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The current development of soft shape-memory materials is typically restricted to the synthesis of thin-walled samples, which greatly limits their practical application. Three-dimensional specimens can be produced using complex manufacturing methods, e.g. with additive manufacturing, but these require specialized equipment, while the production output is usually very low. M. Bobnar, N. Derets, S. Umerova, N. Novak, M. Lavrič, G. Cordoyiannis, B. Zalar and A. Rešetič, together with V. Domenici from Italy developed a new composite shape-memory material made from main-chain liquid crystal elastomer microparticles (LCEs) dispersed in a silicone polymer matrix. The composite dispersions can be effortlessly molded into arbitrary shapes or sizes, most significantly, into bulk-sized solids, which is challenging to achieve using conventional synthesis methods. Shape-memory capabilities result from temperature depended mechanical properties of the LCE inclusions. These become significantly softer at higher temperatures, when the particles reach the isotropic phase, and harden while cooled back into the glassy phase. The composite material can thus be shape-programmed by deforming the material at higher temperature and cooling it into the new stable shape, fixed by the stiffened LCE inclusions. The new shape can then be reset by heating above the isotropic phase temperature. LCE particles can be additionally magnetically ordered, providing for an additional thermomechanical reversible response.… Read the rest “Article in Nature Communications”

One of the major challenges in developing materials for energy storage systems is realizing high energy density while maintaining low dielectric losses. The composite approach, where conductive particles are dispersed in the dielectric matrix, effectively increases the dielectric permittivity but also boosts the losses. An alternative approach is an operation under high electric fields, i.e. increasing the electric breakdown strength (Eb) without increasing the dielectric permittivity.

Phenyl groups are fundamental chain components of many high-temperature polymers and, depending on the polymer’s molecular structure, delocalized electrons in these groups may exhibit a partially positive or negative charge. We prepared blends of polyetherimide (PEI) and polyimide (PI) by the solution casting method and performed their extensive dielectric characterization. We demonstrated a significant enhancement of Eb in blends due to strong electrostatic interactions between different polymer chains; PEI namely contains three negatively charged phenyls, while PI has two strong positively charged phenyl groups. Electrostatic interactions (i) strongly reduce the number of space charges and (ii) lead to much higher chain packing density in blends. Since the breakdown is initiated by charges that are accelerated by an applied electric field in weak points, i.e. voids in the system, both features contribute to the enhancement of Eb.… Read the rest “Strong enhancement of the electric breakdown strength in properly matched polymer blends”

Assistant Professors Uroš Tkalec and Simon Čopar, together with a group of Assistant Professor Xiaoguang Wang from the Ohio State University, published an article Magnetocontrollable droplet mobility on liquid crystal-infused porous surfaces in Nano Research. The authors report the effects of the magnetic field on the wettability and mobility of water droplets on three typical mesophases of liquid crystal films. The results enable new designs for responsive surfaces that can manipulate the mobility of water droplets.

Assis. prof. Anton Gradišek and colleagues published a paper Bumble bee nest thermoregulation: a field study in Journal of Apicultural Research. They studied six bumblebee colonies of different species using a home-made setup. The study focused on the nest thermoregulation, which is important in order for the larvae to develop properly. They identified some thermoregulation strategies that have not previously been reported in bumblebees.

Abdelrahim Ibrahim Hassanien, PhD from the Department of Condensed Matter Physics F5 and colleagues from Germany have published in Particle & Particle Systems Characterization the article Neuronal-like Irregular Spiking Dynamics in Highly Volatile Memristive Intermediate-scale AgPt-Nanoparticle Assemblies.

Neuromorphic computing seeks functional materials capable of emulating brain-like dynamics to solve complex computational problems. Interestingly, the transport properties of memristive materials show feature that is closely oriented toward the behavior of artificial neurons. However, artificial neurons are rather rigid mathematical concepts than realistic projections of complex neuronal dynamics.

Neuroscience suggests that highly efficient information representation on the level of individual neurons relies on dynamical features such as excitatory and inhibitory contributions, irregularity of firing patterns, and temporal correlations. Here, a conductive atomic force microscopy approach is applied to probe the memristive dynamics of nanoscale assemblies of AgPt-nanoparticles at the stability border of the conducting state, where physical forces causing the formation and decay of filamentary structures appear to be balanced. This unveils a dynamic regime, where the memristive response is governed by irregular firing patterns. The significance of such a dynamical regime is motivated by close similarities to excitation and inhibition-governed behavior in biological neuronal systems, which is crucial to tune biological neuronal systems into a state most suitable for information representation and computation.