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Binary mixtures of two phosphatidylcholines of different chain lengths are simulated in the bilayer state. We find a phase transition between a liquid state and a gel state at all concentrations. This phase transition is characterized by the area per lipid headgroup, the order parameter, and a change in dynamics. At concentrations with a majority of the longer lipid, we find phase separation into a gel and a liquid state in a small temperature window. This leads to a strong dynamic heterogeneity. Experimental phase transition temperatures are reproduced semiquantitatively. We see a clear shift in the phase transition to higher temperatures with increasing concentration of the longer lipid.

Azobenzenes substituted with two urea groups, and especially the 2,2‘-disubstituted azobenzenes, form thermoreversible gels with a wide range of organic solvents at concentrations which are in some cases even as low as 0.2 mM. Most remarkably, the 2,2‘-disubstituted azobenzene gelator can form two different morphs, which is governed by the properties of the solvent and kinetic factors.

Growth front scaling aspects are investigated for poly-( p -phenylene–vinylene)-type oligomer thin films vapor-deposited onto silicon substrates at room temperature. For a film thickness d in the range from 15 to 300 nm, commonly used in optoelectronic devices, measurements of the correlation function by atomic force microscopy yields roughness exponents in the range H =0.45±0.04, and an rms roughness amplitude which evolves with film thickness as a power law σ ∝ d β with β =0.28±0.05. The non-Gaussian height distribution and the measured scaling exponents ( H and β ) suggest a roughening mechanism close to that described by the Kardar–Parisi–Zhang scenario which is characteristic of non-surface diffussive growth processes.

The aggregation behavior of a series of alkyltrimethylammonium 5-ethylsalicylate surfactants (CnTA5ES, n = 12, 14, 16) in aqueous solution has been investigated employing turbidity measurements, fluorescence anisotropy experiments (using 3-hydroxynaphthalene-2-carboxylate, HNC-), and cryo transmission electron microscopy (cryo TEM). Critical aggregation concentrations (cac) were determined by surface tension experiments; they are smaller than those of their salicylate analogues. CnTA5ES surfactants form vesicles immediately above the cac rather than wormlike micelles such as their salicylate counterparts. C12TA5ES was found to form large unilamellar vesicles (LUVs) which transformed into surfactant layers upon increasing surfactant concentration. The transition was characterized by an increase in turbidity. C14TA5ES and C16TA5ES were found to form LUVs and long wormlike vesicles which are assumed to be responsible for the viscoelasticity of the solutions. Upon increase of the surfactant concentration, a t...

The thermotropic and viscoelastic properties and the structure of thermoreversible organogels composed of enantiomerically pure trans-1,2-bis(3-dodecylureido)cyclohexane (1) and primary alcohols, i.e., propanol, butanol, hexanol, and octanol, have been investigated by melting-point measurements, differential scanning calorimetry (DSC), rheology, and electron microscopy. The electron microscopic studies revealed that gelation of these solvents occurred through the formation of an entangled network by 1. In all solvents, the gels behave as viscoelastic solids, with G‘ ≫ G‘ ‘ at frequencies >0.01 Hz (time scales

The domain morphology of a polystyrene/poly(methyl methacrylate)/poly(2-vinylpyridine) (PS/PMMA/PVP) polymer blend was studied after spin-coating a film from a common solvent. The strongly incompatible polymer mixture phase-separates during spin-coating. Atomic force microscopy, combined with selective dissolution of the different polymer phases was used to obtain information on the polymer distribution in the film. By changing the relative composition of the mixture, a great variety of different morphologies was observed. The common feature of all observed morphologies is the compatibilizing function of poly(methyl methacrylate), which intercalates between the more incompatible polystyrene and polyvinylpyridine domains to prevent the formation of high-energy interfaces.

This issue of Advances is devoted to the memory of Hans-Joachim Schulze who, before his untimely death, made substantial contributions in the domains of flotation, wetting and particle interaction, often under adverse working conditions. Many of his publications involve hetero-interaction between different oxides or between solids and air bubbles. In the present paper, the theory for the electric interaction between charged interfaces is reviewed and extended by considering regulation on the Gouy-Stern level, including hetero-interaction. We start from a generalization of the phenomenon of regulation, distinguishing electrostatic, chemical and entropic contributions to the regulation capacity. The analysis is carried out in the mean field approximation for flat double layers. Against this background we review and discuss the existing literature. It is shown that for an appropriate account it is mandatory to include Stern layers, to which not only electrical but also chemical and entropic contributions to the regulation capacity can be attributed. It is demonstrated that interaction at constant diffuse double layer potential or -charge works only at rather large distance of separation. At shorter distance, substantial deviations from this behaviour are found, with a trend that interaction at (about) constant potential is the better obeyed the higher the corresponding regulation capacities are. A lattice model is elaborated to visualize the profiles of the (surface, Stern and diffuse) charges and the corresponding potential changes upon overlap, including the cases where strong induction leads to charge-inversion of the layer with the larger regulation capacity. A number of elaborations is presented, but the potentialities of the model are virtually unlimited.

The appearance of gap states in benzylic amide catenane thin films following potassium intercalation was investigated by electron energy loss spectroscopy and quantum chemical calculations. Both theory and experience find an excitation energy for transitions into these new states of ∼2 eV. The characteristics of these states are discussed.

We investigate roughness effects on electrical conductivity and giant magnetoresistance (GMR) in thin films with self-affine roughness, characterized by the r.m.s. roughness amplitude w , the in-plane correlation length ξ , and the roughness exponent H . It is shown that dynamic roughening (evolution of the roughness parameters) plays an important role in electrical conductivity of growing films, and consequently also in the GMR. In both cases our theoretical predictions are in qualitative agreement with experimental observations.

Interactions between the azobenzene-containing amphiphile methyl octyl orange (MOO) and n-alkyltrimethylammonium bromides (CnTAB, n = 1, 6, 8, 10, 12, 16) in aqueous solution have been studied using UV−vis spectroscopy. Interactions occur at concentrations below the critical micelle concentrations of the individual cationic surfactants (n = 8, 10, 12, 16) as indicated by a ca. 80 nm blue shift of the main absorption band of MOO. In addition, aggregation of MOO with C6TAB, which is a hydrotrope rather than a surfactant, was also observed. The critical aggregation concentration (cac) of MOO determined by surface tension experiments was 0.68 mM. The cac's of aqueous mixtures of CnTAB and MOO (1:1) were considerably lower than those of the individual surfactants. The absorption spectrum of MOO at concentrations above the cac in the 1:1 mixtures was also blue shifted with respect to the absorption spectrum of MOO in aqueous solution. Vesicular aggregates formed in equimolar aqueous mixtures of CnTAB and MOO we...

Fullerene and azafullerene films were studied by electron energy loss spectroscopy in reflection geometry. Compared to C 60 , (C 59 N) 2 multilayers show additional vibrational modes that are characteristic of the dimer structure. The (C 59 N) 2 is semiconductor-like and giant optically allowed excitonic transitions are found in the gap in drastic contrast with C 60 . The azafullerene monolayer on Cu(1 1 1) no longer shows the presence of dimers, indicating monomer adsorption. Similarly to C 60 , azafullerene molecules in contact with the metal substrate receive a transferred charge between two and three electrons. However, the C 59 N appears more covalently bound to Cu because it decomposes when heated above 660 K while C 60 only desorbs.

Magneto-resistance (MR) measurements on epitaxial Fe3O4 films grown on polished MgO have been performed. The measurements presented here are interpreted by a model that describes the MR behaviour as spin-polarised transport across anti-ferromagnetic (AF) interfaces. The Fe3O4 films consist of structural domains, separated by anti-phase boundaries where an AF coupling is present. These AF interfaces enhance the resistance of the films. Upon application of a magnetic field the AF-spins rotate towards each other and the resistance decreases. The AF interfaces are thus behaving as spin-valves. In agreement with the model, the observed magneto-resistance is negative and shows linear and quadratic field dependence up to the anisotropy field for fields applied parallel and perpendicular to the film plane respectively. Above the anisotropy field, the slopes of the two MR curves are expected to be equal, which is observed at 60 K. Above the Verwey transition, the shape of the normalised MR curves is independent of temperature. Below the Verwey transition the MR curve becomes more linear with decreasing temperature. A large difference between parallel and perpendicular MR is observed at the Verwey transition.

This letter concentrates on phenomena of the electron beam (e-beam) induced oxidation of surfaces of Ni 3 Al-base alloys. In particular it is shown that an e-beam may contribute substantially to the oxidation behavior of polycrystalline Ni 3 Al and Ni 3 Al–B surfaces during Auger analysis at room temperature. Upon e-beam exposure oxidation occurs rapidly, even though any regime of oxygen chemisorption is absent. Auger peak-to-peak oxygen curves for Ni 3 Al(–B) surfaces appear to support the model by Li et al. [J. Vac. Sci. Technol. A 13 (1995) 1574] based on the premise that the e-beam creates additional nucleation sites for oxidation. In contrast, for pure Ni containing B in solid solution a chemisorption regime is indeed present which is then followed by a rapid formation of oxides that saturates quickly at a time scale similar to that of the Ni 3 Al-base systems. Although Al does not participate in the e-beam induced oxidation, the cross-sections for creation of oxide sites are found to be drastically higher than those of Ni/B and pure Ni.

We investigate the influence of the roughness at a nanometre scale on the electrical capacitance of thin films. It is shown that the surface roughness causes an increase of the electrical capacitance depending on the details of the roughness characteristics. For mound rough surfaces, the increase of the electrical capacitance depends strongly on the relative magnitude of the average mound separation λ and the system correlation length ζ. A rather complex behaviour develops for ζ>λ, whereas for ζ

Densification of sol–gel derived thin nanoceramic coatings by laser irradiation and furnace treatment is discussed. Deposition of the zirconia coatings is by means of spin coating. Sintering of the coated layer is observed using a number of different measuring techniques, with special attention paid to densification behaviour and to grain growth in the coating layer using scanning electron microscopy and ellipsometry. The different crystal phases observed are also examined. During sintering at constant temperature a change in the sintering behaviour with time is observed at most temperatures. A theory is presented to explain this observed change in sintering behaviour of the sol–gel layer. Both the initial fast sintering (for all sintering temperatures) and the final slow sintering (at only the higher sintering temperatures) are explained.

Various properties of vesicles prepared from different ratios of the bolaform (bipolar) amphiphile disodium di-n-decyl R,ˆ-eicosanyl bisphosphate (EBP) and the nonbolaform (monopolar) sodium di-n-decyl phosphate (DDP) have been studied. The colloidal stability decreased upon the increasing sodium di-n-decyl phosphate content. The main phase transitions, studied by fluorescence depolarization and differential scanning calorimetry, become less cooperative and occur at decreasing temperatures upon increasing sodium din-decyl phosphate content. The bolaform amphiphile was found to be membrane spanning as indicated by the lamellar repeat spacing obtained by X-ray powder diffraction. Electron microscopic studies of the small vesicles prepared from pure EBP revealed that addition of the fusogen Ca 2+ caused formation of tubules for the EBP. The tubules did not revert to vesicles upon addition of the Ca2+ chelator EDTA, whereas mixed vesicles with 20-50 mol % DDP content showed enlarged vesicles after subsequent addition of Ca 2+ and EDTA. A preliminary conclusion is that a substantial amount of nonbolaform amphiphiles must be present in a bolaform membrane to enable fusion to occur.

The rheological behavior of concentrated dispersions of sterically stabilized lamellar droplets has been studied as a function of the molecular weight and of the amount of adsorbed hydrophobically endcapped poly(sodium acrylate)s. The chemical compositions of the samples are identical to those described before. Despite the polydispersity of the sample, scaling laws and equations that are well established in the rheology of monodisperse colloidal suspensions can be successfully applied. Although the amount of added stabilizing polymer at constant molecular weight hardly influences the elastic modulus (G') as a function of(core) volume fraction of lamellar droplets (o lam ), increasing the polymer molecular weight at constant grafting density results in a pronounced increase of the elastic modulus. The ratio of particle radius to adsorbed layer thickness (R/Δ) decreases with molecular weight, thereby increasing the effective volume fraction. A peculiar effect occurs if the polymer molecular weight drops below 1000. Polymer molecules penetrate into the lamellar droplets, and o lam is increased (at constant surfactant concentration). This so-called building-in effect can be used to thicken lamellar dispersions. Thickening can also be induced by addition of bridging polymers, which carry multiple hydrophobic anchors, linking several droplets. Concomitant adverse effects of bridging flocculation can be counteracted by admixing of hydrophobically endcapped polymers; the resulting dispersions are characterized by enhanced shear-thinning behavior and good physical stability.

The aggregation of a series of n-alkyltrimethylammonium bromide (CnTAB, n = 10, 12, 14, 16, and 18) and 4-n-alkyl-1-methylpyridinium iodide amphiphiles (CmpyI, m = 8, 10, 12, and 14) induced by low concentrations of azo dyes in aqueous solution has been investigated by means of ultraviolet (UV) spectroscopy. It was observed that aggregation takes place at surfactant concentrations far below the cmc of C12TAB, C14TAB, C16TAB, and C18TAB with methyl orange (MO), ethyl orange (EO), and para-methyl red (pMR). Aggregation below the cmc of C10TAB was also induced by EO. In the case of MO and pMR, however, higher dye concentrations were necessary to induce aggregation. Interactions at low surfactant concentrations have also been observed in aqueous solutions of C10pyI, C12pyI, and C14pyI with MO. Binding of methyl red (MR), methyl yellow (MY), and azobenzene sulfonate (ABS) with cationic surfactants below their cmc did not occur. Aggregation was reflected by the appearance of a blue-shifted absorption band in th...

At relatively low temperatures (room temperature and 200 °C) nitrogen was introduced into an iron layer underneath a top layer of nickel. This was done by implanting the nitrogen into the Ni layer. It was observed that subsequently part of the N diffuses into the Fe layer. The concentration depth profiles of N in the Ni/Fe bilayers were recorded with the nuclear reaction analysis technique using the 15 N(p,α) 12 C reaction at E p = 1.02 MeV. From these depth profiles, measured as a function of implantation dose, implantation temperature and anneal temperature, it was suggested that nitrides are formed in iron. To our knowledge, nitride formation has not been reported before at such low temperatures in the absence of radiation damage.

The intramolecular vibrations of a thick epitaxial C 70(111) film on GeS (001) have been measured by high-resolution electron energy-loss spectroscopy (HREELS). A negative-ion resonant behavior is observed in the energy dependence of the impact scattering differential cross sections. These resonances are described as electronic excitation associated shape resonances, which are coincident with the electron energy loss and free-electron capture experiments. Finally, the effect of charge transfer on the resonance behavior is discussed through the comparison of bulk spectra with those from an adsorbed monolayer of C 70 on Au (110).