Isabelle Grillo

Insight into Asphaltene Nanoaggregate Structure Inferred by Small Angle Neutron and X-ray Scattering

Complementary neutron and X-ray small angle scattering results give prominent information on the asphaltene nanostructure. Precise SANS and SAXS measurements on a large q-scale were performed on the same dilute asphaltene-toluene solution, and absolute intensity scaling was carried out. Direct comparison of neutron and X-ray spectra enables description of a fractal organization made from the aggregation of small entities of 16 kDa, exhibiting an internal fine structure. Neutron contrast variation experiments enhance the description of this nanoaggregate in terms of core-shell disk organization, giving insight into core and shell dimensions and chemical compositions. The nanoaggregates are best described by a disk of total radius 32 Å with 30% polydispersity and a height of 6.7 Å. Composition and density calculations show that the core is a dense and aromatic structure, contrary to the shell, which is highly aliphatic. These results show a good agreement with the general view of the Yen model (Yen, T. F.; et al. Anal. Chem.1961, 33, 1587-1594) and as for the modified Yen model (Mullins, O. C. Energy Fuels2010, 24, 2179-2207), provide characteristic dimensions of the asphaltene nanoaggregate in good solvent.

Magnetic Control over Liquid Surface Properties with Responsive Surfactants

are well known. Here we report for the first time ionicliquid surfactants that are magneto-responsive, thus offeringthe potential to perturb liquid emulsions simply by theapplication of an external magnetic field. Although ionicliquids(ILs)containingtransitionmetalcomplexeshavebeenknown for some time,

Anionic Surfactant Ionic Liquids with 1-Butyl-3-methyl-imidazolium Cations: Characterization and Application

For the first time a series of anionic surfactant ionic liquids (SAILs) has been synthesized based on organic surfactant anions and 1-butyl-3-methyl-imidazolium cations. These compounds are more environmentally friendly and chemically tunable as compared to other common ionic liquids. A detailed investigation of physicochemical properties highlights potential applications from battery design to reaction control, and studies into aqueous aggregation behavior, as well as structuring in pure ILs, point to possible uses in electrochemistry.

Anionic Surfactants and Surfactant Ionic Liquids with Quaternary Ammonium Counterions

Small-angle neutron scattering and surface tension have been used to characterize a class of surfactants (SURFs), including surfactant ionic liquids (SAILs). These SURFs and SAILs are based on organic surfactant anions (single-tail dodecyl sulfate, DS, double-chain aerosol-OT, AOT, and the trichain, TC) with substituted quaternary ammonium cations. This class of surfactants can be obtained by straightforward chemistry, being cheaper and more environmentally benign than standard cationic SAILs. A surprising aspect of the results is that, broadly speaking, the physicochemical properties of these SURFs and SAILs are dominated by the nature of the surfactant anion and that the chemical structure of the added cation plays only a secondary role.

Surfactant (Bi)Layers on Gold Nanorods

Gold nanorods in aqueous solution are generally surrounded by surfactants or capping agents. This is crucial for anisotropic growth during synthesis and for their final stability in solution. When CTAB is used, a bilayer has been evidenced from analytical methods even though no direct morphological characterization of the precise thickness and compactness has been reported. The type of surfactant layer is also relevant to understand the marked difference in further self-assembling properties of gold nanorods as experienced using 16-EO(1)-16 gemini surfactant instead of CTAB. To obtain a direct measure of the thickness of the surfactant layer on gold nanorods synthesized by the seeded growth method, we coupled TEM, SAXS, and SANS experiments for the two different cases, CTAB and gemini 16-EO(1)-16. Despite the strong residual signal from micelles in excess, it can be concluded that the thickness is imposed by the chain length of the surfactant and corresponds to a bilayer with partial interdigitation.

Structure of Micelles of a Nonionic Block Copolymer Determined by SANS and SAXS

The micellar state of Pluronic P123, which is a poly(ethylene oxide)-b-poly(propylene oxide)-b- poly(ethylene oxide) block polymer (EO(20)PO(70)EO(20)), has been investigated using SANS, SAXS, and differential scanning calorimetry under the conditions utilized in the synthesis of ordered mesoporous materials, such as SBA-15. The absolute intensity measurements, both with SANS and SAXS, have provided a detailed quantitative description of the P123 micelles in the framework of a simple core-shell spherical model. The model developed has been used to establish the structure of the copolymer micelles, including their size, shape, aggregation number and detailed composition, as well as the structural changes induced by varying reaction conditions. The effects of temperature, pH, acidic source and the addition of swelling agents (toluene and TMB) are reported and discussed.

Directed assembly of optoelectronically active alkyl–π-conjugated molecules by adding n-alkanes or π-conjugated species

Supramolecular assembly can yield ordered structures by taking advantage of the cumulative effect of multiple non-covalent interactions between adjacent molecules. The thermodynamic origin of many self-assembled structures in water is the balance between the hydrophilic and hydrophobic segments of the molecule. Here, we show that this approach can be generalized to use solvophobic and solvophilic segments of fully hydrophobic alkylated fullerene molecules. Addition of n-alkanes results in their assembly--due to the antipathy of C60 towards n-alkanes--into micelles and hexagonally packed gel-fibres containing insulated C60 nanowires. The addition of pristine C60 instead directs the assembly into lamellar mesophases by increasing the proportion of π-conjugated material in the mixture. The assembled structures contain a large fraction of optoelectronically active material and exhibit comparably high photoconductivities. This method is shown to be applicable to several alkyl-π-conjugated molecules, and can be used to construct organized functional materials with π-conjugated sections.

Effect of solvent quality on aggregate structures of common surfactants

Aggregate structures of two model surfactants, AOT and C12E5 are studied in pure solvents D2O, dioxane-d8 (d-diox) and cyclohexane-d12 (C6D12) as well as in formulated D2O/d-diox and d-diox/C6D12 mixtures. As such these solvents and mixtures span a wide and continuous range of polarities. Small-angle neutron scattering (SANS) has been employed to follow an evolution of the preferred aggregate curvature, from normal micelles in high polarity solvents, through to reversed micelles in low polarity media. SANS has also been used to elucidate the micellar size, shape as well as to highlight intermicellar interactions. The results shed new light on the nature of aggregation structures in intermediate polarity solvents, and point to a region of solvent quality (as characterized by Hildebrand Solubility Parameter, Snyder polarity parameter or dielectric constant) in which aggregation is not favored. Finally these observed trends in aggregation as a function of solvent quality are successfully used to predict the self-assembly behavior of C12E5 in a different solvent, hexane-d14 (C6D14).

Initial stages of SBA-15 synthesis: An overview☆

This work presents an overview of the data obtained for SBA-15 synthesis under the reaction conditions using synchrotron based small angle X-ray scattering and small angle neutron scattering. Three major stages in the synthesis of SBA-15 materials proceeding according to the cooperative self-assembly mechanism have been identified, and the structures of the intermediates species have been established. Our in situ time-resolved neutron scattering experiments demonstrate that only spherical micelles of the templating agent are present in the synthesis mixture during the first stage of the reaction. According to the neutron scattering and X-ray scattering data, in the second stage of the reaction the formation of hybrid organic-inorganic micelles is accompanied with the transformation from spherical to cylindrical micelles, which takes place before the precipitation of the ordered SBA-15 phase. During the third stage, these micelles aggregate into a two-dimensional hexagonal structure, confirming that the precipitation takes place as the result of self-assembly of the hybrid cylindrical micelles. As the synthesis proceeds, the voids between the cylinders are filled with the silicate species which undergo condensation reactions resulting in cross-linking and covalent bonding, leading to the formation of highly ordered SBA-15 mesostructure. This work demonstrates that valuable structural information can be obtained from X-ray and neutron scattering characterisation of complex systems containing periodic phases with d-spacing values up to 30 nm, and that both techniques are powerful means for in situ monitoring of the formation of nanostructured materials.

Ionic Liquids in Microemulsions-A Concept To Extend the Conventional Thermal Stability Range of Microemulsions

Ionic liquids (ILs), which are defined as salts with a melting point below 100°C are often considered as future solvents for catalysis, chemical reactions, extractions and electrochemical purposes. Apart from these classical applications, ILs have also gained interest in classical colloid and surface chemistry. The formation of amphiphilic association structures in and with ionic liquids, such as micelles, vesicles, microemulsions and liquid crystalline phases have been described in literature. The thesis can be subdivided into three main parts: Conductivity studies of the anion effect on imidazolium based ionic liquids over a wide temperature range (-25-195)°C, formulation and characterization of nonaqueous, high temperature stable microemulsions with room temperature ionic liquids as polar phase and the synthesis and characterization of new ionic liquids based on alkali cations. In the first part conductivities of four different highly pure imidazolium based room temperature ionic liquids (RTILs) have been studied within a temperature range between (-25 to 195)°C. Thereby, the cationic scaffold, the 1-butyl-3-methylimidazolium cation ([bmim+]), was kept constant while the anions were varied. The investigated anions were dicyanamide ([DCA-]), hexafluorophosphate ([PF6-]), trifluoroacetate ([TA-]) and trifluoromethanesulfonate ([TfO-]). It is quite surprising that studies of important physicochemical transport properties are still scarce in the field of ionic liquids. At a given temperature the conductivity decreased in the order [bmim][DCA] > [bmim][TA] > [bmim][TfO] > [bmim][PF6]. Temperature dependence of the conductivity could be well described by the empirical Vogel-Fulcher-Tammann equation. Whilst our data compare favorably with some literature results, significant deviations from others were noted. To calculate the molar conductivity of the RTILs densities were measured between (5 and 65)°C. Walden plots of the molar conductance, available for [bmim][PF6], [bmim][TfO] and [bmim][TA] in the limited temperature range of (5 to 65)°C, suggest that these RTILs can be classified as high-ionicity ionic liquids. All studies concerning ILs in microemulsions described in literature have been performed below the boiling point of water. In the present work, we were interested in microemulsions that are stable over a wide temperature range at ambient pressure. For this purpose, water must be replaced by a RTIL. Two different RTILs were used to replace water in microemulsions, namely ethyl ammonium nitrate (EAN) and 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim]][BF4]). Furthermore, the microemulsions contained the long- chain ionic liquid 1-hexadecyl-3-methyl-imidazolium chloride ([C16mim][Cl]) as surfactant, decanol as cosurfactant, and dodecane as oil phase. Both systems were studied in a temperature range between (30 and 150)°C. The most promising microemulsions were obtained with EAN. The microemulsions were characterized by means of conductivity, rheology, dynamic light scattering (DLS), small angel X-Ray (SAXS) and small angle neutron scattering (SANS). In the case of EAN reverse microemulsions with EAN cores were obtained. The EAN systems exhibited a typical percolation behavior over the whole investigated temperature range, the corresponding percolation threshold volume fractions were significantly influenced by temperature. All scattering experiments were in agreement with EAN droplets stabilized by surfactants in a continuous oil matrix. The temperature dependent SANS experiments confirmed the existence of microemulsions up to 150°C. The results obtained for the [bmim]][BF4] system demonstrate the high thermal stability of these microemulsions as well, whereby the structures are less defined and can be assumed to be more a bicontinuous one than a reverse microemulsion. Conventional ILs typically contain bulky organic cations with a low degree of symmetry such as imidazolium, pyrrolidinium, tetraalkylphosphonium, trialkylsulfonium or quaternary ammonium. These cations hinder the regular packing in a crystal lattice. Consequently, the solid crystalline state becomes energetically less favorable, leading to low melting points. This effect can be enhanced further by the implementation of an anion with a delocalized charge, resulting in decreased interionic interactions. To date, little attention has been paid to systems of ionic liquids involving small inorganic cations. In this work, ionic liquids based on small inorganic cations and oligoether carboxylate anions were successfully synthesized. A new family of ILs comprising alkali cations and 2,5,8,11-tetraoxatridecan-13-oate (TOTO) as anion and alkali cations have been developed. These substances are promising materials due to their pronounced electrochemical and thermal stability. The concept of the ionicity plot was successfully applied to the sodium salt for which strong ion pairing was observed. Further, it was shown that the cytotoxicity of such “simple” alkali carboxylate ionic liquids compared to conventional imidazolium based ILs is very low.