Interaction of the nonionic surfactant C12E8 with high molar mass poly(ethylene oxide) studied by dynamic light scattering and fluorescence quenching methods

Dynamic light scattering has been used to investigate ternary aqueous solutions of n-dodecyl octaoxyethylene glycol monoetber (C12E8) with high molar mass poly(ethylene oxide) (PEO). The measurements were made at 20 °C, always below the cloud point temperature (Tc) of the mixed solutions. The relaxation time distributions are bimodal at higher PEO and surfactant concentrations, owing to the preacute of free surfactant micelles, which coexist with the slower component, representing the polymer coil/micellar cluster comptex. As the surfactant concentration is increased, the apparent hydrodynamic radius (RH) of the coil becomes progressively larger. It is suggested that the complex structure consists of clusters of micelles sited within the polymer coil, as previously concluded for the PEO-C12E8-water system. However. C12E8 interacts less strongly than C12E8 with PEO; at low concentrations of surfactant the complex does not contribute significantly to the total scattered intensity. The perturbation of the PEO coil radius with C12E8 is also smaller than that in the C12E8 system. The addition of PEO strongly decreases the clouding temperature of the system, as previously observed for C12E8/PEO mixtures in solution Addition of PEO up to 0.2% to C12E8 (10 wt %) solutions doss not alter the aggregation number (Nagg) of the micelles probably because the surfactant monomers are equally partitioned as bound and unbound micelles. The critical micelle concentration (cmc), obtained from the I1/I3 ratio (a measure of the dependence of the vibronic band intensities on the pyrene probe environment), does not change when PEO is added, suggesting that for neutral polymer/surfactant systems the trends in Nagg and the cmc do not unambiguously reflect the strength of interaction

Salt-induced sphere-to-disk transition of octadecyltrimethylammonium bromide micelles

We have used surface tension measurements, differential scanning calorimetry (DSC), dynamic light scattering (DLS), and cryo-transmission electron microscopy (cryo-TEM) to investigate the dynamic and structural behavior of octadecyltrimethylammonium bromide (C(18)TAB) micelles in water and NaBr solution. The surface tension data for fixed C(18)TAB concentrations of 25 mM and varied NaBr additions (0-50 mM) shows that the critical micelle concentration (cmc) increases after an initial decrease at 0.5 mM NaBr. This unusual effect has been explained using results from DSC and DLS. At low salt concentrations (below ca. 25 mM) the relaxation time distribution is bimodal with a dominant fast mode due to spherical micelles. Above ca. 35 mM NaBr disklike structures are favored and the relaxation time distribution is more closely unimodal. The postulated sphere-to-disk transition is supported by cryo-TEM micrographs. A pronounced increase in the micellar effective hydrodynamic radius (R-H) is observed as the NaBr concentration is increased above about 35 mM; below 35 mM the R-H of the spherical micelles changes Little with ionic strength

Mixed micelles of cationic surfactants and sodium cholate in water

107-112Critical micelle concentrations (CMCs) of cationic surfactant (alkyltrimethylammonium bromides, CnTABr, where n = 10, 12, 14, 16 and 18), and a bile salt sodium cholate (NaC) were determined from surface tension, conductance and dye solubilization methods, while of their equimolar mixtures from surface tension and dye solubilization methods. The interaction parameter (β) obtained from analysis of data, using Rubingh’s theory showed strong interaction between NaC and cationic surfactant. Time-resolved fluorescence-quenching results revealed small-sized mixed spherical micelle with aggregation number much less than micelles of cationic surfactant

New micellar morphologies from amphiphilic block copolymers: disks, toroids and bicontinuous micelles

Amphiphilic AB and ABA block copolymers have been demonstrated to form a variety of self-assembled aggregate structures in dilute solutions where the solvent preferentially solvates one of the blocks. The most common structures formed by these amphiphilic macromolecules are spherical micelles, cylindrical micelles and vesicles (polymersomes). Interest into the characterisation and controlled formation of block copolymer aggregates has been spurred on by their potential as surfactants, nano- to micro-sized carriers for active compounds, for the controlled release of encapsulated compounds and for inorganic materials templating, amongst numerous other proposed applications. Research in the past decade has focussed not only on manipulating the properties of aggregates through control of both the chemistry of the constituent polymer blocks but also the external and internal morphology of the aggregates. This review article will present an overview of recent approaches to controlling the self-assembly of amphiphilic block copolymers with a view to obtaining novel micellar morphologies. Whilst the article touches upon multi-compartment micelles particular focus is placed upon control of the overall shape of micelles; i.e. those systems that expand the range of accessible morphologies beyond ‘simple’ spherical and cylindrical micelles namely disk-like, toroidal and bicontinuous micelles

Preparation of Solid Alkaline Fuel Cell Binders Based on Fluorinated Poly(diallyldimethylammonium chloride)s [Poly(DADMAC)] or Poly(chlorotrifluoroethylene-co-DADMAC) Copolymers

A membrane or an electrode binder to be used in a solid alkaline fuel cell (SAFC) needs to (i) be insoluble in both aqueous solutions and the required fuels, and (ii) exhibit an hydroxide ion conductivity. To achieve these goals, two pathways were employed: (i) one consists of the radical copolymerization of diallyldimethylam-monium chloride (DADMAC) with chlorotrifluoroethylene (CTFE) while (ii) the other one is based on the counter-ion exchange of a poly(DADMAC) by fluorinated anions. First, the radical copolymerization of CTFE with DADMAC under various experimental conditions was achieved in yields up to 85%, and DADMAC percentages in the copolymers were higher than those in the feed compositions. To obtain insoluble copolymers, high CTFE feed contents (>70 mol %) were required. The other route consisting in the partial replacement of the Cl- counter-ions in the water-soluble poly(DADMAC) by bistrifluoromethanesulfonimide (TFSI-) did confer the starting material insolubility in water while maintaining its conductivity. When the fluorinated poly(DADMAC) was obtained from concentrated solutions of fluorinated surfactant, it was observed that the amount of counter-ions exchanged was difficult to control, which limits optimization. Nevertheless, under diluted conditions, membranes with ion exchange capacity up to 0.7 meq g-1, and conductivities close to 1 mS cm-1 were obtained. Although their conductivities were low, these membranes fulfill the requirements for a SAFC membrane in terms of solubility in DMSO, water insolubility, and thermal stability (Td 10% > 320 °C). When used in a fuel cell, as a binder in the membrane-electrode assembly (MEA), significant improvements were noted (+50% of the open circuit voltage, +580% in current density, and +540% in accessible power)