Search results for "scattering"

The influence of hydrophobic substitution on self-association of poly(ethylene oxide)-b-poly(n-alkyl glycidyl carbamate)s-b-poly(ethylene oxide) trib…

2007

Abstract A series of amphiphilic poly(ethylene oxide)-b-poly(n-alkyl glycidyl carbamate)s-b-poly(ethylene oxide) triblock copolymers were synthesized by reaction between poly(ethylene oxide)-b-polyglycidol-b-poly(ethylene oxide) precursor copolymer and four n-alkyl isocyanates: ethyl, propyl, butyl and pentyl. After dissolution in water at room temperature the copolymers spontaneously form micelles. The critical micellization concentrations were determined by UV–VIS spectroscopy. The dimensions of the micelles, the aggregation numbers, and in some cases the micellar shape were determined by dynamic and static light scattering in a relatively broad temperature range. Special attention has be…

The protein dynamical transition does not require the protein polypeptide chain

2011

We give experimental evidence that the main features of protein dynamics revealed by neutron scattering, i.e., the “protein dynamical transition” and the “boson peak”, do not need the protein polypeptide chain. We show that a rapid increase of hydrogen atoms fluctuations at about 220 K, analogous to the one observed in hydrated myoglobin powders, is also observed in a hydrated amino acids mixture with the chemical composition of myoglobin but lacking the polypeptide chain; in agreement with the protein behavior, the transition is abolished in the dry mixture. Further, an excess of low-frequency vibrational modes around 3 meV, typically observed in protein powders, is also observed in our mi…

Competing salt effects on phase behavior of protein solutions: tailoring of protein interaction by the binding of multivalent ions and charge screeni…

2014

The phase behavior of protein solutions is affected by additives such as crowder molecules or salts. In particular, upon addition of multivalent counterions, a reentrant condensation can occur; i.e., protein solutions are stable for low and high multivalent ion concentrations but aggregating at intermediate salt concentrations. The addition of monovalent ions shifts the phase boundaries to higher multivalent ion concentrations. This effect is found to be reflected in the protein interactions, as accessed via small-angle X-ray scattering. Two simulation schemes (a Monte Carlo sampling of the counterion binding configurations using the detailed protein structure and an analytical coarse-grain…

Aggregation processes of perylene bisimide diimidazolium salts

2015

The supramolecular aggregation of three diimidazolium- functionalized perylene bisimides, differing in the alkyl chain length was investigated. These salts form aggregates in solvents like chloroform, dichloromethane, and glycerol. Solvent-, concentration-, and temperature-dependent spectroscopic studies were carried out, evidencing the occurrence of an isodesmic, enthalpy-driven aggregation process, underpinned by p–p stacking and hydrogen bonding. Moreover, dynamic light scattering (DLS) measurements and SEM images revealed that these salts aggregate in chloroform into elongated structures.

Tracer diffusion properties of core-shell latex films studied by photoinduced grating relaxation

2007

This article reports the application of the Photo-Induced Grating Relaxation technique (also known as Forced Rayleigh Scattering) to investigate the dynamics of films prepared from structured core–shell latex particles via the transport property of the photochromic tracer molecule Aberchrome 540®. The core–shell particles were prepared with a fluoropolymer core (immiscible and impenetrable to the tracer) and a poly(butyl methacrylate) shell. The incompletely dried films (with residual water) manifest their spatial heterogeneity via non-Fickian behavior (spatial scale- dependent apparent diffusion coefficient). The diffusion data was interpreted using the two-state diffusion model, previousl…

2020

Tristriazolotriazines (TTTs) with a threefold alkoxyphenyl substitution were prepared and studied by DSC, polarized optical microscopy (POM) and X-ray scattering. Six pentyloxy chains are sufficient to induce liquid-crystalline behavior in these star-shaped compounds. Thermotropic properties of TTTs with varying substitution patterns and a periphery of linear chains of different lengths, branching in the chain and swallow-tails, are compared. Generally, these disks display broad and stable thermotropic mesophases, with the tangential TTT being superior to the radial isomer. The structure–property relationships of the number of alkyl chains, their position, length and structure were studied.

X-ray-absorption study of rheniumL3andL1edges inReO3: Multiple-scattering approach

1993

We present ab initio calculations of x-ray-absorption fine structure for the Re L 3 and L 1 edges in crystalline ReO 3 based on an exact curved-wave multiple-scattering approach. Good agreement between theoretical and experimental data has been found for both edges. We show that, as expected, the contribution of multiple-scattering signals from linear chains, like Re-O-Re and O-Re-O, is very large both in the L 3 - and L 1 -edge spectra due to the strong focusing effect caused by the middle atom

Photodegradation of polyglycidol in aqueous solutions exposed to UV irradiation

2011

The photodegradation of polyglycidol in aqueous solution with UV wavelength of 254 nm was investigated. The experiments were carried out in air at a constant temperature and the photodegradation of polyglycidol (PGl) was compared to that of poly(ethylene oxide) (PEO), the most widely studied polyether. Size exclusion chromatography with multiangle light scattering detection (SEC-MALLS) was used to measure the changes in the molar masses and molar mass dispersities of polymers during degradation. The molar mass of PGl decreased dramatically during the first period of UV irradiation and then gradually approached a limiting value of 17,000 g/mol, regardless of the initial polymer concentration…

Determination of degree of crystallinity of drawn polymers by means of density measurements

1969

The well known procedure of determining the degree of crystallinity by means of measuring the density presupposes the knowledge of both the densities ρc and ρa of the crystalline and of the noncrystalline regions. By combination of small-angle and wide-angle x-ray scattering and of density measurements it can be shown that this method is not justified in the case of drawn polyethylene if the values of ρc and ρa known from isotropic material are used. Both ρc and ρa depend considerably on annealing and drawing conditions. In addition the effective density ρc* of the more densely packed phase in a two-phase structure is much lower than the value ρc calculated from the positions of the x-ray r…

Surface and Intercalation Chemistry of Polycarboxylate Copolymers in Cementitious Systems.

2009

International audience; The Ca–Al-layered double hydroxide, the so-called AFm phase, is a product of cement hydration. It is shown that the interaction of this phase with anionic polycarboxylate ether (PCE)-based dispersant polymers is not a simple adsorption but a more complex intercalation phenomenon leading to the transient sequestration of the PCE within the AFm crystallites. As a result, part of the PCE is immobilized, forming a layered organo-mineral composite, and does not play its role of a dispersing agent. This article presents, along general considerations on the links between cement chemistry and rheology, a detailed investigation of the formation, structure, and stability of a …