What smart polymers can do: a panacea for the future
The original article was published on the website of the journal “For Science” of the Moscow Institute of Physics and Technology.
The polymer revolution began in the 40s of the XX century, when people for the first time abandoned natural materials and synthesized what was never in nature. A striking example is polyamides (nylon) and polyethylene. Such an absolutely artificial material as polyethylene turned out to be unique in its structures and mechanical properties: polyethylene fiber, for example, is stronger than steel. Correlations between the structures of materials and their properties began to stand out in the whole direction of materials science, scientists began to specifically study such correlations to create new functional materials - this was the birth of the science of polymers.
Battle for Specialization
In the 60s it was believed that the future lay in specialized polymers. Then it seemed that very soon polymer materials would be discovered, each ideally suited for their task, and the large-tonnage production of universal plastics would be reduced.
This prediction did not come true, the industry of specialized polymers has not grown over the years. This is due to the fact that all industrial production today, like half a century ago, is optimized for individual universal polymers, and it is very expensive to rebuild it. For half a century, the main effort of developers has remained to learn how to control the macromolecular structure and properties of the polymer. Today's universal plastics - such as polypropylene - are not at all the materials that were produced under the same names decades ago. As a rule, these are whole families of copolymers with different properties.
But today they are returning to specialized polymers - though, for the time being, they are more often in university laboratories than in factory shops. Modern technologies make it possible to obtain polymers with amazing properties - and to solve incredible problems with their help, from desalination to targeted drug delivery. About how and why smart polymers are made, the head of the laboratory of engineering materials science at Moscow State University and the laboratory of functional organic and hybrid materials at the Moscow Institute of Physics and Technology Dmitry Ivanov and his staff tell.
Smart polymers have the ability to respond strongly to relatively weak external influences. They can dramatically change their shape or state when changing temperature, humidity, acidity, lighting. These materials respond even to the smallest external disturbance. It is possible, for example, by radiation to cause a change in the conformation of polymer chains, which will lead to a global restructuring of the entire polymer structure. Classical materials - alloys, ceramics - consist of fairly simple bricks: atoms, ions or compounds of several atoms. Therefore, for them, such strong responses to a small external disturbance are practically unattainable.
“The area in which we operate is called“ complex fluids. ” This is another term for smart materials. In each elementary “brick” of such material there can be tens and even hundreds of atoms that make up the monomer. From these monomers we build a polymer chain. The structural complexity of the monomers determines the complexity of the interactions between them. Due to the fact that the material is organized on a wide range of scales (from Angstroms to hundreds of nanometers), it has a rich palette of possible interactions, ”says the research director at the French National Center for Scientific Research, the head of the Laboratory of Engineering Materials Science of Moscow State University and the Laboratory of Functional Organic and Hybrid MIPT materials Dmitry Ivanov.
Now a whole direction is being developed related to microrobots based on soft media (soft media is another name for these materials). Under the influence of radiation, they can cause mechanical deformation of microobjects - and move them in the right direction.
“For example, a polymer dissolves in water at temperatures below 31 ℃. As soon as the temperature exceeds 31 ° C, the polymer undergoes a phase transformation, the polymer chains lose their solubility property, their collapse sets in, the polymer matrix contracts sharply, and the object begins to move. Such objects from nanoparticles (in our case, gold ones) are called microwaves; acting on them with infrared laser pulses, we make them swim in the right direction. Someday, quicksanding will play a big role in nanomedicine, ”explains laboratory employee Yegor Bersenev.
Another example is the creation of special multilayer micro- and even nano-sized bubbles for drug delivery. By directing radiation with a certain wavelength to the bubble, a phase transition can be caused — the shell will open and the medicine that was inside the bubble will be released in the place of the body where it is needed. So it is possible to deliver toxic drugs to cancerous tumors: the more accurate the delivery, the less the dose is needed, and the weaker the side effects.
Smart plastics can also be used to desalinate water. “Now at Fiztekh an international project is being implemented in which we are trying to create synthetic polymers having selective affinity for alkali metal cations. One of the goals of this project is to create a new generation of desalination systems, ”says Yegor Bersenev. - It is impossible to chemically remove sodium ions from the aqueous medium. Our polymers are fairly simple macromolecules that incorporate electrostatic charges, the so-called polyelectrolytes. "They selectively bind sodium cations in water, after which they precipitate."