Ferro-self-assembly: magnetic and electrochemical adaptation of a multiresponsive zwitterionic metalloamphiphile showing a shape-hysteresis effect.

Metallosurfactants are molecular compounds which combine the unique features of amphiphiles, like their capability of self-organization, with the peculiar properties of metal complexes like magnetism and a rich redox chemistry. Considering the high relevance of surfactants in industry and science, amphiphiles that change their properties on applying an external trigger are highly desirable. A special feature of the surfactant reported here, 1-(Z)-heptenyl-1'-dimethylammonium-methyl-(3-sulfopropyl)ferrocene (6), is that the redox-active ferrocene constituent is in a gemini-position. Oxidation to 6+ induces a drastic change of the surfactant's properties accompanied by the emergence of paramagnetism. The effects of an external magnetic field on vesicles formed by 6+ and the associated dynamics were monitored in situ using a custom-made optical birefringence and dual dynamic light scattering setup. This allowed us to observe the optical anisotropy as well as the anisotropy of the diffusion coefficient and revealed the field-induced formation of oriented string-of-pearls-like aggregates and their delayed disappearance after the field is switched off.

Magnetic field-assisted assembly of iron oxide mesocrystals: a matter of nanoparticle shape and magnetic anisotropy.

This letter describes the formation and detailed characterization of iron oxide mesocrystals produced by the directed assembly of superparamagnetic iron oxide-truncated nanocubes using the slow evaporation of the solvent within an externally applied homogeneous magnetic field. Anisotropic mesocrystals with an elongation along the direction of the magnetic field can be produced. The structure of the directed mesocrystals is compared to self-assembled mesocrystalline films, which are formed without the influence of a magnetic field. The remarkable structural difference of mesocrystals produced within the external magnetic field from those self-assembled without field indicates that the specific nanoparticle ordering within the superstructure is driven by competing of two types of anisotropic interactions caused by particle shape (i.e., faceting) and orientation of the magnetic moment (i.e., easy axes: <111>magnetite). Hence, these findings provide a fundamental understanding of formation mechanisms and structuring of mesocrystals built up from superparamagnetic nanoparticles and how a magnetic field can be used to design anisotropic mesocrystals with different structures.

Nanocomposites of phosphonic-acid-functionalized polyethylenes with inorganic quantum dots.

Insertion of diethyl vinyl phosphonates and free vinyl phosphonic acid, respectively, into [(P^O)Pd(Me)(dmso)] ((P^O) = κ(2)-P,O-Ar2PC6H4SO2O with Ar = 2-MeOC6H4) (1-dmso) occurs in a 2,1- as well as 1,2-fashion, to form a four-and a five-membered chelate [(P^O)Pd{κ(2)-C,O-CH(P(O)(OR)2)CH2CH3}] and [(P^O)Pd{κ(2)-C,O-CH2CH(P(O)(OR)2)CH3}] (R = H, Et). No decomposition or other reactions of 1 by free phosphonic acid moieties occur. Copolymerization in a pressure reactor by 1-dmso yields linear random poly(ethylene-co-diethyl vinyl phosphonate) and poly(ethylene-co-vinyl phosphonic acid). In these copolymerizations, reversible coordination of the phosphonate moieties of free monomer as well as chelate formation by incorporated monomer retards chain growth as also evidenced by relative binding studies of diethyl phosphonate towards 1. Post-polymerization emulsification of poly(ethylene-co-vinyl phosphonic acid) together with CdSe/CdS quantum dots (QDs) yields submicron (ca. 50 nm from dynamic light scattering (DLS) and transmission electron microscopy (TEM)) polymer particles with the QDs embedded in the functionalized polyethylene in a nonaggregated fashion. This embedding benefits the fluorescence behavior in terms of continuous emission and life-time as revealed by wide-field fluorescence measurements. These composite particle dispersions are employed as a ″masterbatch" together with an aqueous high density polyethylene (HDPE) dispersion to generate thin films (by spin-coating) and bulk materials (from the melt), respectively, in which the inorganic nanoparticles remain highly disperse.

Hybrid nanoparticles by step-growth Sonogashira coupling in disperse systems.

Organic/inorganic hybrid nanoparticles were prepared by a Sonogashira miniemulsion polymerization of dibromo aryl and diethynyl aryl monomers and modified titanium dioxide and cadmium selenide nanocrystals, respectively. The poly(arylene ethynylene) microstructure and polymerization rates, as reflected by monomer reactivity, decisively impact whether inorganic guest particles can be trapped to afford a uniform distribution within a newly formed polymer particle or phase separate. This issue was found to be more critical for the TiO2 rods studied here. To this end, the compatibility of the organic and inorganic portions could be improved substantially by the incorporation of functional groups that bind the inorganic surface to the polymer via an appropriate termonomer. This concept, in combination with rapid particle formation via a postpolymerization dispersion of a premade poly(arylene ethynylene)/TiO2 composite as an alternative technique, yielded composite particles with a high loading of the inorganic nanoparticles.

Sample preparation methods for femtosecond electron diffraction experiments.

Exploring the dynamics of Charge density wave system 1T-TaS2 via femtosecond electron diffraction demonstrated the power of this technique for studying ultrafast structural phenomena in strongly correlated electron materials [1]. The results revealed first direct information on the order parameter dynamics of Charge Density Waves as well as on their photo-induced phase transition. A prerequisite to perform such experiments on modern quantum materials is the availability of laterally large (~100 µm) and sufficiently thin (<100 nm) single crystalline samples. Different approaches to reach these specifications have been tried out and their effect on sample integrity has been investigated. Finally, using an ultra-microtome, we were able to prepare 30 nm free standing single crystalline films of 1T-TaS2 with lateral dimensions of 200 µm × 200 µm. We have characterized these films with different techniques for their stoichiometric and crystalline integrity, ensuring no measurable alternation of sample properties. The application of this sample thinning technique is expected to find its use in further structural dynamics studies, as well as in optical time-resolved studies where homogeneous excitation profile and/or data in transmission geometry may be required.

Precise Microstructure Self-Stabilized Polymer Nanocrystals.

Nanoparticles with a defined shape and surface chemistry result from an encoding of crystal size directly in the polymer microstructure. This is brought about by carboxy groups spaced precisely on every 21st or 45th carbon atom of linear polyethylene chains synthesized by acyclic diene metathesis polymerization (ADMET) of precisely branched, long-chain α,ω-dienes. These hydrophilic functional groups form a layer on the nanocrystal surface, which interacts with the aqueous dispersing medium and, thus, self-stabilizes the nanocrystals. The nanocrystal thickness is directly predeterminded by the length of the long-chain methylene spacer between the functional groups.

Anisotropic nanoparticles of precise microstructure polyolefins.

Nanoparticles of precisely branched polyethylenes possess a distinct oblate shape resulting from a crystalline lamella in the particle as revealed by SAXS and TEM, and display controllable and well-behaved thermal behaviour.

Snapshots of cooperative atomic motions in the optical suppression of charge density waves.

Macroscopic quantum phenomena such as high-temperature superconductivity, colossal magnetoresistance, ferrimagnetism and ferromagnetism arise from a delicate balance of different interactions among electrons, phonons and spins on the nanoscale. The study of the interplay among these various degrees of freedom in strongly coupled electron-lattice systems is thus crucial to their understanding and for optimizing their properties. Charge-density-wave (CDW) materials, with their inherent modulation of the electron density and associated periodic lattice distortion, represent ideal model systems for the study of such highly cooperative phenomena. With femtosecond time-resolved techniques, it is possible to observe these interactions directly by abruptly perturbing the electronic distribution while keeping track of energy relaxation pathways and coupling strengths among the different subsystems. Numerous time-resolved experiments have been performed on CDWs, probing the dynamics of the electronic subsystem. However, the dynamics of the periodic lattice distortion have been only indirectly inferred. Here we provide direct atomic-level information on the structural dynamics by using femtosecond electron diffraction to study the quasi two-dimensional CDW system 1T-TaS(2). Effectively, we have directly observed the atomic motions that result from the optically induced change in the electronic spatial distribution. The periodic lattice distortion, which has an amplitude of ∼0.1 Å, is suppressed by about 20% on a timescale (∼250 femtoseconds) comparable to half the period of the corresponding collective mode. These highly cooperative, electronically driven atomic motions are accompanied by a rapid electron-phonon energy transfer (∼350 femtoseconds) and are followed by fast recovery of the CDW (∼4 picoseconds). The degree of cooperativity in the observed structural dynamics is remarkable and illustrates the importance of obtaining atomic-level perspectives of the processes directing the physics of strongly correlated systems.

Crystallization as a means for the switching of nanoscale containers.

Melting and crystallization are reported as a means for reversible switching of nanoscale containers. Aqueous dispersions of 10 nm particles of polyethylene with variable branching and crystallinity were prepared by catalytic polymerization with water-soluble Ni(II) complexes. Fluorescence studies of lipophilic probe molecules show that in the low-crystallinity particles they experience a more apolar environment. In crystalline particles, the amorphous portions which can accommodate guest molecules are at the periphery of the particle, such that the probe experiences the water-particle interface to some extent. The polarity experienced by the probe molecules can be switched reversibly by melting and crystallization of the individual dispersed particles. The temperature at which this occurs can be adjusted via the microstructure, that is, degree of branching, of the polymer.

Pressure jump relaxation setup with IR detection and millisecond time resolution.

An instrument is described that allows the use of Fourier transform infrared (FTIR) spectroscopy as a detection system for kinetic processes after a pressure jump of up to 100 bars. The pressure is generated using a high performance liquid chromatography (HPLC) pump and water as a pressure transducing medium. A flexible membrane separates the liquid sample in the IR cell from the pressure transducing medium. Two electromagnetic switching valves in the setup enable pressure jumps with a decay time of 4 ms. The FTIR spectrometer is configured to measure time resolved spectra in the millisecond time regime using the rapid scan mode. All components are computer controlled. For a demonstration of the capability of the method first results on the kinetics of a phase transition between two lamellar phases of an aqueous phospholipid dispersion are presented. This combination of FTIR spectroscopy with the pressure jump relaxation technique can also be used for other systems which display cooperative transitions with concomitant volume changes.