Conference Agenda

In this contribution, we give an overview of methods and techniques

that we apply in our group to elucidate the specific behaviour

of functional nano-structures in the condensed phase on a molecular basis.

A special focus will be on materials that can be reversibly photoswitched by external light stimulus.

When molecular photo-switches, such as azobenzene or norbornadiene, are embedded into a sufficiently soft polymer matrix the resulting compound can undergo a mechanical deformation induced by light of a specific wavelength. These photo-sensitive compounds have the potential to be applied as soft actuators without the need for hard wired electronics or a separate energy source. Such characteristics are especially attractive in the design of micro-scale robots but also other applications such as high-speed data transfer or the conversion of photonic energy into a mechanical response holds great promise.

Despite these almost futuristic possibilities, photo-sensitive polymers have not yet experienced a sufficient attention in industrial applications. One important factor to increase the acceptance of this group of soft smart materials is the formulation of a rigorous constitutive modeling approach in combination with numerical simulation methods. Thus, in this contribution we present a photo-mechanical modeling approach solved with the help of a finite element implementation.

We develop a theoretical and computational framework to perform topology optimization of the representative volume element (RVE) of flexoelectric metamaterials [2].

The flexoelectric effect is an electromechanical coupling between polarization and strain gradient as well as strain and electric field gradients, present in small (micro-to-nano) scales [1]. It is universal to dielectrics, but, as compared to piezoelectricity, it is more difficult to harness as it requires small scales and field gradients. These drawbacks can be overcome by suitably designing geometrically polarized metamaterials made of a nonpiezoelectric base material but exhibiting apparent piezoelectricity [3].

We solve the governing equations of flexoelectricity on a high-order generalized-periodic Cartesian B-spline approximation space. The geometry is unfitted to the mesh, and described by a periodic level set function. Genetic algorithms are considered for the multi-objective optimization of the RVE topology, where area fraction competes with four fundamental piezoelectric functionalities (stress/strain sensor/actuator). During the optimization process, the RVE topologies are restricted to be fully-connected in a single group of material.

We obtain Pareto fronts and discuss the different material topologies depending on the area fraction and the apparent piezoelectric coefficient being optimized. Overall, we find RVE topologies exhibiting a competitive apparent piezoelectric behavior as compared to reference piezoelectric materials such as quartz and PZT ceramics. This opens the possibility to design a new generation of devices for sensing, actuation and energy harvesting application using a broad class of base materials.

References

[1] D. Codony, A. Mocci, J. Barceló-Mercader, and I. Arias: Mathematical and computational modeling of flexoelectricity. Journal of Applied Physics 130(23) (2021), 231102.

[2] F. Greco, D. Codony, H. Mohammadi, S. Fernández-Méndez, and I. Arias: Topology optimization of flexoelectric metamaterials with apparent piezoelectricity. arXiv preprint arXiv:2303.09448 (2023).

[3] A. Mocci, J. Barceló-Mercader, D. Codony, and I. Arias: Geometrically polarized architected dielectrics with apparent piezoelectricity. Journal of the Mechanics and Physics of Solids 157 (2021), 104643.