Shape Memory Behaviour of PMMA-Coated NiTi Alloy under Thermal Cycle

Area of Science:

• Materials Science
• Composite Materials
• Biocompatible Polymers

Background:

• Poly(methyl methacrylate) (PMMA) and Nickel-Titanium (NiTi) alloys are known for shape memory and biocompatibility.
• The macroscopic properties of PMMA-NiTi composites are significantly influenced by the interfacial interactions between the alloy and polymer components.

Purpose of the Study:

• To investigate the development and characterization of PMMA-NiTi composites for potential actuator and sensor applications.
• To analyze the relationship between material properties, composite structure, and actuation behavior under thermal cycling.

Main Methods:

• NiTi shape memory alloy (SMA) and superelastic (SE) sheets were coated with PMMA using a spin-coating technique at an alloy-to-polymer thickness ratio of 1:3.
• Bending stiffness and radius of curvature were determined through both numerical modeling and experimental measurements during thermal cycles.
• Young's modulus of PMMA was fixed at 3 GPa, while the Young's modulus of NiTi varied between 30 and 70 GPa.

Main Results:

• Experimental measurements of radius of curvature during actuation showed good agreement with the developed numerical model.
• The observed shape change in the composites is attributed to the differential coefficients of thermal expansion between PMMA and NiTi.
• The SMA-PMMA composite demonstrated actuation temperatures between 0 and 100 °C, with a significant change in curvature from 10 to 120 mm.

Conclusions:

• PMMA-NiTi composites exhibit tunable shape-changing capabilities driven by thermal stimuli.
• The findings validate the use of numerical and experimental methods for predicting composite behavior.
• These biocompatible composites show promise for applications as actuator and sensor elements in various fields.