Reactive and stimuli-responsive maleic anhydride containing macromers – multi-functional cross-linkers and building blocks for hydrogel fabrication

Macromers with functional groups that allow for chemical derivatization, polymerization reactions or impart specific physico-chemical properties are functional building blocks for polymeric systems used in different biomedical applications. With this motivation, a series of oligomeric macromers was synthesized by free radical polymerization of maleic anhydride (MA) with N-isopropylacrylamide (NiPAAm) and pentaerythritol diacrylate monostearate (PEDAS). This chemical design provides anhydride groups for effective reactivity of the macromers with amines and other nucleophiles, copolymerized NiPAAm for temperature responsiveness and lipophilic stearate domains for increased hydrogel stability. Macromers were synthesized with different MA co-monomer feeds and oligomeric molecules (Mn below 5000 Da) were obtained with MA contents between 7% and 27% as determined by titration. The fraction of chemically intact anhydrides was calculated to range from 75% to 80%. The ability of the macromers to cross-link di- or oligovalent amines as a function of MA content was investigated rheologically. It was also demonstrated that monovalent amines, e.g. aminofluorescein, could be grafted to the macromer chain utilizing only a fraction of the anhydride functionalities. The derivatized macromers could still participate in cross-linking reactions due to the remaining anhydrides. Temperature sensitivity was shown for aqueous solutions of macromers with fully dissociated anhydride groups. The solutions were additionally responsive to changes in calcium ion concentration and pH. Extracts from macromer cross-linked polyether hydrogels showed no toxicity on L929 fibroblasts.The macromers have perspective as biocompatible cross-linkers for hydrogel fabrication from various biomacromolecules with the opportunity to decorate the gels with monoamine molecules that alter the biological or physico-chemical properties.     

Voltage polarity dependent current paths through polycrystalline ZnO varistors

Due to the scatter of properties of individual grain boundaries, a scatter of the behavior of low-voltage varistor components and asymmetric current–voltage characteristics with respect to the electrical field direction is observed. Using complementary methods (thermography, scanning surface probe microscopy, electron back-scattered diffraction), we investigated the grain boundary behavior of Praseodymium type varistors. Measurements on the relevant grain boundaries revealed a newly observed effect: dependent on the field direction, the main current flows via different spatial paths.     

Studies on obtaining of aluminium ammonium calcium phosphates

Aluminium ammonium calcium phosphates were prepared with the use of AlCl₃, CaCO₃, H₃PO₄. The influence of the process parameters (pH 5 ± 3, the molar ratios of Ca²⁺:Al⁺³:PO₄^?3 in the substrates, respectively 0.31:0.62:1; 0.5:0.5:1; 0.72:0.36:1, temperature 40 ± 20 °C) on the phase composition and the product properties was determined. The process parameters that enable to obtain the material with expected physicochemical properties were determined based on the statistical evaluation of the experiments (fractional factorial design at three levels 3^(k?p)27). The phase composition of the obtained samples was studied with the use of XRD analysis. The specific surface area was calculated with the use of S_BET method and the particle size was determined by the laser scanning microscopy. The materials with the molar ratio of Al³⁺/NH₄⁺ and Al³⁺/Ca²⁺ in the range of 0.70–27.93 and 0.47–24.48, respectively, with an absorption oil number of 95–157 g/100 g paraffin oil, the S_BET within 25–118 m²/g, the pore volume within 0.14–0.74 cm³/g and the particle size in the range of 168–285 nm were obtained.     

Tetrakis(nitratoxycarbon)methane (Née CLL‐1) as a Potential Explosive Ingredient: a Theoretical Study

Ab initio electronic structure calculations at the MP2/cc‐pVTZ level predict the vibrational stability of the theoretical molecule tetrakis(nitratoxycarbon)methane, designated CLL‐1. The gas phase enthalpy of formation, predicted to be +1029.3 kJ mol⁻¹ using the G3(MP2) method, and the estimated density of 1.87 g cm⁻³ are used to predict the explosive performance properties using the equilibrium thermochemical code CHEETAH. The predicted detonation velocity (8.61 km s⁻¹) and pressure (33.1 GPa) are similar to those of RDX, but with a significantly higher detonation temperature (6740 K). Finally, the stability of this theoretical molecule is investigated by calculating the lowest energy unimolecular decomposition pathways of the HCO₃N model compound as well as barriers to rearrangement upon interaction of two HCO₃N molecules.     

Desalination by electret technology

A purification process of making use of electret technology for efficient but cost effective deionization was discussed in this paper. Douglas MacGregor claimed that PTFE electret works as a means of ions separation for desalination due to the polarization of an electrolyte and ions migration under a permanent electrostatic field generated by a pair of electrets with opposite polarities. The electrostatic field attracts counter-ions to the charged solid surface, and thus generates a purified effluent in the mainstream. Theoretical and experimental analyses were made to investigate the practicality of desalination by electret technology. It is found that MacGregor's design is meaningful only for a dilute electrolyte or a system with very high surface charge density because the number of the counter-ions attracted to the surface is limited and cannot exceed that of the surface charges at the electret.     

Effects of the Use of Pore Formers on Performance of an Anode Supported Solid Oxide Fuel Cell

The effects of amount of pore former used to produce porosity in the anode of an anode supported planar solid oxide fuel cell were examined. The pore-forming material utilized was rice starch. The reduction rate of the anode material was measured by Thermogravimetric analysis to qualitatively characterize the gas transport within the porous anode materials. Fuel cells with varying amounts of porosity produced by using rice starch as a pore former were tested. The performance of the fuel cell was the greatest with an optimum amount of pore former used to create porosity in the anode. This optimum is believed to be related to a trade off between increasing gas diffusion to the active three-phase boundary region of the anode and the loss of performance because of the replacement of active three-phase boundary regions of the anode with porosity.     

Ceramic Composites with Three-Dimensional Architectures Designed to Produce a Threshold Strength—II. Mechanical Observations

Finite element modeling and linear elastic fracture mechanics are used to model the residual stresses and failure stress of ceramic composites consisting of polyhedral alumina cores surrounded by thin alumina/mullite layers in residual compression. This type of composite architecture is expected to exhibit isotropic threshold strength behavior, in which the strength of the composite for a particular assumed flaw will be constant and independent of the orientation of tensile loading. The results of the modeling indicate that the strengths of such architectures will be higher than those of laminates of similar architectural dimensions that were previously found to exhibit threshold strength behavior for a particular flaw type. Flexural testing of the polyhedral architectures reveals that failure is dominated by processing defects found at junctions between the polyhedra. Fractography revealed the interaction of these defects with the residual stresses in the compressive layers that separate the polyhedra.     

Self-aligned fabrication of single crystal diamond gated field emitter array

This paper describes a self-aligned fabrication process for diamond gated field emitter array (FEA). Utilizing the non-conformal coverage sputtering conditions of silicon oxide, an interesting “sphere on cone” structure is formed on diamond nano tip array, which is the key point of gate hole opening process. This structure causes shadowing at certain regions of side-wall during Ti / Au gate metal deposition. Removal of “sphere” by wet etching leads to the successful fabrication of a single crystalline diamond gated FEA. Scanning electron microscope observations reveal the fabrication of a uniform emitter array with tip radius of curvature (20 nm) and gate hole (1.4 μm). We also confirmed that no noticeable physical damage exists on tip. In field emission characteristics of the fabricated single crystal diamond gated FEA, gate voltage control of field emission current is realized.     

Prediction of protein secondary structure by mining structural fragment database

A new method for predicting protein secondary structure from amino acid sequence has been developed. The method is based on multiple sequence alignment of the query sequence with all other sequences with known structure from the protein data bank (PDB) by using BLAST. The fragments of the alignments belonging to proteins from the PBD are then used for further analysis. We have studied various schemes of assigning weights for matching segments and calculated normalized scores to predict one of the three secondary structures: α-helix, β-sheet, or coil. We applied several artificial intelligence techniques: decision trees (DT), neural networks (NN) and support vector machines (SVM) to improve the accuracy of predictions and found that SVM gave the best performance. Preliminary data show that combining the fragment mining approach with GOR V (Kloczkowski et al, Proteins 49 (2002) 154-166) for regions of low sequence similarity improves the prediction accuracy.     

Toughening of a Cordierite Glass–Ceramic by Compressive Surface Layers

An indentation fracture mechanics analysis is developed to characterize the toughening effects of a compressive surface layer in brittle materials. The analysis is used to describe the enhanced toughness of cordierite glass–ceramic laminate composites, in which thermal-expansion mismatch effects induced uniform stress in the exterior layers of the symmetric exterior:interior:exterior structures. Interpretation of indentation crack length and inert strength tests via the analysis shows that cracks can be viewed as experiencing discrete regions of decreasing stabilization on propagation from small cracks and complete containment within the compressive layer to large cracks and partial extension into the compensating tensile interior. The observations are described using a stress-intensity factor for circular cracks in linear stress fields that includes different base and surface values for extended cracks. Deconvolution of inert strength data for the model cordierite system studied suggested an increase in toughness from 1.4 MPa·m^1/2 for the base material to a peak of about 5 MPa·m^1/2 for a 1:18:1 composite structure, with attendant increases in strength and flaw tolerance.