Reversible Shape Memory Polymers for Ambient Actuation
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Solution Overview
Problem
Current shape memory alloys (SMAs) have limitations such as limited recoverable strains, high stiffness, high cost, and inflexible transition temperatures, which restrict their application, prompting the need for alternative materials like polymeric shape memory materials that can achieve reversible actuation at ambient temperatures for integration with fabrics.
Innovation Solution
Development of shape memory polymers with crystallizable network chains, crosslinking (physical or covalent), and stress bias, allowing for reversible actuation, featuring polymers that can crystallize near ambient temperatures with minimal undercooling, and multiple crosslinking methods to balance processability and reversibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If shape memory alloys (SMAs) are used to achieve shape memory effect, then high strength and reliability are obtained, but limited recoverable strains, high stiffness, high cost, and inflexible transition temperatures occur
Solution Approach 1:
The patent changes the material parameters by transitioning from metal alloys to polymeric materials, specifically using polymers with glass transition temperatures (Tg) in the ambient range (20-40°C). This parameter change enables flexible transition temperatures while maintaining shape memory reliability, directly resolving the contradiction between reliability and temperature adaptability.
Solution Approach 2:
The patent employs composite polymeric structures combining crystallizable segments (for shape fixing) with amorphous segments (for reversibility). This composite approach at the molecular level enables the material to achieve both high reliability through crystalline structure and flexible transition temperatures through amorphous phase behavior.
2Strength
If shape memory alloys (SMAs) are used to achieve shape memory effect, then high strength is obtained, but limited recoverable strains and high cost occur
Solution Approach 1:
The patent changes the material class from metallic to polymeric, where polymers inherently provide greater extensibility and recoverable strain capacity (exceeding 8% as stated in the patent) while maintaining adequate strength through crosslinked network structures. This parameter change resolves the contradiction between strength and strain capacity.
3Adaptability or versatility
If two-way shape memory polymer is developed for reversible actuation, then ambient temperature actuation is achieved, but no such polymer has been reported to date with fabric integration capability
Solution Approach 1:
The patent develops thin-film polymeric shape memory materials that can be integrated into fabric structures. These flexible thin films enable ambient temperature actuation while being compatible with textile manufacturing processes, resolving the contradiction between ambient actuation capability and ease of fabric integration.
4Ease of manufacture
If physical crosslinks are used in polymer to achieve reversibility, then processing flexibility is improved, but imperfect memory (reversibility) occurs
Solution Approach 1:
The patent creates a composite crosslinking system combining physical crosslinks (providing processing flexibility and reversible behavior) with covalent crosslinks (providing stable memory). This composite approach at the molecular level allows the material to exhibit both processing flexibility and reliable reversible shape memory, resolving the contradiction between ease of manufacture and shape memory reliability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The polymers achieve reversible actuation with suitable actuation force, strain, and cycle fatigue, enabling applications in apparel integration and various actuator designs, including bimorph curling, linear, and volumetric actuators, with transitions between -10°C and 50°C, enhancing the flexibility and efficiency of shape memory functionality.
Implementation Method 1
the present invention involves polymers that can crystallize at a temperature near ambient temperatures and with minimal undercooling (hysteresis)
Implementation Method 2
Shape memory materials are those materials that have the ability to 'memorize' a macroscopic (permanent) shape, be manipulated and 'fixed' to a temporary and dormant shape under specific conditions of temperature and stress, and then later relax to the original, stress-free, condition under thermal, electrical, or environmental command
Implementation Method 3
This relaxation is associated with elastic deformation stored during prior manipulation
Data Source
AI summary
Shape memory polymers featuring reversible actuation capability under ambient stimulus for integration with apparel. One approach is to use a multiblock polymer consisting of two (or potentially more) blocks in which the one block is the crystalline switching block with relatively low melting transitions, the other block has a higher thermal transition, and the two blocks are linked together by a linker molecule. Another approach is to use a graft copolymer having high and low melting transitions where the graft copolymer has a first polymer serving as the backbone and a second polymer being grafted to or from the backbone at certain graft locations. A further approach is to use latent crosslinking of a semicrystalline polymer with reactive groups placed on the backbone. Finally, these polymers may be formed as actuators that undergo curling, twisting and even volumetric expansion.