Nanostructured Epoxy Composites

Polymerization-Induced Phase Separation in Rubber-Toughened Amine-Cured Epoxy Resins: Tuning Morphology from the Nano- to Macro-scale

“…Indeed, various morphologies have been produced with the PIPS strategy including co-continuous, − isolated or fused globular structures, − lamellae, − and cylinders , with applications for membranes, − sorbents, , functional coatings, , and UV-cured dental materials. , Owing to their versatile and pre-designed molecular nature, block copolymers are well suited for PIPS in thermosets where the molecular weight and volume fraction of polymer blocks regulate the domain size and morphology of the phase-separated systems. Early examples of block copolymer-driven PIPS employed amphiphilic copolymers blended with epoxy systems to yield highly ordered domains down to tens of nm. ,− However, the lack of a covalent bond connecting the secondary polymer and the thermoset matrix in these early works resulted in the expulsion of the copolymers from the matrix and set a lower bound for the domain size (e.g., above ∼10 nm) . Conversely, reactive block copolymers capable of forming cross-links in situ ensure that the segregating phases are covalently linked, thereby providing a convenient handle to tune domain size through the relative volume fraction of the segregating components. , In perhaps the most pertinent example, Seo and Hillmyer prepared polylactide (PLA) terminated with a trithiocarbonate chain-transfer agent to serve as an initiator for the subsequent in situ polymerization and PIPS of poly­(styrene- co -divinylbenzene) (PS-DVB), leading ultimately to a bicontinuous array of 4–10 nm PLA and PS-DVB domains .…”

Self-Assembly and Phase Transformation of Block Copolymer Nanostructures in Ionic Liquid-Cured Epoxy

“…There are two primary mechanisms for the formation of nanostructures in epoxy/BCP blends: self-assembly and reaction-induced microphase separation (RIMPS). 4,9 In both cases, the structures are the result of the relative miscibility of the BCP polymer blocks in the epoxy resin, where the less miscible block forms the nanophase-separated domains and the more miscible block forms the interface with the epoxy. In the self-assembly mechanism, the epoxy-phobic block immediately phase separates from the epoxy resins, while the epoxy-philic block is dissolved in the resin.…”

“…The incorporation of block copolymers (BCPs) into epoxy is an important method for improving the properties of epoxy thermosets. The BCPs can form nanostructures in the epoxy, which not only increase the toughness of the material − but also provide opportunities for nanoparticle templating which can impart multifunctional properties to the epoxy . A variety of nanostructures have been demonstrated, including disordered spherical micelles, wormlike micelles, and vesicles as well as ordered structures- for example, spheres on a body centered-cubic (BCC) lattice, hexagonally packed cylinders, and lamellar morphologies. ,, The nanostructures are highly dependent on the free energy interactions between BCP components, epoxy monomers, and the curing agents.…”

“…There are two primary mechanisms for the formation of nanostructures in epoxy/BCP blends: self-assembly and reaction-induced microphase separation (RIMPS). , In both cases, the structures are the result of the relative miscibility of the BCP polymer blocks in the epoxy resin, where the less miscible block forms the nanophase-separated domains and the more miscible block forms the interface with the epoxy. In the self-assembly mechanism, the epoxy-phobic block immediately phase separates from the epoxy resins, while the epoxy-philic block is dissolved in the resin. − For RIMPS, both blocks are initially miscible in the epoxy resin, but as the epoxy begins to cure, one of the blocks is expelled from the growing network and nanophase separates. − While either mechanism can be used to induce improved toughness in the materials, the self-assembly mechanism is preferred for applications that involve nanoparticle templating since the micelles can remain intact throughout the curing process, thus minimizing nanoparticle aggregation.…”

“…Much of the previous work on changing the nanostructure and the formation mechanisms in the literature has focused on varying the BCPs in traditional epoxy resin/diamine curing agent formulations. ,,, However, many of these BCPs are cumbersome to synthesize, which can limit their applications. One exception is poly­(ethylene oxide- b -propylene oxide- b -ethylene oxide) (PEO–PPO–PEO).…”