Physical analyses of gel-like behavior of binary mixtures of high- and low-melting fats

Gel-like fat mixtures of high-melting (HM) and low-melting (LM) fats were formed by means of rapid cooling and subsequent heating. No “non-fat” ingredients such as emulsifiers, water, or waxes were added to the mixtures. The gel-like fats having solid fat content (SFC) values below 2.0 wt% formed crystal networks of HM-fats that entrapped the liquid oil fraction of LM-fats. In a search for optimal fat combinations exhibiting gel-like behavior, fully hydrogenated rapeseed oil with a high amount of behenic acid (FHR-B), fully hydrogenated rapeseed oil with a high amount of stearic acid (FHR-S), tristearoylglycerol (SSS), triarachidonoyl-glycerol (AAA), and tribehenoylglycerol (BBB) were examined as the HM-fats. For LM-fats, sal fat olein (SFO), cocoa butter (CB), palm super olein (PSO), and olive oil were examined. The following results were obtained: (i) the gel-like behavior was observed in mixtures of FHR-B/SFO and FHR-B/CB with initial concentrations of FHR-B of 1.5–4.0 wt%. (ii) Rapid cooling to T _c (crystallization temperature) from 70°C and subsequent heating to T _f (final temperature) were necessary to reveal the gel-like behavior, whereas simple cooling without a cooling/heating procedure did not form the gel-like fat mixture. (iii) Optimal values of T _c and T _f were related to the m.p. of the LM-fat and HM-fat, respectively. (iv) Temperature variations of SFC as well as X-ray diffraction spectra showed that the melt-mediated transformation from α to β of the HM-fat crystals was a prerequisite to reveal the gel-like behavior. Consequently, the fat mixture revealing the gel-like behavior might be called β-fat gel.     

Rheological properties of cement paste: Thixotropic behavior and structural breakdown

In this work, a new material model is presented to simulate rheological behavior of cement paste. This material model is among others based on combined concepts by Hattori and Izumi and by Tattersall and Banfill. More precisely, coagulation, dispersion and re-coagulation of the cement particles (giving a true thixotropic behavior) in combination with the breaking of certain chemically formed linkages between the particles (giving a so-called structural breakdown behavior) are assumed to play an important role in generating the overall time-dependent behavior of the cement paste. The model evaluation is done by comparing experimental data with model prediction.     

Polymerization in gel-like emulsions

Polymerization of styrene in gel-like emulsions (concentrated emulsions which have a volume fraction of monomer greater than 0.74), by using sodium dodecylsulfate as emulsifier and small amounts of water, was carried out with an oil-soluble initiator, AIBN. Both higher conversions and higher molecular weights of the polymer were obtained as compared to the polymerization in bulk. The higher “rigidity” of the monomer in the interior of the cells of the gel is responsible for the increased rate of polymerization and molecular weight. The polymer particles thus obtained have diameters in the range of 0.1 to 0.3 μm, depending upon the conditions of preparation of the gel. The effects of the concentration of the initiator, the concentration of surfactant, the monomer volume fraction, termperature, and ionic strength of the aqueous solution have been investigated.     

Thixotropic behaviour of cement pastes

In the present work the thixotropic behaviour of fresh Portland cement pastes is examined on the basis of the stress transients determined at constant shear rate. Some significant quantities are considered: the difference between maximum and equilibrium shear stresses, the breakdown area and the density of the energy absorbed by thē material for the breakdown of the thixotropic structure. A distance parameter is proposed in order to evaluate the influence of the specific surface and water/cement ratio on these quantities.     

High-performance materials from gel-like spherulites of ultra-high-molecular-weight polyethylene

A new method using gel-like spherulites will be presented for obtaining high-performance materials of ultra-high-molecular-weight polyethylene (UHMW-PE), which is available for the production of high-strength and high-modulus materials having a large cross-sectional area, for example, rods and thicker tapes. Such high-performance organic materials were not known until the development of this method in 1983. Ultra-drawability and characteristics of UHMW-PE produced by this method are discussed, based on the fine structure of gel press sheet.     

Rheology in the technology of ceramics and refractories. 4. Thixotropic systems and factors determining their properties

An analysis of rheological curves characterized by a superanomalous viscosity is presented. Disperse systems of this type possess a region of decreasing shear stress at an accelerated shear. The mechanism of the appearance of thixotropy is analyzed. Hysteresis phenomena in thixotropic systems are considered and a technique for their experimental study is presented. The effect of the main factors on thixotropic properties of ceramic suspensions (dispersity, hydration, and nature of the solid phase, shape of particles, composition of the dispersion medium, temperature) is described. The mechanism of thixotropic structure formation manifested through thickening of the casting systems is considered for fine ceramic suspensions.Translated from Ogneupory i Tekhnicheskaya Keramika, No. 10, pp. 9 – 16, October, 1996.The previous articles of the series Rheology in the Technology of Ceramics and Refractories have been published in No. 3 of 1994, No. 12 of 1995, and No. 1 of 1996.     

浅谈乳胶漆的触变性

探讨了乳胶漆触变性的影响因素,并结合实例讨论了乳胶漆从生产、贮存、施工到成膜各个阶段所应控制的粘度范围。     

触变性氰基丙烯酸酯胶粘剂的开发研究

阐述了触变性氰基丙烯酸酯胶粘剂的合成方法及其优越性。     

触变性反应型树脂在汽车涂料中的应用

他触变性反应型树脂对汽车涂料性能的影响。研究结果表明：ＡＣ树脂对不同色种的涂料施工性能,表观性能都有较大的改善,并对不同的涂料,添加量都有一个最佳范围。     

培养基凝固剂及触变性培养基

介绍常用培养基凝固剂琼脂、卡拉胶和黄原胶的凝胶性质。将这三种凝胶配伍使用可配制出具有触变性的培养基,用于特殊的微生物检测。     

Rheological behavior of aqueous mullite-albumin-methylcellulose systems

In this work, the thermogelling behavior of aqueous mullite-bovine serum albumin (BSA) suspensions was studied by dynamic rheology in order to determine the experimental conditions that must be used to form mullite green bodies by thermal consolidation. Viscoelastic properties (G′ and G′′) as a function of temperature (30–95 °C) and time were determined by temperature sweep tests and time sweep tests, respectively. On the other hand, the influence of methylcellulose (MC) (2 wt%) as a binder on the viscoelastic properties of the aqueous mullite-protein system as a function of both experimental parameters (temperature and time) was also studied. In addition, shear flow properties of aqueous mullite (40 vol%; 0.45 wt% of polyacrylic polyelectrolyte as a dispersant)–BSA (10 and 15 vol%)-MC (2 wt%) suspensions were analyzed to obtain information on the rheological behavior of the suspensions at room temperature. The results obtained showed that the presence of mullite particles and MC changed the onset temperature of gelation of the protein and increased the gelation time. Thus, both the mullite particles and methylcellulose intervened in the formation of the developed protein gel.     

Soot aggregates,superaggregates and gel-like networks in laminar diffusion flames

We show that soot formed in laminar diffusion flames of heavily sooting fuels evolves through four distinct growth stages which give rise to four distinct aggregate fractal morphologies. Each successive stage grows upon the previous stage; hence aggregates of one morphology, parameterized by a fractal dimension, form larger superaggregates or gels of a different morphology with a different fractal dimension. These results were inferred from large and small angle static light scattering from the flames, microphotography of the flames, and analysis of soot sampled from the flames. These results and the analysis were substantiated by comparison to computer simulations. The growth stages occur approximately over four successive orders of magnitude in aggregate size. Each growth stage is a fundamental physical process: Stages 1 and 3 are diffusion limited cluster aggregation in three and two dimensions, respectively; Stages 2 and 4 are percolation in three and two dimension, respectively.     

触变性酮肟型单组分有机硅密封胶的研制

研究了触变性酮肟型有机硅密封胶的交联体系和填料体系的组成及其对密封胶表干时间,电绝缘性能,力学性能和触变性能的影响,得出结论：交联体系中锡催化剂的适宜用量为０．４－０．５份,气相ＳｉＯ２和活性ＣａＣｏ３填料可提高密封胶的强度,且赋予其优良的触变性能。     

假塑触变性炭黑水基分散体的制备和胶体性质

考察了采用聚苯乙烯马来酸酐高分子作为分散剂,用三种分散设备制备超细炭黑水基分散体系的研磨过程,然后采用黄原胶对分散体系增稠,测定了增稠后炭黑水基体系的粒径分布、黏度曲线特征和分散稳定性.实验结果表明采用密闭循环式研磨机,炭黑分散体粒径D99可达到2 μm以下.粒径分布主要与采用的研磨介质大小有关.0.4 mm的氧化锆珠比0.8 mm的氧化锆珠能够得到更小的粒径分布.增稠后炭黑水基分散体系体现假塑性和触变性黏度.在高速离心加速度为2 300×g条件下离心7 h,分散体系不发生沉降,具有极好的动力学稳定性.     

触变型不饱和聚酯漆淋涂工艺的探讨

利用触变型不饱和聚酯漆（PE漆）剪切后变稀，静置后返稠的特性，将其用于大平面木工件的淋涂涂装。介绍了淋涂工艺的工件预处理、施工环境的温度和湿度的控制、淋涂工艺参数以及淋涂涂装时的注意事项。     

Phase behavior of aqueous systems of monoglycerides

Monoglyceride-H₂O systems in the range above about 5% H₂O exhibit a varied phase behavior with a number of mesomorphic states reminiscent of those found for soap-H₂O systems. There are fluid neat, stiff and “short” viscous isotropic, and plastic or stringy middle states. In the case of saturated monoglycerides, neat states prevail at low molecular weight as with monolaurin, but viscous isotropic and finally middle states appear at higher chain length as with monoarchidin and monobehenin. The phase diagrams for systems of unsaturated compounds resemble those for systems of saturated compounds, with corresponding phase regions occurring at lower temperatures. The monoelaidin-H₂O system closely resembles a shifted monostearin-H₂O system, neither system showing middle. Middle phase appears in a small island for monoolein and monolinolein near 90C and 20% water. Water dissolves negligible amounts of monoglycerides so that phases which are nearly 100% H₂O exist for substantially all systems and conditions when H₂O content is 60% or more.     

Scratch resistance behavior of model coating systems

Coatings are often subjected to physical deformations caused by car wash brushes, tree limbs, keys, fingernails, and the like, which may result in mechanical abrasion. The resistance of the coating to scratches imposed by such mechanical abrasions has been studied through the utilization of laboratory tests such as nanoindentors, crockmeters, scanning probe microscopes, and taber abraders. Little emphasis, however, has been placed on the influence of coating attributes on measured scratch resistance. In this study we attempt to relate the effect of coating glass transition temperature, crosslink density, and crosslink type in a series of formulated waterborne polyurethane dispersion clearcoats on resultant scratch resistance. Methods utilized to impart the scratches, e.g., scanning probe microscopy, weighted fingernail, and crockmeter, as well as related coating physical properties measured, e.g., viscoelastic behavior, hardness, and tensile strength, are discussed. The scratch resistance of model coating systems analyzed was found to be dependent upon the base resin T_g, which affected the surface hardness of the coating and the toughness of the crosslinked network, as measured by the method of essential work. Coatings that exhibited both hard surfaces and tough-elastic network integrity afforded the optimized scratch resistance behavior. Presented at the 26th International Waterborne, High-Solids, and Powder Coatings Symposium, February 10–12, 1999, New Orleans, LA. 401 Southfield Rd., P.O. Box 6231, Dearborn, MI 48121-6231.     

On the asymmetric behavior of distillation systems

The aim of this paper is to characterize a particular but relevant aspect of the dynamic behavior of binary distillation systems. More in detail, attention is paid to the well known result that, for step changes of reflux, the leaving and back transients of the top product concentration have different lastings. Such a phenomenon, here referred as “asymmetry”, is described by means of an “asymmetric function”, defined as the ratio of the settling times of the leaving and back transients. The analysis of the asymmetry function leads to the conclusion that the equilibrum state, at which distillation systems usually work, is such that every transient leaving this state is faster than the corresponding back one. Moreover, it is shown how the phenomenon is influenced by the operating conditions of the distillation system and by some characteristic parameters of the binary mixture (relative volatility and concentration).