Cross-Disciplinary Activities

• Topics
• Members
• Equipments
• Ongoing theses

Cross-Disciplinary Activities

D. Aubel, J. L. Bubendorf, M. Cranney, E. Denys, A. Florentin, F. Vonau et L. Simon

In our more cross-disciplinary activities, we focus on various systems and materials synthesized and studied at IS2M, and more broadly on polymers/photopolymers and supramolecular assemblies. Our approach aims to address fundamental questions raised by macroscale processes at the mesoscale level. Conversely, we also seek to explore the properties of systems such as supramolecular assemblies, and even to fabricate devices based on them. We are able to investigate these systems from the single molecule up to micrometer-scale single crystals, with regard to their organization, self-assembly processes, electronic properties, and more.
Over the past few years, we have developed novel characterization setups, such as STM at the liquid–solid interface or advanced AFM modes, including PeakForce mode coupled with conductive c-AFM. In parallel, we also study increasingly “exotic” systems from the perspective of physicists specialized in UHV and thin films.
We have published a study on photopolymers synthesized via an orthogonal chemistry approach derived from additive manufacturing. Our focus was specifically on Polydiacetylene (PDA), a quasi-one-dimensional conjugated polymer. The adjacent figure illustrates this work. PDA is formed through the self-assembly of diacetylene monomers, followed by the creation of linear covalent bonds between them via either photopolymerization or thermal activation. PDA exhibits two main phases : the so-called “blue” phase, characterized by a planar macromolecular backbone, and the “red” phase, where the backbone linearity is disrupted. The blue phase, with strong absorption in the 600–640 nm range, can undergo a blue-to-red phase transition triggered by various stimuli (mechanical, thermal, pH, etc.). The red phase then becomes photoluminescent, with absorption shifting to the 500–550 nm range. This optoelectronic change from non-fluorescent (blue phase) to fluorescent (red phase), which is visible to the naked eye, has made PDA-based photopolymers extensively studied for over three decades in a wide array of sensing applications.
A known mechanism in additive manufacturing is phase separation induced by photopolymerization. This out-of-equilibrium process is expected to result in material shrinkage, phase separation, and conformational stabilization. By combining acrylate and PDA, which polymerize under different wavelengths, we have demonstrated the formation of perfectly ordered PCDA crystals, which become either embedded in or released from the acrylate matrix due to photon-induced phase separation. We also show that the expected blue-to-red thermal transition is delayed or even suppressed when the PDA in the blue phase is mechanically constrained by the acrylate matrix. This work provides deeper insight into the role of lateral alkyl chains and their conformations on the conformation of the central PDA backbone [1].

Mesoscale Study of an Additive Manufacturing Process. The mixture of two resins—PCDA and polyacrylate—which polymerize under different wavelengths (orthogonal chemistry), leads to phase separation accompanied by dewetting of part of the acrylate, resulting in the release of highly ordered PCDA crystals. In this out-of-equilibrium process, some of the crystals become trapped within the acrylate matrix and remain under mechanical constraint, which inhibits the thermally induced “blue-to-red” phase transition of PCDA. Correlative SEM-CL is schown on the left. Polydiacetylene photocomposite material obtained by orthogonal chemistry : a detailed study at the mesoscopic scale J. Teyssandier, M. Fouchier, J. Lalevée and L. Simon Materials Advances 3(5), 2558-2567 (2022) DOI : 10.1039/d1ma01099a

In this work, we also report for the first time the use of cathodoluminescence (CL) on polymeric structures. Four distinct emission components are observed, which we attribute to different conformations of the polymer backbone — ranging from short and defect-rich chains at lower wavelengths to longer, more ordered chains at higher wavelengths. The features at 600 and 700 nm likely correspond to the well-known blue-to-red phase transition. This will need to be confirmed by correlative photoluminescence (PL) measurements, which will be carried out using our new Attolight® tool which combine CL, Raman and PL as part of the Mat-Light 4.0 project.

Following up on this work, we have extended our interest to a PDA-type system in which the side chains are minimized, in order to limit the influence of functional groups on the conformation of the central PDA backbone. These chains are reduced to their simplest form (as short as possible) to minimize environmental effects—such as crystallinity—on the conformation of the central PDA polymer, and to preserve the possibility of a well-defined Peierls-type blue-to-red phase transition.

The current PhD project (PhD : Yurii Zubchuck, in collaboration with N. Blanchard, LIMA-CNRS-UHA) focuses on the synthesis of PIDA (Poly-Iodo-Diacetylene) polymers, where the alkyl side chain is reduced to a single iodine atom.

To achieve the polymerization conditions of DA into PDA—referred to as topochemistry—the DA monomers must be precisely aligned with specific angles and inter-monomer distances to enable polymerization, either through photochemical activation or thermal treatment. Since the functional side chains are reduced to a single atom, they cannot facilitate supramolecular organization on their own. Therefore, it is necessary to design a suitable ‘host’ molecule to enable co-crystallization and form a supramolecular co-crystal, as illustrated in the figure below.

Guest A and Hosts B leading to co-crystal C, the precursor for topochemical polymerization.The best result obtained so far is based on N1,N2-bis(2-(pyridin-3-yl)ethyl)oxalamide as the host molecule (Py Host)

This PIDA polymer is also of great interest, as it represents a potential precursor to the last remaining unsynthesized carbon allotrope—following graphene, nanotubes, and carbon nano-onions : the Carbyne wire. Carbyne is a truly one-dimensional molecule composed of an infinitely long chain of polyynes (–[C≡C–]ₙ). This opens the opportunity to study a novel type of 1D wire, as well as the potential transition between PIDA and Carbyne, along with the inherent stability challenges associated with such systems.

Schematic mechanism of the transition PIDA to Carbyne by deiodination

Development of new tools.

We have recently developed a nanoprobing station equipped with micro/nano-manipulators under SEM, combined with a cryostat stage (300°C to 77K), as part of the Grand Est NanoteraHertz project (see adjacent figure). This open-access platform now enables us to perform mesoscale characterization of a wide range of materials, from 2D materials to supramolecular crystals and photopolymers. The figure shows several examples of studied systems.