Cell attachment and proliferation on poly(carbonate urethanes) with various degrees of nanophase separation

In this work, we synthesized six 4,4'-diphenylmethane diisocyanate (MDI)-based poly(carbonate urethanes) (PCU) by using the macrodiol poly(1,6-hexyl, 1,2-ethyl carbonate) diol (MW = 2,017) in different molar ratios to MDI. The bulk and surface properties of cast PCU films were analyzed. The glass transition temperatures measured by dynamic mechanical analysis (DMA) and surface images obtained from atomic force microscopy (AFM) indicated that these PCU had various degrees of nanophase separation that changed with the time and film casting temperatures. The degree of nanophase separation correlated very well with endothelial cell attachment and proliferation on PCU.     

Photochemical functionalization of hydrogen-terminated diamond surfaces: a structural and mechanistic study

Hydrogen-terminated diamond surfaces can be covalently modified with molecules bearing a terminal vinyl (C=C) group via a photochemical process using sub-band-gap light at 254 nm. We have investigated the photochemical modification of hydrogen-terminated surfaces of nanocrystalline and single-crystal diamond (111) to help understand the structure of the films and the underlying mechanism of photochemical functionalization. A comparison of the rates of photochemical modification of single-crystal diamond and nanocrystalline diamond films shows no significant difference in reactivity, demonstrating that the modification process is not controlled by grain boundaries or other structures unique to polycrystalline films. We find that both single-crystal and polycrystalline hydrogen-terminated diamond samples exhibit negative electron affinity and are functionalized at comparable rates, while oxidized surfaces with positive electron affinity undergo no detectable reaction. Gas chromatography-mass spectrometry (GC-MS) analysis shows the formation of new chemical products in the liquid phase that are formed only when the alkenes are illuminated in direct contact with H-terminated diamond, while control experiments with other surfaces and in the dark show no reaction. Our results show that the functionalization is a surface-mediated photochemical reaction and suggest that modification is initiated by the photoejection of electrons from the diamond surfaces into the liquid phase.     

Calorimetry of nanoparticles,surfaces, interfaces,thin films,and multilayers

Calorimetry gives insight into the stability of nanophase materials. Using TiO₂ as an example, the interplay of energetics of polymorphism, surface energy, and surface hydration is discussed. Oxide melt solution calorimetry, water adsorption calorimetry, and adiabatic heat capacity studies together show the following. The metastability of bulk polymorphs increases in the order rutile, brookite, anatase, while the surface energy increases in the opposite order. This leads to crossovers in phase stability at the nanoscale, which appears to be a general phenomenon. Hydration plays a major role in stabilizing nanoparticles and the first layers of water are tightly bound. There is little excess heat capacity and no significant excess vibrational entropy in nanophase rutile or anatase. Further applications of calorimetry to thin films, interfaces, multilayers, and sub-milligram samples are presented.     

Physical insights into the photoactivated Ullmann coupling process producing highly conjugated oligothiophene films on a copper substrate

This paper describes the details of surface reactions producing >100-nm-thick conjugated polymer films. When 2,5-diiodothiophene films deposited on copper are irradiated with UV at room temperature in Ar environments, oligothiophene films are synthesized. The average conjugation length of the produced film varies from approximately 7 to 3-4 as the film thickness increases from approximately 100 to approximately 500 nm. The X-ray photoelectron spectroscopy analysis of the produced films reveals evidence for the formation of organo-copper intermediate species at the copper-monomer film interface and their diffusion from the copper surface into the monomer film during the photochemical process. A one-dimensional diffusion-reaction model is presented to explain the formation, diffusion, and reaction of organo-copper intermediates in the multilayer film during the photochemical reaction. The model simulation results qualitatively explain the decrease of the Ullmann coupling contribution in the photochemical reaction with the film thickness.     

Photoinjection of hydrogen and the nature of a giant shift of the fundamental absorption edge in highly disordered V2O5 films

Production of atomic photochemical hydrogen under the action of light and its subsequent injection into transition metal oxides has yielded numerous interesting results. Here we report on the mechanism of the photo-induced hydrogen transfer between adsorbed organic molecules and the surface of highly disordered V(2)O(5) films. We have managed to carry out the photoinjection of hydrogen into the V(2)O(5) films at very low temperatures, which is very important both for investigations of the reaction mechanism and for the optical properties of the V(2)O(5) films. The photochemical reaction exhibits all features of proton-coupled electron transfer which is a basic mechanism for bioenergetics conversion. Second, the new possibility to carry out experiments at very low temperatures has yielded a new approach in investigations of the nature of color centers and of the giant "blue" shift of the fundamental absorption edge in the V(2)O(5) films both arising due to injection of hydrogen atoms.     

Uptake and UV-photooxidation of gas-phase polyaromatic hydrocarbons on the surface of atmospheric water films. 2. Effects of dissolved surfactants on naphthalene photooxidation

The adsorption and photochemical transformations of gas-phase naphthalene were studied in a flow-tube reactor with a view to understanding the photochemical reactions occurring in thin water films such as those of aerosols and fogs. Suwannee River fulvic acid (SRFA) was chosen as a surrogate for the surface active humic-like substances present in atmospheric water films. Experiments were performed on both 450 and 22 mum water films over a wide concentration range of SRFA (0-1000 mg.L-1). The effect of singlet oxygen on the reaction rate in the presence and absence of SRFA was ascertained. Naphthalene molecules can be bound to SRFA through hydrophobic interactions and be distributed in both the water and the SRFA regions. The rate constants for the photochemical reactions of naphthalene were fitted to a model that described the effect of SRFA in these two regions. The kinetic study on the 22 mum film revealed a greater surface reaction enhancement than for the 450 mum film at low SRFA concentrations. However, there was no surface reaction enhancement at high SRFA concentrations. To compare with SRFA, the effect of a conventional surfactant, sodium dodecyl sulfate, on the uptake and photochemical transformations of naphthalene was also studied.     

Photochemical synthesis of colloidal metals

New photochemical method for preparation of colloidal metal particles (Cu, Ag, Au) as a films on the quartz surface and colloidal dispersion in different matrixes has been devised. Possibilities to control the properties of photogenerated colloidal metal particles are discussed.     

Dye-polyoxometalate composite films: self-assembly, thermal and photochemical properties

A series of dye-polyoxometalate composite films were prepared by alternately depositing cationic dye molecules and anionic polyoxometalates such as Keggin-type [BW(12)O(40)](5-) and the sandwich complex [Co(4)(H(2)O)(2)(PW(9)O(34))(2)](10-)via layer-by-layer (LbL) self-assembly method. These cationic dye molecules (MB, AA, TH, BB3, BCB and NB) are heterocyclic planar and rigid phenothiazine and phenoxazine dye molecules with different substituting groups in the side chains. The self-assembly of the films was studied by UV-vis and IR spectra. The results show that the substituting groups of dye molecules such as NH(2) and CH(2)CH(3) have influence on the self-assembly properties. The continuous and regular growth of the films was also dependent upon hydrogen bonding (NHO) formed between the amino groups of dye molecules and oxygen atoms of POMs as well as electrostatic interactions. The investigation of thermal and photochemical treatments of the composite films is also presented. The thermal stability experiments indicate that the composite films of TH with two NH(2) substitute groups and NB with more pi-conjugated system exhibit high thermal stability, whereas the sunlight irradiation results indicate that the composite films of TH have good photochemical stability.     

Crosslinking of oligomers bearing carbamoyloxyimino groups with their photochemical and thermal reactions

Carbamoyloxyimino (COI) groups are precursors of photochemically base‐generating groups as well as those of thermally isocyanate‐generating groups. In this study, photochemical and thermal reactions of COI groups in oligomers were investigated by spectral analyses and solubility changes. Oligomers bearing three types of COI groups were prepared. COI groups in all oligomer films were photolyzed on irradiation with 254 nm of light and were deblocked to form isocyanato groups on heating. From the IR spectral analyses, the formation of urea linkage was confirmed by the decrease in isocyanato groups and peak generation because of urea groups on postexposure bake (PEB) treatment. For all oligomer films, PEB was effective for the enhancement of insolubilization of the films in tetrahydrofuran. Heating followed by irradiation was also effective for the insolubilization. These results indicated that photochemical and thermal treatments of COI groups afforded highly sensitive crosslinking systems because of photochemically generated basic groups and thermally generated isocyanato groups. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2612–2620, 2004     

Temperature-assisted photochemical construction of CdS-based ordered porous films with photocatalytic activities on solution surfaces

Taking a colloidal monolayer floating on the surface of a precursor solution as template, free-standing CdS/Cd composites and pure CdS (CdS-based) ordered porous films had been prepared by a temperature-assisted photochemical strategy. After irradiation with UV-light and heat treatment, the films formed hemi-spherical pores due to the preferable deposition of CdS and Cd onto the PS spheres during the photochemical and interfacial reactions. When the temperature increased from 15 to 60°C, the air/water interface gradually changed into a vapor/water interface on the surface of the solution, resulting in variations of the final compositions. The optical properties of the films were hence changed. Because of the free-standing characteristic, the ordered porous films were first transferred on surface of polluted solutions as photocatalysts, which was a new mode in application of photocatalysts. The photocatalytic activities of films showed regular variations with the compositions in photodegradation of Rhodamine B. This method provides a simple route for tuning the properties of porous films through control of its composition and a flexible application of films on any surface.     

Vibrational and surface-enhanced vibrational spectra of 6-nitrochrysene

The infrared and Raman spectra of solids and thin solid films of 6-nitrochrysene, its electronic spectra, and resonance Raman scattering (RRS) obtained with UV-laser excitation at 325 nm are reported. The vibrational assignment is supported by ab initio computations at the B3LYP/6-311G(d, p) level of theory. The molecular organization in nanometric films evaporated onto smooth metal surfaces of silver and copper was probed using reflection-absorption infrared spectroscopy (RAIRS). The results of the surface-enhanced Raman scattering (SERS) and surface-enhanced infrared absorption (SEIRA) obtained from nanometric films evaporated onto silver island films are also discussed. It was found that the molecule efficiently interacts with silver island film surfaces, and that the interaction leads to extensive photochemical reaction at the metal surface under laser illumination.     

Photolysis of polymeric organosilicon systems. III. Synthesis and photochemical behavior of polysiloxanes containing phenyldisilanyl units

The synthesis and photochemical behavior of three types of polysiloxanes containing phenyldisilanyl units as chromophore have been reported. Irradiation of thin liquid films of the polymer (2) prepared from copolymerization of octamethylcyclotetrasiloxane and 1,3,5-triphenyl-1,3,5-tris(trimethylsilyl)cyclostrisiloxane (1) with a 500-W Xe-Hg lamp afforded transparent solid films which are insoluble in common organic solvents. Similar irradiation of thin liquid films of polysiloxane (8) containing both phenyldisilanyl units and vinyl groups resulted in formation of crosslinked solid films. When thick films of the polymers 2 and 8 were irradiated with a Xe-Hg lamp, crosslinking occurred only on the surface of the films, but inside remained as liquid. Irradiation of the films prepared from the polysiloxane involving the phenyldisilanyl units and butenyl groups, however, gave crosslinked solid films, whatever thickness of the films. The mechanism of photochemically induced crosslinking of the copolymers is discussed on the basis of the results obtained from the photolysis of 1,1-bis(trimethylsiloxy)-1-phenyl(trimethyl)disilane as a model compound.     

Synthesis, fluorescence and photoisomerization studies of azobenzene-functionalized poly(alkyl aryl ether) dendrimers

A series of azobenzene-functionalized poly(alkyl aryl ether) dendrimers have been synthesized and their photochemical and photophysical properties in solution and as thin films have been investigated. Although the photochemical behavior of the azodendrimers in solution indicated that the azobenzene units behave independently, very similar to the constituent monomer azobenzene unit, the properties of thin solid films of the dendrimers were distinctly different. The azodendrimers, AzoG1, AzoG2, and AzoG3 were observed to form stable supercooled glasses, which showed long-wavelength absorption and red emission characteristics of J-aggregates of the azobenzene chromophores. Reversible photoinduced isomerization of the azodendrimers in the glassy state is described.     

Triplet‐sensitized irradiation of a main‐chain liquid crystalline poly(aryl cinnamate) in three different phases

Visible light irradiation of thin films of a main‐chain liquid crystalline poly(aryl cinnamate) using ketocoumarins as triplet sensitizers leads to photochemical crosslinking and UV‐vis and FTIR spectroscopic changes associated with saturation of the cinnamate double bond, most likely by 2 + 2 photocycloaddition. The triplet sensitizers are themselves photolabile and are lost by photochemical reactions during the sensitization process. A new ketocoumarin sensitizer with decyloxy substituents and a reduced tendency to phase separate from the polymer is reported. A simple calculation of the sensitization stoichiometry shows that a single molecule of this ketocoumarin sensitizes the destruction of approximately 90 cinnamate chromophores in the “as cast” films below T_g and about 300 chromophores in the more‐ordered glassy nematic films and in “as cast” films of poly(vinyl cinnamate). Triplet sensitization of fluid nematic films leads, upon initial irradiation, to UV‐vis hyperchromism that is attributed to disruption of chromophore aggregation and, possibly, to disruption of the nematic mesophase as photoproducts begin to form. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 134–144, 2001     

Photochemical processes in graphene oxide films

Experimentally revealed features of thermal and photochemical deoxidation of graphene oxide (GO) in films are reported. A difference in mechanism between the photoreduction and thermal reduction of GO has been shown. The mechanism of photochemical deoxidation of graphene oxide has been rationalized using the concepts of molecular photochemistry. A new model of photoelimination of molecular oxygen from epoxy groups on graphene nanosheet has been proposed. The photoprocesses lead to growing of π-domains of graphene.     

Photocatalytic lithography based on thin films of amorphous hydrated titanium dioxide

The mechanism of photoactivation of amorphous hydrated titanium dioxide thin films containing palladium ions toward the reaction of electroless deposition of nickel was studied. It was shown that the photocatalytic reduction of palladium ions during UV irradiation results in the formation of intermediate Pd(I) states that subsequently disproportionate, yielding a Pd nanophase. The palladium nanoparticle-catalyzed electroless deposition of nickel on exposed areas of the titanium dioxide photolayer makes it possible to fabricate metal patterns having a 5-μm resolution, with the fast and irreversible capture of photoelectrons at the latent image formation step preventing the image from blurring, including the process on conducting substrates.     

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.     

Photochemical stability of collagen/poly(ethylene oxide) blends

The photochemical stability of the blends of collagen and poly(ethylene oxide) PEO has been studied by Fourier transform infrared spectroscopy (FTIR), UV–vis spectroscopy and viscosimetry. Surface properties before and after UV irradiation were observed using an optical microscope.Collagen and PEO were immiscible in diluted solution and only small interactions between the two components in the solid state were observed. New materials based on the blending of collagen and PEO that we obtained have a different photochemical stability than those of single components. In general, collagen/PEO blends are less stable under UV irradiation than pure collagen. The influence of PEO on the photochemical stability of collagen depends on the concentration of this polymer in the blend. Microscopic photographs show that the surface characteristics of thin films of collagen/PEO blends are not drastically altered after UV irradiation.     

Polymer-initiated photogeneration of silver nanoparticles in SPEEK/PVA films: direct metal photopatterning

Cross-linking of sulfonated poly(ether-ether)ketone-poly(vinyl alcohol) (SPEEK-PVA) materials yields flexible polymer films, possessing high light-sensitivity and ion-exchange capabilities. Adsorbed Ag+ ions are photoreduced in the film under illumination (lambda = 350 nm), leading to metal nanoparticle formation in places where the film has been exposed to the light. Nanoparticles form via reduction of Ag+ by the polymeric alcohol radicals, generated in the system as a result of photochemical H-abstraction from PVA molecules by the excited carbonyl triplet state of SPEEK. Use of the films for direct metal photopatterning is demonstrated.     

界面光化学反应研究进展

本文介绍了在气液界面上和LB 膜中的光化学反应特点及不同的类型, 从界面光聚合、界面光致变色、界面光致电子转移、光电转化等几个方面对最近几年来在界面光化学领域内的重要成果及最新进展进行了综述, 并对这一领域的发展和应用前景进行了展望。