There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

http://experimentationlab.berkeley.edu/sites/default/files/AFMImages/butt_AFM.pdf

Force measurements with the atomic force microscope: Technique, interpretation and applications

Molecular self-assembly is the spontaneous association of molecules under equilibrium conditions into stable, structurally well-defined aggregates joined by noncovalent bonds. Molecular self-assembly is ubiquitous in biological systems and underlies the formation of a wide variety of complex biological structures. Understanding self-assembly and the associated noncovalent interactions that connect complementary interacting molecular surfaces in biological aggregates is a central concern in structural biochemistry. Self-assembly is also emerging as a new strategy in chemical synthesis, with the potential of generating nonbiological structures with dimensions of 1 to 10(2) nanometers (with molecular weights of 10(4) to 10(10) daltons). Structures in the upper part of this range of sizes are presently inaccessible through chemical synthesis, and the ability to prepare them would open a route to structures comparable in size (and perhaps complementary in function) to those that can be prepared by microlithography and other techniques of microfabrication.

Molecular self-assembly and nanochemistry: A chemical strategy for the synthesis of nanostructures

Janus particles: synthesis, self-assembly, physical properties, and applications.

Functional π-Gelators and Their Applications

Many smart materials in bioengineering, nanotechnology and medicine allow the storage and release of encapsulated drugs on demand at a specific location by an external stimulus. Owing to their versatility in material selection, polyelectrolyte multilayers are very promising systems in the development of microencapsulation technologies with permeation control1, 2, 3, 4 governed by variations in the environmental conditions5, 6, 7, 8. Here, organometallic polyelectrolyte multilayer capsules, composed of polyanions and polycations of poly(ferrocenylsilane) (PFS), are introduced. Their preparation involved layer-by-layer self-assembly onto colloidal templates followed by core removal. PFS polyelectrolytes feature redox-active ferrocene units in the main chain. Incorporation of PFS into the capsule walls allowed us to explore the effects of a new stimulus, that is, changing the redox state9, 10, on capsule wall permeability. The permeability of these capsules could be sensitively tuned via chemical oxidation, resulting in a fast capsule expansion accompanied by a drastic permeability increase in response to a very small trigger. The substantial swelling could be suppressed by the application of an additional coating bearing common redox-inert species of poly(styrene sulfonate) (PSS-) and poly(allylamine hydrochloride) (PAH+) on the outer wall of the capsules. Hence, we obtained a unique capsule system with redox-controlled permeability and swellability with a high application potential in materials as well as in bioscience.

Redox-controlled molecular permeability of composite-wall microcapsules.

https://ris.utwente.nl/ws/files/6592787/polymers.pdf

Polymers in conventional and alternative lithography for the fabrication of nanostructures

The use of organic-organometallic block copolymers as catalyst precursors for templated carbon nanotube (CNT) growth (see Figure) is demonstrated for the first time. A thin film of block copolymer was treated with O2 plasma to produce ordered iron-containing catalyst nanoparticle arrays, which are efficient catalysts for CNT growth. This approach allows control of catalyst domain size and spacing by tailoring block copolymer composition.

Organometallic Block Copolymers as Catalyst Precursors for Templated Carbon Nanotube Growth

Seeing the right face: Mono- and bifunctionalized Janus particles with controllable chemical patchiness are prepared by a general masking/unmasking technique and subsequent chemical functionalization (see picture). Supramolecular "host"- and "guest"-functionalized Janus particles were prepared, and specific noncovalent host-guest interactions were used to controllably assemble heterogeneous particles.

Janus Particles with Controllable Patchiness and Their Chemical Functionalization and Supramolecular Assembly

This concise paper discusses poly(ferrocenylsilane) (PFS)-based organometallic gels and hydrogels as a novel class of redox-responsive materials. First, the use of silicon-bridged spirocyclic [1]ferrocenophane crosslinkers for creating PFS networks swellable in organic solvents is described. Optical properties of PFS composite colloidal crystal films, composed of monodisperse silica spheres embedded in such PFS networks, are shown to be influenced by solvent swelling or redox chemistry, allowing the use of these composites in photonic crystal full-color displays. The synthesis of networks composed of water-soluble PFS polyanions or polycations is discussed. In response to redox stimuli, a polyanionic PFS-hydrogel exerted a pressure, which could render it useful as an actuator.

Mark A. Hempenius

Papers

Redox-controlled molecular permeability of composite-wall microcapsules.

Polymers in conventional and alternative lithography for the fabrication of nanostructures

Organometallic Block Copolymers as Catalyst Precursors for Templated Carbon Nanotube Growth

Janus Particles with Controllable Patchiness and Their Chemical Functionalization and Supramolecular Assembly

Poly(ferrocenylsilane) Gels and Hydrogels with Redox-Controlled Actuation.