Persistence of strong electron coupling to a narrow boson spectrum in overdoped Bi2Sr2CaCu2O(8+delta) tunneling data

A d-wave, Eliashberg analysis of break-junction and STM tunneling spectra on Bi2Sr2CaCu2O(8+delta) (Bi2212) reveals that the spectral dip feature is directly linked to strong electronic coupling to a narrow boson spectrum, evidenced by a large peak in alpha2F(omega). The tunneling dip feature remains robust in the overdoped regime of Bi2212 with bulk T(c) values of 56 K-62 K. This is contrary to recent optical conductivity measurements of the self-energy that suggest the narrow boson spectrum disappears in overdoped Bi2212 and therefore cannot be essential for the pairing mechanism. The discrepancy is resolved by considering the way each technique probes the electron self-energy, in particular, the unique sensitivity of tunneling to the off-diagonal or pairing part of the self-energy.     

Viscosity of two-dimensional suspensions

Over a range of conditions, lipid and surfactant monolayers exhibit coexistence of discrete solid domains in a continuous liquid. The surface shear viscosity, mu(s), of such monolayers collapses onto a single curve: mu(s)/mu(so) = [1-(A/A(c))](-1), in which mu(so) is the viscosity of the liquid phase, A is the area fraction of the solid phase measured by fluorescence microscopy, and A(c) is a critical solid phase fraction. This scaling relationship is directly analogous to that of three-dimensional dispersion of spheres in a solvent with long-range repulsive interactions, with area fraction replacing volume fraction.     

Modifying calf lung surfactant by hexadecanol

Monolayer properties such as phase behavior, collapse pressure, and surface viscosity are determined by monolayer composition. Learning how to control these properties through simple additives is important to understanding lung surfactant monolayers and to designing optimal replacement surfactants for treatment of disease. The properties of Infasurf, a replacement lung surfactant derived from calf lung lavage organic extract, can be modified in a controlled fashion by adding hexadecanol (HD). Grazing incidence X-ray diffraction shows that the HD preferentially interacts with dipalmitoylphosphatidylcholine (DPPC), the main phospholipid component of Infasurf, in the same way as in binary mixtures of DPPC and HD. HD intercalates between the DPPC chains, which leads to a tighter packing of the two-dimensional lattice and greater stability of the solid phase. This molecular reorganization triggers changes at the macroscopic scale, leading to a greatly increased solid-phase fraction at a given surface pressure and order of magnitude increases in the surface shear viscosity. However, the collapse pressure decreases, and, hence, the minimum surface tension of the film increases.     

Surface ordering of a perfluorinated, self-assembled, dendrimer on a water subphase

We have investigated the surface ordering of a synthetic, asymmetric, fan-shaped dendrimer containing a carboxyl core and perfluorinated tails which was obtained by the esterification of the intermediary. X-ray diffraction patterns and transmission electron microscopy (TEM) images show the molecules self-assemble into a hexagonal, cylindrical mesophase. Surface pressure-area isotherms and Brewster angle microscopy measurements show the molecule forms a stable monolayer at the air-water interface with a single phase transition. As a condensed monolayer, the perfluorinated tails are well-packed with hexagonal symmetry with (10) spacing of approximately 0.5 nm from molecular-scale atomic force microscopy (AFM) images. Such dense molecular-scale packing has not been observed in other dendritic molecules thus far. Compared to the case of conventional dendritic molecules with alkyl tails, these molecules occupy a much smaller molecular area due to the strong microphase separation between the carboxylic core and perfluorinated tails at the air-water interface. After monolayer collapse, the irregular islands with terrace morphology are observed in contrast with conventional alkyl-terminated self-assembled dendritic molecules where irregular islands do not appear. The interfacial and internal structure of every terrace shows planar columnar morphology from AFM and TEM imaging. From these results, we discuss the stability of perfluorinated, self-assembled dendrimers on water, as well as how to generate planar morphology on a hydrophilic surface.     

A brief review of the relationships between monolayer viscosity, phase behavior, surface pressure, and temperature using a simple monolayer viscometer

The two-dimensional surface shear viscosity, eta, of fatty acid monolayers of different chain lengths, measured using a simple magnetic needle viscometer, strongly correlates with the molecular organization in condensed phases and the absolute temperature. eta can increase by orders of magnitude at phase boundaries associated with tilted to untilted molecular order, providing the underlying order is semicrystalline. Hence, untilted, long-range ordered CS phases are the most viscous films. However, despite being untilted, the LS rotator phase is less viscous than certain laterally ordered tilted phases, suggesting a decrease of the van der Waals interactions due to molecular rotation. In certain regions of the L2 phase, eta reaches a maximum before the L2-LS transition, an anomalous behavior correlated with the change in the lattice symmetry of the headgroup. Surface shear viscosity, even when measured with a macroscopic probe, is particularly sensitive to the microscopic organization of monolayers.     

Lamellar gels and spontaneous vesicles in catanionic surfactant mixtures

Caillé analysis of the small-angle X-ray line shape of the lamellar phase of 7:3 wt/wt cetyltrimethylammonium tosylate (CTAT)/sodium dodecylbenzene sulfonate (SDBS) bilayers shows that the bending elastic constant is kappa = (0.62 +/- 0.09)k(B)T. From this and previous results, the Gaussian curvature constant is kappa = (-0.9 +/- 0.2)k(B)T. For 13:7 wt/wt CTAT/SDBS bilayers, the measured bending elasticity decreases with increasing water dilution, in good agreement with predictions based on renormalization theory, giving kappa(o) = 0.28k(B)T. These results show that surfactant mixing is sufficient to make kappa approximately k(B)T, which promotes strong, Helfrich-type repulsion between bilayers that can dominate the van der Waals attraction. These are necessary conditions for spontaneous vesicles to be equilibrium structures. The measurements of the bending elasticity are confirmed by the transition of the lamellar phase of CTAT/SDBS from a turbid, viscoelastic gel to a translucent fluid as the water fraction is decreased below 40 wt %. Freeze-fracture electron microscopy shows that the gel is characterized by spherulite defects made possible by spontaneous bilayer curvature and low bending elasticity. This lamellar gel phase is common to a number of catanionic surfactant mixtures, suggesting that low bending elasticity and spontaneous curvature are typical of these mixtures that form spontaneous vesicles.     

Near-Infrared Light Triggered-Release in Deep Brain Regions Using Ultra-photosensitive Nanovesicles

Remote and minimally-invasive modulation of biological systems with light has transformed modern biology and neuroscience. However, light absorption and scattering significantly prevents penetration to deep brain regions. Herein, we describe the use of gold-coated mechanoresponsive nanovesicles, which consist of liposomes made from the artificial phospholipid Rad-PC-Rad as a tool for the delivery of bioactive molecules into brain tissue. Near-infrared picosecond laser pulses activated the gold-coating on the surface of nanovesicles, creating nanomechanical stress and leading to near-complete vesicle cargo release in sub-seconds. Compared to natural phospholipid liposomes, the photo-release was possible at 40 times lower laser energy. This high photosensitivity enables photorelease of molecules down to a depth of 4 mm in mouse brain. This promising tool provides a versatile platform to optically release functional molecules to modulate brain circuits.