Quasi-Elastic Neutron Scattering Study on Dynamically Asymmetric Polymer Blends

Our current work explores how the segmental dynamics of poly(methyl acrylate) (PMA) chains are affected in the presence of other polymers of different miscibility and rigidity. Precisely, we studied using the differential scanning calorimetry (DSC) and quasi-elastic neutron scattering (QENS) dynamic heterogeneity in bulk blends of PMA within poly(methyl methacrylate) (PMMA), polystyrene (PS), and poly(ethylene oxide) (PEO), below and above the glass transition temperature of PMMA and PS. The double glass transition (T_g) for PMA/PMMA and PMA/PS blends, and the single transition for PMA/PEO indicate immiscible and miscible of the blends respectively. Also, the reduced cooperative motion was observed from the dynamic fragility measurement which suggests a corresponding reduced interchain cooperativity of PMA in the immiscible blends. Detailed QENS measurement revealed the findings: (i) an increased segmental jump distanced of PMA at lower temperatures, (ii) the suppression of effective diffusivity of PMA when in contact with PMMA or PS, and (ii) about ten times magnitude increase in the diffusivity of PMA in contact with PEO. These are explained in the context of free volume created by blending, the flexibility of chain environments, and the plasticizing effect of PEO respectively. These measurements were conducted in bulk, and hence confinement of the blends might seem worth exploring. We suffice that the miscibility will be improved by nanoconfinement and the expected dynamic response of the blends to deviate from that of the bulk. These findings will help us unravel the microscopic origin of property enhancement in these dynamically asymmetric blends with the addition of nanoparticles and pose a possible pathway for a wide range of applications of this system.