Effect of droplet size on lipid oxidation rates of oil-in-water emulsions stabilized by protein

In emulsions lipid oxidation is mainly influenced by the properties of the interface. The aim of this work was to investigate the effects of droplet size and interfacial area on lipid oxidation in protein-stabilized emulsions. Emulsions, made of stripped sunflower oil (30% vol/vol) and stabilized by BSA were characterized by surface area values equal to 0.7, 5.1, and 16.3 m²·cm⁻³ oil. The kinetics of O₂ consumption and conjugated diene (CD) formation, performed on emulsions and nonemulsified controls, showed that emulsification prompted oxidation at an early stage. On condition that oxygen concentration was not limiting, the rates of O₂ consumption and CD formation were higher when the interfacial area was larger. Protein adsorbed at the interface probably restrained this pro-oxidant effect. Once most of the O₂ in the system was consumed (6–8 h), CD remained steady at a level depending directly on the ratio between oxidizable substrate and total amount of oxygen. At this stage of aging, the amounts of primary oxidation products were similar whatever the droplet size of the emulsion. Hexanal and pentane could be detected in the headspace of emulsions only at this stage. They were subsequently produced at rates not depending on oil droplet size and interfacial area.     

Role of operating conditions in determining droplet size and viscosity of tackifier emulsions formed via phase inversion

Water‐based pressure‐sensitive adhesives are formulated by combining a polymer latex with a tackifier emulsion. The latter is an oil‐in‐water emulsion made by the process of phase inversion. The phase inversion itself is carried out in a stirred tank fitted with a heating jacket by progressively adding water to a water‐in‐oil emulsion. The point of onset of phase inversion and the characteristics of the emulsion that is formed depend on process conditions; these include temperature, rate of water addition, and agitation speed. The role of these operating conditions is elucidated here. Increasing temperature delayed the onset of phase inversion slightly, but it did not affect emulsion particle size, provided it remained below a critical value. Agitation speed had to be increased upon increasing the water flow rate to prevent increasing the particle size. Finally, the point of onset of phase inversion could be predicted reasonably well using a model available in the literature. © 2010 American Institute of Chemical Engineers AIChE J, 57: 96–106, 2011     

A review of nonlinear oscillatory shear tests: Analysis and application of large amplitude oscillatory shear (LAOS)

Dynamic oscillatory shear tests are common in rheology and have been used to investigate a wide range of soft matter and complex fluids including polymer melts and solutions, block copolymers, biological macromolecules, polyelectrolytes, surfactants, suspensions, emulsions and beyond. More specifically, small amplitude oscillatory shear (SAOS) tests have become the canonical method for probing the linear viscoelastic properties of these complex fluids because of the firm theoretical background [1], [2], [3] and [4] and the ease of implementing suitable test protocols. However, in most processing operations the deformations can be large and rapid: it is therefore the nonlinear material properties that control the system response. A full sample characterization thus requires well-defined nonlinear test protocols. Consequently there has been a recent renewal of interest in exploiting large amplitude oscillatory shear (LAOS) tests to investigate and quantify the nonlinear viscoelastic behavior of complex fluids. In terms of the experimental input, both LAOS and SAOS require the user to select appropriate ranges of strain amplitude (γ₀) and frequency (ω). However, there is a distinct difference in the analysis of experimental output, i.e. the material response. At sufficiently large strain amplitude, the material response will become nonlinear in LAOS tests and the familiar material functions used to quantify the linear behavior in SAOS tests are no longer sufficient. For example, the definitions of the linear viscoelastic moduli G′(ω) and G″(ω) are based inherently on the assumption that the stress response is purely sinusoidal (linear). However, a nonlinear stress response is not a perfect sinusoid and therefore the viscoelastic moduli are not uniquely defined; other methods are needed for quantifying the nonlinear material response under LAOS deformation. In the present review article, we first summarize the typical nonlinear responses observed with complex fluids under LAOS deformations. We then introduce and critically compare several methods that quantify the nonlinear oscillatory stress response. We illustrate the utility and sensitivity of these protocols by investigating the nonlinear response of various complex fluids over a wide range of frequency and amplitude of deformation, and show that LAOS characterization is a rigorous test for rheological models and advanced quality control.     

高固含量乳液性能与粒径分布及反应条件的关系

以乳胶粒粒径分布为切入点,讨论了制备高固含量乳液的反应条件与产品性能的关系     

激光粒度仪测定PTA粒径分布

介绍了激光粒度仪测定PTA粒径分布的分析方法 ,通过试验确定了分析条件 ,并与筛分法分析结果进行了对比。该方法简捷、快速、重现性好 ,适用于PTA产品的粒度分析。     

现代颗粒粒度测量技术

颗粒粒度的测定已成为现代测量学的一个重要分支。介绍了筛分法、显微镜法、沉降分析法、电感应法等传统颗粒粒度测量技术的方法和原理 ,并着重介绍了光散射法、质谱法、基于布朗运动的粒度测量法等近年来发展起来的颗粒粒度测量新方法     

Latex particle size and CPVC

Monodisperse vinyl acetate/butyl acrylate (85/15) latexes were prepared with particle sizes between 200 and 1200 nm. These were used in a simple paint formulation with TiO₂ as the only pigment. Two optical methods were used for determination of the critical pigment volume concentration (CPVC) of these paints. These are specular gloss at an incidence angle of 85 ° and CIE Z (lightness) values of a blue tinted formulation. Both methods gave coincident results for the CPVC as a function of latex particle size. Our data fit the expression X = 1.44Y^2.65 where X = number of latex particles/number of pigment particles, at CPVC and Y = diameter of pigment particles/diameter of latex particles. Earlier, Bowell reported the same exponential relation, with a different pre-exponential factor, for acrylic latexes. The common exponent is explained with a model in which the latex and pigment particles assume a condition close to minimum porosity during packing. CPVC reflects the packing of particles during the initial stages of dryness of the latex. The ‘universal’ relation reported here permits facile prediction of the effects of latex particle size on the CPVC and binding capacity in water-based paints.     

Emulsification of a viscous monomer mix: Particle size and size distribution

A non-Newtonian mixture of monomers, their copolymer and pigment was dispersed into water with emulsifier by a rotor-stator homogenizer (Brinkmann Polytron). Volume median diameters d₅₀ of the droplets, measured by Coulter Counter or optical microscopy, were typically 4–20 μm; d₅₀ was about inversely proportional to monomer fraction (0.2 to 1.0), or to rotor speed (4000 to 11000 rpm). Increasing the emulsifier from 0.1 % to 3% roughly halved d₅₀; volume fraction of organic phase had little effect. Turbulent dispersion theory (Calabrese et al., 1986a, b), adapted to non-Newtonian drops, represented the data but with different numerical constants. A high geometric standard deviation, around 1.7 but increasing slightly as monomer fraction decreased, may be due to non-uniform turbulence and to the complexity of breakup at high viscosity.     

Effect of microchannel structure on droplet size during crossflow microchannel emulsification

A monodispersed oil-in-water emulsion was continuously produced using a crossflow-type silicon microchannel plate in which a liquid flow path for the continuous phase was made, and on each side of the wall of the path, an array of regular-sized slits (microchannels) was precisely fabricated on a micrometer scale by photolithography. A flat glass plate was tightly attached to the microchannel plate to cover the top of the microchannels. Regular-sized oil (triolein) droplets were generated by pressing the oil through the microchannels into a continuous phase of 0.3 wt% aqueous sodium lauryl sulfate. The average size of the oil droplets was regulated within a range of 11.3 to 28.2 μm by changing the microchannel structural features such as the shape of the cross section and outlet, the equivalent diameter, and the length of the terrace, which is a flat area fabricated at the outlet of the microchannels. In every case, the droplet size distribution was narrow, and the geometric standard deviation was 1.03 or less.     

SPG膜乳化与界面聚合法制备单分散多孔微囊膜

小粒径单分散中空储库结构微囊膜的制备具有重要学术意义和实用价值。为此采用了SPG(Shirasu-Porous-Glass)膜乳化法和界面聚合法,对小粒径单分散多孔微囊膜的制备进行了较系统的实验研究,以期为进一步制备多孔内接枝环境感应型功能凝胶开关的小粒径单分散微囊型靶向式药物载体提供基体。研究结果表明,采用SPG膜乳化法可制得单分散性良好的乳液液滴,进而采用界面聚合法可得到单分散微囊。用膜乳化方法易于控制乳液液滴及微囊的大小,在研究中SPG膜乳化法制备的乳液液滴及微囊的平均粒径大约是所用膜孔径的3．6倍。微囊膜的多孔性可以靠改变溶剂和单体的成分来进行控制,扫描电镜检测结果表明所制备出的不同粒径级别的单分散微囊膜均具有良好的多孔结构。     

Large amplitude oscillatory shear rheology for nonlinear viscoelasticity in hectorite suspensions containing poly(ethylene glycol)

The effect of poly(ethylene glycol) (PEG) on the nonlinear viscoelasticity of Laponite suspensions containing NaCl was investigated with large amplitude oscillatory shear rheology. The molecular weight (M_w) of PEG was 4k, 10k and 35k, and the concentration of PEG was varied from 0.063 wt% to 2.4 wt%. The dynamic strain sweep showed that the nonlinearity appeared at γ₀ > 30% with a stress overshoot at γ₀ = 50-70%. The intensity ratio I_3/1 from Fourier-transform increased with γ₀ when entering the nonlinear regime and leveled off at γ₀ ≥ 100% with higher slope and constant value for the PEG of higher M_w or lower concentration. I_3/1 revealed the structure difference in the suspensions induced by adsorbing PEG in the nonlinear regime. The minimum- and large-strain rate viscosities η_M and η_L from the Lissajous curve were found to be sensitive to the nonlinear viscoelasticity and the peak of η_M and η_L appeared at lower γ₀ with higher maximum following the same dependency as I_3/1 on PEG M_w and concentration. The overall nonlinearity parameters N_E and N_V were proposed in this paper and demonstrated to reflect the difference in the Laponite suspensions with PEG more clearly and more effectively.     

超细粉体粒度测试方法浅析

介绍了超细粉体粒度测试的几种主要方法(激光衍射散射法、离心沉降法、颗粒图像处理仪和库尔特颗粒计数器)的测试原理及性能特点，并进行了比较。讨论了粒度测试中应注意的几个问题，重点分析了测试条件不同对粒度测定的影响，得出分散介质、分散剂、超声功率及超声时间等是影响粒度测定的最主要的因素；指出了重复性、真实性、易操作性、量程和动态范围是评价粒度仪测试性能的几个重要指标。     

微细物料颗粒大小的测定(续)

4.2 显微镜法 显微镜法包括使用光学显微镜和电子显微镜,是唯一可以观察和测量颗粒的方法。几种显微镜在测定颗粒大小时的性能如表3。     

固体颗粒稳定乳状液研究进展

从脱附功、最大毛细压、界面和体相流变性质及颗粒在界面上的相互作用等方面综述了固体颗粒乳状液的稳定机理;介绍了影响固体颗粒稳定乳状液性质的相关因素,如颗粒的性质,水相的矿化度和pH,油相性质,颗粒初始时所在的相以及颗粒与表面活性物质的协同作用;指出了固体颗粒稳定乳状液存在的问题和发展前景。     

确定喷雾干燥中雾滴粒度分布的轨迹分析法

由于喷雾干燥中雾滴的运动较复杂,所以目前多是通过实验测量来确定雾滴粒度分布,有限多不便因素。通过模拟粒子受力情况以及与空气的传质传热,采用时间增量法和拖动坐标系逐步跟踪粒子的运动轨迹,建立数学模型,再结合实验中样板取样所得到的数据,即可确定喷雾干燥中雾滴粒度分布。     

激光粒度仪测试阻燃剂级氢氧化镁粒度分布

建立了实用、准确和快速的阻燃剂级氢氧化镁粉体粒度分布的测试方法。采用MS2000激光粒度分析仪研究了待测样品质量、泵转速、分散时间、分散介质、分散剂种类以及分散剂质量浓度等因素对阻燃剂级氢氧化镁粉体粒度分布测试结果的影响。适宜条件:以700 mL水为分散介质,洗洁精为分散剂,分散剂质量浓度控制在0.1~0.3 g/L,氢氧化镁粉体样品质量范围为0.020~0.035 g,泵转速为1 400~2 000 r/min,超声波分散时间为2~5 min,超声波分散后立即测量。     

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.     

颗粒的粒径及形貌对ZrB2陶瓷等静压成型和注浆成型的影响

对研磨前后ZrB2粉料的粒径分布、颗粒形貌、等静压坯体密度和料浆粘度的变化作了对比分析,研究结果表明:研磨后ZrB2颗粒的粒径明显减小,约为1.3μm;研磨前ZrB2颗粒多为球形,研磨后棱角明显;等静压坯体密度由研磨前的2.9g/cm3提高到研磨后的3.3g/cm3;研磨前的ZrB2粉料料浆的粘度较小。