Influence of surfactant structures in luminescence enhancement dynamics during nucleation and growth of aqueous ZnS nanoparticles and their photoactivation due to illumination with UV/visible light

Nanostructured semiconductor architectures have attractive optical properties mainly including bright photoluminescence (PL) resulting from the radiative recombination of charge carriers on surface states. Various approaches have been employed for the modification of surface states of these nanostructures to design new nanomaterials with enhanced PL primarily in aqueous medium to enable their applications in biological samples. Here, we report the varying efficiencies of three commercial surfactants viz. cetyltrimethylammonium bromide (CTAB), cetyltrimethylammonium chloride (CTAC) and cetylpyridinium chloride (CPyC) on the dynamics of PL emission enhancement during initial growth and Ostwald ripening of ZnS nanoparticles (NPs). The counterion has been estimated to behave differently to govern the PL enhancement. The exceptionally high tendency of CPyC in PL enhancement has been assigned to participation of π-electrons of pyridinium ring. The impact of UV-light in photoactivation of surfactant stabilized ZnS NPs has been utilized in exploring significance of surfactants in improving the surface emitting states in water soluble semiconductor NPs.     

Isotactic poly(acrylonitrile) via ultraviolet irradiation of acrylonitrile-urea canal complex

Isotactic poly(acrylonitrile) (PAN) has been prepared by means of a conventional ultraviolet (UV) irradiation apparatus without γ-ray sources; an acrylonitrile-urea canal complex was directly formed at the surface of the UV (Hg) emission tube at low temperatures (～ ?78°C). When the complex was UV-irradiated at this temperature, a stereoregular polymer was formed in the canal. The ¹³C-NMR analyses indicate that (1) these PAN are rich in isotactic configuration, (2) the extent of the isotactic triad is in the range of 56?71%, and (3) the penultimate unit effect, 4 (mm) (rr)/(mr)², is linearly correlated with the ultimate unit effect, (mm)/(rr). From the plots of log{4(mm)(rr)/(mr)²} vs log{(mm)/(rr)}, the anomaly in the polymerization of AN is discussed. The molecular characteristics of the UV canal PAN such as molecular weight, etc., were briefly noted. © 1995 John Wiley & Sons, Inc.     

Preparation of new photosensitive TiO2 gel films using chemical additives including nitrogen and their patterning

TiO₂ gel films were prepared from titanium tetra-n-butoxide chemically modified with benzoylacetoanilide including nitrogen by the sol-gel method. The obtained gel film showed an absorption band, characteristic of the chelate ring, at 325 nm. The absorption band disappeared almost completely with UV-irradiation (2.7 J cm⁻²) using a high pressure mercury lamp. This indicates that the gel film exhibits photosensitivity. The decomposition rate of the chelate ring was the fastest in the photosensitive TiO₂ gel films which we have examined. Using the photosensitivity, fine patterns (about 5 μm) could be fabricated by UV-irradiation through a mask and leaching.     

Surface properties of UV-irradiated poly(vinyl alcohol) films containing small amount of collagen

The surface properties of poly(vinyl alcohol) (PVA) films in the presence of 1%, 3% and 5% of collagen before and after UV-irradiation have been studied by atomic force microscopy (AFM) and by contact angle measurements. PVA films have been obtained by solvent evaporation from water solution of PVA and PVA containing small amount of collagen. After drying, the samples were irradiated with UV light wavelength λ = 254 nm in air. Surface properties before and after UV-irradiation were observed using AFM. Contact angles of two liquids: diiodomethane (D) and glycerol (G) on polymeric films were measured at constant temperature using goniometer.The results have shown that the contact angle and the surface free energy for PVA films were altered by UV-irradiation. These alterations indicate photooxidation and an increase of polarity of the surface. The comparison of surface properties of PVA films and PVA containing collagen points out that collagen is more sensitive to photooxidation than PVA and PVA/collagen blends. PVA films containing collagen easier undergo photooxidation process with formation of new polar groups than pure PVA films.     

Property changes in polyoxymethylene (POM) resulting from processing, ageing and recycling

The degradation processes initiated by thermo-mechanical and thermo-oxidative loading as well as exposure to ultraviolet irradiation weathering were examined in commercially available semi-crystalline polyoxymethylene (POM), using predominantly thermo-analytical methods.With reference to different injection moulding conditions and moulding geometries (such as loudspeaker grilles and safety-belt components) it is demonstrated that POM-copolymer chain is not affected, even under higher shear stresses and complicated moulding geometries, if an appropriate additive is used.Thermogravimetric Analysis (TGA) was used to observe stabiliser consumption and further degradation, whereas investigations of melt-flow index and molar mass show effects correlated to late-term changes of the molar mass distribution. Mass-spectrometry investigations performed in parallel to the thermogravimetric analysis identified formaldehyde and carbon dioxide as the main degradation products.Weathering by ultraviolet irradiation results in damage similar to the thermo-oxidative impact.Generally, the copolymers are less sensitive to thermo-mechanical and thermo-oxidative degradations than the homopolymers due to the chain modification. Furthermore, reprocessing results in a decrease of the elongation at break and thermo-oxidative induced degradation proceeds faster for the additional UV-stabilised materials.