The development of soft anisotropic building blocks is of great interest for various applications in soft matter. Furthermore, such systems would be important model systems for ordering phenomena in fundamental soft matter science. In this work, we address the challenge of creating hollow and anisotropically shaped thermoresponsive microgels, polymeric networks with a solvent filled cavity in their center that are swollen in a good solvent. Sacrificial elliptical hematite silica particles were utilized as a template for the synthesis of a cross-linked N-isopropylacrylamide (NIPAm) shell. By varying the amount of NIPAm, two anisotropic microgels were synthesized with either a thin or thick microgel shell. We characterized these precursor core–shell and the resulting hollow microgels using a combination of light, X-ray, and neutron scattering. New form factor models, accounting for the cavity, the polymer distribution and the anisotropy, have been developed for fitting the scattering data. With such models, we demonstrated the existence of the cavity and simultaneously the anisotropic character of the microgels. Furthermore, we show that the thickness of the shell has a major influence on the shape and the cavity dimension of the microgel after etching of the sacrificial core. Finally, the effect of temperature is investigated, showing that changes in size, softness, and aspect ratio are triggered by temperature.

Wormlike micelles formed by the addition to cetyltrimethylammonium bromide (CTAB) of a range of aromatic cosolutes with small molecular variations in their structure were systematically studied. Phenol and derivatives of benzoate and cinnamate were used, and the resulting mixtures were studied by oscillatory, steady-shear rheology, and the microstructure was probed by small-angle neutron scattering. The lengthening of the micelles and their entanglement result in remarkable viscoelastic properties, making rheology a useful tool to assess the effect of structural variations of the cosolutes on wormlike micelle formation. For a fixed concentration of CTAB and cosolute (200 mmol L(-1)), the relaxation time decreases in the following order: phenol > cinnamate> o-hydroxycinnamate > salicylate > o-methoxycinnamate > benzoate > o-methoxybenzoate. The variations in viscoelastic response are rationalized by using Mulliken population analysis to map out the electronic density of the cosolutes and quantify the barrier to rotation of specific groups on the aromatics. We find that the ability of the group attached to the aromatic ring to rotate is crucial in determining the packing of the cosolute at the micellar interface and thus critically impacts the micellar growth and, in turn, the rheological response. These results enable us for the first time to propose design rules for the self-assembly of the surfactants and cosolutes resulting in the formation of wormlike micelles with the cationic surfactant CTAB.

Although wormlike micelles (WLM) were first described more than 30 years ago, many aspects of their formation process are still unclear. Herein, a systematic experimental investigation of the process for wormlike micelle (WLM) formation in mixtures of tetradecyltrimethylammonium bromide (C14TAB) and salicylate (2-hydroxybenzoate) was carried out. This system was used as a model to investigate the conditions for the formation of the giant aggregate. For comparison, the other two isomers of salicylate (3- and 4-hydroxybenzoate) were also investigated, once in these cases wormlike micelles are not formed. The studies were based on calorimetric titration, static light scattering, and rheological measurements. Enthalpy changes upon titration of C14TAB into 2-hydroxybenzoate solutions revealed a highly cooperative and exothermic process that was associated with micelle growth. The size of the aggregates, obtained by static light scattering measurements, confirms the shape transition. In addition, the correlation of these two sets of results with measurements of micelle charge surface indicates that this transition occurs around the point of charge neutralization.

Anisotropic dynamics on the colloidal length scale is ubiquitous in nature. Of particular interest is the dynamics of systems approaching a kinetically arrested state. The failure of classical techniques for investigating the dynamics of highly turbid suspensions has contributed toward the limited experimental information available up until now. Exploiting the recent developments in the technique of differential dynamic microscopy (DDM), we report the first experimental study of the anisotropic collective dynamics of colloidal ellipsoids with a magnetic hematite core over a wide concentration range approaching kinetic arrest. In addition, we have investigated the effect of an external magnetic field on the resulting anisotropic collective diffusion. We combine DDM with small-angle x-ray scattering and rheological measurements to locate the glass transition and to relate the collective short- and long-time diffusion coefficients to the structural correlations and the evolution of the zero shear viscosity as the system approaches an arrested state.

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