Benzyl Dimethyl Ketal Research Articles

Femtosecond laser point-by-point Bragg grating inscription in BDK-doped step-index PMMA optical fibers.

In this paper, the inscription of 2-mm-long fiber Bragg gratings (FBGs) on benzyl dimethyl ketal (BDK)-doped poly(methyl methacrylate) (PMMA) optical fibers by means of a femtosecond laser and a point-by-point FBG inscription technique is reported. The highest reflectivity of approximately 99% is obtained with a pulse energy of 68.5 nJ, showing a large refractive index modulation amplitude of 7.2 × 10-4. Afterwards, grating stabilities at room and higher temperatures of up to 80°C are investigated.

Large refractive index modulation based on a BDK-doped step-index PMMA optical fiber for highly reflective Bragg grating inscription.

We experimentally report high reflectivity on the poly(methyl methacrylate) (PMMA)-based polymer optical fiber Bragg gratings by means of a 266 nm pulsed laser and phase mask technique. In the first recipe, fiber Bragg gratings (FBGs) were manufactured with a single pulse up to 3.7 mJ. After post-annealing, a stable refractive index change up to 4.2×10-4 was obtained. In the second recipe, FBGs were inscribed by 22 pulses with a lower pulse energy of 1.4 mJ, showing a stable refractive index change of 6.2×10-4. Both behaviors may mainly be attributed to the movement of initiating radicals arising from benzyl dimethyl ketal (BDK) under UV irradiation. The high refractive index change in step-index fibers paves the way to tilted FBG manufacturing with large tilt angles potentially for biomedical applications.

Optical properties and photo-isomerization processes of PMMA–BDK–MR nanocomposite thin films doped by silica nanoparticles

A novel nanocomposite thin films based on azo dye methyl red (MR) hosted in polymethylmethacrylate (PMMA) incorporated with benzyl dimethyl ketal (BDK) as a photo-initiator and doped with 2.5% and 5% of silica NPs are prepared by dip coating technique on fused silica substrates. We investigate the optical, chemical and thermal properties of (PMMA–BDK–MR)/silica NPs nanocomposite thin films by performing UV–Vis spectrometer, Fourier transform infrared spectroscopy (FTIR) and Thermogravimetric analyser (TGA). The purpose of inserting the azo dye MR in the composite is to stimulate the nanocomposite to perform the cis ↔ trans cycles through illumination ↔ thermal relaxation for Write/Read/Erase optical data storage and UV-light sensors. Our UV–Vis and FTIR findings confirm the hysteresis cycle of trans- and cis-states. Consequently, (PMMA–BDK–MR)/silica NPs thin films could be successfully used in Write/Read/Erase optical data storage and UV-light sensors. The TGA measurements show that the weight loss of the nanocomposites is reversibly proportional to the silica NPs concentration indicating the reinforcement of physicochemical bonding density as the concentration of silica NPs is increased.

Kinematics of Photoisomerization Processes of PMMA-BDK-MR Polymer Composite Thin Films.

We investigate and report on the kinematics of photoisomerization processes of polymer composite thin films based on azo dye methyl red (MR) hosted in polymethylmethacrylate (PMMA) incorporated with Benzyl dimethyl ketal (BDK) as a photo-initiator. Understanding photoisomerization mechanisms is crucial for several optical applications such as Read/Write/Erase (WRE) optical data storage media, UV light Read/Write heads, and UV light sensors. The as-prepared polymer composite thin films are characterized using UV–Vis spectroscopy. Furthermore, Fourier transform infrared spectroscopy (FTIR) and scanning electron microscope (SEM) are employed to investigate the optical, chemical, and morphological properties of trans- and cis-states of PMMA-BDK-MR polymer composite thin films. The presence of the azo dye MR in the composite is essential for the efficient performance of the cis ↔ trans cycles through illumination ↔ thermal relaxation for Write/Read/Erase optical data storage and UV-light sensors. Moreover, UV–Vis and FTIR results confirm the hysteresis cycle of trans- and cis-states and that PMMA-BDK-MR thin films may be regarded as potential candidates for successful Write/Read/Erase optical data storage and UV-light sensors. In addition, the morphology of the thin film surface is investigated by SEM technique. The SEM images indicate that uncured surfaces of PMMA-BDK-MR thin films are inhomogeneous compared with the corresponding surfaces after curing. The transformation from inhomogeneous surfaces to homogeneous surfaces is attributed to the polymerization of thin films by UV curing.

Gas Pressure Sensor Based on BDK-Doped Polymer Optical Fiber

This paper presents a high sensitivity gas pressure sensor with benzyl-dimethylketal (BDK)-doped polymer optical fiber Bragg grating (POFBG), whose sensitivity is up to 8.12 pm/kPa and 12.12 pm/kPa in positive and negative pressure atmosphere, respectively. The high sensitivity can be explained by its porous chemical structure. The stability and response behavior under air pressure atmosphere has also been investigated. The new understanding of the air pressure response principle and sensitivity difference for the presented sensor can be a worthy reference.

Polymer optical fiber Bragg grating inscription with a single Nd:YAG laser pulse.

We experimentally demonstrate the first polymer optical fiber Bragg gratings inscribed with only one Nd:YAG laser (266 nm) pulse. The gratings have been inscribed in a single-mode poly (methyl methacrylate) optical fiber, with a core doped with benzyl dimethyl ketal for photosensitivity enhancement. One laser pulse with a duration of 8 ns and energy of 72 µJ is adequate to introduce a refractive index change of 0.5 × 10-4 in the fiber core. The stability of the gratings has been confirmed and the strain and temperature sensitivity measurements demonstrate their tunable properties.

Advances on Polymer Optical Fiber Gratings Using a KrF Pulsed Laser System Operating at 248 nm

This paper presents the achievements and progress made on the polymer optical fiber (POF) gratings inscription in different types of Fiber Bragg Gratings (FBGs) and long period gratings (LPGs). Since the first demonstration of POFBGs in 1999, significant progress has been made where the inscription times that were higher than 1 h have been reduced to 15 ns with the application of the krypton fluoride (KrF) pulsed laser operating at 248 nm and thermal treatments such as the pre-annealing of fibers. In addition, the application of dopants such as benzyl dimethyl ketal (BDK) has provided a significant decrease of the fiber inscription time. Furthermore, such improvements lead to the possibility of inscribing POF gratings in 850 nm and 600 nm, instead of only the 1550 nm region. The progress on the inscription of different types of polymer optical fiber Bragg gratings (POFBGs) such as chirped POFBGs and phase-shifted POFBGs are also reported in this review.

Fast Inscription of Long Period Gratings in Microstructured Polymer Optical Fibers

We demonstrate 20 dB long period grating (LPG) fast inscription in microstructured polymer optical fibers (mPOFs) using a point-by-point technique obtaining an LPG total length of 25 mm. Two 248 nm UV laser pulses of 15 ns duration have been employed for every inscription point, which means a time reduction by over 21 times compared with the fastest inscription time already reported in literature. The device has been fabricated in a single-mode mPOF with a core that has been doped with benzyl dimethyl ketal for photosensitivity enhancement. Moreover, we characterize the strain and temperature responses and the stability of the fabricated gratings response under different conditions in order to assess the viability for different applications.

Fabrication of tunable chirped mPOF Bragg gratings using a uniform phase mask.

We demonstrate chirped Bragg gratings fabrication in doped microstructured tapered polymer fibers by using a uniform phase mask. The use of high photosensitive benzyl dimethyl ketal (BDK) doped core fiber allows to obtain chirped Bragg gratings by means of a single krypton fluoride laser pulse. The stability of the gratings has been confirmed and the strain and temperature sensitivity measurements demonstrate their tunable properties. Finally, different tapered profiles have been implemented in order to show the potentiality of this fabrication technique in polymer optical fibers.

Phase-Shifted Bragg Grating Inscription in PMMA Microstructured POF Using 248-nm UV Radiation

In this work, we experimentally validate and characterize the first phase-shifted polymer optical fiber Bragg gratings (PS-POFBGs) produced using a single pulse from a 248-nm krypton fluoride laser. A single-mode poly (methyl methacrylate) optical fiber with a core doped with benzyl dimethyl ketal for photosensitivity improvement was used. A uniform phase mask customized for 850-nm grating inscription was used to inscribe these Bragg structures. The phase shift defect was created directly during the grating inscription process by placing a narrow blocking aperture in the center of the UV beam. The produced high-quality Bragg grating structures, presenting a double dips, reject 16.3 dB (97.6% reflectivity) and 13.2 dB (95.2% reflectivity) of the transmitted power, being therefore appropriate for sensing or other photonic applications. Its transmission spectrum possesses two sharp transmission notches, allowing a significant increase in measurement resolution compared to direct interrogation of a single grating. The reflection and transmission spectra when multiple phase shifts are introduced in the fiber Bragg grating structure are also shown. The PS-POFBG's strain, temperature, pressure, and humidity characteristics have been experimentally analyzed in detail to assess their potential usage as sensors.

BDK-doped core microstructured PMMA optical fiber for effective Bragg grating photo-inscription.

An endlessly single-mode doped microstructured poly(methyl methacrylate) (PMMA) optical fiber is produced for effective fiber Bragg grating (FBG) photo-inscription by means of a 400nm femtosecond pulsed laser and the phase mask technique. The fiber presents a uniform benzyl dimethyl ketal (BDK) distribution in its core without drastic loss increase. It was produced using the selected center hole doping technique, and the BDK dopant acts as a photoinitiator. In this Letter, we report a rapidly growing process of the grating reflection band. For an 11mW mean laser power, the FBG reflectivity reaches 83% in only 40s.

Polymer optical fiber Bragg grating inscription with a single UV laser pulse.

We experimentally demonstrate the first polymer optical fiber Bragg grating inscribed with only one krypton fluoride laser pulse. The device has been recorded in a single-mode poly(methyl methacrylate) optical fiber, with a core doped with benzyl dimethyl ketal for photosensitivity enhancement. One laser pulse with a duration of 15 ns, which provide energy density of 974 mJ/cm2, is adequate to introduce a refractive index change of 0.74×10-4 in the fiber core. After the exposure, the reflectivity of the grating increases for a few minutes following a second order exponential saturation. The produced Bragg grating structure rejects 17.9 dB transmitted power, thus providing 98.4% reflectivity, which is well suited for sensing applications. In addition, we report the importance of the fiber thermal treatment before or after the inscription, showing its effects on the lifetime and quality of the grating structures. Optimizing the irradiation conditions and the material chemical composition, a higher refractive index change in the fiber core is feasible. This demonstration significantly improves the potential for commercial exploitation of the technology.

The UV and Laser Aging for PMMA/BDK/Azo-dye Polymer Blend Cured by UV Light Beams

A polymeric-based solution blend composed of Azo-dye methyl red (MR) doped with polymethelmethacrelate (PMMA) solution, in addition, to the BenzylDimethylKetal (BDK) photoinitiator was made with optimum molar ratios and deposited on glass substrate by spin coating technique. The samples were then exposed to UV light beams in order to assist the layers polymerization by the proper exposure process. The photo chemical reaction occurred during the UV light polymerization process induces photo refractive changes which were presented as a function of wavelength or photon energy. Two main strong absorption peaks were observed in the films at around 330 nm (3.75 eV) and 500 nm (2.48 eV) for different curing time periods. This phenomenon enhances the films usage for optical data storage media at these two wavelengths. Since the deposited films were then useful as based layers for Read/Write optical data storage media, they were then tested by UV or laser Read/Write beams independently. The optical properties of the films were investigated while exposed to each beam. Finally, their optical properties were investigated as a function of aging time in order to relate the temporary and/or permanent light-exposure effect on the films compared to their optical properties before the light exposure. The films show a low absorbance at 630 nm (1.97 eV) and high absorbance at 480 nm (2.58 eV). This fact makes it possible to record holographic gratings in the polymeric film upon light exposure. In all cases the optical properties were evaluated by using the very sensitive, non destructive surface testing spectroscopic ellipsometry technique. The films were characterized in the spectral range of 300 to 1000 nm using Lorentz oscillator model with one oscillator centred at 4.15 eV. This study has been supported by the SEM and EDAX results to investigate the effect of the UV and visible beams on their optical properties. The results of this research determined the proper conditions for depositing the proper optical materials for light sensors or Read/Write optical data storage media for the UV or the laser Read/Write heads.

UV 경화형 우레탄 아크릴레이트/MMT 나노복합체의 기계적 성질과 내흡수성에 대한 광개시제의 영향

우레탄 아크릴레이트에 montmorillonite(MMT)를 첨가한 UV 경화형 나노복합체 제조 시 사용하는 광개시제의 종류에 따른 기계적 성질 및 내흡수성을 조사하였다. 1 wt%의 MMT가 첨가될 경우 가장 우수한 인장강도와 내흡수성을 나타내었으며, 광개시제의 경우 기존의 benzyldimethylketal 계열 광개시제와 bisacyl phosphine oxide 계열의 광개시제를 함께 사용할 경우 3 wt%의 MMT 함량에서도 사용된 UV 램프의 방출 파장대인 340~450 nm에서의 광흡수가 강화되어 나노복합체의 경화거동에 보다 효과적인 것으로 확인되었다. The addition of montmorillonite (MMT) in the UV curable polyurethane diacrylate based resins was investigated to fabricate nanocomposites with improved mechanical properties and water sorption behavior using different photoinitiator systems. As a result, it was observed that 1 wt% of clay loading fairly improved tensile resistance and water uptake behavior. It can be also confirmed that dual photoinitiator system consisted of benzyldimethyl ketal and bisacyl phosphine oxide exhibited enhanced energy absorption band 340~450 nm even with 3 wt% of MMT concentration, which may affect the curing behavior of nanocomposite especially in our UV lamp system.

광개시제의 종류에 따른 2-EHA/AA 점착제의 접착특성

UV조사에 의한 2-EHA(ethylhexyl acrylate)/AA(acrylic acid) 점착제를 제조하고 이때 첨가되는 광 개시제의 종류가 점차제의 접착물성에 미치는 영향을 조사하였다. Irgacure<TEX>$^{(R)}$</TEX>651(benzyldimethyl ketal)과 Irgacure<TEX>$^{(R)}$</TEX>184(1-hydroxy-cyclohexylphenyl ketone) 광 개시제를 도입한 점차제의 경우 UV램프의 방출 스펙트럼 근처에서의 높은 흡수율과 단량체 혼합물과의 상용성에 기인하여 우수한 접착물성을 나타낸 반면 Irgacure<TEX>$^{(R)}$</TEX>819(bisacylphosphine oxides) 광 개시제를 도입한 경우 사용된 UV램프의 방출 스펙트럼과 가장 겹치는 흡수 파장대를 가짐에도 불구하고 고농도에서 박리 시 응집파괴가 일어났으며 이것은 높은 함량에서 광 개시제 일부가 산소와 반응하고 이것이 수소 공여체 역할을 하여 추가적인 라디칼 형성을 일으키기 때문으로 생각된다. Pressure sensitive adhesive (PSA) based on 2-ethylhexyl acrylate (2-EHA)/acrylic acid (AA) copolymer was synthesized using different photoinitiators. Results showed that PSA with Irgacure<TEX>$^{(R)}$</TEX>651 (benzyldimethylketal) and Irgacure<TEX>$^{(R)}$</TEX>184(1-hydroxy-cyclohexylphenyl ketone) proved to be good for adhesion properties. This may be attributed to strong absorption near 350 nm wavelength and also high solubility in monomer mixtures. The addition of Irgacure<TEX>$^{(R)}$</TEX>819, bisacylphosphine oxides as a photoinitiator caused cohesive failure with high loading in a peel test owing to the additional radical formation. It is assumed that the insoluble photoinitiator reacts with oxygene, which may act as a hydrogen donor.

Highly photosensitive polymethyl methacrylate microstructured polymer optical fiber with doped core

In this Letter, we report the fabrication of a highly photosensitive, microstructured polymer optical fiber using benzyl dimethyl ketal as a dopant, as well as the inscription of a fiber Bragg grating in the fiber. A refractive index change in the core of at least 3.2×10(-4) has been achieved, providing a grating with a strong transmission rejection of -23 dB with an inscription time of only 13 min. The fabrication method has a big advantage compared to doping step index fiber since it enables doping of the fiber without using extra dopants to compensate for the index reduction in the core introduced by the photosensitive agent.

Factors Affecting Migration of Contaminants from Paper through Polymer Coating into Food Simulants

The migration of two surrogate contaminants, 1‐hydroxycyclohexyl‐1‐phenyl ketone (184) and benzyldimethyl ketal (651), from different paper into different food simulant (10% ethanol, 95% ethanol and isooctane) through different polymer coating low density polyethylene (LDPE) and polypropylene (PP) was studied. The paper samples were spiked with anhydrous ethanol solution containing the two surrogates and were dried using vacuum dry oven with vacuum degree 0.01 MPa and temperature 55°C and then subjected to migration experiments by using single‐sided contact method at 20°C. The concentration of surrogates in 10% ethanol, 95% ethanol and isooctane food simulants were determined by gas chromatography with flame ionization detector after predisposal. Effect factors on migration were discussed from different aspect such as food simulant, paper property, thickness of polymer coating and type of polymer coating. The results showed that the migration rate was faster in fatty food simulant 95% ethanol and isooctane than in aqueous food simulant 10% ethanol, a thicker LDPE coating delayed the migration process of contaminant, paper with lower density and higher porosity would increase migration speed and the barrier property of PP was far away higher than that of LDPE, even if the thickness of LDPE was thicker a lot than PP. Copyright © 2012 John Wiley &amp; Sons, Ltd.

A systematic study on the stability of UV ink photoinitiators in food simulants using GC

AbstractSeveral studies have been published on the stability of plastic monomers and additives in food simulants. However, there are practically no published results about the stability of ink components in food simulants. In this work, the stability of two ultraviolet (UV) ink photoinitiators (PIs) in one aqueous and in two substitute fat food simulants was studied under various time–temperature conditions. Furthermore, the addition of the stabilizing agent hydroquinone monomethyl ester (HQMME) in the same conditions was considered as a comparative experiment. The PIs tested were 1‐hydroxycyclohexyl‐1‐phenyl ketone (Irgacure‐184) and benzyldimethyl ketal (Irgacure‐651). The various test conditions included exposure of 10 days to temperatures of 20, 40 and 60°C for 10% ethanol and 95% ethanol simulants, and exposure of 2 days to temperatures of 20, 40 and 60°C for isooctane. Following exposure to these conditions, the additive samples were analysed. The extracts of samples exposed to various temperature conditions as well as unexposed spiked controls and blanks were analysed by gas chromatography (GC) on a non‐polar (5%‐phenyl)‐methylpolysiloxane capillary column. The results showed that the protective effect of HQMME was not obvious in all test conditions under dark conditions. The Irgacure‐184 was quite stable under all test conditions whether the stabilizing agent was added or not. Irgacure‐651 was stable almost under all test conditions, except in 10% ethanol at 60°C. The mass spectrum of decomposed product of Irgacure‐651 was detected by GC‐MS (Mass Spectrum), and the structure of the decomposed product was obtained by mass spectrographic analysis. The method of detection and disposal is also applicable for UV ink PI migration testing from several different paper or paperboard‐plastic coating layer materials into the food simulants used in the study. Copyright © 2008 John Wiley &amp; Sons, Ltd. 2008

Reversible photoreduction of methylene blue in acrylate media containing benzyl dimethyl ketal

The reversible photoreduction of methylene blue in acrylate media is studied here. Methylene blue can be photoreduced using a benzyl dimethyl ketal photoinitiator upon 365 nm irradiation. The photoreduction is due to the interaction of methylene blue with methyl radical which is generated when benzyl dimethyl ketal is photocleaved. The photoreduced polyacrylate sample exhibits reversible photoreduction behavior due to the cyclic processes of oxidation in air and reduction in nitrogen upon UV exposure. Since methylene blue is widely used across many disciplines, our results have many potential applications in sensors, data storage, electronic devices, etc.

A new highly photorefractive polymer composite for optical data storage application

A novel photorefractive effect based on a photochemical process has been developed. The system is composed of methyl red (MR) doped poly(methylmethacrylate) (PMMA) polymer with benzyldimethylketal (BDK) as a photoinitiator. Large changes in optical constants were obtained in the MR/BDK film upon exposure to extremely low power UV light (265 µW cm−2) at wavelength 254 nm. These changes reach about 90% of their maximum value in 5 s. Changes in the refractive index Δn = −0.47 at 570 nm and in the absorption coefficient Δα = −1.4 × 105 cm−1 at 470 nm in the MR/BDK film and Δn = 0.03 and Δα = −8 × 104 cm−1 in MR/BDK/PMMA film were measured. The origin of such high changes in optical constants may be attributed to the photodeprotonation of MR by the radicals formed by the photodecomposition of BDK by UV light. The optical constants and film thickness change were measured using a variable angle spectroscopic ellipsometer.