Anomalous Birefringence in Discretely Phase-Separated Glasses

Rods of Corning code 7070 alkali borosilicate glass were stretched or compressed at 600° to 700°C before or after discrete phase separation and given a postpulling heat treatment at around 500°C. As expected, sections of the rods displayed anomalous birefringence which has been identified by Takamori to originate from anisotropy in the form and the distribution of the second-phase particles. Specimens so obtained were reheated, and the birefringence measured as a function of temperature to separate the contributions of form, distribution, and the thermal expansion mismatch (if any) between the separated phases. It is clear that the form birefringence in 7070 glass is positive for stretched rods and negative for compressed rods and decays at lower temperatures than does the distribution birefringence which has an opposite sign. TEM replica micrographs show that the distribution birefringence decays as a function of temperature mostly because of phase dissolution and the reappearance of yet another phase randomly.     

Sodium Motion in Phase-Separated Sodium Silicate Glasses

The thermally stimulated polarization and depolarization current (TSPC/TSDC) technique was used to study Na^plus; ion motion in phase-separated silicate glasses containing between 10.3 and 20 mol% Na₂O. Generally, two TSDC peaks and a high-temperature background (HTB) current were observed. The two TSDC peaks were attributed to different types of Na^plus; motion, i.e. a short-range reorientation process and a longer-range translational motion. Changes in the microstructure affected only the size of the larger TSDC peak located at higher temperatures.     

Relaxation of Thermal Stress in Phase-Separated Borosilicate Glasses

Although the "apparent" viscosity of borosilicate glasses is known to increase with the progress of phase separation, temperatures at which the thermal strain is relieved are seen to decrease by the increase of phase separation. This behavior is explained by the difference in the "real" viscosity of each phase in the phase-separated glass and by the very low thermal expansion of the higher viscosity SiO₂-rich phase. The "annealing point" based on ASTM designations loses its meaning for phase-separated glasses of this type.     

Peculiar Morphology in Some Phase-Separated Multicomponent Silicate Glasses

Several researchers have reported the formation of convoluted, silica-rich, dispersed-phase particles during amorphous phase separation in some glass-forming silicate systems. These appear to be analogous to crystalline growth instabilities such as dendritic, fingered, and cellular structures that can arise during diffusion-controlled solidification in undercooled systems.     

Viscosity and Microstructure of Phase-Separated Borosilicate Glasses

The viscosity of a sodium borosilicate glass (SiO₂ 70, B₂O₃ 23, and Na₂O 7 wt%) was measured as a function of heat-treatment temperature and time for phase separation. The viscosity was shown to approach an equilibrium value unique to the heat-treatment temperature. The magnitude of the equilibrium viscosity increased as the heat-treatment temperature decreased. These results, plus electron microscopy of microstructure development, established that the viscosity of phase-separated borosilicate glasses is primarily controlled by the composition of the continuous, high-viscosity phase and that the effect, if any, of the microstructure size is small. In contrast to previous reports, the heat-treatment time required to attain the equilibrium composition was extremely long.     

Anisotropy of Second-Phase Distribution in Phase-Separated and Stretched Glasses

Computer simulation of the change in the distribution of second-phase particles, on stretching a phase-separated glass with randomly dispersed second-phase particles surrounded by a depleted region, indicated the development of a uniaxial anisotropy in distribution. The anisotropy, expressed by the ratio of the magnitude of directional components of nearest-neighbor distances, indicated a maximum at an elongation ratio (final length/initial length) <2, decreasing at further elongation. This is qualitatively similar to the microstructural birefringence data by Thomas. The results further indicate that, the higher the particle density, the greater the maximum anisotropy appearing at the smaller elongation ratio.     

Origin of Viscosity Increase of Phase-Separated Borosilicate Glasses

The viscosity of some borosilicate glasses increases with heat-treatment time for phase separation. The viscosity increase in the initial stage of phase separation is attributed to the composition change of the separated phases. The origin of the viscosity increase in the later stage of phase separation is the subject of controversy. Namely, the viscosity increase has been attributed to two different mechanisms: (1) environmental relaxation and (2) the increase of silica content in the high-viscosity silica-rich continuous phase. Analyses are presented to show that the latter model is consistent with the experimental data.     

Positron Annihilation in Phase-Separated BaO-SiO2 Glasses

The kinetics of amorphous phase separation in BaO-SiO₂ glasses was studied by small-angle X-ray scattering and positron annihilation. Results show that the annihilation of positrons depends primarily on the average composition of the glasses; it therefore does not depend on compositional fluctuations caused by phase separation and cannot be used to determine the kinetics of phase separation in glasses.     

Light Scattering from Phase-Separated Glass

The intensity of the light scattered from phase-separated glasses, rather than being constant as a function of angle as expected, exhibits increased backscattering. When interference effects can be neglected, Goldstein's diffusion-zone model, proposed to explain the scattering data, has been supported by experimental results. Although the refractive-index profile predicted by Goldstein seems to agree well with existing data, the present workers believe that the source of this profile is not a diffusion zone but rather the stress that results from the differing thermal-expansion characteristics of the 2 phases. By measuring depolarized scattering as a function of temperature in various scattering planes, the 2 models were compared directly. The diffusion model is shown to be inappropriate, whereas the qualitative predictions of the proposed stress model are confirmed, and the model is established.     

Rheology of Emulsion Explosives: a Practical Method

The Laray viscometer has been found to be useful for rheological characterization of the type of invert emulsion currently being utilized in commercial explosives. Shear rate can be varied over a range which encompasses typical emulsion processing conditions. The viscometer is also relatively inexpensive and simple to operate. Emulsion rheology is distinctly non-Kewtonian. Dependence of shear stress on shear rate is in accord with the power law, with shear rate exponents (n) varying from 0.3 to 0.6. Both n and the pre-exponential factor τ_ref depend on emulsion composition and processing history in a manner consistent with known emulsion rheology.     

保护胶体稳定的丙烯酸酯乳液流变性

分别采用常规乳化剂和羟乙基纤维素为保护胶体制备丙烯酸酯乳液。通过TEM分别观察乳胶粒的形态。利用流变仪测定剪切速率（Ds）-剪切应力（τ）关系、剪切速率（Ds）-黏度（η）关系。结果表明：采用羟乙基纤维素为保护胶体制备的乳液与常规乳液具有不同结构，该结构使其乳液体系流变性能不同。在相同剪切速率下，保护胶体制备的丙烯酸酯乳液的剪切力明显大于常规乳液的剪切力，该乳液在一定剪切速率范围内有剪切稀化现象。     

Characterizing Lecithin Interactions in Chocolate Using Interfacial Properties and Rheology

The functionality of chocolate is based on specific properties including how it flows. Cocoa butter and lecithin are two ingredients that help to control the flow properties of melted chocolate. Lecithin is an emulsifier that has been the preferred method of providing yield stress and viscosity control while reducing production costs by decreasing the amount of cocoa butter needed to achieve similar flow results. In this industrially oriented study, soy, sunflower, and dairy lecithin were compared by quantifying interfacial and rheological properties of lecithin in dark chocolate. Each lecithin source was added up to the 1.0% limit, which is the emulsifier maximum set forth by the Code of Federal Regulations. The compositions of each lecithin source were analyzed for total phospholipid composition, which were used to normalize data based on the total added phosphatides added for all samples. Differences in both phosphatide composition and fatty acid composition were found. Both interfacial tension between oil and water phases and contact angle between a cocoa butter drop and flat sucrose crystal surface decreased as the phosphatide concentration increased for each lecithin source. In terms of rheology, the yield stress first decreased with increasing lecithin content and then began to increase, whereas plastic viscosity continually decreased with addition of lecithin. Significant differences were seen for the different lecithin sources, even when compared on an equivalent phosphatide content. No correlations were found between interfacial properties and yield stress; however, direct correlations were found between both interfacial measures and plastic viscosity.     

The Origin of a Nonmonotonic Change in the Transparency of a Material during Crystallization of Phase-Separated Glasses

A model for calculating the light scattering by a material during crystallization of phase-separated glasses is proposed. The crystallization of inhomogeneity regions (particles) formed as a result of liquid–liquid phase separation and distributed over the vitreous matrix is considered within the proposed model. It is shown that a maximum in the light scattering by the material can be observed when the degree of crystallinity is equal to 0.5–1. The maximum is caused by incoherent scattering that occurs in a mixture of amorphous and crystallized particles, and the conditions of its appearance are associated with the presence of the ordering elements in the mutual arrangement of particles. It is noted that these conditions are probably realized upon crystallization of sodium niobium silicate glasses.     

Evolution of Interfacial Microstructure between Barium Titanate and Binary Glasses

Evolution of interfacial microstructure between BaTiO₃ and the binary glasses used as frits in thick-film technology has been studied. Possible reaction mechanisms for the interfacial compounds have been determined by comparing the results of the sintering study with the reaction of BaTiO₃, powder with glass powders. The interfacial microstructure can be divided into two types. The first type of interfacial microstructure is observed for glasses rich in PbO or Bi₂O₃ network modifiers and is characterized by the penetration of glass into the BaTiO₃ grain boundaries, accompanied by incorporation of Pb into the perovskite lattice. The second type of interfacial microstructure is observed for glasses rich in B₂O₃ or SiO₂ network formers and is characterized by the formation of interfacial compounds.     

Stress in Leached Phase-Separated Glass

When a phase-separated glass is leached, stresses develop because of release of thermal stresses, creation of surface area, ion exchange, and hydration. Analyses are presented for the thermal stresses, including the portion that develops on cooling from the heat-treatment temperature to the setting temperature of the less viscous phase. During leaching, the interfacial energy of the residual phase increases, so that phase tends to contract. A more important effect is the contraction caused by removal of alkali and B₂O₃ from the residual phase during leaching. The extent of removal of B₂O₂ decreases with heat-treatment time, t_H , because the scale of the microstructure increases as t^1/3_H. The change in residual B₂O₂ content with t_H is shown to be consistent with diffusion-controlled ion exchange. The dependence of stress on t_H in partially leached glasses, measured by Drexhage and Gupta, results principally from the change in extent of ion exchange; the reduction in surface area with increasing t_H also has a significant effect on the stresses.     

界面剪切流变技术在化学驱油体系应用研究进展

界面剪切流变技术可以提供化学驱油体系油水界面的结构和强度等信息,因此逐渐成为近年来研究化学驱油机理的重要方法。介绍了界面剪切流变技术的理论基础与测量方法,并对该技术在化学驱油体系的研究进展进行了综述,重点包括在驱油剂溶液、原油(模拟油)/水和原油(模拟油)/驱油剂三类体系中的应用现状。对界面剪切流变技术面临主要挑战和未来发展方向进行了展望。     

界面扩张流变性对碱驱采收率影响的研究

利用填砂管驱替实验和微观可视化实验,考察了不同质量分数NaOH体系的驱油规律,然后使用DSA100型界面扩张流变仪分析了原油/NaOH体系的界面性质,建立了NaOH驱油体系采收率与界面性质之间的联系。研究结果表明,NaOH质量分数由0.1%增加到2.0%,油水界面张力逐渐降低,碱驱体系提高采收率幅度先增后减,NaOH最佳质量分数为1.5%。界面扩张流变性对碱驱体系采收率的影响比界面张力更为直观,即界面弹性模量越大,油水界面强度越高,其封堵高渗通道的能力越强,可显著扩大波及体积;界面黏性模量越大,弹性模量和洗油效率越低,采收率也随之下降。     

Interfacial Rheology of Mixed Surfactants at the Oil/Water Interface

The interfacial rheology of surfactant mixtures (SBT and Tween^® 80) at the oil/water interface is investigated using toluene as a model oil. The surfactant ratio in the mixed system has an important impact on the interfacial properties. After adding Tween^® 80, the interfacial tension and modulus of SBT show remarkable changes. Compared with the individual SBT or Tween^® 80 systems, the interfacial properties of the mixed surfactant system improve, especially at a 1:1 ratio. At the optimum ratio, synergistic adsorption takes place resulting in improved asphalt emulsion stability.     

核／壳羧基乳液的合成,形态及流变性

本文研究了聚苯乙烯/聚(丙烯酸-2-乙基己酯-丙烯酸)核/壳型(?)基乳液的合成工艺,乳胶粒形态及乳液的流变性。实验结果表明,采用两阶段法制得的核/壳型羧基乳胶粒具有翻转结构,且其翻转结构不受引发剂浓度和搅拌速度的影响。还研究了丙烯酸的用量与加料方式,核/壳阶段比对乳液流变性的影响,结果表明采用梯度式分批滴加丙烯酸的方法,可得到具有碱增稠性的乳液。