Radiochemical stability of imidazolium-based ionic liquids constituted of the BuMeIm(+) cation and associated with four commonly used anions (X(-): Tf(2)N(-), TfO(-), PF(6)(-) and BF(4)(-)) has been investigated under gamma irradiation for high irradiation doses (up to 2.0 MGy). The anion effect has been examined by quantifying the radiolytic yields of disappearance for cation and anions and by identifying corresponding radiolysis products with several analytical techniques. On the one hand, a large number of radiolysis products are formed throughout the irradiation in ionic liquid solutions, resulting from reactions of primary generated species of cation and anion by indirect radiolysis. Primary generated species can react together throughout the irradiation by indirect radiolysis to form numerous radiolysis products in small quantities, indicating that several complex degradation pathways are involved for these radiation doses. This degradation pattern has been confirmed by identification of numerous gaseous radiolytic products. On the other hand, quantitative studies show that radiochemical stabilities of ionic liquids are in the same range of values as systems envisioned in nuclear fuel reprocessing with relatively low hydrogen yields. Indeed, this present work emphasizes the suitability of ionic liquids for applications in the nuclear fuel cycle.

The aim of this paper is to introduce dual-material auxetic meta-sandwiches by four-dimensional (4D) printing technology for reversible energy absorption applications. The meta-sandwiches are developed based on an understanding of hyper-elastic feature of soft polymers and elasto-plastic behaviors of shape memory polymers and cold programming derived from theory and experiments. Dual-material lattice-based meta-structures with different combinations of soft and hard components are fabricated by 4D printing fused deposition modelling technology. The feasibility and performance of reversible dual-material meta-structures are assessed experimentally and numerically. Computational models for the meta-structures are developed and verified by the experiments. Research trials show that the dual-material auxetic designs are capable of generating a range of non-linear stiffness as per the requirement of energy absorbing applications. It is found that the meta-structures with hyper-elastic and/or elasto-plastic features dissipate energy and exhibit mechanical hysteresis characterized by non-coincident compressive loading-unloading curves. Mechanical hysteresis can be achieved by leveraging elasto-plasticity and snap-through-like mechanical instability through compression. Experiments also reveal that the mechanically induced plastic deformation and dissipation processes are fully reversible by simply heating. The material-structural model, concepts and results provided in this paper are expected to be instrumental towards 4D printing tunable meta-sandwiches for reversible energy absorption applications.