(366f) Development of Poly(ionic liquid) Copolymers and Composites for Electromechanical Actuators and Other Applications

Poly(ionic liquid)s (PILs) are a subclass of strong polyelectrolytes which combines the unique properties of ionic liquids (ILs) with the processability and mechanical integrity of polymers. PILs are inherently ion conductive and are typically characterized by high thermal stability, non-flammability, and wide electrochemical windows. Due to these properties, PILs have shown potential as solid and pseudo-solid polyelectrolytes for use in electro-responsive materials and other electrochemical applications such as electromechanical sensors and actuators, batteries, and flexible electronics. Ionic electroactive soft actuators (IEAPs) consist of a polyelectrolyte layer sandwiched between two electrodes. When under an applied electrical voltage, the polyelectrolyte can mechanically respond, or actuate, due to ion migration and localized swelling within the polymer system. PILs, especially when combined with free ionic liquid to form ionogels, exhibit the high ion conductivity needed for actuation behavior, but can face challenges in maintaining the necessary mechanical properties for actuation behavior. The presented work explores the balance between ion conductivity and mechanical modulus through the development of poly(ionic liquid)-based ionogel block copolymers and reinforced composites for their application as electro-responsive actuators. Initially an all-polyelectrolyte block copolymer PIL was developed which exhibited micron-scale actuation behavior with ion conductivities of ~10^-7 S/cm and Young’s moduli (E) between 50-200 MPa. In order to improve actuation behavior to the millimeter scale, a series of PIL ionogels reinforced with graphene oxide and PVDF were developed to increase the mechanical modulus (100-1000 MPa) while maintaining high ion conductivity (~10^-4 S/cm). The PIL actuator composites were characterized for their chemical (FTIR), thermal (DSC and TGA), mechanical (stress-strain), and electrochemical properties (stress-strain tests). Glass transition temperature and thermal stability were evaluated with DSC and TGA characterizations, respectively. Ion conductivity was determined with electrical impedance spectroscopy (EIS) spectroscopy, and the mechanical properties were evaluated through stress-strain tests. Based on the electrochemical and mechanical properties, select PIL ionogel composites were sandwiched between two layers of electrode materials, and their actuation performance was investigated at low voltages (<5 V).

Research Interests:

In addition to electrochemical applications, my PhD research work has also involved exploring the use of poly(ionic liquid)s in self-assembly of soft nanomaterials and in stimuli-responsive or ‘smart’ polymer applications. I am also interested in pursuing industry-based research in polymer science, nanomaterials and fibers, and spectroscopic and structural material characterizations.

My research has led to 4 first author journal articles in print as well as 3 manuscripts under review or in preparation and 12 (inter)national conference talks and presentations. In addition to contributing to the development of 10 grant proposals, I have also participated in collaboration with both industry and national laboratory research projects and characterization work. During my academic career, I was involved in multiple leadership roles in several student-lead organizations, including the Chemical Engineering Graduate Society and the Society of Plastic Engineers.

Self-assembly and ion-responsive block copolymers: PILs combined with a co-polymers or surfactants can self-assemble into microphase separated regions in the bulk which can enhance specific material properties such as ion conductivity, mechanical properties, or chemical bonding. This self-assembly behavior is particularly important for developing materials with favorable properties for electrochemical applications such as solid battery electrolytes and flexible electronics. In solution, PILs can form unique nanostructures which lead to interesting fluidic properties. I have focused on synthesizing and exploring the self-assembly behavior of PILs combined with weak polyelectrolytes and examining their nanostructure and chemical bonding interactions in response to added salts in both the bulk and solution states.

Magnetic Responsive PILs and Nanostructures: I have also developed PIL materials and nanostructures that can respond to magnetic fields. In particular, this work has focused on two primary goals: (1) enhancing the magnetic properties of magnetically responsive PILs in multi-component systems (e.g., copolymers and blends) and (2) applying a magnetic field as a self-assembly tool to develop films with well-ordered structures. In (1), I utilized a suite of chemical spectroscopy techniques (FTIR, Raman, UV-vis, XPS) and magnetometry (AC susceptibility and vibrating sample magnetometry) to highlight the importance of co-material impacts on the magnetic properties and response of PIL materials. In (2), the magnetically responsive PILs were complexed with surfactants to formed nanostructure complexes. Particle sizing, electron and atomic force microscopy imaging, and small angle x-ray scattering characterizations were applied to examine the mechanism of complex formation and the use of magnetic fields on ordered film assembly. I am currently exploring the development of poly(ionic liquid) magnetite nanoparticle composites for water treatment applications.

Fibers: My master’s work involved investigating the successful use of air foils on the optimization of the melt blowing process, a polymer processing technique for forming nonwoven polymer fiber mats. During this work, I utilized high speed and IR thermal photography to evaluate the impact of air foils on fiber attenuation in the high velocity airfields used in the melt blowing technique. I am currently interested in learning and exploring other fiber spinning techniques, such as electrospinning, that can be combined with my experience in strong polyelectrolytes to develop smart textiles and flexible electronics.

Key Words: poly(ionic liquid)s, ionic liquids, ionogels, stimuli-responsive polymers, magnetic and electrically responsive polymers, controlled ‘living’ radical polymerization, block copolymers, polymer processing, fibers.

Select First Author Articles

1. Kayla Foley, Keisha B. Walters. “Solution and Film Self-Assembly of a Block Copolymer Composed of a Poly(ionic liquid) and a Stimuli-Responsive Weak Polyelectrolyte,” ACS Omega, 8(37):33684–33700. DOI: https://doi.org/10.1021/acsomega.3c03989
2. Kayla Foley, Lucas Condes, Keisha B. Walters. “Influence of metal-coordinating comonomers on the coordination structure and binding in magnetic poly(ionic liquid)s,” Syst. Des. Eng., 2023,8, 1402-1417 DOI: https://doi.org/10.1039/D3ME00076A
3. Kayla Foley, Keisha B. Walters. (2022) “Development of Nano- and Micro- Fluids Using Magnetic Poly(ionic liquid)-Surfactant Complexes for Stimuli Response,” Proceedings of the ASME 2022 Fluids Engineering Division Summer Meeting. Volume 2: Multiphase Flow (MFTC); Computational Fluid Dynamics (CFDTC); Micro and Nano Fluid Dynamics (MNFDTC), V002T06A006. DOI:1115/FEDSM2022-87758.
4. Foley, K. A., Shambaugh, R. L. (2018). “Fiber spinning with airfields enhanced by airfoil louvers,” Textile Research Journal, 89(15):3150-3158, DOI: 1177/0040517518807444