Understanding the Rheology of Polymer–Polymer Interfaces Covered with Janus Nanoparticles: Polymer Blends versus Particle Sandwiched Multilayers

Abstract

Interfacial rheology is crucial in dictating morphology and ultimate properties of particle-stabilized polymer blends, but is challenging to be determined. In this study, a fully polymeric dumbbell-shaped Janus nanoparticle (JNP) of polymethyl methacrylate (PMMA) and polystyrene (PS) spheres with equal sizes (∼80 nm) was prepared and used as an efficient compatibilizer for PMMA/PS blends. The JNPs were preferentially localized at the PMMA/PS interface, thereby reducing the interfacial tension and refining the morphology in both droplet-matrix and co-continuous type blends, whereby a JNP concentration ∼2.5 wt % is sufficient to reach a saturation in droplet size reduction due to compatibilization. Based on the linear viscoelastic moduli and corresponding relaxation spectra (H(τ)*τ) of JNP-compatibilized droplet-matrix blends, besides the droplet shape relaxation time (τF), a longer relaxation time (τβ), typically related to interfacial viscoelasticity, was readily identified. The dependence of τβ on the JNP concentration (W JNPs) was significantly dominated by the droplet size reduction induced by the JNP compatibilization, with τβ decreasing with increasing W JNPs. The viscoelastic properties extracted from τβ typically originate from a combination of gradients in interfacial tension due to the particle redistribution at the droplet interface (Marangoni stresses) and the deviatoric stresses of intrinsic rheological origin. The latter originate from the intrinsic viscoelasticity of the particle-laden interface, which is enhanced by particle jamming and particle–polymer interactions, such as entanglements between chains from the polymeric spheres and those penetrating from the bulk into the spheres. To address the challenge of isolating these contributions, a JNP-sandwiched PMMA/PS multilayer structure was designed to exclude the effect of Marangoni stresses and droplet curvature, thus having no τF but a new relaxation (τ′β), which characterizes the contribution of intrinsic interfacial viscoelasticity. The τ′β was observed to increase with JNP coverage (Σ) following the Vogel–Fulcher–Tammann model that is typically used to describe the divergent behavior of the “cage” effect in classical colloidal glasses. Moreover, a multimode Maxwell model fitting allows to split the interfacial relaxation into the confined diffusion of JNPs within their cage and the entanglements between the JNPs and the bulk.

Fabrication of High Mechanical Properties and Wear: Resistance UHMWPE/PP Composites by Incorporating SiC Nanoparticles under a Consecutive Elongational Flow

“…Many strategies have been developed to improve the compatibility of blends, such as adding reactive polymers, block copolymers and functional nano-particles [12][13][14]. Among them, the unique properties of nano-particles have promoted a great deal of interest to improve the compatibility of blends and explore advanced multifunctional materials [15,16]. The silicon carbide nanoparticles (nano-SiC), possessing high hardness, resistance to abrasion, high thermal conductivity along with unique nanometer effect have been used as wear resistance modifier or thermal conductivity filler for the enhanced function of polymer composites [17,18].…”

Extensional Viscosity of Immiscible Polymer Multi-Nanolayer Films: Signature of the Interphase

“…To circumvent these phenomena, compatibilization has been mastered for a long time industrially to achieve suitable properties for such immiscible blends. It consists of modifying the interface with several possible strategies, such as the addition or the in situ formation of a copolymer that will segregate at the interface, resulting in a more diffused interface that allows entanglements similar to what is occurring at short times in miscible systems, , the use of nanoparticles − and cosolvents, or through ionic bonds and electrostatic correlations …”

Janus Hemispheres through Controlled Polymerization-Induced Phase Separations within Wax Droplets

“…Janus particles, containing distinct multifunctional partitions, have attracted increasing academic and industrial interests due to their ingenious microstructures, controllable preparation, and customizable functionalization. − Most Janus particles are amphiphilic, showing unique behaviors at a biphasic interface . Janus particles have been employed as emulsifiers at the liquid–liquid interface, − stabilizers at the air–liquid interface, − compatibilizers at the solid–solid interface, − and functional layers on the air–solid surface. − Janus particles, meanwhile, can spontaneously assemble as an oriented monolayer at the interface, forming a functional interface in the high-performance composite. ,− Hence, a feasible synthetic strategy is required to control the microstructures of Janus particles and endow them with multifunctionalities.…”