Electromagnetic Activation of Shape Memory Polymer Networks Containing Magnetic Nanoparticles

Summary: By incorporation of surface‐modified superparamagnetic nanoparticles into shape memory polymer matrices, remote actuation of complex shape transitions by electromagnetic fields is possible. The composite thermosets of oligo(ε‐caprolactone)dimethacrylate/butyl acrylate contain between 2 and 12 wt.‐% magnetite nanoparticles serving as nanoantennas for magnetic heating. It is shown that the particles are dispersed homogenously within the matrix and that the basic thermal and mechanical properties of the polymer matrix are maintained. The specific loss power of the particles is determined to be 30 W · g⁻¹ at 300 kHz and 5.0 W. During the shape transition at 43 °C, no further temperature increase is observed.

     

Octasodium hexatungstomanganate(IV) octadecahydrate

The title compound, Na₈[MnW₆O₂₄]·18H₂O, exhibits a structure with six WO₆ octahedral edge‐sharing units surrounding a central centrosymmetric MnO₆ octahedron, with all metal atoms in a common plane. There are three unique Mn—O distances of 1.903 (7), 1.905 (7) and 1.941 (7) Å [average 1.916 (17) Å], while the average W—O distances are 2.17 (4), 1.938 (8) and 1.749 (12) Å for three‐, two‐ and one‐coordinate O atoms, respectively.     

Toward Artificial Mussel-Glue Proteins: Differentiating Sequence Modules for Adhesion and Switchable Cohesion

Artificial mussel-glue proteins with pH-triggered cohesion control were synthesized by extending the tyrosinase activated polymerization of peptides to sequences with specific modules for cohesion control. The high propensity of these sequence sections to adopt β-sheets is suppressed by switch defects. This allows enzymatic activation and polymerization to proceed undisturbed. The β-sheet formation is regained after polymerization by changing the pH from 5.5 to 6.8, thereby triggering O→N acyl transfer rearrangements that activate the cohesion mechanism. The resulting artificial mussel glue proteins exhibit rapid adsorption on alumina surfaces. The coatings resist harsh hypersaline conditions, and reach remarkable adhesive energies of 2.64 mJ m⁻² on silica at pH 6.8. In in situ switch experiments, the minor pH change increases the adhesive properties of a coating by 300 % and nanoindentation confirms the cohesion mechanism to improve bulk stiffness by around 200 %.     

A tropical view on Bruhat-Tits buildings and their compactifications

We relate some features of Bruhat-Tits buildings and their compactifications to tropical geometry. If G is a semisimple group over a suitable non-Archimedean field, the stabilizers of points in the Bruhat-Tits building of G and in some of its compactifications are described by tropical linear algebra. The compactifications we consider arise from algebraic representations of G. We show that the fan which is used to compactify an apartment in this theory is given by the weight polytope of the representation and that it is related to the tropicalization of the hypersurface given by the character of the representation.