Photopolymer Material Research Articles

Fabrication of two- and three-dimensional periodic submicron structures by holographic lithography with a 635 nm laser and matched photopolymer

2D and 3D submicron periodic structures are first fabricated by red-induced photopolymerization using a common 635 nm semiconductor laser and specially developed red-sensitive polymer material. The principle of this new photopolymer material fabrication is explained and the absorption spectra of the material are measured. This fabrication technique allows a deeper penetration into volume and larger interference irradiation area which is more than 1 cm2. The optical design, theoretical calculations and experimental results including diffraction patterns verifying the formation of periodic structures are presented. Compared with other fabrication technologies using high-power lasers, this approach has greatly reduced the demand for laser apparatus. Therefore, it is much more accessible to most laboratories and potentially usable in holographic fabrication of photonic crystals and devices in micro electro-mechanical systems (MEMS).

Extended model of the photoinitiation mechanisms in photopolymer materials

In order to further improve photopolymer materials for applications such as data storage, a deeper understanding of the photochemical mechanisms which are present during the formation of holographic gratings has become ever more crucial. This is especially true of the photoinitiation processes, since holographic data storage requires multiple sequential short exposures. Previously, models describing the temporal variation in the photosensitizer (dye) concentration as a function of exposure have been presented and applied to two different types of photosensitizer, i.e., Methylene Blue and Erythrosine B, in a polyvinyl alcohol/acrylamide based photopolymer. These models include the effects of photosensitizer recovery and bleaching under certain limiting conditions. In this paper, based on a detailed study of the photochemical reactions, the previous models are further developed to more physically represent these effects. This enables a more accurate description of the time varying dye absorption, recovery, and bleaching, and therefore of the generation of primary radicals in photopolymers containing such dyes.

Improvement of photopolymer materials for holographic data storage

Photopolymer materials are practical materials for use as holographic recording media due to the fact that they are inexpensive, self-processing materials with the ability to record low loss, highly diffraction efficient volume holographic gratings. In general these materials absorb light of an appropriate wavelength, causing photo-polymerization of the local monomer, inducing a change in the material’s refractive index. These small changes in refractive index enable the storage of large quantities of data using holographic techniques. In an attempt to further develop the data storage capacity and quality of the information stored, i.e., resolution, in such materials, a deeper understanding of the photochemical mechanisms present during the formation of holographic gratings has become ever more crucial. From this understanding the response of an acrylamide/polyvinylalcohol based photopolymer to high spatial frequency information is improved through the addition of a chain transfer agent, i.e., sodium formate, HCOONa.

Reactive calcium-phosphate-containing poly(ester- co-ether) methacrylate bone adhesives: Chemical, mechanical and biological considerations

A poly(propylene glycol- co-lactide) dimethacrylate adhesive with monocalcium phosphate monohydrate (MCPM)/β-tricalcium phosphate (β-TCP) fillers in various levels has been investigated. Water sorption by the photo-polymerized materials catalyzed varying filler conversion to dicalcium phosphate (DCP). Polymer modulus was found to be enhanced upon raising total calcium phosphate content. With greater DCP levels, faster release of phosphate and calcium ions and improved buffering of polymer degradation products were observed. This could reduce the likelihood of pH-catalyzed bulk degradation and localized acid production and thereby may prevent adverse biological responses. Bone-like MG-63 cells were found to attach, spread and have normal morphology on both the polymer and composite surfaces. Moreover, composites implanted into chick embryo femurs became closely apposed to the host tissue and did not appear to induce adverse immunological reaction. The above results suggest that the new composite materials hold promise as clinical effective bone adhesives.

Photo-Cross-Linked Hydrogels from Thermoresponsive PEGMEMA-PPGMA-EGDMA Copolymers Containing Multiple Methacrylate Groups: Mechanical Property, Swelling, Protein Release, and Cytotoxicity

Photo-cross-linked hydrogels from thermoresponsive polymers can be used as advanced injectable biomaterials via a combination of physical interaction (in situ thermal gelation) and covalent cross-links (in situ photopolymerization). This can lead to gels with significantly enhanced mechanical properties compared to non-photo-cross-linked thermoresponsive hydrogels. Moreover, the thermally phase-separated gels have attractive advantages over non-thermoresponsive gels because thermal gelation upon injection allows easy handling and holds the shape of the gels prior to photopolymerization. In this study, water-soluble thermoresponsive copolymers containing multiple methacrylate groups were synthesized via one-step deactivation enhanced atom transfer radical polymerization (ATRP) of poly(ethylene glycol) methyl ether methacrylate (PEGMEMA, M(n) = 475), poly(propylene glycol) methacrylate (PPGMA, M(n) = 375), and ethylene glycol dimethacrylate (EGDMA) and were used to form covalent cross-linked hydrogels by photopolymerization. The cross-linking density was found to have a significant influence on the mechanical and swelling properties of the photo-cross-linked gels. Release studies using lysozyme as a model protein demonstrated a sustained release profile that varied dependent on the copolymer composition, cross-linking density, and the temperature. Mouse C2C12 myoblast cells were cultured in the presence of the copolymers at concentrations up to 1 mg/mL. It was found that the majority of the cells remained viable, as assessed by Alamar Blue, lactate dehydrogenase (LDH), and Live/Dead cell viability/cytotoxicity assays. These studies demonstrate that thermoresponsive PEGMEMA-PPGMA-EGDMA copolymers offer potential as in situ photopolymerizable materials for tissue engineering and drug delivery applications through a combination of facile synthesis, enhanced mechanical properties, tunable cross-linking density, low cytotoxicity, and accessible functionality for further structure modifications.

Nonlocal photopolymerization kinetics including multiple termination mechanisms and dark reactions Part II Experimental validation

In the first of this series of papers [J. Opt. Soc. Am. B26, 1736 (2009)], a new kinetic model, which includes most of the major photochemical and nonlocal photopolymerization driven diffusion effects, was proposed. Predictions made using the model were presented, and the numerical convergence of these simulations were examined when retaining higher-concentration harmonics. The validity and generality of the model is examined by applying it to fit experimental data for two different types of photopolymer material appearing in the literature. The first of these photopolymer materials involves an acrylamide monomer in a polyvinylalcohol matrix. The second is a more complex photopolymer in an epoxy resin matrix. Using the new model, key material parameters are extracted by numerically fitting experimentally obtained diffraction efficiency growth curves. The growth curves used include data captured both during exposure and post-exposure, allowing examination and analysis of “dark reactions.”

Optical compensation of distorted data image caused by interference fringe distortion in holographic data storage

Photopolymer materials shrink because of photopolymerization. This shrinkage distorts the recorded interference fringes in a medium made of such material, which in turn degrades the reconstructed image quality. Adaptive optics controlled by a genetic algorithm was developed to optimize the wavefront of the reference beam while reproducing in order to compensate for the interference fringe distortion. We defined a fitness measure for this genetic algorithm that involves the mean brightness and coefficients of the variations of bit data "1" and "0". In an experiment, the adaptive optics improved the reconstructed image to the extent that data could be reproduced from the entire area of the image, and the signal to noise ratio of the reproduced data could be improved.

Refractive X-ray lenses with rotation profile and curvature-radius scale reduction

Refractive X-ray optics, the physical fundamentals of which were considered by us previously [1], is presented mainly by focusing devices. Among them, an important role is played by compound lenses, the constructions of which are based on the additivity of optical forces of individual lenses. The law of additivity is experimentally proved for the X-ray range [2] by the example of a set of identical lenses having a constant curvature radius. It should be noted that the possibility of a stage-by-stage increase in the optical forces of individual lenses due to reducing the radius of circular apertures was indicated already in the first description of compound lenses [3]. Previously [4], we designed and investigated the planar lenses from silicon, where the curvature-radius scale reduction was introduced for individual lenses. The described type of planar lenses is considered nowadays [5] as most prominent for focusing the beams in the nanodimensional range. In this work, we describe the compound lenses, which were created for the first time with the curvatures-radius scale reduction and the rotation profile by the method of laser stereolithography from photopolymeric materials.

Variational method in soliton theory

We have reported earlier the observation of a self-written waveguide inside a bulk methylene blue sensitized poly (Vinyl Alcohol) /Acrylamide photopolymer material [1]. In this work we develop a theoretical model to explain the experimental observation. We reduce the governing equations for the propagation of a low power laser beam through such a medium into the form of nonlinear Schrodinger equation with a cubic-quintic nonlinearity and solve this equation using variational method. It is found that there is agreement between experimental and theoretical results.

Effect of Photosensitizers on the Shrinkage Characteristics of Blue Laser Sensitive Holographic Epoxy Materials

Polymerization mechanism of epoxy material is based on ring-opening reaction, which generally results in lower shrinkage. In this study, the effect of different photosensitive dyes on the shrinkage characteristics of room temperature fast-curable epoxy polymer media for blue laser holographic recording is reported. Two photosensitive dyes, namely EB and EY dyes, for the holographic epoxy resin photopolymer material were investigated. The EB dye can induce free radical from TEA, which in turn can initiate acrylamide monomer polymerization in holographic material after irradiated by a 405 nm blue laser. The photosensitivity of dye can influence the shrinkage properties of the epoxy media after recording process. The measurement results indicate that the epoxy media addition with higher photosensitive EB dye has lower shrinkage value of about 0.25%, which is much smaller than general accepted value of about 0.5%.

Evaluation of new 3‐mercaptopropionate thiols for thiol‐ene photopolymerization coatings using experimental design

AbstractThree 3‐mercaptopropionate thiols, 1,6‐Hexane bis(3‐mercaptopropionate) (HD‐SH), trans‐1,4‐Cyclohexanedimethyl bis(3‐mercaptopropionate) (CHDM‐SH), and 4,4′‐Isopropylidenedicyclohexane bis(3‐mercaptopropionate) (HBPA‐SH) were formulated with 1,3,5‐triallyl‐1,3,5‐triazine‐2,4,6(1H,3H,5H)‐trione (TATATO) and photoinitiator. The formulations were photopolymerized via thiol‐ene photopolymerization. A ternary experimental design was employed to elucidate the influence the three thiols on the thermomechanical and coatings properties of thiol‐ene photopolymerizable materials. Tensile strength, tensile modulus, elongation‐to‐break, glass transition temperature (Tg), and crosslink density (XLD) were investigated. Coating properties including pencil hardness, pull‐off adhesion, MEK double rubs, and gloss were also investigated. Relative reaction conversion was determined by photo differential scanning calorimeter (PDSC). Thiol‐ene photopolymerizable materials containing HBPA‐SH resulted in improving tensile strength, tensile modulus, Tg, and pencil hardness but lowering of crosslink density and relative conversion. This was attributed to steric and rigidity of the double cycloaliphatic structure. The inclusion of CHDM‐SH into the systems resulted in the synergistic effect on elongation‐to‐break and pull‐off adhesion. The HD‐SH generally resulted in a diminution of thermomechanical and coating properties, but improved the crosslink density. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Optic diffusers based on photopolymerizable hologram material with an ionic liquid as additive

Symmetric and asymmetric diffusers with a directional diffusion property were both fabricated based on a photopolymerizable hologram material using an ionic liquid as an additive. The diffusion property can be regulated by changing the concentration of the ionic liquid. The fiber structure, the surface-relief structure, and the formation of nanoparticles led to the directional diffusion property of the diffuser.

Position sensitive, continuous wavelength tunable laser based on photopolymerizable cholesteric liquid crystals with an in-plane helix alignment

Position sensitive lasing with continuous wavelength tunability and emission in the cell-plane direction is demonstrated from a photopolymerized cholesteric liquid crystal film. The device has a gradually dilating helix lying in the cell-plane direction and is fabricated by applying a vertical electric field in a conventionally rubbed wedge cell while cooling the sample from the isotropic phase. Tuning range of ∼100nm is achieved by translating the device with respect to the pump beam. Photopolymerizable materials are especially useful in this configuration since a freestanding film, not requiring any external voltage to maintain the molecular ordering, can be prepared.

Analysis of the photoabsorptive behavior of two different photosensitizers in a photopolymer material

Photopolymer materials are practical materials for use as holographic recording media. To further develop such materials, a deeper understanding of the photochemical mechanisms present during the formation of holographic gratings in these materials has become ever more crucial. This is especially true of the photoinitiation process, which has already received much attention in the literature. Typically the absorption mechanism varies with exposure time. This has been previously investigated in association with several effects taking place during recording. Since holographic data storage requires multiple sequential short exposures, it is necessary to verify the temporal change in photosensitizer concentration. Postexposure effects have also been discussed in the literature, however, such studies do not include effects such as photosensitizer recovery and bleaching. We report on experimental results and theoretical analysis of the recovery and bleaching mechanisms, which arise during exposure and postexposure for two different types of photosensitizers, methylene blue and erythrosine B in a polyvinylalcohol-acrylamide based photopolymer material.

Fabrication of micro-optical devices by self-guiding photopolymerization in the near IR

Micropillars and microlenses, integrated at the end of optical fibers, were fabricated by microfabrication by direct photopolymerization in the near-IR (NIR) region (700-950 nm). They were built by self-guiding polymerization using the NIR-light emerging from the optical fiber. The aim is to demonstrate that photopolymer material can be used to fabricate micro-optical devices by a single step process utilizing NIR activation. The material and process described here fulfill the requirements for a simple and fast implementation of micro-optics onto NIR sources.

Direct Observation of Intermediates in Sensitization Reaction of Anthracenes and Oxime Type Photoacid Generator in Polymer Matrix

In the anthracene derivatives (XA) /an oxime type photoacid generator (PAG), (Z,E)-2-(4-methoxy-phenyl)-2-[(4-methylphenyl-sulphonyl)oxyimino]-acetonitrile (PAIOTos) photoinitiating system to give high photosensitivities, radical cations XA.+ were directly observed. It clearly supports that the sensitization mechanism is the singlet electron transfer from XA to the PAG. The XA/PAIOTos system gave higher sensitivity than PAIOTos did in a photopolymer materials.

Characterizing and designing photopolymer materials

Photopolymers are organic materials that polymerize when illuminated with a suitable wavelength of light. They have many potential applications, such as optically written waveguides for 3D photonic circuits. Perhaps the most exciting applications are in the area of data storage. Holographic data storage has been identified as a significant goal, and photopolymers are the medium of choice for the digital versatile disc (DVD)-sized devices with terabyte-plus data densities promised by these 3D optical storage techniques. High-density magnetic tapes can currently hold∼500GB (approximately 200 million pages of text). Magnetic tape libraries, sold to governments and large companies, are made by connecting cabinets that hold ∼5,000 tapes. Companies like StorageTech sell over 22,000 of these cabinets annually, so the need for high-volume storage exists. Several important technical milestones have recently been achieved in this area, such as InPhase Technologies launching their holographic disc-drive in 2008. The commercial possibilities may explain why several companies, including Bayer, DuPont, General Electric, and Sony have entered this research area. Since 2000,1 our group has been developing detailed electromagnetic and material models to describe the operation of photopolymers.2–5 The aim has been to develop simulations4 that characterize the physical and chemical effects taking place within the material during and after exposure. These efforts could allow scientists to optimize materials and simulate their applications. Figure 1 shows the material processes involved. Exposing light produces a sinusoidal interference pattern. The grating causes diffraction of the probing beam in the non-latent material. Polymerization (initiated in the bright regions of the material layer) removes the monomer, producing a concentration gradient. The monomer diffuses from the dark to the bright regions. Non-local growth of the polymer chains (away from the point of Figure 1. Material processes occurring in photopolymers during and after exposure

Self-written waveguide in methylene blue sensitized poly(vinyl alcohol)/acrylamide photopolymer material

We report the observation of a self-written waveguide inside a bulk methylene blue sensitized poly/vinyl alcohol)/acrylamide photopolymer material. Light from a low power He-Ne laser is focused into the material, and the evolution of the beam is monitored. The refractive index of the material is modulated in the region of high intensity due to photobleaching and photopolymerization effects occurring in the material. As a result, the beam propagates through the medium without any diffraction effects.

Фотополімерні композиційні матеріали для захисних покриттів друкованих плат

Фотополімерні композиційні матеріали для захисних покриттів друкованих плат

Photopolymerized silver-containing conducting polymer films. Part II. Physico-chemical characterization and mechanism of photopolymerization process

Physico-chemical and mechanical characterizations of nanophase silver-containing polypyrrole films prepared using a new photopolymerization process were performed. In general, the recorded physical, chemical, and mechanical data characteristic of these films was similar to corresponding literature data obtained from electropolymerized or chemically polymerized polypyrrole. However, photopolymerized polypyrrole films possessed an unusually high anion-to-monomer ratio of 0.8:1. Also, the photopolymerized material contained silver nanoparticles, having diameters of 2 μm or less, uniformally distributed throughout the polymer matrix. While the photopolymerization mechanism is complex, it is suggested that a pyrrole–silver cation complex is most likely the key component involved in the photopolymerization initiation step.