ADVERTISEMENT

Shape Memory Polymers Could Program And Recover At Room Temperature

Shape memory polymers (SMPs) are a class of polymer that changes its shape with external stimuli, such as heat. The ability to memorize its original shape makes SMPs an intriguing material for many applications – reconfigurable nano-optics, biomedical devices, smart fabrics, or self-deployable aerospace structures. Typical SMPs can be activated by direct or indirect (e.g., light absorption and alternating magnetic field) heating. However, heat-demanding shape memory cycle significantly limits the broad applications of SMPs (especially as reconfigurable nano-optical devices). The tedious heating-and-cooling cycle impedes the application of SMPs under ambient conditions.

A photonic crystal is regarded as a periodic nanostructure that could interact with light. The most notable phenomenon of a natural photonic crystal is the striking bluish color shown by the morpho butterfly wings. This color is not a result of pigmentation but instead due to the interaction between visible light and photonic crystal nanostructures existing on the butterfly wings. Advances in nanotechnology have enabled scientists to mimic and fabricate the nanostructures akin to those contributed to butterfly wing coloration. In addition, small changes of these nanostructures can lead to different optical properties and colors. Hence, it is highly desirable to design smart and tunable optical nanostructures for various device applications.

ADVERTISEMENT

To achieve real-world applications in smart and reconfigurable nano-optical devices, Dr. Peng Jiang’s group at the University of Florida has been focusing on developing rigid SMPs that can be programmed and recovered at room temperature. The merit of all-room-temperature operation can add significant values to SMPs. We could expand the application to many areas that previously seem impossible. Regarding the material itself, a highly rigid shape memory polymer can enhance its durability. With these design goals, the authors developed a new SMP, combine with unique nanostructures (photonic crystals) on the SMP surface, when programmed or recovered, exhibit a striking and easily perceived change in optical properties (color).

 

In the recent article published in Advanced Functional Materials, the authors presented a novel shape memory polymer that exhibited nontraditional and all-room-temperature shape memory cycle by integrating the concepts of SMPs with macroporous photonic crystals. This study chose a highly rigid polyurethane-based SMP. The final polyurethane photonic crystal membrane comprises 300 nm macroporous nanostructure on its surface. Crucially, this permanent glassy/rigid macroporous nanostructure could be cold-programmed into temporary disordered configurations under ambient conditions by slowly evaporating organic solvents that imbibed in the interconnecting macropore. The deformed macropores can be recovered, at room temperature by exposing it to vapors and liquids of organic solvents. The cyclic deformation and recovery of the macroporous nanostructures enable us to change the perceived colors of the sample.

The authors found that the interaction between the solvents and SMPs are crucial in affecting both the deformation and recovery processes. Swelling solvents (e.g., ethanol) can trigger “cold” programming and SM recovery; however, nonswelling solvents (e.g., hexane) cannot. The experiments revealed that the dynamics of swelling-induced plasticizing effects dominated both ‘cold’ programming and recovery process. Good solvent molecules that have a positive affinity towards the polymer could diffuse into the walls of macropores at the nanoscopic scale. Subsequently, the capillary force induced by solvent evaporation could induce temporary structural deformation of the softened macropores.

ADVERTISEMENT

Importantly, swelling tests showed that the new SMP material exhibits negligible swelling in alkanes (e.g., hexane). By using the unique room temperature recovery property, the authors explored an exemplary system of ethanol-hexane solutions as a gasoline analog. The material could selectively detect trace amounts of ethanol in hexane with a detection limit of 150 ppm by monitoring the apparent color changes associated with the SM recovery. This work facilitated a better understanding of the unique properties of the novel SMP and demonstrated a new type of chromogenic sensor that can be applied to detecting trace amounts of analytes in a spectrum of solution and/or vapor mixture systems.

This study, Programmable Macroporous Photonic Crystals Enabled by Swelling-Induced All-Room-Temperature Shape Memory Effects was recently published in the journal Advanced Functional Materials.

Comments

READ THIS NEXT

Are Ecological Interactions More Intense In The Tropics?

THE QUESTION When we think about a tropical site, what commonly comes in mind is heat, rainforests, beaches, and colorful […]

Scientists Create Incredible 3D Models Of The Scene In Which Images Were Taken

Here is a fun experiment to do: Find a room in your house or apartment that only has one window. […]

“Moral Machine Experiment”: Large-Scale Study Reveals Regional Differences In Ethical Preferences For Self-Driving Cars

One of the most pressing questions facing current AI research is: How do you program an AI to behave ethically? […]

Meiosis Prophase 1

The human body needs to create new cells to replace old, worn out ones. Mitosis is the process that creates […]

Instagram Just Developed A Warning System To Combat Animal Abuse

As social media gains greater and greater presence in our lives, greater attention is being paid to its impacts on […]

Yo-Yo Diets Don’t Work

Published by Jack Pryor and Stephanie Simonds Department of Physiology, Monash Biomedical Discovery Institute, Monash University, Australia These findings are […]

Happy Faces And Friendly Choices: Analyzing Reactivity During Social Interactions

Pedagogic literature usually emphasizes the importance of being proactive rather than reactive. It is suggested that people who are reactive […]

Science Trends is a popular source of science news and education around the world. We cover everything from solar power cell technology to climate change to cancer research. We help hundreds of thousands of people every month learn about the world we live in and the latest scientific breakthroughs. Want to know more?