Increased Surface Activity Research Articles

Comparative study of the emulsifying and foaming properties of defatted coriander ( Coriandrum sativum) seed flour and protein concentrate

Emulsifying and foaming properties were determined for coriander protein products (defatted flour and protein concentrate) at pH 4.0, 7.0 and 9.0 and the results compared with those obtained for defatted soybean flour. Mean oil droplet size and interfacial protein concentration was smallest for emulsions (∼17% oil, v/v) stabilized by the coriander protein concentrate, when compared to the coriander and soybean flours. Polypeptide composition of the interfacial protein membrane of the emulsions was different from the polypeptide composition present in the respective coriander flour and protein concentrate. In contrast, soybean flour-stabilized emulsions contained similar polypeptide composition to that of the flour. Soybean flour formed the greatest amount of foams at pH 4.0, 7.0 and 9.0 followed by the coriander flour, which had greater amounts of foam at pH 4.0 and 5.0. The foam stability of both the coriander flour and protein concentrate were significantly ( P⩽0.05) less than those of the soybean flour. It was concluded that the reduced level of non-protein components in the coriander protein concentrate favoured increased surface activity at the oil–water interface but not at the air–water interface.

Evidence that the parasitic nematode Skrjabinoclava manipulates host Corophium behavior to increase transmission to the sandpiper, Calidris pusilla

We found evidence that a nematode (Skrjabinoclava morrisoni) adaptively manipulates the behavior of its intermediate host (the amphipod Corophium volutator) to increase its likelihood of transmission to its final host (the semipalmated sandpiper, Calidris pusilla). We found that male and female amphipods parasitized by nematodes increased their surface activity in the field during daytime, but not during nighttime hours. Increased surface activity is known to increase susceptibility of amphipods to predation by sandpipers during the day, but not at night, when sandpipers do not feed visually. Also, as predicted by the manipulation hypothesis, only late-stage (infective) larvae of nematodes were associated with behavioral changes of amphipods. We found no evidence that parasites were associated with other amphipod behaviors in the laboratory, such as trail complexity, distance traveled, or burrow-probing activity of crawling males as would be expected if parasitized hosts altered their own behavior. Survivorship of amphipods was also unaffected by parasitism, which may favor parasite transmission. Thus, behavioral changes of parasitized hosts were simple, and their expression was context-dependent and related to likelihood of predation. We argue that maturation times of nematodes in relation to migration schedules of sandpipers provide a narrow window of opportunity and may explain why nematodes manipulate amphipod behavior. Key words: amphipod, Bay of Fundy, Calidris pusilla, Corophium volutator, host behavior, nematodes, parasite manipulation, sandpipers, Skrjabinoclava morrisoni. [Behav Ecol 10:351‐357 (1999)]

Surface characterization of electrochemically oxidized carbon fibers

High strength PAN-based carbon fibers were continuously electrochemically oxidized by applying current to the fibers serving as an anode in 1% wt aqueous KNO3. Progressive fiber weight loss occurred with increasing extents of electrochemical oxidation. XPS studies (C 1s and O 1s) indicated that the oxygen/carbon atomic ratio rose rapidly to 0.24 as the extent of electrochemical oxidation was increased from 0 to 133 C/g and then remained almost constant as the extent of electrochemical oxidation rose to 10 600 C/g. Fitting the C 1s spectra demonstrated that the rise in surface oxygenated functional groups was mainly due to an increase in carboxyl (COOH) or ester (COOR) groups. An increase in the intensity of the O 1s peak (534.6–535.4 eV) after electrochemical oxidation corresponded to chemisorbed oxygen and/or adsorbed water. Electrochemical oxidation increased surface activity by generating more surface area via the formation of ultramicropores, and by introducing polar oxygen-containing groups over this extended porous surface. FT-IR spectra showed a broad peak at about 1727 cm−1 from C=O stretching vibrations of carboxyl and/or ketone groups, the relative intensity of which increased significantly with the extent of electrochemical oxidation. Post-oxidation heat-treatments in flowing nitrogen at 550°C for 30 min. caused further weight losses due to decarboxylation of carboxyl groups and other reactions in which oxygenated functions decomposed. These weight losses increased with the extent of electrochemical oxidation. This demonstrated that more oxygenated groups formed on the internal pore surfaces as pores increasingly penetrated deeper into the fibers with increased electrochemical treatment. Weight loss depended on the heat treatment temperature since different types of carbon–oxygen surface groups were formed during the electrochemical oxidations. Different functions have different abilities to decarboxylate or decarbonylate. The amount of Ag+ and NaOH uptake by electrochemically oxidized fibers rapidly decreased as the temperature of the post heat treatment increased to 550°C. Beyond 550°C the progressive decrease in Ag+ adsorption and NaOH uptake continued at a slower rate and approached 0 μmol/g after heating to 850°C. Conversely, after heat treatment I2 adsorption showed a marked increase as the treatment temperature was raised. Thermal decomposition of carbon–oxygen complexes within the pore structure leads to a lower hydrophilicity of the pore surface. The extensive micropore surface area generated by electrochemical oxidation becomes more accessible to I2 as CO2 and CO evolve. Very narrow pores (<10 Å diameter) blocked by hydrogen bonding and oxygenated functions become more open. XPS analyses illustrated that the surface oxygen content decreased significantly after heat-treating to 550 or 850°C and was lowest after the 850°C treatment.

Neutron Reflectivity of Adsorbed Water-Soluble Block Copolymers at the Air/Water Interface: the Effects of Composition and Molecular Weight

We have used neutron reflection to follow the effects of composition and molecular weight on the structure of layers of poly(2-(dimethylamino)ethyl methacrylate-block-methyl methacrylate) copolymer (poly(DMAEMA-b-MMA)) adsorbed at the air/water interface. We had previously shown that for a 70% DMAEMA copolymer of M n about 10K at a pH of 7.5 there is a surface phase transition from a layer about 20 A thick to one about 40 A thick and that the adsorbed layer at the higher concentration has a layered cross-sectional structure with the most hydrophobic part of the polymer forming a central layer rather than the outer layer in contact with air, as would be expected. The present work shows that copolymers containing 80% DMAEMA (about the same M n ) and 70% DMAEMA (M n about 20K) form the same layered structure at the surface. The 80% DMAEMA copolymer is more surface active than the 70% copolymer, and this parallels the tendency to aggregate into micelles in bulk solution. The increase in molecular weight from 10K to 20K decreases the surface activity of the 70% DMAEMA copolymer. Addition of electrolyte enhances the formation of the layered structure at the interface but tends to equalize the surface activities of the three copolymers. Other surprising features are the increase of surface activity with increasing polyelectrolyte block size when the block is the larger component and the apparent suppression of ionization in the surface region.

Zwitterionic (Ammoniomethyl)tetrafluorosilicates of the Formula Types F4SiCH2NH2(CH2)nMe (n = 5−11) and F4SiCH2NMe2(CH2)5Me: A New Class of Highly Efficient Surface-Active Compounds

The zwitterionic (ammoniomethyl)tetrafluorosilicates F4SiCH2NH2(CH2)nMe (n = 5−11; compounds 4−10) were synthesized by reaction of the corresponding (aminomethyl)triethoxysilanes (EtO)3SiCH2NH(CH2)nMe (n = 5−11; compounds 13−19) with HF. The silanes 13−19 were obtained by reaction of (EtO)3SiCH2Cl with the corresponding n-alkylamines H2N(CH2)nMe (n = 5−11). The zwitterionic (ammoniomethyl)tetrafluorosilicate F4SiCH2NMe2(CH2)5Me (11), the N,N-dimethyl derivative of 4, was synthesized by reaction of (MeO)3SiCH2NMe2 with n-C6H13Br, followed by reaction of the resulting quaternary ammonium salt [(MeO)3SiCH2NMe2(CH2)5Me]Br with HF. Compounds 4−11 are characterized by the presence of a pentacoordinate (formally negatively charged) silicon atom and a tetracoordinate (formally positively charged) nitrogen atom. F4SiCH2NH2(CH2)9Me (8) was structurally characterized by single-crystal X-ray diffraction. The coordination polyhedron around the silicon atom of 8 in the crystal is a slightly distorted trigonal bipyramid, with fluorine atoms in the axial positions (Berry distortion 8%). Intermolecular N−H···F hydrogen bonds influence the packing of the zwitterions in the crystal. Surface tension measurements with solutions of 4−11 in 0.01 M hydrochloric acid demonstrated that these compounds are highly efficient surfactants. Increase of the n-alkyl chain length (4 → 10) was found to result in an increase of surface activity. The equilibrium surface tension vs concentration isotherms for 4 and 11 (solutions of “surface-chemically pure” samples in 0.01 M hydrochloric acid) were analyzed quantitatively and the surface thermodynamics of these surfactants interpreted on the molecular level. Preliminary studies demonstrated that aqueous solutions of 4−11 led to a hydrophobizing of glass surfaces.

Adsorption behavior of oxyethylated anionic surfactants Part 1. Adsorption equilibrium

Anionic surfactants containing one to three oxyethylene groups have been synthesized and their adsorption behavior at the water/air interface studied by measurement of their surface tension isotherms. On the basis of a long-time approximation model of the diffusion-controlled adsorption model, the equilibrium surface tension of low dilute solutions is determined. The experimental results support the theory and show that in a certain time range the approximation yields realistic equilibrium surface tension values. These values are not affected by surface active impurities.Oxyethylene groups in the anionic surfactant molecule increase surface activity. The effect of oxyethylene groups is comparable to that of methylene groups in the alkyl chain. The analysis of the adsorption isotherms suggests that at low surface pressure the oxyethylene groups are localized within the water/air interface. With increasing surface pressure an orientation change normal to the interface may occur.

Parasite transmission between soft-bottom invertebrates:temperature mediated infection rates and mortality in Corophium volutator

Circumstantial evidence has suggested that marine mlcrophallid ti-ematodes using gastropods Hydrobia spp. as flrst lnterlnedlate hosts, amphipods Corophlum spp. as second intermediate hosts, and various waterblrds as final hosts, may cause temperature-dependent epizootics and eventually local extinction of ~ntel-mediate host populations. Therefore, we examined experirnentally the impact of the microphallid trematode Mar~trenia subdolum on Corophluni volutator wlth special relerence to the influence of temperature, during the parasltes' transmission from s n a ~ l to amphipod. Trematode infected snails and amphipods were estabhshed togtlther in experimental aquaria at temperatures of 15, 2 2 and 24°C for 9 d. Amphipod surface activ~ty, survlvdl rate, parasite prevalence, lnfectioil rate, and paraslte dlstnbution both within and between amphlpod ~nt i~vlduals were recorded dunng , or at the end of, the experiment The snalls' shedding rate of larval ti-clnatodes as a function of temperature was also exam~ned . Increasing temperature resulted 111 higher Infection levels and parasite-induced mortality in the amphipods, most Ilkely governed by a similar temperature-dependent emergence of larval trc'matodes from the snails. No transmission occurred at I j 'C , whereas at 24°C the paraslte prevalence approached 100,1 and the parasite-induced mortality exceeded 50%) in relation to controls As assessed by the transparency of the amphipods' gills, infestation inflicted anaemia was the llkely mechanism behind the Increased surface activity observed among infected specimens. This paraslteinduced behavioural change niay facilitate transmission of infective stages to shorebird hosts feeding on C. volutator The results demonstrate that microphalhd trematodes are able to induce a significant additive mortality in C. volutator populatlons. The temperature mediated mortality emphasizes the potential significance of a density-~ndependent process in controlling the impact of parasltes on host organisms and thereby host population dynamics.

Polarographic studies of non-ionic surfactants with reference to their structural influence on surface activity

Abstract The surface activity of a homologous series of non-ionic surfactants having 12–16 carbon atoms in the alkyl chain and different lengths of the polyoxyethylene (POE) group was studied by a direct current polarographic method. Polarographic micelle points (PMPs) were used to compare the surface activities of the non-ionic surfactants in dimethylformamide (DMF) media. Results obtained from this study showed that the PMP increased regularly as the percentage of DMF in the solutions increased, indicating a decrease in the surface activity. In DMF media, as in water, the surface activity of the non-ionic surfactants depends on the hydrophilic/lipophilic ratio. Either increasing the length of the alkyl chain or decreasing the length of the polyoxyethylene chain contributes both to an enhanced hydrophobicity and an increased surface activity of the non-ionic surfactants.

Binding of sodium dodecylsulphate to starch polysaccharides quantified by surface tension measurements

The binding of the anionic surfactant sodium dodecylsulphate (SDS) to the starch polysaccharides amylose and amylopectin, extracted from potato, was studied by surface tension measurements utilizing a drop volume technique. The results demonstrate that surface tension measurements have potential for characterising interactions between surfactants and the two starch polysaccharides amylose and amylopectin. The estimated binding of SDS to amylose was around 35 SDS molecules per 1000 glucosidic units measured on a 0.2% (w/w) amylose solution, and the binding curve indicates increased surface activity of the amylose-SDS system at high surfactant concentrations. The binding of SDS to amylopectin was more restricted, with a degree of binding of only 6–7 SDS molecules per 1000 glucose units when measured on 3 and 5% (w/w) amylopectin solutions. The binding curves of the SDS-amylopectin solutions with a low degree of binding support the view that some of the chains in the amylopectin molecule have the capacity to interact with the surfactant.

Surface Properties, Micellization, and Premicellar Aggregation of Gemini Surfactants with Rigid and Flexible Spacers

Micellization and premicellar behavior of the two series of cationic surfactants, each with two hydrophilic and two hydrophobic groups in the molecule (“gemini” surfactants), one series with a rigid, hydrophobic spacer, and second with a flexible, hydrophilic one, have been studied by use of surface tension measurements. The data show the expected regular increase in surface activity with an increase in alkyl chain length for the shorter chain homologs but show increased deviation from the regularity with an increase in chain length when the number of carbon atoms in the alkyl chain exceeds a certain number. This deviation in surface activity appears to be due to the formation of small, non-surface active aggregates. Equilibrium constants calculated for the aggregation reaction show that the conditions facilitating micelle formation also favor formation of these premicelles, such as lower temperature, stronger ionic strength of the solution, and increased alkyl chain length. Geminis with a flexible, hydro...

Characterization of cure profiles of anaerobic adhesives by real-time FT-IR spectroscopy. Part II. Surface activation

A real-time Fourier transform-infrared (RT/FT-IR) spectroscopic technique has been used to study the cure profile of surface-activated anaerobic polymerization on metal surfaces at room temperature. The cure characterization of redox polymerization of anaerobic composition on several metal surfaces has been studied which included copper, aluminum, galvanized steel, zinc-plated steel, stainless steel, and passivated stainless steel. The copper surface was found to be the most active surface for initiating the polymerization. The effectiveness of various surface treatments for anaerobic cure was also studied. The results indicated that 316L stainless steel specimens, which have been passivated for corrosion preventive purposes, show an increase in activity for surface-initiated anaerobic polymerization over the specimen without passivation. The anaerobic cure on passivated 316L stainless steel specimens shows a higher ultimate degree of conversion and cure speed than on non-passivated steel. The buffing and passivation treatments produced the most active surface. This increase in surface activity appears to be due to the buffing and passivation treatment, resulting in roughening the surface as well as removing the inert oxide layer and scales. The role of nitric acid/EDTA in the passivation treatment for surface reactivity enhancement has also been discussed. The surface reactivity was evaluated based on the ability to accelerate an anaerobic cure in a real-time mode and has been correlated with the metal type and content in the interface region. The surface texture and metal contents were measured using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS), respectively.

Effect of Polydimethylsiloxane Concentration on Ester Foaming Tendency

A recently formulated hypothesis relates the viscosity of polydimethylsiloxane (PDMS) additives to neutral, profoamant, or antifoamant performance in esters. At ten parts-per-million of PDMS addition, very low viscosity PDMS additives are hypothesized as neutral or ineffectual, due to solubility in the ester. Intermediate viscosity PDMS additives are profoamant due to increased surface activity attributed to more limited solubility of the partially miscible PDMS in esters, and Lewis acid-base interaction of the siloxaneester couple. High viscosity dispersed particulate polydimethylsiloxanes are antifoamant, inducing bubble collapse by a Griffith flaw mechanism. The foaming tendencies of an ester are related here to varying concentrations of PDMS of intermediate viscosities, i.e., 500, 1000, and 5000 mm2s−1 (cSt), which are similarly neutral, profoamant, and antifoamant as concentration is increased. The hypothesis proposed is supported by the observations reported and provides a basis for a more complete understanding of observed foaming behavior.

Foam and Dynamic Surface Properties of Micellar Alkyl Benzene Sulphonates

The amount of foam formed when micellar solutions of a homologous series of anionic surfactants are subjected to a fixed agitation in the presence of antifoam often exhibits a maximum at a certain chain length. Here we consider the behavior of an homologous series of alkyl benzene sulphonates in the presence of a synergistic hydrophobic particle/hydrophobic oil antifoam. The equilibrium surface tensions of micellar solutions of homologous anionic surfactant solutions decrease with increase in chain length. However the gradients of dynamic surface tensions against reciprocal time increase with increasing chain length. This implies progressive decreases in the efficiency of transport of surfactant to air-water surfaces as the chain length increases. Measurements of micellar diffusion coefficients imply that this is not due to decreasing rates of diffusion. We tentatively ascribe it to decreasing rates of micelle breakdown as the chain length increases and the CMC decreases. The combination of decreasing equilibrium surface tension and increasing gradients of dynamic surface tension with reciprocal time means that plots of dynamic surface tension (at sufficiently high reciprocal times) against chain length will reveal a minimum. Here we correlate that minimum with the maximum in foam formed in the presence of antifoam. That maximum then arises as a consequence of a compromise between increasing surface activity and decreasing efficiency of transport of surfactant to air-water surfaces during foam generation. Foam and surface tension measurements are compared with theoretical considerations concerning the mode of action of the antifoam.

Filler-Elastomer Interactions. Part VI. Characterization of Carbon Blacks by Inverse Gas Chromatography at Finite Concentration

Abstract Carbon blacks ranging from N110 to N990 were characterized by means of inverse gas chromatography at finite concentration. The isotherms, net heat, and spreading pressures for benzene and cyclohexane adsorption suggest a general trend of increasing surface activity with increases in specific surface area. This is in good agreement with surface-energy measurements reported previously. The energy-distribution function of adsorption shows that while the concentrations of low-energy sites are comparable for most of the carbon blacks, differences exist with regard to high-energy sites. These suggest that small-particle-size blacks possess a greater number of high-energy centers. The graphitization of carbon blacks results in a considerable reduction in their adsorption capacity and narrows the energy distribution of their surfaces. One can therefore conclude that high-energy sites play an important role in the determination of the surface energies and reinforcing ability of carbon blacks.

Grenzflächenspannungserniedrigung durch chemisch modifiziertes Ovalbumin / Interfacial Tension Reduction by Chemically Modified Ovalbumin

Native Ovalbumin was chemically modified with various alkyl chain lengths, to several extents of modification. It was found that the surface activity which was determined by interfacial tension reduction, increased with the increase in degree of modification for all alkyl chain lengths. Increasing chain length led to a gradual decrease in interfacial tension between water and tetradecan. The most significant increase in surface activity was observed either at low degree of modification or at proteins modified with short alkyl chains

Substance P and antagonists. Surface activity and molecular shapes

The molecular properties of substance P (SP) (Arg-Pro-Lys-Pro-Gln-Gln-Phe-Phe-Gly-Leu-Met amide) and three of its antagonists were derived by measuring the Gibbs adsorption isotherm, providing information on the surface activity, the molecular shape, and the p K values of the different molecules. The following three antagonists were investigated: [ D-Arg 1, D-Pro 2, D-Trp 7,9, Leu 11]SP,ANT I; [ D-Arg 1, D-Trp 7,9,Leu 11]SP, ANT II and [ D-Pro 2, D- Trp 7,9]SP, ANT III. SP is only moderately surface active. The amino acid substitutions lead, however, to an increased surface activity of the antagonists. From the concentration dependence of the surface activity it was possible to quantify the packing characteristcs of the individual neuropeptides. SP shows cross-sectional areas of 300 ± 5 A ̊ 2 to 240 ± 5 A ̊ 2 (pH 5 to 8, 154 mM NaCl) at concentrations below 10 -5 M, i.e., in the physiological concentration range, indicating a folded SP conformation. Upon increasing the packing density to concentrations larger than 10 -5 M the surface area was only half as large ( 148 ± 5 A ̊ 2 to 124 ± 3 A ̊ 2 ) suggesting now a relatively extended conformation of the SP molecule with its long molecular axis perpendicular to the air / water interface. In contrast, the three antagonists were characterized by surface areas of 147 ± 3 A ̊ 2 to 126 ± 3 A ̊ 2 which were almost independent of concentration. The antagonists thus adopt a relatively extended conformation in the whole concentration range measured. This is further supported by computer modelling which shows that the antagonists are motionally restricted and can adopt neither a bent nor a α-helical conformation. The surface activity of the neuropeptides was dependent on the pH of the solution. At low peptide concentrations (about 10 -6 M) it was possible to resolve and determine the p K values of all individual charged amino acid side chains. The p K values observed for the neuropeptides were about two p K units lower than those of the free amino acids in solution. The p K shifts of the neuropeptides at the air / water interface are explained in terms of the Gouy-Chapman theory. SP and its antagonists bind to lipid bilayers in the order of their surface activity. While the binding of SP is mainly due to electrostatic interactions, hydrophobic peptide-lipid interactions contribute to the binding of the antagonists.

Effects of Acidic Monomers, Proposed Components of Self-etching Dentin Primers, on Dentin Surface, Surface Tension and Rat Erythrocytes

An experimental self-etching dentin primer, prepared by dissolving an acidic monomer, methacryloxyethyl succinate (MES), dimethacryloxyethyl phosphate (DMEP) or tertiarybutyl acrylamide sulfonic acid (TBAS), in an aqueous solution of 2.9M 2-hydroxyethyl methacrylate (HEMA), has been shown to promote adhesion by a bonding agent between a composite resin and dentin. To clarify the mechanism of this promotion we examined the effects of acidic monomers on dentin cleansing, surface tension of water and hypotonic hemolysis of rat erythrocytes. In scanning electron microscope observation of the dentin surface, the smear layer remained slightly evident after MES-HEMA treatment. DMEP-HEMA or TBAS-HEMA caused complete removal of the smear layer, and openings of dentinal tubules were clearly evident. MES and DMEP, 1×10-6 M and 1×10-4 M, respectively, decreased the surface tension of distilled water (72 dyne/cm) . The surface tension depression by 0.3M HEMA was apparently not further affected by MES, DMEP or TBAS at 1×10-7 to 1×10-2M. The osmotic pressure of hypotonic buffer was increased by MES, DMEP, TBAS and HEMA at concentrations greater than 1×10-2M. The hypotonic hemolysis of erythrocytes was inhibited by MES and TBAS at 4×10-3 to 1×10-2M and by HEMA at 4×10-1M. DMEP promoted hypotonic hemolysis at 4×10-5 to 1×10-4M, but caused inhibition in the concentration range of 4×10-4 to 1×10-3M. The protective effect of acidic monomers on the erythrocytes was promoted by the presence of 0.1 M HEMA, while DMEP at 1×10-2 M showed only a lytic effect. These results suggest that the mechanism of promotion of the adhesive ability of a bonding agent by self-etching dentin primers containing these acidic monomers is related to the increased surface activity of water and membrane stability of erythrocytes, since these effects of acidic monomers might be caused by the reduction in surface tension of secretion from dentin and inhibition of secretion from dentinal tubules.

Isolation and chemical composition of surface‐active material from human lung lavage

Surface-active material (SF) was isolated from human lung lavage fluid collected at autopsy employing differential and sucrose density gradient centrifugation. The isolated material showed well-defined electron microscopic structure, consisting of clearly preserved, closely packed vesicles with limiting membranes and inclusion bodies. It showed a very high degree of alkaline phosphatase specific activity and was devoid of other subcellular contaminants. The isolated material also showed a high phospholipid/protein ratio and increasing surface activity when monitored at different stages of purification. It contained 68.5% phosphatidylcholine, 11.5% phosphatidylglycerol and relatively smaller amounts of phosphatidylethanolamine and other individual phospholipid (PL) classes. In addition, cholesterol, unesterified fatty acids, triacylglycerols and other neutral lipids were found. Saturated fatty acids, particularly palmitic acid (16:0), predominated in the major PL fractions. However, various fatty acids of which oleic acid (18:1) constituted a large proportion also are present. Chemical analysis of the material showed that besides lipids and proteins, nucleic acids, sialic acid, hexose, amino sugars, nitrogen and phosphorus were present. The delipidated material showed the presence of three to four proteins as characterized by sodium dodecylsulfate (SDS)-polyacrylamide gel electrophoresis, and gel permeation chromatography on Sephadex G-200 resolved two well-separated peaks. The first fraction contained serum-associated 68 kDa protein, while the second fraction had two apoproteins with molecular weights of 34 kDa and 10 kDa. These two proteins were associated with the SF and they, as well as the whole surface-active material, strongly reacted with the antibody directed against the whole SF in a double-diffusion immunoprecipitation assay.(ABSTRACT TRUNCATED AT 250 WORDS)

Studies on Sintering of Technical Grade Alumina—Part II: Influence of Grinding and Minor Additions on Densification of Commercial Alumina

The influence of grinding process and minor additions like MgCO3 and TiO2 on sintering behaviour of technical grade commercial alumina has been studied with a view to making dense and impervious alumina wares. The grinding process has significant influence on densification of these powders prepared by variation in the ratio of material and ball used in comminution for reduction of particle size as well as increasing surface activity of the powders. Powders prepared by this method showed rapid densification between 1500° and 1600°C while minor addition of TiO2 resulted in dense compacts of these powders (over 90% T.D.) at temperatures as low as 1400°C. Sintering treatment at higher temperature (up to 1800°C) did not indicate further densification; however, it helped in improving microstructural characteristics and resulted in translucency in these samples (imperviousness), indicating recrystallization of alumina.

The role of lipid abnormalities, aqueous and mucus deficiencies in the tear film breakup, and implications for tear substitutes and contact lens tolerance

We had earlier proposed a “two-step, double-film” mechanism of tear film rupture, which traces the instability of the tear film in the van der Waals interaction mediated rupture of the thin mucus coating of the corneal epithelium. A transport model is now formulated for investigating the instability of the mucus layer in the presence of naturally occurring solutes of the tear film. It is shown that the normal lipids of the tear film play a dual role in stabilizing the mucus layer: (1) they augment the mucous-aqueous interfacial tension and (2) they induce an interfacial tension driven Marangoni convection. Both of these oppose the growing interfacial perturbations and consequently, the thinning of the mucus layer which is caused by the van der Waals interactions. An increased surface activity of lipids, due to numerous pathological conditions of the eyes, is shown to affect the tear film breakup time (BUT) adversely. The observed deleterious effects of highly surface active ingredients of tear substitutes, clinical stains, and anesthetics on BUT are also explained within the framework of the proposed mechanism. The aqueous tear deficiency which is reflected in the reduced thickness of the tear film, is shown to facilitate a rapid redistribution of solutes and thus undermines the stabilizing effect of the Marangoni convection. A marginally healthy eye may thus develop dry eye syndromes because of the aqueous tear deficiency. The proposed mechanism is in agreement with clinical observations of the factors causing the dry eyes and numerous other experimental and clinical findings related to the phenomenon of tear film rupture. The role of tear substitutes in prolonging the time of rupture as well as the implications of the present mechanism for the formulation of tear substitutes are delineated. The factors affecting the contact lens tolerance due to the altered physiology of the tear film are discussed. A particular emphasis is, however, placed on the possible adhesion of the contact lens to the cornea. Finally, it is emphasized that the clinical measurements of BUT are an overall outward manifestation of several factors discussed above and their synergisms thereof.