Search results for "Phase"
showing 10 items of 6344 documents
Dicyanobenzothiadiazole Derivatives Possessing Switchable Dielectric Permittivities
2017
Benzothiadiazoles are important electron acceptors and are frequently employed as electron-deficient components of donor-acceptor polymers. We report the effect of nitrile functionalities on the reactivity, steric hindrance, optoelectronic properties, and dielectric permittivity in dicyanobenzothioadiazole (DCNBT). Dielectric spectroscopy in the bulk and in solution assisted by DFT-calculations revealed that these molecules can be engineered to engender maximum values of the dipole moment and of dielectric permittivity due to the strong electron-withdrawing effect of the nitrile groups. The self-assembly in the bulk was investigated by X-ray scattering performed on single crystals, fibers (…
Sanidics: A new class of mesophases, displayed by highly substituted rigid-rod polyesters and polyamides
1990
Abstract The structure of rigid-chain polyesters and polyamides which possess flexible side chains consisting of methylene or 1,4,7-trioxaoctyl oxide units have been investigated by means of X-ray scattering. The X-ray studies were performed on fibres and monodomains. Additional information was gained from calorimetric, dilatometric and microscopic studies. The investigations revealed that these polymers display mesophases and that the structures of the mesophases differ from those observed for discotic and calamitic phases. They are characterized by the fact that in the ordered and disordered phases board-like molecules are stacked parallel on top of each other and that these stacks of mol…
Simulation of Dense Polymer Systems in Two and Three Dimensions
1991
Dense polymer systems are modeled by self- and mutually avoiding walks on lattices. Both simple models where the step length is one lattice spacing and more complicated models where the step length is distinctly longer and may fluctuate (“bond fluctuation model”) are discussed, and it is shown that the computer simulation of such models gives useful insight to understand the thermodynamic phase behavior and the relaxational dynamics of dense polymer solutions and polymer melts. The huge demands in computing power needed for a successful simulation of such systems can be covered by parallel computers such as the multitransputer facility of the University of Mainz.
Photoresponsive Ferroelectric Liquid-Crystalline Polymers
2007
The photoresponse of ferroelectric smectic side-chain liquid-crystalline (LC) polymers containing a photoisomerizable azobenzene derivative as a covalently linked photochromic side group is investigated. By static measurements in different photostationary states, the effect of trans-cis isomerization on the material's phase-transition temperatures and its ferroelectric properties (spontaneous electric polarization Ps and director tilt angle 0) are analyzed. It turns out that the Curie temperature (transition S C * to S A ) can be reversibly shifted by up to 17 °C. The molecular mechanism of this "photoferroelectric effect" is studied in detail using time-resolved measurements of the dye's o…
Blends from redox active liquid crystal ionomers and amorphous ionomers
1994
Abstract Biphasic blends (mixtures) of liquid crystal ionomers (prepared from ferrocene containing liquid crystal polymers by a redox reaction) and partially sulfonated polystyrene combine the constituent properties in a way, which is dependent on the measuring method. Polarizing microscopy shows homogenous textures similar to the pure liquid crystal polymer. Mechanical measurements show however the elastomeric behaviour of sulfonated polystyrene. The phase separated structure of these blends is proved by differential scanning calorimetry measurements.
Discotic liquid crystals at the air water interface
1991
The monolayer properties of two types of discotic liquid crystals, hexasubstituted triphenylenes 1 and azo derivatives of phloroglucinol 5, were examined. First investigations show that these discotic liquid crystals form stable monolayers. It could be shown that electron acceptors insert into the monolayer of 1. Azo discs display a packing behaviour at the monolayer that is ascribed to a side-on packing of the molecules.
Impact of Amino-Functionalization on the Response of Poly(ethylene glycol) (PEG) to External Stimuli
2022
It is shown that amino-functionalization of poly(ethylene glycol) (PEG) with the comonomer N,N-diethyl glycidyl amine (DEGA) triggers the emergence of extraordinary stimuli responsiveness and phase behavior of PEG. In dependence of the solution pH, tapered PEG-co-PDEGA exhibits a highly cooperative two-step inverse phase transition with respect to temperature. The polymer forms dispersed metastable nanoglobules in the medically relevant temperature range around human body temperature. Independently, cloud points can be adjusted between 40 and 90 °C via the pH of the solution. Changing the polymer architecture to a block structure, in pronounced contrast, the polymer exhibits a gradual growt…
Large Scale Fractionation of Macromolecules
2004
Access to sufficiently large amounts of material with adequate molecular and chemical uniformity from polydisperse natural products or synthetic materials has been a long-standing challenge to polymer scientists. We have developed a broadly applicable preparative fractionation method consisting of a special kind of continuous extraction removing the easier soluble components from the initial product. It is rendered possible by the use of spinning nozzles throught which a concentrated polymer solution is pressed into a liquid of tailored thermodynamic quality. The initially produced jets of the source phase disintegrate rapidly into minute droplets of typically 50 μm diameter. This efficient…
Indentation test as a tool for monitoring the solidification process during injection molding
2003
An inline method for monitoring the solidification process during the injection molding of semicrystalline polymers is demonstrated. The method has been applied to various poly(ethylene terephthalate) (PET) and poly(buthylene terephthalate) (PBT) samples. The technique is based on a simple device by which an additional ejector pin is pushed onto the injection-molded part with a fixed force at different times during the solidification phase while the mold remains closed. The residual deformation (the so-called indentation depth) due to the applied load is measured offline after ejection. By the performance of indentation at different times during the cooling phase, an indentation depth profi…
Effect of adding new phosphazene compounds to poly(butylene terephthalate)/polyamide blends. II: Effect of different polyamides on the properties of …
2006
Poly(butylene terephthalate) (PBT) and a sample of polyamide have been melt processed in the presence of two new phosphazene compounds, namely 2,2-dichloro-4,4,6,6-bis[spyro(2',2"-dioxy-1',1"-biphenyl)]cyclotriphosphazene (2Cl-CP) and 2,2-bis(2-methoxy-4-methyleneoxy-phenoxy)-4,4,6,6-bis[spyro(2',2"-dioxy-1',1"-biphenyl)]cyclophosphazene (CP-2EPOX). The blends were prepared by using polyamide 6 (PA6) and polyamide 6,6 (PA66) in 25/75 and 75/25 w/w compositions by using a co-rotating twin-screw extruder. The materials have been completely characterized from a mechanical, rheological, and morphological point of view. The results indicate that the additives used cause an increase of the ruptur…