Interfacial viscosity and the stability of emulsions

A viscous traction interfacial viscometer was constructed to study a mineral oil-water-emulsifier system. The effect on interfacial viscosity of the synthetic emulsifiers Span 80 and Pluronic L42 were investigated, along with the bioemulsifier produced by the yeast Torulopsis petrophilum. In the case of the synthetic emulsifiers, it was found that conditions which maximized interfacial viscosity also maximized emulsion stability. The same relation held for T. petrophilum emulsifier once all free fatty acids had been removed from the broth. Emulsion stability was measured by calculating mean diameters, as well as emulsion indices.     

Rheology of oil in water emulsions with added solids

The effect of added solids on the rheology of oil in water emulsions was investigated. The range of the oil concentration, solids free basis, was (0-70%) and the solids volume fraction was (0-0.16). The solids mean diameter was 45 μm and it was about four times larger than the oil droplets. In the absence of added solids, non-Newtonian behaviour was observed for oil concentrations above 40%. The added solids increased the emulsion viscosity in a manner similar to the addition of solids to a homogeneous fluid. The rheological data of all the emulsion-solids mixtures investigated were correlated as relative viscosity versus solids volume fraction, where the relative viscosity is defined as the ratio of the emulsion-solids mixture viscosity to the solids-free emulsion viscosity. In the case of non-Newtonian systems, the emulsion-solids mixture viscosity and the solids-free emulsion viscosity were calculated at the same shear stress. The Barnea and Mizrahi viscosity correlation was found to fit the data well.     

Rheology of lecithin dispersions

Dispersions of lecithin (1–25% solids, dry basis) in soybean oil or water were subjected to rheological measurement in a coaxial-cylinder viscometer. The different rheological characteristics determined included yield stress, flow behavior index, consistency index, and apparent viscosity. Pseudoplastic behavior was observed for all lecithin emulsions in oil and for dispersions in water. The flow behavior indices for lecithin-oil emulsions (0.855–0.875) were higher than for lecithin-water dispersions (0.472–0.584). Yield stresses were observed only for lecithin-water dispersions. An increase in the concentration of lecithin in oil or water increased yield stress, consistency index, and apparent viscosity. The apparent viscosities of the lecithin-oil emulsions were higher than those for corresponding lecithin-water dispersions. The power law model can adequately fit (r≥0.988, p≤0.01) the shear-rate vs. shear-stress data for lecithin-oil emulsions, whereas the Herschel-Bulkley model was suitable (r≥0.988, p≤0.01) for lecithin-water dispersions.     

Effect of sunflower lecithins on the stability of water-in-oil and oil-in-water emulsions

Lecithins are frequently applied in the food industry as emulsifiers, viscosity regulators, and dispersing agents. The main aim of the present work was to study the emulsifying capability of diverse sunflower lecithins so as to evaluate the functionality of these by-products, which are not extensively used at present. The experimental results obtained for water-in-oil (W/O) emulsions showe that dispersions containing levels of 0.1% lecithins were more stable against coalescence than a control system, whereas those with 1% emulsifying agent exhibited the opposite behavior. On the other hand, faster sedimentation kinetics were observed at a concentration of 0.1% than at 1%. Lecithins with high phospholipid content, especially phosphatidylethanolamine and phosphatidylinositol, were found to be the best emulsifying agents for W/O dispersions. In the case of oil-in-water emulsions, it was possible to observe two processes: creaming of emulsions with the addition of 1% of lecithins, and instant creaming followed by coalescence of the cream phase in those cases corresponding to 0.1% added lecithin.     

Improvement of lecithin as an emulsifier for water-in-oil emulsions by thermalization

The various forms (granular, liquid, gum) of lecithin can be heated under certain conditions of time and temperature to greatly improve their properties as emulsifiers for water-in-oil emulsions. Viscosity, discontinuous phase-holding capacity, stability and water retention were greatly enhanced in emulsions containing thermalized lecithins as the emulsifier compared to those prepared with corresponding amounts of nonthermalized lecithins. The improved emulsification properties of the thermalized lecithins appeared to be due, at least in part, to an increase in diglycerides and free fatty acids resulting from the thermal degradation of phosphatides.     

A fourier transform infrared spectroscopy study of the effect of temperature on soy lecithin-stabilized emulsions

The effect of temperature on soy lecithin-stabilized emulsions was studied using Fourier transform infrared spectroscopy (FTIR). Oil-in-water (o/w) 4% (wt/vol) soy lecithin emulsions were prepared in 6% (vol/vol) medium-chain triglycerides and 94% (vol/vol) water using a two-stage homogenizer set at a pressure of 3000 psig. Three types of emulsions were used in this study: emulsions containing Lecigran and Lecimulthin as emulsifiers and a control emulsion, with no emulsifier added. After preparation, the emulsions were cooled to 4°C, held at this temperature, and spectra were collected after 1 h. The emulsions and reference water were raised to room temperature (22°C) and held at that temperature for 1 h and the spectra collected. The temperature was raised 15°C over the temperature range of 22 to 82°C, and spectral data were collected similarly. The four regions used for this determination in the subtracted spectra of the emulsion were those contributing to -OH vibration, -CH₂ stretching, H-O-H bending vibrations, and P=O, C-O-C, and P-O-C vibrations. The control emulsion was greatly affected at temperatures other than room temperature. This was due to the lack of lecithin as an emulsifier, resulting in a destabilization of the emulsion with temperature increases. The vibrational peaks for the emulsion containing Lecimulthin were found to be lower than those for the emulsion made with Lecigran due to greater water bonding. The control had the highest peaks at the -OH regions because of reduced interaction at the oil-water interface. Both of the emulsions with phospholipids remained stable throughout the temperature range. FTIR is a potentially powerful tool that could be used in the rapid determination of emulsion stability in food systems by measuring emulsifier-water interactions.     

含聚合型乳化剂反相乳液体系的稳定性研究

以煤油为油相,丙烯酸钠水溶液为水相,自制的非离子聚合型乳化剂-Span80丙烯酸酯(Span80AA)、Span80和Twen80组成复合乳化剂,制备反相乳液。计算出Span80AA的HLB值,考察了乳化剂浓度、水相体积分数Φ及单体浓度对乳液类型及稳定性的影响。结果表明:HLB(Span80AA)=2.709;Span80AA、Span80和Twen80的最佳质量比为0.8∶0.3∶0.1。形成稳定的反相乳液理想条件是:复合乳化剂质量分数为6%~8%;Φ<57%;单体浓度为2.0~3.5 mol/L。     

Rheological properties of hydrophobically modified alkali-swellable acrysol emulsions

The rheological behaviour of aqueous solutions of two commercial anionic hydrophobically modified alkali-swellable emulsions (HASE), Acrysol TT615 and RM5, was studied. These polymeric systems, initially in the form of low-viscosity latices at low pH, tend to swell and increase their viscosity when neutralised with base. The steady-shear and dynamic properties of these polymers were measured over a wide range of concentration, at constant pH=9 and temperature of 20°C. The intrinsic and zero-shear viscosities were used to identify the concentration regimes of the polymer solutions. In the case of Acrysol TT615, the solution exhibited shear-thinning characteristics at a concentration above 500 ppm. The Carreau model described well the viscosity function of the 1000 and 2000 ppm solutions. Considerable viscosity enhancement and a change in the flow curve profile were observed at concentrations above 2000 ppm. At high polymer concentration. the zero-shear viscosity was not detectable, and the power law model was adequate to characterize these solutions. By contrast, the RM5 solutions exhibited nearly Newtonian behaviour over the whole concentration range considered. Elasticity measured from the first normal stress difference indicated that Acrysol TT615 was more elastic than Acrysol RM5. Dynamic measurements revealed that both storage (G′) and loss (G″) moduli increased with polymer concentration. In the higher frequency and concentration regions, G′ > G″ was obseved for TT615, whereas G″ > G′ for RM5.     

Rheological properties of emulsions containing modified soy protein isolates

The feasibility of replacing common emulsifiers with soy protein isolates (SPI) in low-calorie salad dressings was evaluated. Structural modifications of SPI were obtained by thermal-acidic treatment with or without neutralization (TH1.6N and TH1.6, respectively). Modification of flow properties of TH1.6 and TH1.6N emulsions by thermal treatment and different protein concentrations was evaluated through shear stress vs. shear rate measurements in a rotational viscometer. TH1.6N isolates generated emulsions with higher shear stress and apparent viscosity than those prepared with TH1.6. Heated TH1.6N emulsions at 10% protein gave the highest values of shear stress and plastic flow behavior. These emulsions had high consistency, viscosity, and elasticity. TH1.6N isolates had lower emulsifying capacity than TH1.6, probably due to the higher protein aggregation produced during neutralization, which prevented protein unfolding. These isolates would be suitable for the preparation of stable emulsions with adequate consistency and elasticity.     

pH值对氧化铝高浓度悬浊液剪切流变性能的影响

1 INTRODUCTION The suspensions employed in ceramic processing are highly concentrated. These snspensions are normally known as slip or slurry in materials science and engi-neering. It is of great interest that concentrated sus-pension exhibit many of the phenomena of very dilute colloidal suspensions[i]. This is probablybecause both the snspension systems have charged particles, so that the principles of colloid chemistry can be applied for them.     

反应型乳化剂对丙烯酸酯乳液稳定性和粘度的影响

使用反应型乳化剂烯丙氧基壬基酚聚氧乙烯(10)醚硫酸铵(DNS-86)和常规乳化剂十二烷基硫酸钠(SDS)制备丙烯酸酯乳液,研究了这两种乳化剂对乳液稳定性的影响,比较了两种乳化剂对乳液粘度的作用方式,探讨了反应型乳化剂对乳液粘度的影响机理。结果表明:与常规乳化剂SDS相比,使用反应型乳化剂DNS-86制得的乳液稳定性得到提高,当DNS-86的用量为2.0%时,乳液的稳定性最好。乳液的粘度随乳化剂用量的增大呈锯齿状增加。使用DNS-86制备的乳液粒径较大、粒径分布较窄、粘度较小。     

Effect of oil viscosity on the rheology of oil-in-water emulsions with added solids

This paper reports an experimental study on the effect of oil viscosity on the rheology of oil-in-water (o/w) emulsions with added solids. Four oils having a viscosity range of 0.0024 to 306 Pa . s were used. The size ratio of the solids to oil droplets was varied from 2 to 16. The addition of smaller size solids to the emulsions yielded a higher viscosity than that of larger solids at the same solids volume fraction. However, when the solids were sufficiently large such that the emulsions behaved as a continuous phase towards the solids, the viscosity of the emulsion-solids mixtures tended to be independent of the solids size. The critical size ratio of the solids to oil droplets, above which the emulsions behaved as a continuous phase towards the solids, increased with the oil viscosity. The critical size ratio varied between 3 and 10.     

Rheology of ordinary and low-impact environmental concretes

This study deals with the rheological properties of concrete mixtures incorporating various types of mineral additions as a partial replacement of cement in order to produce a low-impact environmental concrete. The control mixture contained only Portland cement as the binder, while the remaining mixtures incorporated binary cementitious blends of slag, limestone filler, and fly ash with different rates of replacement. After mixing, the plastic viscosity and yield stress of the concretes were evaluated at different slump values using a rheometer apparatus. The results showed that the type of mineral additions and the rate of substitution affect the rheological parameters of low-impact environmental concrete. Indeed, increasing the degree of substitution leads to an increase in the plastic viscosity of the concrete made with different types of additions used in this study.     

聚丙烯酸改性高固含量漆蜡乳液的制备及性能

以漆蜡为原料,制备高固含量的漆蜡乳液,并进一步采用聚丙烯酸改性对高固含量的漆蜡乳液进行改性。以乳液固含量、离心稳定性和黏度为考察指标,研究引发剂用量、温度、时间和乳化剂用量对乳液性能的影响。采用四因素四水平的正交实验设计优化聚丙烯酸改性改性漆蜡乳液的工艺条件。结果表明,在引发剂用量0.3%、温度90℃、乳化时间300min、乳化剂用量10%的条件下,聚丙烯酸改性高固含量漆蜡乳液的固含量为60%,黏度为38500mPa·s,离心稳定性为1级。     

Effects of emulsifiers on the oxidative stability of soybean oil TAG in emulsions

The effects of two types of commercial emulsifiers, sucrose FA esters and polyglycerol FA esters, on the oxidation of soybean oil TAG-in-water emulsions were studied. Both emulsifiers influenced the oxidative stability of soybean oil TAG in the emulsion, but they had little effect on the oxidation of TAG in bulk phase. When the TAG were dispersed with sucrose esters having the same FA composition, the oxidative stability increased as their hydrophilic-lipophilic balance (HLB) increased. On the other hand, when the HLB was the same, the oxidative stability increased with increasing acyl chain length of the FA esterified on sucrose ester. However, the effect of the polyglycerol ester could not be explained by the relationship with HLB or the acyl composition. When the stability of TAG in emulsion was compared under the same concentrations of TAG, emulsifier, and oxidation inducer, the TAG dispersed with sucrose esters were oxidatively less stable than with polyglycerol esters. Analysis of the emulsion droplet size suggested that the lower oxidative stability of TAG dispersed with sucrose esters was partly due to their relatively smaller droplet sizes.     

Oil-in-water emulsions formulated with sunflower lecithins: Vesicle formation and stability

Oil-in-water emulsions (30∶70, vol/vol) were formulated with sunflower lecithin to characterize the destabilization processes and the vesicles formed. Dispersions containing levels of 0.1% lecithin were more stable against coalescence than the control system. When the lecithin concentration was increased to 0.5%, the presence of spherical structures, such as vesicles, was recorded that occluded the emulsion inside. Vesicles underwent a creaming process, and a narrow coalescence zone was detected in the upper layers of the samples. As the lecithin concentration was increased, more vesicles were formed, representing as much as 80% of the system volume. A reduction in the average size of vesicles was observed at high lecithin concentrations (2.5 and 5.0%). The vesicle size distribution changed as a function of lecithin concentration, decreasing the ratio of large to small particles in the same way. Coalescence took place in zones where large-volume vesicles were in contact in the upper portion of the tube sample. The results obtained suggest that sunflower lecithins present interesting emulsifying properties that may prove useful in food technology.     

The photooxidation and stabilisation of water-borne acrylic emulsions

The influence of light exposure on the photooxidative stability of aqueous acrylic based latices is examined by Fourier transform-infrared spectroscopy (FT-IR) and hydroperoxide analysis. These are based on emulsion polymerised formulations of methyl methacrylate and butyl acrylate. Here acrylic latices based on different formulations are chosen as homo-polymers and copolymers. The nature of impurities and oxidation products generated during their manufacture are characterised and inter-related to their influence on subsequent photooxidative degradation. This involves the use of reflectance FT-IR spectroscopy to show functional group changes together with colorimetric UV analysis to determine photochemical generation of hydroperoxides. The early chemical changes and their subsequent influence on the physical and chemical properties of the latices during the later stages of photooxidation are found to exhibit a close inter-relationship. In terms of stabilisation co-reactive hindered piperidine stabilisers are found to be effective and nono-extractable. However, the incorporation of simple terminal dialkyl acrylamide/methacrylamide groups are equally as effective.     

Preparation of water-in-oil and ethanol-in-oil emulsions by membrane emulsification

In this work, water-in-oil emulsions (W/O) and ethanol-in-oil emulsions (E/O) emulsions were prepared successfully by membrane emulsification. The emulsifiers selected were PGPR and MO-750 for the W/O and E/O emulsions, respectively. For W/O emulsions prepared with an oil pre-filled membrane, the dispersed flux was lower and the droplet size sharper than that obtained with a water pre-filled membrane. On the contrary, for E/O emulsions prepared with the membrane pre-filled with oil, the dispersed phase (ethanol) rapidly pushed out the oil from the membrane pores. Therefore, the pre-treatment of the membrane had almost no effect on the dispersed phase flux and on the droplet size. The droplet size distribution of the E/O emulsion was close to that obtained with a classical homogenizer. The dispersed phase fluxes were high and no fouling was observed for our experimental conditions (1.6 l emulsion, 10 wt% ethanol). These results confirm that membrane emulsification could be an interesting alternative for the preparation of E/O emulsions for the purpose of biodiesel fuels, considering the scale-up ability of membranes and their potentiality for industrial processes.     

无机盐阴阳离子对稠油水包油型乳状液稳定性的影响

考察了两性/非离子复配表面活性剂浓度、无机/有机复配碱浓度、不同价态正负离子对稠油水包油型乳状液稳定性的影响规律。实验结果表明:随着复配表面活性剂浓度的增加,乳状液的分水率先急剧降低后缓慢下降;复配碱对乳状液的稳定性存在最优浓度;无机盐对乳状液的稳定性具有双重作用,低浓度盐提高乳状液的稳定性,高浓度盐降低乳状液的稳定性;一价阳离子对乳状液的稳定性影响顺序为KCl> NaCl> LiCl;二价阳离子对乳状液稳定性的影响程度为MgCl₂> CaCl₂;一价阴离子对分水率的影响顺序为NaCl> NaBr> NaI;高价阴离子对乳状液稳定性的影响程度为Na₂SO₄> NaCl> Na₃PO₄。     

丙烯酸酯乳液改性的研究进展

文章就丙烯酸酯乳液改性的研究现状及其用途作了详细论述,重点介绍了有机硅改性丙烯酸酯乳液和聚氨酯改性的丙烯酸酯乳液(PUA)以及氟改性丙烯酸酯乳液的发展情况,并简要地对丙烯酸酯乳液改性的未来方向作了展望。