Colloidosomes: selectively permeable capsules composed of colloidal particles

We present an approach to fabricate solid capsules with precise control of size, permeability, mechanical strength, and compatibility. The capsules are fabricated by the self-assembly of colloidal particles onto the interface of emulsion droplets. After the particles are locked together to form elastic shells, the emulsion droplets are transferred to a fresh continuous-phase fluid that is the same as that inside the droplets. The resultant structures, which we call "colloidosomes," are hollow, elastic shells whose permeability and elasticity can be precisely controlled. The generality and robustness of these structures and their potential for cellular immunoisolation are demonstrated by the use of a variety of solvents, particles, and contents.     

Novel Colloidal Interactions in Anisotropic Fluids

Small water droplets dispersed in a nematic liquid crystal exhibit a novel class of colloidal interactions, arising from the orientational elastic energy of the anisotropic host fluid. These interactions include a short-range repulsion and a long-range dipolar attraction, and they lead to the formation of anisotropic chainlike structures by the colloidal particles. The repulsive interaction can lead to novel mechanisms for colloid stabilization.     

A class of microstructured particles through colloidal crystallization

Microstructured particles were synthesized by growing colloidal crystals in aqueous droplets suspended on fluorinated oil. The droplets template highly ordered and smooth particle assemblies, which diffract light and have remarkable structural stability. The method allows control of particle size and shape from spheres through ellipsoids to toroids by varying the droplet composition. Cocrystallization in colloidal mixtures yields anisotropic particles of organic and inorganic materials that can, for example, be oriented and turned over by magnetic fields. The results open the way to controllable formation of a wide variety of microstructures.     

Fast drop movements resulting from the phase change on a gradient surface

The movement of liquid drops on a surface with a radial surface tension gradient is described here. When saturated steam passes over a colder hydrophobic substrate, numerous water droplets nucleate and grow by coalescence with the surrounding drops. The merging droplets exhibit two-dimensional random motion somewhat like the Brownian movements of colloidal particles. When a surface tension gradient is designed into the substrate surface, the random movements of droplets are biased toward the more wettable side of the surface. Powered by the energies of coalescence and collimated by the forces of the chemical gradient, small drops (0.1 to 0.3 millimeter) display speeds that are hundreds to thousands of times faster than those of typical Marangoni flows. This effect has implications for passively enhancing heat transfer in heat exchangers and heat pipes.     

Monodisperse double emulsions generated from a microcapillary device

Double emulsions are highly structured fluids consisting of emulsion drops that contain smaller droplets inside. Although double emulsions are potentially of commercial value, traditional fabrication by means of two emulsification steps leads to very ill-controlled structuring. Using a microcapillary device, we fabricated double emulsions that contained a single internal droplet in a core-shell geometry. We show that the droplet size can be quantitatively predicted from the flow profiles of the fluids. The double emulsions were used to generate encapsulation structures by manipulating the properties of the fluid that makes up the shell. The high degree of control afforded by this method and the completely separate fluid streams make this a flexible and promising technique.     

甘薯果胶的乳化特性研究

【目的】探讨甘薯果胶构成及乳化特性,为开发和利用薯渣中的果胶资源提供理论依据。【方法】采用酸法从薯渣中制备果胶,咔唑硫酸法测定果胶半乳糖醛酸含量,滴定法测定酯化度,高效液相色谱法测定果胶分子量。在不同果胶浓度(0.5%-4.0%,w/v)和不同油相体积分数(5%-40%,v/v)条件下进行乳化液特性研究。【结果】甘薯果胶半乳糖醛酸含量为73.28%,酯化度31.71%,分子量约为292kD。随着果胶浓度升高,乳化液粒径(d4,3)减小,乳化颗粒吸附果胶比例显著升高,乳化液表观黏度增大,乳化活性(EA)和乳化稳定性(ES)升高(P0.05)。此外,随着油相体积分数的增加,d4,3增大,EA及乳化液表观黏度升高(P0.05),被乳化颗粒吸附果胶比例下降及ES呈现出先升高后降低的趋势。【结论】薯渣是制备果胶的良好材料,酸法制备甘薯果胶属低甲氧基果胶,具有良好的乳化能力和乳化稳定性。     

油包水乳化物在交流电场中流动时的聚结特性

在矩形聚结管道上对基础油包水乳化物在层流流态下通过50Hz的交流电场时,乳化物中的水滴发生的聚结现象进行了研究。重点研究了电极板施加的电压,乳化物的含水量和乳化物在电场中的流速对乳化物中水滴聚结的影响。试验结果表明,电极板施加的电压(即聚结电场的强度)和乳化物在电场中的流速对乳化物中的水滴的聚结影响显著,而乳化物的含水量对水滴的聚结影响很小。     

Space-filling polyhedron: its relation to aggregates of soap bubbles, plant cells, and metal crystallites

A fourteen-faced space-filling polyhedron which closely approximates the actual distribution of four-, five- and six-sided polygons found in packings of soap bubbles and biological cells is proposed as an alternative to the Kelvin tetrakaidecahedron as the ideal polyhedron for these packings. This polyhedron may also have relevance to crystallite morphologies and crystal structures.     

细胞脂滴的物理结构及影响其稳定的因素

脂滴是储存中性脂质的细胞器,对能量代谢至关重要,它们广泛存在于存在于动物、植 物、真菌,甚至细菌中。脂滴是油包水乳液在细胞水溶液中的分散相,乳液的基本生物物理原理 对于脂滴生物学的重要性正在被人们所重视。由于其存在于分散油相和水胞质之间的独特结 构,其形成,生长和收缩的具体机制尤为复杂,这种机制使细胞能够在代谢能量或膜合成需求发 生变化时使用乳化油,有利于为细胞新陈代谢提供更有利的途径。此外,脂滴表面的磷脂作为 表面活性剂组成的调控对脂滴的稳态和表面蛋白靶向至关重要。在这里,我们回顾脂滴的乳液 结构及其在     

番鸭(Cairina moschata)甲状腺的显微与亚微结构

番鸭甲状腺实质由大小不一、近似球形的滤泡组成,其上皮细胞呈低立方形至扁平形.电镜下的滤泡上皮细胞,胞质内存在多量由被吞饮的胶状质与溶酶体相结合的胶质滴,线粒体外围有以核糖体规律排列的粗面内质网,网腔内多被低密度的无定形内容物所扩大.番鸭甲状腺实质存在滤泡旁细胞(C细胞).经Ehrlich苏木素染色的滤泡旁细胞呈球形、体积大、染色较浅,单个散在或2个并列位于滤泡外围的结缔组织内,不与滤泡腔接触,可明显与滤泡上皮细胞相区别.     

Layer-by-layer growth of binary colloidal crystals

We report the growth of binary colloidal crystals with control over the crystal orientation through a simple layer-by-layer process. Well-ordered single binary colloidal crystals with a stoichiometry of large (L) and small (S) particles of LS2 and LS were generated. In addition, we observed the formation of an LS3 superstructure. The structures formed as a result of the templating effect of the first layer and the forces exerted by the surface tension of the drying liquid. By using spheres of different composition, one component can be selectively removed, as is demonstrated in the growth of a hexagonal non-close-packed colloidal crystal.     

牛初乳乳清W/O型乳状液稳定性

乳状液稳定性和流动性是制备牛初乳乳清微胶囊的关键因素.采用Span和Tween 2种非离子型乳化剂,制备了含有5％阿拉伯胶和麦芽糊精的牛初乳乳清W/O乳状液.比较亲水亲油平衡(HLB)值、乳化剂复配、油水比、乳化剂添加量和超声乳化次数等工艺参数对乳状液稳定性的影响,确定了最佳工艺参数:HLB值为4.8,Span - 85和Tween - 60为复配乳化剂,油水比1:1,超声乳化12次(每次超声8 s,间歇5 s).显微镜下观察分散液滴大小均一,乳状液平均粒径约为2μm.流变学分析结果表明,该乳状液具有剪切稀化特征,符合Herschel- Bulkley模型.     

Supracolloidal reaction kinetics of Janus spheres

Clusters in the form of aggregates of a small number of elemental units display structural, thermodynamic, and dynamic properties different from those of bulk materials. We studied the kinetic pathways of self-assembly of "Janus spheres" with hemispherical hydrophobic attraction and found key differences from those characteristic of molecular amphiphiles. Experimental visualization combined with theory and molecular dynamics simulation shows that small, kinetically favored isomers fuse, before they equilibrate, into fibrillar triple helices with at most six nearest neighbors per particle. The time scales of colloidal rearrangement combined with the directional interactions resulting from Janus geometry make this a prototypical system to elucidate, on a mechanistic level and with single-particle kinetic resolution, how chemical anisotropy and reaction kinetics coordinate to generate highly ordered structures.     

Origin and Migration of Oil: Oil may consist of hydrocarbons that collected from waters containing natural solubilizers

A relationship exists between the composition of crude oil and the solubility of the component hydrocarbons in dilute colloidal electrolyte solutions, suggesting that crude oil consists of hydrocarbons that were once solubilized in formation waters. It is not solubility in ordinary water or solubility in complete soap solution that correlates with the composition of oil but, rather, solubility in soap micelles. Because it implies a possible unloading mechanism, this concept is attractive, for it follows that when a soap solution is diluted with water, the soap micelles disperse and the hydrocarbons solubilized therein appear as discrete, filterable oil droplets. Thus, it would seem that crude oil originates during the compaction of a sedimentary basin by virtue of the fact that sediment hydrocarbons dissolve in waters containing natural solubilizers and then come out of solution as oil droplets. The composition of crude oil as now understood is consistent with this hypothesis. And-most important-it is now possible to formulate meaningful questions, the answers to which, upon investigation in both field and laboratory, will go far toward enabling us to assess the validity of the mechanism presented here. In addition to the implications regarding the composition of crude oil that are inherent in the hypothesis that crude oil collects from aqueous colloidal electrolyte solutions, there are several interesting implications from the geological viewpoint. To mention one, such a mechanism would lend credence to the suggestion that the source beds of petroleum are not necessarily unique accumulations of hydrocarbons in a limited area but, rather, may generally be coincident with the area from which water is expressed into the porous strata that eventually form the reservoirs.     

Surfactant-mediated two-dimensional crystallization of colloidal crystals

Colloidal particles can form unexpected two-dimensional ordered colloidal crystals when they interact with surfactants of the opposite charge. Coulomb interactions lead to self-limited adsorption of the particles on the surface of vesicles formed by the surfactants. The adsorbed particles form ordered but fluid rafts on the vesicle surfaces, and these ultimately form robust two-dimensional crystals. This use of attractive Coulomb interaction between colloidal particles and surfactant structures offers a potential new route to self-assembly of ordered colloidal structures.     

植物叶面农药雾滴蒸发时间研究在我国的应用

病虫害防治效果的决定因素之一是叶面对药液吸收速度的快慢.作物叶子表面的微观构造不同,对农药药液的吸收速度也不同.而雾滴在叶面上蒸发时间的长短,会改变叶子对药液的吸收量和吸收速度,从而影响农药施用效率.介绍了近期围内外农药雾滴在植物叶面上蒸发时间的研究方法,包括雾滴蒸发过程测试系统的建立、试验设计方法和数据网片的处理方法等,为提高农药施用效率指明了方向.     

航空喷施与人工喷施方式对水稻施药效果比较

【目的】找出小型无人直升机航空喷施雾滴在水稻植株的沉积分布规律,并比较农用无人机航空喷施方式和人工喷施方式的不同。【方法】通过喷施试验研究了市场上主流的2种不同型号无人机(油动单旋翼和电动单旋翼小型无人直升机)、不同作业参数对水稻冠层雾滴沉积分布结果的影响,并比较了不同农用无人机航空喷施方式和人工喷施方式的效果和效率。【结果】航空喷施方式下的作业参数对雾滴沉积量和穿透性均有着相同的影响趋势,均表现出作业速度越慢,雾滴在植株间的沉积量越多,穿透性越好;作业高度越低,沉积量越多,但穿透性较差。但由于不同类型无人机旋翼风场强度的不同,油动单旋翼小型无人直升机喷施作业时作业高度对雾滴的沉积均匀性影响明显,而电动单旋翼小型无人直升机喷施作业时作业速度对雾滴的沉积均匀性影响明显。人工喷施作业的雾滴在水稻植株上、中、下3层的沉积均匀性最差,且雾滴在水稻植株间的穿透性也最差,为110.42%,人工喷施雾滴大部分都沉积在植株上层,只有3.27%的药液量到达植株的底部,而航空喷施作业有10%~30%的药液量能到达植株的底部。【结论】从不同喷施作业方式的效果和效益来看,航空喷施雾滴沉积效果优于人工喷施雾滴沉积效果,作业效率约为人工喷施方式的10倍,且成本低,效益高。     

Field-Induced Layering of Colloidal Crystals

An electrohydrodynamic methodology has been developed that makes possible the precise assembly of two- and three-dimensional colloidal crystals on electrode surfaces. Electrophoretically deposited colloidal particles were observed to move toward one another over very large distances (greater than five particle diameters) to form two-dimensional colloidal crystals for both micrometer- and nanometer-size particles. This coalescence of particles with the same charge is opposite to what is expected from electrostatic considerations and appears to result from electrohydrodynamic fluid flow arising from an ionic current flowing through the solution. The ability to modulate this "lateral attraction" between particles, by adjusting field strength or frequency, facilitates the reversible formation of two-dimensional fluid and crystalline colloidal states on the electrode surface. Further manipulation allows controlled structures to be assembled.     

Two-dimensional nematic colloidal crystals self-assembled by topological defects

The ability to generate regular spatial arrangements of particles is an important technological and fundamental aspect of colloidal science. We showed that colloidal particles confined to a few-micrometer-thick layer of a nematic liquid crystal form two-dimensional crystal structures that are bound by topological defects. Two basic crystalline structures were observed, depending on the ordering of the liquid crystal around the particle. Colloids inducing quadrupolar order crystallize into weakly bound two-dimensional ordered structure, where the particle interaction is mediated by the sharing of localized topological defects. Colloids inducing dipolar order are strongly bound into antiferroelectric-like two-dimensional crystallites of dipolar colloidal chains. Self-assembly by topological defects could be applied to other systems with similar symmetry.