Steve Landsmann

A new class of surfactants with multinuclear, Inorganic Head Groups

The main ability of amphiphilic molecules is to alter the energy of interfaces. They aid in the formation of various materials characterized by a high surface to volume ratio. Furthermore, amphiphiles tend to self-organize into structures of higher complexity. In the current study anionic surfactants containing a purely inorganic multinuclear head group of the polytungstate type R-[PW(11)O(39)](3-) were synthesized. Alkyl chains of different length were attached to the head group via siloxy bridges. Furthermore, the counterions could be varied. Ultimately, a heteropolyacid surfactant (H(+) as the counterion) could be prepared. The self-assembly behavior of the polyoxometalate surfactants into micelles and even lyotropic phases was studied. For instance, the formation of a phase with P6/mm symmetry containing hexagonally packed cylinders has been observed. Finally, it was possible to extend the functionality of classical amphiphiles. The polyoxometalate amphiphiles have been used for the emulsification of and, at the same time, as the initiator for the cationic polymerization of styrene. As a result, interesting organic-inorganic hybrid polymer latexes with surfaces containing heteropolyacid entities were prepared.

Bolaform surfactants with polyoxometalate head groups and their assembly into ultra-small monolayer membrane vesicles

Surfactants are indispensable in established technologies as detergents or emulsification agents, and also in recent studies for controlling the growth of nanoparticles or for creating nanocarriers. Although the properties of conventional, organic surfactants are thoroughly explored, strong interest persists in surfactants that possess unique features inaccessible for ordinary systems. Here we present dipolar, bolaform surfactants with a head group comprising of 11 tungsten atoms. These novel compounds are characterized by an exceptionally low critical self-organization concentration, which leads to monolayer vesicles with a diameter of only 15 nm, that is, substantially smaller than for any other system. The membrane of the vesicles is impermeable for water-soluble and oil-soluble guests. Control over release kinetics, which can be followed via the quantitative fluorescence quenching of confined fluorophores, is gained by means of pH adjustments.

Hybrid Surfactant Systems with Inorganic Constituents

Surfactants are molecules of enormous scientific and technological importance, which are widely used as detergents, emulsifiers, and for the preparation of diverse nanostructures. Their fascinating ability to form self-organized structures, such as micelles or liquid crystals, originate from their amphiphilic architecture-a polar head group linked to a hydrophobic chain. While almost all known surfactants are organic, a new family of surfactants is now emerging, which combines amphiphilic properties with the advanced functionality of transition-metal building blocks, for example, redox or catalytic activity and magnetism. These hybrid surfactants exhibit novel self-organization features because of the unique size and electronic properties of the metal-containing entities.

Polyoxometalate Surfactants as Unique Molecules for Interfacial Self-Assembly.

Whereas, commonly, Langmuir monolayers are structurally dominated by the aliphatic chains, we present here the first case of monolayers where the chains merely serve anchoring at the air/water interface and the organization is dictated by the hydrophilic head group self-assembling in a hexagonal lattice. These head groups are polyoxometalates known for their multifunctional potential. The chain length has been systematically varied, allowing for a general study of the impact of the chain length on the supramolecular structure. These model structures are studied here by a combination of modern techniques, the leading ones being X-ray reflectivity and grazing incidence X-ray diffraction. The quantitative structural insights offered in this Letter might represent a starting point for the rational design and study of a new class of emulsions, including an organic tail and a multifunctional inorganic polar head.

Panoscopic Structures by Hierarchical Cascade Self-Assembly of Inorganic Surfactants with Magnetic Heads Containing Dysprosium Ions†

Magnetic moustaches: Inorganic surfactants (I-SURFs) with head groups containing Dy(3+) undergo a hierarchical self-organization cascade controlled by magnetic interactions. The resulting aggregates are shaped like dumbbells with frayed, moustache-like ends.

Fourfold action of surfactants with superacid head groups: polyoxometalate–silicone nanocomposites as promising candidates for proton-conducting materials

Conventional, organic surfactants normally fulfill only one task associated with their amphiphilic character. The situation changes and multifunctionality is granted for surfactants containing inorganic entities, so-called I-SURFs. Here, we demonstrate that an I-SURF with a heteropolyacid head fulfills four tasks at once. It acts as an effective emulsification agent, it catalyzes the polymerization of silicone monomers, it provides proton-conductivity in a PDMS/polyoxometalate hybrid, and it acts as a precursor for a nanostructured WO3 material.

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.