Rigid Epoxy Resin Research Articles

A rigid microfluidic chip for high-throughput fluorescence-activated cell sorting

Fluorescence-activated cell sorting (FACS) holds great promise for the separation of single cells or cell populations according to specific light scattering and fluorescent characteristics. Here, we present a new perspective on microfluidic FACS (μFACS) with predictable geometry, which meets the requirements of high-throughput analysis and sorting. Instead of the widely applied elastic polydimethylsiloxane (PDMS), a rigid epoxy resin chip was rapidly fabricated and irreversibly encapsulated to eliminate channel deformation (tenfold reduction) and enhance performance while meeting high pressure (>600 kPa) and high flow rate application scenarios. Fluorescence discrimination and particle differentiation were additionally validated in a self-contained μFACS system using calibration microspheres and mammalian cells. The μFACS chip and system were integrally optimized to achieve a minimum interval (0.58 ms) with a mean flow rate of 1.5 m/s. Ultimately, event recording and automated sorting were accomplished in real time while achieving a sorting efficiency of 87% at cell throughput of 8,000 events/s. This rigid chip for high-throughput μFACS, which is independent of the physical properties of cells could pave the way for cell screening in plasma samples for personalized medicine.

Evaluations of atomic-resolution strain fields using molecular dynamics simulations combined with corrected smoothed particle hydrodynamics

Deformation analyses of polymeric materials using molecular dynamics (MD) simulations are very useful in evaluating the physical properties based on the atomic features. Generally, the average responses of a system, such as the stress–strain response, are evaluated, but a molecular chain around a solid should deform in an unusual manner in a composite system, such as a solid/polymer system. This may lead to damage and a microscopic inelastic deformation, ultimately affecting the macroscopic behavior of the material. In this study, we propose a technique for use in evaluating the local pseudo-continuum deformation quantities, such as strain and stretch, during MD simulations by introducing deformation analysis via corrected smoothed particle hydrodynamics in a total Lagrangian formulation. Three different types of systems (uniform deformation of an Au crystal, cured resin sandwiched between silica walls, and cured resin containing a nanofiller) are considered, and the unique local deformations in the composite systems are quantitatively evaluated. In particular, local constitutive behavior can be evaluated using this technique, and in the sandwiched system, a high correlation is observed between the local stiffness inhomogeneity and the cohesive failure point. In the filler-containing system, a highly rigid epoxy resin layer is observed around the filler, and local deformation at the poles of the filler is confirmed owing to elongation. The observed trends are consistent with the experimental results. The insights obtained should contribute to the evaluation and understanding of microscopic deformation and damage, which is the beginning of macroscopic failure in a composite material.

Bulk Polymerization of Thermoplastic Shape Memory Epoxy Polymer for Recycling Applications.

Conventional epoxy polymers are thermo-set and difficult to recycle and reuse. In this study, a series of linear thermoplastic epoxy polymers (EPx) with shape memory properties were prepared by using a bifunctional monoamine diglycolamine (DGA) as a curing agent and an equivalent amount of bifunctional rigid epoxy resin (E-51) and bifunctional flexible epoxy resin (polypropylenglycol diglycidyl ether, PPGDGE) in a bulk polymerization reaction. The results showed that these samples can fully react under the curing process of, 60 °C/2 h, followed by 80 °C/2 h, followed by 120 °C/2 h. The introduction of different contents of PPGDGE can adjust the Tg of the material to adapt to different environmental requirements, and can significantly increase the fracture strain of the material and improve its micro-phase separation structure. Thus, Rf of the material is close to 100%, and Rr is increased from 87.98% to 97.76%. Importantly, this linear chain structure allows the material to be easily recycled and reprocessed by dissolving or melting, and also means the material shows potential for 3D printing or other thermoplastic remolding.

Ultra-high modulus epoxy resin reinforced by intensive hydrogen bond network: From design, synthesis, mechanism to applications

According to classic polymer physics, free volume is the decisive factor for the modulus of resin matrix. In rigid epoxy resin systems with high crosslink density, it's difficult to further reduce the free volume. Designing new epoxy resins from the perspective of molecular structure design is a feasible approach, however, how to select potential structures is a great challenge. In this paper, a polar epoxy resin with amide bond was efficiently synthesized, which was ingeniously designed according to the relationship between structure and performance as well as high-throughput screening. The free volume of this resin could be reduced by introducing high density of hydrogen bonds with strong bond energy based on Density Functional Theory (DFT) calculations. After formulation design, the flexural modulus of this resin was up to 6568 MPa using m-phenylenediamine (MPD) as curing agent, which is the highest level ever reported, and the theoretical mechanism of hydrogen bond on the modulus enhancement for high crosslink density epoxy resin was investigated in detail. The resin with ultra-high modulus as well as good interface property has great potential in high-performance carbon fiber composite industry.

Design Guidelines for Rigid Epoxy Resins with High Photon Upconversion Efficiency: Critical Role of Emitter Concentration.

For the practical application of triplet-triplet annihilation-based photon upconversion (TTA-UC), the development of rigid, transparent, air-stable, and moldable materials with a high TTA-UC efficiency remains a challenging issue. In addition to the noncovalent introduction of ionic liquid emitters into the epoxy network, we covalently introduce emitters with polymerization sites to increase the emitter concentration to 35.6 wt %. A TTA-UC quantum yield ΦUC of 5.7% (theoretical maximum: 50%) or a TTA-UC efficiency ηUC of 11.4% (theoretical maximum: 100%) is achieved, which is the highest value ever achieved for a rigid polymer material. More importantly, the high emitter concentration speeds up the triplet diffusion and suppresses the back energy transfer from the emitter to sensitizer so that the sensitized emitter triplet can be effectively utilized for TTA. The generality of our finding is also confirmed for epoxy resins of similar emitter unit concentrations without the ionic liquid. This work provides important design guidelines for achieving highly efficient TTA-UC in rigid solid materials, which has been very difficult to achieve in the past. Furthermore, the solid-state TTA-UC exhibits high air stability, reflecting the high oxygen barrier performance of epoxy resins. The high moldability of epoxy resins allows the construction of upconversion materials with complex geometries at nano- to macroscopic scales.

Low-Cost Fabrication of Polyvinyl Alcohol-Based Personalized Vascular Phantoms for In Vitro Hemodynamic Studies: Three Applications

Abstract Vascular phantoms mimicking human vessels are commonly used to perform in vitro hemodynamic studies for a number of bioengineering applications, such as medical device testing, clinical simulators, and medical imaging research. Simplified geometries are useful to perform parametric studies, but accurate representations of the complexity of the in vivo system are essential in several applications as personalized features have been found to play a crucial role in the management and treatment of many vascular pathologies. Despite numerous studies employing vascular phantoms produced through different manufacturing techniques, an economically viable technique, able to generate large complex patient-specific vascular anatomies, accessible to nonspecialist laboratories, still needs to be identified. In this work, a manufacturing framework to create personalized and complex phantoms with easily accessible and affordable materials and equipment is presented. In particular, three-dimensional (3D) printing with polyvinyl alcohol (PVA) is employed to create the mold, and lost core casting is performed to create the physical model. The applicability and flexibility of the proposed fabrication protocol is demonstrated through three phantom case studies—an idealized aortic arch, a patient-specific aortic arch, and a patient-specific aortic dissection model. The phantoms were successfully manufactured in a rigid silicone, a compliant silicone, and a rigid epoxy resin, respectively; using two different 3D printers and two casting techniques, without the need of specialist equipment.

Bio-based epoxy resin toughening with cashew nut shell liquid-derived resin

With the combinations of diglycidyl ether diphenolate methyl ester (DGEDP-Me), a rigid high-viscosity bio-based epoxy resin and a flexible lower viscosity epoxy resin from cashew nut shell liquid (NC-514), resin viscosity was controlled and important improvements were realized in cured epoxy resin toughness relative to the neat resins. The viscosities of DGEDP-Me/NC-514 mixtures varied from 660 to 26 Pa.s, and curing was performed using stoichiometric amounts of a diamine cross-linker. Using scanning electron microscopy analysis of fractured surfaces, the cured materials were shown to be one-phase. Furthermore, all resin compositions were transparent and have one alpha transition temperature, confirming resin miscibility. Storage modulus values for cured thermosets range from 3000 to 1000 MPa, and alpha transition temperatures varied linearly (158 to 27°C) as a function of the epoxy resin composition. Oscillatory rheology at different weight percentages of the flexible and rigid epoxy resin components was used to determine the average molecular weight between cross-links which was correlated to material toughness. Relative to the neat high-viscosity resin, 1:1 wt/wt mixtures of the rigid and flexible epoxy resin components gave increases in the impact strength and mode I fracture toughness of 136 and 66%, respectively. Higher percentages of the flexible epoxy resin resulted in decreased toughness.

Low Fluorescence Enzyme Matrices Based on Microfabricated SU-8 Films for a Phenol Micro-Biosensor Application

In this contribution, the possibility of using SU-8 photoresist, a polymer widely used in MEMS applications, for the development of inexpensive and disposable optical phenol micro-biosensors is explored. The immobilisation of the enzyme, the encapsulation of the indicator and the patterning of the SU-8 were accomplished simultaneously in a simple one step microfabrication process. The enzyme still showed activity after encapsulation in SU-8 although the process involved its embedding in a hard and rigid epoxy resin matrix. This was carried out by measuring the signal of an oxygen-sensitive indicator (ruthenium-complex) through monitoring of the enzymatic oxidation of phenol which consumes oxygen. Films without enzyme showed negligible variation in fluorescence intensity upon phenol addition, whereas films with encapsulated enzyme and oxygen-sensitive fluorescent indicators showed a very clear change in fluorescence intensity upon addition of phenol. The current work demonstrates a new concept of a low cost immobilisation technique in combination with the microfabrication process for biosensor technology.

A novel enzyme entrapment in SU-8 microfabricated films for glucose micro-biosensors

The present work investigates the utilisation of the widely used SU-8 photoresist as an immobilisation matrix for glucose oxidase (GOx) for the development of glucose micro-biosensors. The strong advantage of the proposed approach is the simultaneous enzyme entrapment during the microfabrication process within a single step, which is of high importance for the simplification of the BioMEMS procedures. Successful encapsulation of the enzyme GOx in “customised” SU-8 microfabricated structures was achieved through optimisation of the one-step microfabrication process. Although the process involved contact with organic solvents, UV-light exposure, heating for pre- and post-bake and enzyme entrapment in a hard and rigid epoxy resin matrix, the enzyme retained its activity after encapsulation in SU-8. Measurements of the immobilised enzyme's activity inside the SU-8 matrix were carried out using amperometric detection of hydrogen peroxide in a 3-electrode setup. Films without enzyme showed negligible variation in current upon the addition of glucose, as opposed to films with encapsulated enzyme which showed a very clear increase in current. Experiments using films of increased thickness or enzyme concentration, showed a higher response, thus proving that the enzyme remained active not only on the film's surface, but also inside the matrix as well. The proposed enzyme immobilisation in SU-8 films opens up new possibilities for combining BioMEMS with biosensors and organic electronics.

Curing kinetics and morphology of IPNs from a flexible dimethacrylate and a rigid epoxy via sequential photo and thermal polymerization

The curing kinetics and morphology of Interpenetrating polymer networks (IPNs) formed from a rigid epoxy resin thermally cured by an anhydride, and a photocured flexible dimethacrylate resin, have been studied by temperature ramping differential scanning calorimetry (DSC), near-infrared (NIR), and dynamic mechanical thermal analyzer (DMTA). This combination of cross-linkable resins permits the partial or complete cure of each component independent of the other. Also, since the monomers are polar but chemically dissimilar thermosetting resins, their IPNs should offer considerable variation in properties. DSC studies showed that the possible interactions between each component in the IPN could be minimized, but that the curing rate and conversion of the second polymerizing component was affected by vitrification, network topology, or phase separation in the IPN. NIR was also used to confirm that virtually independent cure was achievable by the combination of the thermal and photochemical methods. Dynamical mechanical thermal analysis was used to investigate the effect of curing one or both components and of order of curing on the phase morphology of the IPN. The modulus in the rubbery region also provided information on loop formation and co-continuity of each network component through the polymer matrix. The modulus and tan δ curves showed large differences in the glass transition region of the IPNs with different curing schedules, however phase separation occurred in all fully cured IPNs. These observations conflict with a previously advanced hypothesis that rapid polymerization and gelation of the last-cured component interlocks the two networks into a single phase structure and leads to the inclusion of a caveat that the components require sufficient attraction for interlocking of the networks to occur.

Polyester composites reinforced with recycled FR‐4 epoxy laminates

AbstractThe feasibility of using recycled FR‐4 epoxy laminates as reinforcing fillers in manufacturing unsaturated polyester (UP) composites was studied using differential scanning calorimetry (DSC), and flexural tests. UP resins filled with recycled laminates had a higher flexural strength and modulus than the plain UP because of energy dissipation effects from glass fibers and rigid epoxy resins in the laminates. The size and loading of the laminates affected the flexural properties of the molded products. The addition of CaCO3 fillers and Cu decreased the flexural strength but promoted the flexural modulus of the UP. As revealed by DSC measurements the presence of laminates affected the free‐radical reaction of the UP resin and decreased the curing rate. The curing kinetics were also dependent on the size and relative content of the laminates added.

The use of recycled printed circuit boards as reinforcing fillers in the polyester composite

Abstract The feasibility of using recycled printed circuit boards (PCB) as reinforcing fillers in manufacturing unsaturated polyester (UP) composites was studied using differential scanning calorimetry (DSC), and mechanical test. The concentrations of Cu leached from the molded products were also tested. From the DSC measurement, it was obtained that the addition of PCB affected the free radical reaction of the UP resin and decreased curing rates at the beginning stage. The methods of surface treatments also affected the curing kinetics of the UP resin. PCB modified UP resins had higher Tg, and were tougher and stronger than the plain UP because of energy dissipation effects from glass fibers and rigid epoxy resins in the PCB. The impact energy of the specimen increased with increasing the loading of PCB fillers. The size of PCB fillers and the type of surface treatments affected the mechanical properties and the concentrations of copper leached from molded products. As much as 150 parts per hundred PCB c...

Fractographic study of transverse cracks in a fibre composite

Transverse fracture of unidirectional fibre composites was studied in a model glass/epoxy composite in which 1 mm-diameter rods had been used in place of fibres. The fracture surface resulting from transverse cracking in this model system was studied by scanning electron microscopy (SEM). The interaction of the crack with the epoxy matrix resin and the glass rods was the following: Cracks in the resin appeared to have effected a debonding at the glassmatrix interface before reaching the glass. The debonding then propagated along the interface and induced secondary cracks ahead of the primary debonding crack. The confluence of the secondary and primary cracks resulted in sharp ridges being formed on the matrix resin surface, produced by plastic deformation of the rigid epoxy resin. These appeared as a field of parabolic marks. Considering the brittleness of the resin, the amount of plastic deformation indicated by the ridges was astonishing. As the debonding continued around the glass rod, a transverse corrugated texture developed on the resin surface, again produced by plastic deformation. Finally, the cracks reentered the matrix from small patches of polymer adhering especially strongly to the glass surface. The overall fracture energy of transverse cracking of unidirectional fibre composites is suggested to consist, therefore, of the following elements in addition to crack propagation in the matrix resin: (a) the glass-resin debonding before the incoming cracks reach the glass, (b) the initiation of secondary cracks or debonds at the interface, (c) the plastic deformation in generating the ridges on the rigid resin surface, appearing both as the paraboloids and the transverse corrugation, and (d) cracking of the matrix reinitiated at the opposite side of the glass. The use of an enlarged glass reinforcement in this study provided a more direct observation of the properties of transverse crack propagation in composite materials than would have been possible with the small, roughly 10μm fibres.