186 research outputs found
Self-Assembly of Supramolecules Consisting of Octyl Gallate Hydrogen Bonded to Polyisoprene-block-poly(vinylpyridine) Diblock Copolymers
Synchrotron radiation was used to investigate the self-assembly in two comb-shaped supramolecules systems consisting of octyl gallate (OG), i.e., 1-octyl-3,4,5-trihydroxybenzoate, hydrogen bonded to the pyridine groups of polyisoprene-block-poly(vinylpyridine) diblock copolymers. In the case of the 1,2-polyisoprene-block-poly(4-vinylpyridine)(OG)x system, self-assembly was only observed for x β₯0.5, where x denotes the number of OG molecules per pyridine group. For x = 0.5, 0.75, 1.0, and 1.2 the system self-assembled in the form of hexagonally ordered cylinders of P4VP(OG) throughout the entire temperature range of 25-200 Β°C investigated. For the 1,4-polyisoprene-block-poly(2-vinylpyridine)(OG)x system, on the other hand, a considerably more complex phase behavior was found, including the formation of cubic, hexagonally ordered cylinders and lamellar morphologies. In this case several order-order transitions were observed as a function of temperature, including a lamellar to lamellar transition involving a collapse of the layer thickness. The absence of hydrogen bonding between the octyl gallate molecules and the pyridine groups at elevated temperatures is argued to be a key factor for many of the phenomena observed.
Magnetic nanocomposites at microwave frequencies
Most conventional magnetic materials used in the electronic devices are
ferrites, which are composed of micrometer-size grains. But ferrites have small
saturation magnetization, therefore the performance at GHz frequencies is
rather poor. That is why functionalized nanocomposites comprising magnetic
nanoparticles (e.g. Fe, Co) with dimensions ranging from a few nm to 100 nm,
and embedded in dielectric matrices (e.g. silicon oxide, aluminium oxide) have
a significant potential for the electronics industry. When the size of the
nanoparticles is smaller than the critical size for multidomain formation,
these nanocomposites can be regarded as an ensemble of particles in
single-domain states and the losses (due for example to eddy currents) are
expected to be relatively small. Here we review the theory of magnetism in such
materials, and we present a novel measurement method used for the
characterization of the electromagnetic properties of composites with
nanomagnetic insertions. We also present a few experimental results obtained on
composites consisting of iron nanoparticles in a dielectric matrix.Comment: 20 pages, 10 figures, 5 table
Extended conformations of isolated molecular bottle-brushes:Influence of side-chain topology
A Monte Carlo study is presented to discuss the influence of the side-chain topology on the enhancement of the persistence length of a molecular bottle-brush in a dilute athermal solution due to the excluded volume interactions between the side chains. The structures investigated consisted of freely jointed backbones of 100 hard spheres (beads) of diameter 1 to which 50 equally flexible side chains were grafted. The diameter of the side-chain beads was varied from 1 to 3 in the same units. For every given size of the side-chain bead, the length of the side chains was varied from 4 to 20 beads. The ratio between the persistence length and the bottle-brush diameter, which is the determining factor for lyotropic behavior of conventional semi-flexible chains, was found to be almost independent of the side-chain length. At the same time, it was found to increase considerably with increasing size of the side-chain beads, suggesting that by a proper choice of the chemistry lyotropic behavior of molecular bottle-brushes due to excluded-volume interactions between the side chains might be achieved. Moreover, relatively short side chains can be used since the side-chain length has only a minor influence on the ratio between the persistence length and the diameter. These findings are in a good agreement with recent experimental observations
Magnetically tunable electrokinetic instability and structuring of non-equilibrium nanoparticle gradients
Inspired by emergent behaviors of living matter, there is increasing interest
in developing approaches to create dynamic patterns and structures in synthetic
materials with controllable complexity to enable functionalities that are not
possible in thermodynamic equilibrium. Here we show that electrophoretically
driven and maintained non-equilibrium gradients of magnetic nanoparticles in
non-polar solvent can undergo electrokinetic instabilities (EKI), leading to
various electrically controllable spatiotemporally patterned states. These
electrokinetic instabilities and patterns can be tuned with a magnetic field
via magnetostatic energy reduction mechanism to both increase and decrease the
pattern complexity. We reflect the experimental observations on the theoretical
electrokinetic and magnetostatic arguments. We further show that small amounts
of polar water in the otherwise non-polar system are critical enablers for the
electrophoretic mobility of the nanoparticles. Since functionalities of
magnetic nanoparticles are widely tunable, we foresee that the combination of
dissipative electrokinetic driving and magnetic energy reduction can lead to
novel functional dissipative materials
Ferromagnetic resonance in -Co magnetic composites
We investigate the electromagnetic properties of assemblies of nanoscale
-cobalt crystals with size range between 5 nm to 35 nm, embedded in a
polystyrene (PS) matrix, at microwave (1-12 GHz) frequencies. We investigate
the samples by transmission electron microscopy (TEM) imaging, demonstrating
that the particles aggregate and form chains and clusters. By using a broadband
coaxial-line method, we extract the magnetic permeability in the frequency
range from 1 to 12 GHz, and we study the shift of the ferromagnetic resonance
with respect to an externally applied magnetic field. We find that the
zero-magnetic field ferromagnetic resonant peak shifts towards higher
frequencies at finite magnetic fields, and the magnitude of complex
permeability is reduced. At fields larger than 2.5 kOe the resonant frequency
changes linearly with the applied magnetic field, demonstrating the transition
to a state in which the nanoparticles become dynamically decoupled. In this
regime, the particles inside clusters can be treated as non-interacting, and
the peak position can be predicted from Kittel's ferromagnetic resonance theory
for non-interacting uniaxial spherical particles combined with the
Landau-Lifshitz-Gilbert (LLG) equation. In contrast, at low magnetic fields
this magnetic order breaks down and the resonant frequency in zero magnetic
field reaches a saturation value reflecting the interparticle interactions as
resulting from aggregation. Our results show that the electromagnetic
properties of these composite materials can be tuned by external magnetic
fields and by changes in the aggregation structure.Comment: 14 pages, 13 figure
In-situ SAXS study on the alignment of ordered systems of comb-shaped supramolecules:A shear-induced cylinder-to-cylinder transition
A tooth rheometer, designed to investigate in-situ the influence of large-amplitude oscillatory shear on the macroscopic orientation of complex fluids, is used to study the alignment of two supramolecular systems composed of a polyisoprene-block-poly(2-vinylpyi-idine) block copolymer with octyl gallate (OG) hydrogen bonded to the vinylpyridine block. The molecular ratio x between OG and pyridine groups in these two PI-b-P2VP(OG)(x) systems is 0.50 and 0.75, respectively. In both cases, a hexagonally ordered cylindrical self-assembly was revealed by small-angle X-ray scattering in a broad temperature range. The spacing of the hexagonal structure decreases significantly on heating and reversibly increases on cooling. In in-situ SAXS experiments, performed with the tooth rheometer, a gradual macroscopic alignment of the nanoscale structure is observed on heating for both supramolecular systems. The most striking feature is a shear-induced transition from one hexagonal structure to another, more aligned, hexagonal structure observed for PI-b-P2VP(OG)0.75 in the temperature range 120-140degreesC. The transition is accompanied by an abrupt reduction of the domain spacing and additionally by a decrease of the phase angle measured by the rheometer. In the PI-b-P2V-P(OG)(0.5) system a comparable reduction in the spacing is observed at 90-95degreesC. In this case, it coincides with the most intensive macroscopic alignment of the sample, proceeding in a continuous rather than discontinuous fashion. This behavior is discussed in terms of the breaking of the hydrogen bonds between OG and P2VP being facilitated by shear
Π Π°Π·ΡΠ°Π±ΠΎΡΠΊΠ° ΡΠ΅Ρ Π½ΠΎΠ»ΠΎΠ³ΠΈΠΈ Ρ ΡΠ΄ΠΎΠΆΠ΅ΡΡΠ²Π΅Π½Π½ΠΎΠ³ΠΎ ΠΈΠ·Π΄Π΅Π»ΠΈΡ ΠΈΠ· ΠΌΠ΅ΡΠ°Π»Π»Π° ΠΏΠΎ ΡΠ΅Ρ Π½ΠΎΠ»ΠΎΠ³ΠΈΠΈ ΠΊΠΎΠ²ΠΊΠΈ
ΠΡΠΏΡΡΠΊΠ½Π°Ρ ΠΊΠ²Π°Π»ΠΈΡΠΈΠΊΠ°ΡΠΈΠΎΠ½Π½Π°Ρ ΡΠ°Π±ΠΎΡΠ° 80Ρ., 24 ΡΠΈΡ., 16 ΡΠ°Π±Π»., 10 ΠΈΡΡΠΎΡΠ½ΠΈΠΊΠΎΠ², 2 ΠΏΡΠΈΠ».
ΠΠ»ΡΡΠ΅Π²ΡΠ΅ ΡΠ»ΠΎΠ²Π°: Ρ
ΡΠ΄ΠΎΠΆΠ΅ΡΡΠ²Π΅Π½Π½Π°Ρ ΠΊΠΎΠ²ΠΊΠ°, ΡΠ²Π°ΡΠΊΠ°, ΡΠ΅Ρ
Π½ΠΎΠ»ΠΎΠ³ΠΈΡ, ΡΠ²Π΅ΡΠΈΠ»ΡΠ½ΠΈΠΊ, ΠΌΠ΅ΡΠ°Π»Π», Π±ΠΈΠΎΠ½ΠΈΡΠ΅ΡΠΊΠΈΠΉ ΡΡΠΈΠ»Ρ, ΡΡΠΈΠ»ΠΈΠ·Π°ΡΠΈΡ.
ΠΠ±ΡΠ΅ΠΊΡΠΎΠΌ ΠΈΡΡΠ»Π΅Π΄ΠΎΠ²Π°Π½ΠΈΡ ΡΠ²Π»ΡΠ΅ΡΡΡ ΡΠ΅Ρ
Π½ΠΎΠ»ΠΎΠ³ΠΈΡ Ρ
ΡΠ΄ΠΎΠΆΠ΅ΡΡΠ²Π΅Π½Π½ΠΎΠΉ ΠΊΠΎΠ²ΠΊΠΈ, ΠΊΠ°ΠΊ Π² ΡΠ΅Π»ΠΎΠΌ, ΡΠ°ΠΊ ΠΈ ΠΏΡΠΈΠΌΠ΅Π½ΠΈΡΠ΅Π»ΡΠ½ΠΎ ΠΊ ΠΊΠΎΠ½ΠΊΡΠ΅ΡΠ½ΠΎΠΌΡ ΠΈΠ·Π΄Π΅Π»ΠΈΡ.
Π¦Π΅Π»Ρ ΡΠ°Π±ΠΎΡΡ β ΡΠΎΠ·Π΄Π°Π½ΠΈΠ΅ Π΄Π΅ΠΊΠΎΡΠ°ΡΠΈΠ²Π½ΠΎΠ³ΠΎ Π½Π°ΠΏΠΎΠ»ΡΠ½ΠΎΠ³ΠΎ ΡΠ²Π΅ΡΠΈΠ»ΡΠ½ΠΈΠΊΠ° ΠΏΠΎ ΡΠ΅Ρ
Π½ΠΎΠ»ΠΎΠ³ΠΈΠΈ Ρ
ΡΠ΄ΠΎΠΆΠ΅ΡΡΠ²Π΅Π½Π½ΠΎΠΉ ΠΊΠΎΠ²ΠΊΠΈ.
Π ΠΏΡΠΎΡΠ΅ΡΡΠ΅ ΠΈΡΡΠ»Π΅Π΄ΠΎΠ²Π°Π½ΠΈΡ ΠΏΡΠΎΠ²ΠΎΠ΄ΠΈΠ»ΠΈΡΡ ΠΊΠ»Π°ΡΡΠΈΡΠΈΠΊΠ°ΡΠΈΠΎΠ½Π½ΡΠ΅ ΠΈ ΠΊΠΎΠΌΠΏΠ»Π΅ΠΊΡΠ½ΡΠ΅ Π°Π½Π°Π»ΠΈΠ·Ρ ΡΡΠ½ΠΊΡΠΈΠΉ ΡΠ²Π΅ΡΠΈΠ»ΡΠ½ΠΈΠΊΠ°, ΡΠ»Π΅ΠΌΠ΅Π½ΡΠΎΠ² ΠΊΠΎΠ½ΡΡΡΡΠΊΡΠΈΠΈ, ΡΡΠ°ΠΏΠΎΠ² ΡΠΎΡΠΌΠΎΠΎΠ±ΡΠ°Π·ΠΎΠ²Π°Π½ΠΈΡ ΠΈ ΡΡΠΈΠ»ΠΈΠ·Π°ΡΠΈΠΈ, Π° ΡΠ°ΠΊΠΆΠ΅ ΡΠ²ΠΎΠΉΡΡΠ² ΠΌΠ°ΡΠ΅ΡΠΈΠ°Π»ΠΎΠ², ΠΏΡΠΈΠΌΠ΅Π½ΡΠ΅ΠΌΡΡ
Π΄Π»Ρ ΡΠΎΠ·Π΄Π°Π½ΠΈΡ ΠΈΠ·Π΄Π΅Π»ΠΈΡ.
Π ΡΠ΅Π·ΡΠ»ΡΡΠ°ΡΠ΅ ΠΈΡΡΠ»Π΅Π΄ΠΎΠ²Π°Π½ΠΈΡ Π±ΡΠ»ΠΈ ΠΏΠΎΠ»ΡΡΠ΅Π½Ρ ΠΈ ΠΊΠ»Π°ΡΡΠΈΡΠΈΡΠΈΡΠΎΠ²Π°Π½Ρ Π΄Π°Π½Π½ΡΠ΅ ΠΎ ΡΠ°Π·Π»ΠΈΡΠ½ΡΡ
ΡΡΠ½ΠΊΡΠΈΡΡ
ΠΈ ΠΏΠ°ΡΠ°ΠΌΠ΅ΡΡΠ°Ρ
ΡΠ°Π·ΡΠ°Π±Π°ΡΡΠ²Π°Π΅ΠΌΠΎΠ³ΠΎ ΠΎΠ±ΡΠ΅ΠΊΡΠ°, ΡΡΠΎ ΠΏΠΎΠ·Π²ΠΎΠ»ΠΈΠ»ΠΎ Π² Π΄Π°Π»ΡΠ½Π΅ΠΉΡΠ΅ΠΌ ΡΠΎΠ·Π΄Π°ΡΡ ΡΠ°Π±ΠΎΡFinal qualifying work of 80c., 24 fig., 16 tab., 10 sources, 2 adj.
Keywords: art forging, welding, technology, lamp, metal, bionic style, stylization.
The object of research is the technology of artistic forging, both in general and in relation to a particular product.
The purpose of the work - the creation of a decorative floor lamp by art forging technology.
The study carried out classification and complex analyzes luminaire features design elements, the stages of shaping and styling, as well as the properties of the materials used to create the product.
The study was prepared and classified data about the various features and options developed by the object, which will continue to create the workpiece in real using the claimed technology.
The basic constructive, technological a
Self-Assembly of Supramolecular Triblock Copolymer Complexes
Four different poly(tert-butoxystyrene)-b-polystyrene-b-poly(4-vinylpyridine) (PtBOS-b-PS-b-P4VP) linear triblock copolymers, with the P4VP weight fraction varying from 0.08 to 0.39, were synthesized via sequential anionic polymerization. The values of the unknown interaction parameters between styrene and tert-butoxystyrene and between tert-butoxystyrene and 4-vinylpyridine were determined from random copolymer blend miscibility studies and found to satisfy 0.031<ΟS,tBOS<0.034 and 0.39<Ο4VP,tBOS<0.43, the latter being slightly larger than the known 0.30<ΟS,4VPβ€0.35 value range. All triblock copolymers synthesized adopted a P4VP/PS core/shell cylindrical self-assembled morphology. From these four triblock copolymers supramolecular complexes were prepared by hydrogen bonding a stoichiometric amount of pentadecylphenol (PDP) to the P4VP blocks. Three of these complexes formed a triple lamellar ordered state with additional short length scale ordering inside the P4VP(PDP) layers. The self-assembled state of the supramolecular complex based on the triblock copolymer with the largest fraction of P4VP consisted of alternating layers of PtBOS and P4VP(PDP) layers with PS cylinders inside the latter layers. The difference in morphology between the triblock copolymers and the supramolecular complexes is due to two effects: (i) a change in effective composition and, (ii) a reduction in interfacial tension between the PS and P4VP containing domains. The small angle X-ray scattering patterns of the supramolecules systems are very temperature sensitive. A striking feature is the disappearance of the first order scattering peak of the triple lamellar state in certain temperature intervals, while the higher order peaks (including the third order) remain. This is argued to be due to the thermal sensitivity of the hydrogen bonding and thus directly related to the very nature of these systems.
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(Ξ©), where Ξ© is the angular velocity of rotation; at the same time the line broadens. Near Tc, f(T) is a linear function of 1βT/Tc. At small velocities g(Ξ©)βΞ©. These observations are consistent with the existence of vortices in rotating 3He-A.Peer reviewe
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