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The nucleation events of synthesis reactions of ZSM5 and Na-A zeolites were studied, with particular emphasis on the role of organic template, TPA+(tetrapropylammonium), in the ZSM5 synthesis. Qualitative evaluation of the structural units was obtained by Small-Angle X-ray Scattering (SAXS) measurements which were analyzed using an indirect Fourier transform method. ln the presence of organic cation TPA+in the ZSM5 synthesis we found globular structural units, 5 nm in diameter, which aggregate to elongated bodies 44 nm long. These results suggest that the zeolite ZSM5 building blocks are globular structural units, 5 nm in diameter, containing silica, alumina, organic cation and water, which fuse together to produce elongated aggregates that may compose the final unit cell. We found that the Na-A zeolite follows nucleation via 1 nm globular particles, which suggests that the existence of globular structural units in the nucleation of zeolites is a general phenomenon.

The structural and dynamic properties of low ionic strength micellar solutions of the cationic surfactant perfluorooctylbutane trimethylammonium bromide have been investigated by cryo-TEM, small-angle neutron scattering, small-angle X-ray scattering, T-jump and rheological experiments. The surfactant molecules self-assemble into narrow ribbons with average dimensions on the order of 4 nm × 3 nm, either under salt-free conditions or in the presence of up to 30 mM KBr or NaF. Cryo-TEM also reveals in the salt-free systems the presence of networks of multiconnected micelles. Rheological experiments showed that these surfactant systems exhibit a strong shear-thickening effect even in the presence of up to 30 mM KBr. The T-jump response of the micellar solutions was found to be multiexponential. This observation rules out the presence of only linear micelles with an exponential length distribution and suggests more complex topologies of the micellar aggregates. The relaxation time associated with the predominant process in the T-jump relaxation is strongly correlated to the critical shear rate beyond which shear thickening occurs, thus indicating that this critical shear rate is controlled by the micellar kinetics.

A series of long and ultralong chain tetrabutylammonium alkyl carboxylate (TBACm, TBA = tetrabutylammonium ion; Cm = carboxylate ion Cm-1H2m-1CO2^- of total carbon number m) surfactants have been obtained by direct neutralization of the fatty acids with m = 12, 14, 18, 22, and 24 by tetrabutylammonium hydroxide. Time-resolved fluorescence quenching has been used to determine the micelle aggregation number (N) of the surfactants with m = 12, 14, and 18 in the temperature range 10−50 °C and of the surfactants with m = 22 and 24 in the temperature range 25−60 °C. In all instances the values of N were well below those that can be calculated for the maximum spherical micelle formed by surfactants with the same alkyl chain as the investigated surfactants on the basis of the oil drop model for the micelle core. The microstructure of selected solutions of TBAC22 was examined using transmission electron microscopy at cryogenic temperature and compared to the microstructure of solutions of TBA dodecyl and tetradecyl sulfates. These observations generally confirmed the findings of TRFQ. The self-association behavior of these anionic surfactants with TBA counterions is explained on the basis of the large size and the hydrophobicity of the tetrabutylammonium ions. The important differences in behavior that have been evidenced between tetrabutylammonium alkyl carboxylates and alkyl sulfates are discussed in terms of differences in distribution of the surfactant electrical charge on the headgroup and alkyl chain predicted by quantum chemical calculations (Langmuir 1999, 15, 7546).

We have studied the nano- and microparticles formed by complexation of PDAC [poly(diallyldimethylammoniumchloride)] and SDS (sodium dodecyl sulfate). The complexation phenomenon was characterized by light scattering and ζ-potential measurements. The nature of the complexes was revealed by direct-imaging cryogenic temperature transmission electron microscopy (cryo-TEM), showing nanometric details of the complexes formed around the point of neutralization. The images also reveal how those aggregates are solubilized by excess surfactant, first into faceted particles with threadlike micelles attached to their surfaces, prior to complete solubilization, then into lacelike aggregates, and finally into spheroidal micelles. The nanostructure of the complexes strongly suggests they are made of a hexagonal liquid crystalline phase. This was further supported by small-angle X-ray scattering (SAXS).

It has been known that lithocholic acid self-assembles in highly alkaline aqueous dispersions. By a combination of cryogenic-temperature transmission electron microscopy and small-angle neutron and X-ray scattering, we were able to characterize the long single-walled nanotubules that are formed in the system. We have found that the nanotubules appear quite monodisperse with cross sections of 52 nm outer diameter and an internal cylindrical cavity of 49 nm diameter. Such a steroid introduces a new class of tubule-forming systems with cavity dimensions in a not previously reported nanoscale range. The flowing properties of the lithocholate suspensions are analyzed, and it is concluded that the uniform nanotubules are interacting moderately in the suspensions. As these nanotubes are fairly insensitive to the presence of salts, they are potentially good candidates for metallization and mineralization templates.

We present the results of the insertion of self-made polyethylene T-tubes for a period of 15–24 months for the treatment of chronic middle-ear effusion. We compare the outcome of our patients to the reported outcome of patients treated with other commonly used ventilation tubes for either shorter or longer periods of time. In a retrospective review of 603 T-tubes inserted in 306 children up to the age of 12 years, charts were reviewed for age, sex, surgical procedure performed, duration of ventilation and complications. In all cases the indication for surgery was chronic middle-ear effusion. The tubes were electively removed by the authors after 15–24 months of ventilation. Spontaneous extrusion was considered a complication. The mean period of ventilation was 20 months. Post-operative otorrhoea was experienced in 6.6 per cent of ears; 4.8 per cent of tubes extruded spontaneously, whereas 3.15 per cent had to be removed earlier than originally planned; 4.9 per cent of ears were re-ventilated at a later date, and 1.49 per cent of ears developed a persistent perforation. We demonstrate that the outcome of patients treated with our self-manufactured tubes for a period of 15–24 months is, in many respects, better or at least comparable to the reported outcome of patients treated with other commonly used ventilation tubes for either shorter or longer periods of time, and that the many complications associated with the conventional T-tube can be reduced. We suggest that our favourable outcome may be due to the duration of ventilation, which was controlled to be shorter than the conventional long-term T-tubes and longer than that of grommets.

We have used cryo-transmission electron microscopy (cryo-TEM), small-angle neutron scattering (SANS), differential scanning calorimetry (DSC), and circular dichroism (CD) for microstructural characterization of amphiphiles that have a model collagen peptide headgroup. Single-tail amphiphiles and double-tail amphiphiles with short tails such as C12 and C14 formed spheroidal micelles. Further increase in tail length of the double-tail amphiphiles led to the formation of disklike micelles that aggregated to form a strandlike structure. SANS curves for double-tail amphiphiles were obtained at different contrasts by using different fractions of D2O in the D2O/H2O mixture. SANS data analysis using the sphere method confirmed the structures imaged by cryo-TEM and provided a detailed structural characterization. CD data showed that the peptide's capacity to organize into a triple helix by intertwining with two neighboring molecules can be affected by increasing the tail length. Double-tail amphiphiles with tails such as C18 and C20 that are crystalline at room temperature disrupt the association of the triple helix at room temperature. Increasing the temperature to melt the crystalline tails helps restore the triple-helical conformation in the headgroups.

The synthesis, phase behavior, and mixing properties of cationic dimeric (gemini) surfactants having one or two perfluoroalkyl chains is described and compared to that of analogue hydrocarbon surfactants. The combination of the dimeric character of the amphiphiles with the high hydrophobicity of the fluorocarbon chains leads to very low critical micelle concentration values and unusually low characteristic times of exchange between surfactants in the bulk solution and surfactants in the aggregate. This results in slow exchange on the NMR time scale, which allows a practical study of micellization and comicellization by NMR. With respect to the morphology of the aggregates, the fluorocarbon amphiphiles do not simply behave as more hydrophobic amphiphiles. Instead, they assemble into various structures including very stable unilamellar and multilamellar vesicles not seen in their hydrocarbon analogues. The hybrid hydrocarbon−fluorocarbon dimeric surfactant exhibits features of both families. In particular it mixes with either hydrocarbon or fluorocarbon surfactants, whereas the latter two undergo a macroscopic phase separation.

The microstructures in mixtures of two dimeric (gemini) surfactants, the dimethylene-1,2- and eicosamethylene-1,20-bis(dimethyldodecylammonium bromide), referred to as 12-2-12 and 12-20-12, have been investigated at 25 °C by electrical conductivity, spectrophotometry, digital light microscopy (DLM), and transmission electron microscopy at cryogenic temperature (cryo-TEM). This mixture was selected because 12-20-12 forms vesicles in a wide range of concentration whereas 12-2-12 forms micelles that are spherical at low concentration then rapidly elongate, branch, or give rise to toroidal micelles (rings), and finally form a network of threadlike micelles at 2 wt %. The measurements were performed keeping the 12-20-12 concentration at 0.09 wt % and progressively increasing the 12-2-12 concentration from 0.1 to 2.0 wt %. The electrical conductivity data clearly showed that in the early stages of 12-2-12 addition to the 12-20-12 vesicles, 12-2-12 was strongly adsorbed by the vesicles. Spectrophotometry and DLM showed that, under the conditions used, the vesicles were nearly eliminated at above 0.7 wt % 12-2-12. The cryo-TEM observations were performed on samples vitrified two months after preparing the mixtures. The progressive increase of the 12-2-12 content in the mixture resulted first in vesicle growth (0.1 wt %), followed by vesicle breakage into smaller vesicles (0.26 wt %), the formation of disklike micelles (0.4−0.75 wt %), then of ring-like micelles and short elongated threadlike micelles (1 wt %), the growth of those threads (1.5 wt %), and finally the formation of a network (2 wt %), where threads and rings were interconnected. The network contained also a few isolated rings. The same structures were observed when the mixtures for cryo-TEM observation were vitrified 5−7 days or two months after mixture preparation, for the mixtures containing 0.5 wt % or less, and 1 wt % or more 12-2-12. Aging of the systems was observed for mixtures containing 0.65−0.75 wt % 12-2-12. When examined 5−7 days after preparation the mixtures showed long rigid rodlike micelles and irregular ribbons. Those structures disappeared when the mixtures were allowed to equilibrate for two months. The results are discussed and a model is presented to explain the observed behavior.

Abstract: Experimental studies of the effects of mixtures of cationic surfactants on their drag reduction and rheological behaviors are reported. Cationic alkyl trimethyl quaternary ammonium surfactants with alkyl chain lengths of C12 and C22 were mixed at different molar ratios (total surfactant concentrations were kept at 5 mM with 12.5 mM sodium salicylate (NaSal) as counterion). Drag reduction tests showed that by adding 10% (mol) of C12, the effective drag reduction range expanded to 4–120 C, compared with 80–130 C with only the C22 surfactant. Thus mixing cationic surfactants with different alkyl chain lengths is an effective way of tuning the drag reduction temperature range. Cryo-TEM micrographs revealed thread-like micellar networks for surfactant solutions in the drag reducing temperature range, while vesicles were the dominant microstructures at non-drag reducing temperatures. High extensional viscosity was the main rheological feature for all solutions except 50% C12 (mol) solution, which also does not show strong viscoelasticity. It is not clear why this low extensional viscosity solution with relatively weak viscoelasticity is a good drag reducer.

In solutions of hydrophobically modified hydroxyethyl cellulose (HMHEC) and two oppositely charged surfactants, sodium dodecyl sulfate (SDS) and dodecyl trimethylammonium chloride (DoTAC), an organized structure of micelles has been observed by using cryogenic temperature transmission electron microscopy (cryo-TEM). On the cryoelectron micrographs the micelles appear to be thread on strings, arranged in a cell-like pattern. This organized structure is induced by the polymer when the average number of polymer hydrophobic tails per mixed micelle is about 3−5, allowing hydrophobic tails from different polymer molecules to bind to the same surfactant micelle. The organized structure was not observed either in the surfactant mixture alone or in a low-viscous solution with a low number of polymer hydrophobic tails per mixed micelle. The oppositely charged surfactant mixture was studied at a total surfactant concentration of 30 mm in the presence and in the absence of 1% w/w polymer. The number of polymer hydrophobic tails per mixed micelle was varied by decreasing the micelle concentration through induced micellar growth. The micelles grow when the mole fraction of DoTAC (X) on the SDS-rich side of the phase diagram is increased. At low X values, only micelles are found, but from X = 0.29 upward an increasing fraction of vesicles is present. Pulsed field gradient NMR was used to measure the self-diffusion of water for determining the aggregate structure and self-diffusion of the surfactant for determining the micellar aggregation number and the concentration of free SDS molecules.

Transition of vesicles to micelles induced by flow of dilute aqueous cetyltrimethylammonium chloride (CTAC)/sodium 3-methylsalicylate (CH3Sal^-) dispersion was directly imaged by rapidly vitrifying small ultrathin specimens after varying periods of postflow on-the-grid relaxation, and then examining them by cryogenic-temperature transmission electron microscopy (cryo-TEM). Vesicles prevail in quiescent equimolar 5 mM dispersions of CTAC and NaCH3Sal at equilibrium. When the dispersions are deformed and strained by rapid drainage of the excess from the specimens, the vesicles transform into an entangled network of threadlike micelles. The micelles revert to vesicles with time after drainage flow ceases. Intermediate structures during the transition were also captured by cryo-TEM. We hypothesize that the straining actions of flow disrupt vesicles, distort the distribution of, or strip, the counterions around vesicle fragments, shift the binding and dissociation equilibrium of counterions, alter the local preferred curvature of the surfactant assemblies, and thus induce structural instability of the fragments that leads to their reconstruction into networks of branching threadlike micelles.

The dimeric (gemini) surfactant 12-2-12 (dimethylene-1,2-bis(dodecyl dimethylammonium bromide)) has been known to form threadlike micelles at relatively low concentrations. We investigated the micellar growth of this surfactant in aqueous solutions by the much-improved cryo-TEM technique (transmission electron microscopy at cryogenic temperature) in the concentration range between 0.26 and 1.5 wt %. The digitally acquired electron micrographs of solutions, with concentrations up to about 1 wt %, show the coexistence of spheroidal micelles and long, threadlike micelles, the number and length of the latter increasing with concentration at the expense of the former. The micrographs show very few elongated micelles of intermediate sizes. Also, the endcaps of the elongated micelles can be seen to be of a larger diameter than the cylindrical body of those micelles. These results lend support to the theories, developed by various workers, that predicted these features. Some branching is observed at a surfactant concentration of 0.62 wt %. Above 1 wt %, the elongated micelles show frequent branching. The electron micrographs of the 1.5 wt % solution have the appearance of the saturated network postulated by theory.

We report the results of a study on aqueous solutions of hydrophobically modified polyelectrolytes (charge-neutral diblock copolymers) by different techniques which have been specifically chosen for demonstrating unambiguously the existence of micelles. Self-diffusion measurements by fluorescence recovery after photobleaching (FRAPP) and pulsed NMR spectroscopy measure the micellar sizes which are in agreement with light scattering data on dilute solutions. Cryo-transmission electron microscopy (Cryo-TEM) pictures confirm the existence of the micellar cores in contrast with homopolyelectrolyte solutions where no features are observed.

We used cryo-TEM and light scattering to study the micellar growth and subsequent network formation in aqueous solutions of the nonionic surfactant C12E5. Cryo-TEM shows the first direct evidence for the existence of connected topology in the vicinity of the critical point and the two-phase separation curve of the C12E5/water micellar system. The coexisting phases within the two-phase region consist of one concentrated and one dilute network of interconnected cylindrical micelles. These findings are consistent with the recent theoretical explanation of criticality and phase separation in certain nonionic surfactant systems as resulting from entropic attraction between network junctions. Away from the two-phase separation curve, we have identified uniaxial micellar growth, with increasing temperature and concentration, into long threadlike micelles. From the power-law dependence of the radius of gyration, RG,z, and the hydrodynamic diameter, &Dmacr;H, on the molecular weight (RG,z, &Dmacr;H ~ Mw^ν), we find that these threadlike micelles have properties resembling those of flexible polymers in a good solvent (ν ~ 0.6). Static and dynamic light scattering show that the mean micelle contour length &Lvector; increases as c^0.5 (c is the surfactant concentration) in agreement with theory. Finally, we show that the end-cap energy Ec increases linearly with temperature.

The evolution of the droplet size distribution of a tetradecane in water emulsion, stabilized by sodium dodecyl benzene sulfonate (SDBS) was followed by cryo-TEM during a 51 day period. As a reference for the initial distribution of a freshly prepared emulsion, the size distribution of a virtually nongrowing squalane in water emulsion was also monitored. It appears that the initial distribution is right skewed and close to log-normal with a broadness parameter of σ = 0.5. This distribution evolved rapidly to a more symmetrical one. At the end of the observation the average particle size increased by a factor of about 2.5, but the limiting left skewed distribution, predicted by the LSW (Lifshitz−Slyozov−Wagner) theory, was not obtained. The ripening rate estimated from the slope of an³ (an is the number averaged radius) as a function of time is in agreement with the prediction from the LSW theory.

Direct evidence by cryogenic temperature transmission electron microscopy shows the existence of networks in microemulsions near the two-phase closed loops. Networks formed by interconnected oil-swollen cylinders were observed in the water-rich regions of the phase diagram of the C12E5 /water/n-octane system. The coexisting phases within the loops were shown to be concentrated and dilute networks. Similar micellar networks were also found in the binary system. These observations substantiate the suggested theoretical link between the structural bicontinuity and the unique phase separation and criticality of microemulsions:  All these regimes are governed by the entropic attraction between network junctions.

The aim of this study was to evaluate the effect of long-term clozapine treatment on body weight changes in neurolepticresistant chronic schizophrenic patients and to compare it with that of classical antipsychotic agents. The body mass index (BMI) of 96 neuroleptic-resistant chronic schizophrenic patients was calculated before the beginning and after long-term (mean ± SD 1.7 ± 1.3 years) clozapine treatment. These data were compared to the BMI of 98 chronic schizophrenic patients maintained on classical antipsychotic agents for a similar duration (mean ± SD 1.9 ± 1.6 years). A significant elevation in BMI was detected in both groups during these periods (P<0.0001 versus baseline, for both groups). The change in BMI (A BMI) was similar in both groups (P<0.9). We conclude that the increase in body weight caused by longterm (> 6 months) clozapine treatment is comparable to that obtained following long-term classical antipsychotic agents treatment.

Devolatilization of different types of polymer melts was studied experimentally and theoretically. The experimental work was carried out in a “falling‐strand”‐type apparatus built especially for this study. Polymer samples after devolatilization were examined by scanning electron microscopy. The micrographs obtained showed that strong nucleation of bubble nuclei occurs first in the vicinity of existing primary microbubbles. These bubble nuclei (secondary nuclei) form blisters (microbubbles) growing under appropriate conditions. The growth is controlled by momentum transfer and diffusion. The microbubbles then coalesce leading to formation of large voids and foaming of the polymer strands. The key parameter, the critical bubble radius triggering the process of growth, was assessed from the micrographs. The time dependence of the concentration of the residual styrene (dissolved gas) in polystyrene melt was determined by gas chromatography. A theoretical model of stress‐enhanced secondary nucleation in polymer melts during their devolatilization was developed. It shows that nucleation proceeds due to the growth of initially existing gas bubbles, when a sample is exposed to vacuum. In the vicinity of the bubbles homogeneous nucleation proceeds at an accelerated rate, because it is strongly enhanced by mechanical degradation of polymer macromolecules. The rate of devolatilization was calculated and compared with the experimental data. Theoretical results agreed with the experimental data rather good, although no adjustable parameters characteristic of some of the existing nucleation models were involved.

Core-corona structures of poly(ethyleneoxide)/polybutadiene (PEO/PB) block copolymer micelles are directly resolved for the first time by examining rapidly vitrified samples by transmission electron microscopy at liquid nitrogen temperature (Cryo-TEM). Spherical micelles form at higher PEO/PB block volume ratio; cylindrical form at lower block volume ratio. Images of both shapes of micelles show a dense core and a diffuse corona. The core and corona sizes agree well with theoretical prediction from the “star” model of polymer micelles.

The morphologies of fast-frozen, thin-film samples of pure and dilute solutions of salts and surfactants in hexagonal ice are investigated with transmission electron microscopy. The cold-stage microscopy technique is described briefly and limitations imposed by the equipment and the sample itself are discussed. Ice grains, grain boundaries, dislocations, and stacking faults are imaged before radiolysis from the electron beam can alter their structures. The technique shows that screw dislocations in the ice basal plane are common, in accord with observations from X-ray topography and etch-replication microscopy. It also makes visible nonbasal dislocations in hexagonal ice, including dislocations in first prismatic planes, nonprismatic dislocation loops, and stacking faults on first pyramidal planes; heretofore, these defects have not been confirmed experimentally. Implications of the work for cold-stage microscopy of microstructured fluids are mentioned.

Mixtures of water and of the nonionic surfactant C12E8(octaoxyethyleneglycol monododecylether) have been investigated by time-resolved fluorescence quenching (TRFQ) and transmission electron microscopy at cryogenic temperature (cryo-TEM) to obtain information on the size and shape of the surfactant aggregates and on the microstructure of the mixtures. The studies were performed at surfactant contents and temperatures where the micelles grew significantly and also where the systems undergo phase transitions from micellar-to-cubic upon increasing surfactant content or decreasing temperature and from cubic-to-hexagonal-to-micellar upon increasing temperature. No rapid change or discontinuity was observed in the variation of the aggregation number with the surfactant content or temperature upon crossing the micellar-to-cubic phase boundary nor at the approach of the hexagonal phase from the cubic phase. The results confirmed that the cubic phase consists of spheroidal micelles forming a three-dimensional array. The aggregation numbers at high surfactant content or temperature can be much larger than that of the minimum spherical micelle for a surfactant with a dodecyl chain, suggesting that the micelles should be anisotropic. However, cryo-TEM showed that in the micellar phase the micelles are always spheroidal. These apparently inconsistent results are explained in terms of a partial mixing of the surfactant dodecyl chains and octaoxyethylene head groups which allows for spheroidal micelles of aggregation number much larger than for a surfactant with a dodecyl chain. The results show extensive exchange of material at 40°C, taking place most likely via temporary merging of micelles in micelle clusters then present in the system.

Drag reduction, shear and extensional rheometry, and cryogenic transmission electron microscopy (cryo-TEM) were used to study aqueous solutions of one cationic surfactant, Arquad 16-50 (5 mM), with three isomeric counterions, 2-, 3-, or 4-Cl-benzoate at 12.5 mM. Each isomer showed different types of rheological and drag reduction behavior and different micellar structures. The 4-Cl system showed good drag reduction, high apparent extensional viscosity, and a thread-like micellar network, while the 2-Cl system showed no drag reduction, low apparent extensional viscosity, and only spherical micelles. The 3-Cl system was drag reducing and had high extensional viscosities at 30 °C. However, at 20 °C, the 3-Cl solution precipitated at high shear or extensional rates, leading to loss of drag reduction and low apparent extensional viscosity. The 3-Cl at 20 °C showed threadlike structures in some pictures and vesicles in others, presumably because of variations in the level of shear the samples were subjected to during sample preparation. The differences in behavior are explained by the position of the chlorine group on the benzoate ring. The hydrophobic chlorine in the 2-Cl system must reside in an unfavorable position in the aqueous phase and hence only spherical micelles are formed, which leads to no drag reduction and very low apparent extensional viscosity. The chlorine groups in the 3-Cl and 4-Cl counterions reside in the nonpolar hydrocarbon core of the micelles and, hence, stable elongated micelles can form. A schematic micellar phase diagram is proposed to summarize the transformations of surfactant molecular aggregates at different temperatures and external forces.

We present the first direct imaging of swollen lamellar phases by transmission electron microscopy on thin vitrified liquid films. We were able to obtain good contrast of the surfactant membranes. The micrographs allow the description of the microstructure of the phases and demonstrate the differences between electrostatically and sterically stabilized lamellar phases:  the first ones consist of rigid and well-ordered membranes whereas the latter consist of soft and fluctuating membranes.

A long-term study was conducted to determine the rate of re-emergence of throat carriage of meningococci in a semi-closed kibbutz community after the administration of chemoprophylaxis to all its members. Serotype B:4 was selected as marker organism since it was isolated from a fatal case and was the most frequently occurring strain (80 %) among serogroup B isolates, which themselves comprised 54 % of all meningococci. The carriage rate among Israeli residents (volunteer workers were analyzed separately) before treatment was 6.6 % (49/748) overall, with 4.3 % group B strains. Three weeks after treatment, in most cases with rifampicin (whereby three persistently positive persons were retreated with minocycline), no meningococci were recovered. Six months later, 1.9 % of a population sample aged ≤30 years were positive, while before treatment and one and three years later, 9.4 %, 8.6 % and 4.6 % respectively were positive in this age group. Serotype B:4 comprised 81.3 % of group B strains before prophylaxis, 5.3 % after one year, and 28.6 % after three years, thus possibly re-establishing itself as the single dominant serotype. The marked suppression of carriage after mass chemoprophylaxis appeared to last at least six months, with the meningococcal population being re-established within a year.

The phase behavior of a low molecular weight (Mw = 6000) symmetric triblock copolymer of poly(ethylene oxide) and poly(isobutylene), PEO−PIB−PEO, in the bulk as well in aqueous, D2O, solutions has been studied using small-angle neutron scattering and cryo-transmission electron microscopy. In aqueous solutions PEO−PIB−PEO self-associates into micelles. At low polymer concentration, the micelles predominantly have threadlike form, with lengths of typically 1−2000 Å. Those coexist, however, with spheroidal micelles of similar diameter. For a polymer concentration above roughly 20% the aggregates probably have a more disclike shape, as the micelles organize in lamellar structure. The 30% solution forms a bulk lamellar structure which, upon shear, organizes in a monodomain crystal. The bulk, PEO−PIB−PEO block copolymer forms at low temperatures a lamellar ordered phase induced by the PEO crystallization into lamellar sheets of PEO chains, presumably in helical form with a single fold. In a temperature regime near the transition temperature of Tc ≈ 45 °C, the PEO chains unfold, giving rise to significant swelling of the lamellar. Above Tc ≈ 45 °C, a strong correlation peak is observed corresponding to that observed in amorphous block copolymer systems, but it is still not clear whether this peak reflects strong concentration fluctuations of a disordered phase or the Bragg scattering of an ordered mesophase of amorphous blocks.

Abstract: Rheology, drag reduction and cryo-TEM experiments were performed on Arquad 16–50/NaSal and Ethoquad O/12/NaSal surfactant systems at different counterion-to-surfactant ratios and at constant low surfactant concentrations, 5 mM, appropriate for drag reduction. The molar ratio of counterion-to-surface was varied from 0.6 to 2.5. All the surfactant systems described here are viscoelastic and drag reducing. The viscoelasticity and drag reducing effectiveness increase with increase in counterion/surfactant ratio. Network are present in the solutions with high ratio, and they are viscoelastic. However, shear is needed to induce network formation for solutions at low ratio. Cryo-TEM images confirm the existence of thread-like micelles which form entanglement networks, and show that the micellar network becomes denser with increasing counterion/surfactant ratio in one surfactant series. Both increase in the counterion/surfactant ratio and increase in the shear rate result in shorter relaxation times. For some of these systems, abrupt increase in viscosity is observed at certain shear rates which are time effects affecting microstructure rearrangements rather than formation of shear induced structures.

Microstructures in a mixed solution of sodium dodecyl sulfate (SDS) and the oppositely charged quaternary ammonium-substituted hydroxyethylcellulose polymer JR-400 were imaged by two complementary methods: light microscopy and cryo-transmission electron microscopy. Direct images were taken of the microstructures formed throughout the interaction zones at increasing SDS concentration. In solutions of low SDS concentration, bilayer fragments, small vesicles and disc-like aggregates form. As the SDS concentration is increased and approaches charge neutrality, the solution becomes turbid. Particles imaged by light microscopy and electron microscopy indicate microphase separation with clear flocs of mainly globular structure. No microstructures were observed in the supernatant in the precipitation zone. The precipitate, made of particles of different sizes, was imaged using light microscopy. Further addition of surfactant produced a turbid solution, where electron microscopy images indicated microphase separation with well developed flocs of spherical aggregates. At higher concentrations of SDS, resolubilization took place and a variety of microstructures appeared: vesicles, disc-like and thread-like structures. Upon increased surfactant excess, resolubilization was completed with the formation of spheroidal micelles.

The mixed micellization between cetyltrimethylammonium bromide (CTAB) and the anionic dimeric surfactant disodium 1,11-didecyl-3,6,9-trioxaundecane)-1,11-disulfate (2) has been investigated by electrical conductivity (Krafft temperature, TK, critical micellization concentration, cmc, and micelle ionization degree), spectrofluorometry (cmc, micelle polarity), time-resolved fluorescence quenching (micelle aggregation numbers), and transmission electron microscopy at cryogenic temperature (microstructure of the system) in water + 50 mM NaBr. Most measurements were performed at a CTAB concentration of 5 mM, a mole fraction of 2 X = 0.091, and 30 °C. Some measurements were performed in pure water for assessing the effect of NaBr. The presence of 2 enlarged the range of temperature in which a 5 mM CTAB suspension in water + 50 mM NaBr clarifies. The initial micellization step which probably leads to micelles of 2 nearly fully neutralized by CTA⁺ ions was detected by spectrofluorometry with pyrene as fluorescent probe and took place at a CTAB concentration, C, below 0.1 mM. In both water and water + 50 mM NaBr, the electrical conductivity method was not sensitive to this micellization step. However, it detected a cmc at a much higher value of C which closely corresponds to a free CTA⁺ concentration equal to the cmc of CTAB alone. This second cmc is not detected by spectrofluorometry. The aggregation numbers of the mixed micelles are larger than those of CTAB micelles even at X as low as 0.02. At X = 0.091, the apparent aggregation number is very large, with a lower bound value of 410. Electron microscopy shows in this system the presence of vesicles and of very large aggregates, revealing that the system is close to precipitation under the experimental conditions used. Overall the results do not support the existence of the “cross-linked” micelles postulated to explain the large decrease of the NMR relaxation time T2 taking place upon addition of another anionic dimeric surfactant to the same CTAB system (Menger and Eliseev, Langmuir 1995, 11, 1855).

One recently reported application of microemulsions is as a fire-resistant hydraulic fluid where efficacy and stability depend among other factors upon the water-solubilizing capacity of the microemulsion and on the relative concentration of the surfactant. A model for such a microemulsion system has been studied using cryo-transmission electron microscopy (cryo-TEM), ¹H NMR self-diffusion, and small angle X-ray (SAXS) and neutron scattering (SANS). The phase behavior of the system containing a 1:1:2 oil:alcohol:surfactant weight ratio is characterized by a single continuous microemulsion region starting from a solution containing no water and approaching the water corner. Along this dilution line, a structural transition sequence:  oil drops → short range, noncontinuous lamellar microstructure → weakly hydrated aggregates is inferred as the water concentration is decreased. The local lamellar microstructure, i.e., stacks of surfactant sheets, oil, and water, randomly oriented in space without the long range correlations that characterize a lamellar liquid crystal is imaged for the first time.

Most industrial hydrogenators are of the dead end type where the gas is bubbled at the bottom of the apparatus, builds up a certain pressure on top of the oil, and is not recirculated. The hydrogen needed by the reaction comes partly from the fraction of the bubbles that is absorbed and partly from the gas space. It was found that sodium sulfite oxidation follows the same mixing pattern, i.e., the highest rate of oxidation always occurred in the upper half of the liquid and correlated strongly with the Reynolds number of the turbine. it is shown that for Reynolds numbers above 600 the optimum impeller position is about two thirds the liquid height measured from the bottom of the vessel. Information is given regarding the variations in selectivity, isomerization and hydrogenation of oils when the speed, relative location and dimensions of the turbine are varied.

Most industrial hydrogenators are of the dead end type where the gas is bubbled at the bottom of the apparatus, builds up a certain pressure on top of the oil, and is not recirculated. The hydrogen needed by the reaction comes partly from the fraction of the bubbles that is absorbed and partly from the gas space. It was found that sodium sulfite oxidation follows the same mixing pattern, i.e., the highest rate of oxidation always occurred in the upper half of the liquid and correlated strongly with the Reynolds number of the turbine. it is shown that for Reynolds numbers above 600 the optimum impeller position is about two thirds the liquid height measured from the bottom of the vessel. Information is given regarding the variations in selectivity, isomerization and hydrogenation of oils when the speed, relative location and dimensions of the turbine are varied.

Vascular transformation of lymph node sinuses is an uncommon condition and only isolated cases have been reported. It is characterized by conversion of nodal sinuses into capillary-like channels, often accompanied by fibrosis. Venous or lymphatic obstruction is thought to be the underlying mechanism, and in most cases factors that may contribute to lymphovascular obstruction can be identified such as tumour in the vicinity, vascular thrombosis, heart failure, previous surgery or radiotherapy. Most cases involve abdominal lymph nodes, and head and neck involvement is rare. We present two cases of vascular transformation of lymph node sinuses presenting only as cervical lymphadenopathy, without an obvious cause of lymphovascular obstruction.