Deposition and wetting characteristics of polyelectrolyte multilayers on plasma-modified porous polyethylene

Hydrophilic and chemically reactive porous media were prepared by adsorbing functional polymers at the surface of sintered polyethylene membranes. Modification of the membrane was accomplished by first exposing the membrane to an oxygen glow discharge gas plasma to introduce an electrostatic charge at the membrane surfaces. Cationic polyelectrolyte polyethylenimine (PEI) was adsorbed from solution to the anionic-charged surface to form an adsorbed monolayer. The adsorption of a second anionic polyelectrolyte onto the PEI layer allows further modification of the membrane surface to form a polyelectrolyte-bilayer complex. The conformation and stability of the adsorbed monolayers and bilayers comprising the modified surface are probed as a function of the polymer structure, charge density, and solubility. Using X-ray photoelectron spectroscopy analysis, we demonstrate that the presence of the polyelectrolyte multilayers drastically increases the density and specificity of the functional groups at the surface, more than what can be achieved through the plasma modification alone. Also, using the wicking rate of deionized, distilled water through the porous membrane to gauge the interfacial energy of the modified surface, we show that the membrane wicking rate can be controlled by varying the chemistry of the adsorbing polyelectrolytes and, to a lesser extent, by adjusting the polarity or ionic strength of the polyelectrolyte solution.

Study on the dyeing properties of hemicyanine dyes. I. Acrylic fabrics

Three hemicyanine dyes were employed in dyeing acrylic fabrics following traditional cationic dyeing procedures. The influence of the substituting groups of the dye molecule on the sorption rate and sorption isotherms was analyzed. The results showed that those dyed acrylic fabrics using hemicyanine dyes had obvious fluorescent effect in the spectra range 550–750 nm. In addition, according to the EN-471 standard (2003), the chromaticity of dyed acrylic fabric was calculated to evaluate whether hemicyanine dye could meet the requirements of the fluorescent dye for high visibility warning clothing.

Overcoming interfacial affinity issues in natural fiber reinforced polylactide biocomposites by surface adsorption of amphiphilic block copolymers

This work demonstrates that the interfacial properties in a natural fiber reinforced polylactide biocomposite can be tailored through surface adsorption of amphiphilic and biodegradable poly (ethylene glycol)-b-poly-(L-lactide) (PEG-PLLA) block copolymers. The deposition from solvent solution of PEG-PLLA copolymers onto the fibrous substrate induced distinct mechanisms of molecular organization at the cellulosic interface, which are correlated to the hydrophobic/hydrophilic ratios and the type of solvent used. The findings of the study evidenced that the performance of the corresponding biocomposites with polylactide were effectively enhanced by using these copolymers as interfacial coupling agents. During the fabrication stage, diffusion of the polylactide in the melt induced a change in the environment surrounding block copolymers which became hydrophobic. It is proposed that molecular reorganization of the block copolymers at the interface occurred, which favored the interactions with both the hydrophilic fibers and hydrophobic polylactide matrix. The strong interactions such as intra- and intermolecular hydrogen bonds formed across the fiber−matrix interface can be accounted for the enhancement in properties displayed by the biocomposites. Although the results reported here are confined, this concept is unique as it shows that by tuning the amphiphilicity and the type of building blocks, it is possible to control the surface properties of the substrate by self-assembly and disassembly of the amphiphiles for functional materials.

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.

Graphene/zinc nano-composites by electrochemical co-deposition

We describe for the first time the electrochemical co-deposition of composites based on a reactive base metal and graphene directly from a one-pot aqueous mixture containing graphene oxide and Zn2+. In order to overcome stability issues the Zn2+ concentration was kept below a critical threshold concentration, ensuring stable graphene oxide suspensions in the presence of cationic base metal precursors. This approach ensures the compatibility between the cationic base metal precursor and graphene oxide, which is more challenging compared to previously reported anionic noble metal complexes. Spectroscopic evidence suggests that the reason for destabilisation is zinc complexation involving the carboxylate groups of graphene oxide. The composition of the electrodeposited co-composites can be tuned by adjusting the concentration of the precursors in the starting mixture. The nano-composites show zinc particles (<3 nm) being uniformly dispersed amongst the graphene sheets. It is also demonstrated that the composites are electrochemically active and suitable for energy storage and energy conversion applications. However, a factor limiting the discharge efficiency is the reactivity of the base metal (low reduction potential and small particle size) which undergoes rapid oxidation when exposed to aqueous electrolytes.

Peptide mimics targeting bacterial membranes

In recent years, society has been increasingly concerned with bacteria that are no longer susceptible to commercial antibiotics. Faced with a lack of tools, medical practitioners today are forced to prescribe medicines that, although effective, cause as much harm to the patient as the principal infection. The purpose of this research project is to develop novel antibacterials that remain potent against bacterial infections without being toxic to the patient.

Synthesis and preliminary investigations into norbornane-based amphiphiles and their self-assembly

A range of norbornane based amphiphiles, which possess a rigid 'kink' in the centre of amphiphiles, were accessed via a concise four step synthesis. The self-assembly properties of these novel compounds were then investigated and the critical aggregation concentration (CAC), hydrodynamic diameter (DH) by dynamic light scattering (DLS) and their morphology by cryogenic transmission electron microscopy (cryoTEM) and negatively stained transmission electron microscopy (TEM) were determined. These compounds while possessing similar CAC values (50-70 μM) exhibited a wide variety of particle size (60-140 nm) and morphologies, including vesicles, cigar-shaped aggregates and rod-like micelles. Considering the similarities in molecular structure we have proposed that the unique nature of the molecular 'kink' is affecting molecular assembly in which subtle changes in molecular structure have large ramifications on aggregate size and morphology.

Electrically conductive graphene-filled polymer composites with well organized three-dimensional microstructure

Electrically conductive graphene-filled polystyrene nanocomposites with well-organized three dimensional (3D) microstructures were simply prepared by electrostatic assembly integrated latex technology. First, positively charged polystyrene was synthesized via disperse polymerization in ethanol/water medium by using a cationic co-monomer, and then directly co-assembled with graphene oxide. Eventually, a honeycomb-like graphene 3D framework was embedded in polystyrene matrix after in situ chemical reduction and hot compression molding. Due to the 3D conductive pathway derived from graphene based network evidenced by morphology studies, the fabricated nanocomposites show excellent electrical properties, i.e. extremely low percolation threshold of 0.09 vol% and high saturated conductivity of 25.2 S/m at GNs content of 1.22 vol%. © 2014 Elsevier B.V.

A parametric study of a monolithic microfluidic system for on-chip biomolecular separation

A microfabricated poly(dimethylsiloxane) (PDMS) chip containing channel filled with polymer monolith has been developed for on-chip biomolecule separation. Methacrylate monolithic polymers were prepared by photo-initiated polymerization within the channel to serve as a continuous stationary phase. The monolithic polymer was functionalized with a weak anion-exchange ligand, and key parameters affecting the binding characteristics of the system were investigated. The total binding capacity was unaffected by the flow rate of the mobile phase but varied significantly with changes in ionic strength and pH of the binding buffer. The binding capacity decreased with increasing buffer ionic strength, and this is due to the limited available binding sites for protein adsorption resulting from cationic shielding effect. Similarly, the binding capacity decreased with decreasing buffer pH towards the isoelectric point of the protein. A protein mixture, BSA and ovalbumin, was used to illustrate the capacity of the methacrylate-based microfluidic chip for rapid biomolecule separation.

Degradation of organic dyes by P25-reduced graphene oxide: influence of inorganic salts and surfactants

Treatment of coloured effluent treatment is a major issue for the textile industry. In this study, catalyst P25-graphene was prepared and applied for degrading dye from an aqueous solution. Three types of dyes were selected to determine the feasibility of the catalyst for the dye degradation, including sulphonic, azoic, and fluorescent dyes. P25-graphene catalyst showed good ability to degrade all selected dyes. The influence of inorganic salts and surfactants on the photocatalytic degradation of rhodamine B using catalyst P25-graphene was also investigated. The degradation of rhodamine B was suppressed by the presence of NaCl, but the effect of Na2SO4 was negligible. The degradation of rhodamine B was significantly suppressed by all three types of surfactant, namely anionic, cationic and non-ionic surfactants. NMR technique was used to investigate the mechanisms associated with this suppression.

Synthesis of norbornane bisether antibiotics via silver-mediated alkylation

A small series of norbornane bisether diguanidines have been synthesized and evaluated as antibacterial agents. The key transformation-bisalkylation of norbornane diol 6-was not successful using Williamson methodology but has been accomplished using Ag2O mediated alkylation. Further functionalization to incorporate two guanidinium groups gave rise to a series of structurally rigid cationic amphiphiles; several of which (16d, 16g and 16h) exhibited antibiotic activity. For example, compound 16d was active against a broad range of bacteria including Pseudomonas aeruginosa (MIC = 8 µg/mL), Escherichia coli (MIC = 8 µg/mL) and methicillin-resistant Staphylococcus aureus (MIC = 8 µg/mL).

Conditions favoring the formation of monomeric Pt(III) derivatives in the electrochemical oxidation of trans-[Pt(II){(p-BrC6F4)NCH2CH2NEt2}Cl(py)]

Characterization of the anticancer active compound trans-[Pt^II{(p-BrC6F4)NCH2CH2NEt2}Cl(py)] is described along with identification of electrochemical conditions that favor formation of a monomeric one-electron-oxidized Pt^III derivative. The square-planar organoamidoplatinum(II) compound was synthesized through a carbon dioxide elimination reaction. Structural characterization by using single-crystal X-Ray diffraction reveals a trans configuration with respect to donor atoms of like charges. As Pt^III intermediates have been implicated in the reactions of platinum anticancer agents, electrochemical conditions favoring the formation of one-electron-oxidized species were sought. Transient cyclic voltammetry at fast scan rates or steady-state rotating disc and microelectrode techniques in a range of molecular solvents and an ionic liquid confirm the existence of a well-defined, chemically and electrochemically reversible one-electron oxidation process that, under suitable conditions, generates a Pt^III complex, which is proposed to be monomeric [Pt^III{(p-BrC6F4)NCH2CH2NEt2}Cl(py)]⁺. Electron paramagnetic resonance spectra obtained from highly non-coordinating dichloromethane/([Bu4N][B(C6F5)4]) solutions, frozen to liquid nitrogen temperature immediately after bulk electrolysis in a glove box, support the Pt^III assignment rather than formation of a Pt^II cation radical. However, the voltammetric behavior is highly dependent on the timescale of the experiments, temperature, concentration of trans-[Pt^II{(p-BrC6F4)NCH2CH2NEt2}- Cl(py)], and the solvent/electrolyte. In the low-polarity solvent CH2Cl2 containing the very weakly coordinating electrolyte [Bu4N][B(C6F5)4], a well-defined reversible one-electron oxidation process is observed on relatively long timescales, which is consistent with the stabilization of the cationic platinum(III) complex in non-coordinating media. Bulk electrolysis of low concentrations of [Pt{(p-BrC6F4)NCH2CH2NEt2}Cl(py)] favors the formation of monomeric [Pt^III{(p-BrC6F4)NCH2CH2NEt2}Cl(py)]⁺. Simulations allow the reversible potential of the Pt^II/Pt^III process and the diffusion coefficient of [Pt^III{(p-BrC6F4)- NCH2CH2NEt2}Cl(py)]⁺ to be calculated. Reversible electrochemical behavior, giving rise to monomeric platinum(III) derivatives, is rare in the field of platinum chemistry.

Enhancing thermal stability and mechanical properties of lyotropic liquid crystals through incorporation of a polymerizable surfactant.

We present a facile method to prepare thermally stable and mechanically robust crosslinked lyotropic liquid crystals (LLCs) through incorporation of a polymerizable amphiphile into a binary LLC system comprising commercially available surfactant Brij 97 and water. Thermal stability and mechanical properties of the polymerized LLCs were significantly enhanced after polymerization of the incorporated polymerizable surfactant. The effect of incorporating a polymerizable amphiphile on the phase behavior of the LLC system was studied in detail. In situ photo-rheology was used to monitor the change in the mechanical properties of the LLCs, namely the storage modulus, loss modulus, and viscosity, upon polymerization. The retention of the LLC nanostructures was evaluated by small angle X-ray scattering (SAXS). The ability to control the thermal stability and mechanical strength of LLCs simply by adding a polymerizable amphiphile, without tedious organic synthesis or harsh polymerization conditions, could prove highly advantageous in the preparation of robust nanomaterials with well-defined periodic structures.

Self-assembled peptide nanostructures for the fabrication of cell scaffolds

The fabrication of artificial scaffolds that effectively mimic the host environment of the cell have exciting potential for the treatment of many diseases in regenerative medicine. In particular, appropriately designed scaffolds have the capacity to support, replace, and mediate the transplantation of therapeutic cells in order to regenerate damaged or diseased tissues. To achieve these goals for regeneration, the engineering of an environment structurally similar to the native extracellular matrix (ECM) is necessary in order to closely match the chemical and physical conditions found within the extracellular niche. Recently, self-assembled peptide (SAP) hydrogels have shown great potential for such biological applications due to their inherent biocompatibility, propensity to form higher order structures, rich chemical functionality and ease of synthesis. Importantly, it is possible to control the organization and properties of the target materials as the chemical structure is determined by amino acid sequence. Here, the development of SAP hydrogels as functional cell scaffolds and useful tools in tissue engineering is reviewed.