Conducting gel-fibres based on carrageenan, chitosan and carbon nanotubes

A simple continuous flow wet-spinning method for assembling fibres consisting of two oppositely charged biopolymers (chitosan and carrageenan) and carbon nanotubes is reported. It was observed that the order in which the biopolymers are added, i.e. spinning chitosan into one of the carrageenans (or vice versa), affects the fibre composition as well as the resulting electrical and mechanical properties. The addition of carbon nanotubes into the fibres was found to improve Young's modulus values coupled with a significant improvement in the electrical conductivity by up to 6 orders of magnitude.

Spinning Carbon Nanotube-Gel Fibers Using Polyelectrolyte Complexation

Biopolymer-single walled carbon nanotube (SWNT)-biopolymer fibers were prepared using a continuous flow spinning approach. Polyelectrolyte complexation was facilitated by injecting a SWNT-biopolymer dispersion into a coagulation bath containing a biopolymer of opposite charge. We showed that the ability to spin fibers and their properties depend on processing conditions such as polyelectrolyte pH, sonolysis regime (conditions employed to disperse SWNT) and the order of adding the anionic and cationic biopolymer solutions. Maximizing the ionic nature through changes in the pH increased spin-ability, while combining a sonicated dispersion with an as-prepared (non-sonicated) polyelectrolyte solution allowed us to optimize sonolysis conditions while retaining spin-ability of fibers with smooth surface morphology. Addition of the cationic biopolymer-SWNT dispersion to the anionic biopolymer solution resulted in mechanical reinforcement with the increase in SWNT loading fraction. All fibers decreased their electrical resistance upon exposure to water vapor.

Reduced graphene oxide directed self-assembly of phospholipid monolayers in liquid and gel phases

The response of cell membranes to the local physical environment significantly determines many biological processes and the practical applications of biomaterials. A better understanding of the dynamic assembly and environmental response of lipid membranes can help understand these processes and design novel nanomaterials for biomedical applications. The present work demonstrates the directed assembly of lipid monolayers, in both liquid and gel phases, on the surface of a monolayered reduced graphene oxide (rGO). The results from atomic force microscopy indicate that the hydrophobic aromatic plane and the defect holes due to reduction of GO sheets, along with the phase state and planar surface pressure of lipids, corporately determine the morphology and lateral structure of the assembled lipid monolayers. The DOPC molecules, in liquid phase, probably spread over the rGO surface with their tails associating closely with the hydrophobic aromatic plane, and accumulate to form circles of high area surrounding the defect holes on rGO sheets. However, the DPPC molecules, in gel phase, prefer to form a layer of continuous membrane covering the whole rGO sheet including defect holes. The strong association between rGO sheets and lipid tails further influences the melting behavior of lipids. This work reveals a dramatic effect of the local structure and surface property of rGO sheets on the substrate-directed assembly and subsequent phase behavior of the supported lipid membranes.

Distinct kinetics of molecular gelation in a confined space and its relation to the structure and property of thin gel films

Thin films of molecular gels formed in a confined space have potential applications in transdermal delivery, artificial skin, molecular electronics, etc. The microstructures and properties of thin gel films can be significantly different from those of their bulk counterparts. However, so far a comprehensive understanding of the effects of spatial confinement on the molecular gelation kinetics, fiber network structure and related mechanical properties is still lacking. In this work, using rheological techniques, we investigated the effect of one-dimensional confinement on the formation kinetics of fiber networks in the molecular gelation process. Fractal analyses of the kinetic information in terms of an extended Dickinson model enabled us to describe quantitatively the distinct kinetic signature of molecular gelation. The structural features derived from gelation kinetics support well the fractal patterns of the fiber networks acquired by optical and electron microscopy. With the kinetics-structure correlation, we can gain an in-depth understanding of the confinement-induced differences in the structure and consequently the mechanical properties of a model molecular gelling system. Particularly, the confinement induced structural transition, from a three-dimensional, dense and compact spherulitic network composed of highly branched fibers to a quasi-two-dimensional sparse spherulitic network composed of less branched fibers and entangled fibrils at the boundary areas, renders a gel film to become less stiff but more ductile. Our study suggests here a new strategy of engineering the fiber network microstructure to achieve functional gel films with unusual but useful properties.

Influence of non-hydrolysable groups in silane precursor on pore dimension and photochromic properties of sol-gel silica embedded with a spirooxazine dye

In this work, silica embedded with a spirooxazine dye was prepared by hydrolysis of silanes that bear a nonhydrolyzable group of different structures through a sol-gel route in the presence of a spirooxazine dye, and the pore dimension and photochromic properties of photochromic silica coatings on fabric were studied. The pore dimension in the silica was examined by small angle X-ray scattering (SAXS), transmission electron microscopy (TEM), and nitrogen adsorption porosimetry. The SAXS results revealed that the distance between pores was in the range between 0.8 nm and 1.9 nm and it increased with increasing the size of the non-hydrolyzable group. Pore size measured by nitrogen adsorption porosimetry was in the range of 2.1-2.7 nm. The photochromic optical absorption was influenced mainly by the hydrophobicity of the non-hydrolyzable groups, while the color changing rates were influenced by the steric effect of the non-hydrolyzable groups and their interaction with the dye.