Effect of selective localization of cellulose nanowhiskers on viscoelastic phase separation

Abstract

Viscoelastic phase separation (VPS) is a fundamental physical phenomenon that creates percolated network structure in dynamically asymmetric mixtures. The object of this study was to investigate the effect of rod shape nanoparticles with different surface chemistries on VPS in the polystyrene/poly(vinyl methyl ether), PS/PVME, blend. For this purpose, hydrophilic (CNWs) and hydrophobic (M‐CNWs) cellulose nanowhiskers (CNWs) were prepared to be used as nanorods. Rheological measurments were employed to investigate the effect of nanowhiskers on phase separation temperature, kinetics of phase separation, and dynamic asymmetry. The evolution of morphology during the phase separation at a fixed quench depth was assessed using polarized optical microscopy. The nanowhiskers were effective in decreasing the correlation length, which slowed down the phase separation. CNWs self‐assembled into the PVME‐rich phase during the phase separation, which led to a decrease in the dynamic asymmetry and beyond a critical volume fraction of CNWs, the VPS mechanism changed to spinodal decomposition (SD). However, in the presence of M‐CNW, the localization of M‐CNWs into the PS‐rich phase enhanced the dynamic asymmetry and at 2 vol% M‐CNWs, the induced PS‐rich network by VPS was arrested. The linear and non‐linear viscoelastic behavior of the samples were studied as well. POLYM. ENG. SCI., 58:928–942, 2018. © 2017 Society of Plastics Engineers

Spherical nanoparticle effects on the lower critical solution temperature phase behavior of poly(ε‐caprolactone)/poly(styrene‐co‐acrylonitrile) blends: Separation of thermodynamic aspects from kinetics

“…Nanofillers in polymer mixtures have been the core subject of lots of studies because of the synergistic effects of nanoparticles on different polymer mixture properties . The large specific surface area of nanofillers has been introduced as the cause of higher thermodynamic stability of polymer mixtures in addition to the enhanced physical, thermal, barrier, and mechanical properties at low loadings . The nanoparticles have been classified as beneficial compatibilizers in immiscible polymer blends, which can effectuate the formation of finer morphology, improved toughness, lower interfacial tension, larger miscibility window, slower phase separation kinetics, and the enhanced solubility of polymeric phases .…”

“…The large specific surface area of nanofillers has been introduced as the cause of higher thermodynamic stability of polymer mixtures in addition to the enhanced physical, thermal, barrier, and mechanical properties at low loadings . The nanoparticles have been classified as beneficial compatibilizers in immiscible polymer blends, which can effectuate the formation of finer morphology, improved toughness, lower interfacial tension, larger miscibility window, slower phase separation kinetics, and the enhanced solubility of polymeric phases . As one of the key characteristics of the multicomponent polymer mixtures containing nanofillers, the phase separation behavior has been the main issue of lots of researches over the last decades …”

“…Along with the theoretical works, the effects of nanofillers on the phase behavior of polymer blends have been critically investigated by using different experimental approaches . Small‐angle light scattering (SALS) and optical microscopy have been widely applied to determine the phase‐transition points of binary polymer blends and filled polymer mixtures . The refractive indices of polymers, film transparency, and thickness are the most important parameters in SALS and optical microscopy measurements that can affect the validity of the results .…”

“…Following the linear viscoelastic responses over the phase transition is one of the well‐established strategies to study the phase behavior of polymer mixtures, which is less affected by the film transparency and thickness . Because of the high sensitivity to the chain repetition time, diffusion, and interfacial viscoelasticity, the rheological measurements can correlate the linear viscoelastic responses of polymer mixtures with subtle structural changes during phase separation process and detect the phase transition in rather early stages . The isothermal frequency sweep at different temperatures over the phase boundary and the isochronal dynamic temperature sweeps by slow heating/cooling the samples from the homogeneous to the phase‐separated region are the general protocols to determine the phase diagram of polymer blends and filled polymer mixtures .…”

“…Because of the high sensitivity to the chain repetition time, diffusion, and interfacial viscoelasticity, the rheological measurements can correlate the linear viscoelastic responses of polymer mixtures with subtle structural changes during phase separation process and detect the phase transition in rather early stages . The isothermal frequency sweep at different temperatures over the phase boundary and the isochronal dynamic temperature sweeps by slow heating/cooling the samples from the homogeneous to the phase‐separated region are the general protocols to determine the phase diagram of polymer blends and filled polymer mixtures . These protocols, especially the dynamic temperature sweeps, have been frequently used for the polymeric mixtures with both upper critical solution temperature (UCST) and lower critical solution temperature (LCST) phase behavior …”