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Rich Phase Behavior (rich + phase_behavior)

Distribution by Scientific Domains

Polymers and Materials Science	60%
Chemistry	40%

Selected Abstracts

Rich Phase Behavior in a Supramolecular Conducting Material Derived from an Organogelator

ADVANCED FUNCTIONAL MATERIALS, Issue 6 2009
Josep Puigmartí-Luis
Abstract Organic conducting fiber-like materials hold great promise for the development of nanowires that can act as connections in miniature electronic devices, as an alternative to inorganic nanometer scale structures. This article presents a conducting organic tetrathiafulvalene-based supramolecular material which possesses a rich phase behavior with different packing of the molecules in the different forms, evidenced by electron spin resonance (ESR) spectroscopy. The distinct phases of conducting nanofibers can be easily fabricated through the temperature control of their preparation process from a xerogel by doping with iodine vapors. A total of four conducting phases have been identified conclusively using ESR spectroscopy as the key analytical tool. Three of the phases show a good long-term stability and areas in which the I,V curves have ohmic behavior when studied by current sensing (conducting) AFM. They offer promise for applications where electrical nanometer scale connections are required. [source]

The two-Yukawa model and its applications: the cases of charged proteins and copolymer micellar solutions

JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2007
Sow-Hsin Chen
Charged and uncharged colloidal systems are known from experiment to display an extremely rich phase behavior, which is ultimately determined by the effective pair potential between particles in solution. As a confirmation, the recent striking observation of an equilibrium cluster phase in charged globular protein solutions [Stradner, Sedgwick, Cardinaux, Poon, Egelhaaf & Schurtenberger (2004). Nature, 432, 492,495] has been interpreted as the effect of competing short-range attractive and long-range repulsive interactions. The `two-Yukawa (2Y) fluid' model assumes an interparticle potential consisting of a hard core plus an attractive and a repulsive Yukawa tail. We show that this rather simple model can indeed explain satisfactorily the structural properties of diverse colloidal materials, measured in small-angle neutron scattering (SANS) experiments, including the cases of equilibrium cluster formation and soft-core repulsion. We apply this model to the analysis of SANS data from horse-heart cytochrome c protein solutions (whose effective potential can be modeled as a hard-sphere part plus a short-range attraction and a weaker screened electrostatic repulsion) and micellar solutions of a triblock copolymer (whose effective potential can be modeled as a hard-sphere part plus a repulsive shoulder and a short-range attraction). The accuracy of the 2Y model predictions is successfully tested against Monte Carlo simulations in both cases. [source]

Reversible Hydrogels from an Ampholytic An(B -b- C)n Heteroarm Star Block Terpolymer

MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 21 2008
Nikoletta Stavrouli
Abstract An asymmetric, amphiphilic, An(B- b -C)n heteroarm star block terpolymer bearing polystyrene and poly(2-vinyl pyridine)- block -poly(acrylic acid) arms, was synthesized by anionic polymerization, using an extending "in-out" method and a post polymerization deprotection reaction. Due to the pH-dependent protonation/deprotonation equilibrium of the P2VP/PAA blocks, a rich phase behavior was observed as a function of pH. At pH,=,2, the star terpolymers form a physical hydrogel through a solvent-induced sol/gel transition in a DMF/water solvent mixture. The gelation mechanism was attributed to a jamming effect mediated by increasing the dielectric permittivity of the medium. [source]

Oligomer-to-Polymer Transition in Short Ethylene Glycol Chains Connected to Mobile Hydrophobic Anchors

CHEMPHYSCHEM, Issue 1 2005
Motomu Tanaka Dr.
Abstract We studied the structure of short ethylene glycol (EG) chains with N repeating units (EGN, N=3, 6, 9, 12, and 15) connected to hydrophobic dihexadecyl chains by means of a combination of differential scanning calorimetry (DSC) and small- and wide-angle X-ray scattering (SAXS/WAXS). These synthetic amphiphiles dispersed in water form planar lamellar stacks and hexagonal cylinders confining the EG chains to restricted geometries. Owing to the self-assembly of the anchoring points, the lateral density of EG chains in planar lamella can be quantitatively controlled. Furthermore, the chain-melting phase transition of the anchors enables us to "switch" the intermolecular distance reversibly. SAXS/WAXS results suggest that the shorter EG chains (N=3, 6, and 9) assume a helical conformation in stacks of planar lamella. When the EG chains are further elongated (N=12 and 15), the lamellar periodicities cannot be explained by a linear extrapolation of shorter oligomers, but can be interpreted well as polymer brushes following the scaling theorem. Such rich phase behaviors of EGN molecules can be used as a simple model of oligo/poly-saccharide chains on cell surfaces, which act not only as flexible repellers between neighboring cells but also as stable spacers for functional ligands. [source]