We measured the viscosity of poly(ethylene glycol) (PEG 6000, 12,000, 20,000) in water using capillary electrophoresis and fluorescence correlation spectroscopy with nanoscopic probes of different diameters (from 1.7 to 114 nm). For a probe of diameter smaller than the radius of gyration of PEG (e.g. rhodamine B or lyzozyme) the measured nanoviscosity was orders of magnitude smaller than the macroviscosity. For sizes equal to (or larger than) the polymer radius of gyration, macroscopic value of viscosity was measured. A mathematical relation for macro and nanoviscosity was found as a function of PEG radius of gyration, R(g), correlation length in semi-dilute solution, xi, and probe size, R. For R < R(g), the nanoviscosity (normalized by water viscosity) is given by exp(b(R/xi)a), and for R > R(g), both nano and macroviscosity follow the same curve, exp(b(R/xi)a), where a and b are two constants close to unity. This mathematical relation was shown to equally well describe rhodamine (of size 1.7 nm) in PEG 20,000 and the macroviscosity of PEG 8,000,000, whose radius of gyration exceeds 200 nm. Additionally, for the smallest probes (rhodamine B and lysozyme) we have verified, using capillary electrophoresis and fluorescence correlation spectroscopy, that the Stokes-Einstein (SE) relation holds, providing that we use a size-dependent viscosity in the formula. The SE relation is correct even in PEG solutions of very high viscosity (three orders of magnitude larger than that of water).

We investigate possible usage of single-walled carbon nanotubes (SWNTs) as an efficient storage and separation device of hydrogen−methane mixtures at room temperature. The study has been done using Grand Canonical Monte Carlo simulations for modeling storage and separation of hydrogen−methane mixtures in idealized SWNTs bundles. These mixtures have been studied at several pressures, up to 12 MPa. We have found that the values of the stored volumetric energy and equilibrium selectivity greatly depend on the chiral vector (i.e., pore diameter) of the nanotubes. The bundle formed by [5,4] SWNTs (nanotube diameter of 6.2 Å) can be regarded as a threshold value. Below that value the densification of hydrogen or methane is negligible. Bundles with wider nanotube diameter (i.e., 12.2, 13.6, 24.4 Å) seem to be promising nanomaterials for hydrogen−methane storage and separation at 293 K. SWNTs with pore diameters greater than 24.4 Å (i.e., [18,18]) are less efficient for both on-board vehicle energy storage and separation of hydrogen−methane mixture at 293 K with pressures up to 12 MPa. SWNTs comprised of cylindrical pores of 8.2 and 6.8 Å in diameter (equivalent chiral vector [6,6] and [5,5], respectively) are the most promising for separation of the hydrogen−methane mixture at room temperature, with the former selectively adsorbing methane and the latter selectively adsorbing hydrogen. We observed that inside the pores of [6,6] nanotubes absorbed methane forms a quasi-one-dimensional crystal when the system has thermalized. The average intermolecular distance of such a crystal is smaller than the one of liquid methane in bulk at 111.5 K, therefore exhibiting the quasi-one-dimensional system clear compression characteristics. On the other hand, for a smaller nanotube diameter of 6.8 Å the hydrogen can enter into the tubes and methane remaining in bulk. We found that in the interior of [5,5] nanotubes adsorbed/compressed hydrogen forms a quasi-one-dimensional crystal.

of the original manuscript:Ungar, G.; Tschierske, C.; Abetz, V.; Holyst, R.; Bates, M.A.; Lui, F.; Prehm, M.; Kieffer, R.; Zeng, X.; Walker, M.; Glettner, B.; Zywocinski, A.: Keywords: columnar liquid crystals, polygonal honeycombs, polyphiles, miktoarm star terpolymers, simulation, Langmuir films, rod-coil molecules, surface alignment Abstract: This article reviews the diversity of phase morphologies observed recently in starbranched liquid crystalline and polymeric compounds containing at least three immiscible segments. Bolaamphiphiles and facial amphiphiles with a rod-like aromatic core, two endgroups and one (T-shape) or two chains (X-shape) attached laterally to the core form numerous honeycomb-like liquid crystal phases, as well as a variety of novel lamellar and 3D-ordered mesophases. Molecular self-organization is described in bulk phases and in thin films on solid and liquid surfaces, as well as in Langmuir-Blodgett films. The remarkably reversible formation of mono-and tri-layer films is highlighted. In the bulk, T-shaped "rod-coil" molecules without the appended end-groups form predominantly lamellar phases if the core is a straight rod, but the bent-core variety forms hexagonal honeycombs. Furthermore, selfassembly of "Janus"-type molecules, such as those with Y-shaped star mesogens bearing different mutually incompatible side-groups, is discussed. Also covered is the diversity of morphologies observed in miktoarm star terpolymers i.e. polymers with three different and 3 incompatible arms of well-defined lengths. A range of bulk phases with 3D or 2D order are observed, combining layers, cylinders and cocontinuous networks. Similarities and differences are highlighted between the liquid crystal morphologies on the 3-15 nm scale and the polymer morphologies on the scale 10-100 nm. A separate section is dedicated to computer simulations of such systems, particularly those using dissipative particle and molecular dynamics. Of special interest are the recently synthesised X-shaped tetraphilic molecules, where two different and incompatible side-chains are attached at opposite sides of the rod-like core. The tendency for their phase separation produces LC honeycombs with cells of different compositions that can be represented as paving a plane with different color tiles. Self-Assembly at Different Length Scales: Polyphilic StarBranched Liquid Crystals and Miktoarm Star CopolymersThe independent variation of chain length and "color" creates the potential for developing a considerable range of complex new 2d-and 3d soft nanostructures. Analogous X-shaped rodcoil compounds with unequal side groups are also of considerable interest, forming tubular lyotropic structures capable of confining strings of guest molecules.

Dynamic self-assembly is an emerging scientific concept aimed to construct artificial systems of adaptative behavior. Here, we present a first nanoscopic system that is able to dynamically self-assemble in two dimensions. This system is composed of charged gold nanoparticles, dispersed at the air-water interface, which self-assemble into a dense monolayer of area of several square centimeters in response to surface tension gradient. The surface tension gradient is imposed by localized addition or removal of organic solvent from the interface. After the surface tension is equalized over the whole fluid interface, the nanoparticles return to their initial dispersed state. The arrangement of nanoparticles before and after the self-assembly was characterized using SEM microscopy and SAXS spectroscopy. The constructed self-assembling system offers a "chemical" alternative for the Langmuir-Blodgett technique. Also, it was applied for creating self-erasing nanoparticle patterns on a fluid surface.

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We propose a surface treatment allowing one to obtain a sliding planar anchoring of nematic (or cholesteric) liquid crystals. It consists of depositing a thin layer of the polymercaptan hardener of an epoxy resin on an isotropic substrate (bare or ITO-coated glass plates). Microscopic observations of defect annihilations and capacitance measurements show that the molecules align parallel to the surface and slide viscously on it when they change orientation, which implies a zero (or extremely small) azimuthal anchoring energy. In contrast, the zenithal anchoring energy W theta is found to be larger than 3 x 10(-5)J/m2. We also measured the liquid crystal rotational surface viscosity gammaS by a thermo-optical method using the large temperature variation of the pitch of a compensated cholesteric mixture. We found that the sliding length gammaS/gamma1 (where gamma1 is the bulk rotational viscosity) is very large in comparison with the length of a liquid crystal molecule. This result is explained by a simple model which takes into account the diffusion of the liquid crystal within the polymer layer.

Aggregation in Langmuir films is usually understood as being a disorderly grouping of molecules turning into chaotic three-dimensional aggregates and is considered an unwanted phenomenon causing irreversible changes. In this work we present the studies of 11 compounds from the group of specific surfactants, known as bolaamphiphiles, that exhibit reversible aggregation and, in many cases, transition to well-defined multilayers, which can be considered as a layering transition. These bolaamphiphiles incorporate rigid π-conjugated aromatics as hydrophobic cores, glycerol-based polar groups and hydrophobic lateral chains. Molecules of different shapes (X-, T-, and anchor) were studied and compared. The key property of these compounds is the partial fluorination of the lateral chains linked to the rigid cores of the molecules. The most interesting feature of the compounds is that, depending on their shape and degree of fluorination, they are able to resist aggregation and preserve a monolayer structure up to relatively high surface pressures (T-shaped and some X-shaped molecules), or create well-defined trilayers (X- and anchor-shaped molecules). Experimental studies were performed using Langmuir balance, surface potential and X-ray reflectivity measurements.