Photochemical Modification Research Articles

Laser photochemical modification of poly-p-xylylene

The spectral luminescence properties of poly-p-xylylene films irradiated by impulse UV- laser were studied. It was shown that the UV-laser irradiation to leads to the effective formation of new optical emission centers in the polymer chain. The fluorescence band of these centers is found over the visible range.

Adhesion Promotion in Fibers and Textiles Using Photonic Surface Modifications

Obtaining good bonding between two dissimilar materials is critical for several aspects in textile finishing, processing and application, including the durability of common textile finishes and fabric coatings, and the performance of fiber reinforced composites. Both functional properties and long term performance are dependent on the effective adhesion between the fiber on one hand and finishing agent, coating polymer or resin on the other. It is generally accepted that good adhesion is achieved through covalent chemical bonding, acid–base interactions or hydrogen bonding, surface energies that favor complete wetting of the fibers, large specific surface area of fibers, and surface roughness that allows lock and key type mechanical bonding. In practice, various surface treatments have been applied to fibers to alter their surface characteristics and to improve their adhesion properties. For example, chemical modifications such as acid oxidation, corona or plasma pre-treatments have been commonly employed. This paper aims to provide some insight into photon-based processes which, depending on the spectral range of radiation and the characteristics of the radiation sources, can be used to bring about chemical as well as morphological changes to fiber surfaces. We have considered two major applications of surface modification; (1) textiles for improving adhesion to finishes and (2) fiber/resin adhesion enhancement in fiber reinforced composites to improve their mechanical properties. The technical approaches cover photo-chemical surface modification and micro-roughening of fiber surfaces using monochromatic UV lamps and pulsed UV excimer lasers.

Photochemical modification and functionalization of carbon surfaces with fluorine moieties

The photolysis of perfluoroazooctane in the presence of carbon materials, such as diamond powder, films, diamond-like carbon films, nanodiamond films and single-walled carbon nanotubes, led to the chemical modification of their surface by the introduction of perfluorooctyl functional groups, which was confirmed by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, time-of-flight secondary ionization mass spectrometry, Raman spectroscopy and mass spectroscopy measurements. The carbon materials modified with fluorine moieties exhibited a reduced friction coefficient and a reduction of their surface energy, evaluated by the contact angle with water, compared with those of pristine carbon materials.

Origin of Photochemical Modification of the Resistivity of Ag(DMe-DCNQI)2 Studied by X-ray Absorption Fine Structure

The Ag(DMe-DCNQI)2 (DMe-DCNQI = 2,5-dimethyl-N,N′-dicyanoquinonediimine, or DM) charge-transfer salt is a promising material for production by photolithography as it displays a unique photoinduced change in conduction. Photoproducts (β1 and γ) of Ag(DM)2 were investigated using the X-ray absorption fine structure (XAFS) technique in order to understand the origin of their conduction properties. In contrast to the metallic conduction exhibited by a pristine sample (α), β1 is a semiconductor, whereas γ is an insulator, even though the original Ag(DM)2 composition is maintained in both the β1 and the γ forms. A redox mechanism has been postulated to explain the photoinduced change in conduction. However, measurement of the Ag L3-edge XANES (X-ray absorption near-edge structure) did not provide any evidence of electron transfer from the DM radical anion to the Ag cation in the β1 and γ products. Ag K-edge extended X-ray absorption fine structure (EXAFS) data demonstrated that β1 is a mixture of the original pristine α phase and a newly found α′ phase, which has a shorter bond distance between the Ag cations and the N atoms of DM molecules. The conduction electrons remain in the DM column of α and α′, but the domain boundaries between α and α′ present an activation barrier for the conduction electrons to cross these boundaries, which provides a rationale for the semiconductive behavior of β1. The Ag K-edge EXAFS results showed that the γ photoproduct has a different local structure from α, with a shorter distance and smaller coordination number of the Ag−N bond. The DM radical anions in the γ compound form covalent bonds between themselves, resulting in a loss of the columnar structure. The complex local structure around Ag cations explains the insulating behavior of the γ compound.

Photochemical Surface Modification of Silicone Rubber into Photoluminescent Material by 193 nm ArF Excimer Laser Irradiation

A transparent, flexible silicone rubber ([SiO(CH3)2]n) surface was photochemically modified into a photoluminescent material using a 193 nm ArF excimer laser. The photomodified silicone rubber emitted white light under a 325 nm He–Cd laser or a 375 nm light-emitting diode. The chemical bonding of the photomodified silicone rubber was found to be similar to that of a silica-like silicone, as analyzed by Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy. The photoluminescence of the rubber originated from oxygen deficiency centers and peroxy centers of the silica structure in the photomodified silicone rubber. Fine particles 200 nm in diameter were also formed in the photomodified silicone rubber to enhance the intensity of the photoluminescence.

Cobalt Phthalocyanine-Modified Boron-Doped Diamond Electrode for Highly Sensitive Detection of Hydrogen Peroxide

A cobalt phthalocyanine-modified boron-doped diamond (CoPc-BDD) electrode was fabricated for a sensitive detection of hydrogen peroxide. The hydrogen-terminated BDD electrode surface was terminated with pyridine moieties via photochemical modification with 4-vinylpyridine followed by immobilization of CoPc on the surface by immersion in a CoPc solution. X-ray photoelectron spectroscopy studies suggested that the coordination of the surface pyridine and the Co atom in CoPc contributes to surface modification. Electrochemical detection of hydrogen peroxide at the modified electrode was also investigated. Cyclic voltammetry confirmed that the CoPc-BDD electrode exhibited a catalytic activity for the electrochemical oxidation of hydrogen peroxide. Using a flow-injection analysis–electrochemical detection system, we demonstrated that the CoPc-BDD electrode is well suited for the detection of hydrogen peroxide, with a limit of detection of 4.9 nM.

Pulsed-laser-induced photochemical growth of the periodic surface structure on InP

We report the laser-induced surface modification of InP in a HF electrolyte by second harmonic (532 nm) or fourth harmonic (266 nm) wavelengths of a Nd:YAG laser at a constant energy density of 125 mJ cm−2 and by varying the number of laser pulses. Laser-induced periodic surface structures (LIPSS) parallel to laser polarization are fabricated on InP by photochemical surface modification. Atomic force microscopy (AFM) is used to study the surface morphology of the modified InP surface. Photoluminescence (PL), micro-Raman spectroscopy investigations on LIPSS provide clear evidence of the crystalline nature of the fabricated structures. In addition, PL line-shape analysis is used to estimate size and size distribution of nanoscale features in the LIPSS fabricated by UV laser beams.

Photochemical modification of magnetic properties in organic low-dimensional conductors

Magnetic properties of organic charge transfer salts Ag( DX) 2 ( DX=2,5-dihalogeno- N, N′-dicyanoquinonediimine; X=Cl, Br, I) were modified by UV irradiation from paramagnetism to diamagnetism in an irreversible way. The temperature dependence of susceptibility revealed that such change in magnetic behavior could be continuously controlled by the duration of irradiation. The observation with scanning electron microprobe revealed that the original appearance of samples, e.g. black well-defined needle-shaped shiny single crystals, remained after irradiation irrespective of the irradiation conditions and the duration. Thermochemical analysis and X-ray diffraction study demonstrated that the change in the physical properties were due to (partial) decomposition of Ag( DX) 2 to Ag X, which was incorporated in the original Ag( DX) 2 lattices. Because the physical properties of low-dimensional organic conductors are very sensitive to lattice defects, even a small amount of Ag X could effectively modify the electronic properties of Ag( DX) 2 without making the original crystalline appearance collapse.

Photochemical surface modification of PP for abrasion resistance

The potential of a photo-chemical approach to increase the surface hardness of polypropylene (PP) has been studied. Using a 222 nm excimer lamp, fibers and film were irradiated in the presence of multi-functional substances diallylphthalate (DAP), tetraallyloxyethane (TAE), and pentaerithritoltriacylate (PETA) and characterized with regard to the resulting effect on abrasion resistance. AFM-based methods were employed to analyze thermo-mechanical surface properties. Nanoindentation and microthermal analyses of the outermost surface layers of UV treated fibers gave clear indications of an effective cross-linking of reactive substances present during irradiation. One may assume that the reactive media polymerize on top of the surface of the PP substrate and form a thin-layer. The abrasion resistance of the PP fibers was tested by applying stress through a rotating and axially oscillating roller of defined roughness and measuring the mass loss as a function of time. The abrasion resistance was found to be remarkably improved compared to the untreated fiber. Best effects were achieved using PETA as reactive substance. The experiments clearly showed the influence of processing conditions, namely with regard to homogeneous coverage of the substrate surface with the reactive medium.

Photochemical welding of silica microspheres to silicone rubber by ArF excimer laser

Transparent fused silica (SiO 2) microspheres 2.5 μm in diameter were photochemically welded to transparent, flexible silicone rubber ([SiO(CH 3) 2] n ) substrate by 193 nm ArF excimer laser induced photochemical modification of silicone into silicon oxide. Single layer of silica microspheres was easily formed on an adhesive silicone rubber before laser irradiation after dropping of silica microspheres dispersed in ethanol and subsequent tape peeling. The welding rate, the percentage of welded microspheres tested by ultrasonic cleaning with ethanol, was examined by varying the single pulse fluence and irradiation time of ArF excimer laser. The welding layer underneath microsphere, silicon oxide, was also found to emit white light of strong intensity under UV light illumination.

Selective Dissociation of 4-Chloroaniline on the Si(111)-7×7 Surface through N−H Bond Breakage

The covalent attachment of 4-chloroaniline on the Si(111)-7×7 surface was investigated by using a combination of X-ray photoelectron spectroscopy (XPS), high-resolution electron energy loss spectroscopy (HREELS), and density functional theory (DFT) calculations. The HREELS spectra suggest that one of the N−H bonds dissociates to form Si−N and Si−H bonds with the phenyl ring and the C−Cl bond unperturbed upon chemisorption. The XPS results confirm that only the NH2 group participates in the surface binding. This binding mode and surface reaction pathway are further supported by the DFT calculation. The resulting chlorobenene-like structure on Si(111)-7×7 can be employed for further photochemical modification and functionalization.

A new approach to photoalignment: photo-addition to a self-assembled monolayer

Photoalignment used to control the orientation of nematic liquid crystals in LCDs usually involves the photochemical modification of the chemical structure of an organic thin film so that an optical and/or steric anisotropy is developed. We now demonstrate a novel photoadditive alternative whereby small photoreactive molecules are bound to a photoreactive SAM surface by irradiation with polarised UV so that the surface properties are changed and a surface anisotropy is developed.

Photochemical modification of diamond powders with elemental sulfur and their surface-attachment behavior on gold surfaces

A useful method of modifying the surface of diamond powder with sulfur-containing functionalities was developed by the photolysis of elemental sulfur. The introduction of sulfur-containing functional groups on the diamond surfaces was confirmed by X-ray photoelectron spectroscopy (XPS), diffuse reflectance Fourier transform infrared spectroscopy (DRIFT) and mass spectroscopy analyses. The sulfur-modified diamond powder attached to gold surfaces through sulfur-containing linkages. In brief, the exposure of the modified diamond powder to a gold colloid resulted in gold nanoparticles being attached to the diamond powder. The treatment of the modified diamond powder with thin gold film on a Si substrate resulted in the alignment of surface-attached diamond powder through sulfur linkages formed by self-assembly.

Photochemical Surface Modification of Polyethylene Films by New Azidobenzenesulfonamides

New azidobenzenesulfonamides are synthesized. Their photophysical and photochemical properties have been investigated. The photophysical properties of these compounds were investigated by 1H NMR, IR, and UV spectroscopy. The surface photomodification of polyethylene (PE) films by using new azidobenzenesulfonamides is carried out. The wetting angles for three liquids of different polarities (water, formamide, and diiodomethane) have been studied to estimate the surface modification performed. The obtained wetting angles are used for the determination of the surface free energy γS (γ), as well as its polar , dispersive Owens–Wendt , Lifshits–van der Waals γLW, and acid-base γAB components, by applying the Lifshits–van der Waals/acid-base methods.

Micrometer and Nanometer Scale Patterning Using the Photo-Fries Rearrangement: Toward Selective Execution of Molecular Transformations with Nanoscale Spatial Resolution

The photolithographic modification of monolayers provides a versatile and powerful means of fabricating functionalized nanostructured surfaces. In this contribution, we present photosensitive thiol-bearing aryl ester groups which are capable of undergoing the so-called photo-Fries rearrangement to yield hydroxyketones. Phenyl 16-mercaptohexadecanoate was prepared by a three-step synthesis. This molecule undergoes a photoisomerization reaction upon illumination with UV light at ca. 250 nm. Subsequently this molecule was applied as a self-assembled monolayer on gold. Following photochemical modification, the adsorbates were selectively derivatized to yield amino-functionalized surfaces using a simple two-step reaction. This reaction was monitored by X-ray photoelectron spectroscopy and contact angle measurements and friction force microscopy. Micrometer-scale patterned surfaces were produced using a contact mask in conjunction with a frequency-doubled argon ion laser (lambda=244 nm). Near-field optical exposure was carried out by coupling the laser to a scanning near-field optical microscope and yielded nanometer-scale resolution. Following derivatization, the resulting structures were analyzed by friction force microscopy. Clear contrast was observed in the friction signal following surface modification.

High Sensitivity Electrochemical Detection of Hydrogen Peroxide at a Cobalt Phthalocyanine-Modified Boron-Doped Diamond Electrode

A cobalt phthalocyanine-modified boron-doped diamond (CoPc-BDD) electrode was fabricated. The hydrogen-terminated BDD electrode surface was terminated with the pyridine moieties via photochemical modification with 4-vinylpyridine (4VP), followed by immobilization of CoPc on the surface by immersion of the 4VP-BDD samples in a CoPc solution. X-ray photoelectron spectroscopy studies suggested that coordination of the surface pyridine to the Co atom in CoPc contributes to the surface modification. Electrochemical detection of hydrogen peroxide at the modified electrode was also investigated. Cyclic voltammetry confirmed that the CoPc-BDD electrode exhibits catalytic activity for the electrochemical oxidation of H2O2. Using a flow-injection analysis-electrochemical detection (FIA-EC) system, CoPc-BDD electrode was estimated as being highly suitable for the detection of H2O2 with a practical detection limit in the order of several tens of nanomolars.

Preparation of protein microarrays on non‐fouling and hydrated poly(ethylene glycol) hydrogel substrates using photochemical surface modification

AbstractBACKGROUND: Conventional protein microarrays prepared on hard, dry substrates, such as glass and silicone, have several limitations, as proteins may easily denature and lose their structure. To overcome such problems, the fabrication of wet protein microarrays on non‐fouling and hydrated PEG‐based hydrogels was investigated.RESULT: Bovine serum albumin (BSA) and glucose oxidase (GOX), chosen as model proteins, were covalently immobilized on PEG hydrogel surfaces via 5‐azidonitrobenzoyloxy N‐hydroxysuccinimide, a photoreactive bifunctional linker. Successful fixation of the bifunctional linker and subsequent immobilization of the proteins on the PEG hydrogel surfaces were confirmed with X‐ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) studies. GOX immobilized on the hydrogel surface maintained approximately 50% of its initial activity after 24 h when left in dry conditions, but maintained only 20% when immobilized on a dry substrate. Photochemical fixation combined with photolithography produced well‐defined protein micropatterns with sizes ranging from 50–500 µm, and molecular recognition‐mediated specific binding between biotin and streptavidin was successfully assayed using microarrays on PEG hydrogels.CONCLUSION: A protein‐repellent PEG hydrogel surface was photochemically modified to covalently immobilize proteins and create protein microarrays. The use of hydrated hydrogels as substrates for protein microarrays could minimize the deactivation of proteins in dry conditions, and the non‐fouling property of PEG hydrogels allows the passivation step of protein microarray preparation to be skipped. Copyright © 2008 Society of Chemical Industry

Thickness Dependence of Surface Wettability Change by Photoreactive Polymer Nanosheets

This paper describes the photochemical surface modification of a solid substrate using a photoreactive polymer nanosheets. A neo-pentylmethacrylamide-co-phenylmethacrylamide (p(nPMA/PhMA)), which has been reported to form a stable monolayer was transferred onto a solid substrate using the Langmuir-Blodgett (LB) technique. The p(nPMA/PhMA) copolymer was deposited with different number of layers onto a solid substrate. Then the wettability change after deep UV-irradiation was observed. The water contact angle (CA) of a substrate coated with p(nPMA/PhMA) nanosheet initially shows a value of 80° attributed to alkyl and phenyl side chains of p(nPMA/PhMA). After 30 min irradiation, the water CA of the surface decreases to 14° because of formation of carbonyl groups (COO) of ketone, aldehyde and carboxylic acid from photodecomposition of the nanosheet. The decrease in contact angle depends on number of deposited layers: a thicker film implies smaller surface CA. Results of UV-vis spectroscopy, Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectrscopy (XPS) suggest that more numerous nanosheets produce more oxygen containing species after deep UV irradiation, which implies that the number of the deposited nanosheets can control surface wettability.

Photochemical Modification of a Boron-doped Diamond Electrode Surface with Vinylferrocene

Boron-doped diamond (BDD) surfaces were photochemically modified with vinylferrocene (VFC), and the modified surfaces were analyzed both qualitatively and quantitatively by electrochemical techniques. VFC-modified BDD (VFC-BDD) was prepared by ultraviolet (254 nm) irradiation of hydrogen-terminated BDD in mesitylene, acetonitrile, or n-alkane solutions of VFC. Cyclic voltammetry (CV) results indicated facile electron transfer between ferrocenyl groups and the BDD substrate. The surface coverage of VFC-modified polycrystalline and single-crystal (100) BDD was also estimated by CV and was found to reach saturation at a value possibly corresponding to monolayer coverage by ferrocenyl groups. The electrochemical stability of VFC-BDD to successive potential cycling in acetonitrile was found to be much higher than that of a self-assembled ferrocenylalkanethiol monolayer on an Au electrode surface. This study is the first to show that appropriate solutions of a terminal alkene can be used in the photochemical modification of diamond, yielding monolayer coverage of the surface.

Photochemical Modification of an Optical Fiber Tip with a Silver Nanoparticle Film: A SERS Chemical Sensor

We present a method of photochemical modification of an optical fiber tip with a silver nanoparticle film. The deposited silver nanoparticle film displays alternating light and dark circles, which are similar to a radial diffraction pattern. The modified optical fiber is examined as a chemical sensor for in situ detection. The modified fibers show excellent SERS activity, a low limit of detection (LOD), and good reproducibility. The maximum SERS activity of the sensor was achieved within 5.0 min of deposition. Thus, the method is also quite rapid.