This study reports the lyotropic phase behavior of two poly(ethylene oxide)-b-poly(butadiene) diblock copolymers and their cross-linking in the mesophase under retention of the mesoscopic order. The lyotropic phase behavior in water was characterized by polarized light microscopy and small-angle X-ray scattering (SAXS) in the concentration range from 0 to 100 wt % and in a temperature range between 20 and 100 °C. Depending on polymer composition and concentration micellar, hexagonal, lamellar, and cubic phases are found. Their ranges as well as pronounced coexisting phase regions were determined. Several of these mesophases were cross-linked via γ-irradiation to form mesostructured hydrogels. It is shown that the cross-linked polymer gel essentially maintains the parental lyotropic order, as proven by SAXS, polarized light microscopy, and transmission electron microscopy (TEM). TEM enables imaging of the polymer gel structure and thereby the visualization of the liquid-crystalline mesophase morphologies in themselves. The lyotropic mesophases as well as the lyotropic gels were used as templates for the synthesis of mesoporous silica, which is expected to give a negative solid copy of the ordered soft matter structure. The influence of the different templates on the silica structure formation is discussed.

The use of cationic dimeric (“gemini”) surfactants in the oil in water (o/w) microemulsion polymerization of styrene is reported. Gemini surfactants of the alkanediyl-α,ω-bis(dimethylalkylammonium bromide) type (m-s-m) with m being 12 and s being 2, 4, 6, 8, 10, and 12 were used. The phase behavior of the microemulsion is decisively influenced by the spacer length s. All surfactants form single-phase o/w microemulsions with styrene in a temperature range from 25 to 60 °C. For s being 2, only very small stable microemulsion regions were observed, while for s being 4, 6, and 8, the clear and stable regions were gradually increased. The shape of the single-phase regions was very similar to that of the analogous single tail surfactant dodecyltrimethylammonium bromide. For s being 10, the microemulsion region was distinctly extended, while for s being 12, it was decreased again at low temperature, but even more increased at high temperature. Polymerization of the monomeric microemulsions led to spherical latex particles, whose size range could be easily controlled by the monomer/surfactant ratio. A significant dependence of the particle size on the surfactant spacer length was observed. At 25 °C, the particle size was maximum for s being 10, at 60 °C the particle size increased with s. Therefore, the particle size was directly correlated with the size of the single-phase microemulsion region. The molecular weight was maximum at medium spacer length. The experimental results are discussed by taking into account hydrophobic and electrostatic effects and the respective microdroplet structure resulting from the varying interfacial spontaneous curvature due to the different surfactant shapes.

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.