Three grades of poly(ethylene terephthalate) (PET) produced by different synthesis routes and with different molar masses were reactively extruded with two tetra‐functional chain extenders, i.e., pyromellitic dianhydride (PMDA) and tetraglycidyl diamino diphenyl methane (TGDDM). The preferred reactivity of the coupling agents led to different long‐chain branched (LCB) structures, which can be related to different hydroxyl and carboxyl end group concentrations of the PET grades investigated. The complex viscosity and the transient elongational viscosity increased by up to two decades. Both the activation energy of flow and the loss angle indicate long‐chain branching. A more quantitative assessment of the extent of strain hardening was achieved by application of the molecular stress function (MSF) model. The two material parameters of the model revealed different behaviors depending on the chain extender used. The initial molar mass of PET and the concentration of end groups, i.e., hydroxyl and carboxyl, determine the structure of the polymer molecules. PMDA proved to be an excellent coupling agent for industrial processing which induces reproducibly either a star‐like, comb‐like, or randomly branched structure depending on the concentration of coupling agent added and the hydroxyl concentration of the PET employed. TGDDM led to a hyperbranched structure. POLYM. ENG. SCI., 59:396–410, 2019. © 2018 Society of Plastics Engineers

Domains of cocontinuous polymer blends coarsen during annealing. In general, coarsening undergoes two regimes: linear growth followed by slower nonlinear growth. While the linear regime is well understood by several theories, the number of studies on the nonlinear regime is scarce and often inconclusive. Herein, we examine the entire spectrum of the coarsening of cocontinuous polymer blends using an in situ high-temperature confocal rheology technique. By linking 4-dimensional microscopic details (time evolution of three-dimensional microscopic details) with the rheological properties, we demonstrate that the transition to the nonlinear regime is associated with the onset of droplet formation during the coarsening of these blends. Such transitions and morphological changes occurred only in the blends with high interfacial tension to zero-shear viscosity ratio (Γ/η0). This phenomenon provides a framework for comprehensive model development. By analyzing the data from the literature, we propose that there exists a critical Γ/η0 ratio beyond which the system undergoes such transitions.

Arresting morphological evolution of spinodally decomposing heterogeneous mixtures via the addition of colloidal particles has resulted in the discovery of new classes of bicontinuous materials, viz., bicontinuous interfacially jammed emulsion gels (bijels) and most recently bicontinuous intraphase jammed emulsion gels (bipjels). Here, we demonstrate how the extent of particle wettability and particle–particle interactions govern the ultimate structure formed. We present the multi-phase lattice Boltzmann method (LBM) integrated with a discrete particle model with two particle–particle collision models, the classic hard-sphere model and a new bonding collision model, to predict the final state of spinodally decomposing fluid mixtures containing solid particles. We show that the elastic collision model yields either the formation of emulsions or bijels, while only the bonding collision model on particles with preferential wettability for one phase can predict bipjels formation. In the case of bipjels, a delicate balance between the dynamics of evolving interface and the strength of particle–particle aggregates is required to restrict the interfacial motion. These results are consistent with experimental findings, suggesting that the presence of smaller particles with high particle–particle interactions can yield the formation of bipjels and consequent isolation of hierarchically porous materials.

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Interfacially localizing particles in co-continuous polymer blends requires a complex interplay between the properties of polymers, such as interfacial tension between them, Γ, viscosity, η, viscosity ratio between them, and particle properties, such as particle size and particle surface chemistry. Here, we investigate the formation and coarsening dynamics of four co-continuous blend composites based on polypropylene, PP (or linear low-density polyethylene), and poly(ethylene-co-vinyl acetate), EVA filled with pristine silica of two sizes (140 and 250 nm). By choosing polymer blend components with different viscosities and interfacial tensions and particles with varying size and size distributions, we were able to elucidate their relative contributions in the stabilization of co-continuous polymer microstructures. By utilizing confocal rheology, we show that the evolution of storage modulus during coarsening of polymer blend composites is primarily dependent on the strength of the initial interfacial particle network. Our findings indicate that the initial domain size and kinetic control of interfacial particle localization in co-continuous polymer blends are determined by the Γ/η ratio of the neat blend. However, this relationship does not hold in low viscosity systems. When polymer blend viscosity is lower, it reduces the kinetic barrier at the interface, leading to a higher proportion of particles localizing in the favorable EVA phase. We also find that the smaller particles have a higher propensity for interfacial localization. These findings provide insight into the success of kinetic particle trapping at the interface of co-continuous blends and the resulting composite properties based on the choice of component properties.