Search results for "Aggregation number"
showing 10 items of 30 documents
Self-assembly and intra-cluster reactions of erbium and ytterbium bis(2-ethylhexyl)sulfosuccinates in the gas phase
2014
RATIONALE The study of surfactant organization in vacuum allows surfactant–surfactant interaction to be unveiled in the absence of surrounding solvent molecules. Knowledge on their chemical-physical properties may also lead to the definition of more efficient gas-phase carriers, air-cleaning agents and nanoreactors. In addition, the presence of lanthanide-group ions adds unique photochemical properties to surfactants. METHODS The structural features, stability and fragmentation patterns of charged aggregates formed by lanthanide-functionalized surfactants, ytterbium and erbium bis(2-ethylhexyl)sulfosuccinate ((AOT)3Yb and (AOT)3Er), have been investigated by electrospray ionization mass spe…
Structural organization of surfactant aggregates in vacuo: a molecular dynamics and well-tempered metadynamics study
2015
Experimental investigations using mass spectrometry have established that surfactant molecules are able to form aggregates in the gas phase. However, there is no general consensus on the organization of these aggregates and how it depends on the aggregation number and surfactant molecular structure. In the present paper we investigate the structural organization of some surfactants in vacuo by molecular dynamics and well-tempered metadynamics simulations to widely explore the space of their possible conformations in vacuo. To study how the specific molecular features of such compounds affect their organization, we have considered as paradigmatic surfactants, the anionic single-chain sodium …
Electrospray ion mobility mass spectrometry of positively and negatively charged (1R,2S)-dodecyl(2-hydroxy-1-methyl-2-phenylethyl)dimethylammonium br…
2015
Rationale Self-assembling processes of surfactants in the gas phase constitute a developing research field of interest since they allow information to be gained on the peculiar structural organization of these aggregates, on their ability to incorporate from small molecules up to proteins and on their possible use as carriers of drugs in the gas phase or as cleaning agents and exotic reaction media. Methods The mass spectra of charged aggregates of the chiral surfactant (1R,2S)-dodecyl(2-hydroxy-1-methyl-2-phenylethyl)dimethylammonium bromide (DMEB) in the gas phase have been recorded using a Synapt G2-Si mass spectrometer in the positive and negative ion mode. For comparison purposes, the …
Small angle scattering study of poly(methylmethacrylate)-blockpoly(ethylene oxide) block co-polymer in aqueous solution
2005
A combined Small Angle X ray (SAXS) and Neutron (SANS) Scattering study of aqueous solutions of a symmetric block copolymer consisting of poly(methyl methacrylate) (PMMA) and poly(ethylene oxide) (PEO) moieties is presented. The polymer forms slightly polydisperse spherical micelles in a wide range of concentration (0.03 – 6.7 w/V) and temperature (20°C ≤ T ≤ 65°C). A good description of the SANS data is obtained using a polydisperse core-shell model with a structure factor for a modified hard sphere potential. By increasing the concentration at constant T we observed a decrease of the aggregation number and an increase of solvation of PEO groups in the shell, opposite to what happens by in…
Structure and Shear Response of Janus Colloid–Polymer Mixtures in Solution
2020
We investigate the structure and rheological properties of dilute colloid-polymer mixtures at rest and under shear via molecular simulations that take into account hydrodynamic interactions. Mixtures of amphiphilic Janus colloids (JCs) and hydrophobic/amphiphilic polymers are considered for various solvent qualities and polymer concentrations. Free polymers, small polymer droplets, and hybrid aggregates coexist in mixtures with slightly hydrophobic homopolymers. As the solvent quality worsens, all polymers aggregate into small droplets, covered and stabilized by the JCs. In mixtures with amphiphilic polymers, we observe the coexistence of free polymers, purely polymeric micelles, and hybrid…
Spatially ordered surfactant assemblies in the gas phase: negatively charged bis(2-ethylhexyl)sulfosuccinate-alkaline metal ion aggregates
2009
The formation and structural features of negatively charged aggregates of sodium bis(2-ethylhexyl)sulfosuccinate (AOTNa) surfactant molecules in the gas phase have been investigated by electrospray ionization mass spectrometry (ESI-MS) and density functional theory calculations. Mainly driven by the interactions of alkali metal ions both with the oxygen atoms of the sulfonate group and with the succinate moiety of the AOT− anion, spatially ordered supramolecular assemblies, characterized by an internal core composed of surfactant counterions and hydrophilic head groups surrounded by the surfactant alkyl chains pointing outwards, are formed. Calculations have shown that surfactant self-organ…
Structural and Transport Properties of Bola C-16 Micelles in Water and in Aqueous Electrolyte Solutions
2003
Aqueous solutions containing a bolaform surfactant [R,ω-(4,7,10,13-pentaoxa-16-azacyclooctadecane)- hexadecane], with and without electrolytes have been investigated as a function of surfactant concentration and ionic strength. Small angle neutron scattering (SANS), NMR self-diffusion, and other physical-chemical methods were used. From the analysis of SANS data it was inferred that in water the surfactant forms slightly charged ellipsoidal micelles, because of the partial hydrolysis of amino groups. The aggregates grow with the increase of concentration, becoming more elongated. Due to the selective complexing ability of aza crown ether units, significant differences were observed upon add…
The morphology of block copolymer micelles in supercritical carbon dioxide by small-angle neutron and x-ray scattering
1997
Above its critical point, carbon dioxide forms a super-critical fluid, which promises to be an environmentally responsible replacement for the organic solvents traditionally used in polymerizations. Many lipophilic polymers such as polystyrene (PS) are insoluble in CO2, though polymerizations may be accomplished via the use of PS-fluoropolymer stabilizers, which act as emulsifying agents. Small-angle neutron and X-ray scattering have been used to show that these molecules form micelles with a CO2-phobic PS core and a CO2-philic fluoropolymer corona. When the PS block was fixed in length and the fluorinated corona block was varied, the number of block copolymer molecules per micelle (six to …
Electrospray ion mobility mass spectrometry of positively charged sodium bis[2-ethythexyl)sulfosuccinate aggregates.
2014
Collision cross-sections (CCS) of positively singly and multiply charged aggregates of the surfactant sodium bis(2-ethylhexyl)sulfosuccinate (AOTNa) in the gas phase have been measured by quadrupole ion mobility time-of-flight mass spectrometry. Calibration of the observed drift times to the CCS of the AOTNa non-covalent aggregates was achieved by collecting, under the same experimental conditions, the drift times of a range of singly and multiply charged polyalanine peptides whose CCS had been obtained by conventional ion mobility spectrometry. Together with an obvious increase of the aggregate cross-section with the aggregation number, it was found that the aggregate cross-section increa…
Formation of α-ω(4,7,10,13-pentaoxa-16-azacyclooctadecane) hexadecane micelles in aqueous solution – effect of HCl addition
2003
The structure of aggregates of a new bolaform surfactant [α-ω (4,7,10,13-pentaoxa-16-azacyclooctadecane) hexadecane] in neat aqueous solution has been investigated by small-angle neutron scattering. Preliminary data analysis unequivocally indicates that globular micelles are formed. This finding has been confirmed by the analysis of data obtained upon addition of hydrochloric acid. The observed significant reduction of micelle aggregation number has been attributed to the peculiar complexing ability of the two aza-crown ether units in the surfactant molecule; this is in line with information inferred from the complexation of ions into the non alkylated azacrown ethers. As a consequence of h…