Antimicrobial Polymeric Composites with Embedded Nanotextured Magnesium Oxide

Nanotextured magnesium oxide (MgO) can exhibit both antibacterial and tissue regeneration activity, which makes it very useful for implant protection. To successfully combine these two properties, MgO needs to be processed within an appropriate carrier system that can keep MgO surface available for interactions with cells, slow down the conversion of MgO to the less active hydroxide and control MgO solubility. Here we present new composites with nanotextured MgO microrods embedded in different biodegradable polymer matrixes: poly-lactide-co-glycolide (PLGA), poly-lactide (PLA) and polycaprolactone (PCL). Relative to their hydrophilicity, polarity and degradability, the matrices were able to affect and control the structural and functional properties of the resulting composites in different manners. We found PLGA matrix the most effective in performing this task. The application of the nanotextured 1D morphology and the appropriate balancing of MgO/PLGA interphase interactions with optimal polymer degradation kinetics resulted in superior bactericidal activity of the composites against either planktonic E. coli or sessile S. epidermidis, S. aureus (multidrug resistant-MRSA) and three clinical strains isolated from implant-associated infections (S. aureus, E. coli and P. aeruginosa), while ensuring controllable release of magnesium ions and showing no harmful effects on red blood cells.

The pulsating nature of bubble boiling of subcooled water flow during cooling of a metal heater

This paper presents the results of an experimental study of the subcooled water flow boiling on the surface of a metal rod 12 mm in diameter. As a result of the rapid heat release that occurs when an electric current is pulsed through a metal heater, the latter reaches certain temperature levels above the saturation temperature of water at the corresponding pressure (p = 0.17 MPa). In a system formed by a cold liquid and a heated solid body, the process of intense heat exchange begins, the cooling rate of the metal in which reaches its maximum when the nucleate boiling is realized. Interest in such scenarios is remaining high and is caused by the need for quantitative prediction of the characteristics of nucleate boiling and the existence boundaries of this boiling mode. As well-known, nucleate boiling is limited from above by the onset of film boiling and from below by the required surface temperature for which a significant number of nucleation centers are activated. The pressure waves arising during film boiling have a significant amplitude, as a result of which special conditions of interphase interactions may occur. The results of the study showed that self-oscillating pressure pulsations may occur which is associated with the nucleate boiling in an annular channel.

Fabrication, characterization and optical properties of transparent PP/Yttria-stabilizied zirconia (YSZ) based nanocomposites

In this study have been prepared optically transparent polymeric nanocomposites based on PP/YSZ by combination of ex-situ and hot pressing methods. The structure of the synthesized nanocomposites was studied by XRD analysis, UV spectroscopy, scanning electron microscopy. The optical and photoluminescent (PL) properties of polymer nanocomposites were investigated. It was found that with an increase in the concentration of YSZ nanoparticles in the PP matrix to 3% of the content of nanoparticles, the PL intensity increases, with a further increase in the nanoparticles content, the PL intensity decreases. This is explained by the fact that with an increase in the concentration of YSZ nanoparticles, their size increases and their specific surface decreases, and this leads to a decrease in the contacting region between the polymer and the nanoparticle. A decrease in the interphase boundary leads to a decrease in interphase interactions, and this in turn leads to a change in the PL intensity. It was also shown that the PL intensity for nanocomposites at all wavelengths increases with increasing annealing temperature to 120°C, and then decreases. Possible reasons for a significant increase in the PL intensity after thermal annealing are the redistribution of charge carriers between levels in the band gap or the recharging of recombination centers and the removal of organic compounds adsorbed on the surface of nanocomposites.

Review on Microbubbles and Microdroplets Flowing through Microfluidic Geometrical Elements

Two-phase flows are found in several industrial systems/applications, including boilers and condensers, which are used in power generation or refrigeration, steam generators, oil/gas extraction wells and refineries, flame stabilizers, safety valves, among many others. The structure of these flows is complex, and it is largely governed by the extent of interphase interactions. In the last two decades, due to a large development of microfabrication technologies, many microstructured devices involving several elements (constrictions, contractions, expansions, obstacles, or T-junctions) have been designed and manufactured. The pursuit for innovation in two-phase flows in these elements require an understanding and control of the behaviour of bubble/droplet flow. The need to systematize the most relevant studies that involve these issues constitutes the motivation for this review. In the present work, literature addressing gas-liquid and liquid-liquid flows, with Newtonian and non-Newtonian fluids, and covering theoretical, experimental, and numerical approaches, is reviewed. Particular focus is given to the deformation, coalescence, and breakup mechanisms when bubbles and droplets pass through the aforementioned microfluidic elements.

BLENDS OF ALIPHATIC POLYAMIDES WITH FUNCTIONALIZED POLYOLEFINS: INTERPHASE INTERACTIONS, FEATURES OF THE RHEOLOGICAL BEHAVIOR OF MELTS, STRUCTURE AND MECHANICAL PROPERTIES

The effect of addition of functionalized polyolefins (fPO) in an amount of 28 wt. % – mixtures of polyethylene and copolymer of ethylene with higher olefin containing 0.43 and 0.77 wt. % grafted monomer having two carboxyl groups in its composition – to aliphatic polyamides PA6 and PA66 on the structural features, the rheological behavior of melts and the mechanical properties of mixed materials was investigated. The materials studied were prepared by reactive mixing of the components in a melt in an extrusion reactor. It is shown that mixtures of PA66/fPO are characterized by more significant changes in the characteristics under analysis compared with those based on PA6 when the concentration of a grafted monomer is varied. An abnormally sharp increase (by more than two decimal orders) of the melt viscosity of a mixture of PA66 with fPO containing 0.77 wt. % of the grafted monomer, compared with the viscosity of initial PA66, is due to the specificity of the interphase interactions in the mixtures.

An Investigation of the Mechanical Properties of Nanocomposites Based on Polyepoxy Isocyanurates and Monodispersed Carbon Nanoparticles

Nanocomposites based on polyepoxy isocyanurate crosslinked systems of different chemical composition were produced in order to investigate the specific effect of technical nanocarbon on each individual polymer network. Monodispersed carbon particles were produced by methane chlorination conducted in a continuous reactor in a non-equilibrium regime with a chlorine deficit. The dependences of the forced elasticity limit, stress relaxation, etc., on the degree of filling were analysed. The possibility of interphase interaction between a specific polyepoxy isocyanurate network and ‘nanofiller’ was investigated. It was shown that a fairly low concentration (1 wt%) of monodispersed carbon particles of 20–25 nm size leads to a 25–30% increase in the elastic modulus and forced elasticity limit; similarly, the relaxation characteristics are also increased. It was established that improvement in a number of such properties is connected with the greater influence of interphase interactions between the polymer and filler on account of the large surface layer area.

Characterization of Dielectric Nanocomposites with Electrostatic Force Microscopy

Nanocomposites physical properties unexplainable by general mixture laws are usually supposed to be related to interphases, highly present at the nanoscale. The intrinsic dielectric constant of the interphase and its volume need to be considered in the prediction of the effective permittivity of nanodielectrics, for example. The electrostatic force microscope (EFM) constitutes a promising technique to probe interphases locally. This work reports theoretical finite-elements simulations and experimental measurements to interpret EFM signals in front of nanocomposites with the aim of detecting and characterizing interphases. According to simulations, we designed and synthesized appropriate samples to verify experimentally the ability of EFM to characterize a nanoshell covering nanoparticles, for different shell thicknesses. This type of samples constitutes a simplified electrostatic model of a nanodielectric. Experiments were conducted using either DC or AC-EFM polarization, with force gradient detection method. A comparison between our numerical model and experimental results was performed in order to validate our predictions for general EFM-interphase interactions.