Ridge energy for thin nematic polymer networks

Minimizing the elastic free energy of a thin sheet of nematic polymer network among smooth isometric immersions is the strategy purported by the mainstream theory. In this paper, we broaden the class of admissible spontaneous deformations: we consider ridged isometric immersions, which can cause a sharp ridge in the immersed surfaces. We propose a model to compute the extra energy distributed along such ridges. This energy comes from bending; it is shown under what circumstances it scales quadratically with the sheet’s thickness, falling just in between stretching and bending energies. We put our theory to the test by studying the spontaneous deformation of a disk on which a radial hedgehog was imprinted at the time of crosslinking. We predict the number of folds that develop in terms of the degree of order induced in the material by external agents (such as heat and illumination). Graphic Abstract

Electron Localizations in Alloy Exhibiting Nanotwinning

Ni2MnGa is a ferromagnetic shape memory alloy in which a large spontaneous deformation up to 12% has been observed after application of an external magnetic field [1]. [...]

New insight on cubic–tetragonal–monoclinic phase transitions in ZrO2: ab initio study and symmetry analysis

A group-theory analysis of temperature-induced phase transitions in ZrO2 has been performed in the framework of the group–subgroup relationship tree (Bärnighausen tree) with the computer tools of the Bilbao Crystallographic Server. The transition paths including symmetry-allowed intermediate phases have been established. The active irreducible representations corresponding to soft phonon modes and spontaneous deformation strains responsible for the phase transitions have been determined. The phonon mode frequencies at the symmetry points of the Brillouin zones of cubic, tetragonal and monoclinic phases have been calculated using the ab initio density functional theory method. As a result, the soft modes and their symmetries have been revealed, which are in a complete agreement with the group-theoretical predictions.