Reaction-Induced Phase Separation in Crystallizable Micro- and Nanostructured High Melting Thermoplastic/Epoxy Resin Blends

Dissipative Particle Dynamics Simulation for Reaction-Induced Phase Separation of Thermoset/Thermoplastic Blends

Reaction-induced phase separation occurs during the curing reaction when a thermoplastic resin is dissolved in a thermoset resin, which enables toughening of the thermoset resin. As resin properties vary significantly depending on the morphology of the phase-separated structure, controlling the morphology formation is of critical importance. Reaction-induced phase separation is a phenomenon that ranges from the chemical reaction scale to the mesoscale dynamics of polymer molecules. In this study, we performed curing simulations using dissipative particle dynamics (DPD) coupled with a reaction model to reproduce reaction-induced phase separation. The curing reaction properties of the thermoset resin were determined by ab initio quantum chemical calculations, and the DPD parameters were determined by all-atom molecular dynamics simulations. This enabled mesoscopic simulations, including reactions that reflect the intrinsic material properties. The effects of the thermoplastic resin concentration, molecular weight, and curing conditions on the phase-separation morphology were evaluated, and the cure shrinkage and stiffness of each cured resin were confirmed to be consistent with the experimental trends. Furthermore, the local strain field under tensile deformation was visualized, and the inhomogeneous strain field caused by the phase-separated structures of two resins with different stiffnesses was revealed. These results can aid in understanding the toughening properties of thermoplastic additives at the molecular level.

An overview of viscoelastic phase separation in epoxy based blends

The viscoelastic effects during reaction induced phase separation play an important role in toughening epoxy-based blends. The large difference in molecular weight/glass transition temperature between the blend components before the curing reaction results in dynamic asymmetry, causing viscoelastic effects during phase separation accompanying the curing reaction. This review will focus on the key factors responsible for viscoelastic phase separation in epoxy-based blends and hybrid nanocomposites. Time-resolved characterization techniques such as rheometry, small angle laser light scattering, optical microscopy etc., are mainly used for monitoring the viscoelastic effects during phase separation. Incorporation of nanofillers in epoxy thermoplastic blends enhances the viscoelastic phase separation due to the increase in dynamic asymmetry. Different theoretical models are identified for the determination of processing parameters such as temperature, viscosity, phase domain size, and other parameters during the viscoelastic phase separation process. The effect of viscoelastic phase separation has a very strong influence on the domain parameters of the blends and thereby on the ultimate properties and applications.

Epoxy/methyl methacrylate acrylonitrile butadiene styrene (MABS) copolymer blends: reaction-induced viscoelastic phase separation, morphology development and mechanical properties

Epoxy/MABS blends undergo viscoelastic phase separation during curing due to the dynamic asymmetry of the phases and a significant improvement in the mechanical properties of the system is observed.

Fabrication of a superhydrophilic epoxy resin surface via polymerization-induced viscoelastic phase separation

A superhydrophilic epoxy resin surface was fabricated through polymerization-induced viscoelastic phase separation, which could be eliminated by chain disentanglement.

Morphological adjustment determines the properties of cationically polymerized epoxy resins

Method of integrating a crystalline polyester into an epoxy resin determines morphology and by this mechanical properties.

Dual effects of mesoscopic fillers on the polyethersulfone modified cyanate ester: enhanced viscoelastic effect and mechanical properties

Enlarging the filler content and decreasing the filler size contribute to enhancing both viscoelastic effect and mechanical property of polyethersulfone modified cyanate system.

Complex phase separation in poly(acrylonitrile-butadiene-styrene)-modified epoxy/4,4'-diaminodiphenyl sulfone blends: generation of new micro- and nanosubstructures

The epoxy system containing diglycidyl ether of bisphenol A and 4,4'-diaminodiphenyl sulfone is modified with poly(acrylonitrile-butadiene-styrene) (ABS) to explore the effects of the ABS content on the phase morphology, mechanism of phase separation, and viscoelastic properties. The amount of ABS in the blends was 5, 10, 15, and 20 parts per hundred of epoxy resin (phr). Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were employed to investigate the final morphology of ABS-modified epoxy blends. Scanning electron microscopic studies of 15 phr ABS-modified epoxy blends reveal a bicontinuous structure in which both epoxy and ABS are continuous, with substructures of the ABS phase dispersed in the continuous epoxy phase and substructures of the epoxy phase dispersed in the continuous ABS phase. TEM micrographs of 15 phr ABS-modified epoxy blends confirm the results observed by SEM. TEM micrographs reveal the existence of nanosubstructures of ABS in 20 phr ABS-modified epoxy blends. To the best of our knowledge, to date, nanosubstructures have never been reported in any epoxy/thermoplastic blends. The influence of the concentration of the thermoplastic on the generated morphology as analyzed by SEM and TEM was explained in detail. The evolution and mechanism of phase separation was investigated in detail by optical microscopy (OM) and small-angle laser light scattering (SALLS). At concentrations lower than 10 phr the system phase separates through nucleation and growth (NG). However, at higher concentrations, 15 and 20 phr, the blends phase separate through both NG and spinodal decomposition mechanisms. On the basis of OM and SALLS, we conclude that the phenomenon of complex substructure formation in dynamic asymmetric blends is due to the combined effect of hydrodynamics and viscoelasticity. Additionally, dynamic mechanical analysis was carried out to evaluate the viscoelastic behavior of the cross-linked epoxy/ABS blends. Finally, apparent weight fractions of epoxy and ABS components in epoxy- and ABS-rich phases were evaluated from T(g) analysis.

Theory and computation of photopolymerization-induced phase transition and morphology development in blends of crystalline polymer and photoreactive monomer

A hypothetical phase diagram of a crystalline polymer/photoreactive monomer mixture has been calculated on the basis of phase field (PF) free energy of crystal solidification in conjunction with Flory-Huggins (FH) free energy of liquid-liquid demixing to guide the morphology development during photopolymerization of poly(ethylene oxide)/triacrylate blend. The self-consistent solution of the combined PF-FH theory exhibits a crystalline-amorphous phase diagram showing the coexistence of solid+liquid gap bound by the liquidus and solidus lines, followed by an upper critical solution temperature at a lower temperature. When photopolymerization was triggered in the isotropic region, i.e., slightly above the crystal melting transition temperatures, the depressed melting transition line moves upward. When it surpasses the reaction temperature, both crystallization and phase separation occur. The temporal evolution of phase morphology is examined in the context of time-dependent Ginzburg-Landau equations coupled with the energy balance (heat conduction) equation using the aforementioned PF-FH free-energy densities. Of particular interest is that the emerged morphology in the crystalline blends depends on the competition between dynamics of liquid-liquid phase separation and/or liquid-solid phase transition (i.e., crystallization) and photopolymerization rates.

Facile approach to the fabrication of a micropattern possessing nanoscale substructure

On the basis of the combined technologies of photolithography and reaction-induced phase separation (RIPS), a facile approach has been successfully developed for the fabrication of a micropattern possessing nanoscale substructure on the thin film surface. This approach involves three steps. In the first step, a thin film was prepared by spin coating from a solution of a commercial random copolymer, polystyrene-r-poly(methyl methacrylate) (PS-r-PMMA) and a commercial crosslinker, trimethylolpropane triacrylate (TMPTA). In the second step, photolithograph was performed with the thin film using a 250 W high-pressure mercury lamp to produce the micropattern. Finally, the resulting micropattern was annealed at 200 degrees C for a certain time, and reaction-induced phase separation occurred. After soaking in chloroform for 4 h, nanoscale substructure was obtained. The whole processes were traced by atomic force microscopy (AFM), X-ray photoelectron spectrometry (XPS), and Fourier transform infrared (FTIR) spectroscopy, and the results supported the proposed structure.