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Séminaire PMMH - Min-Hui LI (Chimie ParisTech )
1er févrierVendredi 8 mars de 11h00 à 12h00 - Salle réunion PMMH 1Electroactive Bi-functional Liquid Crystal Elastomer Actuators
Liquid crystal elastomers (LCEs) show promising potentials as smart actuators, for example, those contracting/expanding linearly like mammalian muscles.[1] Direct heating and light illumination are the most used activation mode in LCE actuators because LCEs are based on thermotropic or phototropic liquid crystals.[1,2,3] However, in the world of actuators, electrical energy is the most convenient and the most in demand stimuli. Indeed, the nature does use electrical impulses between nerves and muscles or skins for actuation or sensing with extraordinary efficacy, and electrical stimulation is also more widely utilizable as driving forces in industrial devices. Efforts have been made to achieve electroactive LCEs (eLCEs).
In this talk, I will present a trilayer electroactive LCE (eLCE) system by combining two smart materials, LCE and ionic electroactive polymer device (i-EAD), which is bi-functional and can perform either bending or contractile deformations under low voltage stimulation.[4] By applying a voltage of ±2 V at 0.1 Hz, the redox behavior and associated ionic motion in the two conducting polymer electrodes of i-EAD provide bending deformation of the device up to a bending strain difference of 0.8% for a sample of 0.5 mm thickness. On the other hand, by applying a voltage of ± 6V at 10 Hz, the ionic current-induced Joule heating triggers the muscle-like contractile response of the central ion-conducting LCE component, a linear contraction ratio of 20% being obtained without load. Moreover, a load of 270 times of the weight of trilayer eLCE film can be left with a strain of 20%. This approach of combining two smart polymer technologies, i.e., LCE and i-EAD, in a single device, is promising for the development of smart materials with multiple degrees of freedom in soft robotics, electronic devices, and sensors.
References
[1] M.-H. Li, P. Keller P., Artificial muscles based on liquid crystal elastomers, Phil. Trans. A. 364, 2763 (2006).
[2] B. Ni, G. Liu, M. Zhang, P. Keller, M. Tatoulian, M.-H. Li, Large-Size Honeycomb-Shaped and Iris-Like Liquid Crystal Elastomer Actuators, CCS Chemistry, 4, 847 (2022).
[3] B. Ni, G. Liu, M. Zhang, M. Tatoulian, P. Keller, M.-H. Li, Customizable Sophisticated 3D Shape Changes of Large-size Liquid Crystal Elastomer Actuators, ACS Appl. Mater. Interfaces, 13, 54439 (2021).
[4] G. Liu, Y. Deng, G. Nguyen, C. Vancaeyzeele, A. Brûlet, F. Vidal, C. Plesse, M.-H. Li, Electroactive Bi-functional Liquid Crystal Elastomer Actuators, Small, 2023, 2307565. -
Séminaire PMMH - Jon Otto Fossum (Dept of Physics , NTNU, Trondheim, Norway)
1er févrierVendredi 16 février de 11h00 à 12h00 - Salle réunion PMMH 1Clay minerals as 2D natural nanomaterials for sustainable applications
Clay minerals are among the most abundant and sustainable on earth, and due to this and their low-cost they are found in many traditional applications that exploit their physical and chemical properties, including their mechanical stability, their non-toxicity and in effect their underlying 2D nanoscale character. These traditional applications can for the most part be categorized as low-tech based on empirical knowledge, and they include use of clay mineral particles in bricks and pottery, clay mineral partivles as rheology modifiers, and clay powders or clay nanoporous structures as sorbents or catalysts.
Synthetic clays are of superior quality compared to natural clays, and they have opened up and enabled pathways towards new applications, such as clay minerals for structural coloration, for use in 2D electronic nanodevices, for targeted gas barriers or gas separation, for instance separation of H2 and CO2.
In this lecture such recent developments in natural nanomaterials science, discovered and investigated in our group, will be presented, pointing out that for instance clay minerals are unexploited materials for future sustainable technologies. -
Séminaire PMMH - Thomas Salez (LOMA, Bordeaux)
11 janvierVendredi 9 février de 11h00 à 12h00 - Salle réunion PMMH 1Brownian motion in confinement
Brownian motion near interfaces is a canonical situation, encountered from fundamental biophysics to nanoscale engineering. Using a combination of experimental, theoretical and numerical methods, we study the thermally-induced random tridimensional trajectories of individual microparticles, within salty aqueous solutions, in the vicinity of rigid walls, and in the presence of surface charges. We construct the time-dependent position and displacement probability density functions, and study the non-Gaussian character of the latter which is a direct signature of the hindered mobility near the wall. Furthermore, we implement a robust multifitting method, allowing for the thermal-noise-limited inference of diffusion coefficients spatially resolved at the nanoscale, equilibrium potentials, and forces at the femtonewton resolution. Finally, we discuss more complex situations, such as the ones involving soft boundaries, external flows or active microswimmers.
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Séminaire PMMH - Sylvain Lefebvre (INRIA Nancy)
11 janvierVendredi 26 janvier de 11h00 à 12h00 - Salle réunion PMMH 1Controlling the appearance and deformation of 3D printed objects.
This seminar will focus on how to design shapes and plates that exhibit specific
behaviors thanks to a precise control of their fabrication process.
Specifically, by orienting the deposition trajectories of a fused filament 3D
printer, we introduce anisotropies that impact the observed properties of the
final object. In one case, the orientations trigger anisotropic deformations
under heat, allowing a plate to take a target curved shape. In the second case,
the changes in deposition orientation trigger an anisotropic light reflectance,
creating brushed-metal effects on the surface of the 3D printed object.Both approaches rely on the optimization of oscillating fields, a topic we
initially explored in the context of Computer Graphics, and that naturally
evolved toward fabricating shapes with anisotropic structures. -
Séminaire PMMH, Joshua Dijksman (UVA)
10 janvierVendredi 19 janvier de 11h00 à 12h00 - Salle réunion PMMH 1Covalent adaptable polymer networks provide mechanical tunability via molecular and mesoscopic lengthscales
Polymeric materials are ubiquitous in society but also present a large source of waste. There is an ongoing search for polymeric materials that can be better tuned and recycled. One class of polymers that came into the spotlight for this purpose are so-called covalent adaptable polymer networks. Such polymer networks are dynamic due to the reversible nature of some of the bonds. We demonstrate that fine-grained, quantitative control over macroscopic dynamic material properties can be achieved in such materials using the Hammett equation that controls the strength of the dynamic bonds. Moreover, we reveal with Raman spectroscopy that mesoscopic phase separation occurs in these materials. The phase separation can be controlled via concentration and molecular design. The mechanisms of phase separation in dynamic polymer networks are particularly interesting as the reversible nature of the network participates in the structuring of the micro- and macromolecular domains, for which theoretical development is still largely incomplete.