Search results for "plastics"
showing 10 items of 2724 documents
Dielectric properties of 0.4Na0.5Bi0.5TiO3–(0.6-x)SrTiO3–xPbTiO3 solid solutions
2014
Abstract In this paper we present our measurements of the linear and nonlinear dielectric permittivity of 0.4 Na 0.5 Bi 0.5 TiO 3 – ( 0.6 - x ) SrTiO 3 – xPbTiO 3 solid solutions (x = 0, 0.05, 0.1, 0.15). The dielectric anomaly increases in the system with respect to the concentration of lead, showing that interactions between dipolar entities are modified. The system exhibits dipolar-glass-like behaviour at low values of x ( 0 ⩽ x 0.1 ). Relaxor behaviour emerges in the sample where x = 0.1 . Furthermore, a spontaneous first-order phase transition from relaxor to normal ferroelectric is observed at x ⩾ 0.15 . A few peculiar dispersion regions are observed in the ferroelectric phase, which …
Orientation and Dynamics of ZnO Nanorod Liquid Crystals in Electric Fields.
2010
ZnO nanorod polymer hybrids (i.e., ZnO nanorods coated with a block copolymer with a short anchor block (dopamine) and a longer solubilizing block of polystyrene (PS)) form liquid crystalline (LC) phases if they are dispersed at high concentration e.g., in a PS oligomer matrix. Due to the high mobility of the low T(g)-matrix the nanorod polymer hybrids show a switching behavior under an applied AC electric field. Hence, the orientation of the nanorod mesogens can be changed from planar (parallel to the substrate) to homeotropic (perpendicular) in full analogy to the switching of low molecular liquid crystals in an electric field. Dielectric measurements show that such a switching is mainly …
Can Hyperbranched Polymers Entangle? Effect of Hydrogen Bonding on Entanglement Transition and Thermorheological Properties of Hyperbranched Polyglyc…
2016
Melt rheology and thermal phase transition of a series of hyperbranched polyglycerol samples (hbPG) (DB ≈ 60%) in a broad molecular weight range (Mn = 600–440 000 g/mol) were investigated and correlated to both molecular weight and nature of the end group (hydroxyl vs permethylated and trimethylsilylated). The well-characterized and defined flexible polyethers are particularly suitable to shed light on the linear viscoelastic behavior with respect to (i) hyperbranched topology and (ii) hydrogen bond interactions, particularly in comparison to the perfectly linear polyglycerol counterparts studied recently [Osterwinter, C.; Macromolecules 2015, 48, 119−130]. We present a detailed examination…
Dimesogenic ferroelectric polysiloxanes
1994
Dimesogenic polysiloxane [Si(Me) 2 O] m [Si(Me)(R)O] n (R= (CH 2 ) 3 CH(COO[CH 2 ] 11 OPhPhOCOPh(NO 2 )OC * H(Me)C 6 H 13 ) 2 are synthesized by hydrosilylation. The phase transition temperaturs are determined and the ferroelectric properties are investigated
Monodomain Liquid Crystal Main Chain Elastomers by Photocrosslinking
2007
A new synthetic strategy for the preparation of macroscopically oriented smectic main chain liquid crystal elastomers (MC-LCE) by the photocrosslinking of laterally functionalized polyesters is presented. X-ray measurements proved the formation of the monodomain and allowed a quantitative determination of the order parameter. The thermo-actuation of our material at the phase transition from the liquid-crystalline to the isotropic phase was demonstrated by temperature dependent measurements of the sample length, showing a fully reversible shape change of � 40%. Mechanical measurements showed that the sample can be stretched by up to 60% along the smectic layer normal without any reorientatio…
Nanosized shape-changing colloids from liquid crystalline elastomers.
2010
A method to prepare shape-changing nanospheres from liquid crystalline elastomers is reported. The nanosized colloids are prepared by a miniemulsion process. During this process, colloids are prepared from a liquid crystalline (LC) main-chain polyester and subsequently crosslinked into a nanometer-sized LC elastomer. The ability of these LC elastomers to change their shape at the phase transition temperature from the smectic A to the isotropic phase was detected by temperature-dependent transmission electron microscopy. The phase transition-induced shape change leads to strongly shape anisotropic nanosized elastomer particles.
Order-Order Phase Transitions Induced by Supercritical Carbon Dioxide in Triblock Copolymer Thin Films
2019
We study the influence of supercritical carbon dioxide (scCO2) on the phase behavior of a cylinder-forming polystyrene-block-polybutadiene-b-polystyrenetriblock copolymer thin film. Solvent annealing with scCO2 can produce patterns with long-range order but these structures become unstable for thin films with small thicknesses. These results are in good agreement with self-consistent mean field calculations, which indicate that a drying transition occurs for thicknesses below the radius of gyration of the molecule.After decompression and solvent extraction, the initially swollen polymer nanostructure suffers a strong reduction in the average domain spacing, which has a deleterious effect on…
Semiflexible Polymers Interacting with Planar Surfaces: Weak versus Strong Adsorption
2020
Semiflexible polymers bound to planar substrates by a short-range surface potential are studied by Molecular Dynamics simulations to clarify the extent to which these chain molecules can be considered as strictly two-dimensional. Applying a coarse-grained bead-spring model, the chain length N and stiffness &kappa
Molecular dynamics in liquid crystalline N-acylated oligoethylenimines as studied by broadband dielectric spectroscopy
1996
The molecular dynamics and the charge transport in six liquid crystalline N-acylated oligoethylenimines were investigated by dielectric spectroscopy. The dielectric spectra in the temperature range from 125 K up to 400 K and in the frequency range between 10 -2 Hz and 10 7 Hz could be described by a conductivity contribution and three relaxation processes. The molecular assignment of the α-process is a relaxation of the rigid benzamide unit. Its mean relaxation time is influenced by the length of the alkoxy side chains, the spacer length (ethylene or propylene groups) and the neighboring repeating units. In the columnar mesophase this process is cooperative due to sterical hindrance. A norm…
Ellipsometric studies of behenic acid at the air-water interface
1991
The rich phase behaviour of monolayers of behenic acid (=docosanoic acid) has been analyzed by null ellipsometry in isothermic and isobaric measurements. By using structural data known from x-ray measurements the anisotropy and refractive indices in the vicinity of the S-CS phase transition have been calculated with a minimum of model assumptions. The calculated values are: nsx=1.47. ncsx=1.48. nsz=1.54. ncsz=1.55. and anisotropy γ=nx/nz ≈0.95. It is also shown that ellipsometry is a very sensitive and convenient method of detecting phase transitions. Its value for quantifying the roughness of the monolayer in the close vicinity of phase transitions due to thickness and density fluctuations…