DESIGN AND CHARACTERIZATION OF MAGNETIC FIELD ACTUATED MULTILAYERED POLYMERS
Open Access
- Author:
- Leng, Rui
- Graduate Program:
- Mechanical Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- March 30, 2022
- Committee Members:
- Mary Frecker, Program Head/Chair
Zoubeida Ounaies, Thesis Advisor/Co-Advisor
Mary I Frecker, Committee Member
Daniel Connell Haworth, Committee Member - Keywords:
- Smart materials
Magneto-active elastomers
Magneto-active polymer-based materials
Shape memory polymers
Polymer actuation
Polymer Characterization
Additive manufacturing
Printability
Unimorph
Biomedical field - Abstract:
- This thesis investigates multi-field actuated smart materials for potential biomedical applications. Magneto-active elastomers (MAEs) consisting of magnetic particles and a two-part elastomer were first designed and tested for their degree of actuation as unimorphs. The study considered two types of magnetic particles, hard and soft. For hard magnetic particles, barium hexaferrite (BHF) microparticles were chosen based on their responsiveness to magnetic field and their hard magnetic properties. The permanent magnetic dipoles of BHF resulting in large remanent magnetization can be polarized by magnetic field into designed directions. For soft magnetic particles, iron oxide microparticles were chosen where application of magnetic field results in induced dipoles. The elastomer matrix for the MAEs was fabricated using a two-part polydimethylsiloxane (PDMS) base and curing agent. BHF-PDMS and iron oxide-PDMS were fabricated using conventional casting method, processed into unimorphs and actuated as proof of concept. A unimorph structure is a layered structure where a substrate material is deformed using an active material and designed for large bending deformation. Bending and folding actuation was elicited with BHF-PDMS thin films as the particle magnetic dipoles were poled in a uniform direction beforehand. The film then reacts to external magnetic field by aligning the dipole directions with the external magnetic field direction. Iron oxide-PDMS was also studied and actuated using external magnetic field. Other actuation configurations designed included gripping and flower blooming motions. Large bending actuation was achieved with both hard and soft MAEs, and the next step was to test for printability. Iron oxide-PDMS was chosen for the printability test and the material compositions was tuned by adjusting base to curing agent ratio and by the addition of thickening agent. The printability study considered parameters such as temperature and number of printed layers, and results showed that printable iron oxide-PDMS slurries were obtained with 5wt% fumed silica added. The matrix of the magneto-active polymer-based materials was also investigated by comparing PDMS with mechanically stiffer polyvinyl alcohol (PVA) in degree of actuation. In the last step, multi-field actuation was studied using both conventional casting and additive manufacturing (AM) methods. Shape memory polymers (SMPs) were chosen to act as the “active” substrate for their shape fixing and recovery abilities under different temperatures. Unimorph structures were again used to test actuation of MAE-SMP under both magnetic and thermal fields. A gripping configuration was designed and demonstrated using conventionally cast iron oxide-PDMS and SMPs. Printed iron oxide-SMP thin films were actuated to assess the impact of the functional gradient design, showing different degree of actuation with different compositions of materials. The outcome of this research aims at potential biomedical applications using smart materials to allow non-contact control with large actuations. Additive manufacturing will enable the facile fabrication of actuators using these multiple materials, and would allow more customized devices to be printed for ease of use, while adapting to each patient’s unique condition and requirement.