Photo-switchable mechanical response of polymer thin films: application to flexible printed electronic – PhotoPrint

The interest is increasingly high in adding flexible electronics to everyday items including the wearable space, smart packaging and smart labels. Every month a new printed system emerges from the flexible electronics industry and the economic growth is not slowing down since the market is expected to reach 100B$ in 2025. For these reasons any progress in the development of such materials that could be processed at high speed and at a relative low cost may really impact on our everyday life. There is also an increasing demand in industry for smart materials/coatings that exhibit advanced properties that enables the coating to respond to environmental changes. Light-responsive materials in which a quick and reversible response can be achieved are of particular interest. As a consequence, any development of photo-responsive materials that can offer the opportunity to bring new reversible properties such as self-repairing or actuator functions in an efficient manner remains a research challenge.

Objectives
The photo-sensitive polymers chosen for this project are polyethylene terephtalate (PET) block copolymers with an azobenzene type molecules block (e.g. azopolymer). For some azopolymers, the trans-cis photo-isomerisation induces reversible modification of the glass transition temperature (Tg) leading to a reversible solid to liquid phase transition (RSLPT).
The first objective of the PhotoPrint project is to demonstrate the potential application of the reversible solid to liquid phase transition of azopolymers in the flexible electronic industry with a focus on the printing process and self-healing properties.
The second objective, more theoretical, is to clarify the structure/properties relationships allowing the control of the RSLPT by studying the influence of the chemical structure of the azo-PET block copolymer using an original characterization technique based on AFM force spectroscopy.

Originalities and novelties of the proposal
Theoretical: 1) First systematic study on the impact of the polymer structure on RSLPT mechanism. 2) First investigation of the RSLPT for coatings and thin films thanks to in situ methods based on AFM
Applicative: 1) First synthesis of PET based polymers and coatings compatible with reversible adhesion properties 2) First applications of RSLPT to flexible electronics

Expected impact
Flexible electronics are integrated in everyday items, as a consequence, any progress in this field will have high social and economic impacts. Scientifically, elucidation of the RSLPT process in azopolymer is a “hot” scientific topic in the material community. The success of this project is expected to lead to the publications of several papers (synthesis, control of surface properties) and also to some patenting (synthesis).

Organization and implementation
The success of the PhotoPrint project is guaranteed by the gathering of complementary competencies and experiences of acknowledged research teams: organic chemists (IMMM), polymer chemists (IPREM), specialist of polymer film preparation and characterization (IMMM, IRDL), and experts in printing processes (LG2P).
The strong involvement of the coordinator (67% of its research time) is also a guarantee for the project to be well managed. The funding request (432,0 k€) is in agreement with the ANR offers and take into account the estimated costs for each partners needed to achieve the objectives of the project.