A. Faraone

The puzzle of poly(ethylene oxide) aggregation in water: Experimental findings

Aqueous solutions of poly(ethylene oxide) were investigated using the ultrasonic technique, photon correlation spectroscopy (PCS) and nuclear magnetic resonance (NMR), in a wide range of molecular weight (from ethylene glycol to poly(ethylene oxide) 4u2009000u2009000 Da). Ultrasonic data reveal that the mixing process is not ideal and show that the polymer–water interaction strength increases with the polymerization degree. PCS and NMR, on the other hand, furnish a free particle diffusion coefficient which satisfies a unique scaling law from 8000 to 4u2009000u2009000 Da and demonstrates the good solvent nature of water. These experimental findings indicate that polymer–polymer aggregation processes are not an inherent property of these systems.

Quasielastic neutron scattering from trehalose aqueous solutions

The work reports quasielastic neutron scattering (QENS) results on aqueous solutions of trehalose, a biologically and biomedically important disaccharide. We collected data at the Berlin Neutron Scattering Center (BENSC) on α,α-trehalose deuterated (C12H14O11D8) samples in D2O and on α,α-trehalose hydrogenated (C12H22O11) samples in H2O at different water content. The employment of selectively deuterated samples allows the separation of the diffusive dynamics of water from that of trehalose. The aim of the work is to furnish new results on the molecular dynamics of trehalose and to investigate the effect of this disaccharide on the neighboring water. This study is part of a comprehensive research effort to understand the molecular processes underlying the bio-protectant effectiveness of the disaccharide using plenty of physical techniques [light scattering, nuclear magnetic resonance (NMR), neutron scattering, thermodynamic measurements]. The data analysis furnishes a microscopic whole-molecule diffusion ...

Can the isotopic HleftrightarrowD substitution affect the conformational properties of polymeric aqueous solutions? The poly(ethylene oxide)-water case

This paper deals with measurements, performed using dynamic light scattering (photon correlation spectroscopy (PCS) and Raman spectroscopy) and small angle neutron scattering (SANS), on solutions of poly(ethylene oxide) (PEO) in water and heavy water. The joint employment of these techniques allows us to carry out a side by side comparison between the PEO/H2O and the PEO/D2O systems. The coil conformation dependence on temperature and concentration is studied; in particular, the hydrodynamic radius, as evaluated from the diffusion coefficient at infinite dilution using PCS, and the gyration radius, evaluated by SANS, are determined at different temperatures, i.e. as a function of the solvent quality. On the other, the study of the Raman D-LAM spectral contribution furnishes valuable information on the structural arrangement of the molecules. The experimental findings clearly show from the different diffusive properties of polymer chains that the isotopic substitution affects the hydrodynamic radius behaviour with temperature, and from the Raman scattering results that it induces a lowering of the conformational order degree. Such findings provide evidence of the different behavioural properties of macromolecules in H2O and D2O, and could be relevant for the areas of research in which the deuterium labelling technique is commonly employed.

Swelling processes in aqueous polymer solutions by PCS and Raman scattering

Abstract The purpose of the present work is to show how the joint employment of Raman scattering and Photon Correlation Spectroscopy (PCS), can furnish helpful information for a better comprehension of the properties of poly(ethylene oxide) in aqueous solutions. The analysis of the Raman D-LAM (Disordered Longitudinal Acoustic Mode) spectral contribution as a function of temperature reveals a slight center frequency decrease and a broadening of the D-LAM mode up to 45°C. These findings, if interpreted in conjunction with PCS results, show a temperature dependence of the effective interactions between monomer units and an increase of the swollen coil size up to T =45°C.

Comparison of disaccharide solutions across glass transition

Abstract Quasi-elastic neutron scattering (QENS) measurements on trehalose/H 2 O and sucrose/H 2 O mixtures have been carried out using the spectrometer MIBEMOL at the Laboratoire Leon Brillouin (LLB, Saclay). The study, addressed to the comparison of the vibrational properties of the two homologous disaccharide water mixtures across the glass transition, allows to characterize the different rigidity of both the disaccharide/H 2 O mixtures.

Anomalous conformational properties of PEO in H2O and D2O by SANS, PCS and Raman scattering

PEO solutions in water and heavy water have been investigated using SANS, PCS and Raman spectroscopy. The employement of these techniques allows to carry out a comparison between the diffusive properties of PEO/H 2 O and PEO/D 2 O systems, in order to study the coil conformation dependence on temperature and concentration. The data reveal the different conformational properties of PEO in the two solvents which have been attributed to a different solvent quality of H 2 O and D 2 O. These results provide evidence to the fact that the properties of macromolecules, even of simple structure, can be influenced by the isotopic composition of the solvent.

Possibilities and limits of photon correlation spectroscopy in determining polymer molecular weight distributions

The effect of concentration and polydispersity on the collective diffusion coefficient D c , evaluated using Photon Correlation Spectroscopy (PCS), has been investigated on poly(methyl methacrylate) (PMMA) in acetone solutions. The concentration dependence of the collective diffusion coefficient follows a linear regression law, the slope being fairly independent of polydispersity, molecular weight and temperature. The diffusion coefficient at infinite dilution D 0 obeys the scaling law D 0 = AM w -v in the range from M w = 10000 to M w = 800000; the value of the scaling exponent, v = 0.57, proves the good solvent quality of acetone. The inversion of the scattered intensity autocorrelation data by the regularization method CONTIN allowed the evaluation of the molecular weight distribution function of the polymeric samples. Although this algorithm gives valuable information on average quantities or on the width of the distribution, it has limited resolution power; therefore a comparison with the results obtained by Size Exclusion Chromatography (SEC) was carried out for a set of samples having monomodal and bimodal distribution functions.

Effect of the monomer structure on the dynamics of semidilute polyalkylmethacrylate solutions: A quasielastic light and neutron scattering investigation

The study of the microscopic origin of the slow relaxation modes in the autocorrelation functions of some entangled polymer solutions has recently given rise to much experimental and theoretical work. The aim is to highlight the role of concentration, molecular weight, and temperature on the slow modes and to what extent the entanglement phenomena are responsible for their appearance. The present work reports on the comparison between the dynamics of homologous polymers with different side unit lengths, by use of quasi-elastic light and neutron scattering. The investigation, carried out on both mesoscopic and microscopic scales, with different concentrations and chain lengths, evidenced different dynamical properties in the three polymer solutions. In particular, longer side chains give rise to a bigger volume excluded to the other segments, obstructing the entanglements responsible for the slow relaxation modes and favoring the mobility of segments.

QENS and PCS study of aqueous BSA–PEO `crowded’ solutions

Abstract In this contribution we report first results from a study of aqueous protein–polymer solutions using the complementary techniques of quasielastic neutron scattering (QENS) and photon correlation spectroscopy (PCS). A 15% solution of bovine serum albumin (BSA) without and with 10% PEO600 (polyethylene oxide, M w =600) is used as a model system to study changes in proton micro-diffusivity by analysing QENS broadenings at low and high momentum transfers.

Effect of H-bond active sites on transport properties of poly(ethylene oxide) dissolved in its monomers: Shear viscosity and diffusion coefficient studies

The possibility of dissolving poly(ethylene oxide) [PEO:H–(O–CH2–CH2)n–OH] in its monomeric liquid ethylene glycol [EG:H–(O–CH2–CH2)–OH] represents the only way to verify the complex polymer–monomer interactions, through the OH end groups, resulting in the scaling law R∝Nν. We report viscosity results, in conjunction with photon correlation spectroscopy data, on different molecular weight PEO samples, in a wide range of concentrations, dissolved in EG. In order to distinguish among various interaction mechanisms, we also studied PEO dissolved in EG monomethyl ether [EGmE:CH3–(O–CH2–CH2)–OH] and EG dimethyl ether [EGdE:CH3–(O–CH2–CH2)OCH3], the latter not having in its chemical structure OH hydroxylic groups available to give rise to hydrogen bond interactions. In particular, the quality (good-theta-poor) of the solvents has been analyzed by verifying the well-known Mark–Houwink–Sakurada scaling law and the effects of the polymer–solvent interactions on the coils diffusive properties.