Vacuum-ultraviolet photochemically initiated modification of polystyrene surfaces: morphological changes and mechanistic investigations

Vacuum-ultraviolet (VUV) irradiation (kexc: 172 ± 12 nm) of polystyrene films in the presence of oxygen produced not only oxidatively functionalized surfaces, but generated also morphological changes. Whereas OH- and C=O-functionalized surfaces might be used for e.g. secondary functionalization, enhanced aggregation or printing, processes leading to morphological changes open new possibilities of microstructurization. Series of experiments made under different experimental conditions brought evidence of two different reaction pathways: introduction of OH- and C=O-groups at the polystyrene pathways is mainly due to the reaction of reactive oxygen species (hydroxyl radicals, atomic oxygen, ozone) produced in the gas phase between the VUV-radiation source and the substrate. However, oxidative fragmentation leading to morphological changes, oxidation products of low molecular weight and eventually to mineralization of the organic substrate is initiated by electronic excitation of the polymer leading to C–C-bond homolysis and to a complex oxidation manifold after trapping of the C-centred radicals by molecular oxygen. The pathways of oxidative functionalization or fragmentation could be differentiated by FTIR-ATR analysis of irradiated polystyrene surfaces before and after washing with acetonitrile and microscopic fluorescence analysis of the surfaces secondarily functionalized with the N,N,N-tridodecyl-triaza-triangulenium (TATA) cation. Ozonization of the polystyrene leads to oxidative functionalization of the polymer surface but cannot initiate the fragmentation of the polymer backbone. Oxidative fragmentation is initiated by electronic excitation of the polymer (contact-mode AFM analysis), and evidence of the generation of intermediate C-centred radicals is given e.g. by experiments in the absence of oxygen leading to cross-linking (solubility effects, optical microscopy, friction-mode AFM) and disproportionation (fluorescence).

Linear Low Density Polyethylene-Biodegradability Using Bacteria from Marine Benthic Environment and Photodegradability Using Ultraviolet Light

Various compositions of linear low density polyethylene(LLDPE) containing bio-filler(either starch or dextrin)of various particle sizes were prepared.The mechanical,thermal,FTIR,morphological(SEM),water absorption and melt flow(MFI) studies were carried out.Biodegradability of the compositions were determined using a shake culture flask containing amylase producing bacteria(vibrios),which were isolated from marine benthic environment and by soil burial test. The effect of low quantities of metal oxides and metal stearate as pro-oxidants in LLDPE and in the LLDPE-biofiller compositions was established by exposing the samples to ultraviolet light.The combination of bio-filler and a pro-oxidant improves the degradation of linear low density polyethylene.The maleation of LLDPE improves the compatibility of the c blend components and thepro-oxidants enhance the photodegradability of the compatibilised blends.The responsibility studies on the partially biodegradable LLDPE containing bio-fillers and pro-oxidants suggest that the blends could be repeatedly reprocessed without deterioration in mechanical properties.

Modelling of Ultraviolet and Vissible Emissions in Comets

Comets are the spectacular objects in the night sky since the dawn of mankind. Due to their giant apparitions and enigmatic behavior, followed by coincidental calamities, they were termed as notorious and called as `bad omens'. With a systematic study of these objects modern scienti c community understood that these objects are part of our solar system. Comets are believed to be remnant bodies of at the end of evolution of solar system and possess the material of solar nebula. Hence, these are considered as most pristine objects which can provide the information about the conditions of solar nebula. These are small bodies of our solar system, with a typical size of about a kilometer to a few tens of kilometers orbiting the Sun in highly elliptical orbits. The solid body of a comet is nucleus which is a conglomerated mixture of water ice, dust and some other gases. When the cometary nucleus advances towards the Sun in its orbit the ices sublimates and produces the gaseous envelope around the nucleus which is called coma. The gravity of cometary nucleus is very small and hence can not in uence the motion of gases in the cometary coma. Though the cometary nucleus is a few kilometers in size they can produce a transient, extensive, and expanding atmosphere with size several orders of magnitude larger in space. By ejecting gas and dust into space comets became the most active members of the solar system. The solar radiation and the solar wind in uences the motion of dust and ions and produces dust and ion tails, respectively. Comets have been observed in di erent spectral regions from rocket, ground and space borne optical instruments. The observed emission intensities are used to quantify the chemical abundances of di erent species in the comets. The study of various physical and chemical processes that govern these emissions is essential before estimating chemical abundances in the coma. Cameron band emission of CO molecule has been used to derive CO2 abundance in the comets based on the assumption that photodissociation of CO2 mainly produces these emissions. Similarly, the atomic oxygen visible emissions have been used to probe H2O in the cometary coma. The observed green ([OI] 5577 A) to red-doublet emission ([OI] 6300 and 6364 A) ratio has been used to con rm H2O as the parent species of these emissions. In this thesis a model is developed to understand the photochemistry of these emissions and applied to several comets. The model calculated emission intensities are compared with the observations done by space borne instruments like International Ultraviolet Explorer (IUE) and Hubble Space Telescope (HST) and also by various ground based telescopes.

Cobalt (II), Nickel (II), and Copper (II) Complexes of Polystyrene-Supported Schiff Bases

Two novel polystyrene-supported Schiff bases, PSOPD and PSHQAD, were synthesized. A polymerbound aldehyde was condensed with o-phenylenediamine to prepare the Schiff base PSOPD, and a polymer-bound amine was condensed with 3-hydroxyquinoxaline-2-carboxaldehyde to prepare the Schiff base PSHQAD. This article addresses the study of cobalt (II), nickel (II), and copper (II) complexes of these polymer-bound Schiff bases. All the complexes were characterized, and the probable geometry was suggested using elemental analysis, diffuse reflectance ultraviolet, Fourier transform infrared spectroscopy, thermal studies, surface area studies, and magnetic measurements.

Effect of annealing on the spectral and nonlinear optical characteristics of thin films of nano-ZnO

The annealing effect on the spectral and nonlinear optical NLO characteristics of ZnO thin films deposited on quartz substrates by sol-gel process is investigated. As the annealing temperature increases from 300–1050 °C, there is a decrease in the band gap, which indicates the changes of the interface of ZnO. ZnO is reported to show two emission bands, an ultraviolet UV emission band and another in the green region. The intensity of the UV peak remains the same while the intensity of the visible peak increases with increase in annealing temperature. The role of oxygen in ZnO thin films during the annealing process is important to the change in optical properties. The mechanism of the luminescence suggests that UV luminescence of ZnO thin films is related to the transition from conduction band edge to valence band, and green luminescence is caused by the transition from deep donor level to valence band due to oxygen vacancies. The NLO response of these samples is studied using nanosecond laser pulses at off-resonance wavelengths. The nonlinear absorption coefficient increases from 2.9 ×10−6 to 1.0 ×10−4 m/W when the annealing temperature is increased from 300 to 1050 °C, mainly due to the enhancement of interfacial state and exciton oscillator strength. The third order optical susceptibility x(3) increases with increase in annealing temperature (T) within the range of our investigations. In the weak confinement regime, T2.4 dependence of x(3) is obtained for ZnO thin films. The role of annealing temperature on the optical limiting response is also studied.

Spectral studies of naphthalocyanine (Nc) and rare earth phthalocyanine (RePc) molecules in an inorganic glassy borate matrix

Optical absorption and emission spectral studies of free and metal naphthalocyanine doped borate glass matrix are reported for the first time. Absorption spectra recorded in the UV- VIS-NIR region show the characteristic absorption bands, namely, the B-band and Q-band of the naphthalocyanine (Nc) molecule. Some of the important spectral parameters, namely, the optical absorption coefficient (α), molar extinction coefficient (ε) and absorption cross section (σa) of the principal absorption transitions are determined. Optical band gap (Eg) of the materials evaluated from the functional dependence of absorption coefficient on photon energy lies in the range 1.6 eV≤Eg≤2.1 eV. All fluorescence spectra except that of EuNc consist of an intense band in the 765 nm region corresponding to the excitation of Q-band. In EuNc the maximum fluorescence intensity band is observed at 824 nm. The intensity of the principal fluorescence band is maximum in ZnNc, whereas it is minimum in H2Nc. Radiative parameters of the principal fluorescence transitions corresponding to the Q-band excitation are also reported for the naphthalocyanine and phthalocyanine based matrices.

Optical absorption studies of free (H2Pc) and rare earth (RePc) phthalocyanine doped borate glasses

Optical absorption studies of free base and rare earth incorporated phthalocyanine doped borate glass matrix are reported for the first lime. The absorption spectra recorded in the UV- VIS region show two well defined absorption bands of phthalocyanine (Pc) molecule, namely the Soret band (B) and the Q band. The Q band always shows its characteristic splitting in all the doped glass matrices and the intensities of these components are found to vary from one Pc to another. Some of the important optical parameters, namely optical absorption coefficient (a), molar extinction coefficient (ε), absorption cross section (σa), oscillator strength (f), electric dipole strength (q2), absorption half bandwidth (Δλ) of the principal optical transitions have also been evaluated. Moreover, the spectral dependence of refractive index (n) and thereby the optical dielectric constant (ε) on wavelength yielded values of carrier concentration to effective mass ratio (N/m*) of the phthalocyanine molecule in the present glassy systems. Optical band gap (Eg) and width of the band tail (Et) are computed and their variations among the prepared samples are also discussed.

Spectral and nonlinear optical characteristics of nanocomposites of ZnO–Ag

In this Letter we present the spectral and nonlinear optical properties of ZnO–Ag nanocomposites prepared by colloidal chemical synthesis. Obvious enhancement of ultraviolet (UV) emission of the samples is observed and the strongest UV emission is over three times than that of pure ZnO. These nanocomposites show self-defocusing nonlinearity and good nonlinear absorption behaviour which increases with increasing Ag volume fraction. The observed nonlinear absorption is explained through two photon absorption followed by free carrier absorption. ZnO–Ag is a potential nanocomposite material for the UV light emission and for the development of nonlinear optical devices with a relatively small limiting threshold.

Linear and nonlinear optical characteristics of ZnO-SiO2 nanocomposites.

We present the spectral and nonlinear optical properties of ZnO-SiO2 nanocomposites prepared by colloidal chemical synthesis. Obvious enhancement of ultraviolet (UV) emission of the samples is observed, and the strongest UV emission of a typical ZnO-SiO2 nanocomposite is over three times stronger than that of pure ZnO. The nonlinearity of the silica colloid is low, and its nonlinear response can be improved by making composites with ZnO. These nanocomposites show self-defocusing nonlinearity and good nonlinear absorption behavior. The observed nonlinear absorption is explained through two photon absorption followed by weak free carrier absorption and nonlinear scattering. The nonlinear refractive index and the nonlinear absorption increase with increasing ZnO volume fraction and can be attributed to the enhancement of exciton oscillator strength. ZnO-SiO2 is a potential nanocomposite material for the UV light emission and for the development of nonlinear optical devices with a relatively small limiting threshold.

Enhanced luminescence and nonlinear optical properties of nanocomposites of ZnO–Cu

In this article, we present the spectral and nonlinear optical properties of ZnOCu nanocomposites prepared by colloidal chemical synthesis. The emission consisted of two peaks. The 385-nm ultraviolet (UV) peak is attributed to ZnO and the 550-nm visible peak is attributed to Cu nanocolloids. Obvious enhancement of UV and visible emission of the samples is observed and the strongest UV emission of a typical ZnOCu nanocomposite is over three times stronger than that of pure ZnO. Cu acts as a sensitizer and the enhancement of UV emission are caused by excitons formed at the interface between Cu and ZnO. As the volume fraction of Cu increases beyond a particular value, the intensity of the UV peak decreases while the intensity of the visible peak increases, and the strongest visible emission of a typical ZnOCu nanocomposite is over ten times stronger than that of pure Cu. The emission mechanism is discussed. Nonlinear optical response of these samples is studied using nanosecond laser pulses from a tunable laser in the wavelength range of 450650 nm, which includes the surface plasmon absorption (SPA) band. The nonlinear response is wavelength dependent and switching from reverse saturable absorption (RSA) to saturable absorption (SA) has been observed for Cu nanocolloids as the excitation wavelength changes from the low absorption window region to higher absorption regime near the SPA band. However, ZnO colloids and ZnOCu nanocomposites exhibit induced absorption at this wavelength. Such a changeover in the sign of the nonlinearity of ZnOCu nanocomposites, with respect to Cu nanocolloids, is related to the interplay of plasmon band bleach and optical limiting mechanisms. The SA again changes back to RSA when we move over to the infrared region. The ZnOCu nanocomposites show self-defocusing nonlinearity and good nonlinear absorption behavior. The nonlinear refractive index and the nonlinear absorption increases with increasing Cu volume fraction at 532 nm. The observed nonlinear absorption is explained through two-photon absorption followed by weak free-carrier absorption and interband absorption mechanisms. This study is important in identifying the spectral range and composition over which the nonlinear material acts as a RSA-based optical limiter. ZnOCu is a potential nanocomposite material for the light emission and for the development of nonlinear optical devices with a relatively small limiting threshold.

Effect of Ce3+ Ion on the X-Ray Induced Fluorescence Emission from CaS

The effect of Ce3+ on the fluorescence emission from CaS:Ce3+ phosphor is studied using X-ray excitation. Apart from the emission in the visible region, the phosphor also shows fluorescence emission in the ultraviolet region. Variation in wavelengths and intensities of these emissions due to change in dopant concentration is also analysed.

Size dependent fluorescence spectroscopy of nanocolloids of ZnO

In this article we present size dependent spectroscopic observations of nanocolloids of ZnO. ZnO is reported to show two emission bands, an ultraviolet (UV) emission band and another in the green region. Apart from the known band gap 380 nm and impurity 530 nm emissions, we have found some peculiar features in the fluorescence spectra that are consistent with the nanoparticle size distribution. Results show that additional emissions at 420 and 490 nm are developed with particle size. The origin of the visible band emission is discussed. The mechanism of the luminescence suggests that UV luminescence of ZnO colloid is related to the transition from conduction band edge to valence band, and visible luminescence is caused by the transition from deep donor level to valence band due to oxygen vacancies and by the transition from conduction band to deep acceptor level due to impurities and defect states. A correlation analysis between the particle size and spectroscopic observations is also discussed.

Studies on the isolation and characterization of flavones and triterpenoids from a few plants

In the present scenario, there is an increasing demand for natural products in food industry, pharmaceuticals, cosmetics and agricultural sectors. In this context phytochemical study to identify newer chemicals has got great relevance. Phytochemical studies have become more reliable and encouraging with the development of modern analytical techniques.In the present work the leaves of Piper colubrinum (Piperaceae), aerial parts of Mussaenda fiondosa (Rubiaceae) and Humboldtia vahliana (Leguminosae) and the pericarp of fruits of Artocarpus heterophyllus (Moraceae) were investigated for their secondary metabolites. The major compounds isolated belong to the groups of flavonoids and triterpenoids.Naturally occurring flavonoids have been used widely in chemotaxonomic studies of plants. Flavones and flavonols constitute a group of biosynthetically related natural products. No universal function has been established for flavones and flavonols in plants. However, many functions in individual plants have been demonstrated. These include protection of plants from ultraviolet light, insects and pests; pollinator attractants; antioxidants; plant hormone controllers; enzyme inhibitors and allelopathic agents. Flavonoids are attracting the attention of medical scientists in recent years because of their anticarcinogenic, antiallergic and antiinflammatory properties. The recent discovery that flavonoids are involved in the process of nitrogen fixation in plants also opens the way for agricultural application of these constituents.Triterpenoids are another class of compounds that are ubiquitous in plants. Some triterpenoids present in the latex and resins of plants are believed to be involved in chemical defence against pathogens and herbivores. Triterpenoids possess various biological properties including anti-inflammatory, antifeedant, pesticidal, fungitoxic and antimicrobial activities. Triterpenoids with cytotoxic activity and inhibitory effect on seed germination are also known.

Synthesis and reactions of flavazoles

The study deals with the production of l-phenylflavazoles with chloro, amino, hydroxy, chloromethyl, carboxamido, trichloromethyl, N-pyrrolidyl and N-pyrrolidylmethyl groups substituted at position 3. The interconversions of 3-amino, 3-hydroxy and 3-chlorol- phenylflavazoles were also investigated. Further, an unusual phenylation reaction was found to take place if stored or air-oxidised phenylhydrazine was used as the condensing agent for the formation of flavazoles from quinoxaline-2-carboxaldehyde phenylhydrazones. By this phenylation reaction 1,3-diphenyl, l-p-tolyl-3-phenyl, l-p-chlorophenyl-3-phenyl, l-p-bromophenyl- 3-phenyl and l-phenyl-3-p-tolylflavazoles were prepared. In addition to establishing the structure of the phenylation products, the reaction was shown to take place by a free radical mechanism involving phenyl radicals formed from oxidised phenylhydrazine. Also the oxidation, reduction and bromination reactions of l-phenylflavazole were investigated. The product obtained when a mixture of l-phenylflavazole and sodium borohydride in isopropanol was heated under reflux was shown to be 2-anilinoquinoxaline-3-carboxamide which when refluxed with concentrated hydrochloric acid gave the known 2-anilinoquinoxaline. New procedures were worked out for the oxidative cyclisation reactions of quinoxaline-2carboxaldehyde phenylhydrazones to l-phenylflavazoles in excellent yields using azobenzene as a dehydrogenating agent. These cyclisations were also shown to take place, though in low Yield, if the quinoxaline2- carboxaldehyde phenylhydrazones were heated above their melting points in an atmosphere containing oxygen.

Synthesis And Reactions Of Pyrazoldouinoxalines

The present work reports the synthesis of 2-ary1—3—oxo-3—pyrazolino[3,4-b]quinoxalines for the first time. These compounds have been prepared by the reaction of ethyl 2-chloroquinoxaline—3—carboxylate with different phenylhydrazines. 2-Aryl—3-oxo—3—pyrazolino[3,4—b]quinoxalines are generally light yellow in either neutral or acid solutions but changed the colour to deep violet or green in basic media. The change in colour appears to be sharp and therefore these compounds may be used as acid base indicators. Their UV absorption maxima under acidic and basic media are also very different. However, the actual conditions under which these compounds may be used as indicators have not been worked out. The synthesis and reactions of a new heterocyclic system, lH—l,5—benzodiazepino[2,3—b]quinoxaline is also reported here. This novel nitrogen heterocycke was prepared by the condensation of ethyl 2-chloroquinoxaline-3—carboxylate with o-phenylene diamine and subsequent manipulationsa to give the parent compound. Several derivatives which are expected tx> have valuable biological properties have also beenlreported. The structures of all new compounds have been established by elemental analysis and also by analysing their spectral data smch as ultraviolet, infrared, nuclear magnetic resonance and mass spectrometry. Compounds obtained from this work will be submitted for screening their biological properties.