This study examines amphipod phylogeny based on small subunit (18S) rDNA sequence data. Complete sequences of 25 species representing six families were used to test the phylogenetic information content of this gene for reconstruction of amphipod phylogeny. The alignment proved to be informative for most of the studied taxa. The monophyly of the families Gammaridae, Crangonyctidae, Niphargidae and Oedicerotidae is supported. The Melitidae are not monophyletic in the reconstructed topologies, but weak molecular evidence for the monophyly of this group could be observed in spectra of supporting positions. A close relationship of Gammaridae + Melitidae or Gammaridae + Crangonyctidae is not supported, rather there are supporting positions for the incompatible sister-group relationship (Gammaridae+Niphargidae) and (Crangonyctidae+Niphargidae). The molecular evidence is in favour of the latter relationship. The evolution of cephalothoracic apodemes is discussed in the light of other phylogenetic hypotheses resulting from molecular data.

The investigation of organic multilayer structures prepared by means of the Langmuir-Blodgett (LB) technique is found to be complex due to molecular intermixing arising during the preparation procedure. To fully understand the intermixing processes, not only the X-ray reflectivity, but also neutron reflectivity measurement, must be carried out. It has been already reported 1,2] that it is impossible to investigate the chain-chain intermixing process only by X-ray reflectivity. This due to the lack of electron density contrast within the mixed materials. Sufficient contrast, however, can be achieved by applying neutron reflectivity [3,4], because of the possibility to generate a strong contrast between chains by the deuteration process which only slightly changes the material properties. On the other hand, X-ray reflectivity provides sharp layer structure peaks and Kiessig oscillations from which the period of structure and total thickness of film system can be determined.

Langmuir-Blodgett (LB) multilayer systems are found to be inhomogeneous in morphology and structure. The most characteristic feature of these multilayer films is the appearance of three-dimensional domains in which the molecules arrange themselves as a result of the film transfer onto the substrate. A series of lead arachidate (PbA(2)) LB multilayers have been prepared as model systems to study the dependence of film morphology on the pH value in the subphase. Atomic force microscopy (AFM) and two different x-ray scattering methods [specular (XSR) and diffuse (XDS) x-ray reflectometry] have been used to investigate the intrinsic interface properties, such as the vertical electron density profile and lateral distribution of head groups and chains, as well as the microscopic description of the interface structure, thus providing an overall picture of the investigated multilayers. With AFM, discrete height variations of domains with minimum step widths of one double layer independent of the salt concentration in the films were observed. The lateral domain size shows a dependence on pH. It was found to be maximum at pH=4.2 (pure acid) but minimum at pH 7.0 (maximum salt content). The AFM pictures were treated by a statistical analysis to extract quantities that can be compared with the x-ray results. A considerable number of Bragg maxima were observed in XSR. The vertical correlation length L-z was calculated from the angular width of Bragg maxima along 2 theta and was found to vary with pH value. It follows, in general, the tendency of the domain sizes, being maximum at pH=4.8 and minimum at pH=7.0, respectively. The lateral correlation length L-x has been evaluated via XDS from the half widths Delta omega measured by rocking the sample across a fixed 2 theta. It decreases for increasing pH. L-x was compared with the respective quantity of the AFM analysis. Estimated by XDS, the correlation lengths for inner interfaces and domains complement one another with the lateral length scales resulting from AFM analysis of the surface. (C) 1999 American Institute of Physics. [S0021-9606(99)52116-8].

A Langmuir-Blodgett multilayer film of cadmium arachidate and a complex multilayer system of cadmium stearate bilayers separated by copolymer interlayers have been prepared by sequential transfer of deuterated and nondeuterated bilayers on a solid support. They were investigated at different temperatures using X-ray and neutron specular as well as diffuse reflectivity measurements. The neutron scattering was used to determine the vertical arrangement of deuterated chains within the multilayers and to study the different roughnesses at the chain-chain and chain-metal ion interface separately. The specular reflectivity patterns of both samples could only be interpreted considering the contribution of resonant-diffuse scattering caused by the perfect vertical correlation of individual interface roughnesses within a certain domain. For the two samples the superstructure peak intensity appearing in the respective neutron reflectivity curve decreases dramatically during annealing between 50 and 65 degrees C. This indicates an intermixing of deuterated and nondeuterated molecules within the film. The molecular exchange cannot be suppressed by the incorporation of copolymer interlayers between the deuterated and nondeuterated chains. Because the X-ray reflectivity patterns remain nearly unaffected by the annealing and because the annealing temperature was lower than the melting point of the pure fatty acid phase (about 70 degrees C), we interpret this effect by a vertical movement of fatty acid molecules across the still lamellarly stacked framework of fatty acid salt molecules. The temperature dependence of this process shows Arrhenius-libe behavior. For both samples the estimated activation energy is 1.7 +/- 0.5 eV (164 +/- 48 kJ/mol) and is assigned to the van der Waals bonding energy of single molecules in a 2D hexagonal lattice. From time-dependent measurements we estimated a vertical diffusion coefficient in the order of 10(-22) m(2)/s.

Langmuir–Blodgett (LB) multilayers of fatty acid salt molecules have been investigated by neutron specular reflectivity (NSR) at the reflectometer ADAM at the Institute Laue-Langevin in Grenoble, France. Due to the high flux at the sample site, the NSR curve could be recorded over more than six orders of magnitude, corresponding with qz≤0.3 Å−1. Because of the incoherent hydrogen scattering, the detectable coherent NSR curve is limited to 10−5. The incoherent background of the multilayer systems could be determined for the first time by means of a spin-polarized NSR experiment. The observed intermixing at freshly prepared LB multilayers increases during thermal annealing below the phase transition temperature, whereas the vertical structure remains. This is explained by thermally induced vertical reorganisation of molecules across the multilayer system. The molecular exchange can be described as an analogue to an order–disorder transition. The evaluated activation energy of about 1.7 eV is related to the breaking of van der Waals bonds between one particular molecule and its hexagonal neighbourhood. Time-resolved measurements at particular temperatures allow us to estimate a vertical “diffusion constant” in the range of 10−23 m2/s.

Langmuir-Blodgett (LB) multilayer systems are found to be inhomogeneous in morphology and structure. The most characteristic feature of these multilayer films is the appearance of three-dimensional domains in which the molecules arrange themselves as a result of the film transfer onto the substrate. A series of lead arachidate (PbA2) LB multilayers have been prepared as model systems to study the dependence of film morphology on the pH value in the subphase. Atomic force microscopy (AFM) and two different x-ray scattering methods [specular (XSR) and diffuse (XDS) x-ray reflectometry] have been used to investigate the intrinsic interface properties, such as the vertical electron density profile and lateral distribution of head groups and chains, as well as the microscopic description of the interface structure, thus providing an overall picture of the investigated multilayers. With AFM, discrete height variations of domains with minimum step widths of one double layer independent of the salt concentration ...

A vertically stacked Langmuir-Blodgett (LB) multilayer system composed of undeuterated and deuterated Cd-stearate bilayers being separated by bilayers of the amphiphilic copolymer MSA22 has been investigated. Specular and off-specular scattering curves were collected at room temperature and under thermal annealing up to 85 degrees C. The neutron measurements have been performed on the new neutron reflectometer ADAM at the Institute Laue-Langevin at Grenoble for the first time. Already at room temperature the intermixing between deuterated and non-deuterated molecules amounts to 20% and increases during thermal annealing. In contrast to recent measurements of samples without copolymers the thermally induced interdiffusion is significantly reduced now, unfortunately at the cost of losing the lamellar order. The evaluated activation energy of molecular exchange confirms our recent results.X-ray and neutron specular reflectivity curves cannot be interpreted solely by the Parrat formalism. Under relaxed condition of experimental resolution the off-specular scattering dominates the reflectivity curves even for large q(z). On the other hand, the evaluated q(z)-dependence of the resonant-diffuse scattering reveals that the height-height correlation of interfaces roughness is the main origin of diffuse scattering in such multilayers. (C) 1998 Elsevier Science B.V. All rights reserved.

The new reflectometer ADAM at the ILL is described and some of the results obtained in the first year of operation are presented. These include a reflectivity of a Si wafer over eight orders of magnitude, a measurement of a thick [56Fe/57Fe] isotope superlattice, and a polarised reflectivity of a Co/Cu multilayer. The instrument is now available to outside users.

Langmuir-Blodgett (LB) multilayers of cadmium and uranyl stearate salts, prepared by sequential transfer of deuterated and non-deuterated bilayers on a silicon support, have been investigated by neutron reflectivity measurements at the TAS8 beam line at Risø. Freshly prepared LB multilayers already show an intermixing of the bilayers which can be attributed to incomplete transfer of the monolayer from the water surface to the substrate. This becomes visible via the reduced intensity of that superlattice peak which probes the contrast in scattering length density between the deuterated and the non-deuterated monolayers. Further experiments reveal that the intermixing increases as a function of temperature. The kinetics of this process have been investigated by combined temperature- and time-dependent X-ray and neutron reflectivity measurements. For annealing temperatures below 55 °C cadmium stearate films show a dramatic decrease in intensities of the superstructure peaks, indicating an increase of intermixing. Taking into account the fact that the X-ray reflectivity patterns remain nearly unchanged, this intermixing is interpreted as discrete hopping of the fatty acid salt molecules between various bilayer sites. Its time constant decreases as a function of temperature and vanishes close to the melting point of the stearic acid phase at about 75 °C. The Arrhenius-like activation energy for the hopping process was estimated to be about 1.9 eV. For uranyl stearate samples we already observed complete intermixing at about 40 °C, which is interpreted in terms of the reduced lateral interaction among the hydrocarbon chains induced by the bigger counterions.

Barium stearate multilayer films have been prepared by use of the Langmuir-Blodgett technique transferring sequentially deuterated and nondeuterated bilayers on a silicon support. Combined X-ray and neutron scattering experiments show a rearrangement of the molecules when the films have been annealed at temperatures higher than 60 degrees C. Whereas the periodicity of the barium sheets is unchanged, the intensity of the superstructure peak decreases close to the melting point of the stearic acid component (about 70 degrees C) and vanishes completely above. This behaviour is explained by the vertical movements and rearrangements of stearic acid molecules without noticeable evaporation of molecules.

Langmuir-Blodgett (LB) multilayers from fatty acid salts can be characterized by finite sized scattering aggregates. High-resolution atomic force microscopy maps reveal a substructure of molecular ordering. These blocks are to be considered as 3D domains. Furthermore, macroscopic holes and scratches appear at the surface. These defect structures have to be taken into account when interpreting observed X-ray and neutron reflectivity curves. The density loss due to the holes can be detected from the angular shift of the critical angle of total external reflection. Off-diagonal scans demonstrate a slight inclination of domains relative to each other. Neutron reflectivity patterns of sequentially deuterated and hydrogenated carbon chains provide information about the disorder of the organic chains. In the second part of the paper a structure model of the molecular order within the domains is developed using 16 in-plane Bragg peaks and their truncation rods measured by X-ray grazing incidence diffraction. The refined 3D unit cell contains at least four monolayers in a herringbone arrangement of the hydrocarbon chains. Its stability is given by the inter-chain coupling between two neighbouring monolayers.

X-ray (XDS) and neutron (NDS) diffuse scattering are used for nondestructive investigation of the domain structure of organic multilayers prepared by the Langmuir-Blodgett (LB) technique. The multilayers under investigation were lamellae of Cd-stearate and Pb-stearate molecules, XDS measurements are performed to determine the lateral correlation length of scattering aggregates as well as the angular distribution of domains, NDS experiments of sequentially deuterated films show the higher disorder of fatty acid chains compared to the stacking of metallic heads. Holes and scratches are responsible for the density loss within the film and cause the X-rays scattered coherently to vanish completely. We present a simple model to evaluate the XDS and NDS, taking both height fluctuation and density fluctuation of scattering aggregates into account. Height-height correlation given by Sinha and density-density correlation known from small angle X-ray scattering (SAXS) are unified to a general density-density correlation function for small interfaces.

A partially deuterated Pb-stearate multilayer prepared by means of the Langmuir-Blodgett technique on a Si support was investigated by X-ray and neutron reflectometry. It consists of a superstructure built by two protonated and two deuterated hydrocarbon chains. The X-ray reflectivity is sensitive to the gradient of the electron density between the hydrocarbon chains and the sheets of metallic counter-ions whereas the neutron reflectometry measures the gradient of scattering length density which is a maximum at the interface between the deuterated and protonated chains. Sharp Bragg peaks were found which are due to the periodic distance between the metallic sheets whereas the peaks responsible for the interface between deuterated and protonated chains are smeared out. The intensities of these peaks can only be explained assuming a partial exchange of deuterated and protonated chains between the sublayers.