Antoni Sánchez-Ferrer

Liquid‐Crystalline Elastomer Microvalve for Microfluidics

Dr. A. Sanchez-Ferrer Food & Soft Materials Science Group Institute of Food, Nutrition & Health ETH Zurich, Schmelzbergstrasse 9, 8092 Zurich, Switzerland E-mail: antoni.sanchez@agrl.ethz.ch Dr. A. Sanchez-Ferrer , Prof. H. Finkelmann Albert Ludwigs University Institute for Macromolecular Chemistry Stefan-Meier-Str. 31, 79104 Freiburg, Germany Fischl , Dr. . T Dr. M. Stubenrauch , Dr. A. Albrecht , Prof. H. Wurmus , Prof. M. Hoffmann Ilmenau University of Technology Faculty of Mechanical Engineering Department of Micromechanical Systems Max-Planck-Ring 14, 98693 Ilmenau, Germany

Opto-mechanical effect in photoactive nematic side-chain liquid-crystalline elastomers.

The mechanical behaviour of monodomain nematic side-chain liquid-crystalline elastomers containing azoderivatives as pendant groups or crosslinkers has been studied under UV irradiation and in the darkness at different temperatures. From the evaluation of the opto-mechanical experiments, the mechanical efficiency, kinetic rates, activation energies and the isomerization mechanism of the azocompounds in the liquid-crystalline matrix could be determined, as well as the effect of the chemical constitution of the azobenzene derivatives and their role in the elastomeric network.

Hierarchically Structured Microfibers of “Single Stack” Perylene Bisimide and Quaterthiophene Nanowires

Organic nanowires and microfibers are excellent model systems for charge transport in organic semiconductors under nanoscopic confinement and may be relevant for future nanoelectronic devices. For this purpose, however, the preparation of well-ordered organic nanowires with uniform lateral dimensions remains a challenge to achieve. Here, we used the self-assembly of oligopeptide-substituted perylene bisimides and quaterthiophenes to obtain well-ordered nanofibrils. The individual nanofibrils were investigated by spectroscopic and imaging methods, and the preparation of hierarchically structured microfibers of aligned nanofibrils allowed for a comprehensive structural characterization on all length scales with molecular level precision. Thus, we showed that the molecular chirality resulted in supramolecular helicity, which supposedly serves to suppress lateral aggregation. We also proved that, as a result, the individual nanofibrils comprised a single stack of the π-conjugated molecules at their core. Moreover, the conformational flexibility between the hydrogen-bonded oligopeptides and the π-π stacked chromophores gave rise to synergistically enhanced strong π-π interactions and hydrogen-bonding. The result is a remarkably tight π-π stacking inside the nanofibrils, irrespective of the electronic nature of the employed chromophores, which may render them suitable nanowire models to investigate one-dimensional charge transport along defined π-π stacks of p-type or n-type semiconductors.

Liquid‐Crystalline Elastomer‐Nanoparticle Hybrids with Reversible Switch of Magnetic Memory

A stimuli-responsive material is synthesized that combines the actuation potential of liquid-crystalline elastomers with the anisotropic magnetic properties of ellipsoidal iron oxide nanoparticles. The resulting nanocomposite exhibits unique shape-memory features with magnetic information, which can be reversibly stored and erased via parameters typical of soft materials, such as high deformations, low stresses, and liquid-crystalline smectic-isotropic transition temperatures.

Polydomain–Monodomain Orientational Process in Smectic‐C Main‐Chain Liquid‐Crystalline Elastomers

The polydomain-monodomain (PM) transformation takes place when a polydomain of a smectic-C main-chain liquid-crystalline elastomer (SmC MCLCE) is uniaxially stretched. We present results based on a combination of mechanical and X-ray experiments which show how the domains initially rearrange to finally form a perfect conical layer distribution (monodomain) when the sample is fully stretched. The rearrangement and orientational process of the domains is quantified and compared to the parallel and perpendicular uniaxial stress-strain deformations of a monodomain sample. The stress-strain behaviour of the polydomain lays between the uniaxial deformations, parallel and perpendicular to the director, of the monodomain sample.

Resolving Self-Assembly of Bile Acids at the Molecular Length Scale

The self-assembly behavior of the naturally occurring steroidal bile compounds cholic, deoxycholic, ursodeoxycholic, and lithocholic acid was studied by combining atomic force microscopy (AFM), polarized optical microscopy (POM), Fourier-transform infrared spectroscopy (FTIR), absorption spectroscopy (UV-vis), circular dichroism (CD), and wide-angle X-ray scattering (WAXS). Molecular solutions of these mono-, di-, and trihydroxyl substituted bile acids spontaneously evolved into supramolecular aggregates upon the incremental addition of H(2)O as a poor solvent. Highly crystalline nanostructured multilayered assemblies were formed, which revealed a very rich polymorphism of micro- and macro-structures depending on the chemical structure of the bile acid and the properties of the cosolvent (EtOH or DMSO) used. In particular, AFM allowed resolving the crystalline structure to an unprecedented level. It was thus possible to establish that bile acids associate into H-bonded chiral dimer building blocks, which organize in 2D layers of nanostructured lamellar surface topologies with unique facial amphiphilicity. The detailed understanding of the hierarchical organization in bile acid assemblies may contribute to develop strategies to design bioinspired materials with tailor-made nanostructured surface topologies.

Inorganic–organic elastomer nanocomposites from integrated ellipsoidal silica-coated hematite nanoparticles as crosslinking agents

We report on the synthesis of nanocomposites with integrated ellipsoidal silica-coated hematite (SCH) spindle type nanoparticles which can act as crosslinking agents within an elastomeric matrix. Influence of the surface chemistry of the hematite, leading either to dispersed particles or crosslinked particles to the elastomer matrix, was studied via swelling, scattering and microscopy experiments. It appeared that without surface modification the SCH particles aggregate and act as defects whereas the surface modified SCH particles increase the crosslinking density and thus reduce the swelling properties of the nanocomposite in good solvent conditions. For the first time, inorganic SCH particles can be easily dispersed into a polymer network avoiding aggregation and enhancing the properties of the resulting inorganic-organic elastomer nanocomposite (IOEN).

Thermal and Mechanical Properties of New Main-Chain Liquid-Crystalline Elastomers

New Main-Chain Liquid-Crystalline Elastomers (MCLCEs) were synthesised based on reacting vinyloxy-terminated mesogens under hydrosilylation conditions with a flexible crosslinker. These main-chain systems showed smectic and nematic mesophases and their anisotropic properties were mechanically and thermally analysed as function of the crosslinking density. Due to the suitable chemistry used in this work low crosslinking densities have been achieved (2.5 mol-%) with low soluble content (5%). For the first time, the degree of crosslinking could be adjusted and nematic or smectic MCLCEs with tuneable thermal and mechanical properties were obtained.

Liquid-crystalline elastomer micropillar array for haptic actuation

A new liquid-crystalline elastomer-based micropillar array with pushing properties is obtained by the two-step crosslinking process, where the micropillars are oriented by uniaxial compression before the final curing. This orientation process allows the formation of a two-dimensional prolate polydomain conformation of the polymer backbone and the mesogens, and opens huge opportunities for the use of liquid-crystalline elastomers in microsystems and haptic applications.

Core-shell nanoparticle monolayers at planar liquid- liquid interfaces: effects of polymer architecture on the interface microstructure†

Self-assembly of core–shell nanoparticles (NPs) at liquid–liquid interfaces is rapidly emerging as a strategy for the production of novel nano-materials bearing vast potential for applications, including membrane fabrication, drug delivery and emulsion stabilization. The development of such nanoparticle-based materials is facilitated by structural characterization techniques that are able to monitor in situ the self-assembly process during its evolution. Here, we present an in situ high-energy X-ray reflectivity study of the evolution of the vertical position (contact angle) and inter-particle spacing of core–shell iron oxide–poly(ethylene glycol) (PEG) nanoparticles adsorbing at flat, horizontal buried water–n-decane interfaces. The results are compared with time-resolved interfacial tension data acquired with the conventional pendant drop method. We investigate in particular the effect of varying polymer molecular weights (2–5 kDa) and architectures (linear vs. dendritic) on the self-assembly process and the final structure of the interfacially adsorbed NP monolayers. Linear PEG particles adsorb more rapidly than dendritic PEG ones and reach full interface coverage and stable NP monolayer structure, while dendritic PEG particles undergo a slower adsorption process, which is not completed within the experimental time window of ∼6 hours. All NPs are highly hydrophilic with effective contact angles that depend weakly on PEG molecular weight and architecture. Conversely, the in-plane NP separation depends strongly on PEG molecular weight. The measured inter-particle separation at full interface coverage yields low iron oxide core content, indicating a strong deformation and flattening of the linear PEG shell at the interface. This finding is supported by modeling and has direct implications for materials fabrication, e.g. for the realization of core–shell NP membranes by in situ cross-linking of the polymer shells.