Darmstadt researchers plan to selectively control the properties of underlying materials utilizing thin, "smart," plastic films. For example, paper might be induced to release printing inks, if necessary, chemical reactions might be started and interrupted as required, or medications might be tailored to affect only certain parts of the body.
Polymers have become essential parts of our daily lives. Polymers, which are more commonly referred to as "plastics," are lightweight, soft, readily formable substances, and therefore suitable for use in a wide variety of applications. An interdisciplinary group of Darmstadt researchers is taking a look at a very special function of polymers: They are investigating "smart" macromolecules that react to external stimuli, such as light or electric or magnetic fields, by changing their structures.
New material properties, thanks to ultrathin polymer films
Applied as thin, plastic films, polymers can modify the properties of the underlying materials, since even a film just a single molecule thick, i.e., a film whose thickness falls in the nanometer range, is enough to fully mask the properties of its underlying material, making the polymer film, rather than its underlying material, of importance for reactions of the composite structure with its environment.
Working in collaboration with the German Plastics Institute, the Technische Universität (TU) Darmstadt, and the TU Darmstadt's Center of Smart Interfaces excellence cluster as associate partner, the Darmstadt researchers are conducting investigations of ultrathin films of polymer molecules covering various classes of polymers whose structures and chemical compositions vary widely. One is in the form of solid rods, some have flexible "tails" on their rod-like structures that can link them together, forming membranes, while others behave like a ball of yarn or overcooked spaghetti. Under an initial stage, the researchers are trying to understand the basic mechanisms that will allow configuring efficient, rapid-acting, electronic circuitry.
Once those basic mechanisms have been understood, countless applications of such thin, polymer films applied to various materials will become feasible. Dr. Markus Biesalski, of the TU Darmstadt's Chemistry Dept., who is coordinator of the "Soft Control" project, explained that, "A practical implementation of such switchable surfaces is the reversible wetting of surfaces for, e.g., applications involving printing inks." "Smart" plastic films on materials to be imprinted will initially optimize the adhesions of printing inks, and later simplify their removal during recycling by switching to a repulsive action. Another application area is catalysis, i.e., controlling chemical reactions. Light having a certain wavelength might change the structures of polymers such that the catalytic action of a catalyzer situated beneath a polymer film will be inhibited, while light having another wavelength restarts catalysis. Similar effects might be utilized for switching sensors on and off. Substances for use in configuring new types of biosensors for, e.g., detecting environmental pollutants or diagnosing diseases, might also be developed over the long term.
The properties of biological materials can also be changed
The Darmstadt researchers are also targeting biological materials. For example, protein molecules that act as channels for potassium ions, calcium ions, or other ions in cell membranes might be reconfigured into new types of nanoswitches using biogenetic methods. Such channels might be incorporated into polymers in the form of tiny switching units that respond to external stimuli, such as light. As Prof. Gerhard Thiel, of the TU Darmstadt's Biology Dept., put it, "That might allow highly selectively transmitting medications to just those parts of the body where they are needed." Patients would swallow capsules containing small, spherical, polymer shells containing the medication, and the shells would then be distributed throughout their bodies. The shells would contain an ion channel that responds to light. Irradiation of the location where the medication is to be liberated would then cause the shells to dissolve, releasing the medication at just that location.