Erratum: Self-Diffusion in Amorphous Silicon [Phys. Rev. Lett. 116, 025901 (2016)].

This corrects the article DOI: 10.1103/PhysRevLett.116.025901.

Mechanically Enhanced Liquid Interfaces at Human Body Temperature Using Thermosensitive Methylated Nanocrystalline Cellulose.

The mechanical performance of materials at oil/water interfaces after consumption is a key factor affecting hydrophobic drug release. In this study, we methylated the surface of nanocrystalline cellulose (NCC) by mercerization and dimethyl sulfate exposure to produce thermosensitive biopolymers. These methylated NCC (metNCC) were used to investigate interfacial thermogelation at air/water and medium-chain triglyceride (MCT)/water interfaces at body temperature. In contrast to bulk fluid dynamics, elastic layers were formed at room temperature, and elasticity increased significantly at body temperature, which was measured by interfacial shear and dilatational rheology in situ. This unique phenomenon depends on solvent quality, temperature, and polymer concentration at interfaces. Thus, by adjusting the degree of hydrophobicity of metNCC, the interfacial elasticity and thermogelation of the interfaces could be varied. In general, these new materials (metNCC) formed more brittle interfacial layers compared to commercial methylcellulose (MC A15). Thermogelation of methylcellulose promotes attractive intermolecular forces, which were reflected in a change in self-assembly of metNCC at the interface. As a consequence, layer thickness and density increased as a function of temperature. These effects were measured by atomic force microscopy (AFM) images of the displaced interface and confirmed by neutron reflection. The substantial structural and mechanical change of methylcellulose interfaces at body temperature represents a controllable encapsulation parameter allowing optimization of lipid-based drug formulations.

Tailored interfacial rheology for gastric stable adsorption layers.

Human lipid digestion begins at the interface of oil and water by interfacial adsorption of lipases. Tailoring the available surface area for lipase activity can lead to specific lipid sensing in the body, thus, tailored satiety hormone release. In this study we present biopolymer layers at the MCT-oil/water interface with different stabilities under human gastric environment (37 °C, pH 2, pepsin). Physicochemical changes and enzymatic degradation of interfacial layers were monitored online by interfacial shear rheology. We show the weakening of ß-lactoglobulin (ß-lg) layers at body temperature and acidification and their hydrolysis by pepsin. If sufficient concentrations of nanocrystalline cellulose (NCC) are given to an existing ß-lg layer, this weakening is buffered and the proteolysis delayed. A synergistic, composite layer is formed by adding methylated NCC to the ß-lg layer. This layer thermogels at body temperature and resists hydrolysis by pepsin. Coexistence of these two emulsifiers at the air/water interface is evidenced by neutron reflectometry measurements, where morphological information are extracted. The utilized layers and their analysis provide knowledge of physicochemical changes during in vitro digestion of interfaces, which promote functional food formulations.

Lithium diffusion in congruent LiNbO3 single crystals at low temperatures probed by neutron reflectometry.

The self-diffusion of lithium in congruent LiNbO3 single crystals was investigated at low temperatures between 379 and 523 K by neutron reflectometry. From measurements on (6)LiNbO3 (amorphous film)/(nat)LiNbO3 (single crystal) samples, Li self-diffusivities were determined in single crystals down to extremely low values of 1 × 10(-25) m(2) s(-1) on small length scales of 1-10 nm. The measured diffusivities are in excellent agreement with (extrapolated) literature data obtained by experiments based on Secondary Ion Mass Spectrometry and Impedance Spectroscopy. The tracer diffusivities can be described by a single Arrhenius line over ten orders of magnitude with an activation enthalpy of 1.33 eV, which corresponds to the migration energy of a single Li vacancy. A deviation from the Arrhenius behaviour at low temperatures, e.g., due to defect cluster formation is not observed.

New sources and instrumentation for neutrons in biology.

Neutron radiation offers significant advantages for the study of biological molecular structure and dynamics. A broad and significant effort towards instrumental and methodological development to facilitate biology experiments at neutron sources worldwide is reviewed.

Conformation of poly(L-lysine)-graft-poly(ethylene glycol) molecular brushes in aqueous solution studied by small-angle neutron scattering.

Small-angle neutron scattering (SANS) has been employed for the analysis of conformations of poly(L-lysine)-graft-poly(ethylene glycol) (PLL-g-PEG) molecular bottle brushes in aqueous solutions. The degree of polymerisation of the PEG chains was systematically varied in order to unravel dependence of the conformational properties of the bottle brushes on the molecular weight of the grafted chains. The grafting density was kept constant and high enough to ensure strong overlap of the PEG chains. The scattering spectra were fitted on the basis of the model of an effective worm-like chain with the account of average radial distribution and local fluctuations of the PEG density in the bottle brush. The results of the fits indicate that molecular brushes retain weakly bent configuration on the length scale of the order of (or larger than) the brush thickness. This finding is in agreement with earlier simulation and recent theoretical results.

Optical patterning in azobenzene polymer films.

Thin azobenzene polymer films show a very unusual property, namely optically induced material transport. The underlying physics for this phenomenon has not yet been thoroughly explained. Nevertheless, this effect enables one to inscribe different patterns onto film surfaces, including one- and two-dimensional periodic structures. Typical sizes of such structures are of the order of micrometers, i.e. related to the interference pattern made by the laser used for optical excitation. In this study we have measured the mechanical properties of one- and two-dimensional gratings, with a high lateral resolution, using force-distance curves and pulse force mode of the atomic force microscope. We also report on the generation of considerably finer structures, with a typical size of 100 nm, which were inscribed onto the polymer surface by the tip of a scanning near-field optical microscope used as an optical pen. Such inscription not only opens new application possibilities but also gives deeper insight into the fundamentals physics underlying optically induced material transport.

Formation mechanism and dynamics in polymer surface gratings.

We present the results of time-dependent x-ray and visible light (VIS) scattering measurements during formation of surface relief grating (SRG). These gratings are formed on polymer films containing azobenzene side groups during pulselike exposure with a holographic pattern of circularly polarized light at 488 nm. The SRG formation is accompanied by a density grating just below the film surface. Assuming viscoelastic flow, a change in polymer's elastic properties upon light exposure can explain the massive material transport. Finite element calculations reveal a dynamic model of grating formation characterized by different relaxation times. The simultaneous formation of a surface relief grating and of a density grating explains quantitatively the findings of the VIS experiment, but only qualitatively the findings of the x-ray measurements.

Self-Ordering within Thin Films of Poly(olefin sulfone)s.

A study has been performed of the manner in which two structural features of poly(olefin sulfone)s, helical backbones and calamitic side chains, create order in films. For this purpose copolymers were prepared with one (polymer I) or two (polymer III) cyanobiphenyls per residue, and terpolymers were prepared with both such residues diluted to below the 5% level within an otherwise poly(eicosene sulfone) chain (respectively, polymers II and IV). The polymers all have ordered phases according to X-ray powder diffraction studies on samples cooled from the melt, a layer spacing of about 45 Å being detected in the films as in the bulk. Those polymers with mainly eicosene sulfone residues had crystalline phases with large domains, the layers deriving from the helical backbones alone, the smectic A phases of the parent poly(eicosene sulfone) being either suppressed or reduced in extent by the presence of the aromatic moieties, which were almost randomly orientated. Those with one or two cyanobiphenyls per residue were liquid crystalline. In the latter the layer spacing derives from both backbone and side chains and is reduced when the residues bear a second mesogen as a consequence of a constraining effect from the stiff backbone, as a novel model predicts. The spacers give rise to a glass transition and segregate the planes in which the stiff backbones are assembled from the regions in which the aromatic groups aggregate on account of the strong pi-pi interactions. Amorphous and optically isotropic spun cast films of these polymers became ordered on cooling from the melt or just on annealing, with the order, as determined by studies on the optical properties, being homeotropic for the aromatics and being planar for the backbones in a monodomain. For this arrangement we introduce the term homeo-planar smectic. Order parameters as high as 0.63 were measured for polymer I, from a clear film. The cyanobiphenyl chromophores formed H aggregates, with blue shifts in absorption and red shifts in fluoresence, and a little surprisingly these resulted in a circular dichroism, detectable when the films were inspected at an angle of 45 degrees to the normal.