Phase miscibility and dynamic heterogeneity in PMMA/SAN blends through solvent free reactive grafting of SAN on graphene oxide

Abstract

The spatial distribution of nanoparticles in a particular host polymer matrix can be improved by using brush coated nanoparticles. In this work we have grafted styrene-acrylonitrile (SAN) onto the surface of graphene oxide (GO) and investigated as to how the demixing temperature, morphology and volume cooperativity of PMMA/SAN blends are influenced. Grafting of polymer chains on the surface of nanoparticles usually involves the use of large amounts of solvents, many which are detrimental to the environment besides involving cumbersome processes. SAN-g-GO was prepared by a robust solvent-free strategy wherein the cyano group in SAN was replaced by oxazoline groups during melt mixing in the presence of zinc acetate and ethanol amine. These newly created oxazoline groups reacted with the COOH group of GO under melt extrusion resulting in grafting of SAN on the surface of GO sheets. The effect of SAN-g-GO nanoparticles on the demixing, local segmental motions and morphology evolution for different annealing times was carefully investigated in a classical LCST system, PMMA/SAN blend, using melt rheology, modulated DSC and AFM, respectively. The changes in viscoelastic behavior in the vicinity of demixing are investigated systematically for the control, and blends with GO and SAN-g-GO. Various models were used to gain insight into the spinodal decomposition temperatures of the blends. Interestingly, the demixing temperature determined rheologically and the spinodal decomposition temperature increased significantly in the presence of polymer grafted nanoparticles in comparison to the control and blends with GO. The evolution of the morphology, interfacial driven coarsening as a function of temperature and the localization of nanoparticles were assessed using atomic force microscopy. The cooperatively re-arranging regions estimated from calorimetric measurements begin to suggest enhanced dynamic heterogeneity in the presence of GO and SAN-g-GO in the blends. Taken together, our study reveals that the solvent-free approach of grafting SAN onto GO delays demixing, suppresses coalescence and alters cooperative relaxation in PMMA/SAN blends.

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

“…However, G ′ and G ″ increase more quickly by crossing over the metastable region and entering the miscible state. This sharper increment is the result of a reduction in interfacial tension elasticity and stresses arisen from concentration fluctuation . By cooling the sample and entering the well‐mixed region, the dissolved SAN molecules with lower chain flexibility and higher molecular weight exit from the PCL‐rich domains, hence intensifying the temperature effect on the viscoelastic responses, especially the responses of the fast polymeric component.…”

“…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 .…”

“…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 .…”

“…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 …”

“…Using different experimental research strategies, it has been assessed that adding nanoparticles to the A binary blend can change the phase behavior by shifting the LCST‐type phase diagram to higher temperatures, making the phase diagram more asymmetrical, slowing down the phase separation/dissolution and changing the phase separation mechanism from spinodal decomposition to nucleation and growth . Most of these researches employed the rheological measurements for evaluating the phase behavior changes of the polymer mixtures . However, the measured viscoelastic responses over the phase‐transition boundary are the complex combinations of several controlling factors including thermodynamics, kinetics, and viscoelasticity …”