Phase behaviors of diblock copolymer/nanorod composites under oscillatory shear flow

The phase behaviors of lamellar diblock copolymers (DBCPs) melts and lamellar DBCPs/nanorods (NRs) composites subjected to oscillatory shear flow, have been investigated using dissipative particle dynamics. The oscillatory shear is a quite common shearing mode used in experiments and manufacturing processes. The rich lamellar (LAM) reorientation and morphological transition of systems strongly depend on the shear amplitude and shear frequency. At very low frequency, the amplitude‐induced phase behaviors of DBCPs melts or DBCPs/NRs composites are quite similar to those subjected to a steady shear. For DBCPs/NRs case, we control NRs concentration low 15% to preserve LAM morphology in the nanocomposites, and simultaneously consider both types of selective and nonselective NRs. Our aim is to compare the different inductions on DBCPs melts or nanocomposites caused by shear amplitude and frequency, and observe how the NRs are oriented and dispersed in phase‐separated copolymers matrix while under oscillatory shear, and how the presence of selective/nonselective NRs affects the shear‐induced LAM reorientations and rheological properties of systems. Our results show the NRs orientation not only directly depend on the imposed shear flow but also is interfered by the alignment of shear‐stretched copolymer molecules. The shear viscosity decreases with the frequency decreases, also influenced by the NRs concentration and surface property. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

用于超声造影成像的颗粒稳定气泡制备

超声成像由于其无创无痛、可实时监测以及成本低廉等优点,被广泛用于多种疾病诊断。但是,某些人体组织回声较弱,需要借助具有强回声特性的超声造影剂微气泡来实现对比成像。目前临床批准使用的微气泡多采用表面活性剂或磷脂作为稳定剂,其稳定效果有限、血液循环时间短,限制了对小病灶等需要长时间观察的病变部位的检查能力。颗粒稳定气泡(Particle Stabilized Bubbles, PSBs)是由颗粒代替传统表面活性剂稳定的气泡,由于其具有高稳定性、低毒性等优势,有望用于超声造影。但目前关于颗粒稳定气泡的制备及应用研究较少,其原因主要在于体系对颗粒的接触角范围要求很窄,一旦超过界定范围,则气泡稳定性急速下降。本工作以制备出稳定的颗粒稳定气泡,考察其作为超声造影剂的效果为目标。通过筛选不同亲疏水性的颗粒作为稳定剂,并对其荷电性、浓度、粒径、水相及气相等因素进行考察,制备得到了由壳聚糖纳米颗粒(CNPs)稳定的颗粒稳定气泡(CPSBs)。并在此基础上,通过细胞毒性实验、溶血性、病理切片等实验评价了体系的生物安全性,通过小动物超声成像仪考察了其体内外造影性能。实验结果表明该体系具有良好的生物安全性以及良好的体内外造影能力,表明其具有作为超声造影剂应用的潜力。     

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     

Morphology and particle size of nanograde polyurethane/polyacrylate hybrid emulsions

Poly(urethane acrylate) (PUA) composite particles were prepared by seeded surfactant‐free emulsion polymerization. The aqueous polyurethane (PU) dispersions were used as seed particles. The diameters of the seed particles of the aqueous PU dispersions and PUA composite latexes were measured by dynamic light scattering. The microstructures of the PUA composite emulsion particles were observed by transmission electron microscopy. The influences of the amount of the hydrophilic chain extender, the types of initiators, and the PU/polyacrylate (PA) weight ratios on the diameters of the aqueous PU and composite emulsions were also studied. The results showed that the PUA composite emulsions formed a core–shell structure with PU as the shell and with PA as the core. The diameter of the PU seed particles and the particle size of the PUA composite emulsions greatly depended on the amounts of the hydrophilic chain extender used in the preparation of the PU seed; when the hydrophilic chain extender concentration was 7.4%, the average diameter of the PUA composite emulsion particles showed the minimum value. The types of initiators and PU/PA weight ratios did not have a significant influence on the diameter of the PUA composite latex particles. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

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.     

Rheology of crosslinked entangled polymers: Shear stiffening in oscillatory shear

Polyborosiloxane (PBS) was synthesized from boric acid and hydroxyl-terminated polydimethylsiloxane (PDMS). The oscillatory shear behavior of PBS formed by PDMS with different molecular weight was studied. The relaxation time of PBS was calculated by Doi-Edwards model. Finally, the shear-stiffening mechanism of reversibly crosslinked entangled polymer was obtained. Shear stiffening occurs at lower shear frequencies, which is mainly due to crosslinking bonds and friction between molecules hindering the movement of molecules. The increase in storage modulus at high frequencies is attributed to the resistance caused by entanglement in the stretching process of molecular chains. In addition, the molecular weight is greater and the degree of shear stiffening is higher. Such a conclusion is useful to further study the application of shear stiffening. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48421.     

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     

一体式陶瓷外膜直接乳化法制备单分散水包油乳液

膜乳化法是靠膜两侧的压差使分散相通过微孔膜,以小液滴的形式分散在连续相中而形成乳状液的方法．与转一定体系、高压均化等传统制乳方法相比,膜乳化法所制得的乳液具有液滴尺寸均一、节能、剪应力小等特点,可应用于食品、医药、聚合物工业等领域．过去的十几年中,尽管在膜乳化方面进行了大量的工作,过程参数对乳滴尺寸的影响并未完全研究清楚．甚至在一些研究中,仅仅把平均乳滴直径作为分布参数．     

大粒径硅溶胶粒径增长及其控制工艺的研究

大粒径硅溶胶在涂料、化学机械抛光、催化剂载体等工业领域中都有着极其广泛的应用。在添加适量催化剂的条件下,采用单质硅粉氧化法制备了大粒径溶胶。重点介绍了大粒径硅溶胶的分类、性质及应用,通过研究不同条件下大粒径硅溶胶的粒径增长过程分析了大粒径硅溶胶制备过程中的粒径增长机理。在添加阴离子表面活性剂的条件下,采用浓缩蒸馏实验研究了大粒径硅溶胶粒径增长与其浓度的关系,结果表明：随着大粒径硅溶胶浓度的增大,大粒径硅溶胶的粒径呈先减小后增大的趋势。最后提出了制备大粒径硅溶胶的粒径控制工艺。     

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。     

Droplet size and viscosity of tackifier emulsions formed via phase inversion

Tackifier dispersions used in pressure‐sensitive adhesives are made by phase inverting an aqueous rosin ester emulsion. The recipe also includes rosin acid and potassium hydroxide which react to form a surfactant. The amount of surfactant available plays a key role in determining dispersion properties. As the surfactant concentration increases, the point of phase inversion is delayed to larger dispersed phase concentrations. This also results in excess dispersant in the liquid phase and a narrower particle size distribution, even though the droplet size remains relatively unchanged.     

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     

Relationship between droplet size and fluid flow characteristics in miniemulsion polymerization of methyl methacrylate

Static mixer (SM) can be applied for emulsification, but the fundamental understanding of the nature of fluid flow and mixing in static mixers, is however poor. Droplet size is a very important parameter in miniemulsion systems and affects strongly the mechanism of particle formation in polymerization reactions. In this study, static mixer was used as homogenization device for emulsification of methyl methacrylate (MMA). Re number (Re) was obtained for SM inserted tube in different flow rates. It was demonstrated the nature of fluid flow was turbulent under our experimental conditions. The relationship between droplet size—the most important variable in our study—and Weber number (We) was investigated. The results showed that the ratio of the droplet size to the pipe diameter was fit as an exponential function with an order of −0.35. The polymerization of created droplets under certain We values by SM showed that it is possible to obtain a reasonable 1 : 1 copy of droplets to the particles. All these, indicate that using relationship between We and droplet size allow one to obtain acceptable condition of droplet nucleation in miniemulsion polymerization. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

激光粒度仪测定纳米磷酸铁粉体粒度的研究

采用Zetasizer Nano S90型激光粒度分析仪对纳米磷酸铁粉体进行粒度测定的实验研究。主要考察了分散剂及其用量、超声时间、磷酸铁在测定液中的含量等因素对粉体分散性能及粒径测定的影响,确定了纳米磷酸铁粉体粒度分析的最佳条件,即以蒸馏水为分散介质,质量浓度为1 g/L的十二烷基硫酸钠为分散剂,纳米磷酸铁质量浓度为0.2 g/L,超声时间为15 min时,激光粒度仪测得的结果与扫描电镜表征结果基本一致。     

激光粒度仪测量PVC树脂粒径的影响因素

通过激光粒度仪仪器参数设置和不同样品加入量的对比试验,确定了测量PVC树脂粒径分布的Mastersizer 3000型激光粒度仪最佳仪器参数:搅拌速度2 700 r/min、超声时间60 s、遮光度7.0％～9.0％.     

制备单分散含单体O/W乳液的SPG膜乳化过程

采用Shirasu多孔玻璃（SPG）膜乳化法制备了单分散含对苯二甲酰氯（TDC）单体的O/W乳液,系统地研究了SPG膜乳化过程的影响因素.实验结果表明,采用SPG膜乳化法制备单分散O/W乳液时,选择阴离子表面活性剂比考虑亲水亲油平衡（HLB）匹配更重要;增大分散相或连续相的黏度,能够改善乳液的单分散性和稳定性;随着单体浓度增加,乳液的单分散性变差,液滴的平均粒径逐渐变小.当SPG膜孔径大于1.0 μm左右时,可得到单分散的含TDC单体乳液;而当孔径小于1.0 μm左右时,水分子更容易扩散并溶解到油水界面甚至油相内部与TDC生成对苯二甲酸（TPA）,TPA积累到一定程度在油水界面上析出将膜孔堵塞,从而无法制得单分散乳液.随着乳化时间增长,乳液的平均直径逐渐变小、单分散性逐渐变差.     

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.     

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.