Tensiometric Measurements Research Articles

Synthesis and Characterization of Ruthenium Doped TiO2Nanofibers

Ruthenium(Ru)-doped <TEX>$TiO_2$</TEX> nanofibers were prepared using electrospun Ru-<TEX>$TiO_2$</TEX>/poly(vinyl acetate) (PVAc) fibers and subsequent annealing for 1 h at temperatures in the range of <TEX>$500^{\circ}C$</TEX> to <TEX>$1000^{\circ}C$</TEX> in air. The properties of the Ru-<TEX>$TiO_2$</TEX> fibers were characterized as a function of the Ru content and calcination temperature using X-ray diffraction, thermal gravimetry with differential scanning calorimetry, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, and viscometer, pycnometer and dynamic tensiometer measurements. Although the diameter of the fiber decreased slightly with increasing calcination temperature, no dramatic changes were observed with respect to the ruthenium content. The XRD and FT-IR results revealed that anatase phase and ruthenium metal began to be formed after calcination at temperatures above <TEX>$500^{\circ}C$</TEX>. Anatase and rutile phases and ruthenium metal coexisted in the fibers calcined above <TEX>$600^{\circ}C$</TEX>. No anatase phase was detected in the fibers containing ruthenium when they were calcined at <TEX>$1000^{\circ}C$</TEX>. The morphology of the fibers changed from smooth and uniform to porous with increasing temperature. The experimental results suggest that the calcination temperature and Ru content were influential in determining the morphology and structure of the fibers.

Simplified Multistep Outflow Method to Estimate Unsaturated Hydraulic Functions for Coarse‐Textured Soils

Although the multistep outflow (MSO) method is well suited for the estimation of soil hydraulic properties by inverse solution techniques, this method has not been widely adopted because it requires advanced instrumentation and is time consuming. The objective of this study was to develop a modified version of the multistep outflow technique that largely simplifies laboratory procedures and reduces costs and time. The numerical inversion procedures require applying user‐friendly HYDRUS software to estimate fitting parameters for soil water retention and unsaturated hydraulic conductivity curves. Whereas values of saturated water content and saturated hydraulic conductivity must be measured independently, the remaining functional parameters are estimated using an inverse solution of a transient drainage experiment using multiple suction steps and a hanging water column, with drainage outflows measured during drainage. A comparison test showed that the simplified experiment without tensiometric measurements provided sufficient information in the parameter identification compared with a traditional pressure outflow experiment with tensiometric measurements for an Oso Flaco sand and a loamy sand field soil in the suction range of 0 to 17 kPa.

Microencapsulation of bioactive bilberry anthocyanins by means of whey protein gels

Microencapsulation is a promising possibility to stabilise anthocyanins in foods. However, the use of protein hydrogels as matrix materials for microcapsules has not yet been investigated. In this study we show that by means of the emulsion method thermally induced whey protein-based microcapsules which are applicable for the encapsulation of an anthocyanin-rich bilberry extract can be generated from whey protein solutions. The influence of manufacturing conditions, like stirrer speed and emulsifier addition, on the morphological properties of the microcapsules at pH 1.5 and pH 3 was assessed. In tensiometric measurements, the water-in-oil (w/o)-emulsifiers phosphatidylcholinedepleted lecithin (PCDL) and Span 80 significantly reduced the interfacial tension at the w/o-interface in the presence of the whey proteins in the water phase and were therefore applied for the production of microcapsules. When no emulsifier or the emulsifier Span 80 was used during the microencapsulation process, aggregated and coalesced microcapsules were obtained. This indicates a loss of the interfacial activity of Span 80 due to the conditions during microencapsulation. Only PCDL was effective in stabilising the emulsion droplets during gelation and the mean diameter of the generated microcapsules could be significantly decreased to 20–70μm. Finally, microcapsules containing up to 10% bilberry extract with a mean diameter below 50μm could be prepared by use of PCDL. For this, a microcapsule formed at pH 1.5 was favourable for the encapsulation of bilberry extract due to observed detrimental interactions between whey proteins and bilberry extract compounds at pH 3. The results of this study shall help to facilitate the development of innovative protein-based encapsulation systems using the emulsion method.

Structures and hydrologic function of soil landscapes with kettle holes using an integrated hydropedological approach

The hummocky post-glacial soil landscapes with kettle holes as internal drainage systems are characterized by ponds that trap lateral fluxes in topographic depressions. A quantitative description is mostly limited by the unknown complexity of hydraulically relevant soil and sediment structures. This paper is focussing on a structure-based approach to identify relevant field-scale flow and transport processes. Illustrative examples demonstrate extreme variations in water table fluctuation for adjoining kettle holes. Explanations require a pedohydrologic concept of the arable soil landscape. Identification of structures is based on geophysical methods and soil hydraulic measurements. Electrical resistivity imaging yields 0.5 m-scale spatial structures that correspond with soil texture distributions. Electromagnetic induction provides larger-scale field maps that reflect major soil and sediment features. Results of both methods correspond within the limits of the different spatial resolutions. With geophysical exploration methods, colluvial areas with textural differences between upper and deeper soil layers, coarse-textured sediment lenses, and stony colluvial regions around kettle holes are identified as potentially relevant flow structures. The colluvial fringe around the pond seems to be a sensitive area with important lateral exchange fluxes. Tensiometer measurements perpendicular to this boundary indicate hydraulic gradients directed from the pond towards the partially saturated soil. The localized infiltration of trapped water in kettle holes can control large fractions of ground water recharge and may have implications for the fate of agricultural chemicals in post-glacial landscapes. While surface and subsurface hydraulic structures may be inferred using minimal-invasive techniques, better understanding of processes and properties governing lateral exchange fluxes between pond and surrounding soil are required.

Potentiometric Titrations of Five Synthetic Tetraacids as Models for Indigenous C80 Tetraacids

The acid/base properties, critical micelle concentrations (cmcs), and pH-dependent solubility of five synthetic tetraacids have been studied at several ionic strengths (20-600 mM NaCl) and in the pH range of 1.5-11 using high precision potentiometric titrations, tensiometer measurements, and UV spectroscopy, respectively. The molecular weight of the tetraacids ranged between 478 and 983 g/mol. The potentiometric titration data was evaluated in terms of thermodynamic equilibrium models, developed in the light of relevant solubility data, Langmuir monolayer compressions and cmc of the different tetraacids. The results indicate that for two of the tetraacids, called BP5 and BP7, two chemical forms fully dominate the speciation of the monomers; the insoluble fully protonated form, and the soluble fully deprotonated form. The partly protonated species, only play a very minor role in the speciation of these tetraacids. For the other tetraacids the results are more complicated; for the smallest tetraacid, called BP1, all species seem to play important roles, and for the most hydrophobic, BP10, the formation of micelles and aggregates severely complicates the evaluation of the speciation. For the tetraacid BP3 one of the partly deprotonated forms seems to be important, thus confirming the structure to properties relationship. In spite of the complicated micelle formation chemistry, and although not actually measured, the acid/base properties for the monomers of BP10 were interpreted by means of surface charge densities of the micellar aggregates. The modeling indicates an increase of the aggregation number of the micelle upon acidification, a result of formation of mixed micelles incorporating the fully protonated and deprotonated species. An intrinsic pK(a) of 5.4 for BP5 was used to model the monomer pK(a) of BP10, and corresponded well with a monolayer acidity constant pK(s)(a) of 5.5 obtained from surface collapse pressures of Langmuir monolayers as a function of pH.

Effect of spacer length on the micellization and interfacial behavior of mixed alkanediyl-α,ω-bis(dimethylcetylammonium bromide) Gemini homologues

The interfacial and micellization properties of binary and ternary mixtures of Gemini homologues, viz., tetramethylene-1,4-bis(N-hexadecyl-N,N-dimethylammonium bromide), pentamethylene-1,5-bis(N-hexadecyl-N,N-dimethylammonium bromide), and hexamethylene-1,6-bis(N-hexadecyl-N,N-dimethylammonium bromide), with various compositions were investigated at 25 degrees C using conductometric and tensiometric measurements. The micellar and adsorption characteristics like composition, activity coefficients, mutual interaction parameter, minimum area per molecule, free energy of micellization and adsorption have been evaluated and compared. The ideality/nonideality of the mixed micelles were tested in light of Clint, Rubingh, and Rubingh-Holland approaches. The mixed systems were found to undergo synergistic interaction, more so in mixed monolayer than in mixed micelle formation, and the micellar and interfacial properties were found to depend on the selection of surfactant pairing.

Spatial variability of steady-state infiltration into a two-layer soil system on burned hillslopes

Rainfall–runoff simulations were conducted to estimate the characteristics of the steady-state infiltration rate into 1-m 2 north- and south-facing hillslope plots burned by a wildfire in October 2003. Soil profiles in the plots consisted of a two-layer system composed of an ash on top of sandy mineral soil. Multiple rainfall rates (18.4–51.2 mm h −1 ) were used during 14 short-duration (30 min) and 2 long-duration simulations (2–4 h). Steady state was reached in 7–26 min. Observed spatially-averaged steady-state infiltration rates ranged from 18.2 to 23.8 mm h −1 for north-facing and from 17.9 to 36.0 mm h −1 for south-facing plots. Three different theoretical spatial distribution models of steady-state infiltration rate were fit to the measurements of rainfall rate and steady-state discharge to provided estimates of the spatial average (19.2–22.2 mm h −1 ) and the coefficient of variation (0.11–0.40) of infiltration rates, overland flow contributing area (74–90% of the plot area), and infiltration threshold (19.0–26 mm h −1 ). Tensiometer measurements indicated a downward moving pressure wave and suggest that infiltration-excess overland flow is the runoff process on these burned hillslope with a two-layer system. Moreover, the results indicate that the ash layer is wettable, may restrict water flow into the underlying layer, and increase the infiltration threshold; whereas, the underlying mineral soil, though coarser, limits the infiltration rate. These results of the spatial variability of steady-state infiltration can be used to develop physically-based rainfall–runoff models for burned areas with a two-layer soil system.

Design of a User‐Friendly Automated Multistep Outflow Apparatus

The multistep outflow (MSO) test is a widely used laboratory method for direct measurement of the soil moisture retention curve, θ(h), or indirect estimation of θ(h) and the unsaturated hydraulic conductivity curve, K(h). Manual MSO testing is time consuming and while automated systems have been described in the literature, many require significant effort to fabricate and operate, or have not been described in sufficient detail to allow rapid setup and implementation by others. In this work, a user‐friendly, easily assembled, automated multistep outflow (AMSO) test apparatus was designed and built using National Instruments (Austin, TX) hardware and LabVIEW software. Control codes were written to support four testing regimes. The first option allows the pressure steps to be set manually while continuously measuring the water level in the burette. Three fully automated options are also available in which pressure steps are changed automatically after (i) a user‐specified time period has elapsed, (ii) water level changes in the burette are negligible, or (iii) tensiometer measurements of the soil‐water pressure head in the sample become constant for a specified period of time. To verify performance, five soil samples were subjected to a manual hanging column test and then retested using the automated system. Good correspondence between soil moisture values at the applied pressure steps with manual and AMSO tests was observed (RMSE values &lt; 0.0125 m3 m−3). Two samples were also drained and rewetted with the new system to show its utility for studying hysteresis.

Interfacial and micellar properties of anionic azo dye-surfactant binary systems

The association of an anionic dye C.I. Reactive Orange 16 (RO16) and different types of surfactants, i.e., anionic surfactant sodium dodecylsulfate, nonionic surfactants poly(oxyethylene) ethers (C m POE10, m = 12, 16, and 18; C12POE n , n = 4, 10, and 23), was investigated using tensiometry in a certain micellar concentration range. RO16 was shown to aggregate in water when its concentration is above the threshold value. The surface tension lowering and critical micellar concentration (CMC) values were interpreted on the same grounds as those for surfactants mixtures. The tensiometric measurements of dye-surfactant systems are carried out as a function of the molar concentration of solution at 25°C. Using Rubingh’s regular solution theory, the values of interaction parameters were found to be negative for all studied binary mixtures. These negative values indicate that there is an attractive interaction of the surfactants in mixed micelles and reflect synergistic behavior of a mixture. In all studied systems, deviations from ideal behavior were observed depending on the type of surfactant. Interaction parameters calculated using regular solution theory are changed from −2.62 to −12.43. The smallest deviation from ideal behavior is obtained for the RO16-C12POE4 mixed system; i.e., in the case when nonionic surfactant has the shortest alkyl chain and the smallest number of ethylene oxide units.

EFFECTS OF HETEROGENEOUS FLOW ON DISCHARGE GENERATION AND SOLUTE TRANSPORT

After dye tracer tests that confirmed significant finger flow in a sandy soil, an undisturbed soil monolith with a volume of 0.78 m 3 (r = 0.5 m) was extracted and mounted on a lysimeter stand. The aim was to experimentally quantify finger flow effects on the flux field as characterized by measurements of soil water pressure head (ψ) and volumetric soil water content (θ), and on discharge generation and solute transport. The experimental setup allowed discharge registration from six triangular center compartments and one side-wall segment. Time domain reflectometry and tensiometer measurements taken during an 80-day infiltration experiment at several locations within the lysimeter confirmed the nonhomogeneity of the flux pattern at early stages of the experiment. However, calculations of the hydraulic gradient suggested that the hydraulic conditions within the soil profile had nearly equilibrated after 7 days of continuous infiltration at 0.26 mm h -1 . Nevertheless, the onset of discharge varied between lysimeter segments by up to 33 days, demonstrating the profound effect of finger flow on water flux variability. Final flux rates varied consistently between spatial segments by a factor of 5 over 13 days, confirming the persistence of established flow regions. Initially, dry soil areas delivered less discharge, although the possibility of three-dimensional flux patterns with water exchange between segments did not allow us to draw definite conclusions for all lysimeter segments. Although discharge was generated from all segments, tracer leaching data indicated that large fractions of the soil monolith were almost nonoperational in solute transport. It is concluded that two- or three-dimensional flux field patterns obtained from ψ and θ measurements at the onset of infiltration events are helpful in quantitatively deducing discharge variability. At later stages of infiltration, however, spatial θ data may be insufficient to explain discharge variability over a given flux plane. Especially in coarse-textured single-grained substrates that possess material functions that are characterized by a steep increase in hydraulic conductivity in the near-saturation range, the resolution of measurements might be insufficient to detect minor variations in θ and w that cause large differences in flow and transport.

A new application of ionic liquids: hydrophobic properties of tetraalkylammonium-based poly(ionic liquid)s

The potential of using poly(ionic liquid)s as a new family of hydrorepellent materials has been explored. Free-radical polymerization of a series of ionic liquids based on the polymerizable cation [2-(methacryloyloxy)ethyl]trimethylammonium and on the hydrophobic anions bis(trifluoromethylsulfonyl)imide, nonafluoro-1-butanesulfonate and dodecylbenzenesulfonate led to the corresponding poly(ionic liquid)s that were characterized by TGA and DSC analysis, SEM, MALDI-TOF and XPS spectroscopy. Contact angle investigations show that the nature of the surface of the poly(ionic liquid)s based on the nonafluoro-1-butanesulfonate and dodecylbenzenesulfonate anions are featured by remarkable hydrophobic properties with advancing contact angles (θadv) lying in the range 113–118°, while to the polymer poly[2-(methacryloyloxy)ethyl]trimethylammonium bis(trifluoromethylsulfonyl)imide is associated poor hydrorepellent activity (θadv = 76°). The tensiometric measurements also experience receding contact angles (θrec) lying in the range 16–20° and a consequent high hysteresis suggesting that, on the outermost layers of the polymers, very high and very low-energy surface portions are present.

Secondary structure and orientation of the pore-forming toxin lysenin in a sphingomyelin-containing membrane

Lysenin is a sphingomyelin-recognizing toxin which forms stable oligomers upon membrane binding and causes cell lysis. To get insight into the mechanism of the transition of lysenin from a soluble to a membrane-bound form, surface activity of the protein and its binding to lipid membranes were studied using tensiometric measurements, Fourier-transform infrared spectroscopy (FTIR) and FTIR-linear dichroism. The results showed cooperative adsorption of recombinant lysenin-His at the argon–water interface from the water subphase which suggested self-association of lysenin-His in solution. An assembly of premature oligomers by lysenin-His in solution was confirmed by blue native gel electrophoresis. When a monolayer composed of sphingomyelin and cholesterol was present at the interface, the rate of insertion of lysenin-His into the monolayer was considerably enhanced. Analysis of FTIR spectra of soluble lysenin-His demonstrated that the protein contained 27% β-sheet, 28% aggregated β-strands, 10% α-helix, 23% turns and loops and 12% different kinds of aggregated forms. In membrane-bound lysenin-His the total content of α-helices, turns and loops, and β-structures did not change, however, the 1636cm −1 β-sheet band increased from 18% to 31% at the expense of the 1680cm −1 β-sheet structure. Spectral analysis of the amide I band showed that the α-helical component was oriented with at 41° to the normal to the membrane, indicating that this protein segment could be anchored in the hydrophobic core of the membrane.

Diapause hormone in the corn earworm, Helicoverpa zea: Optimum temperature for activity, structure–activity relationships, and efficacy in accelerating flesh fly pupariation

Diapause hormone (DH) effectively terminated pupal diapause in Helicoverpa zea. This effect was temperature-dependent, with an optimum of 21 °C. The dose–response curve indicated an ED 50 of DH for diapause termination of approximately 100 pmol. The core sequence and essential amino acids were determined by bioassays using modified and truncated DH analogs. A C-terminal hepta-peptide, LWFGPRLa, was the core sequence required for diapause termination. Activity was lost when Alanine was substituted for any of the amino acids in the hepta-peptide, with the exception of Glycine. A fragment series of analogs suggested that the amide and Arginine were the most important components needed for terminating diapause. Leucine, Tryptophan, and Phenylalanine at the N-terminus of the hepta-peptide were also critical for activity. The C-terminal Leucine was less important: deletion resulted in decreased activity, although it could not be substituted by Alanine. The fact that a portion of the DH sequence is similar to the pyrokinin that accelerates fly pupariation prompted us to also evaluate the capability of DH to accelerate development in the flesh fly, Sarcophaga bullata. The threshold dose of DH essential to accelerate fly pupariation was 5 pmol for immobilization/retraction and longitudinal contraction and 10 pmol for tanning, approximately one or two orders of magnitude lower than the effective dose required for diapause termination in H. zea. Tensiometric measurements revealed that DH affected neuromuscular patterns of pupariation behavior and associated cuticular changes in a manner similar to that of the fly pyrokinins and their analogs.

Spontaneous change in thermosensitive properties of aqueous solutions of poly(N,N-dimethylaminoethyl methacrylate) and its mixtures with sodium dodecyl sulfate

It is shown that the properties of aqueous solutions of poly(N,N-dimethylaminoethyl methacrylate) are unstable over time: the pH value spontaneously decreases, the phase separation temperature grows, and the light scattering ability of dispersions arising above the said temperature weakens. These effects are enhanced after dilution of solutions, become less pronounced with an increase in pH, and disappear when the solutions are isolated from atmosphere (under argon). It is inferred that the lability of the indicated properties is associated with acidification of polymer solutions due to their interaction with air carbon dioxide and the enhancement of protonation of macromolecules. Potentiometric and tensiometric measurements have demonstrated that upon introduction of sodium dodecyl sulfate into solutions of poly(N,N-dimethylaminoethyl methacrylate), the surfactant-polymer interaction slows down owing to a spontaneous increase in the charging of macromolecules in the course of time.

Modification of Tryptophan and Methionine Residues Is Implicated in the Oxidative Inactivation of Surfactant Protein B

Exposing BLES (bovine lipid extract surfactant), a clinical surfactant, to reactive oxygen species (ROS) alters surfactant protein B (SP-B), as indicated by Coomassie Blue staining, silver staining, and Western analysis. Hypochlorous acid (HOCl) treatment leads to elevated maximum surface tension (gammamax) and a deterioration in minimum gamma (gammamin) during surface area cycling. Fenton reaction resulted in immediate increases in gammamin and gammamax. Intrinsic fluorescence measurements indicated Fenton, but not HOCl, induced conversion of Trp9 of SP-B to hydroxyTrp (OHTrp), N-formylkynurenine (NFKyn), and kynurenine (Kyn). Electrospray ionization mass spectrometry (ESI-MS) revealed molecular weight alterations consistent with oxidation of Met (HOCl, Fenton) and Trp (Fenton) residues. Oxidative alterations to Met29 and Met65 (HOCl, Fenton) and to Trp9 (OHTrp with HOCL and NFKyn plus Kyn with Fenton) were confirmed by matrix-assisted laser desorption mass spectrometry (MALDI-MS) studies on SP-B tryptic fragments. Some Met oxidation was observed with control SP-B. When taken together with captive bubble tensiometer measurements, these studies suggest that Met oxidation of SP-B by HOCl or Fenton interferes with phospholipid respreading during compression-expansion of surfactant films, while Fenton oxidation, which produces more extensive Met oxidation and disruption of the indole ring of Trp9, further abrogated the ability of such films to attain low surface tensions during compression. These studies provide insight into the manner by which ROS generated during acute lung injury and the acute respiratory distress syndrome act to inhibit not only endogenous surfactant but also therapeutic surfactants administered to counteract these conditions.

Micellar, interfacial and fluorescence investigation on binary mixtures of dodecyl cationic surfactants in aqueous media

The critical micelle concentration (cmc) of binary mixtures of C 12-triphenyl phosphonium, pyridinium and trimethyl ammonium bromides were determined employing conductometry, surface tensiometry and fluorescence techniques. Binary mixtures of C 12 phosphonium bromide with C 12 trimethyl ammonium and pyridinium bromide surfactants exhibited second breaks due to the structural micellar transition, and are supported by conductometric and flurometric methods. The values of surface excess, minimum area of the C 12 surfactants at the cmc and Gibbs energy of adsorption were evaluated. The ideality/non-ideality of the mixing was analysed using regular solution theory (RST) to obtain the composition of the mixed micelle and the interaction parameter ( β m) to evaluate the strength of interactions of surfactants in the mixed micelles. The tensiometric measurements were also analysed to obtain the interaction parameter ( β σ) for the mixed monolayer at the air/water interface. Activity coefficients and the excess free energy of mixing were also determined.

Sampling Silica and Ferrihydrite Colloids with Fiberglass Wicks under Unsaturated Conditions

The suitability of passive capillary samplers (PCAPS) for collection of representative colloid samples under partially saturated conditions was evaluated by investigating the transport of negatively and positively charged colloids in fiberglass wicks. A synthetic pore water solution was used to suspend silica microspheres (330 nm in diameter) and ferrihydrite (172 nm in diameter) for transport experiments on fiberglass wicks. Breakthrough curves were collected for three unsaturated flow rates with silica microspheres and one unsaturated flow rate with ferrihydrite colloids. A moisture characteristic curve, relating tensiometer measurements of matric potential to moisture content, was developed for the fiberglass wick. Results indicate that retention of the silica and the ferrihydrite on the wick occurred; that is, the wicks did not facilitate quantitative sampling of the colloids. For silica microspheres, 90% of the colloids were transmitted through the wicks. For ferrihydrite, 80 to 90% of the colloids were transmitted. The mechanisms responsible for the retention of the colloids on the fiberglass wicks appeared to be physicochemical attachment and not thin-film, triple-phase entrapment, or mechanical straining. Visualization of pathways by iron staining indicates that flow is preferential at the center of twisted bundles of filaments. Although axial preferential flow in PCAPS may enhance their hydraulic suitability for sampling mobile colloids, we conclude that without specific preparation to reduce attachment or retention, fiberglass wicks should only be used for qualitative sampling of pore water colloids.

Self aggregation of binary surfactant mixtures of a cationic dimeric (gemini) surfactant with nonionic surfactants in aqueous medium

Solubility, tensiometric, fluorometric and dynamic light scattering (DLS) measurements have been used to elucidate the self aggregation of a mixture of alkanediyl-α,ω type cationic gemini surfactant [(C 16H 33N +(CH 3) 2 (CH 2) 10N +(CH 3) 2C 16H 33)2Br −], 16-10-16, 2Br − with POE nonionic surfactants [CH 3(CH 2) 10CH 2-(OCH 2CH 2) 6OH], C 12E 6 and [(CH 3) 3CCH 2C(CH 3) 2C 6H 4-(OCH 2CH 2) 9.5OH] Triton X-100. The critical micelle concentrations (cmc) of the binary mixtures have been investigated at well above their Krafft temperatures in aqueous medium by tensiometric (at different temperatures at 5 °C interval) measurements. Surprisingly it was observed that the Krafft temperatures of binary mixtures were higher than the pure gemini surfactant. Application of the regular solution model to the experimental data yield the interaction parameter at mixed micelles ( β m), and at the air–water interfaces ( β σ), which indicate an attractive interaction and reflect the synergistic behavior in both 16-10-16, 2Br −/C 12E 6 and 16-10-16, 2Br −/TX 100 systems. The micelle aggregation numbers ( N agg) of the binary combinations fall between those of constituent surfactants. The micropolarity values of various combinations and the binding constants ( K sv) were determined from the ratio of intensity of peaks ( I 1/ I 3) of pyrene fluorescence emission spectrum and its quenching, respectively. The micellar interiors were found to be reasonably polar. By using Maeda's concept, it was observed that the chain–chain interactions were very important for stability of mixed micelles in these systems. The hydrodynamic radius ( R h) of TX 100 was higher than that of 16-10-16, 2Br − while the mixed aggregates have intermediate values of R h.

Spatial and temporal distribution of root water uptake of an almond tree under microsprinkler irrigation

The spatial and temporal pattern of root water uptake in partially wetted soil was studied in the root zone of a 6-year-old microsprinkler-irrigated almond tree. The water balance of about one quarter of the root zone's wetted soil volume (2.0·2.0·0.9 m 3 ) was deter- mined by catch cans, neutron probe and tensiometer measurements. Twenty-five neutron probe access tubes with catch cans were distributed in a square grid of 50 cm spacing. Eight pairs of tensiometers were installed at depths of 82.5 and 97.5 cm in a regular pattern be- tween the access tubes. Neutron probe readings at 15 cm depth increments and tensiometer readings were taken at time intervals of 4-24 h. The rate of soil water depletion was calculated and used to estimate the spatial and temporal distributions of root water uptake. Soil water dynamics was studied in two stages: (1) during a week of conventional irrigation management with three irriga- tion events; and (2) during a period of 16 days without irrigation, after the monitored soil volume was thor- oughly moistened so that soil water was easily available everywhere, initially. The zones of maximum root water uptake were the same for both stages in periods of high local rates of water application. After water applica- tions, root water uptake occurred initially near the tree trunk and then progressed towards the root system periphery, thereby changing locations of maximum root water uptake and shifting to root zone regions with minimum soil water stress.

Fluorosurfactants at Structural Extremes: Adsorption and Aggregation

Fluorosurfactants with several structural modifications have been synthesized, and the air/water interface and bulk aggregation properties investigated. The compounds were fluorinated ethylene oxide (EO) nonionics where the number and position of the hydrophilic group(s) has been radically altered to generate linear, bolaform, and Y-shaped analogues. A noticeable structure-interfacial packing relationship was observed via both tensiometric measurements and neutron reflection studies: the limiting molecular areas, a(cmc), and surface excesses, gamma(cmc), are strongly dependent on the number and position of the EO headgroups. Differing bulk aqueous properties were also observed. Small-angle neutron scattering shows an evolution of micelle structure from cylindrical to disk-like aggregates on changing from Y-shaped to bolaform molecular structure.