Photopolymer Composition Research Articles

Fabrication of an efficient green sensitive photopolymer for holographic applications

An efficient green sensitive photopolymer material for holographic applications is indigenously prepared using polyvinyl alcohol binder, acrylamide monomer, triethanolamine photo-initiator and erythrosine B photo-sensitizer under normal laboratory conditions. The influence of monomer cross-linker on the performance of photopolymer material is investigated by incorporating N-N'- methylene-bis-acrylamide as monomer cross-linker in the photopolymer composition. Suitability of photopolymer material for holographic applications is investigated by finding the diffraction efficiency of first order holographic volume transmission gratings recorded in the fabricated photopolymer. Average thickness of the photopolymer film and several recording parameters such as inter-beam angle, inter-beam ratio and laser exposure energy are optimized to enhance the diffraction efficiency of gratings. The fabricated photopolymer is found suitable for holographic applications as the material is capable to record holograms with good diffraction efficiency of 70 %.

3D-Printed Porous Magnetic Carbon Materials Derived from Metal-Organic Frameworks.

Here we report new porous carbon materials obtained by 3D printing from photopolymer compositions with zinc- and nickel-based metal–organic frameworks, ZIF-8 and Ni-BTC, followed by high-temperature pyrolysis. The pyrolyzed materials that retain the shapes of complex objects contain pores, which were produced by boiling zinc and magnetic nickel particles. The two thus provided functionalities—large specific surface area and ferromagnetism—that pave the way towards creating heterogenous catalysts that can be easily removed from reaction mixtures in industrial catalytic processes.

Effects of Cellulose Nanocrystal and Inorganic Nanofillers on the Morphological and Mechanical Properties of Digital Light Processing (DLP) 3D-Printed Photopolymer Composites

Photopolymer composites filled with cellulose nanocrystal (CNC) and/or inorganic nanofillers were fabricated by using digital light processing (DLP) 3D printing. To investigate the effects of different CNC lyophilization concentrations and behaviors of CNC particles in the photopolymer composites, morphological and mechanical properties were analyzed. CNC loading levels affected the morphological and mechanical properties of the filled composites. Better CNC dispersion was seen at a lower lyophilization concentration, and the highest mechanical strength was observed in the 0.25 wt% CNC-filled composite. Furthermore, nano-precipitated calcium carbonate (nano-PCC) and nanoclay were added to photocurable resins, and then the effect of inorganic nanofillers on the morphological and mechanical properties of the composites were evaluated. By analyzing the morphological properties, the stress transfer mechanism of nano-PCC and nanoclay in the photopolymer composites was identified and related models were presented. These supported the improved mechanical strength of the composites filled with CNC, nano-PCC, and nanoclay. This study suggested a new approach using wood-derived cellulose nanomaterials and inorganic nanofillers as effective fillers for DLP 3D printing.

Conductance-strain behavior in silver-nanowire composites: network properties of a tunable strain sensor

Highly flexible and conductive nano-composite materials are promising candidates for stretchable and flexible electronics. We report on the strain–resistance relation of a silver-nanowire photopolymer composite during repetitive stretching. Resistance measurements reveal a gradual change of the hysteretic resistance curves towards a linear and non-hysteretic behavior. Furthermore, a decrease in resistance and an increase in electrical sensitivity to strain over the first five stretching cycles can be observed. Sensitivity gauge factors between 10 and 500 at 23% strain were found depending on the nanowire concentration and stretching cycle. We model the electrical behavior of the investigated silver nanowire composites upon repetitive stretching considering the strain induced changes in the local force distribution within the polymer matrix and the tunnel resistance between the nanowires by using a Monte Carlo method.

Probing Plasmon-Induced Chemical Mechanisms by Free-Radical Nanophotopolymerization

Localized surface plasmon-induced photopolymerization of free-radical acrylate monomers is an efficient, smart, and versatile method for preparing metal/polymer hybrid nanoparticles (NPs) with accurate control of the thickness and spatial distribution of the polymer on the NP surface. Despite a growing number of practical demonstrations, the mechanism leading to polymerization of the acrylate monomer by localized surface plasmon resonance (LSPR) is still controversial. It could be related to either a photochemical mechanism enhanced by electromagnetic hot spots (enhanced near field) or thermoplasmonic (photothermal heating) or electrochemical (via hot-carrier injection) mechanisms, as proposed in different studies. After developing a high-resolution characterization method based on transmission electron microscopy and by tuning the photopolymer composition and the irradiation conditions, the LSPR-induced physicochemical mechanism is revealed. We demonstrate that the photochemical pathway is the main mechanism under the mild irradiation conditions chosen for this process. In a more general way, photopolymerization proves to be a powerful tool to investigate the coupling between metal nanostructures and organic moieties.

Signal Amplification in an Optical and Dielectric Biosensor Employing Liquid Crystal-Photopolymer Composite as the Sensing Medium.

An optical and dielectric biosensor based on a liquid crystal (LC)–photopolymer composite was established in this study for the detection and quantitation of bovine serum albumin (BSA). When the nematic LC E7 was doped with 4-wt.% NOA65, a photo-curable prepolymer, and photopolymerized by UV irradiation at 20 mW/cm2 for 300 s, the limit of detection determined by image analysis of the LC optical texture and dielectric spectroscopic measurements was 3400 and 88 pg/mL for BSA, respectively, which were lower than those detected with E7 alone (10 μg/mL BSA). The photopolymerized NOA65, but not the prepolymer prior to UV exposure, contributed to the enhanced optical signal, and UV irradiation of pristine E7 in the absence of NOA65 had no effect on the optical texture. The effective tilt angle θ, calculated from the real-part dielectric constant ε’, decreased with increasing BSA concentration, providing strong evidence for the correlation of photopolymerized NOA65 to the intensified disruption in the vertically oriented LC molecules to enhance the optical and dielectric signals of BSA. The optical and dielectric anisotropy of LCs and the photo-curable dopant facilitate novel quantitative and signal amplification approaches to potential development of LC-based biosensors.

The viscoelastic mechanical property and constitutive models of 3D printed photopolymer

Purpose The purpose of this paper is to study the mechanical property of three-dimensional (3D) Printed photopolymer (Vero Yellow and Tango Black) with different constant strain rate. According to the experimental results, three constitutive models are used to describe the stress-strain and stress-time relation in the tension and stress relaxation process. Design/methodology/approach The Stratasys Objet 260 was used to prepare the four groups of samples with different photopolymers (Vero Yellow and Tango Black). The stress-strain and stress-time relations are obtained by the uniaxial tensile tests and relaxation tests performed at room temperature with different constant strain rates. The generalized Kelvin model (GKM), standard linearized model (SLM) and fractional order model (FOM) are used to describe experimental data by means of the curve-fitting approach. Findings Experimental results show that the tension stress increases faster at a higher strain-rate for tensile tests. Relaxation stress is influenced by the preload strain-rate for relaxation tests. For the theoretical fitting, the error comparison between three constitutive models and experimental data are calculated to demonstrate the high accuracy in describing the stress-strain relationship for tension. For stress relaxation, the error comparison confirms higher accuracy of FOM with the largest error within 3%, while the error of GKM and SLM up to 10%. Originality/value The paper confirms the viscous-elastic mechanical property of 3D printed photopolymer composites (Vero Yellow and Tango Black) for Stratasys PolyJet. As FOM shows high accuracy both in describing stress-strain and stress-time relation for tension and stress relaxation process, it can be directly used as a constitutive model to predict mechanical properties for engineering application.

Studying the polymerization efficiency of photosensitive compositions by using the surface plasmon resonance method

In a real-time scale, it has been investigated the polymerization process in photosensitive compositions based on oligourethanacrylates with various concentrations of photoinitiators by using the method of surface plasmon resonance. Experimentally determined were the speed of polymerization and induction period for the studied samples of photopolymerization compositions as well as their optimum ratio of components for the chosen illumination wavelength 407 nm. It has been ascertained that with increasing the concentration of photoinitiators Irgacure 651 and Irgacure 819 from 1 up to 2% the speed of polymerization is increased by 3 and 7 times, respectively, while the induction period is decreased by almost 2 and 10 times, respectively. The presence of Irgacure 819 in these compositions provides the highest polymerization speed and the lowest induction period, which is related with the optimal choice of the illumination source wavelength inside the absorption spectrum of initiator, and the competitive absorption in other components of the photopolymer composition is minimal. These investigations are useful for developing optimal compositions of the studied materials for using them in various branches of industry.

3D Printing of polymer composites with material jetting: Mechanical and fractographic analysis

Abstract Material jetting technology is gaining popularity due to its distinctive capability to produce multi-material parts by UV curing in a single process. A unique composite behavior with improved mechanical properties can be achieved due to the ability to spatially vary the composition of hard and soft photopolymer. This characteristic is exceptionally favorable in the fabrication of soft robotics and 4D printed parts, which motivated the study of geometrical analysis and the mechanical analysis of the 3D printed composite structure. The present work initiated with visual analysis of micro composites to better understand the dimensional accuracy of the PolyJet technology. It is shown that geometric resolution is reasonable with feature size larger than 500 μm. The mechanical behaviors of 3D printed polymeric composites with different compositions and arrangements of reinforced particles are investigated. When subjected to compression, it is found that orientations and geometries of reinforced particles affect the stiffness of the composite. Digital material tensile testing results show that samples oriented at 45° on the build platform have a lower ultimate tensile strength and elongation at break than samples oriented in a parallel direction. Composite tensile testing results reveal that with a 5% volume fraction of reinforced particles, print orientation has no significant effect on strength. However, the composition and arrangement of particles greatly affect the behavior of the samples. Fractographic analysis is then conducted on the fractured surface of the tensile samples using scanning electron microscopy. It is found that hard particles strengthen the part, but soft particles serve as a crack initiation site.

Single- and two-photon recording of holograms at combined cationic and free-radical polymerization photoinitiated by thioxanthenone derivatives

Single- and two-photon holographic recordings were performed in a photopolymer material consisting of two types of monomers: an acrylamide (1,4-bis(acryloyl)piperazine) and an epoxide ((bis(4-oxiran-2-ylmethoxy)phenyl) sulfide). Thus, cationic ring-opening polymerization and free-radical polymerization of the monomers were simultaneously initiated. The arylsulfonium salt (2-(N,N,N-triethylammonium)methyl-9-oxo-10-(4-heptyloxyphenyl)-9H-thioxanthenium dihexafluorophosphate) was chosen as the photoinitiator. Effective photopolymerization conditions were found for both (single- and two-photon) photoinitiation modes depending on the recording light intensity. The concentrations of the components (monomers and photoinitiator) in the photopolymer was optimized, and a refractive index change of as much as 0.0015 was achieved. Single- and two-photon holographic recording was investigated in photopolymer material consisting of two types of monomers: acrylamide (BAP) and epoxy (BOPS). Thus a cationic ring-opening polymerization and free-radical polymerization of monomers were initiated simultaneously. The arylsulfonium salt—cationic derivative of thioxanthenonium (CDTX) was chosen as the photoinitiator. The refractive index change n1 and maximum recording rate (dn1/dt)max of holographic gratings were found in two-photon photoinitiation modes depending on the concentration of BAP (the molar fraction of BAP) in photopolymer composition.

Study of the Effect of Methyldiethanolamine Initiator on the Recording Properties of Acrylamide Based Photopolymer.

The use of Holographic Optical Elements (HOEs) in applications, such as in light shaping and redirection, requires certain characteristics such as a high Diffraction Efficiency, low angular selectivity and stability against UV damage. In order to maximize the performance of the HOEs, photosensitive materials are needed that have been optimised for the characteristics that are of particular importance in that application. At the core of the performance of these devices is the refractive index modulation created during holographic recording. Typically, a higher refractive index modulation will enable greater light Diffraction Efficiency and also operation with thinner devices, which in turn decreases the angular selectivity and the stability of the refractive index modulation introduced during recording, which is key to the longevity of the device. Solar concentrators based on volume HOEs can particularly benefit from thinner devices, because, for a solar concentrator to have a high angular working range, thinner photopolymer layers with a smaller angular selectivity are required. This paper presents an optimisation of an acrylamide-based photopolymer formulation for an improved refractive index modulation and recording speed. This was achieved by studying the effect of the concentration of acrylamide and the influence of different initiators in the photopolymer composition on the diffraction efficiency of holographic gratings. Two initiators of different molecular weights were compared: triethanolamine (TEA) and methyldiethanolamine (MDEA). A fivefold increase in the rate of grating formation was achieved through the modification of the acrylamide concentration alone, and it was also found that holograms recorded with MDEA as the initiator performed the best and recorded up to 25% faster than a TEA-based photopolymer. Finally, tests were carried out on the stability of the protected and unprotected photopolymer layers when subjected to UV light. The properties exhibited by this photopolymer composition make it a promising material for the production of optical elements and suitable for use in applications requiring prolonged exposure to UV light when protected by a thin melinex cover.

Electrical and network properties of flexible silver-nanowire composite electrodes under mechanical strain.

Flexible and conductive silver-nanowire photopolymer composites are fabricated and studied under mechanical strain. The initial resistances of the unstretched flexible composites are between 0.27 Ω mm-1 and 1.2 Ω mm-1 for silver-nanowire concentrations between 120 μg cm-2 and 40 μg cm-2. Stretching of the samples leads to an increased resistance by a factor of between 72 for 120 μg cm-2 and 343 for 40 μg cm-2 at elongations of 23%. In order to correlate network morphology and electrical properties, micrographs are recorded during stretching. The Fiber Image Network Evaluation (FINE) algorithm determines morphological silver-nanowire network properties under stretching. For unstretched and stretched samples, an isotropic nanowire network is found with only small changes in fiber orientation. Monte-Carlo simulations on 2D percolation networks of 1D conductive wires and the corresponding network resistance due to tunneling of electrons at nanowire junctions confirm that the elastic polymer matrix under strain exhibits forces in agreement with Hooke's law. By variation of a critical force distribution the resistance curves are accurately reproduced. This results in a model that is dominated by quantum-mechanical tunneling at nanowire junctions explaining the electrical behavior and the sensitivity of nanowire-composites with different filler concentrations under mechanical strain.

Defect control during femtosecond projection two-photon lithography

Two-photon lithography (TPL) is a photopolymerization-based additive manufacturing technique that enables fabrication of millimeter scale complex three-dimensional (3D) structures with submicron features. Despite this unique capability, TPL has experienced limited industrial adoption due to its low throughput. The recently developed parallel projection technique, called femtosecond projection TPL (FP-TPL), is a promising approach to scale up this process as it increases the throughput up to three orders of magnitude. However, it requires tuning of process parameters, including photopolymer material properties, to minimize over-polymerization-based defects. Here, we show how a modification of the optical projection strategy can be used to control these over-polymerization defects without tuning the photopolymer composition. Through optical modeling of the projection technique, we show that these defects can be minimized by altering the density of the projected mask. In addition, the aspect ratio of the submicron features can by reduced from more than 2 to 1.2. Thus, this optimal projection strategy transforms FP-TPL into a more robust process suitable for high-throughput high-quality 3D printing of micro and nanoscale structures.

Устранение дисколорита зубов фронтального отдела верхней челюсти с использованием современных фотокомпозитных материалов

The problem of hard tissues of teeth discoloration treatment is relevant for modern practical dentistry due to the widespread use of endodontic treatment of anterior teeth, dental preservation operations and therapeutic treatment of caries and non-carious lesions of hard tissues of teeth. Teeth discoloration quite often happens as a complication of endodontic treatment, injuries, secondary caries and other lesions of hard tissues. The article describes a clinical case of the removal of discoloration of the front teeth of the upper jaw (after a tooth-preserving operation and previously performed tooth restorations) using the modern photopolymer composites material «Jen-Radiance» and «Jen-Favorite LC» made in Ukraine.

UV-Cured Poly(Ethylene Glycol) Diacrylate/Carbon Nanostructure Thin Films. Preparation, Characterization, and Electrical Properties

Carbon nanoallotropes such as carbon nanotubes, graphene, and their derivatives have been combined with a plethora of polymers in the last years to develop new composite materials with interesting properties and applications. However, the area of photopolymer composites with carbon nanostructures has not been analogously explored. In the present article, we study the photopolymerization of poly(ethylene glycol)diacrylate (PEGDA) enriched with different carbon nanoallotropes like graphene, pristine and chemically modified carbon nanotubes (CNTs and fCNTs), and a hybrid of graphene and CNTs. The products were characterized by several microscopic and spectroscopic techniques and the electrical conductivity was studied as a function of the concentrations of carbon nanoallotropes. In general, stable thin films were produced with a concentration of carbon nanostructures up to 8.5%, although the addition of carbon nanostructures in PEGDA decreases the degree of photopolymerization, and PEDGA/carbon nanostructure composites showed electrical conductivity at a relatively low percentage.

Hydrophobic composite resins using a novel allylic urethane monomer as additive

The purpose of this study is to report the formulation of photopolymerizable composites resins with hydrophobic behavior using a new urethane monomer (ETODC) as additive. The ETODC monomer was used together with Bis-GMA and TEGDMA to formulate a new organic matrix system. Mechanical and hydrophobic behavior were studied, also volumetric shrinkage, viscosity, polymerization kinetics and cytotoxicity were analyzed. Results were compared with a control resin prepared with Bis-GMA and TEGDMA. The results show that mechanical properties and volumetric shrinkage did not present statistical differences between the studied groups. When compared with the control material, the experimental resin formulated with the ETODC monomer showed higher hydrophobic behavior and higher values of degree of conversion and polymerization rate.

Calcium forms of zeolites A and X as fillers in dental restorative materials with remineralizing potential

Abstract Zeolites A- and X-type were synthesized and subjected to the ion exchange to obtain their calcium forms which were further impregnated with methacrylic acid as bonding agent to improve the bonding between these zeolite fillers and components of methacrylic matrix in a final composites. The structure of synthesized zeolites, as well as impregnation efficiency, were confirmed by several analytical methods. The ability to release calcium ions, which are remineralizing agents, was confirmed after incubation of zeolite samples in saline. On the basis of these inorganic fillers a series of methacrylic photopolymerizable composites with potential dental applications were prepared and examined. Typical properties of these composites, such as depth of cure, mass stability and mechanical properties were examined. Their ability to release remineralizing calcium ions was also checked. All examined properties were dependent on the composition of the materials, i.e. the type of a filler, its synthesis method and surface impregnation. Obtained results showed that prepared zeolite fillers are beneficial for dental composites with remineralizing potential.

Formation of Optical Vortices by Controllable Holographic Diffraction Structures in Liquid Crystal – Photopolymer Compositions

Formation of optical vortices by Gaussian light beams diffraction on holographically formed diffractive optical elements (DOE) in polymer-dispersed liquid crystals (PDLC) is theoretically described. The feature of investigated DOEs is in their special structure designed to convert the incident light fields into Bessel-like. Numerical simulations for the external electric field’s interaction on these DOEs are obtained. Its influence on the light beams conversion efficiency is studied. The possibility to create electrically controllable transformation elements in PDLCs is theoretically justified.

Robust thermostable polymer composition based on poly[N,N′-(1,3-phenylene)isophthalamide] and 3,3-bis(4-acrylamidophenyl)phthalide for laser 3D printing

A photopolymer composition based on poly[N,N′-(1,3-phenylene)isophthalamide] and 3,3-bis(4-acrylamidophenyl)phthalide was developed and utilized for the formation of 3-dimensional structures using the laser stereolithography method with a high reproducibility and the absence of any autopolymerization effects. The obtained 3D structures were mechanically strong and characterized by a high thermal stability (up to 415 °C), which makes them promising as high-tech plastics for constructional purposes.

Temperature-sensitive luminescent photopolymer activated by europium β-diketonate complexes

Photopolymer luminescent compositions containing chelate complexes of Eu3 + with 2-naphthoyltrifluoroacetone and trioctylphosphine oxide as a luminescent dopant have been developed for the photopolymer-based 3-D printing techniques. Photocured samples of photopolymer compositions are transparent in the visible range and have bright red luminescence under the UV excitation. Photophysical studies have revealed that photocured samples possess high quantum yields of luminescence up to 0.59 and monoexponential luminescence decay with 640 μs lifetime at 293 K. It was found that the luminescence of photocured samples is temperature-dependent; the luminescence lifetime of Eu3 + ions decreases threefold during the heating from 293 to 373 K. The combination of monoexponential luminescence decay and high quantum yield is very promising for printing of temperature sensors.