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.     

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.     

Droplet surface properties and rheology of concentrated oil in water emulsions stabilized by heat-modified beta-lactoglobulin B

Effects of substituting native beta-lactoglobulin B (beta-lactoglobulin) with heat-treated beta-lactoglobulin as emulsifier in oil in water emulsions were investigated. The emulsions were prepared with a dispersed phase volume fraction of Phi=0.6, and accordingly, oil droplets rather closely packed. Native beta-lactoglobulin and beta-lactoglobulin heated at 69 degrees C for 30 and 45 min, respectively, in aqueous solution at pH 7.0 were compared. Molar mass determination of the species formed upon heating as well as measurements of surface hydrophobicity and adsorption to a planar air/water interface were made. The microstructure of the emulsions was characterized using confocal laser scanning microscopy, light scattering measurements of oil droplet sizes, and assessment of the amount of protein adsorbed to surfaces of oil droplets. Furthermore, oil droplet interactions in the emulsions were quantified rheologically by steady shear and small and large amplitude oscillatory shear measurements. Adsorption of heated and native beta-lactoglobulin to oil droplet surfaces was found to be rather similar while the rheological properties of the emulsions stabilized by heated beta-lactoglobulin and the emulsions stabilized by native beta-lactoglobulin were remarkably different. A 200-fold increase in the zero-shear viscosity and elastic modulus and a 10-fold increase in yield stress were observed when emulsions were stabilized by heat-modified beta-lactoglobulin instead of native beta-lactoglobulin. Aggregates with a radius of gyration in the range from 25 to 40 nm, formed by heating of beta-lactoglobulin, seem to increase oil droplet interactions. Small quantities of emulsifier substituted with aggregates have a major impact on the rheology of oil in water emulsions that consist of rather closely packed oil droplets.     

Influence of Interfacial Engineering on Stability of Emulsions Stabilized with Soy Protein Isolate

The objectives of this study were to examine the influence interfacial composition on environmental stresses stability of oil in water emulsions. An electrostatic layer-by-layer deposition method was used to create the multilayered interfacial membranes with different compositions: (i) primary emulsion (Soy protein Isolate); (ii) secondary emulsion (Soy protein Isolate – OSA-starch); (iii) tertiary emulsion (Soy protein isolate – OSA-starch – chitosan). Fourier transform-infrared (FTIR) and scanning electron microscopy (SEM) results confirmed the adsorption of charged polyelectrolyte onto oppositely charge polyelectrolyte-coated oil droplets. The stability of primary, secondary, and tertiary emulsions to thermal treatment (30 min at 30–90°C), pH (3–7) and NaCl (0–500 mM) were determined using ζ-potential, particle diameter, and microstructure analysis. Primary emulsions were unstable at pH 4–7, salt concentrations, and thermal treatments. Secondary emulsions were stable to creaming and droplet aggregation at pH 3–5, at ≤50 mM NaCl, and unstable at thermal treatments, whereas tertiary emulsions were stable at all salt concentrations, thermal treatments, and at pH 3–6. These results demonstrate that these polymers can be used to engineer oil in water emulsion systems and improve the emulsion stability to environmental stresses.     

Spreading of oil from protein stabilised emulsions at air/water interfaces

Spreading of a drop of an emulsion made with milk proteins on air/water interfaces was studied. From an unheated emulsion, all oil molecules could spread onto the air/water interface, indicating that the protein layers around the oil globules in the emulsion droplet were not coherent enough to withstand the forces involved in spreading. Heat treatment (90 °C) of emulsions made with whey protein concentrate (WPC) or skim milk powder reduced the spreadability, probably because polymerisation of whey protein at the oil/water interface increased the coherence of the protein layer. Heat treatment of emulsions made with WPC and monoglycerides did not reduce spreadability, presumably because the presence of the monoglycerides at the oil/water interface prevented a substantial increase of coherence of the protein layer. Heat treatment of caseinate-stabilised emulsions had no effect on the spreadability. If proteins were already present at the air/water interface, oil did not spread if the surface tension (γ) was <60 mN/m. We introduced a new method to measure the rate at which oil molecules spread from the oil globules in the emulsion droplet by monitoring changes in γ at various positions in a ‘trough’. The spreading rates observed for the various systems agree very well with the values predicted by the theory. Spreading from oil globules in a drop of emulsion was faster than spreading from a single oil drop, possibly due to the greater surface tension gradient between the oil globule and the air/water interface or to the increased oil surface area. Heat treatment of an emulsion made with WPC did not affect the spreading rate. The method was not suitable for measuring the spreading rate at interfaces where surface active material is already present, because changes in γ then were caused by compression of the interfacial layer rather than by the spreading oil.     

THE ADSORPTION OF AN ANIONIC SURFACTANT AT THE OIL WATER INTERFACE DURING EMULSION HOMOGENIZATION

Adsorption of sodium dodecylbenzene sulfonate (NaDBS) on the surfaces of dispersed oil globules during homogenization of paraffin oil in water emulsions has been studied. NaDBS concentration was changed over a wide interval comprising critical micelle concentration. For the emulsions homogenized for different time intervals the total quantity and the percentage of NaDBS adsorbed, the amount and number of NaDBS molecules adsorbed per unit inter-facial area, as well as the specific surface area of dispersed phase and the area per emulsifier molecule have been determined.

The amount adsorbed and density of the emulsifier layer, I.e., the area per NaDBS molecule adsorbed on the oil globule surfaces, depend not only on Initial NaDBS concentration but also, on the homogenization time and the homogenization action. This makes a difference between the adsorption behaviour under the conditions of emulsion formation and its subsequent homogenization, and the adsorption behaviour of the emulsifier at a plane quiescent Interface.     

Production and characterization of oil-in-water emulsions containing droplets stabilized by multilayer membranes consisting of beta-lactoglobulin, iota-carrageenan and gelatin

The influence of environmental conditions (pH, NaCl, CaCl2, and temperature) on the properties and stability of oil-in-water (O/W) emulsions containing oil droplets surrounded by one-, two-, or three-layer interfacial membranes has been investigated. Three oil-in-water emulsions were prepared with the same droplet concentration and buffer (5 wt % corn oil, 5 mM phosphate buffer, pH 6) but with different biopolymers: (i) primary emulsion: 0.5 wt % beta-Lg; (ii) secondary emulsion: 0.5 wt % beta-Lg, 0.1 wt % iota-carrageenan; (iii) tertiary emulsion: 0.5 wt % beta-Lg, 0.1 wt % iota-carrageenan, 0-2 wt % gelatin. The secondary and tertiary emulsions were prepared by electrostatic deposition of the charged biopolymers onto the surfaces of the oil droplets so as to form two- and three-layer interfacial membranes, respectively. The stability of the emulsions to pH (3-8), sodium chloride (0-500 mM), calcium chloride (0-12 mM), and thermal processing (30-90 degrees C) was determined. We found that multilayer emulsions had better stability to droplet aggregation than single-layer emulsions under certain environmental conditions and that one or more of the biopolymer layers could be made to desorb from the droplet surfaces in response to specific environmental changes (e.g., high salt or high temperature). These results suggest that the interfacial engineering technology used in this study could lead to the creation of food emulsions with improved stability to environmental stresses or to emulsions with triggered release characteristics.     

Surface activity and emulsification properties of hydrophobically modified dextrans

Neutral polymeric surfactants were synthesized by covalent attachment of hydrophobic groups (aromatic rings) onto a polysaccharide backbone (dextran). By changing the conditions of the modification reaction, the number of grafted hydrophobic groups per 100 glucopyranose units (substitution ratio) was varied between 7 and 22. In aqueous solution, these polymers behaved like classical associative polymers as demonstrated by viscometric measurements. The associative behavior was more pronounced when the substitution ratio increased. The surface-active properties of the modified dextrans were evidenced by surface tension (air/water) and interfacial tension (dodecane/water) measurements. In each case the surface or interfacial tension leveled down above a critical polymer concentration, which was attributed to the formation of a dense polymer layer at the liquid-air or liquid-liquid interface. Dodecane-in-water emulsions were prepared using the polymeric surfactants as stabilizers, with oil volume fractions ranging between 5 and 20%. The oil droplet size (measured by dynamic light scattering) was correlated to the amount of polymer in the aqueous phase and to the volume of emulsified oil. The thickness of the adsorbed polymer layer was estimated thanks to zeta potential measurements coupled with size measurements. This thickness increased with the amount of polymer available for adsorption at the interface. The dextran-based surfactants were also applied to emulsion polymerization of styrene and stable polystyrene particles were obtained with a permanent adsorbed dextran layer at their surface. The comparison with the use of an unmodified dextran indicated that the polymeric surfactants were densely packed at the surface of the particles. The colloidal stability of the suspensions of polystyrene particles as well as their protection against protein adsorption (bovine serum albumin, BSA, used as a test protein) were also examined.     

Interface composition of multiple emulsions: rheology as a probe

We have investigated the dynamic rheological properties of concentrated multiple emulsions to characterize their amphiphile composition at interfaces. Multiple emulsions (W1/O/W2) consist of water droplets (W1) dispersed into oil globules (O), which are redispersed in an external aqueous phase (W2). A small-molecule surfactant and an amphiphilic polymer were used to stabilize the inverse emulsion (W1 in oil globules) and the inverse emulsion (oil globules in W2), respectively. Rheological and interfacial tension measurements show that the polymeric surfactant adsorbed at the globule interface does not migrate to the droplet interfaces through the oil phase. This explains, at least partly, the stability improvement of multiple emulsions as polymeric surfactants are used instead of small-molecule surfactants.     

Influence of iota-carrageenan on droplet flocculation of beta-lactoglobulin-stabilized oil-in-water emulsions during thermal processing

The influence of thermal processing on droplet flocculation in oil-in-water emulsions stabilized by either beta-lactoglobulin (primary emulsions) or beta-lactoglobulin-iota-carrageenan (secondary emulsions) at pH 6 has been investigated. In the absence of salt, the zeta-potential of the primary emulsion was less negative (-40 mV) than that of the secondary emulsion (-55 mV) due to adsorption of anionic iota-carrageenan to the anionic beta-Lg-coated droplet surfaces. The zeta-potential and mean diameter (d(43) approximately 0.3 microm) of droplets in primary and secondary emulsions did not change after storage at temperatures ranging from 30 to 90 degrees C. In the presence of 150 mM NaCl, the zeta-potential of the primary emulsion was much less negative (-27 mV) than that of the secondary emulsion (-50 mV), suggesting that the latter was less influenced by electrostatic screening effects. The zeta-potential of the primary emulsions did not change after storage at elevated temperatures (30-90 degrees C). The zeta-potential of the secondary emulsions became less negative, and the aqueous phase iota-carrageenan concentration increased at storage temperatures exceeding 50 degrees C, indicating iota-carrageenan desorbed from the beta-Lg-coated droplets. In the primary emulsions, appreciable droplet flocculation (d(43) approximately 8 microm) occurred at temperatures below the thermal denaturation temperature (T(m)) of the adsorbed proteins due to surface denaturation, while more extensive flocculation (d(43) > 20 microm) occurred above T(m) due to thermal denaturation. In the secondary emulsions, the extent of droplet flocculation below T(m) was reduced substantially (d(43) approximately 0.8 microm), which was attributed to the ability of adsorbed carrageenan to increase droplet-droplet repulsion. However, extensive droplet flocculation was observed above T(m) because carrageenan desorbed from the droplet surfaces. Differential scanning calorimetry showed that iota-carrageenan and beta-Lg interacted strongly in aqueous solutions containing 0 mM NaCl, but not in those containing 150 mM NaCl, presumably because salt weakened the electrostatic attraction between the molecules.     

Effect of pH on interface composition and on quality of oil-in-water emulsions made with hen egg yolk

Constituents of egg yolk are key ingredients of many food emulsions. They contribute to create an interfacial film between oil and water, which determines largely the characteristics of the emulsions. Food emulsions prepared with yolk are made at various pHs. However, the effect of pH on the adsorption of yolk constituents and on the composition of the interfacial film is not known. The present study deals with the influence of pH (3, 6 and 9), on protein interface concentration and composition, change in interfacial tension, and oil droplet diameter, of emulsions made with yolk. Emulsions were prepared as follows: 0.5% w/v of yolk; oil volume fraction: 0.375, homogenisation rate: 20 000 rpm/2 min. pH 6 provided the best conditions to prepare emulsion with yolk. The average diameter of oil droplets was lower at pH 6 (8.5 μm) than at pH 3 (11.8 μm) and pH 9 (13.5 μm). The interfacial protein concentration was higher at pH 6 (1.7 mg m⁻²) than at pH 3 and pH 9 (0.5 mg m⁻²). At pH 6, all the proteins of yolk, except phosvitin, were adsorbed at the interface and the interfacial tension at steady-state was lower (10 mN m⁻¹) than at pH 3 (15 mN m⁻¹) and pH 9 (30 mN m⁻¹). At pH 3, proteins at the interface are mainly phosvitin, and, at pH 9, some apoproteins of LDL and HDL. The pH modulates the composition of yolk proteins at the interface, mainly by modifying the net charge of the proteins causing their repulsion or dimerisation.     

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.     

Dynamic adsorption and characterization of phospholipid and mixed phospholipid/protein layers at liquid/liquid interfaces

Drop profile analysis tensiometry is applied to study the adsorption dynamics of phospholipids, proteins and phospholipid/protein mixtures at liquid/liquid interfaces. Measurements of the dynamic interfacial tension of phospholipid layers give information on the adsorption mechanism and the structure of the adsorption layer. The equilibrium and dynamic adsorption of pure protein solutions, i.e. human serum album (HSA), beta-lactoglobulin (beta-LG), beta-casein (beta-CA), can be explained well by the thermodynamic model of Frumkin and the diffusion-controlled adsorption theory. The adsorption behavior from mixed phospholipid/protein solutions was also investigated in terms of dynamic interfacial tensions. Interestingly, a "skin-like" folded film of pure protein or phospholipid/protein complex layers can be observed at curved surfaces at the water/oil interfaces. The addition of phospholipids accelerates the formation of the folded structure at the drop surface through co-adsorption of proteins.     

Methylcellulose-induced stability changes in protein-based emulsions

The emulsifying and oil-in-water stabilizing properties of methylcellulose (MeC) were investigated in bovine serum albumin (BSA)-based emulsions. The creaming stability, flocculation, surface concentration of BSA and MeC and droplet size were determined. Results obtained showed modifications of creaming rates that were related to MeC concentrations in the continuous and dispersed phases. Viscosity effects on creaming and changes in average droplet size (d₄₃) relating to droplet coverage were identified and delineated. Studies performed on macroscopic oil–water and air–water interfaces were used to identify interfacial structuring and composition. A good agreement was found between droplet surface composition and the resistance to coalescence of emulsion droplets. Emulsions that demonstrated a more rigid-like adsorbed interfacial layer were more stable with respect to coalescence. This study involving model emulsion systems provides a new insight into the stability of industrial preparations containing mixtures of proteins and polysaccharides.     

Towards predicting the stability of protein-stabilized emulsions

The protein concentration is known to determine the stability against coalescence during formation of emulsions. Recently, it was observed that the protein concentration also influences the stability of formed emulsions against flocculation as a result of changes in the ionic strength. In both cases, the stability was postulated to be the result of a complete (i.e. saturated) coverage of the interface. By combining the current views on emulsion stability against coalescence and flocculation with new experimental data, an empiric model is established to predict emulsion stability based on protein molecular properties such as exposed hydrophobicity and charge. It was shown that besides protein concentration, the adsorbed layer (i.e. maximum adsorbed amount and interfacial area) dominates emulsion stability against coalescence and flocculation. Surprisingly, the emulsion stability was also affected by the adsorption rate. From these observations, it was concluded that a completely covered interface indeed ensures the stability of an emulsion against coalescence and flocculation. The contribution of adsorption rate and adsorbed amount on the stability of emulsions was combined in a surface coverage model. For this model, the adsorbed amount was predicted from the protein radius, surface charge and ionic strength. Moreover, the adsorption rate, which depends on the protein charge and exposed hydrophobicity, was approximated by the relative exposed hydrophobicity (Q_H). The model in the current state already showed good correspondence with the experimental data, and was furthermore shown to be applicable to describe data obtained from literature.     

Effect of dispersion pH on the formation and stability of Pickering emulsions stabilized by layered double hydroxides particles

Using positively charged plate-like layered double hydroxides (LDHs) particles as emulsifier, liquid paraffin-in-water emulsions stabilized solely by such particles are successfully prepared. The effects of the pH of LDHs aqueous dispersions on the formation and stability of the emulsions are investigated here. The properties of the LDHs dispersions at different pHs are described, including particle zeta potential, particle aggregation, particle contact angle, flow behavior of the dispersions and particle adsorption at a planar oil/water interface. The zeta potential decreases with increasing pH, leading to the aggregation of LDHs particles into large flocs. The structural strength of LDHs dispersions is enhanced by increasing pH and particle concentration. The three-phase contact angle of LDHs also increases with increasing pH, but the variation is very small. Visual observation and SEM images of the interfacial particle layers show that the adsorption behavior of LDHs particles at the planar oil/water interface is controlled by dispersion pH. We consider that the particle-particle (at the interface) and particle-interface electrostatic interactions are well controlled by adjusting the dispersion pH, leading to pH-tailored colloid adsorption. The formation of an adsorbed particle layer around the oil drops is crucial for the formation and stability of the emulsions. Emulsion stability improves with increasing pH and particle concentration because more particles are available to be adsorbed at the oil/water interface. The structural strength of LDHs dispersions and the gel-like structure of emulsions also influence the stability of the emulsions, but they are not necessary for the formation of emulsions. The emulsions cannot be demulsified by adjusting emulsion pH due to the irreversible adsorption of LDHs particles at the oil/water interface. TEM images of the emulsion drops show that a thick particle layer forms around the oil drops, confirming that Pickering emulsions are stabilized by the adsorbed particle layers. The thick adsorbed particle layer may be composed of a stable inner particle layer which is in direct contact with the oil phase and a relatively unstable outer particle layer surrounding the inner layer.     

Evaluation of adsorption of nonionic surfactants blend at water/oil interfaces

The inherent biocompatibility of Span and Tween surfactants makes them an important class of nonionic emulsifiers that are employed extensively in emulsion and foam stabilization. The adsorption of Span-Tween blend at water/oil surface of emulsion has been investigated using a population balance model for the first time. Destability of emulsion was modeled by considering sedimentation, coalescence and interfacial coalescence terms in population balance equation (PBE). The terms of coalescence efficiency and interfacial coalescence time were considered as a function of surface coverage of droplets by surfactant molecules. The surface coverage at different surfactant concentrations was determined by minimization of difference between the model predictions and experimental average droplet sizes. After optimization, the surface coverage outputs were fitted with different adsorption isotherms to evaluate the adsorption behavior of Span-Tween surfactants blend at water/oil surface. The results show that Freundlich isotherm can predict the adsorption behavior of closer to the experimental observation. Moreover, fitted parameters imply the favorable adsorption of Span-Tween blend at water/oil interface.     

Preparation of PEG-modified urethane acrylate emulsion and its emulsion polymerization

In order to improve stability and reduce droplet size, the PEG-modified urethane acrylates were synthesized by the reaction of polyethylene glycol (PEG) with residual isocyanate groups of urethane acrylate to incorporate hydrophilic groups into the molecular ends. The droplet sizes of the PEG-modified urethane acrylate emulsions were much smaller than those of unmodified urethane acrylate emulsions at the same surfactant composition, and the droplet sizes of these emulsions were significantly effected not by surfactant compositions and types, but by the reaction molar ratio of PEG, because the urethane acrylate containing polyoxyethylene groups as terminal groups aided the interfacial activity of surfactant molecules and acted as a polymeric surfactant. The actions of PEG-modified urethane acrylate were confirmed by the investigation of adsorption of urethane acrylate in a water/benzene interface.For polymerization of emulsions, the stability of emulsion in the process of emulsion polymerization was changed by the type of surfactant or initiator. In the case of emulsion polymerization with a water soluble initiator (K₂S₂O₈), the emulsions prepared using TWEEN 60 were broken in the process of polymerization. However, polymerization of these emulsions could be carried out using an oil soluble initiator (AIBN). The conversion of emulsion polymerization changed with the type of urethane acrylates, that is, the reaction molar ratio of PEG to 2-HEMA.     

Emulsification of caraway essential oil in water by lecithin and β-lactoglobulin: emulsion stability and properties of the formed oil–aqueous interface

The stability and droplet size of protein and lipid stabilised emulsions of caraway essential oil as well as the amount of protein on the emulsion droplets have been investigated. The amount of added protein (β-lactoglobulin) and lipid (phosphatidylcholine from soybean (sb-PC)) were varied and the results compared with those obtained with emulsions of a purified olive oil. In general, emulsions with triglyceride oil proved to be more stable compared with those made with caraway essential oil as the dispersed phase. However, the stability of the emulsions can be improved considerably by adding sb-PC. An increase in the protein concentration also promoted emulsion stability. We will also present how ellipsometry can be used to study the adsorption of the lipid from the oil and the protein from the aqueous phase at the oil–water interface. Independently of the used concentration, close to monolayer coverage of sb-PC was observed at the caraway oil–aqueous interface. On the other hand, at the olive oil–aqueous interface, the presence of only a small amount of sb-PC lead to an exponential increase of the layer thickness with time beyond monolayer coverage. The amounts of β-lactoglobulin adsorbed at the caraway oil–aqueous interface and at the olive oil–aqueous interface were similar, corresponding roughly to a protein monolayer coverage.     

Brij类表面活性剂与Laponite纳米颗粒的相互作用及其稳定乳液的研究

通过表面张力、Zeta电位和流变学参数的测定, 研究了聚氧乙烯烷基醚类非离子型表面活性剂(Brij 30和Brij 35)在合成锂皂石(Laponite)纳米颗粒表面的吸附及对Laponite水分散体系中颗粒间相互作用和体系粘度的影响. 结果表明, 这类表面活性剂能显著地吸附在Laponite颗粒表面上, 且吸附量随其分子中POE链长短而不同. 这种吸附没有改变Laponite粒子的带电性质, 但一定程度地降低了Laponite颗粒Zeta电位; 吸附也会减弱颗粒间的相互作用, 降低体系的粘度. 实验以Laponite和Brij为乳化剂, 制备了O/W型乳状液. 乳液稳定性变化和乳液粒径分布结果表明, 体系中Brij的浓度较低时, 乳液的性质主要是由Laponite颗粒决定的; 而Brij浓度较高时, 则主要取决于Brij表面活性剂. 高速剪切含Brij的Laponite水分散体系, 剪切后表面张力随时间的变化表明, 剪切作用会使得吸附在Laponite颗粒表面的Brij分子不同程度地解吸下来. 这也意味着乳液制备时, 高速剪切作用也会造成Brij分子自Laponite颗粒表面的脱附, 这可能是非离子表面活性剂与阳离子表面活性剂对负电固体颗粒稳定乳液影响不同的原因.