smooth GaN surface.     

Proteases to Improve the Mechanical Characteristics of Durable Press Finished Cotton Fabrics

N‐Methylol reagents are conventional crosslinking agents that are still widely used in textile industry to produce crease‐resistant cotton fabrics. In this work serine proteases were used to recover the strength of fabrics, cross‐linked with N‐hydroxymethylacrylamide. Nearly one half of the strength loss of crosslinked cotton fabrics could be restored after protease treatment, while the wrinkle recovery angle (WRA) decreased only slightly. The enzymatic hydrolysis of the amide cross‐links in the durable pressed cellulose was confirmed by FT‐IR analysis and dyeability with an acid dye.

Effect of protease concentration on the tensile strength recovery, WRA and acid dye dyeability at 30 min reaction time.     

Long spin relaxation times in wafer scale epitaxial graphene on SiC(0001)

We developed an easy, upscalable process to prepare lateral spin-valve devices on epitaxially grown monolayer graphene on SiC(0001) and perform nonlocal spin transport measurements. We observe the longest spin relaxation times τ(S) in monolayer graphene, while the spin diffusion coefficient D(S) is strongly reduced compared to typical results on exfoliated graphene. The increase of τ(S) is probably related to the changed substrate, while the cause for the small value of D(S) remains an open question.     

Mapping of local electrical properties in epitaxial graphene using electrostatic force microscopy

Local electrical characterization of epitaxial graphene grown on 4H-SiC(0001) using electrostatic force microscopy (EFM) in ambient conditions and at elevated temperatures is presented. EFM provides a straightforward identification of graphene with different numbers of layers on the substrate where topographical determination is hindered by adsorbates. Novel EFM spectroscopy has been developed measuring the EFM phase as a function of the electrical DC bias, establishing a rigorous way to distinguish graphene domains and facilitating optimization of EFM imaging.     

Nanoscale structural characterization of epitaxial graphene grown on off-axis 4H-SiC (0001)

In this work, we present a nanometer resolution structural characterization of epitaxial graphene (EG) layers grown on 4H-SiC (0001) 8° off-axis, by annealing in inert gas ambient (Ar) in a wide temperature range (T _gr from 1600 to 2000°C). For all the considered growth temperatures, few layers of graphene (FLG) conformally covering the 100 to 200-nm wide terraces of the SiC surface have been observed by high-resolution cross-sectional transmission electron microscopy (HR-XTEM). Tapping mode atomic force microscopy (t-AFM) showed the formation of wrinkles with approx. 1 to 2 nm height and 10 to 20 nm width in the FLG film, as a result of the release of the compressive strain, which builds up in FLG during the sample cooling due to the thermal expansion coefficients mismatch between graphene and SiC. While for EG grown on on-axis 4H-SiC an isotropic mesh-like network of wrinkles interconnected into nodes is commonly reported, in the present case of a vicinal SiC surface, wrinkles are preferentially oriented in the direction perpendicular to the step edges of the SiC terraces. For each T _gr, the number of graphene layers was determined on very small sample areas by HR-XTEM and, with high statistics and on several sample positions, by measuring the depth of selectively etched trenches in FLG by t-AFM. Both the density of wrinkles and the number of graphene layers are found to increase almost linearly as a function of the growth temperature in the considered temperature range.     

Optical sensor for aliphatic amines based on the simultaneous colorimetric and fluorescence responses of smart textile

The pH indicator proposed is a water‐soluble dye based on benzo[de]antracen‐7‐one. Dissolving in buffered aqueous solution, it changes color from yellow to orange and in the mean time decreases its fluorescence emission as a function of the amine concentration. Viscose fabric, dyed with the same dye has been investigated as a new reversible colorimetric and fluorescent sensor material for ammonia and aliphatic amines in buffered solution. The high value of the dye pK_a and the influence of the textile matrix on the selective detection of dimethylamine compared to ammonia, trimethylamine, and metylamine have been studied. The different response of the solution and textile matrix as well as the optical analyses both as a color change and a fluorescence emission have been discussed. The advantage of this sensor is the fact that depending on the analytical problem to be solved and the available instrumentation it can be used either as a fluorogenic or as a chromogenic chemosensor. In addition, the textile sensor is characterized by facile fabrication, low cost, sensibility, and reproducibility. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Laboratory methods for assessing API sensitivity to mechanical stress during agitated drying

Two distinct laboratory methods have been developed to assess the propensity of active pharmaceutical ingredients to undergo particle breakage during agitated drying operations. In the first method, mechanical stress is applied to particles by mechanical agitation of powders compressed under an applied normal force. For the second, particles experience stresses as they are carried within a pressurized gas stream. These methods are simple, relatively compound-sparing, and are used to rank materials according to a quantitative breakage classification scale as hard, medium, or easy to break. Based on the results obtained using these methods at laboratory scale, recommendations and precautions for processing at larger scale are made. In this paper, these methods are described in detail, and the results, obtained for several pharmaceutical compounds, are presented.     

Lipases to Improve the Performance of Formaldehyde‐Free Durable Press Finished Cotton Fabrics

Lipases were used to restore partially the strength losses of cotton fabrics crosslinked with 1,2,3,4‐butanetetracarboxylic acid. The enzymatic hydrolysis of the ester linkages at low temperature and neutral pH resulted in 10% strength recovery, coupled with a slight deterioration of the crease‐resistance effect. The conventional alkaline hydrolysis provided higher strength recovery, however provoked considerable change in the durable press performance of the fabrics.