Experiments on Vortices in Rotating Superfluid 3He-A

A satellite peak has been observed in the NMR spectrum of rotating 3He-A; the peak intensity depends linearly on Ω at the high angular velocities, Ω=0.6−1.5 rad/s, needed to resolve it. The frequency shift of the satellite is independent of Ω. These results strongly suggest the existence of vortices in rotating 3He-A with the vortex density proportional to Ω. Another satellite peak also has been observed which probably is due to solitons.Peer reviewe

NMR Experiments on Rotating Superfluid 3He-A : Evidence for Vorticity

Experiments on rotating superfluid 3He-A in an open cylindrical geometry show a change in the NMR line shape as a result of rotation: The amplitude of the peak decreases in proportion to f(T)g(Ω), where Ω is the angular velocity of rotation; at the same time the line broadens. Near Tc, f(T) is a linear function of 1−T/Tc. At small velocities g(Ω)∝Ω. These observations are consistent with the existence of vortices in rotating 3He-A.Peer reviewe

Hierarchical Supramolecular Cross-Linking of Polymers for Biomimetic Fracture Energy Dissipating Sacrificial Bonds and Defect Tolerance under Mechanical Loading

| openaire: EC/FP7/291364/EU//MIMEFUNBiological structural materials offer fascinating models how to synergistically increase the solid-state defect tolerance, toughness, and strength using nanocomposite structures by incorporating different levels of supramolecular sacrificial bonds to dissipate fracture energy. Inspired thereof, we show how to turn a commodity acrylate polymer, characteristically showing a brittle solid state fracture, to become defect tolerant manifesting noncatastrophic crack propagation by incorporation of different levels of fracture energy dissipating supramolecular interactions. Therein, poly(2-hydroxyethyl methacrylate) (pHEMA) is a feasible model polymer showing brittle solid state fracture in spite of a high maximum strain and clear yielding, where the weak hydroxyl group mediated hydrogen bonds do not suffice to dissipate fracture energy. We provide the next level stronger supramolecular interactions toward solid-state networks by postfunctionalizing a minor part of the HEMA repeat units using 2-ureido-4[1H]-pyrimidinone (UPy), capable of forming four strong parallel hydrogen bonds. Interestingly, such a polymer, denoted here as p(HEMA-co-UPyMA), shows toughening by suppressed catastrophic crack propagation, even if the strength and stiffness are synergistically increased. At the still higher hierarchical level, colloidal level cross-linking using oxidized carbon nanotubes with hydrogen bonding surface decorations, including UPy, COOH, and OH groups, leads to further increased stiffness and ultimate strength, still leading to suppressed catastrophic crack propagation. The findings suggest to incorporate a hierarchy of supramolecular groups of different interactions strengths upon pursuing toward biomimetic toughening.Peer reviewe

Hierarchical Supramolecular Cross-Linking of Polymers for Biomimetic Fracture Energy Dissipating Sacrificial Bonds and Defect Tolerance under Mechanical Loading

Biological structural materials offer fascinating models how to synergistically increase the solid-state defect tolerance, toughness, and strength using nanocomposite structures by incorporating different levels of supramolecular sacrificial bonds to dissipate fracture energy. Inspired thereof, we show how to turn a commodity acrylate polymer, characteristically showing a brittle solid state fracture, to become defect tolerant manifesting noncatastrophic crack propagation by incorporation of different levels of fracture energy dissipating supramolecular interactions. Therein, poly­(2-hydroxyethyl methacrylate) (pHEMA) is a feasible model polymer showing brittle solid state fracture in spite of a high maximum strain and clear yielding, where the weak hydroxyl group mediated hydrogen bonds do not suffice to dissipate fracture energy. We provide the next level stronger supramolecular interactions toward solid-state networks by postfunctionalizing a minor part of the HEMA repeat units using 2-ureido-4­[1<i>H</i>]-pyrimidinone (UPy), capable of forming four strong parallel hydrogen bonds. Interestingly, such a polymer, denoted here as p­(HEMA-<i>co</i>-UPyMA), shows toughening by suppressed catastrophic crack propagation, even if the strength and stiffness are synergistically increased. At the still higher hierarchical level, colloidal level cross-linking using oxidized carbon nanotubes with hydrogen bonding surface decorations, including UPy, COOH, and OH groups, leads to further increased stiffness and ultimate strength, still leading to suppressed catastrophic crack propagation. The findings suggest to incorporate a hierarchy of supramolecular groups of different interactions strengths upon pursuing toward biomimetic toughening

PMSE-489. Tailoring molecular packing for uncommon polymeric self-assemblies.

Tailoring of the interplay of different packing motifs allows to tune the self-assemblies and hierarchies of block copolymers and polymeric complexes. This allows routes to uncommon self-assemblies and even to nanoscale porosity (N. Houbenov et al, Angew. Chem., Int. Ed. 2011, 50, 2516.). However, if the level of frustration becomes excessive, the structure becomes poor. Here we describe two approaches leading to uncommon self-assemblies. The first example deals anionically synthesized polystyrene-block-poly(1,4-isoprene)-block-poly(dimethyl siloxane)-blockpoly(tert-butyl methacrylate)-block-poly(2-vinylpyridine) pentablock copolymers (P. Fragouli et al, J. Polym. Sci, A 2008, 46, 3938). Here its self-assembly to form complicated multicompartmental micelles is described based on transmission electron microscopy tomography and several staining protocols (J. Haataja et al, in progress). The second example deals four-arm miktoarm polyethylene glycol polymer that has ammonium chloride end groups. Upon complexing with iodoperfluoroalkanes by halogen bonding, it adopts a particularly well developed lameller order, due to the very high repulsion between the fluorous tails and the hydrophilic polymer, leading to minimized interface area (N. Houbenov et al, Nature Commun, 2014, 5, 4043). In combination with reduced entanglements as allowed by starshaped polymers in comparison to corresponding linear ones, and the high packing tendency of the fluorous rods, the self-assembly extends from nanometers to millimeters in a common alignment