Adsorption behaviour of lactoferrin in oil-in-water emulsions as influenced by interactions with beta-lactoglobulin

Oil-in-water emulsions (pH 7.0 or pH 3.0) containing 30 wt% soya oil and various concentrations of lactoferrin were made in a two-stage valve homogenizer. The average droplet size (d32), the surface protein coverage (mg/m2) and composition, and the zeta-potential of the emulsions were determined. The value of d32 decreased with increasing lactoferrin concentration up to 1%, and then was almost independent of lactoferrin concentration beyond 1% at both pH 7.0 and pH 3.0. The surface protein coverage of the emulsions made at pH 7.0 increased almost linearly with increasing lactoferrin concentration from 0.3 to 3%, but increased only slightly in emulsions made at pH 3.0 at lactoferrin concentrations >1%. The surface protein coverage of the emulsions made at pH 3.0 was lower than that of the emulsions made at pH 7.0 at a given protein concentration. The emulsion droplets had a strong positive charge at both pH 7.0 and pH 3.0, indicating that stable cationic emulsion droplets could be formed by lactoferrin alone. When emulsions were formed with a mixture of lactoferrin and beta-lactoglobulin (beta-lg) (1:1 by weight), the charge of the emulsion droplets was neutralized at pH 7.0 suggesting the formation of electrostatic complexes between the two proteins. The composition of the droplet surface layer showed that both proteins were adsorbed, presumably as complexes, from the aqueous phase at pH 7.0 in equal proportions, whereas competitive adsorption occurred between lactoferrin and beta-lg at pH 3.0. At this pH, beta-lg was adsorbed in preference to lactoferrin at low protein concentrations (1%), whereas lactoferrin appeared to be adsorbed in preference to beta-lg at high protein concentrations.     

Effects of a phospholipid cosurfactant on external coalescence in water-in-oil-in-water double-emulsion globules

The activated form of N-glutaryl-phosphatidylethanolamine (aNGPE) has been incorporated into water-in-oil-in-water (W₁/O/W₂) double-emulsion globules. Preparation of individual globules within a cylindrical capillary and video microscopy of their behavior enabled determination of the rate of coalescence of internal aqueous droplets (W₁) with the external aqueous phase (W₂), termed external coalescence. The presence of Tween 80 in the external phase at concentrations of 0.01 and 0.012 M effected such coalescence. The concentration of Span 80 in the oil phase exceeded that of aNGPE considerably, with the ratio of Span 80 to aNGPE molecules ranging from 60 to 1363. Despite the low relative concentration of aNGPE, external coalescence of the internal droplets was prolonged in globules containing this cosurfactant as compared to globules containing only Span 80. Increasing the amount of phospholipid in the oil phase did not significantly affect the rate of release, indicating that within our range of concentrations (22.0–91.3 μM) there was little variation in the amount of phospholipid adsorbing at the interface. These results indicate that, in addition to its suitable protein-binding functionality, aNGPE can prolong the release of internal droplets in a W₁/O/W₂ globule; its use as a cosurfactant shows potential benefits for drug-delivery applications.     

丙烯酰胺在聚乙二醇水溶液中聚合产品的微观形态

采用偶氮类水溶性引发剂2,2′-偶氮二异丙基咪唑啉二盐酸盐(VA044)引发丙烯酰胺(AM)在聚乙二醇(PEG)水溶液中的双水相聚合;研究了引发剂、单体、聚乙二醇浓度及温度对最终产品中聚丙烯酰胺(PAM)液滴形态、尺寸的影响.随着引发剂浓度的增加,液滴由球状变为细长条状;随着温度的上升,球状液滴逐渐趋于条状,然后又重新趋于球状;在初始单体浓度较低时,PAM液滴滴径分布较窄,当其浓度增加后,滴径呈多峰分布;随着PEG浓度的增加,聚合物液滴趋于球状。     

Planar chip device for PCR and hybridization with surface acoustic wave pump

We have developed a microfluidic device operating at a planar surface instead of a closed channel network. The fluid is transported in single droplets using surface acoustic waves (SAW) on a piezoelectric LiNbO(3) substrate. The surface of the piezo is chemically structured to induce high contact angles of the droplets or enclose areas where the liquid can wet the substrate. Combining the SAW technique with thin film resistance heaters, a biological analysis chip with integrated DNA amplification by PCR and hybridization was designed. To prevent evaporation of the PCR reagents at high temperatures the sample is enclosed in droplets of mineral oil. On this chip the SAW resolves dried primers, shifts the oil capped liquid between the two heaters and mixes during hybridization. The chip is able to perform a highly sensitive, fast and specific PCR with a volume as low as 200 nl. During the temperature cycles an online monitoring of the DNA concentration is feasible with an optical unit, providing a sensitivity of 0.1 ng. After PCR the product is moved to the second heater for the hybridization on a spotted DNA array. With our chip we were able to detect a single nucleotide polymorphism (SNP) responsible for the Leiden Factor V syndrome from human blood.     

Shapes of dispersed phase in confined PIB/PDMS blends with different compositions during shear flow

The morphology of immiscible fluid mixtures under confined environment usually displays different scenarios compared with those presented in bulk systems. In this work, the influence of confinement and component ratio on the droplet morphology of immiscible polyisobutylene (PIB)/polydimethylsiloxane (PDMS) blends in confined steady shear flow was investigated. While increasing the degree of confinement, the morphology of dispersed phase experienced a transition from the bulk behavior toward the confined behavior. Increasing the concentration of PIB phases in confined blends resulted in more coarsened structure under low shear rate and generated pearl necklace or string-like structures under a higher shear rate. The maximum aspect ratio of PIB droplets increased while increasing PIB concentration. The width and the aspect ratio of PIB droplets obtained experimentally were compared to the predictions of a single droplet MM model for bulk flow and an M model considering confinement. The experimental droplet width agreed well with the predictions of these two models only in the small droplet zone, large deviations appeared for the degree of confinement up to 0.36 and higher, whereas constant droplet width was found. The M model decreased the deviation between the experimental aspect ratio and the prediction of MM model in the high Ca zone. Good agreement between the prediction of M model and experiment results was found when the orientation angles of the droplets were corrected by using the M model.     

Doxorubicin biocompatible O/W microemulsion stabilized by mixed surfactant containing soya phosphatidylcholine

Microemulsions (ME) containing soya phosphatidylcholine (SPC)/polyoxyethylenglycerol trihydroxystearate 40 (EU)/sodium oleate (SO) as surfactant cholesterol (CHO) as oil phase and aqueous buffer were studied. Pseudo-ternary phase diagrams of the investigated systems were obtained at constant SPC/EU/SO weight ratio 3.5:3.5:3.0 by titration, in order to characterize the proportions between the components to form clear systems. The dynamic light scattering results showed that the size of the oil droplets decreases significantly with the ratio of surfactant/oil phase added to system. Depending on the composition ME system could exhibit a thixotropic behavior. The apparent viscosity increased 25- and 13-folds with cholesterol concentration for drug-free and drug-load ME, respectively. It was also verified that the octanol/aqueous buffer partition coefficient (KO/B) of doxorubicin (DOX) was pH dependent increasing abruptly above pH 6.0. It was possible to incorporate 2.24 mg/ml of DOX into ME. The incorporation of DOX in the ME systems increased the droplets size for all surfactant concentrations used in the system. The results suggest that DOX interacts with the microstructure of the ME at the studied pH increasing significantly the drug solubility. It was possible to conclude that the investigated ME can be a very promising vehicle as drug-carrier for administration of doxorubicin.     

Double inversion of emulsions induced by salt concentration

The effects of salt on emulsions containing sorbitan oleate (Span 80) and Laponite particles were investigated. Surprisingly, a novel double phase inversion was induced by simply changing the salt concentration. At fixed concentration of Laponite particles in the aqueous phase and surfactant in paraffin oil, emulsions are oil in water (o/w) when the concentration of NaCl is lower than 5 mM. Emulsions of water in oil (w/o) are obtained when the NaCl concentration is between 5 and 20 mM. Then the emulsions invert to o/w when the salt concentration is higher than 50 mM. In this process, different emulsifiers dominate the composition of the interfacial layer, and the emulsion type is correspondingly controlled. When the salt concentration is low in the aqueous dispersion of Laponite, the particles are discrete and can move to the interface freely. Therefore, the emulsions are stabilized by particles and surfactant, and the type is o/w as particles are in domination. At intermediate salt concentrations, the aqueous dispersions of Laponite are gel-like, the viscosity is high, and the transition of the particles from the aqueous phase to the interface is inhibited. The emulsions are stabilized mainly by lipophilic surfactant, and w/o emulsions are obtained. For high salt concentration, flocculation occurs and the viscosity of the dispersion is reduced; thus, the adsorption of particles is promoted and the type of emulsions inverts to o/w. Laser-induced fluorescent confocal micrographs and cryo transmission electron microscopy clearly confirm the adsorption of Laponite particles on the surface of o/w emulsion droplets, whereas the accumulation of particles at the w/o emulsion droplet surfaces was not observed. This mechanism is also supported by the results of rheology and interfacial tension measurements.     

Flocculation and coalescence of droplets in oil-in-water emulsions formed with highly hydrolysed whey proteins as influenced by starch

The effects of added unmodified amylopectin starch, modified amylopectin starch and amylose starch on the formation and properties of emulsions (4 wt.% corn oil) made with an extensively hydrolysed commercial whey protein (WPH) product under a range of conditions were examined. The rate of coalescence was calculated based on the changes in the droplet size of the emulsions during storage at 20 degrees C. The rates of creaming and coalescence in emulsions containing amylopectin starches were enhanced with increasing concentration of the starches during storage for up to 7 days. At a given starch concentration, the rate of coalescence was higher in the emulsions containing modified amylopectin starch than in those containing unmodified amylopectin starch, whereas it was lowest in the emulsions containing amylose starch. All emulsions containing unmodified and modified amylopectin starches showed flocculation of oil droplets by a depletion mechanism. However, flocculation was not observed in the emulsions containing amylose starch. The extent of flocculation was considered to correlate with the rate of coalescence of oil droplets. The different rates of coalescence could be explained on the basis of the strength of the depletion potential, which was dependent on the molecular weight and the radius of gyration of the starches. At high levels of starch addition (>1.5%), the rate of coalescence decreased gradually, apparently because of the high viscosity of the aqueous phase caused by the starch.     

Flocculation and Coalescence of Oil-in-Water Poly(dimethylsiloxane) Emulsions

The stability of poly(dimethylsiloxane) (PDMS) oil-in-water emulsions has been investigated in the presence of added NaCl as well as in the presence of added surfactant. The emulsions were prepared using a combination of nonionic (C(x)E(y), x and y represent the number of methylene (C) and ethylene oxide (E) groups, respectively) and cationic (quarternary alkylammonium) surfactants. The droplets were observed to exhibit weak flocculation in the presence of high NaCl concentration (1 M). Phase separation and optical microscopic observations revealed that the principal mechanism for emulsion destabilization at high salt concentration was coalescence, which was accelerated at elevated temperature (50 degrees C). The effective coalescence rate for diluted emulsions was investigated using photon correlation spectroscopy. The small effective Hamaker constant for PDMS is the primary reason for the slow rate of coalescence observed for the emulsions at neutral pH in the presence of NaCl. The stability of PDMS emulsions to flocculation is qualitatively similar to that reported for low Hamaker constant dispersions (e.g., microgel particles). Addition of cationic surfactants (cetyltrimethylammonium chloride and dodecyl dimethylbenzylammonium chloride) to the negatively charged droplets after preparation was shown to decrease the emulsion stability once the surfactant concentration exceeded the CMC. Electrophoretic mobility measurements showed that added cationic surfactant changed the sign of the droplet charge from negative to positive at concentrations well below the CMC. Charged micelles of the same sign as the droplets are electrostatically excluded from close approach to the droplet surface within a distance (varepsilon) which results in depletion flocculation. Copyright 2000 Academic Press.     

Reactions of Microsolvated Organic Compounds at Ambient Surfaces: Droplet Velocity,Charge State,and Solvent Effects

The exposure of charged microdroplets containing organic ions to solid-phase reagents at ambient surfaces results in heterogeneous ion/surface reactions. The electrosprayed droplets were driven pneumatically in ambient air and then electrically directed onto a surface coated with reagent. Using this reactive soft landing approach, acid-catalyzed Girard condensation was achieved at an ambient surface by directing droplets containing Girard T ions onto a dry keto-steroid. The charged droplet/surface reaction was much more efficient than the corresponding bulk solution-phase reaction performed on the same scale. The increase in product yield is ascribed to solvent evaporation, which causes moderate pH values in the starting droplet to reach extreme values and increases reagent concentrations. Comparisons are made with an experiment in which the droplets were pneumatically accelerated onto the ambient surface (reactive desorption electrospray ionization, DESI). The same reaction products were observed but differences in spatial distribution were seen associated with the “splash” of the high velocity DESI droplets. In a third type of experiment, the reactions of charged droplets with vapor phase reagents were examined by allowing electrosprayed droplets containing a reagent to intercept the headspace vapor of an analyte. Deposition onto a collector surface and mass analysis showed that samples in the vapor phase were captured by the electrospray droplets, and that instantaneous derivatization of the captured sample is possible in the open air. The systems examined under this condition included the derivatization of cortisone vapor with Girard T and that of 4-phenylpyridine N-oxide and 2-phenylacetophenone vapors with ethanolamine.     

Phase behaviour and electro-optic characteristics of a polymer stabilized ferroelectric liquid crystal

The effects of adding a diacrylate monomer or its polymerized network to a ferroelectric liquid crystal have been characterized. The monomer lowers the temperatures of transition to the more ordered phases, whereas the polymer network phase separates into polymer rich and LC rich phases and has little effect on the LC phase behaviour. Ferroelectric polarization decreases comparably in both monomer and networked systems. As the network concentration increases, the size of LC domains decreases considerably. With low concentrations of polymer and, thus large LC domains, optical response and tilt angle remain fairly independent of polymer concentration, but as the polymer concentration increases, switching speed and tilt angle decrease dramatically. Polymerization rate maxima increase with monomer concentration until saturation of monomer in the liquid crystal is reached. The rate maxima then decrease as monomer must diffuse from monomer rich droplets. Double bond conversion during the polymerization is comparable for all monomer concentrations below 50 per cent.     

Double phase inversion of emulsions containing layered double hydroxide particles induced by adsorption of sodium dodecyl sulfate

A liquid paraffin-water emulsion was investigated using layered double hydroxide (LDH) particles and sodium dodecyl sulfate (SDS) as emulsifiers. Both emulsifiers are well-known to stabilize oil-in-water (o/w) emulsions. Surprisingly, a double phase inversion of the emulsion containing LDH particles is induced by the adsorption of SDS. At a constant LDH concentration, the emulsion is o/w type when SDS concentrations are low. At intermediate SDS concentrations, the first emulsion inversion from o/w to w/o occurs, which is attributed to the enhanced hydrophobicity of LDH particles caused by the desorption of the second layer of surfactant, leaving a densely packed SDS monolayer on the LDH exterior surfaces. The second inversion from water-in-oil (w/o) to o/w occurs at higher SDS concentrations, which may be due to the competitive adsorption at the oil/water interfaces between the LDH particles modified by the SDS bilayers and the free SDS molecules in the bulk solution, but the free SDS molecules dominate and determine the emulsion type. Laser-induced fluorescent confocal micrographs clearly confirm the adsorption of LDH particles on the surfaces of the initial o/w and intermediate w/o emulsion droplets, whereas no LDH particles were adsorbed on the final o/w emulsion droplet surfaces. Also, transmission electron microscopy (TEM) observations indicate that the shape of the final o/w emulsions is similar to that of the monomeric SDS-stabilized emulsion but different from that of the initial o/w emulsions. The adsorption behavior of SDS on LDH particles in water was investigated to offer an explanation for the emulsion double phase inversion. The zeta potential results show that the particles will flocculate first and then redisperse following surfactant addition. Also, X-ray diffraction (XRD) measurements indicate that SDS adsorption on the LDH interior surfaces will be complete at intermediate concentrations.     

The Inhibiting Behavior of Glycerol on the Kinetics of Transesterification of Palm Oil

Glycerol, a by-product from transesterification, is well-known as one of the factors inhibiting the reaction. Previous works have mostly shown that the reaction rate slows to a near-steady state and eventually reaches chemical equilibrium. This work aimed to study the inhibiting behavior of glycerol on the transesterification of palm oil. Observation under an LCD digital microscopy showed that glycerol-coated droplets of catalyst-methanol dispersed in the triglyceride phase. This work proposes that glycerol inhibits transesterification by the following mechanism: Droplets of catalyst-methanol disperse into the triglyceride phase; the reaction takes place at an interphase called the reactive zone; methyl ester, the desired product, has low polarity and moves to the triglyceride phase, whereas glycerol, the non-desired product, is more highly polar and accumulates on the droplet surface of catalyst-methanol droplets, inhibiting triglyceride mass transfer and diluting the concentration of the catalyst-methanol. The triglyceride mass transfer coefficient and reaction rate constant were both investigated and expressed as the exponential function.

     

Effect of Ionic Strength of Dispersed Phase on Ostwald Ripening in Water-in-Oil Emulsions

Water-in-oil emulsions with a low electrolyte content in the internal phase are unstable with respect to Ostwald ripening. The main components of the total pressure acting on the surface of internal phase droplets are considered. The equilibrium values of the diameters of dispersed phase droplets are calculated. The dependences of the difference in the osmotic and Laplace pressures on the droplet size and electrolyte concentration in the droplets are obtained. It is shown that, at the electrolyte concentration below the critical value, the number of droplets in emulsion decreases. If the concentration is above the critical value, water diffuses from small to large droplets, but their number remains unchanged. The change in NaCl concentration in the droplets of internal phase of polydisperse emulsion during the Ostwald ripening is calculated. The results of calculations correlate with the experimental data on the stability of emulsions with respect to coalescence and sedimentation.     

Microscopic analysis of ester hydrolysis reaction catalyzed by Candida rugosa lipase

The relationship between the kinetics of the lipase-catalyzed oil hydrolysis and the surface area distribution of oil droplets was investigated using ethyl decanoate and gum Arabic (GA) as a model oil and an emulsifier, respectively. Along an ethyl decanoate concentration gradient between 2 and 8 mM, the initial hydrolysis rate increased at 0.25% (w/v) GA but did not change at 1.0% (w/v) GA. At 0.25% GA, the surface area of droplets was narrowly distributed regardless of the ethyl decanoate concentration. However, at 1.0% GA and with ethyl decanoate concentrations higher than 2 mM, the fraction of relatively large droplets with a surface area larger than approximately 200 microm2, suddenly increased. The microscopy of ethyl decanoate emulsion during the hydrolysis reaction indicates that the large oil droplets were not hydrolyzed. At 20 mM ethyl decanoate where the hydrolysis rate remained the same between 0.25% and 1.0% GA, the surface area of droplets was narrowly distributed at 0.25% and 1.0% GA. Therefore, the constant hydrolysis rate observed in the emulsion of ethyl decanoate between 2 and 8 mM containing GA at 1.0%, is believed to be caused by the relatively large oil droplets with the interface quality differing from that of the small oil droplets.     

Drying rate variations of latex dispersions due to salt induced skin formation

Film formation from latex dispersions with varying concentrations of sodium dodecylsulfate (SDS) and sodium persulfate (NaPS) was studied with a sorption balance. The drying rate decreased significantly at a critical volume fraction of polymer (phi pc). Under constant drying conditions the phi pc varied due to differences in particle stabilization. In SDS containing samples, the droplets wetted larger areas, the film thicknesses decreased and, consequently, the initial evaporation rate was decreased. The decrease in the initial evaporation rate first continued with increasing SDS concentration but leveled off at an apparent critical micelle concentration (CMC). Samples containing NaPS had different types of film formation mechanisms with large variations in phi pc and the total drying time, which could be explained by differences in the electrostatic stabilization. For dialyzed dispersions containing no NaPS, phi pc was close to 0.7. In samples with medium high NaPS concentration a skin was formed at the air interface causing an early shift in the evaporation rate, resulting in 0.25相似文献   

Stability Characteristics of Dispersed Oil Droplets Prepared by the Microchannel Emulsification Method

A novel emulsification method, microchannel (MC) emulsification, was developed for making monodispersed regular-sized droplets in our laboratory. An oil-in-water dispersed system, in which phosphate buffer was used as the continuous phase, sodium dodecyl sulfate (SDS) as the surfactant, and clove oil as the dispersed phase, was prepared by this technique. The average diameter of oil droplets was about 20 μm, with a narrow size distribution. The stability characteristics of the dispersed oil droplets were investigated by an optical microscope and kinetic light scattering method. The stability of the dispersed oil droplets depended on the SDS concentration. When the SDS concentration was above the critical micelle concentration (CMC), the turbidity of the dispersed solution sharply increased at the initial stage. Optical microscopic observation has confirmed that a part of the oil droplets broke up with time, and submicrometer droplets appeared. On the other hand, when the SDS concentration was below the CMC, the turbidity of the dispersed solution had little change in the initial stage, showing that the oil droplets were very stable. The effect of ion concentration was also examined. The results showed that the stability of the oil droplets depended on the balance of the Van der Waals attraction and electrical repulsion between the oil droplets in low ion concentration. Copyright 2001 Academic Press.     

The morphology of immiscible PDMS/PIB blends filled with silica nanoparticles under shear flow

The influence of surface nature (hydrophobic and hydrophilic) and concentration of silica nanoparticles on the coalescence behavior of immiscible polydimethylsiloxane (PDMS)/polyisobutylene (PIB) (90/10) blends under simple low-rate shear flow were investigated via optical shear technique. It was found that the coalescence of PIB droplets in PDMS matrix was suppressed efficiently by incorporating hydrophobic silica nanoparticles, and a constant droplet size was obtained at high particle contents. The addition of a small amount (<0.4 wt.%) of hydrophilic silica nanoparticles also decreased the size of PIB droplets. Clusters of small PIB droplets were formed at low filler concentration. When the filler concentration exceeded 0.8 wt.%, the clusters of PIB drops disappeared and elongated PIB threads with large size were formed, which suggest that the coalescence of PIB droplets was promoted. The results indicate that the discrepancy in the morphology evolution of PDMS/PIB blends upon the addition of silica nanoparticles is controlled not only by the surface chemistry of nanoparticles but also by their concentration in the blends.     

Semiconductor applications of nanoliter droplet methodology with total reflection x-ray fluorescence analysis

In this study, the nanoliter dried spot method was applied to semiconductor contamination analysis to enhance vapor phase decomposition processes with total reflection X-ray fluorescence detection. Nanoliter-sized droplets (10 and 50 nl) were deposited onto native silicon oxide wafer surfaces in a clean room environment from both single and multielemental standards containing various concentrations of iron in different matrices. Direct comparisons were made to droplets formed by conventional VPD with similar iron standards. Nanoliter dried spots could be reproducibly deposited and dried in air with typical drying times ranging from 20 s to 2 min depending on the nanoliter volume deposited, compared to VPD spots which have drying times ranging from tens of minutes to several hours. Both types of residues showed a linear relationship between Fe intensity and mass deposited. Variable angle experiments showed that both nanoliter and VPD deposits of single element standards were film-like in character, while residues formed from much more complex matrices and higher mass loadings were particulate in character. For the experimental conditions used in this study (30 kV, 100 mA), typical TXRF spectral Fe limits of detection were calculated to be on the order of picograms or ∼1×10¹⁰ atoms/cm² for a 0.8 cm² X-ray excitation beam area for both nanoliter dried spots and VPD spots prepared from single elemental standards. Calculated Fe detection limits for 200 mm diameter silicon wafers used in this study were in the ∼1×10⁸ atoms/cm² range. By using nanoliter sized droplets, the required sample volume is greatly reduced resulting in higher sample throughput than with conventional VPD methods.