Emulsion Ripening through Molecular Exchange at Droplet Contacts

Two coarsening mechanisms of emulsions are well established: droplet coalescence (fusion of two droplets) and Ostwald ripening (molecular exchange through the continuous phase). Here a third mechanism is identified, contact ripening, which operates through molecular exchange upon droplets collisions. A contrast manipulated small‐angle neutron scattering experiment was performed to isolate contact ripening from coalescence and Ostwald ripening. A kinetic study was conducted, using dynamic light scattering and monodisperse nanoemulsions, to obtain the exchange key parameters. Decreasing the concentration or adding ionic repulsions between droplets hinders contact ripening by decreasing the collision frequency. Using long surfactant chains and well‐hydrated heads inhibits contact ripening by hindering fluctuations in the film. Contact ripening can be controlled by these parameters, which is essential for both emulsion formulation and delivery of hydrophobic ingredients.     

Algebraic analysis of multigrid algorithms

We study the convergence rate of multilevel algorithms from an algebraic point of view. This requires a detailed analysis of the constant in the strengthened Cauchy–Schwarz inequality between the coarse‐grid space and a so‐called complementary space. This complementary space may be spanned by standard hierarchical basis functions, prewavelets or generalized prewavelets. Using generalized prewavelets, we are able to derive a constant in the strengthened Cauchy–Schwarz inequality which is less than 0.31 for the L² and H¹ bilinear form. This implies a convergence rate less than 0.15. So, we are able to prove fast multilevel convergence. Furthermore, we obtain robust estimations of the convergence rate for a large class of anisotropic ellipic equations, even for some that are not H¹‐elliptic. Copyright © 1999 John Wiley & Sons, Ltd.     

Influence of the efficacy of interfacial modification on the coarsening of cocontinuous PS/HDPE blends during quiescent annealing

This article studies the quiescent annealing of three different cocontinuous polystyrene/high‐density polyethylene blends modified with two types of interfacial agents of widely different efficacies. Quantitative analysis of phase growth was obtained using mercury porosimetry. In a previous work, it was shown that one of these modifiers, a symmetrical diblock copolymer, has a high affinity for the interface and demonstrates virtually no micelle formation prior to saturation of the blend interface. The other modifier, a hydrogenated SEBS of 70/30 composition, forms micelles at elevated concentrations of modifier. In this study, it is shown that the cocontinuous phase size grows linearly without modifier, whereas the addition of both interfacial modifiers significantly suppresses the PE/PS phase coarsening and results in nonlinear phase growth behavior. The effect of the diblock copolymer on suppressing coarsening, however, is much more effective than that for the triblock case clearly supporting the tendency toward micelle formation for that latter modifier. In the case of unmodified PE/PS, the driving force for capillary pressure effects is so high that it is the capillary instability phenomena that dominate the coarsening and hence result in a linear growth of pore size with annealing time. When interfacial modifiers are added, the influence of reduced interfacial tension and lower pore size polydispersity significantly diminishes both capillary pressure effects and capillary instability phenomena. In that case, capillary pressure becomes the main rate determining step resulting in a nonlinear dependence of pore size with annealing time. It is shown that both the viscosity of the phases and the temperature of annealing can strongly influence coarsening behavior at low levels of interfacial modifier. Under all those conditions, however, nonlinear phase growth for the partially compatibilized system was maintained. These results clearly show that careful quantitative coarsening experiments using mercury porosimetry can be used as a tool to analyze the efficacy of interfacial modifiers for highly continuous or cocontinuous systems. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 711–721, 2006     

Monte Carlo simulation of antiphase boundaries and growth of antiphase domains in Al5Ti3 phase in Al-rich γ-TiAl intermetallics

Predominantly two kinds of antiphase boundaries (APBs) form in Al₅Ti₃, which is an Al-rich ordered derivative of the γ-TiAl (L1₀) phase. This phase can be viewed as a periodic arrangement of lean rhombs and squares on the Ti-rich (002) planes of the tetragonal L1₀. Energies of the two types of APBs were varied in a Monte Carlo simulation by suitably changing the pair interaction parameters. APBs of both types form boundaries of Al₅Ti₃ antiphase domains (APDs), which coarsen with time. An important observation in this regard is that mostly facetted APBs form at lower ageing temperatures, whereas curved APBs appear to form at relatively higher ageing temperatures. The findings of this work suggest that there exists a critical temperature, akin to the roughening transition temperature for crystals, that marks the transition from facetted to curved APBs.     

双色驻波场中梯形三能级原子所受整流偶极力的涨落分析

本文基于文献[1]利用双色驻波场作用于三能级原子获得宏观数量个光学波长上符号保持不变的整流偶极力的工作基础上,运用量子回归定理计算了所得整流偶极力在一个光学波长上的涨落.结果表明:原子偶极零点振动与光场幅度梯度相互作用引起的偶极力的涨落D1的值较大,是整流偶极力涨落的主要因素,且其随空间的变化规律与整流偶极力相似;原子偶极与真空零点振动相互作用导致偶极力的涨落Ds较小,几乎可以忽略不计.由于力的起伏所导致的加热效应不利于中性原子的偶极束缚[6].     

Dislocation dynamics simulations with climb: kinetics of dislocation loop coarsening controlled by bulk diffusion

Dislocation climb mobilities, assuming vacancy bulk diffusion, are derived and implemented in dislocation dynamics simulations to study the coarsening of vacancy prismatic loops in fcc metals. When loops cannot glide, comparison of the simulations with a coarsening model based on the line tension approximation shows good agreement. Dislocation dynamics simulations with both glide and climb are then performed. Allowing for glide of the loops along their prismatic cylinders leads to faster coarsening kinetics, as direct coalescence of the loops is now possible.     

钕对Mg7Zn2Al镁合金显微组织及力学性能的影响

采用光学显微镜、XRD、SEM和万能实验机等手段研究了稀土Nd(0.3%,0.6%,0.9%)对Mg7Zn2Al镁合金显微组织和力学性能的影响。结果表明:Mg7Zn2Al镁合金中添加Nd后,显微组织中有针状或棒状的Al2Nd和AlNd等稀土相生成,合金中的共晶组织(α-Mg+Mg32(Al,Zn)49+Mg7Zn3)得到了明显细化;但是α-Mg有粗化趋势,呈现发达的树枝状或胞状,共晶相由粗大连续的网状变为细小的块状或颗粒状分布在树枝晶的一次枝晶臂或二次枝晶臂的间隙。随着Nd含量的增加,合金的抗拉强度和延伸率呈逐渐下降趋势,显微组织的粗化是造成合金拉伸性能降低的主要原因,而硬度没有明显的变化。     

Non-Self-Similar Behavior in the LSW Theory of Ostwald Ripening

The classical Lifshitz–Slyozov–Wagner theory of domain coarsening predicts asymptotically self-similar behavior for the size distribution of a dilute system of particles that evolve by diffusional mass transfer with a common mean field. Here we consider the long-time behavior of measure-valued solutions for systems in which particle size is uniformly bounded, i.e., for initial measures of compact support. We prove that the long-time behavior of the size distribution depends sensitively on the initial distribution of the largest particles in the system. Convergence to the classically predicted smooth similarity solution is impossible if the initial distribution function is comparable to any finite power of distance to the end of the support. We give a necessary criterion for convergence to other self-similar solutions, and conditional stability theorems for some such solutions. For a dense set of initial data, convergence to any self-similar solution is impossible.