Shear–induced nucleation and annihilation of topological defects due to hydrodynamic instability in nematic liquid crystals is a phenomenon of both scientific interest and practical importance. We use a complete generalized non-linear second order tensor Landau-de Gennes model that takes into account short range order elasticity, long-range elasticity and viscous effects, to simulate the nucleation and annihilation of twist inversion walls in flow-aligning nematic polymers subjected to shear flow. Shearing a homogeneous nematic sample perpendicular to the director results in an linear instability that maybe symmetric at low shear rates, and antisymmetric at higher shear rates. At even higher shear rates the onset of nonlinearities results in the nucleation of a parallel array of twist inversion walls, such that asymmetry prevails. By increasing the shear rate the following director symmetry transition cascade is observed: symmetric → antisymmetric → asymmetric → symmetric. The nucleation of the parallel array of twist inversion walls in the asymmetric mode is due to the degeneracy in reorientation towards the shear plane. The annihilation of twist walls is mediated by twist waves along the velocity gradient direction. Twist walls annihilate by three mechanisms: wall-wall annihilations, wall-wall coalescence, and wall-bounding surface coalescence. The annihilation rate increases with increasing shear rate and at sufficiently high rates the layered structure is replaced by a homogeneously aligned system. The role of short range and long range elasticity on defect nucleation and annihilation is characterized in terms of the Deborah and Ericksen numbers. Close form solutions to approximated equations are used to explain the numerical results of the full Landau-de Gennes equations of nematodynamics.

Ferromagnetic nanocomposites in which magnetic nanoparticles are embedded into a polymeric matrix can replace conventional ferrites in the near future in applications such as: filters, high frequency inductors, chokes, sensors, core-shape and planar transformers, hybrid circuits and transponders. These dense magneto-dielectrics will provide a new approach in the fabrication of soft magnetic materials. In a magnetic/polymeric nanocomposite solid, the resistivity can be drastically increased, leading to significantly reduced eddy-current losses. In addition, the coupling between neighbouring magnetic nanoparticles results in much better soft magnetic properties at high frequencies than those of conventional bulk materials or ferrites. In order to study the influence of dipolar interactions between ferritic nanoparticles, samples of varying ferritic density were prepared. A polymeric binder (pre-swollen in toluene) was added to the nanoparticles, which were then cold-pressed using a standard compaction method. Characterization of the materials was carried out by means of x-ray diffractometry, electron microscopy, magnetometry, and high-frequency complex permeability measurements. Initial results show that tunable static and dynamic magnetic properties of the nanocomposite materials may be achievable.

γ-Aminopropyltriethoxysilane (γ-APS) was grafted on stainless-steel and titanium substrates, and subsequently alginic acid layer was immobilized on them. Their surfaces were characterized with X-ray photoelectron spectroscopy (XPS) and contact angle measurement. Blood compatibility of thus obtained substrates was evaluated in terms of both the number of the adhered platelets and blood clotting factors for plasma contacted with the substrates such as active partial thromboplastin time (PTT), prothrombin time (PT), and amount of fibrinogen (Fib). The steel and titanium substrates with alginic acid layer did not affect blood clotting factors. In vitro platelet adhesion assay indicated that those substrates adhered less number of platelets than non-treated substrates. Hence the alginic acid immobilization leads to blood compatible surfaces.

We have studied the electrical properties of a fluorene-containing copolymer which is currently being developed for state-of-the-art blue polymer LEDs. This copolymer is made up of three functional groups which are nominally the hole-conducting, electron conducting and emissive regions. Using a combination of current/voltage, time-of-flight and dark injection transient versus temperature measurements, the injection and transport properties of the material have been investigated. Hole injection from polystyrene sulphonate doped polyethylenedioxythiophene (PEDOT:PSS) into the polymer is found to be consistent with an ohmic contact. Hole transport within the fluorene copolymer is found to possess a mobility that is two orders of magnitude lower than that for previously studied polymers containing the copolymer constituents. Using the equations for trap-free space-charge limited current, predicted J/V characteristics have been obtained from the mobility values derived using the time-of-flight technique. We discuss both the reduced hole mobility of the copolymer, and the discrepancies between the measured and predicted J/V characteristics, in terms of variations in both the trap and transport site densities and their energetic and spatial distributions.

We studied the poly [2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV)/LiF/Al interface by angle-dependent X-ray photoemission spectroscopy (XPS). The changes in the C1s, O 1s, Al 2p core level spectra, and the evolution of O to C and Li to F atomic ratios at different photoelectron take-off angles were carefully analyzed. A reduced oxygen concentration with a LiF layer at the interface suggests that LiF can help reduce the oxidation of Al. The interface was found rich in Li+ ions, some of which might be attached to MEH-PPV to form “N type” doping. The electron injection layer consists of Li+doped MEH-PPV, LiF, Al oxides, and metallic Al.

Using self-consistent field theory, we attempt to elucidate the links between microscopically determined properties, such as the bridging fraction of chains, and mechanical properties of multiblock copolymer materials. We determine morphological aspects such as period and interfacial width and calculate the bridging fractions, and compare with experimental data.