Investigation of a Nanocomposite of 75 wt % Poly(methyl methacrylate) Nanoparticles with 25 wt % Poly(ethylene oxide) Linear Chains: A Quasielatic Neutron Scattering, Calorimetric, and WAXS Study

Abstract

We have investigated the thermal behavior, local structure, and dynamics in a system where 25 wt % PEO [poly(ethylene oxide)] linear chains are mixed with 75 wt % PMMA [poly(methyl methacrylate)] soft nanoparticles. Calorimetric and wide-angle X-ray scattering experiments point to a weak penetration of the PEO chains in the nanoparticles, qualifying the mixture as a nanocomposite. Quasi-elastic neutron scattering (QENS) experiments on partially deuterated samples has selectively revealed the component dynamics in the system. The α-methyl group dynamics of PMMA, which fall within the QENS time scale in the temperature range investigated, are hardly affected by the presence of PEO except for hints of a more heterogeneous environment in the nanocomposite than in bulk PMMA. The effects on the dynamics of PEO are more interesting. The observation of dynamics in the microseconds range for the PEO component of the nanocomposite at temperatures at which the calorimetric experiments indicate the freezing of its segmental relaxation provides evidence for confined dynamics below the main glass transition of the mixtureattributable to the effective glass transition of the slow component. A parallel study on an equivalent blend of PEO and linear PMMA chains shows that these effects are independent of the topology of the PMMA. However, well above the effective glass transition of the slow component, the dynamics of PEO differ in both systems. In the linear blend, PEO segments move with the typical features of supercooled polymers in metastable equilibrium, while in the nanocomposite PEO dynamics exhibit an anomalously strong deviation from Gaussian behavior. This deviation grows with increased mobility of the nanoparticles. PEO segments are seemingly trapped in effective cages imposed by the nanoparticles for a very long timemore than 2 orders of magnitude longer than in bulk or when surrounded by linear PMMA chainsbefore the subdiffusive process leading to segmental relaxation sets in. We speculate that local loops in the surface of the nanoparticles may play an important role in this trapping mechanism.

Advances in single chain technology

“…132 The use of SCNPs as rheology-improving agents for the melts of thermoplastics, 133 elastomeric polymers, 51 nanocomposites 134,135 and paints, 55,86,96,100,101 or as polyelectrolytes with unconventional behaviour, 52a has been proposed. 136,137 SCNPs are also promising materials for promoting miscibility in immiscible polymer blends, as revealed by several theoretical [138][139][140][141][142] and experimental results. 43a,b The effect of SCNPs on the dynamics of all-polymer nanocomposites is currently the subject of intense interest.…”

Glass-Transition Dynamics of Mixtures of Linear Poly(vinyl methyl ether) with Single-Chain Polymer Nanoparticles: Evidence of a New Type of Nanocomposite Materials

“…PS-SCNPs were also evaluated as useful additives in arresting the phase separation of homogeneous PS/PVME blends showing phase splitting at a high temperature [33]. More recently, the microscopic dynamics of all-polymer nanocomposites composed of single-chain poly(methyl methacrylate) nanoparticles and linear poly(ethylene oxide) have been investigated by neutron spin echo (NSE) experiments, showing a spectacular disentanglement of PEO chain-motions for the all-polymer nanocomposite containing 25% SCNPs [34,35,36,37]. However, when considering the glass transition phenomenon, an open question is how such mixtures of linear polymers with SCNPs compare with conventional polymer-polymer mixtures; namely, with miscible polymer blends [1].…”

Polyblend Nanocomposites

“…The same researchers studied the thermal behavior, structure and dynamics of the system made of 75 wt% PMMA soft nanoparticles with 25 wt% PEO. Among other observations, no significant penetration of PEO macromolecules in the soft PMMA nanoparticles was found (8).…”

“…In general, polymers scarcely mix with one another because the combinational entropy (thermodynamic reasons) between polymers is considerably low (4). In particular, blends based on thermodynamically miscible polymers are the most efficient and economical means to create new materials with tailored features (8).…”