Non-Classical Self-Assembly of Anisotropic Magneto-Organosilica Janus Particles Possessing Surfactant Properties and the Field-Triggered Breakdown of Surface Activity and Amphiphilic Properties.

Using colloidal particles as models to understand processes on a smaller scale is a precious approach. Compared to molecules, particles are less defined, but their architecture can be more complex and so is their long-range interaction. One can observe phenomena that are unknown or much more difficult to realize on the molecular level. The current paper focuses on particle-based surfactants and reports on numerous unexpected properties. The main goal is creating an amphiphilic system with responsiveness in surface activity and associated self-organization phenomena depending on applying an external trigger, preferably a physical field. A key step is the creation of a Janus-type particle characterized by two types of dipoles (electric and magnetic) which geometrically stand orthogonal to each other. In a field, one can control which contribution and direction dominate the interparticle interactions. As a result, one can drastically change the system's properties. The features of ferrite-core organosilica-shell particles with grain-like morphology modified by click chemistry are studied in response to spatially isotropic and anisotropic triggers. A highly unusual aggregation-dissolution-reaggregation sequence w as discovered. Using a magnetic field, one can even switch off the amphiphilic properties and use this for the field-triggered breaking of multiphase systems such as emulsions.

Stimuli-Responsive Particle-Based Amphiphiles as Active Colloids Prepared by Anisotropic Click Chemistry.

Amphiphiles alter the energy of surfaces, but the extent of this feature is typically constant. Smart systems with amphiphilicity as a function of an external, physical trigger are desirable. As a trigger, the exposure to a magnetic field, in particular, is attractive because it is not shielded in water. Amphiphiles like surfactants are well known, but the magnetic response of molecules is typically weak. Vice-versa, magnetic particles with strong response to magnetic triggers are fully established in nanoscience, but they are not amphiphilic. In this work colloids with Janus architecture and ultra-small dimensions (25 nm) have been prepared by spatial control over the thiol-yne click modification of organosilica-magnetite core-shell nanoparticles. The amphiphilic properties of these anisotropically modified particles are proven. Finally, a pronounced and reversible change in interfacial stabilization results from the application of a weak (<1 T) magnetic field.

Maximizing Headgroup Repulsion: Hybrid Surfactants with Ultrahighly Charged Inorganic Heads and Their Unusual Self-Assembly.

Nonequilibrium states of matter are arousing huge interest because of the outstanding possibilities to generate unprecedented structures with novel properties. Self-organizing soft matter is the ideal object of study as it unifies periodic order and high dynamics. Compared to settled systems, it becomes vital to realize more complex interaction patterns. A promising and intricate approach is implementing controlled balance between attractive and repulsive forces. We try to answer a fundamental question in surfactant science: How are processes like lyotropic liquid crystals and micellization affected, when headgroup charge becomes so large that repulsive interactions are inevitable? A particular challenge is that size and shape of the surfactant must not change. We could realize the latter by means of new hybrid surfactants with a heteropolyanion head [EW11O39]n- (E = PV, SiIV, BIII; n = 3, 4, 5). Among the unusual self-assembled structures, we report a new type of micelle with dumbbell morphology.