The Lei Zhu Group has many research interests, from electroactive polymers and optical data storage to ferroelectric and dielectric functional polymers for electrical applications. Learn more about our research below.
High K, Low Loss Polymers for Electrical Applications
Novel High Dielectric Constant and Low Loss Polymer Dielectrics
Polymer dielectrics having high dielectric constant, high temperature capability, and low loss are attractive for a broad range of applications such as film capacitors, gate dielectrics, artificial muscles, and electrocaloric cooling. Unfortunately, it is generally observed that higher polarization of dielectric constants tends to cause significantly enhanced dielectric loss. It is therefore highly desired that the fundamental physics of all types of polarization and loss mechanisms be thoroughly understood for dielectric polymers. In this perspective, we intend to explore advantages and disadvantages for different types of polarization. Among a number of approaches, dipolar polarization is promising for high dielectric constant and low loss polymer dielectrics, if the dipolar relaxation peak can be pushed to above the gigahertz range. In particular, dipolar glass, paraelectric, and relaxor ferroelectric polymers are discussed for the dipolar polarization approach.
Representation Publications:
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Zhu, L.*; Wang, Q.* Novel ferroelectric polymers for high energy density and low loss dielectrics. Macromolecules 2012, 45, 2937–2954.
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Yang, L.; Li, X,; Allahyarov, E.; Taylor, P. L.; Zhang, Q. M.*; Zhu, L.* Novel polymer ferroelectric behavior via crystal isomorphism and the nanoconfinement effect. Polymer 2013, 54, 1709-1728.
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Zhu, L.* Exploring strategies for high dielectric constant and low loss polymer dielectrics. J. Phys. Chem. Lett. 2014, 5, 3677-3687.
Multilayer Film System
Using multilayer coextrusion, a high dielectric constant polymer (e.g. PVDF) can be multi layered with a highly insulating dielectric polymer (e.g. PC, PET and PSF). The dielectric properties of PVDF-based multilayer films depended on both PVDF and the dielectric layers and the interaction between them. First, dipole switching in PVDF is prohibited by non-uniform electric field distributions. Second, decreasing the PVDF layer thickness effectively reduces the impurity migrational loss. Third, interfacial polarization in the PVDF layer enhances the breakdown strength for multilayer films. Fourth, internal electron tunneling can be effectively blocked by relatively thick dielectric polymer layer. Finally, high temperature DC conduction should be minimized by using a high Tg and low conduction dielectric layer.
Representation Publications:
- Baer, E.; Zhu, L.*, Dielectric phenomena in polymers and multilayered dielectric films. Macromolecules 2017, 50, 2239-2256.
Nanodielectrics
It is known that certain ceramics exhibit high dielectric constant in the order of thousands. Naturally, it is desired to blend ceramic nanoparticles into polymers to achieve high dielectric constant nanocomposites with a wish that the dielectric breakdown strength will not substantially decrease. Nanocomposites are preferred over micro-composites because local electric field enhancement in the low dielectric constant polymer matrix between neighboring ceramic particles can be largely reduced to ensure relatively high nominal breakdown strength. Currently, we are working to achieve uniform particle dispersion, reduce internal electron conduction, and reduce the ceramic content to facilitate better processing.
Representation Publications:
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Zhang, G.; Brannum, D.; Dong, D.; Tang, L.; Allahyarov, E.; Tang, S.; Kodweis, K.; Lee, J.-K.; Zhu, L.* Interfacial polarization-induced loss mechanisms in polypropylene/BaTiO3 nanocomposite dielectrics. Chem. Mater. 2016, 28, 4646-4660.
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Zhang, G.; Li, Y.; Tang, S.; Thompson, R. D.; Zhu, L.*, The role of field electron emission in polypropylene/aluminum nanodielectrics under high electric fields. ACS Appl. Mater. Interfaces, 2017, 9, 10106-10119.
Electroactive Polymers
Electrically active polymers are a unique class of materials, where the polymer will contract or bend, in proportion to an applied electric voltage. The stress and strain characteristics of natural muscle are best approximated by dielectric elastomers. Furthermore, the capacity for energy generation per kilogram in dielectric elastomers, across all frequencies, exceeds that of native muscle. Hence, dielectric elastomers appear to be the most promising class for artificial muscles. We are interested in high dielectric constant and low leakage current elastomers for this application.
Representation Publications:
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Liu, L.; Huang, Y.; Allahyarov, E.*; Zhang, Z.; Lv, F.; Zhang, Y.*; Zhu, L.* Understanding reversible Maxwellian electroactuation in a 3M VHB dielectric elastomer with prestrain. Polymer 2018, 144, 150-158.
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Huang, Y.; Rui, G.; Allahyarov, E.; Li, R.; Fukuto, M.; Zhong, G.-J.; Xu, J.-Z.; Li, Z.-M.; Taylor, P.*; Zhu, L.* Enhanced piezoelectricity from highly polarizable oriented amorphous fractions in biaxially oriented poly(vinylidene fluoride) with pure ß crystals. Nat. Commun. 2021, 12, 675.
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Zhu, Z.; Rui, G.; Li, Q.; Allahyarov, E.; Li, R.; Soulestin, T.; Domingues Dos Santos, F.; He, H.*; Taylor, P. L.*; Zhu, L.* Electrostriction-enhanced giant piezoelectricity via relaxor-like secondary crystals in extended-chain ferroelectric polymers. Matter 2021, 4, 3696-3709.
Mixed Brushes
Mixed polymer brush-grafted particles, in which two distinct polymers are randomly or alternately immobilized by one end via a covalent bond on the surface of core particles with sufficiently high grafting densities, represent a new, intriguing class of environmentally responsive nanostructured hybrid materials. The two end-tethered polymers can undergo spontaneous chain reorganization in response to environmental variations, rendering particles' adaptive surface properties and different colloidal behavior. Currently, we are interested in the morphology study of the mixed polymer brush-grafted silicon particles.
Representation Publications:
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Zhao, B.*; Zhu, L. Mixed polymer brush-grafted particles: A new class of environmentally responsive nanostructured materials. Macromolecules 2009,42, 9369-9383.
Our research is supported by:
- The Center for Layered Polymeric Systems and the National Science Foundation Science and Technology Center
- Office of Naval Research
- Air Force Office of Scienctific Research
- Defense Advanced Research Projects Agency
