UV Exposure Time Research Articles

Effect of UV aging on electrochemical behavior of an anticorrosion paint

The effect of the photochemical artificial ageing (UVA) on the electrochemical behavior of an anticorrosion paint has been studied by electrochemical impedance spectroscopy (EIS). Two types of coatings have been tested: a formulated tri coat system (FS) formed by a primer (epoxy), an intermediate coat (epoxy) and a topcoat (alkyd) which presents a total film thickness of 240 μm and, on the other hand, a non-formulated varnish (NFV) which presents a total film thickness of 70 μm. Panels have been aged in a QUV chamber and the maximal exposure's time was about 1000 h. EIS testing were carried out with a naturally aerated 3% NaCl solution. Results present Nyquist diagrams for formulated system (FS) and corresponding varnish (NFV) versus UV exposure time after immersion. Evolutions of water uptake for the FS system and the NFV varnish are also presented. In the two cases, we can observe that UV treatment generates a decrease of up taken volume water due to a post-reticulation process. The post-reticulation process concerns both the varnish and the formulated system but its effects are different in the two cases because of the thickness and formulation influences. In order to precise that result, water uptake evolutions according to UV exposure time have been studied for formulated system and NFV varnish, looking at saturation stage. A post reticulation stage followed by a degradation stage is observed. The evolution of the coefficient of diffusion to half sorption according to UV exposure time completes the previous interpretation.

Optimized photocatalytic degradation of Alcian Blue 8 GX in the presence of TiO 2 suspensions

The photocatalytic degradation of Alcian Blue 8 GX, a cationic copper phthalocyanine dye, has been investigated in aqueous suspensions containing the commercial catalyst TiO 2 P-25. The photodegradation of the organic molecule follows approximately a pseudo-first kinetic order, according to the Langmuir–Hinshelwood model. The effect of catalyst concentration, pH of the initial solution and the H 2O 2 concentration upon the reaction rate was ascertained. It was shown that the photocatalytic degradation reaction can be mathematically described as a function of parameters such as pH, H 2O 2 concentration and irradiation time, being modeled by the use of the response surface methodology. Optimized values for oxidizing agent, concentration, pH and UV exposure time for the studied system were determined.

CHARACTERIZATION OF POLY(ACRYLIC ACID) DIFFUSION DYNAMICS ON THE GRAFTED SURFACE OF POLY(ETHYLENE TEREPHTHALATE) FILMS BY FLUORESCENCE CORRELATION SPECTROSCOPY

Poly(acrylic acid) (PAAc) is a commonly used polymer grafted on poly(ethylene terephthalate) films for the immobilization of bioactive molecules that directly interact with living cells or tissues for the maintenance of their viability and functionality. The diffusion property of the grafted PAAc on the surface is a critical parameter related to the density, length of polymer chains, and ionic strength of the solution. Fluorescence correlation spectroscopy (FCS) is able to measure the diffusion coefficient of fluorescent particles in solution with single molecule sensitivity and specificity. It was used as an effective tool to detect diffusion dynamics of Atto 565 molecules, a good indicator for viscosity of PAAc, in both aqueous polymer solutions and polymer grafted film surfaces immersed in solution. In this work we determine the polymer chain length under different polymerization conditions in solution and deduce the solution viscosity by FCS measurements of Atto 565 as tracer molecule. By using the same tracer on the grafted polymer films we can infer the viscosity of these grafted layers under a variety of conditions, including the PAAc chain length, the UV exposure time during polymerization, the ionic strength, and the pH value of the immersed solution.

Multiwavelength interferometry and competing optical methods for the thermal probing of thin polymeric films

AbstractMultiple‐wavelength interferometry (MWI), a new optical method for the thermal probing of thin polymer films, is introduced and explored. MWI is compared with two standard optical methods, single‐wavelength interferometry and spectroscopic ellipsometry, with regard to the detection of the glass transition temperature (Tg) of thin supported polymer films. Poly(methyl methacrylate) films are deposited by spin coating on Si and SiO2 substrates. MWI is also applied to the study of the effect of film thickness (25–600 nm) and polymer molecular weight (1.5 × 104 to 106) on Tg, the effect of film thickness on the coefficients of thermal expansion both below and above Tg, and the effect of deep UV exposure time on the thermal properties (glass transition and degradation temperatures) of the films. This further exploration of the MWI method provides substantial insights about intricate issues pertinent to the thermal behavior of thin polymer films. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4764–4774, 2006

Statistical Modeling of Pretilt Angle Generation for Nematic Liquid Crystal Using in Situ Photoalignment Method on Treated Plastic Substrate

The response surface modeling of the pretilt angle control using in situ photoalignment with oblique UV exposure on a plastic substrate is investigated. The pretilt angle is the main factor that determines the alignment of the liquid crystal display. The response surface model is used to analyze the variation of the pretilt angle under various process conditions. The heating temperature and UV exposure time are considered as input factors. The liquid crystal pretilt angle increased with increasing heating temperature and UV exposure time. The analysis of variance technique is used to analyze the statistical significance, and effect plots are also investigated to examine the relationships between the process parameters and the response. The model can allow us to reliably predict the pretilt angle with respect to the varying process conditions.

Pixellated Photonic Crystal Films by Selective Photopolymerization

Mosaic patterns of blue, green, and orange colors (see figure) are obtained using a multistep photolithography process. Inverse opal films have been pixellated by this process using colloidal crystals as templates, resulting in multicolor patterns. The degree of photopolymerization is controlled by adjusting the UV exposure time and, thus, the refractive color of the inverse opal can be modulated.

Graft coupling of PEO to mixed cellulose esters microfiltration membranes by UV irradiation

Protein fouling is a critical factor governing membrane performance in various filtration processes. In this study, we report a new surface modification technique to modify 0.22 μm mixed cellulose esters membranes to reduce protein fouling. The first step in this modification process involves coating of the membrane with a monolayer of allyldimethylchlorosilane (ADCS). The silanized membrane is then covalently linked to Pluronic F127, a triblock copolymer of polyethylene oxide and polypropylene oxide (PEO–PPO–PEO) by UV irradiation at wavelengths >215 nm. The presence of PEO groups on the membrane surface increased the wettability of the membrane. Contact angle measurements confirmed that the degree of Pluronic grafting on the silanized membrane was a function of the UV exposure time. The hydraulic permeability and flux decline of the modified membrane during bovine serum albumin (BSA) filtration were nearly identical to the unmodified membrane. The modified membranes exhibited better cleaning characteristics compared to unmodified membranes upon back flushing with saline solution.

Characteristics of multimode fiber Bragg gratings and their influences on external-cavity semiconductor lasers

Characteristics of multimode fiber Bragg gratings (MMFBGs) are systematically studied. Dependence of the reflection spectra of MMFBG on excitation conditions, refractive-index change profile, and grating length is investigated experimentally. It is observed that the transmission spectra of the MMFBGs are more sensitive to the polarization state of input light than that of single-mode FBGs (SMFBGs). The influences of the fabrication conditions of MMFBGs (i.e., UV-exposure time) and the rotation of MMF on the output spectra of the MMFBG-based external-cavity semiconductor lasers are then investigated. It is found that the side-mode-suppression ratio and the spatial wavelength-locking region at a specific Bragg wavelength of an MMFBG are dependent on the refractive-index change profile of the grating.

Effect of water absorption, freezing and thawing, and photo‐aging on flexural properties of extruded HDPE/rice husk composites

AbstractDurability of lingo‐cellulosic fiber composites under environmental conditions such as moisture, freezing and thawing, and UV exposure needs to be determined prior to the use of these composite materials in outdoor applications. Dimensional stability and changes in the flexural strength and stiffness of extruded rice husk filled high‐density polyethylene composites with and without processing additives such as compatibilizers and processing aid were examined after exposing the composites to water, conditions of freeze–thaw cycles, and UV light. Water absorption results indicated a decrease in the rate of penetration of water in the composites in the presence of compatibilizers. The reduction in strength and stiffness after water absorption was lower for composites with compatibilizers than for the composites without any additives. Freezing and thawing experiments also showed the dimensional changes and degradation of strength and stiffness were less in composites with compatibilizers. Presence of processing aid in the composite showed a similar or enhanced water absorption and loss of mechanical properties, compared with those of the composite without processing additives. Although the composites showed a discoloration of the surface after the UV exposure time (745 h) studied, it was found that within this period of UV exposure the flexural strength and stiffness of the composites did not show significant change. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3619–3625, 2006

Quantitative analysis of an oligomeric hindered amine light stabilizer in polypropylene by matrix‐assisted laser desorption/ionization mass spectrometry using a solid sampling technique

A small amount of an oligomeric hindered amine light stabilizer (HALS) (Adekastab LA-68LD) in polypropylene (PP) materials was directly determined by solid sampling matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) using an internal standard method. First the matrix reagent (dithranol), 20 mg, and the empirically selected internal standard, angiotensin I (MW = 1296.5), 5 microg, were premixed in the solid state. The matrix mixture was then co-ground with the PP sample containing the HALS in liquid nitrogen using a freezer mill. The powdered sample mixture was spotted on the sample plate, suspended in ion-exchanged water, dried to adhere on the plate, and subjected to MALDI-MS. Three series of the HALS components accompanied by the oxidized species were clearly observed as their molecular ions (M*+)) along with that of the internal standard in the mass spectra. A fairly good linear relationship (R2 = 0.9991) with a relative standard deviation of ca. 11% was observed between the relative peak intensities of the HALS components and the HALS contents ranging from 0.1-2.5 wt%, which could be used as the calibration line to determine the HALS content in PP composites directly by MALDI-MS. The UV-exposed PP composite samples were evaluated by this method to interpret the photostabilizing action of HALS in the PP materials based on the observed change in the relative abundances of the original and oxidized HALS components as a function of UV-exposure time.

Fracture Property Improvements of a Nanoporous Thin Film via Post Deposition UV Curing

AbstractAs silicon-based microelectronic devices continue to aggressively scale down in size, traditional BEOL dielectric materials have become obsolete due to their relatively high dielectric constant. Organosilicate glass (OSG) materials have emerged as the predominant choice for intermetal dielectrics in advancing technology nodes. A potential failure mechanism for this class of low-k dielectric films during the manufacturing process is catastrophic fracture due to channel cracking. To improve the mechanical strength and stability of these silicon-based materials, the use of post-deposition curing processes is under evaluation. In this work, the effects of UV curing on the properties of OSG films were characterized. After UV curing, film hardness and elastic modulus are improved, with no change in the residual film stress. The average film density increases linearly as a function of UV exposure time. Channel crack propagation velocities decrease with UV exposure. The improvements in the mechanical properties of OSG films are believed to correlate with the increasing Si-O-Si bond population. Comparisons between post-deposition UV and Electron Beam curing processes are provided.

Light-Regulated Electrostatic Interactions in Colloidal Suspensions

The net charge of a colloidal particle was controlled using light and a new photocleavable self-assembled monolayer (SAM). The SAM contained a terminal ammonium group and a centrally located carboxylic acid group that was masked with an ortho-nitrobenzyl functionality. Once exposed to UV light, the 2-nitrobenzyl group was cleaved, therefore transforming the colloidal particle from a net positive (silica-SAM-NH3+) to a net negative (silica-SAM-COO-) charge. By varying the UV exposure time, their zeta potential could be tailored between +26 and -60 mV at neutral pH. To demonstrate a photoinduced gel-to-fluid phase transition, a binary colloidal suspension composed of silica-SAM-NH3+ and negatively charged, rhodamine-labeled silica particles was mixed to form a gel. Exposure to UV light rendered all of the particles negative and therefore converted the system into a colloidal fluid that settles to form a dense sediment.

Photoluminescence characteristics of coupled CdSe∕ZnS quantum dots on self-assembled silica nanospheres

The photoluminescence (PL) characteristics of the self-assembled silica nanospheres containing coupled CdSe∕ZnS core-shell quantum dots (QDs) on the surface of the sphere were studied. The degree of QD-coupling and the distribution of the coupled QDs were controlled by generating spatially separated QD-binding sites on the surface of the spheres and varying the QD concentration during the attachment process. When the sizes of QD spots on the surface probed by atomic force microscopy gradually increased, the band gap energy shifted to lower energy via strong Förster energy transfer between nearby QDs, and when UV-exposure time increased, the band gap energy shifted to slightly higher energy, accompanied by a large enhancement in the emission intensity. Moreover, the Bragg diffraction of the self-assembled crystal structure of the spheres affected the PL characteristics of QDs by shifting the entire emission spectra toward longer wavelength as the incident angles were increased.

Photochemically Patterned Poly(methyl methacrylate) Surfaces Used in the Fabrication of Microanalytical Devices

We report here the photochemical surface modification of poly(methyl methacrylate), PMMA, microfluidic devices by UV light to yield pendant carboxylic acid surface moieties. Patterns of carboxylic acid sites can be formed from the micrometer to millimeter scale by exposure of PMMA through a contact mask, and the chemical patterns allow for further functionalization of PMMA microdevice surfaces to yield arrays or other structured architectures. Demonstrated here is the relationship between UV exposure time and PMMA surface wettability, topography, surface functional group density, and electroosmotic flow (EOF) of aqueous buffer solutions in microchannels made of PMMA. It is found that the water contact angle on PMMA surfaces decreases from 70 degrees to 24 degrees after exposure to UV light as the result of the formation of carboxylic acid sites. However, upon rinsing with 2-propanol, the water contact angle increases to approximately 80 degrees , and this increase is attributed to changes in surface roughness resulting from removal of low molecular weight PMMA formed from scission events. In addition, the surface roughness and surface coverage of carboxylic acid groups exhibit a characteristic trend with UV exposure time. Electroosmotic flow (EOF) in PMMA microchannels increases upon UV modification and is pH dependent. The possible photolysis mechanism for formation of carboxylic acid groups on PMMA surfaces under the conditions outlined in this work is discussed.

Novel waterborne UV-crosslinkable thiol–ene polyurethane dispersions: Synthesis and film formation

A new class of water-dispersible polyurethane pre-polymers bearing pendant unsaturation was synthesized and used with polyfunctional thiol crosslinkers to prepare uniform aqueous colloidal dispersions capable of forming crosslinked films upon UV exposure at 254nm. This novel approach to prepare UV crosslinkable, water-based polyurethane polymers offers numerous advantages over other similar systems. Photocuring behavior of films from such thiol–ene polyurethane dispersions (TE-PUD) was monitored using ATR-FTIR spectroscopy by following consumption of thiol and ene functionalities as a function of UV exposure time. Dynamic mechanical analysis (DMA) revealed a decrease of the glass transition temperature (Tg) with increasing thiol/ene ratios ranging from 0.5 to 1.1.

Alignment Properties and EO Performances of Flexible TN-LCD Using In-Situ Photoalignment Method with the Polymer Film

ABSTRACT We have investigated the generation of pretilt angle for a nematic liquid crystal (NLC) alignment with in-situ photoalignment method on polyimide (PI) surfaces using polymer films. Especially, we studied in-situ photoalignment changing heating temperature from 50°C to 120°C on the polymer film. The LC aligning capabilities and pretilt angle on the polymer substrates were better than those on the glass substrate using in-situ photoalignment method. It is considered that this increase in pretilt angle may be attributed to the roughness of the micro-groove substrate induced by the in-situ photoalignment. As temperature of heated subtrate and UV exposure time increases, pretilt angle of the cell used polymer film increased. It is considered that the heating temperature of substrate is attributed to generate pretilt angle. Also, EO performances of the in-situ photoaligned TN cell using the polymer substrate are almost the same as that of the TN cell using the glass substrate.

EO Performances of Flexible TN-LCD using in-situ Ultraviolet Exposure during Imidization of Polyimide on the Polymer Film

We have investigated the generation of pretilt angle for a nematic liquid crystal (NLC) alignment with in-situ photoalignment method on polyimide (PI) surfaces using polymer films. Especially, we studied in-situ photoalignment changing heating temperature from <TEX>$50^{\circ}C\;to\;120^{\circ}C$</TEX> on the polymer film. The LC aligning capabilities and pretilt angle on the polymer substrates were better than those on the glass substrate using in-situ photoalignment method. It is considered that this increase in pretilt angle may be attributed to the roughness of the micro-groove substrate induced by the in-situ photoalignment. As temperature of heated subtrate and UV exposure time increase, pretilt angle of the cell used polymer film increased. It is considered that the heating temperature of substrate is attributed to generate pretilt angle. Also, electro-optical performances of the in-situ photoaligned TN cell using the polymer substrate are almost the same as that of the TN cell using the glass substrate.

Kinetic study of UV-irradiated amorphous sulfur by EPR spectroscopy

Electron paramagnetic resonance (EPR) spectroscopy is used to investigate UV-irradiation damage in amorphous sulfur by examining post-irradiation kinetics as a function of UV-exposure time. The kinetic study is described by first-order concurrent reactions where the sulfur, as reactant, undergoes two parallel processes leading to the formation of two distinct defects called S1• and S2•. The temperature dependence of the EPR intensities of the signals, related to these defects, is used in the kinetic study.

Resist-Free Patterning of Surface Architectures in Polymer-Based Microanalytical Devices

The ability to form patterns of chemically reactive surface functionalities in microanalytical devices using a simple photopatterning approach without the need for photoresist-based methods is described. Direct UV exposure of the surfaces of poly(methyl methacrylate), PMMA, and poly(carbonate), PC, microfluidic devices through optical masks leads to the production of patterns of near monolayer quantities of surface carboxylic acid groups as determined by surface coverage, X-ray photoelectron spectroscopy, and fluorescence microscopy experiments. Formation of the reactive carboxylic acid groups without significant physical (topographical) damage to the polymer device substrates is achieved by use of low UV fluence and exposure times. Modification of the patterned, surface carboxylic acid groups with metals, thermally responsive polymers, and antibodies results in microfluidic devices possessing metallic interconnects and detection electrodes and the ability to capture intact biological cells and proteins from solution.

Highly efficient silver patterning without photo-resist using simple silver precursors

Highly efficient method for silver patterning without photo-resist was developed by using high photosensitive organo-silver precursors, which were prepared by a simple reaction of silver salts and excess of amines. The FT-IR and GC–MS spectra were recorded depending on UV exposure time, for ( n-PrNH 2)Ag(NO 3)·0.5MeCN and ( n-PrNH 2)Ag(NO 2)·0.5MeCN, to understand the photolysis mechanism. The results indicate not only dissociation of coordinated amine and acetonitrile, but also decomposition of corresponding anion upon UV irradiation. When a precursor thin film was exposed to broadband UV irradiation, a partially reduced and insoluble silver species were formed within several minutes. After development, the irradiated areas were treated with a reducing agent to obtain pure metallic patterns. Subsequently, annealing step was followed at 100–350 °C to increase the adhesion of interface and cohesion of silver particles. The line resolution of 5 μm was obtained by the present silver precursors. Film thickness was also controllable from 50 to 250 nm by repetition of the above procedure. The average electrical conductivity was in the range of 3–43 Ω cm, measured by four-point probe technique. AES depth profile of the silver pattern thus obtained showed carbon and oxygen contents are less than 1% through the whole range. Even though sulfur contaminant exists on the surface, it was believed that nearly pure silver pattern was generated.