In this paper, we studied the alteration of viscoelastic properties of a neat poly(methyl methacrylate) (PMMA), induced by an applied external electric field. The rheological properties of PMMA are measured using a rotational rheometer at elevated temperatures. The electric field effect on the shear resistance of the polymer was studied by examining rheological responses under difference experimental scenarios. We find that the external electric field can remarkably enhance shear resistance and prevent flow of PMMA melt, enabling it to behave more predictably at high temperatures. Dynamic rheological analysis illustrates that the external electric field speeds up the recovery of mechanical properties of the PMMA melt after large deformations, whereas the PMMA melt exhibits thixotropic behaviors. The recovery velocity is influenced by the strength of the electric field, specifically, and is found to be proportional to the electric field strength. Our experimental characterization may provide new evidence on the tuning mechanical properties of polymer melts via controlling segmental polarization.

The electrorheological (ER) effect is crucial for development of responsive materials controlled by electric fields. To exploit the ER effect for designing better phase-change materials with improved shear resistance at elevated temperatures, polymers may be employed as the matrix in functional composites with high-dielectric fillers. Here we demonstrate enhanced ER properties of PMMA–TiO2 nanocomposites, at temperatures up to 200 °C. The influence of temperature, volume fraction, and electric field strength on the rheological properties including flow curves, modulus sensitivities, and temporal response was investigated by a rotational rheometer with electric field accessories. The observed temporal response under a fixed electric field, bearing strong resemblance to the creep and recovery in mechanical testing, quantitatively matches the description by a viscoelastic model. These results may provide solid evidence for a potential route to develop responsive materials.

This study investigates the physical aging process of PMMA‐TiO2 nanocomposites with different particle alignments. By using an external electric field to control the alignment of TiO2 particles, a uniform distribution of TiO2 particles in PMMA is transformed into a micrometer‐level pillar structure. The physical aging process is measured using differential scanning calorimetry, and the particle alignment is confirmed by microscopy. Comparison of the aging behavior of different samples shows that the addition of randomly distributed TiO2 nanoparticles accelerates the aging rate of the material. However, when the nanoparticles are realigned into a pillar structure, the aging rate significantly decreases. Moreover, in our experimental time scale, a dual‐relaxation mechanism of aging is observed in the PMMA/TiO2 nanocomposites. This work highlights the importance of particle alignment and structure on the aging behavior of polymer nanocomposites, which could have implications for designing materials with improved stability in applications that require slow aging.

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