Stimulable materials

Persons in charge: Frederic Vidal - Pierre-Henri Aubert

Functional polymer materials made from both IPNs and electronic conductive polymers have as their main application electrostimulable devices (inducing a change in color or volume/shape when an electrical potential is applied).
In this instance, an electronic conductive polymer, PEDOT, is interpenetrated (1 to 30 µm) beneath the surface of a thin ionic conductive IPN membrane containing the ions necessary for the redox process that make the device function. The interpenetrated architecture of these materials has solved almost all limitations presented by such systems in the literature (delamination, cyclability, open-air operating difficulties, need for backing electrodes, etc.).

Depending on the amount of PCE incorporated, changes in volume or shape (actuator, PEDOT > 7%) or color (electrochromic, PEDOT < 0.5%) are observed as a result of electrical stimulation.

Microactuators have been made by processes specific to microsystems. This work is among the most successful in terms of actuation frequency (>100Hz), of dimensions (the smallest published to date), and a liquid medium actuation possibility, in open air and even in a moderate vacuum (10-5 mbar), thus opening new possibilities in the fields of microsystems, microfluidics and biomedicine.

Pictures of micro-actuators obtained by scanning electron microscopy:
at rest and under actuation (rE = ±3V) in a moderate vacuum (10-5 mbar)

Miniaturization has also significantly reduced the actuation voltage of dielectric actuators, generally higher than a kV. For this purpose, specific electrodes have been developed in the form of films of nanometre thickness, consisting of a 2D interconnected network of carbon nanotubes (NTC) in a pi-conjugated polymer monolayer made using the Langmuir-Blodgett technique. These stretchable electrodes remain conductive up to 100% deformation and allow the development of ultrathin actuators (~1 µm) which generate a linear deformation of 4% for an applied voltage of only 100V. (X.Ji et al. 2018 doi :10.2016/j.snb.2018.01.145)

The large variety of pi-conjugated structures offers a wide range of accessible colors. Thus, alternating copolymers of the D-A-D cyan, magenta and yellow type have been developed. These polymers, along with other polymers with achromatic redox states, have been integrated as thin films within electrochromic cells. Their stability in electrochemical ageing within devices has been evaluated.