Reversible self-assembled structures balance two competing attractions to enable stimuli-responsive materials.
Scientists devised a new approach that balances attractions between particles and promises to become a useful tool to create designer materials that can repair damage. The discovery of a cross point between temperature-dependent interactions between particles – not previously thought possible – opens the doors for more nimble synthesis. The crosspoint exploits the temperature-dependent behavior (solubility and adsorption) of a polymer. Researchers discovered that a liquid polymer-colloid mixture on cooling and heating forms different solid phases reversibly. These solids are formed by two distinct pathways: (1) at low temperature, pressure from collisions with the surrounding non-adsorbing polymer forms a colloidal crystal and (2) at high temperature, the polymer sticks (adsorbs) to particles, forming a random aggregate.
This research opens a new pathway to stimuli-responsive self-assembled structures. Using the crosspoint pathway, it may now be possible to (1) thermally control viscoelastic properties, (2) heal defects that occur during assembly, (3) more controllably sequester and release objects, and (4) exert fine control over inter-particle interactions for sequential assembly of two- and three-dimensional materials with precisely organized optical and mechanical functions.
A new approach that balances attractions between particles promises to become a useful tool to fine-tune self-assembly and add functionality, such as error correction during assembly and damage repair. Previous polymer-directed routes for particle self-assembly were in stark contrast to biological systems that can form, reconfigure, and repair complex assemblies within cells by balancing assembly and disassembly processes.
In this research, understanding of the pathways for both assembly and disassembly was developed. The transformative aspect is the identification by researchers at New York University of a crossing point between the two pathways for a polymer-colloid mixture previously thought impossible; the crossing point mimics the biological assembly-disassembly capability. Adsorption properties of polymers change with temperature. At low temperature, colloidal crystals are formed due to pressure from collisions with surrounding non-adsorbing polymer. Actually, the colloids are squeezed together to increase the volume available to the non-adsorbing polymer. This mechanism for forming colloidal crystals was well known, but what was observed next was quite surprising. On heating, the colloidal crystal melted to form a liquid polymer-colloid mixture. Beyond this point, the solubility of the polymer decreased as the temperature increased; eventually, the polymer was able to weakly stick (adsorb) to the particles, creating bridges that solidify the liquid to a random aggregate gel.
At the crossover point between colloidal crystal deformation and gel formation, these new attractions (so-called enthalpic attraction, in thermodynamic terminology) completely balance the forces exerted by the volume available to the polymer from the particles being squeezed together (so-called entropic attraction). The crossing point depends on the change in solubility of the non-adsorbing polymer, resulting in a liquid-to-solid transition on cooling and heating. Most importantly, this process is thermally reversible at each stage of assembly and disassembly, which could allow entry into and out of the particles. As a result, it may be possible to heal defects in assembled structures, and to fabricate two- and three-dimensional materials with desired optical and mechanical properties. The general nature of these interactions suggests that they can be applied over a broad range of self-assembly approaches, such as the DNA-directed assembly of particle networks, to stimuli-responsive functional materials.
The Latest on: Stimuli-responsive materials
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The Latest on: Stimuli-responsive materials
- A soft photopolymer cuboid that computes with binary strings of white light on May 24, 2019 at 2:24 am
Next-generation stimuli–responsive materials must be configured with local computational ability so that instead of a discrete on-off responsiveness, they sense, process and interact reciprocally with ... […]
- Physical Stimuli Responsive Polymers Market Will Reflect Significant Growth Prospects during 2019 to 2026 on May 10, 2019 at 10:25 am
8.5.1 Advanced Polymer Materials (Canada) Company Details 8.5.2 Company Description and Business Overview 8.5.3 Production and Revenue of Physical Stimuli Responsive Polymers 8.5.4 Physical Stimuli ... […]
- University of Pennsylvania on May 1, 2019 at 5:00 pm
Using stimuli-responsive materials and geometric principles, researchers have designed structures that have "embodied logic." Through their physical and chemical makeup alone, they are able to ... […]
- Muscle-Like Material Contracts When Illuminated on April 5, 2019 at 2:21 pm
... a novel mechanism for actuating materials — making materials shrink, expand, or hold a ‘memory’ of a particular shape — all with a simple stimulus,” Barnes said. Stimuli-responsive materials have ... […]
- Muscle-like material expands and contracts in response to light (video) on April 2, 2019 at 12:51 pm
“The beauty of our system is that we can take a little bit of our polymer, called a polyviologen, and put it in any type of 3D network, turning it into a stimuli-responsive material,” Barnes says. ... […]
- Muscle-like material expands and contracts in response to light on April 2, 2019 at 7:44 am
... a novel mechanism for actuating materials—making materials shrink, expand or hold a 'memory' of a particular shape—all with a simple stimulus," says Jonathan Barnes, Ph.D. Stimuli-responsive ... […]
- With 'Embodied Logic' Smart Objects Won't Need Embedded Systems on February 12, 2019 at 6:30 am
On the other, researchers work with responsive materials, which can change their shape under the correct circumstances. “Bistability is determined by geometry, whereas responsiveness comes out of the ... […]
- UK Researchers Develop Responsive Cellulose-Based Ink for 4D Printing on September 14, 2018 at 12:56 pm
In order to realize this kind of responsive system following the design principles of nature, there are two requirements: a compliant stimuli responsive material, and a process that allows for the ... […]
- Texas A&M partnership developing biomedical 'bandage' for wounds on August 23, 2018 at 12:24 am
From Sukhishvili's A&M campus office, she and Albright explained that part of the A&M side of the work was to build a stimuli-responsive polymeric material that could release and absorb antibiotics in ... […]
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