Polyampholyte-surfactant film tuning in reverse microemulsions

The pH-dependent influence of two different strongly alternating copolymers [poly(N,N'-diallyl-N,N'-dimethylammonium-alt-N-phenylmaleamic carboxylate) (PalPh) and poly(N,N'-diallyl-N,N'-dimethylammonium-alt-3,5-bis(carboxyphenyl)maleamic carboxylate) (PalPhBisCarb)] based on N,N'-diallyl-N,N'-dimethylammonium chloride and maleamic acid derivatives on the phase behavior of a water-in-oil (w/o) microemulsion system made from toluene-pentanol (1:1) and sodium dodecyl sulfate was investigated. It was shown that the optically clear phase range can be extended after incorporation of these copolymers, leading to an increased water solubilization capacity. Additionally, the required amount of surfactant to establish a clear w/o microemulsion depends on the pH value, which means the hydrophobicity of the copolymers. Conductivity measurements show that droplet-droplet interactions in the w/o microemulsion are decreased at acidic but increased at alkaline pH in the presence of the copolymers. From differential scanning calorimetry measurements one can further conclude that these results are in agreement with a change of the position of the copolymer in the interfacial region of the surfactant film. The more hydrophobic PalPh can be directly incorporated into the surfactant film, whereas the phenyl groups of PalPhBisCarb flip into the water core by increasing the pH value.

Covalently closed microemulsions in presence of triblock terpolymers

This paper is focused on the influence of polystyrene (PS)-poly(1,4-butadiene) (PB)-poly(ethylene oxide) (PEO) triblock terpolymers on the w/o microemulsion of the pseudo-ternary system water/sodium dodecylsulfate (SDS)/xylene-pentanol. Despite the insolubility of the copolymer in water as well as in the xylene-pentanol mixture, it can be incorporated into the w/o microemulsion and interactions between the triblock terpolymer molecules and the anionic surfactant headgroups can be detected by differential scanning calorimetry (DSC) measurements. Furthermore, dynamic light scattering measurements were used to determine the aggregate diameter of the modified microemulsions. For lower polymer concentrations large aggregates between 100 and 500 nm can be observed. Surprisingly, at a higher terpolymer concentration of 5 wt%, significant smaller aggregate diameters can be identified by dynamic light scattering and Cryo-SEM. One can conclude that the copolymers are incorporated in the inverse microemulsion droplets, where the PB blocks cover the water droplets. The thermally induced radical cross-linking of the butadiene units in the presence of azobisisobutyronitrile (AIBN) leads then to covalently closed nanocapsules with an average size of 10 nm.

Recovery of nanoparticles produced in phosphatidylcholine-based template phases

This paper focuses on the characterization and use of polymer-modified phosphatidylcholine (PC)/sodium dodecyl sulfate (SDS)-based inverse microemulsions as a template phase for BaSO4 nanoparticle formation. The area of the optically clear inverse microemulsion phase in the isooctane/hexanol/water/PC/SDS system is not significantly changed by adding polyelectrolytes, i.e., poly(diallyldimethylammonium chloride) (PDADMAC), or amphoteric copolymers of diallyldimethylammonium chloride and maleamid acid to the SDS-modified inverse microemulsion. Shear experiments show non-Newtonian flow behavior and oscillation experiments show a frequency-dependent viscosity increase (dilatant behavior) of the microemulsions. Small amounts of bulk water were identified by means of differential scanning calorimetry. One can conclude that the macromolecules are incorporated into the individual droplets, and polymer-filled microemulsions are formed. The polymer-filled microemulsions were used as a template phase for the synthesis of BaSO4 nanoparticles. After solvent evaporation the nanoparticles were redispersed in water and isooctane, respectively. The polymers incorporated into the microemulsion are involved in the redispersion process and influence the size and shape of the redispersed BaSO4 particles in a specific way. The crystallization process mainly depends on the type of solvent and the polymer component added. In the presence of the cationic polyelectrolyte PDADMAC the crystallization to larger cubic crystals is inhibited, and layers consisting of polymer-stabilized spherical nanoparticles of BaSO4 (6 nm in size) will be observed.