Toward microphase separation in epoxy systems containing PEO–PPO–PEO block copolymers by controlling cure conditions and molar ratios between blocks

Nanostructuring of thermosetting systems using the concept of templating and taking advantage of the self-assembling capability of block copolymers is an exciting way for designing new materials for nanotechnological applications. In this first part of the work, reactive blends based on stoichiometric amounts of a diglycidylether of bisphenol-A epoxy resin and 4,4′-diaminodiphenylmethane cure agent modified with three poly(ethylene oxide)-co-poly(propylene oxide)-co-poly(ethylene oxide) block copolymers were studied. Cure advancement of these systems was analyzed by differential scanning calorimetry. The experimental results show a delay of cure rate, which increases as copolymer content and PEO molar ratio in the block copolymer rise. Infrared spectroscopy shows that PEO block is mainly responsible of physical interactions between the hydroxyl groups of growing epoxy thermoset and ether bonds of block copolymer. These interactions are mainly responsible for the delaying of cure kinetics. The molar ratio between blocks also has a critical influence on the delaying of the cure rate. A mechanistic approach of cure kinetics allows us to relate the delay of cure as a consequence of block copolymer adding to physical interactions between components.     

Finite unified models

We present phenomenologically viableSU (5) unified models which are finite to all orders before the spontaneous symmetry breaking. In the case of two models with three families the top quark mass is predicted to be 178.8 GeV.     

Carbon nanotubes as reinforcement of styrene-butadiene rubber

This study reports an easy technique to produce cured styrene-butadiene rubber (SBR)/multi-walled carbon nanotubes (MWCNT) composites with a sulphur/accelerator system at 150 °C. Significant improvement in Young's modulus and tensile strength were achieved by incorporating 0.66 wt% of filler without sacrificing SBR elastomer high elongation at break. A comparison with carbon black filled SBR was also made. Field emission scanning electron microscopy was used to investigate dispersion and fracture surfaces. Results indicated that the homogeneous dispersion of MWCNT throughout SBR matrix and strong interfacial adhesion between oxidized MWCNT and the matrix are responsible for the considerable enhancement of mechanical properties of the composite.     

Multifunctional hybrid nanopapers based on bacterial cellulose and sol–gel synthesized titanium/vanadium oxide nanoparticles

The hybrid inorganic/organic nanopapers based on bacterial cellulose and different type of sol–gel synthesized nanoparticles are fabricated. A simple, rapid, low-cost pathway based on a diffusion step of sol–gel nanoparticles into swollen bacterial cellulose membrane via orbital incubator is developed. This alternative pathway allows to keeping intact the 3D network of the bacterial cellulose membrane while sol–gel nanoparticles are formed in situ and anchored on the nanofibers surface. Titanium, vanadium oxide nanoparticles and a mixture of both are used to functionalize bacterial cellulose membrane. Fabricated hybrid inorganic/organic nanopapers are characterized by thermogravimetric analysis, X-ray diffraction spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, MTS mechanical testing, UV–vis spectroscopy, colorimeter and semiconductor analyzer. Synthesized photochromic hybrid nanopapers modified with vanadium and titanium oxide nanoparticles can find potential application as sensitive displays, biosensors and other optical devices.     

Elucidation of the fibrous structure of <Emphasis Type="Italic">Musaceae</Emphasis> maturate rachis

In the last years several composites and high performance materials with woody and non-woody natural fibers have been developed. In this study, a morphological study of agricultural residues as rachis from Musaceae plants cultivated in Colombia has been carried out. Fibrous structures as fiber bundles, elementary or ultimate fibers and even cellulose microfibrils grouped together into microfibril bundles have been observed. Both biological retting and chemical procedures like alkali treatments combined with alkaline peroxide and acid addition have been used. Different microscopic techniques as optical (OM), confocal (CM), scanning electron (SEM), and atomic force (AFM) ones have been used for analysis of isolated samples. A hierarchical arrangement from conducting tissues and fiber bundles to cellulose microfibrils in Musaceae rachis has been noted. All of these structures can be isolated by biological and chemical processes at the corresponding arrangement level. This means that Musaceae rachises constitute a source of new interesting biodegradable raw materials with multiple possibilities in dimensions and morphologies for several industries. A strong presence of crystal structures exists on fiber surfaces, being their occurrence related to the maturate state of rachis samples. Additionally, a top-down scheme is proposed for understanding the structuration of rachis at each length scale.     

Conductive properties of TiO2/bacterial cellulose hybrid fibres

In this article, we report the first micellization study of amphiphilic copolymers composed of bacterial medium chain length poly(3-hydroxyalkanoates) (mcl-PHAs). A series of diblock copolymers based on fixed poly(ethylene glycol) (PEG) block (5000 g mol(-1)) and a varying poly(3-hydroxyoctanoate-co-3-hydroxyhexanoate) (PHOHHx) segment (1500-7700 g mol(-1)) have been synthesized using "click" chemistry. These copolymers self-assembled to form micelles in aqueous media. The influence of PHOHHx block molar mass on the hydrodynamic size and on the critical micelle concentration (CMC) has been studied using dynamic light scattering and fluorescence spectroscopy, respectively. With increasing PHOHHx length, narrowly distributed micelles with diameters ranging from 44 to 90 nm were obtained, with extremely low CMC (up to 0.85 mg/L). Cryogenic transmission electron microscopy (Cryo-TEM) showed that micelles took on a spherical shape and exhibited narrow polydispersity. Finally, the colloidal stability of the micelles against physiological NaCl concentration has been demonstrated, suggesting they are promising candidates for drug delivery applications.     

Sustainable optically transparent composites based on epoxidized soy-bean oil (ESO) matrix and high contents of bacterial cellulose (BC)

Production of transparent composites from totally renewable resources with extraordinary potential for different applications can be made possible using cellulose. Composites of epoxidized soybean oil (ESO)/bacterial cellulose (BC) nanofibers have been prepared with high fiber content. Due to the nano-order scale network-like structure of BC nanofibers, composite films present high transparency even at high BC content. Transparency of films has been analyzed by UV–visible spectroscopy observing that only 15% of matrix transmittance is lost in the nanocomposites. ESO/BC composites show better mechanical properties with increasing BC content. Composites combine high stiffness and good ductility due to the incorporation of BC network structure in ESO matrix.     

Representations of quiver Hecke algebras via Lyndon bases

A new class of algebras has been introduced by Khovanov and Lauda and independently by Rouquier. These algebras categorify one-half of the Quantum group associated to arbitrary Cartan data. In this paper, we use the combinatorics of Lyndon words to construct the irreducible representations of those algebras associated to Cartan data of finite type. This completes the classification of simple modules for the quiver Hecke algebra initiated by Kleshchev and Ram.