Jülich/Aachen, 9 February 2022 - Scientists from Forschungszentrum Jülich and RWTH Aachen University have for the first time demonstrated thermal writing and data storage in a responsive polymer. This makes it possible to manufacture thermal memory devices and temperature-controlled drug release carriers. In the responsive material investigated, information can be written thermally using a laser, or just simply using heated or cooled pen tips, for example, on a thin film backscattering display. The material possesses two thermal states, which can also be switched by the pH-value, enabling an AND-logic gate function. Since the existence of two states is very common in responsive materials, the principle of encoding and storing information is potentially applicable to a broad range of materials.
Responsive or smart materials change their state in response to external triggers. This allows their physical, chemical or biological properties to be regulated by specific physical, chemical, biological, light or environmental stimuli. These materials are therefore studied intensely for use in a wide range of applications such as in sensors, actuators, and targeted drug delivery.
Switching between different states in principle enables information to be written, read out and stored. The key requirement for information storage is the existence of two states that show bistability and remanence. Bistability means that at a given temperature, the polymer can be triggered to be in either one state or the other. Remanence means that the polymer will remain in this state, until triggered into the opposite one. Until now, bistability and remanence have been considered very difficult to achieve in responsive polymers, because of the typically narrow temperature range in which bistability is possible. Researchers at Forschungszentrum Jülich were able to demonstrate for the first time that the intrinsic two-state property of a responsive polymer is sufficient to achieve both bistability and remanence, and indicate how the bistability range could be enlarged to allow reversible write/read information storage.
PNIPAM is one of the most widely used responsive polymers, with applications in hydrogels, actuators, sensors and drug delivery. It undergoes a reversible phase transition when changing temperature or pH-value, which is accompanied by a significant change in light scattering intensity. This property, together with its bistability, was used by the Jülich-Aachen research team to construct thin film backscattering devices, where the two states lead to black or white display states. This device is similar to LCD pixel devices where light is backscattered from a liquid crystal, or for e-paper displays where light is backscattered from a colloidal solution. For the responsive polymer thin film device, information can be written into the device with a laser, or just manually using a heated or cooled pen.
Thin film backscattering device (top) used to thermally write/read/store information using a laser (lower left) or just manually using simple heated or cooled pen tips.
Copyright: Forschungszentrum Jülich / Johanna Michalska-Walkowiak, Stephan Förster
The researchers were able to show that the molecular basis for the observed bistability and remanence is the association and dissociation of certain polymer domains and interface structures, very similar to magnetic domains and interface structures occurring in magnetic information storage materials. This could be demonstrated for the first time using a new soft matter cryo-electron microscope in operation at the Ernst Ruska-Centre in Jülich. For magnetic information storage, a magnetic field is applied to reverse the magnetization direction of a thin magnetic layer, thus changing the magnetic state. This is very similar to what occurs in a thin film pixel device, where for example, using a hot or cold pen locally changes the state of the responsive polymer. Association and dissociation is driven by the formation and splitting of polymer carbonyl or amine hydrogen bonds, a chemical mechanism resembling one which stabilizes protein folding.
Unusual invisible remanence of the encoded information 'Hi!'. The information is written in the bistability region at a certain temperature, becomes invisible after heating, and surprisingly reappears after cooling back to the initial temperature. The visible/invisible cycle can be repeated many times.
Copyright: Forschungszentrum Jülich / Joanna Michalska-Walkowiak, Stephan Förster
Furthermore, the researchers discovered an unusual hidden, non-erasable memory state. After writing, information such as the word 'Hi!' is clearly visible. Heating the device makes the information disappear. After cooling, it becomes visible again. This can be used to hide encoded information simply by changing the temperature.
Original publication:
J. Michalska-Walkowiak, B. Förster, S. Hauschild, S. Förster, Bistability, remanence, read/write-memory and logic gate function via a stimuli responsive polymer, Adv. Mater. 2022,
