The aggregation and phase behavior, micelle and microemulsion structure, and the polymerization behavior of various binary and ternary systems containing water, (oligooxa)alkanediyl-α,ω-bis(dimethyldodecylammonium bromide) surfactants (12-EO x -12), and styrene are reported. The hydrophilic spacer chain length x in the cationic gemini surfactants was varied between 0 and 5. With increasing spacer chain length the surface area per molecule at the air−water interface increases, whereas the single-phase region of the ternary microemulsion systems is largest for x being 1 and decreases with increasing x in the investigated concentration range. Small-angle neutron scattering (SANS) and cryogenic temperature transmission electron microscopy (cryo-TEM) measurements indicate that the micelle and microdroplet dimensions decrease with increasing x. Polymerization was carried out at 25 and 60 °C using 60Co γ-rays. Spherical polystyrene particles in the nanometer size range were obtained, the particle size being dependent on the spacer length of the gemini surfactants and on the polymerization temperature. At 25 °C, particle size and molecular weight of polystyrene were maximum at medium spacer length, while at 60 °C, the particle size decreased with increasing x, in correspondence to the microstructural properties of the microemulsions observed by SANS. The experimental results suggest that the chemical structure of the surfactant molecules used in the microemulsion formulation has a strong influence on the particle properties after polymerization. This influence depends on the curvature of the interfacial film induced by the surfactant molecules.

This work reports on the dynamics of L2-microemulsions stabilized by Aerosol OT. Time-resolved luminescence quenching measurements using the probe Tb(pda)3 3- show the existence of clusters in water-in-oil (w/o) microemulsions. The fast exchange appearing over several microeseconds is attributed to intracluster quenching, whereas the slow exchange on the millisecond time scale corresponds to intercluster exchange. The fast exchange is decelerated when the temperature is increased and is related to a temperature-induced cluster growth. The slow exchange, conversely, is strongly accelerated within the one-phase region. Below the percolation threshold, the corresponding rate constant obeys an Arrhenius relation. The activation energies increase with the droplet size. In the percolation domain, strong deviations from linearity in the Arrhenius plots occur, which are interpreted by a kinetic scheme considering the limited quenching reaction rate and aggregate collisions disturbing the exchange transition state. Enthalpy−entropy compensation is established from the intercepts of the Arrhenius plots. The activation entropy is discussed in terms of the clustering entropy due to an aggregation equilibrium prior to exchange, yielding ΔS cl in very good agreement with results from other methods. ΔS cl increases with the droplet size and the solvent hydrocarbon length. The percolation phenomenon is discussed as an entropy-driven droplet aggregation accompanied by a facilitated exchange.

A novel route to the formation of large aggregates, with associated rheological enhancement, is provided by formation of inclusion complexes between a telechelic polymer and a second polymer containing appropriate receptor groups. The main focus of this paper describes such complexes between an adamantane end-capped poly(ethylene oxide) (PEO) (M w = 104 gmol-1) with a polymer of β-cyclodextrin (M w = 3.5 × 104 gmol-1) as studied by light scattering. There is a pronounced broadening of the width of the particle size distribution with increasing concentration of end-capped polymer, accompanied by a strong increase in the average relaxation time. Viscosity enhancement in the system was measured on the same samples. Newtonian behavior was observed in the shear rate range 0.017−90 s-1. Light scattering experiments (static and dynamic) were also made on the telechelic PEO itself. Light scattering shows the presence of a slowly relaxing component which dominates the scattering and this reflects large structures (radius 80 nm) created by interchain association to form a loose network, albeit at low concentration. Static and time-resolved fluorescence experiments show that there is no detectable tendency for “micellization” of the adamantane groups.