Concentration effects on the dynamics of liquid crystalline self-assembly: time-resolved X-ray scattering studies

A manifold of ordering transitions relevant to chemical and biological systems occur at interfaces from liquids to self-assembled soft solids like membranes or liquid crystals. In the present case, we were interested in understanding the phase transition from the microemulsion phase to the liquid crystal phase in terms of their driving forces, i.e., activation energy and entropy. The purpose of this work was to clarify the influence of concentration effects of the amphiphilic molecules on the nature of these self-assembly processes. By photosensitization of the model system (polyalkylglycolether (C(10)E(4)), water, decane, and cyclohexane) with laser dyes, we could effectively induce and control the phase transition through the absorption of optical photons. The photo transformation conditions were chosen in such a way that the system was in thermal equilibrium. By application of time-resolved photo small-angle X-ray scattering we could monitor the conversion process and demonstrate that the surfactant concentration has a direct impact on the activation energy, which is observable through the length of the induction time.     

Mean field calculations and defect gases in lattice gauge theory

We investigate the relationship between local defects and the mean field method in lattice gauge theory. In particular we clarify the role of defects in establishing the equivalence between mean field calculations with and without gauge fixing. In two dimensions we derive the area law for the Wilson loop by a mean field calculation incorporating defects. We also establish a general rule about mean field variables which are appropriate to handle defects induced by an action that almost possesses a local symmetry group, and we apply it to theZ(2) Higgs model and to the mixedSU(2)-SO(3) model.     

Neutron decoherence imaging for visualizing bulk magnetic domain structures

Here we introduce a novel neutron imaging method, which is based on the effect that the spatial coherence of the neutron wave front can be changed through small-angle scattering of neutrons at magnetic domain walls in the specimen. We show that the technique can be used to visualize internal bulk magnetic domain structures that are difficult to access by other techniques. The method is transferable to a wide variety of specimens, extendable to three dimensions, and well suited for investigating materials under the influence of external parameters, as, e.g., external magnetic field, temperature, or pressure.     

Coherent diffractive imaging using phase front modifications

We introduce a coherent diffractive imaging technique that utilizes multiple exposures with modifications to the phase profile of the transmitted wave front to compensate for the missing phase information. This is a single spot technique sensitive to both the transmission and phase shift through the sample. Along with the details of the method, we present results from the first proof of principle experiment. The experiment was performed with 6.0 keV x rays, in which an estimated spatial resolution of 200 nm was achieved.     

Electrospray ionization mass spectrometry for the quantitation of albumin in human serum

Capillary reversed-phase liquid chromatography was coupled to electrospray ionization mass spectrometry for determining the concentration of human serum albumin (HSA) in a fresh frozen serum reference material. A biotinylated HSA (bHSA) was prepared and used as an internal standard for the serum albumin determination. The average HSA concentration of the serum sample was determined by mass spectrometry to be 41.5 ± 2.8 g/L at the 95% confidence limit for the measured value. The HSA concentration of the fresh frozen serum was also assayed using the bromocresol green dye-binding method, producing a value of 42.3 ± 1.5 g/L. Calibration curves generated from HSA standards spiked with bHSA showed excellent linearity and the relative standard deviation for replicate analysis of a bHSA spiked serum sample was less than 3%.     

Selective spatial localization of actomyosin motor function by chemical surface patterning

We have previously described the efficient guidance and unidirectional sliding of actin filaments along nanosized tracks with adsorbed heavy meromyosin (HMM; myosin II motor fragment). In those experiments, the tracks were functionalized with trimethylchlorosilane (TMCS) by chemical vapor deposition (CVD) and surrounded by hydrophilic areas. Here we first show, using in vitro motility assays on nonpatterned and micropatterned surfaces, that the quality of HMM function on CVD-TMCS is equivalent to that on standard nitrocellulose substrates. We further examine the influences of physical properties of different surfaces (glass, SiO(2), and TMCS) and chemical properties of the buffer solution on motility. With the presence of methylcellulose in the assay solution, there was HMM-induced actin filament sliding on both glass/SiO(2) and on TMCS, but the velocity was higher on TMCS. This difference in velocity increased with decreasing contact angles of the glass and SiO(2) surfaces in the range of 20-67 degrees (advancing contact angles for water droplets). The corresponding contact angle of CVD-TMCS was 81 degrees. In the absence of methylcellulose, there was high-quality motility on TMCS but no motility on glass/SiO(2). This observation was independent of the contact angle of the glass/SiO(2) surfaces and of HMM incubation concentrations (30-150 microg mL(-)(1)) and ionic strengths of the assay solution (20-50 mM). Complete motility selectivity between TMCS and SiO(2) was observed for both nonpatterned and for micro- and nanopatterned surfaces. Spectrophotometric analysis of HMM depletion during incubation, K/EDTA ATPase measurements, and total internal reflection fluorescence spectroscopy of HMM binding showed only minor differences in HMM surface densities between TMCS and SiO(2)/glass. Thus, the motility contrast between the two surface chemistries seems to be attributable to different modes of HMM binding with the hindrance of actin binding on SiO(2)/glass.     

A perturbative RS I cosmological phase transition

We identify a class of Randall–Sundrum type models with a successful first order cosmological phase transition during which a 5D dual of approximate conformal symmetry is spontaneously broken. Our focus is on soft-wall models that naturally realize a light radion/dilaton and suppressed dynamical contribution to the cosmological constant. We discuss phenomenology of the phase transition after developing a theoretical and numerical analysis of these models both at zero and finite temperature. We demonstrate a model with a TeV-Planck hierarchy and with a successful cosmological phase transition where the UV value of the curvature corresponds, via AdS/CFT, to an N of 20, where 5D gravity is expected to be firmly in the perturbative regime.     

Structure of zone-cast HBC-C12H25 films

The structure of a thin zone-cast film of the hexa-n-dodecyl-substituted hexa-peri-benzocoronene (HBC) has been investigated using grazing incidence X-ray diffraction. A model with an orthorhombic unit cell containing two molecules accounts well for the observations. The molecules are arranged in a "herringbone" structure resembling the packing observed for unsubstituted HBC. The molecular disk planes are oriented perpendicularly to the substrate, rotated by approximately 39 degrees about the film normal. The relatively long side chains of dodecyl were found to be in an ordered interdigitated state. The aliphatic side chains and the aromatic HBC-cores segregate to form regular vertical domains spanning the film thickness. For in-plane rocking scans a discrete orientation distribution is observed with peaks at regular angle intervals. We interpret this as a grain boundary effect induced by alkyl chain stacking faults.     

One‐dimensional small‐angle X‐ray scattering tomography of dip‐coated polyamide 6 monofilaments

A synchrotron study is presented in which the concept of one‐dimensional tomographic reconstruction of small‐angle X‐ray scattering patterns is applied to investigate polyamide 6 monofilaments, dip‐coated with alumina particles. The filaments are scanned with a focused synchrotron beam and the resulting scattering patterns are recorded with a PILATUS 2M detector. The reconstructed sequence of SAXS images reflects the local nanostructure variation along the filament radius. In particular, the influence of coating process parameters on the polyamide 6 is investigated.