Search

The combined application of surface pressure−area (π−A) isotherms, Brewster angle microscopy (BAM), and grazing incidence X-ray diffraction (GIXD) offers a powerful possibility to characterize the amphiphilic P-functionalized calix[4]arene monolayers at the air/water interface. The studies are performed with two calix[4]arene bisphosphonates 1 and 2, which are phosphorylated in the same way at the upper rim and differ only in the number of alkyl chains at the lower rim (compound 1 with four n-dodecyl chains; compound 2 with two n-dodecyl chains in opposite positions). Significant differences exist in the π−A isotherms of the two calix[4]arene bisphosphonates 1 and 2 monolayers. In the case of derivative 1, they resemble those of usual amphiphiles with the characteristic temperature dependence and a coexistence region between a fluid and condensed phase. The π−A isotherms of derivative 2 deviate considerably from those of typical amphiphilic monolayers having no temperature dependence and no “plateau” region. The characteristics of the π−A isotherms of both derivatives 1 and 2 are not affected by interaction with counterions of different valency (Na⁺, Cd²⁺, Eu³⁺, Th⁴⁺) present in the subphase. Both derivatives 1 and 2 form two-dimensional condensed phase domains with a specific shape which is more or less modified by different-valent counterions in the aqueous subphase. The analysis of the BAM results corroborates the general differences between the monolayer properties of derivative 1 and 2. The GIXD results show that only the monolayers of derivative 1 form a 2D lattice structure. The data indicate a rectangular unit cell, which is not changed by the complexation of thorium ions by the phosphonate groups.

The use of INAA and IPAA is illustrated by several applications (Zn-traces in Cu, neutron doping of Zn in copper, implanted Sb in silicon, trace elements in sediment material and polyethylene). The two methods are used to complement or to cross-check each other. Validation by IDA-TIMS was performed in the case of neutron doping and turned out to be a valuable support. Even developed routines of activation analysis need improvement. Two technical solutions, the high energy photon screen (HEPS) and a twin detector assembly, are dealt with in detail.

A loss of long-range tilt orientational order in 1,2-hexadecandiol monolayers is observed by Brewster angle microscopy. It coincides with a coexistence of two different lattices in the monolayer over a large surface pressure range detected by grazing incidence X-ray diffraction. In one lattice the alkyl chains are tilted toward nearest neighbors and in the other toward next-nearest neighbors. In monolayers of 2-hydroxypalmitic acid, 2-palmitoylglycerol, and 2-hexadecanol a condensed phase with short-range tilt orientational order is formed. The diffraction patterns show a superposition of the peaks from lattices which differ with respect to the tilt azimuth of the alkyl chains. The behavior of 1,2-hexadecandiol monolayers is related to that of 2-hydroxypalmitic acid, 2-palmitoylglycerol, and 2-hexadecanol. In monolayers of 2-hydroxypalmitic acid/palmitic acid mixtures a crossover from one behavior to the other is observed. The loss of order in Langmuir monolayers is initiated by a misfit of alkyl chains and headgroups. Chains can only adapt to headgroups which are additionally too large perpendicular to the tilt direction by a distortion of their packing. If the size of the headgroup perpendicular to the tilt direction exceeds a particular value, a disordered packing results. If substances with smaller headgroups are added to such monolayers, initially the spacing perpendicular to the chain tilt direction is optimized and then second the polar tilt angle is reduced.

In this study films of core-shell-structured latex particles are investigated by dynamic scanning force microscopy ‘tapping mode imaging’. Polymer dispersions with cores of the low-viscosity polymer poly(2-ethylhexyl methacrylate) (PEtHMA) and shells of the cross-linked rubber poly(n-butyl acrylate) (PBA) were spread on a flat mica surface to form a monolayer. Topographic as well as phase images were recorded at different amplitudes and damping factors (so-called soft and hard tapping). The topographic images show a continuous matrix formed by the particles, but a clear contrast of individual particles in the phase images could be obtained at high damping factors of the cantilever oscillation. The soft cores embedded in the matrix of the shell polymers caused a perceptible reduction of the phase of oscillation. Consequently, the total particle appeared soft enough because it allowed deformation of the soft cores below. Copyright © 1999 John Wiley & Sons, Ltd.

In this study films of core‐shell‐structured latex particles are investigated by dynamic scanning force microscopy ‘tapping mode imaging’. Polymer dispersions with cores of the low‐viscosity polymer poly(2‐ethylhexyl methacrylate) (PEtHMA) and shells of the cross‐linked rubber poly(n‐butyl acrylate) (PBA) were spread on a flat mica surface to form a monolayer. Topographic as well as phase images were recorded at different amplitudes and damping factors (so‐called soft and hard tapping). The topographic images show a continuous matrix formed by the particles, but a clear contrast of individual particles in the phase images could be obtained at high damping factors of the cantilever oscillation. The soft cores embedded in the matrix of the shell polymers caused a perceptible reduction of the phase of oscillation. Consequently, the total particle appeared soft enough because it allowed deformation of the soft cores below. Copyright © 1999 John Wiley & Sons, Ltd.

Not Available

Monolayers of the racemic 1-palmitoylglycerol (1) and 1-hexadecylglycerol (2) were investigated by grazing incidence X-ray diffraction (GIXD) and Brewster angle microscopy (BAM) at temperatures from 5 to 33 °C. Above 13 °C a liquid-expanded phase was found for 1 and 2, and both compounds show a transition to a condensed phase with a NN tilted centered rectangular structure. This transition pressure increases with increasing temperature. A second transition to a NNN tilted phase was observed using GIXD. In the case of 1 this transition pressure has a stronger temperature dependence than for 2. The NN−NNN transition pressures were additionally found to be much higher for 1 than 2. The surface pressure at which upright oriented molecules should be found was extrapolated from GIXD measurements. The transition was visualized for 1 using Brewster angle microscopy. A nonzero lattice distortion at zero tilt angle was obtained for both compounds, indicating an ordering of chain backbones, possibly herringbone packing. Phase diagrams have been constructed for 1 and 2.

Grazing incidence synchrotron X-ray diffraction (GID) studies of Langmuir monolayers of several substances such as 2-monopalmitoyl-glycerol, 2-hexadecanol, and 2-hydroxypalmitic acid reveal diffraction patterns that indicate a disordered packing of alkyl chains. The diffracted intensity is distributed along a characteristic arc in reciprocal space. A relation between in-plane lattice and two parameters, polar tilt angle and tilt azimuth, is derived in order to describe the observed distribution that results from the superposition of the diffracted intensities of different lattices. It is possible to ascribe the diffraction patterns unambiguously to a variation of the tilt azimuth. Variation of the polar tilt angle was ruled out. A detailed analysis of the distributed intensity allows one to obtain at least the polar tilt angle and the lattice spacing perpendicular to the tilt azimuth in the limit of a lattice with nearest-neighbor tilt.

The morphology of condensed phase domains in monolayers of glycerol amide lipids has been investigated by Brewster angle microscopy (BAM). Different nonequilibrium domains with dendritic shapes arise depending on the experimental conditions. Apart from observations in the micrometer range, grazing incidence X-ray diffraction (GID) experiments have been performed. Results have been compared to those of glycerol ester lipid monolayers. These amphiphiles differ only in the group linking chain and headgroup. The change of this linkage has significant influence on domain morphology and lattice structure. It is shown that the main growth directions of the dendritic domains can be related to directions of the oblique lattice of the molecules. The structures at micrometer resolution and at angstrom range are correlated to each other.

Atomic force microscopy (AFM) in friction mode is successfully used for probing the inner structure of condensed phase domains of 1-monostearoylglycerol (MSG) monolayers transferred from the air−water interface onto mica, glass, and silicon wafers by the Langmuir−Blodgett (LB) technique. The friction anisotropy reveals the same 7-fold domain substructure as observed at the air−water interface by Brewster angle microscopy (BAM). It is caused by differences in the tilt orientation of the molecules within the domain segments. After deposition of the monolayer, the main features of the condensed phase morphology, such as size, shape, and azimuthal tilt, are preserved independent of the solid substrate. The widths of the straight segment lines were found to be <100 nm. This result supports the idea that the segment boundaries of amphiphilic monoglycerol domains are low-energy lattice rows. Differences in the smoothness of the domain boundary at the air−water interface and on solid substrates can be caused by changes in the energetic conditions along the three-phase contact line.

A variety of nonequilibrium growth structures is observed in fatty acid ethyl ester monolayers. In these monolayers, two different condensed phases exist:  one with tilted chains and the other with erected chains. The formation of the domains of these phases from the fluid phase gives rise to completely different shapes under non-equilibrium. In the phase with tilted chains, a dendritic growth regime exists in ethyl stearate monolayers for intermediate compression rates. The arms of the dendrite have a tip-oscillating morphology. At extremely high compression rates the tips are no longer stable and the growth does not follow crystallographic directions. For the shorter chain (ethyl palmitate) the dendritic growth regime is not observed in the phase with tilted chains at low temperatures. Here the domain wall only becomes unstable at extremely high compression rates and the morphology is then fractal-like. However, at temperatures T > 20 °C a dendritic growth regime occurs. The nonequilibrium structures in both ethyl stearate and ethyl palmitate monolayers are transformed into a circular equilibrium shape for the condensed phase with tilted chains during a few minutes. In ethyl palmitate monolayers, a phase with erected chains forms during the first-order phase transition at temperatures T > 26 °C. In this phase the nonequilibrium structures are quite stable and transform very slowly into a compact shape. Even at extremely low compression rates branched structures occur. An increase of the compression rate causes a continuous change from a more dendritic shape to one which is quite similar to the dense-branching morphology.

Monolayers of racemic 1-(2-tetradecylhexadecanoyl)-2-O-hexadecyl-phospholipids 1(2C 14 -16:0)-2H-PE(CH 3 ) n , with n =0, 1, 2 and 3, at the air/water interface are studied by film balance measurements, Brewster angle microscopy (BAM) and grazing incidence X-ray diffraction (GIXD). Although the area per three tails exceeds that per head, an influence of the head group methylation on the monolayer structure is observed. The tilt angles at lower lateral pressures and the transition pressure to a hexagonal packing of upright oriented chains increase with increasing methylation degree. The transition from the NN tilted rectangular to this hexagonal phase is connected with a pressure region where the in-plane components Q xy of the two peaks coincide while the out-of-plane components Q z differ. This indicates an undistorted hexagonal in-plane lattice even for tilted chains. The area-pressure isotherm of the 1(2C 16 -18:0)-2H-PE monolayer shows at 20°C a plateau region which does not directly correspond to the transition from the NN tilted to the hexagonal phase with untilted molecules. BAM measurements show that the large differences between the molecular areas, derived from isotherm and X-ray measurements below 10 mN/m, can be explained by the formation of holes in the monolayer. Possibly the tilting of the triple-chain molecules leads to an orientational ordering of the head group dipoles and therefore to an electrostatic repulsion between condensed phase domains.

The monolayer morphologies of 1-monopalmitoyl-rac-glycerol at the air-water interface are studied at the microscopic level using Brewster angle microscopy (BAM). BAM images are recorded simultaneously with the π - Aisotherms to obtain information on the two-dimensional phase behavior. Condensed-phase domains of 1-monoglycerides exhibit a 7-fold substructure, which is analyzed according to a geometric model. The arrangement of regions of different azimuthal chain orientation affects the molecular orientation at the domain boundary. Therefore, if the line tension is anisotropic, the inner segment structure of a domain influences the outer domain shape. Restructuring processes induced by compression to high surface pressures cause zigzag segment boundary lines and 6-fold domains.

The Axisymmetric Drop Shape Analysis (ADSA) has been used to study the surface pressure/area isotherms of insoluble surfactant monolayers. The continuous measurement of surface tension as a function of surface area by increasing and decreasing the drop volume allows to investigate the phase transitions in monolayers. The isotherms of two phospholipids, dipalmitoyl phosphatidyl choline (DPPC) and dimyristoyl phosphatidyl ethanolamine (DMPE), show good agreement with those measured by using a conventional Langmuir-Blodgett film balance, except in the coexistence region. The observed disagreements are discussed in terms of differences in compression rate, curvature of the surface and effect of impurities. Evidence of possible geometric effects on monolayer domain formation and growth is given on the basis of BAM images.

The construction of a microscope photometer using prefabricated elements is described. To illuminate the tissue, a Leitz Ultropac is applied. To enlarge the wavelength range, its illuminating glass lens is replaced by an Acryl glass zonal lens. Two separate light channels with separate lamps, monochromators and photomultipliers allow the measurement of fluorescence excitation and emission spectra as well as of reflection spectra. By chopping the light, light pulses and dark currents are measured 8.33 times a second. By an integration circuit the signal-to-noise ratio for small signals is improved. The instrument allows us to detect the increase of 4 ng/ml NADH (solution of pH 7.38) in an area of 0.2 mm2.

Palmityl acetate monolayers are studied by grazing-incidence X-ray diffraction (GID). The monolayers are found to undergo a transition from a phase with alkyl chains tilted toward nearest neighbors (NN) to a phase with chains tilted toward next-nearest neighbors (NNN) upon monolayer compression. This transition gives rise to a sudden reorientation of the molecules that is determined by Brewster angle microscopy (BAM). At T > 15 °C, palmityl acetate monolayers undergo a first-order transition from a fluid phase to a condensed phase indicated by a plateau region in the π−A isotherm. The transition pressure increases with increasing temperature. At low temperatures a phase with alkyl chains tilted toward nearest neighbors is formed from the fluid phase. The critical pressure for the transition between the tilted phases changes only slightly with temperature. Consequently, a phase with chains tilted toward next-nearest neighbors is formed directly from the fluid phase at high temperatures. Then no reorientation of molecules is observed by BAM. The textures of the condensed-phase domains formed during the transition from a fluid phase to a condensed phase are temperature-dependent. Some domains are subdivided into six segments of different orientation. In such domains the molecular chains are tilted along the bisector of the segments at T < 22 °C, whereas the tilt azimuth is perpendicular to the bisector at T > 24 °C. The crossover from one texture to the other is separate from the transition between the tilted phases. At T ≤ 26 °C, the sudden reorientation of molecules corresponding to the NN−NNN phase transition is still observed.

First-order phase transitions from the low-density fluidlike phase to the condensed phase of monolayers of N-tetradecyl-γ,δ-dihydroxypentanoic acid amides at the air−water interface have been studied by π−A isotherms, Brewster angle microscopy (BAM), and synchrotron X-ray grazing incidence diffraction (GID). The thermodynamic differences between enantiomeric and racemic monolayers are too small to be measured. However, chiral discrimination is observable in the macroscopic domain morphology by BAM. The domains of the condensed phase grow dendritically. The characteristic shapes of domains of the pure S and R enantiomers are mirror images of each other. The domains of the racemic mixture are quite similar; however, they have no mirror symmetry. Synchrotron X-ray grazing incidence diffraction (GID) measurements reveal an oblique lattice with tilt direction of molecules close to one of the nearest neighbors for condensed-phase monolayers of both enantiomer and racemate. The molecules of the racemic monolayers are more densely arranged indicating a week heterochiral interaction of the molecules. The crystal structure changes only slightly with the surface pressure due to hydrogen bonds between the amide groups of molecules in the condensed phase. Thermodynamic behavior, morphological features, and two-dimensional crystal structure are discussed on the basis of the headgroup interactions, in particular the dominance of strong hydrogen-bonding chains of the amide groups only weakly affected by the hydroxyl groups and the chiral center.

The structure and morphology of the three-dimensional aggregates of arachidic acid were studied by atomic force microscopy (AFM) after transfer onto a silicon wafer and by synchrotron grazing incidence X-ray diffraction (GID) at the helium/water interface. The 3D aggregates on the wafer observed by AFM are islands of granulelike and platelike shapes. The plate islands consist of terraces of different heights. The crystal structure of the plate islands was determined through molecular resolution by AFM. They have the C-crystal structure of arachidic acid at the beginning of the relaxation. During further relaxation the B-crystal structure becomes apparent. The islands with B-crystal structure dominate at the end of the relaxation process. Regions with a disordered molecular structure are found beside the ordered crystal structures. In all ordered regions of a single island the same crystal structure is observed. Using GID, the B- and C-crystal structures of the 3D aggregates of arachidic acid were also found at the helium/water interface. No peaks of any crystal structure are observed until 20% of the monolayer material is transformed into 3D aggregates. Then first the peaks of the B-crystal structure appear, which increase with the relaxation time. Additionally small peaks corresponding to the C-crystal structure are found.

The condensed phase of fatty acid ethyl ester monolayers exhibits long range orientational order. The aliphatic chains are only weakly tilted in these monolayers. This has an effect on the textures of the monolayers. The domains of the condensed phase formed during a transition from the fluid phase to a condensed phase with tilted chains do not have a defined substructure. Different types of domain substructures can be observed. A few domains have a segment structure with chains tilted perpendicular to the bisector of the segment. Other domains of the same monolayer have small parts of a deviating orientation embedded in the major part of the domain having an uniform orientation. Using domains with this texture, the anisotropy of the line tension is qualitatively estimated. Jumps of the molecular orientation occur along various dense lattice directions, which corresponds to the observation of up to four main growth directions in the dendritic growth regime of ethyl stearate monolayers. However the large spread of textures is not only introduced by the dendritic growth. This becomes evident from the study of the ethyl palmitate monolayers, where no dendritic growth regime exists. Also in these monolayers various structures occur; some of them are identical to those of the ethyl stearate monolayers.

Fungi, yeast, and bacteria were cultured from field-collected, discolored (pecky) rice, Oryza sativa L., kernels and from stylets and saliva of the rice stink bug, Oebalus pugnax (F.). A sterilized chrome wire was used to wound and introduce selected inocula into developing kernels on rice panicles. Typical kernel discolorations could not be induced by inoculation with bacterial or yeast isolates. When the caryopsis was wounded during inoculation, several fungi caused discoloration comparable to that of pecky kernels collected from rice fields. Fusarium oxysporum Schlect, caused the greatest discoloration followed by Cochliobolus miyabeanus (Ito & Kuribayashi) Drechsler ex Dastur, Curvularia lunata (Wakker) Boedijn, Alternaria alternate (Fr.) Keissler, and A. Padwickii (Ganguly) M. B. Ellis. Symptoms typifying classical fungal discoloration peaked 5 to 10 dafter anthesis, and classical insect damage symptoms peaked 15 dafter anthesis when rice stink bugs were caged on plants 0, 5, 10, or 15 dafter anthesis. In field tests, density of rice stink bug infestations was associated positively with incidence of discolorations historically attributed to insects and fungi. These data indicate that discolorations in pecky rice result from fungi being introduced at the time of feeding of O. pugnax by means of a loose vector relationship.