1,721,432 research outputs found
Structural properties of binary poly(ethylene-oxide)/room temperature ionic liquids mixtures: an experimental and computational study
No full textPoly (ethylene oxide) is one of the few polymers that are soluble in room temperature ionic liquids. These mixtures can find several applications such as polymer electrolytes or separation media.
A few years ago, we highlighted the good solvent nature of RTILs towards PEO, using SANS technique [1], and Ribeiro simulated the morphology and dynamics of PEO-rich mixtures [2]. Recently the activities of Watanabe’s [3], Rogers’s [4] and Lodge’s [5] groups focused on the phase diagram of PEO-RTIL binary mixtures, detecting the existence of a Lower Critical Solution Temperature for these systems and screening the role of RTIL’s chemical details on this complex behavior.
Here we show recently obtained results from both Small Angle X-ray and Neutron Scattering from PEO-RTILs mixtures at ambient temperature, as a function of polymer concentration, for a variety of RTILs. We screened the role of the RTIL’s alkyl chain length, methylation of position 2 in the RTIL imidazolium ring and other chemical details of the RTIL on the morphology of the macromolecule, extracting information as interesting as its average size, the persistence length and chain rigidity.
These results have been complemented with MD simulation study of oligo (ethylene oxide) dissolved in C2mimTf2N and C2C1mimTf2N, in order to explore the role of hydrogen bonding on microscopic organization in such mixtures
Ionic Liquids and Neutron Scattering
No full textIonic liquids represent an exciting class of compounds that are composed solely of ionic species and are liquid below 100°C. They are attracting great attention as environmentally responsible solvent media, and as such, they are the focus of a profusion of research activities. Aiming at relating their appealing macroscopic properties, in terms of micro- and mesoscopic features, neutron scattering techniques have been successfully applied in the last decade to explore these compounds. In this contribution, an overview of fundamental structural (over the spatial scale ranging from angstrom to several nanometers) and dynamic (across the window from fraction of picosecond to several nanosecond) studies are accounted for, aiming at revealing the contribution that neutron scattering can provide in complementing and extending the level of understanding so far reached
Structural Features of β-Cyclodextrin Solvation in the Deep Eutectic Solvent, Reline
Full text linkThe inherently amphiphilic nature of native cyclodextrins (CDs) determines their peculiar molecular encapsulation features, enabling applications such as targeted drug nanodelivery, aroma protection, etc. On the contrary, it may also lead to poor solubility in water and other organic solvents and to potentially detrimental flocking in these media, thus posing limitations to more extensive usage. Here we use small angle X-ray scattering to show that deep eutectic solvent reline (1:2 choline chloride:urea) succeeds in dissolving large amounts of β-CD (at least 800 mg/mL, compared with the solubility in water of 18 mg/mL), without aggregation phenomena occurring. At the microscopic level, molecular dynamics simulations highlight the complex interplay of hydrogen bonding-mediated hydrophilic interactions and hydrophobic force mitigation occurring between β-CD and reline components, leading to energetically favorable β-CD solvation. The possibility of achieving very high concentration conditions for unaggregated β-CD in an environmentally responsible media, such as reline, can open the way to new, so far unpredictable applications, addressing multiple societal challenges
Liquid structure of a water-based, hydrophobic and natural deep eutectic solvent: The case of thymol-water. A Molecular Dynamics study
Full text linkThe structural organization of the first example of a water-based, type V, hydrophobic, natural deep eutectic solvent (DES) is investigated in this work, exploiting the synergy of X-ray scattering and compu- tational techniques. The stoichiometric mixture of thymol:water (4.8:1) has been recently reported to behave as a DES, with a melting point at 6 C, well below the one foreseen for the ideal liquid mixture. Our study provides an atomistic insight into the structural correlations in this system, highlighting the major role played by hydrogen bonding (HB) correlations in affecting morphology as well as the solid– liquid equilibrium. Thymol engages HB-mediated interactions with both thymol and water molecules: evidences of conventional HB interactions involving the hydroxyl group are found, together with indica- tions of p HAO hydrogen bonding correlations with both thymol and water. Overall, in the mixture, thymol is involved in a larger number of HB interactions than in its neat liquid state. Such a strong inter- ference of water into thymol structural organization strongly hinders the development of HB-mediated thymol hexamers that is the structural leitmotif in crystalline thymol. On the other hand, only 30 % of the present water molecule can engage into correlations with at least another water molecule, thus pre- venting the formation of an extended HB network among water molecules that would result incompat- ible with the otherwise hydrophobic environment. Evidences of mesoscopic organization are observed experimentally and confirmed by simulations: these are related to the clustering of thymol hydroxyl groups with water molecules, leading to the formation on polar nano-pools embedded into the apolar matrix. This new solvent extends the range of water based, type V, hydrophobic DES, and represents an additional contribution to the development of sustainable technologies, with appealing properties
Mesoscopic organization in ionic liquids: structural and dynamic implications.
No full textRoom temperature ionic liquids are an exciting novel class of materials1 that are composed solely of ionic species; nevertheless, due to their asymmetric chemical structure (see the figure), they show a low (<100°C) melting point. They show negligible vapor pressure and a wide tunability of the chemical-physical properties upon slight changes of the chemical details (e.g. anion and cation nature).
One of the most striking features emerging among the properties of these materials is the existence of high degree of structural heterogeneity over the nm spatial scale.
Small-Angle X-ray Scattering (SAXS) patterns have been collected on a series of ILs that are characterized by a varying alkyl chain length2. Remarkably, these materials are characterized by a low Q amorphous, whose amplitude as well as position depends on the chain length. These findings have been rationalized in terms of a nanoscale segregated morphology, where the alkyl chains self-assemble into domains embedded into the charged matrix.
Such a structural scenario can be expected to play a role in the relaxation dynamics in ILs. We collected Neutron Spin Echo measurements on a series of deuterated ILs, in order to access specific information on the collective dynamics in these salts3. These experiments highlighted evidences of deviations from the commonly observed viscosity-driven collective dynamics.
1. E. W. Castner et al., J. Chem. Phys., 2010, 132, 120901; J. Wishart, J. Phys. Chem. Lett., 2010, 1, 1629
2. A. Triolo et al., J. Phys. Chem. B, 2007, 111, 4641; Chem. Phys. Lett., 2008, 457, 362; J. Chem. Phys., 2009, 130, 164521
3. A. Triolo et al., J. Phys. Chem. B, 2009, 113, 846
Morphology of poly ethylene oxide dissolved in a room temperature ionic liquid a small angle neutron scattering study
No full textSolutions of deuterated poly(ethylene oxide) (d-PEO) in 1-butyl-3-methyl imidazolium tetrafluoroborate ([bmim][BF4]), a prototype room-temperature ionic liquid (RTIL), have been studied at room temperature over a range of polymer concentrations, using small angle neutron scattering (SANS), characterizing the conformation of PEO dissolved in RTILs. [bmim][BF4] behaves as a good solvent for d-PEO, which organizes in this solvent in non entangled random coils. These findings will help in optimizing the designing of microemulsions in these potentially environmentally friendly solvents
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
- …
