Gerichtete Bewegung von Nanokompositen mit Hilfe der Elektrostriktion
Herstellung und Eigenschaften von Funktionsmaterialien
Zusammenfassung der Projektergebnisse
The conducted research revealed interesting results about the internal processes in electroactive polymers and composites concerning their tunable actuation properties. Analytical, simulation, and theoretical works were directed to develop new materials with better energy storage properties, stronger actuation abilities, and effective field-energy coupling under external loadings. Rod-like dipoles on spherical substrates were considered to mimic nanocomposites with inclusions on their surface. Simulation results indicated that the curvature of the substrate induces topological defects in the rod system pre-oriented by external fields. The resulting distribution morphology of the rods depends on their packing fraction and their aspect ratio. For a binary mixture of rods we arrived at interesting segregation phenomena with a broad spectra of possible scenarios with clear short/long rod prevalence areas. The obtained results for the topology-to-morphology coupling and for the segregation of mixtures are important information for devising novel smart electroactive materials with controlled locomotion. One of the big issues in getting the desired actuation of the composite under the AC fields is the suppression of the unwanted ionic losses because of the heat generated by impurity ions. These ions, under certain conditions, block the electrodes and decrease the local field near the inclusions, which eventually decreases the poling/orientation of the dipoles. To solve the impurity ion issue, experimentalists need to know how much ions are present in the system and how fast they diffuse. I was able to handle this task analytically and relevant simulations were developed for two different scenarios: the weak (perturbative) and the strong field limits. We have shown that AC+DC field combination is necessary for driving the ion out of the polar polymer and blocking them in the near electrode inert layers can permanently fight ionic losses. For energy storage materials a porous membrane with anchored dipoles is a promising candidate. The dipoles can freely rotate and thus absorb the applied field. However, they also tend to cluster and form a network. How such clustering does appear in cylindrical pores, and what the optimal pore-sidechain parameters are– these questions were answered in our project-related work. We believe that such porous composites are fundamental for the new emerging materials for soft-fluid actuators. For electromechanical applications we looked into the polarization contribution from the oriented amorphous phase between the two poled PVDF crystallines. Usually this contribution was overlooked in previous studies assuming it being small for the amorphous phase. However, in stress-strain deformations this is not the case, and the amorphous phase starts to orient itself along the PVDF dipole. I developed a MD code for stretching the amorphous PVDF phase and showed that it has tremendous contribution to the overall polarization of the composite. I developed a mean-field theory for the effective permittivity of the nanocomposite with incorporated reaction field and dipole-dipole correlation effects. The theory clearly indicated that the energy stored inside the inclusions is the prime suspect for the enhanced permittivity. This energy also strongly contributes to the inclusion dipole moment and the interaction between the dipoles. I was able to apply the theory to the mixing rules and show that the Bruggeman rule is more adequately takes into account necessary field-energy effects. Obtained results are fundamental for better understanding of the physics behind the mixing rules for composites. Direct MD simulations with controlled clustering of inclusions were carried to calculate field distribution and apparent permittivity of the mixture. According to the simulations, the field oriented planar and cylindrical clustering of inclusions provide much higher effective permittivities. Nevertheless, there might be other particle distribution morphologies leading to even higher composite actuation, which is a subject for the future work.
Projektbezogene Publikationen (Auswahl)
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Simulation Study of Ion Diffusion in Charged Nanopores with Anchored Terminal Groups, Elelectrom. Acta 242, 73-85 (2017)
E. Allahyarov, H. Löwen, P. L. Taylor
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Smectic monolayer confined on a sphere: Topology at the particle scale, Soft Matter, 13, 8120-8135 (2017)
E. Allahyarov, A. Voigt, H. Löwen
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Length segregation in mixtures of spherocylinders induced by imposed topological defects Soft Matter 14 8962-8973 (2018)
E. Allahyarov and H. Löwen
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Polymer Nanodielectrics: Current Accomplishments and Future Challenges for Electric Energy Storage, Editors B. Li and T. Jiao, Nano/Micro-Structured Materials for Energy and Biomedical Applications. Springer, Singapore (2018)
G. Zhang, E. Allahyarov, L. Zhu
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Understanding reversible Maxwellian electroactuation in a 3M VHB dielectric elastomer with prestrain, Polymer 144, 150-158 (2018)
L. Liu, Y. Huang, Y. Zhang, E. Allahyarov, Zh. Zhang, F. Lv, L. Zhu
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Reducing dielectric loss and enhancing electrical insulation for multilayer polymer films by nanoconfined ion transport under high poling electric fields, J. Mater. Chem. C 8 6102-6117 (2020)
X. Chen, E. Allahyarov, D. Langhe, M. Ponting, D. E. Schuele, E. Baer, L. Zhu
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Reducing Dielectric Loss by Nanoconfined Impurity Ion Transport in Multilayer Films under Low Electric Fields, Compos. Part B-Eng. 190 107908, 1-16 (2020)
X. Chen, E. Allahyarov, Q. Li, D. Langhe, M. Ponting, D. E. Schuele, E. Baer, L. Zhu
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Theoretical Study of Nanocomposite Permittivity with a Tunable Clustering of Inclusions, Adv. Theory Simul. 3 1-20 (2020)
E. Allahyarov
