0000000000048594
AUTHOR
F. Lo Celso
Critical micellization density: A small-angle-scattering structural study of the monomer-aggregate transition of block copolymers in supercriticalCO2
In this paper we report a small-angle neutron-scattering investigation of micelle formation by the fluorocarbon-hydrocarbon block copolymer, polyvinyl acetate-b-poly (1,1,2,2-tetrahydroperfluoro-octyl acrylate) in supercritical CO{sub 2} (scCO{sub 2}) at 313 K. At high pressure the copolymer is in a monomeric state with a random coil structure, while at low pressure the polymer forms spherical aggregates stable in a wide range of thermodynamic conditions. By profiling pressure, a sharp monomer-micelle transition is obtained due to the tuning of the solvating ability of scCO{sub 2}. We confirm the previous finding that this aggregate-monomer transition is driven by the gradual penetration of…
Modelling small angle neutron scattering data from polymers in supercritical fluids
In this paper we report a SANS investigation of micelle formation by fluorocarbon-hydrocarbon block copolymers in supercritical CO2(scCO2) at 313K. A sharp unimer-micelle transition is obtained due to the tuning of the solvating ability of scCO2 by profiling pressure. At high pressure the copolymer is in a monomeric state with a random coil structure. By lowering the pressure aggregates are formed with the hydrocarbon segments forming the core and the fluorocarbon segments forming the corona of spherical aggregates. This aggregate-unimer transition is driven by the gradual penetration of CO2 molecules toward the core of the aggregate and is critically related to the density of the solvent, …
Mesoscopic structure of marble determined by combined USANS and SANS
Marbles, carbonatic (i.e. calcitic–dolomitic) rocks deriving from the metamorphic evolution of previous carbonates, are often rather similar to each other in many respects (i.e. mineralogical, physical–structural and chemical), and thus difficult to identify. In search for a diagnostic method to provenance marbles, we have selected a limited number of Italian white marbles representing a wide array of metamorphic (i.e. thermal) levels. The mesoscale structural arrangement of these samples was derived by means of combined Ultra Small Angle and Small Angle Neutron Scattering experiments. The parameters of the model used to fit the data have been correlated with the metamorphic history of the …
Structural investigation of hybrid nanocomposites
Ultra small (USANS) and small angle neutron scattering (SANS) techniques were employed to study an elastomer styrene–butadiene, where two kinds of silica fillers have been added in different amounts. Small silica-particle fillers are expected to modify morphological and mechanical properties when dispersed in the copolymer matrix. The USANS and SANS techniques can span a wide range of momentum transfer, investigating morphological properties of the filled elastomer over a number of decades in length scale. Surface and mass fractal behavior has been observed over different length scales.
Direct experimental observation of mesoscopic fluorous domains in fluorinated room temperature ionic liquids
Fluorinated room temperature ionic liquids (FRTILs) represent a class of solvent media that are attracting great attention due to their IL-specific properties as well as features stemming from their fluorous nature. Medium-to-long fluorous tails constitute a well-defined apolar moiety in the otherwise polar environment. Similarly to the case of alkyl tails, such chains are expected to result in the formation of self-assembled fluorous domains. So far, however, no direct experimental observation has been made of the existence of such structural heterogeneities on the nm scale. We report here the first experimental evidence of the existence of mesoscopic spatial segregation of fluorinated dom…
Scattering studies of large scale structures at the ultra small angle neutron scattering instrument S18
Abstract In recent years ultra small angle neutron scattering (USANS) has developed into a powerful standard method for large scale structure investigations. The upgraded instrument S18 at the ILL's 58 MW high flux reactor is operated routinely with increasing beam time demand. The performance of the instrument and its abilities will be discussed in this paper. A peak to background ratio better than 10 5 is reached using Agamalian's tail reduction method. A q -range from 2.10 −5 up to 5.10 −2 A −1 can be covered. This allows a clear overlap with standard pinhole SANS instruments. The new way collecting scattering data logarithmically equidistant in q -space saves measuring time. This allows…
SAXS investigation on aggregation phenomena in supercritical CO2.
Synchrotron Small-Angle X-Ray scattering (SAXS) measurements on aggregate formation of a Polyvinyl acetate- b-Perfluoro octyl acrylate (PVAc- b-PFOA) block copolymer in supercritical CO(2) are here reported. Experiments were carried out for a series of different thermodynamic conditions, changing the solvent density by profiling both the pressure at constant temperature and the temperature at constant pressure. This block copolymer and in general fluorocarbon-hydrocarbon di-blocks form aggregates depending on the value of CO(2) density. A sharp transition between monomers dissolved as random coils and micelles characterized by a solvophilic shell and a solvophobic core occurs when the CO(2)…
Mesoscopic structural organization in fluorinated pyrrolidinium-based room temperature ionic liquids
Abstract In this contribution the microscopic and mesoscopic structural organization in a series of fluorinated room temperature ionic liquids, based on N-methyl-N-alkylpyrrolidinium cations and on bis(perfluoroalkylsulfonyl)imide anions, is investigated, using a synergy of experimental (X-ray and neutron scattering) and computational (Molecular Dynamics) techniques. The proposed ionic liquids are of high interest as electrolyte media for lithium battery applications. Together with information on their good ion transport properties in conjunction with low viscosity, we also describe the existence of nm-scale spatial organization induced by the segregation of fluorous moieties into domains. …
Industrial applications of the aggregation of block copolymers in supercritical CO 2 : a SANS study
Industrial applications of supercritical carbon dioxide (scCO2) rely upon the rather selective and easily adjustable solvent ability of CO2. CO2 near the critical point is a poor solvent for high molecular weight (HMW) hydrocarbon polymers, while it is a very good solvent for amorphous fluorinated polymers. By increasing the pressure, CO2 becomes a good solvent even for HMW hydrogenated chains. Specially engineered amphiphilic di-block copolymers, with CO2-philic and CO2-phobic portions, are expected to undergo trough a monomer–aggregate transition when the solvent density of the scCO2 changes. Here small-angle neutron scattering (SANS) results are reported for a block copolymer dissolved i…
Composition and corrosion phases of Etruscan Bronzes from Villanovan Age
A neutron diffraction (ND) and neutron tomography (NT) study of laminated ancient bronzes was performed at the ISIS (Rutherford Appleton Laboratory, UK) neutron source and at the BENSC reactor (Hahn-Meitner Institut, Germany). The samples are part of an 8th century BC Etruscan collection discovered in the necropolises of Osteria-Poggio Mengarelli and Cavalupo in the Vulci area (Viterbo, Italy). The study allowed us to derive-in a totally non-destructive manner-information related to the main composition of the objects, possible presence of alterations and their nature, crusts and inclusions, as well as structure of the bulk. The presence of some components is linked to a variety of question…
Kinetics of block-copolymer aggregation in super critical CO2
Small angle X-ray and neutron scattering (SAXS and SANS) are used to obtain structural information on the aggregation behavior of block-copolymers dissolved in supercritical CO2. The SANS technique is used to provide a detailed structural model for the micellar aggregates, which form below the critical micellization density (CMD), that we defined in our previous work. The SAXS technique (with a synchrotron source) is used to provide the first experimental information concerning the kinetic features of both formation and decomposition of such aggregates as soon as pressure jumps are applied to the solutions across the CMD. 2002 Elsevier Science B.V. All rights reserved.
Pressure-induced formation of diblock copolymer "micelles" in supercritical fluids. A combined study by small angle scattering experiments and mean-field theory. II. Kinetics of the unimer-aggregate transition
We developed a simple time-dependent mean-field theory to describe the phase separation kinetics of either homopolymers or AB-diblock copolymers in supercritical (SC) fluids. The model, previously used to describe the phase behavior of AB-block copolymers under the assumption of strong solvent selectivity for just one copolymer chain, has been extended to study the kinetics of the phase separation process. Time resolved small angle x-ray scattering (TR-SAXS) measurements have been performed on different AB-diblock copolymers containing a perfluorinated chain and dissolved in SC-CO2. The data obtained over a wide range of pressure and temperature confirm our theoretical predictions. Particul…
QENS investigation of filled rubbers
The polymer segmental dynamics is investigated in a series of silica-filled rubbers. The presence of inert fillers in polymers greatly affects the mechanical and physical performance of the final materials. For example, silica has been proposed as a reinforcing agent of elastomers in tire production. Results from quasielastic neutron scattering and Dynamic Mechanical Thermal Analysis (DMTA) measurements are presented on styrene–ran-butadiene rubber filled with silica. A clear indication is obtained of the existence of a bimodal dynamics, which can be rationalized in terms of the relaxation of bulk rubber and the much slower relaxation of the rubber adsorbed on the filler surface.
Liquid structure and dynamics in the choline acetate:urea 1:2 deep eutectic solvent
We report on the thermodynamic, structural, and dynamic properties of a recently proposed deep eutectic solvent, formed by choline acetate (ChAc) and urea (U) at the stoichiometric ratio 1:2, hereinafter indicated as ChAc:U. Although the crystalline phase melts at 36-38 degrees C depending on the heating rate, ChAc:U can be easily supercooled at sub-ambient conditions, thus maintaining at the liquid state, with a glass-liquid transition at about -50 degrees C. Synchrotron high energy x-ray scattering experiments provide the experimental data for supporting a reverse Monte Carlo analysis to extract structural information at the atomistic level. This exploration of the liquid structure of ChA…
Dilute and semi dilute solutions of block copolymers in water, near-critical and super-critical CO2: a small angle scattering study of the monomer–aggregate transition
Abstract Small angle neutron (SANS) and X-ray (SAXS) Scattering measurements on aggregate formation of block copolymers in water and in near-critical and supercritical CO2 are reported here. Time Resolved SAXS (TR-SAXS) has also been performed in the supercritical region. Experiments have been carried out for a series of different thermodynamic conditions, changing the solvent density by profiling the pressure at constant temperature. A sharp transition between monomers dissolved as random coils and micelles characterized by a solvo-philic shell and a solvo-phobic core occurs when the solvent density reaches the critical micellization value. This is easily shown in the case of scCO2.
Structural and dynamical characterization of melt PEO–salt mixtures
Abstract Salt doped poly ethylene oxide (PEO) mixtures were investigated by means of both small angle neutron scattering and QENS techniques aiming to characterize morphological and dynamical features in the melt state. These experimental evidences provide support to the proposed heterogeneous scenario for polymer electrolytes. In particular, the existence of PEO–cation complexes is proposed to play a major role in intramolecular cooperation and intermolecular transient crosslinks, which affects the mixture properties.
Neutron tomography of ancient lead artefacts
Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich. This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively. The investigations presented here show the results of an epigraphic analysis on ancient Roman lead ingots rescued from shipwrecks along the coast of Sicily (Italy) by means of Neutron Tomography (NT). The artefacts, including a lead horn, can be dated back to a period between the 3rd and 1st century BC. The three dimensional NT reconstructions helped the decipherment of hidden s…
Study of percolation and clustering in supercritical water-CO2 mixtures
The microscopic structure of supercritical water-CO(2) mixture is investigated by neutron diffraction experiments exploiting the isotopic HD substitution. The investigated water reach mixtures are in the liquidlike region of the phase diagram, according to the behavior of the radial distribution functions, yet a reduction of the average number of hydrogen bonds, compared to equivalent states of pure water, is found. As a consequence, the average dimension of water clusters is reduced and the system stays below the percolation threshold. These results, along with the shift of the main peaks of the site-site radial distribution functions, suggest that the excess volume in these supercritical …
Phase separation in multi-component mixtures: the four-component case
Abstract Calculation of ternary phase diagrams for several mixtures formed by two salts and a neutral component is presented here. The phase diagrams are obtained by inspection of the shape of the Gibbs free energy of mixing surface (Gmix) as a function of the composition at constant temperature and pressure. The Gmix surface is calculated by the mean spherical approximation (MSA). The model for the mixtures is represented by hard spheres, with the charged components interacting via a Coulomb potential. The results are interpreted in terms of a thermodynamic analysis of the contributions to the Gibbs free energy of mixing, i.e., the configurational energy, the volume and the entropy of mixi…
Morphology of hybrid polystyrene-block-poly(ethylene oxide) micelles: Analytical ultracentrifugation and SANS studies
Abstract Morphology and structure of aqueous block copolymer solutions based on polystyrene- block -poly(ethylene oxide) (PS- b -PEO) of two different compositions, a cationic surfactant, cetyl pyridinium chloride (CPC), and either platinic acid (H 2 PtCl 6 ⋅6H 2 O) or Pt nanoparticles were studied using a combination of analytical ultracentrifugation (AUC), transmission electron microscopy (TEM), and small angle neutron scattering (SANS). These studies combining methods contributing supplemental and analogous structural information allowed us to comprehensively characterize the complex hybrid systems and to discover an isotope effect when H 2 O was replaced with D 2 O. In particular, TEM s…
CO(2)-water supercritical mixtures: Test of a potential model against neutron diffraction data
Abstract A neutron diffraction experiment on supercritical mixtures of water and CO 2 at two concentrations is presented. Data are analyzed within the EPSR framework and the water–water and water–CO 2 radial distribution functions are compared with those calculated by a Molecular Dynamics simulation performed by using the TIPS2 and EPM-M potential models for water and CO 2 respectively. It is found that the Molecular Dynamics simulation reproduces the overall shape of the site–site radial distribution functions, although missing a few subtle changes brought along when the CO 2 concentration is increased.
Nanoscale organization in the fluorinated room temperature ionic liquid: Tetraethyl ammonium (trifluoromethanesulfonyl)(nonafluorobutylsulfonyl)imide
Fluorinated Room Temperature Ionic Liquids (FRTILs) are a branch of ionic liquids that is the object of growing interest for a wide range of potential applications, due to the synergic combination of specifically ionic features and those properties that stem from fluorous tails. So far limited experimental work exists on the micro-and mesoscopic structural organization in this class of compounds. Such a work is however necessary to fully understand morphological details at atomistic level that would have strong implications in terms of bulk properties. Here we use the synergy between X-ray and neutron scattering together with molecular dynamics simulations to access structural details of a …
Segmental dynamics in polymer electrolytes
Polymer dynamics in poly(ethylene oxide) (PEO)–salt mixtures is investigated by means of quasi-elastic neutron scattering (QENS). In a previous study, we reported QENS data from the NEAT spectrometer (BENSC) that evidenced, for the first time, a dynamic heterogeneity in PEO–salt mixtures induced by salt addition. This finding is supported by molecular dynamics (MD) simulations carried out by Borodin et al. In agreement with MD simulations, our QENS data revealed two distinct processes: a fast motion corresponding to the bulk polymer and a slower relaxation, which we attribute to formation of PEO–cation complexes. In this paper we present new QENS data from the high-resolution spectrometer I…
Pressure-Induced Formation of Diblock Copolymer "Micelles" in Supercritical Fluids. A Combined Study by Small Angle Scattering Experiments and Mean-Field Theory. I: the Critical Micellization Density Concept
We developed a simple mean-field theory to describe polymer and AB diblock copolymer phase separation in supercritical (SC) fluids. The highly compressible SC fluid has been described by using a phenomenological hole theory, properly extended to consider the solvent/polymer/vacancy pseudoternary mixture. The model has been applied to describe the phase behavior of AB-diblock copolymers under the assumption of a strong solvent selectivity for just one copolymer chain. In our model the solvent selectivity is a strong function of the external pressure because in compressible fluids vacancies reduce the number of favorable solvent-polymer contacts. The combined effect of the pressure on the ave…
Fractal approach in petrology: Combining ultra small angle (USANS), and small angle neutron scattering (SANS)
Ultra small angle neutron scattering instruments have recently covered the gap between the size resolution available with conventional intermediate angle neutron scattering and small angle neutron scattering instruments on one side and optical microscopy on the other side. Rocks showing fractal behavior in over two decades of momentum transfer and seven orders of magnitude of intensity are examined and fractal parameters are extracted from the combined USANS and SANS curves.
Morphology of solid polymer electrolytes: a TR WAXS investigation
A wide angle X-ray scattering investigation of (polyethylene oxide)n–sodium thiocyanate [(PEO)nNaSCN] mixtures is reported. Temperature dependence analysis for different mixtures is shown, in order to rationalize the multi-phase behaviour. Depending on the amount of salt added and upon the temperature considered three different phases have been found to simultaneously coexist: crystalline PEO, amorphous PEO, and crystalline complex.
Investigating self-assembly and metal nanoclusters in aqueous di-block copolymers solutions
Self-assembling properties of di-block copolymers/ surfactant hybrids in aqueous solution can be exploited to obtain metal nanoparticles stable dispersion. Results will be presented here for polystyrene-block-poly(ethylene oxide) solutions. A SANS structural investigation has been performed over different molecular weights of both hydrophilic and hydrophobic block, by varying temperature and concentration of the copolymer. A SAXS characterization of micellar systems containing Pt nanoparticles is reported.