Photochemical stability of poly(vinyl pyrrolidone) in the presence of collagen

The photochemical stability of poly(vinyl pyrrolidone) (PVP) in the presence of 1%, 3% and 5% of collagen has been studied by UV-vis spectroscopy, Fourier transform infrared spectroscopy (FTIR), thermogravimetry analysis (TG) and derivative thermogravimetry (DTG). Surface properties have been studied by contact angle measurements. PVP samples and samples containing 1%, 3% and 5% of collagen were irradiated with UV light of wavelength λ = 254 nm in air for up to 24 h. The amount of gel created during UV irradiation was estimated.PVP in the presence of 1%, 3% and 5% of collagen is less stable both thermally and photochemically. Collagen enhances photochemical processes leading to crosslinking of PVP. The contact angle measurements and values of surface free energy showed that the wettability of PVP films was changed by the addition of collagen and by UV irradiation. The increase of polarity of samples indicates an efficient photooxidation on the surface upon UV irradiation.     

Thermal and mechanical properties of UV irradiated collagen/chitosan thin films

The thermal and mechanical properties of collagen/chitosan blends before and after UV irradiation have been investigated using thermal analysis and mechanical (Instron) techniques. Comparisons were made with the thermal and mechanical properties of both collagen and chitosan films. Air-dried collagen, chitosan and collagen/chitosan films were exposed to UV irradiation (wavelength 254 nm) for different time intervals. Thermal properties of collagen/chitosan blends depend on the composition of the blend and are not significantly altered by UV irradiation.Mechanical properties such as ultimate tensile strength and ultimate percentage of elongation were much better for collagen films than for collagen/chitosan films. The results have shown that the mechanical properties of the blends were greatly affected by the duration of UV irradiation. Ultimate tensile strength and ultimate percentage elongation decreased after UV irradiation of the blend. Increasing UV irradiation leads to an increase in Young's modulus of the collagen/chitosan blend.     

Effects of UV irradiation on the wettability of chitosan films containing dansyl derivatives

The morphological and wetting properties of chitosan films containing dansyl derivatives have been investigated. By means of dynamic contact angle measurements, we study the modification of surface properties of chitosan-based films due to UV irradiation. The results were analyzed in the light of the molecular-kinetic theory which describes the wetting phenomena in terms of the statistical dynamics for the displacement of liquid molecules in a solid substrate. Our results show that the immobilization of dansyl groups in the chitosan backbone leads to a pronounced enhancement of the UV sensitivity of polymeric films.     

Studies on the photo-oxidative degradation of LDPE films in the presence of oxidised polyethylene

This paper reports the results of photo-oxidative degradation studies of LDPE in the presence of varying amounts of oxidised polyethylene (OPE), which was prepared by heating LDPE films containing 0.1% cobalt stearate in oxygen atmosphere at 100 °C. OPE, with a CI of 12 was used as an additive for LDPE. Varying amounts of OPE (0.5-5%) were blended with polyethylene in an extruder and films of 70 μm thickness were prepared by film blowing process. The physico-chemical properties of the films were evaluated and these were found to be proportional to the amount of OPE. The films thus obtained were subjected to UV-B exposure at 30 °C for extended time periods. The chemical and physical changes induced by UV exposure were followed by monitoring the changes in mechanical properties (tensile strength and elongation at break), carbonyl index (CI), morphology, molecular weight, MFI and DSC crystallinity. Incorporation of OPE was found to be effective in initiating the photo-degradation of LDPE in relatively short span of time and the degradation was found to be proportional to the amount of OPE in the formulation.     

Photo-induced Janus effect of graphene oxide films

The effect of UV irradiation on the wettability of GO films, as well as the possibility of making a film with different properties of its surface, the Janus film, has been studied. The O/C ratio changes from 0.32 to 0.26 after 6 ​h of UV irradiation. The contact angle of water droplet wetting on an unirradiated surface is θ ​≈ ​35°. The contact angle reaches more than 95° on the irradiated surface, which means that a hydrophobic surface on a film can be obtained. The origin of amphiphilic properties of the GO film are associated with the photochemical reduction of GO.     

Effects of UV irradiation on tribological properties of nano‐TiO2 thin films

One‐layer and two‐layer nano‐TiO₂ thin films were prepared on the surface of common glass by sol–gel processing. Water contact angle, surface morphology, tribological properties of the films before and after ultraviolet (UV) irradiation were investigated using DSA100 drop shape analyzer, scanning probe microscopy (SPM), SEM and universal micro‐materials tester (second generation) (UMT‐2MT) friction and wear tester, respectively. The stored films markedly resumed their hydrophilicity after UV irradiation. But UV irradiation worsened tribological properties of the films. After the film was irradiated by UV, the friction coefficient between the film and GCr15 steel ball increased about 10–50% and its wear life shortened about 20–90%. Abrasive wear, brittle break and adherence wear are the failure mechanisms of nano‐TiO₂ thin films. It was believed that UV irradiation increased surface energy of the film and then aggravated adherence wear of the film at initial stage of friction process leading to severe brittle fracture and abrasive wear. Copyright © 2009 John Wiley & Sons, Ltd.     

The influence of UV-radiation on hyaluronic acid and its blends with addition of collagen and chitosan

In this paper, the results regarding the influence of UV-irradiation with 254?nm wavelength on the surface and mechanical properties of hyaluronic acid, hyaluronic acid/collagen and hyaluronic acid/collagen/chitosan mixtures are presented. For this study, thin films were prepared by solvent evaporation from solution of HA and mixtures made from HA/Coll and HA/Coll with 30% addition of chitosan. The surface properties of films were investigated by AFM and using contact angle measurements, allowing the calculation of surface free energy and its components. Mechanical properties of films made of biopolymeric blends before and after UV-irradiation have been investigated by mechanical testing machine.     

Surface properties of chitosan composites with poly(<Emphasis Type="Italic">N</Emphasis>-vinylpyrrolidone) and montmorillonite

Surface properties of composites containing chitosan (Ch) with poly(N-vinylpyrrolidone) (PVP) and montmorillonite (MMT) additives were investigated by contact angle measurements, thermogravimetric analysis (TGA), atomic force microscopy (AFM) and tensile tests. Composites were obtained by drop casting suspensions of montmorillonite (1 wt % relative to chitosan) and polymer (1 wt %) in 0.1 mol/dm³ acetic acid. Contact angle measurements for diiodomethane (D) and glycerol (G) on the surfaces of the chitosan films, PVP and their composite films were made; surface free energies were also calculated. It was found that the PVP/MMT or Ch/PVP/MMT blend surface is enriched with a high surface energy component, i.e., polyvinylpyrrolidone. The roughness of chitosan composites increases after the addition of montmorillonite; this may indicate an increase in the heterogeneity of this composition in comparison to other compositions. The TGA thermograms and mass loss percentages at different decomposition temperatures showed that the thermal stability of the binary composite slightly increases upon the addition of polyvinylpyrrolidone. The mechanical properties such as tensile strength and Young modulus depend on the composition and varied non-uniformly.     

Photochemical modification of polymer surface by the pendant photobase generator containing oxime‐urethane groups and its application to an image‐recording material

Copolymers containing oxime‐urethane groups were prepared by the copolymerization of methyl methacrylate and benzophenoneoximinocarbonylaminoethyl methacrylate (BCM), and their photochemical properties were examined from the UV and IR absorption spectral changes. The decomposed fraction of oxime‐urethane groups in the copolymer increased with irradiation time, but it decreased with the content of BCM units in the copolymer. Changes of the surface properties of the copolymer film on irradiation were studied by measurements of the contact angle and dyeing with an acid dye. The surface of the copolymer film changed to become more hydrophilic upon irradiation with 254 nm of UV light. After the irradiated copolymer films were treated with HCl or methanol, changes of the contact angle of water on irradiation were compared. The copolymer film was dyed by acid dyes after treatment of the irradiated film with HCl. The degree of dyeing increased with irradiation time and BCM units in the copolymer, but it was unaffected by the film thickness. Various colors were developed on the irradiated area depending on the acid dye as the developer. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1200–1207, 2002     

Investigation of degradation mechanisms in mechanical properties of polyimide films exposed to a low earth orbit environment

The degradation of the mechanical properties of polyimide films was evaluated by means of tensile tests after exposure to a low earth orbit (LEO) environment. Polyimide films irradiated with atomic oxygen (AO), ultraviolet (UV) light, and electron beam (EB) rays using ground simulation facilities were also evaluated similarly and compared. In these experiments tensile stress (7.0 MPa or less) was applied to the samples in order to assess its effects on mechanical properties. The mechanical properties of the flight samples decreased concomitantly with increased exposure duration. The fracture surfaces exhibited characteristic radiated patterns initiating from the exposed surfaces which showed a rough texture. In the AO-irradiated samples the mechanical properties degraded and the surface texture developed as the AO fluence increased; similar fracture surfaces appeared in the flight samples. In contrast, UV and EB irradiation had little impact on mechanical properties. Based on these results, the eroded surfaces by AO irradiation served as the starting points of the rupture, resulting in degradation of mechanical properties of polyimide films exposed to a LEO environment. The tensile stress states induced no difference in evaluations.     

Effect of cobalt carboxylates on the photo-oxidative degradation of low-density polyethylene. Part-I

The effect of three cobalt carboxylates of increasing chain length, namely cobalt laurate, cobalt palmitate and cobalt stearate on the photo-oxidative degradation of low-density polyethylene (LDPE) films has been investigated. LDPE films containing cobalt carboxylates were irradiated with UV-B light at 30 °C for extended time periods. FTIR spectroscopy, mechanical testing, morphological studies, molecular weight, density and MFI measurements were performed to monitor the degradation behaviour. The results of these studies were analysed to explain the structural and chemical modifications taking place in the polyethylene matrix due to UV-B exposure. FTIR studies indicate that the degradation is dominated by formation of carbonyl and vinyl species. The studies on mechanical properties reveal that samples containing cobalt carboxylates, become mechanically fragile after UV exposure for 400 h, while neat LDPE exhibits insignificant changes during this period. The degradation was found to increase proportionally with increasing chain length and follows the order CoSt₃ > CoPal₃ > CoLau₃. Migration studies were performed on food simulant systems to investigate the applicability of these films for food packaging.     

UV-degradation effect on optical and surface properties of polystyrene-TiO<Subscript>2</Subscript> nanocomposite film

Thin films of polystyrene and polystyrene-TiO₂ nanocomposite were prepared by spin coating from a polystyrene solution in which TiO₂ nanoparticles were dispersed by mechanical mixing. Thin films of polystyrene (PS) and polystyrene-TiO₂ nanocomposite were exposed to UV irradiation for varied time intervals. The effect of UV radiation on the optical properties, crystallinity, surface energy and degradation of PS-TiO₂ nano-composite has been studied. X-Ray diffraction analysis (XRD), UV-Vis and FTIR spectroscopy, Atomic Force Microscopy (AFM) and contact angle measurement were used to study the induced changes of the properties of the irradiated PS-TiO₂ nanocomposite. Optical band gaps and hydrophilicity in UV-irradiated samples were altered by destruction processes. The optical band gap values were found to reduce from 4.54 eV in pure PS to 4.45 eV for PS-TiO₂ nanocomposite prior to irradiation. This value is further reduced to 3.46 after UV irradiation for 45 h.     

Influence of nanodispersed boehmite on polypropylene photooxidation

Nanocomposites containing pure or organically modified nanoboehmites of different sizes were prepared by melt compounding with polypropylene. The samples were UV light irradiated in artificial accelerated conditions representative of solar irradiation (λ > 300 nm) at 60 °C in air. The chemical modifications resulting from photooxidation were followed by IR and UV-visible spectroscopies. The presence of pristine nanoboehmites was shown to change the rate of oxidation of polypropylene by reducing the oxidation induction period due to the presence of residual processing antioxidant. The differences of the oxidation induction periods between the nanocomposites and the pristine polymer disappear after solvent extraction of the antioxidant. The inefficiency of traditional antioxidant in retarding the photooxidation of polypropylene containing nanodispersed boehmite is proved. Antioxidant migration to the boehmite surface induced by the preferential interaction with the polar filler is proposed as an explanation. The oxidative behaviour of the organically modified boehmites was shown to depend on the type of organic substituent. p-Toluenesulfonate reduces the adsorption of antioxidants while the presence of a long-chain alkyl benzensulfonate increased the oxidation rate by generation of radical initiators.     

Nanostructured ultraviolet resistant polymer coatings

Nanoparticle-embedded acrylic coatings that can absorb copious amounts of UV radiation yet scatter little were developed to protect base fabrics from sun-induced degradation. Zinc oxide and titanium dioxide nanoparticles with diameters ranging from 15 to 70 nm were used. Nanoparticles (5 wt%) were dispersed in acrylic emulsions. Nanoparticle-embedded acrylic films of 10 μm and 20 μm thick were prepared and bonded to Kevlar fabric. Mechanical tests as well as infrared, visible and UV spectroscopy were used to characterize nanoparticle-embedded acrylic emulsions and coated Kevlar fabric.The changes in mechanical and chemical properties of Kevlar fabric after a day and week of intense UV exposure were assessed using tear and strip tensile testing, UV, visible and infrared spectroscopy, and wide and small angle X-ray analysis. Tear and tensile data, with support from UV results, showed that 20 μm nanoparticle-embedded coatings largely prevented degradation of Kevlar fabric, allowing only 5% of the degradation that occurred in the unprotected fabric after a week of UV exposure.     

Cellulose-based liquid crystalline photoresponsive films with tunable surface wettability

We report on a new type of liquid crystalline cellulosic films with light controllable reversible wettability. The films are prepared from a thermotropic cellulose derivative functionalized with azo-containing groups. These groups exhibit dynamic changes in interfacial properties in response to UV irradiation. The UV irradiation induces trans-to-cis isomerization in the azobenzene moiety, which causes a conformational change in the upper molecular layers of the thin films. These changes originate a hydrophobic to comparatively hydrophilic transformation of the surface. The reversible wettability of the surface results from the cis/trans photo and thermal isomerization. The UV-vis absorption spectra, as well as contact angle measurements with UV irradiation, clearly support the understanding of the phenomenon. This type of surface design enables the amplification of molecular level conformational transitions to macroscopic changes in interface properties using the means of isomerism. This opens new opportunities in surface engineering using eco-friendly cellulose manipulation.     

Swift heavy ion induced modification in dielectric and microhardness properties of polymer composites

Polymer composites with different concentrations of organometallics (ferric oxalate) dispersed PMMA were prepared. PMMA was synthesized by solution polymerization technique. These films were irradiated with 120 MeV Ni¹⁰⁺ ions in the fluence range 10¹¹-5 × 10¹² ions/cm². The radiation induced modifications in dielectric properties, microhardness, structural changes and surface morphology of polymer composite films have been investigated at different concentrations of filler and ion-fluences. It was observed that electrical conductivity and hardness of the films increase with the concentration of the filler and also with the fluence. The dielectric constant (?) obeys the Universal law given by ?αfⁿ⁻¹. The dielectric constant/loss is observed to change significantly due to irradiation. This suggests that ion beam irradiation promotes the metal to polymer bonding and convert polymeric structure into hydrogen depleted carbon network. This makes the composites more conductive and harder. Surface morphology of the films has been studied using atomic force microscopy (AFM) and scanning electron microscopy (SEM). The average surface roughness is observed to increase after irradiation as revealed by AFM studies. The SEM images show the blisters type of phenomenon on the surface due to ion beam irradiation.     

Significant improvements in mechanical property and water stability of chitosan by carbon nanotubes

In this work, high storage modulus and high water stability of chitosan was prepared by incorporating chitosan-grafted carbon nanotubes (CNTs-g-CS). This dramatically improved mechanical property and water stability of chitosan would broaden its biochemical and electrochemical applications. The methodology adopted here by incorporating the CNTs-g-CS allowed a high amount of CNTs incorporation in chitosan without phase separations and enabled the preparations of a durable chitosan/CNTs nanocomposite-modified electrode for biosensor uses. The CNTs-g-CS was synthesized by grafting chitosan onto the carboxylated CNTs in acetic acid-added aqueous solution at 98 °C for 24 h. Thermal gravimetric analysis showed that the content of the chitosan grafts on the CNTs was about 25 wt% of the synthesized CNTs-g-CS. As compared with the ungrafted CNTs, the CNTs-g-CS exhibited a significantly improved dispersion in the chitosan matrix, as examined by optical microscopy and scanning electron microscopy, resulting in significantly improved storage modulus and water stability of the chitosan nanocomposites as revealed by dynamic mechanical analysis and water treatments data, respectively. The storage modulus was significantly up by 134% from 6.4 GPa for the pure chitosan to 15 GPa for the chitosan nanocomposite containing 40 wt% CNTs-g-CS. The water stability of the chitosan nanocomposite films was significantly up from less than 12 h for the chitosan containing various amounts of ungrafted CNTs to at least 48 h for the chitosan containing 20, 30, and 40 wt% CNTs-g-CS.     

Photolabile carboxylic acid protected terpolymers for surface patterning. Part 2: Photocleavage and film patterning

The surface properties of films made of p-methoxyphenacyl derivative terpolymers, associated with photocleavage by UV irradiation, and their optical patterning are investigated. The deprotection reaction has been monitored by UV and FTIR spectroscopy, contact angle measurements, and X-ray photoelectron spectroscopy, revealing the photoremoval of the protecting p-methoxyphenacyl group in high yields under mild conditions. Parallel and serial patterning of the films has been performed by selective irradiation through optical masks and by laser irradiation via fiber tips of a scanning near-field optical microscope, respectively. By irradiation of photolabile protected functional groups, free carboxylic groups become exposed to the surface with which fluorescent dyes and proteins can be associated specifically.     

Studies of photochemical transformations in polystyrene and styrene-maleic anhydride copolymer

Thin films of polystyrene (PS) and styrene-maleic anhydride copolymer (St-MAn) were exposed to monochromatic UV radiation (254 nm) for varied time intervals. The course of photochemical transformations was monitored by absorption spectroscopy (FT-IR, UV-vis) and thermogravimetry, which were also applied for the estimation of the thermal stability of samples studied. The changes of surface properties were monitored by contact angle measurements.Changes in chemical structure were found in irradiated films (inside and at the surface). The efficiency of photooxidative degradation in St-MAn copolymer was slightly lower than that in PS homopolymer but photo-crosslinking and chromophore formation were enhanced. An increase of hydrophilicity and oxidation degree in UV-irradiated samples was accompanied by destruction processes. The thermal stability of St-MAn was lower in comparison to polystyrene alone.The mechanism of photochemical reactions in the copolymer is proposed.     

Durable antifog films from layer-by-layer molecularly blended hydrophilic polysaccharides

Mechanically durable, long-lasting antifog coatings based on polysaccharides were developed using a layer-by-layer (LBL) assembly process. The unique properties of these coatings are a result of a molecular-level blending of the polysaccharides, with multilayers containing chitosan and carboxymethyl cellulose providing the best overall properties. The antifog properties resulted from a strong interaction between the polar and H-bonding elements of the assembled polymers and water molecules and the concomitant formation of thin films of water. Environmental scanning electron microscopy (ESEM) studies confirmed that fogging coatings are decorated with light scattering, micrometer-sized droplets of water whereas antifogging coatings remain droplet free. To improve the mechanical durability of the multilayer films on substrates, the surface was modified via self-assembly of epoxy-functionalized silane molecules. Cross-linking chemistry was then applied to improve the mechanical robustness of the LBL films on various surfaces. These films were characterized using several techniques: optical profilometery (PL), spectroscopic ellipsometry (EL), contact angle goniometry (CA), and atomic force microscopy (AFM). The antifog properties of the films were evaluated by several tests under different environmental conditions. This work demonstrates that the unique water-adsorbing properties of polysaccharides can be exploited to create permanent antifog properties, which may be useful for various applications.