Superspreaders versus "cousin" non-superspreaders: disjoining pressure in gravitational film drainage.

Gravitational drainage of vertical films supported on a wire frame of two superspreaders SILWET L-77 and BREAK-THRU S 278 and their respective "cousin" non-superspreaders SILWET L-7607 and BREAK-THRU S 233 revealed drastic differences. The superspreader films showed complicated dynamic "turbulent"-like interferometric patterns in distinction from the ordered color bands of the "cousin" non-superspreaders, which resembled those of the ordinary surfactants. Nevertheless, the superspreader films stabilized themselves at the thickness about 35 nm and revealed an order of magnitude longer lifetime before bursting compared to that of the "cousin" non-superspreaders. Notably, the superspreaders revealed drastic differences from the non-superspreaders in aqueous solutions with no contact with any solid hydrophobic surface. The self-stabilization of the superspreader films is attributed to significant disjoining pressure probably related to long superspreader bilayers hanging from the free surfaces. The scaling law for the disjoining pressure was found as p(disj)(h) ~ h(-m) (with m ≈ 9-11) for the sufficiently concentrated superspreader solutions, and as p(disj)(h) ~ h(-s) (with s ≈ 6) for more dilute solutions (in both cases, concentrations were above the critical micelle concentration). The non-superspreaders do not possess any significant disjoining pressure even in the films with thicknesses in the 35-100 nm range. The results show that gravitational drainage of vertical films is a useful simple tool for measuring disjoining pressure.

Two-stage desorption-controlled release of fluorescent dye and vitamin from solution-blown and electrospun nanofiber mats containing porogens.

In the present work, a systematic study of the release kinetics of two embedded model drugs (one completely water soluble and one partially water soluble) from hydrophilic and hydrophobic nanofiber mats was conducted. Fluorescent dye Rhodamine B was used as a model hydrophilic drug in controlled release experiments after it was encapsulated in solution-blown soy-protein-containing hydrophilic nanofibers as well as in electrospun hydrophobic poly(ethylene terephthalate) (PET)-containing nanofibers. Vitamin B2 (riboflavin), a partially water-soluble model drug, was also encapsulated in hydrophobic PET-containing nanofiber mats, and its release kinetics was studied. The nanofiber mats were submerged in water, and the amount of drug released was tracked by fluorescence intensity. It was found that the release process saturates well below 100% release of the embedded compound. This is attributed to the fact that desorption is the limiting process in the release from biopolymer-containing nanofibers similar to the previously reported release from petroleum-derived polymer nanofibers. Release from monolithic as well as core-shell nanofibers was studied in the present work. Moreover, to facilitate the release and ultimately to approach 100% release, we also incorporated porogens, for example, poly(ethylene glycol), PEG. It was also found that the release rate can be controlled by the porogen choice in nanofibers. The effect of nanocracks created by leaching porogens on drug release was studied experimentally and evaluated theoretically, and the physical parameters characterizing the release process were established. The objective of the present work is a detailed experimental and theoretical investigation of controlled drug release from nanofibers facilitated by the presence of porogens. The novelty of this work is in forming nanofibers containing biodegradable and biocompatible soy proteins to facilitate controlled drug release as well as in measuring detailed quantitative characteristics of the desorption processes responsible for release of the model substance (fluorescent dye) and the vitamin (riboflavin) in the presence of porogens.

Gravitational drainage of foam films.

Gravitational drainage from thick plane vertical soap films and hemispherical bubbles is studied experimentally and theoretically. The experiments involve microinterferometry kindred to the one used in the experiments in the Scheludko cell. The following surfactants were used in the experiments: cationic dodecyltrimethylammonium bromide (DTAB), anionic sodium dodecyl sulfate (SDS), anionic Pantene shampoo which primarily contains sodium lauryl sulfate, nonionic tetraethylene glycol monooctyl ether (C8E4), and nonionic Pluronic (P-123) surfactants at different concentrations. The theoretical results explain the drainage mechanism and are used to develop a new method of measurement of the surface elasticity and to test it on the above-mentioned surfactants.

Preparation and properties of biodegradable films from Sterculia urens short fiber/cellulose green composites.

The development of commercially viable "green products", based on natural resources for the matrices and reinforcements, in a wide range of applications, is on the rise. The present paper focuses on Sterculia urens short fiber reinforced pure cellulose matrix composite films. The morphologies of the untreated and 5% NaOH (alkali) treated S. urens fibers were observed by SEM. The effect of 5% NaOH treated S. urens fiber (5, 10, 15 and 20% loading) on the mechanical properties and thermal stability of the composites films is discussed. This paper presents the developments made in the area of biodegradable S. urens short fiber/cellulose (SUSF/cellulose) composite films, buried in the soil and later investigated by the (POM), before and after biodegradation has taken place. SUSF/cellulose composite films have great potential in food packaging and for medical applications.

Solution blowing of soy protein fibers.

Solution blowing of soy protein (sp)/polymer blends was used to form monolithic nanofibers. The monolithic fibers were blown from blends of soy protein and nylon-6 in formic acid. The sp/nylon-6 ratio achieved in dry monolithic nanofibers formed using solution blowing of the blend was equal to 40/60. In addition, solution blowing of core-shell nanofibers was realized with soy protein being in the core and the supporting polymer in the shell. The shells were formed from nylon-6. The sp/nylon-6 ratio achieved in dry core-shell fibers was 32/68. The nanofibers developed in the present work contain significant amounts of soy protein and hold great potential in various applications of nonwovens.

Thorny devil nanotextured fibers: the way to cooling rates on the order of 1 kW/cm2.

In the present work high-heat-flux surfaces, which should serve at temperatures of up to 200 °C, were covered by electrospun polymer nanofiber mats with thicknesses of about 30 µm. Then, four different metals were electroplated on separate polymer mats, namely, copper, silver, nickel, and gold. As a result, copper-plated nanofiber mats took on an appearance resembling that of a small Australian thorny devil lizard (i.e., they became very rough on the nanoscale) and acquired a high thermal diffusivity. Silver-plated nanofiber mats also became very rough because of the dendritelike and cactuslike nanostructures on their surfaces. However, nickel-plated nanofibers were only partially rough and their mats incorporated large domains of smooth nickel-plated fibers, and gold-plated nanofibers were practically smooth. Drop impacts on the hot surfaces coated with copper-plated and silver-plated nanofibers revealed tremendously high values of heat removal rates of up to 0.6 kW/cm(2). Such high values of heat flux are more than an order of magnitude higher that the currently available ones and probably can be increased even more using the same technique. They open some intriguing perspectives for the cooling of high-heat-flux microelectronics and optoelectronics and for further miniaturization of such devices, especially for such applications as UAVs and UGVs.

The study on the time dependency and the stability of cobalt sulphide nanoparticles under an electron beam.

We report on the synthesis and characterization of cobalt sulphide (CoS(1.097)) nanoparticles using a cobalt tetramethylthiuram disulphide complex as a single-source precursor. To study the effect of reaction time on the optical and morphological properties of the synthesized nanoparticles, aliquots from the reaction mixture were collected after different intervals of time. The absorption spectra were time dependent, with the 5 min aliquot being the most blue-shifted from bulk and the subsequent samples showing a slight shift towards the bulk. Photoluminescence of the nanoparticles showed a single emission wavelength of 341 nm, however, the peak intensity of nanoparticles decreased with reaction time. The morphology of the synthesized nanoparticles was investigated using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and high-resolution TEM (HR-TEM). Results from the SEM images showed the formation of spherical CoS(1.097) nanoparticles and the size of the observed nanoparticles increase with increasing reaction time. However, the TEM results showed a change in the morphology of the particles from spherical to wire-like. The change in morphology was thought to be induced by the high voltage electron beam and this was supported by the HR-TEM and optical results.

Zinc oxide epitaxial thin film deposited over carbon on various substrate by pulsed laser deposition technique.

Zinc Oxide (ZnO) is a promising candidate material for optical and electronic devices due to its direct wide band gap (3.37 eV) and high exciton binding energy (60 meV). For applications in various fields such as light emitting diode (LED) and laser diodes, growth of p-type ZnO is a prerequisite. ZnO is an intrinsically n-type semiconductor. In this paper we report on the synthesis of Zinc Oxide-Carbon (ZnO:C) thin films using pulsed laser deposition technique (PLD). The deposition parameters were optimized to obtain high quality epitaxial ZnO films over a carbon layer. The structural and optical properties were studied by glazing index X-ray diffraction (GIXRD), photoluminescence (PL), optical absorption (OA), and Raman spectroscopy. Rutherford backscattering spectroscopy (RBS), scanning electron microscopy with energy dispersive spectroscopy (SEMEDS) and atomic force microscopy (AFM) were employed to determine the composition and surface morphology of these thin films. The GIXRD pattern of the synthesized films exhibited hexagonal wurtzite crystal structure with a preferred (002) orientation. PL spectroscopy results showed that the emission intensity was maximum at -380 nm at a deposition temperature of 573 K. In the Raman spectra, the E2 phonon frequency around at 438 cm(-1) is a characteristic peak of the wurtzite lattice and could be seen in all samples. Furthermore, the optical direct band gap of ZnO films was found to be in the visible region. The growth of the epitaxial layer is discussed in the light of carbon atoms from the buffer layer. Our work demonstrates that the carbon is a novel dopant in the group of doped ZnO semiconductor materials. The introduction of carbon impurities enhanced the visible emission of red-green luminescence. It is concluded that the carbon impurities promote the zinc related native defect in ZnO.

Resins with "nano-raisins".

Thermosensitive hydrogels are materials which globally shrink/swell in water when the surrounding temperature crosses the lower critical solution temperature (LCST). We demonstrate here a novel class of cross-linked polymeric materials, which do not shrink/swell in water globally, but nevertheless reveal a hydrogel-like, stimuli-responsive behavior. In particular, they demonstate a positive thermosensitive release of the embedded fluorescent dye significantly modulated when temperature crosses the LCST. Using staining with copper, transmission electron microscopy and energy dispersive X-ray analysis, we show that this effect is associated with nanogel "raisins" dispersed in such materials (e.g., polymer nanofibers). Shrinkage of individual nanogel "raisins" at elevated temperatures increases nanoporosity via increased exposure of the existing nanopores to water, or formation of new nanopores/nanocracks in the overstretched polymer matrix in the vicinity of shrinking nanogel "raisins". As a result, the release rate of the embedded dye from the nanofibers increases at elevated temperatures. We suggest that similar functional materials with embedded nanogel "raisins" will find applications in nanofluidics and as drug carriers for controlled drug release.

Enhanced release of liquid from carbon nanotubes due to entrainment by an air layer.

It is shown that bi-layer (liquid/gas) flows through nanochannels (parallel carbon nanotube bundles) can result in a higher flow rate of liquid as compared to the case when the same liquid flows through the same channels subjected to the same pressure drop and occupies the whole bore. This enhancement of liquid flow happens because a much-less-viscous air layer moves so fast that it entrains the liquid layer occupying only a part of the nanochannel bore.

A novel cellulase free alkaliphilic xylanase from alkali tolerant Penicillium citrinum: production, purification and characterization.

AIMS: The enzymatic hydrolysis of xylan has potential economic and environment-friendly applications. Therefore, attention is focused here on the discovery of new extremophilic xylanase in order to meet the requirements of industry. METHODS AND RESULTS: An extracellular xylanase was purified from the culture filtrate of P. citrinum grown on wheat bran bed in solid substrate fermentation. Single step purification was achieved using hydrophobic interaction chromatography. The purified enzyme showed a single band on SDS-PAGE with an apparent molecular weight of c. 25 kDa and pI of 3.6. Stimulation of the activity by beta mercaptoethanol, dithiotheritol (DTT) and cysteine was observed. Moderately thermostable xylanase showed optimum activity at 50 degrees C at pH 8.5. CONCLUSION: Xylanase purified from P. citrinum was alkaliphilic and moderately thermostable in nature. SIGNIFICANCE AND IMPACT OF THE STUDY: The present work reports for the first time the purification and characterization of a novel endoglucanase free alkaliphilic xylanase from the alkali tolerant fungus Penicillium citrinum. The alkaliphilicity and moderate thermostability of this xylanase may have potential implications in paper and pulp industries.