Influence of Swelling and Disruption of the Starch Granule on the Composition of the Starch-Polyacrylonitrile Copolymer

Abstract

The results of an evaluation of polymers as cryogenic adhesives are presented. It was observed that polyether-based polyurethanes provided the most attractive capability as adhesives for use at liquid hydrogen temperatures.     

Über die Vertheilung der Primzahlen

Ohne Zusammenfassung     

Complex aggregation patterns in drying nanocolloidal suspensions: size matters when it comes to the thermomechanical stability of nanoparticle-based structures

We report the results of a model study on the interrelation among the occurrence of complex aggregation patterns in drying nanofluids, the size of the constitutive nanoparticles (NPs), and the drying temperature, which is a critical issue in the genesis of complex drying patterns that was never systematically reported before. We show that one can achieve fine control over the occurrence and topological features of these drying-mediated complex structures through the combination of the particle size, the drying temperature, and the substrate surface energy. Most importantly, we show that a transition in the occurrence of the patterns appears with the temperature and the particle size, which accounts for the size dependence of the thermomechanical stability of the aggregates in the nanoscale range. Using simple phenomenological and scaling considerations, we showed that the thermomechanical stability of the aggregates was underpinned by physical quantities that scale with the size of the NPs (R) either as R(-2) or R(-3). These insights into the size-dependent dissipation mechanisms in nanoclusters should help in designing NPs-based structures with tailored thermomechanical and environmental stability and hence with an optimized morphological stability that guarantees their long-term functional properties.     

Ceric-initiated polymerization onto polyacrylonitrile with carbohydrate end groups. Graft versus block copolymer formation

Starch-g-polyacrylonitrile (starch-g-PAN) copolymers were prepared by ceric ammonium nitrate initiation, and the major portion of the starch in these graft copolymers was then removed by acid hydrolysis to yield PAN with oligosaccharide end groups. Although these PAN-oligosaccharide samples reacted with methyl methacrylate in the presence of ceric ammonium nitrate, the resulting products were largely graft copolymers rather than the expected PAN-poly(methyl methacrylate) (PMMA) block copolymers. The following evidence is presented for a PAN-g-PMMA structure: (i) PAN without oligosaccharide end groups also produced a copolymer with methyl methacrylate under our reaction conditions. (ii) Starch-g-PAN (51 or 37% add-on) was a less reactive substrate toward ceric-initiated polymerization than PAN with oligosaccharide end groups. (iii) Low-add-on (18%) starch-g-PAN reacted with methyl methacrylate to give a final graft copolymer in which a large percentage of PMMA was grafted to the PAN component rather than to starch.     

Wetting-induced formation of quasiperiodical wrinkling patterns in alginate-based coatings

We present the results of systematic model experimental investigations on wrinkling instabilities which develop on alginate-based coatings when they are wetted by swelling electrolyte drops. The wrinkles first appear randomly within the wet spot, before they selectively protrude out around the periphery in a quasiperiodical wrinkle pattern. We discuss the critical parameters that drive the emergence (ionic strength and swelling rate) and spatial feature (size and periodicity) of these swelling-induced structures on such complex functional coatings. Beyond their relative aesthetics and their fundamental interest related to morphological instabilities, these reconstruction structures which are invisible to the naked eye can develop in a variety of technological processes (inkjet printing for instance), affecting irreversibly the quality of the products.     

A Validated HPLC-PDA-HRMS Method to Investigate the Biological Stability and Metabolism of Antiparasitic Triterpenic Esters

Pentacyclic triterpenes (PTs) are commonly found in medicinal plants with well-known antiparasitic effects. Previous research on C-3 and C-27 triterpenic esters showed effective and selective in vitro antiparasitic activities and in vivo effectiveness by parenteral routes. The aim of this study was to determine triterpenic esters’ stability in different biological-like media and the main microsomal degradation products. An HPLC-PDA method was developed and validated to simultaneously analyze and quantify bioactive triterpenic esters in methanol (LOQ: 2.5 and 1.25–100 µg/mL) and plasma (LOQ: 5–125 µg/mL). Overall, both triterpenic esters showed a stable profile in aqueous and buffered solutions as well as in entire plasma, suggesting gaining access to the ester function is difficult for plasma enzymes. Conversely, after 1 h, 30% esters degradation in acidic media was observed with potential different hydrolysis mechanisms. C-3 (15 and 150 µM) and C-27 esters (150 µM) showed a relatively low hepatic microsomal metabolism (<23%) after 1 h, which was significantly higher in the lowest concentration of C-27 esters (15 µM) (>40% degradation). Metabolic HPLC-PDA-HRMS studies suggested hydrolysis, hydroxylation, dehydration, O-methylation, hydroxylation and/or the reduction of hydrolyzed derivatives, depending on the concentration and the position of the ester link. Further permeability and absorption studies are required to better define triterpenic esters pharmacokinetic and specific formulations designed to increase their oral bioavailability.     

Competitive spreading versus imbibition of polymer liquid drops in nanoporous membranes: scaling behavior with viscosity

The way a liquid drop that is in contact with a nanoporous substrate evolves essentially depends on the competition between imbibition and spreading. Although the scaling behavior of this competitive process with liquid viscosity is important for various applications requiring the filling of nanoporous substrates (template-assisted fabrication, storage, and controlled release of liquids), they appear to be poorly investigated and insufficiently understood. We developed a model study to investigate the wetting and spontaneous imbibition of silicon oil drops of viscosities ranging from 1 to 100 Pa s on nanoporous alumina membranes (pore size of 200 nm). Our results show that the drop radius essentially follows the power law t1/10 time dependence as expected by Tanner's law. However, the scaling of the spreading velocity with the viscosity (approximately eta-n) was found to display an exponent that is comparable on both the reference (impermeable) and nanoporous substrates (n = 0.55) but notably higher than theoretically expected (0.1). More surprisingly, we show that despite the confinement, the rate of imbibition into the nanopores displays a weaker dependence on the viscosity, as compared to the spreading velocity on both the reference and nanoporous substrates. On the basis of Darcy's law for capillary-driven imbibition, this result was discussed in the context of the scaling behavior of the contact angle with the viscosity.     

Al–Cu intermetallic coatings processed by sequential metalorganic chemical vapour deposition and post-deposition annealing

Sequential processing of aluminum and copper followed by reactive diffusion annealing is used as a paradigm for the metalorganic chemical vapour deposition (MOCVD) of coatings containing intermetallic alloys. Dimethylethylamine alane and copper N,N′-di-isopropylacetamidinate are used as aluminum and copper precursors, respectively. Deposition is performed on steel and silica substrates at 1.33 kPa and 493–513 K. Different overall compositions in the entire range of the Al–Cu phase diagram are obtained by varying the relative thickness of the two elemental layers while maintaining the overall thickness of the coating close to 1 μm. As-deposited films present a rough morphology attributed to the difficulty of copper to nucleate on aluminum. Post-deposition annealing is monitored by in situ X-ray diffraction, and allows smoothening the microstructure and identifying conditions leading to several Al–Cu phases. Our results establish a proof of principle following which MOCVD of metallic alloys is feasible, and are expected to extend the materials pool for numerous applications, with innovative thin film processing on, and surface properties of complex in shape parts.