A comparison of block copolymer surfactant gels

The aqueous gel forming properties of three series of block copolymer surfactants, poloxamers, poloxamines, and Butronic® polyols, are briefly reviewed and compared. The differences in their gel formation properties are explained. Aqueous gel formation of these polymers is attributed to the aggregation of extended linear coil micelles in which the hydrophilic ends become entangled as the temperature rises, due to dehydration. The failure of the Butronic polyol gels to exhibit the same reverse thermal behavior shown by the other two polyol series is attributed to a more lipophilic hydrophobe and to the larger number of moles of water associated with the Butronic hydrophile. The reverse thermal characteristics of aqueous poloxamer and poloxamine solutions has led to the development of aerosol detergent systems which can form foamy gels, thereby expanding the usefulness of these surfactants.     

Gelation—A review

This paper reviews the modern ideas on the process of gelation which have arisen from the analogy between gelation and percolation. The basic features which are common to all types of gels, colloidal or polymeric systems are first recalled; then after a simplified presentation of the percolation model, a few examples illustrating these concepts are chosen (for chemical gelation, a copolymerisation reaction and for physical gelation, the gelatin sol-gel transition). In conclusion, electron micrographs of gel networks (gelatin gel and an inorganic gel of thorium phosphate) are shown, which reveal the great diversity and complexity of the structures.     

聚合物地下交联调整注水剖面的数学模型及其应用

建立了一个两维两相五组分聚合物地下交联调剖的数学模型.该模型综合考虑了影响此过程的各种因素,包括各组分在孔隙介质中的运移,聚合物与交联剂的地下交联反应,聚合物和凝胶的流变性、吸附滞留、不可及孔隙体积、降解等特性以及阻力系数和残余阻力系数,可用于模拟单一的水驱、调剖及这两者的任意组合.根据该数学模型研制了模拟器,在给定的油藏模型上进行了一系列计算,得到了一些对实施调剖有指导意义的结论.     

纤维蛋白酶及其对乳制品的影响

纤维蛋白酶及其酶原是存在于乳中的一对主要碱性蛋白酶，通过水解乳蛋白对乳及制品的品质产生形响。简要介绍了该酶的性质、活性测定方法，最后论述了对干酪及UHT乳的影响。     

Texturization of Sweetened Mango Pulp: Optimization using Response Surface Methodology

Sugar added mango pulp was texturized with alginate. To optimize both the mechanical properties and thermostability of the products, an experimental design was used combined with response surface methodology. Alginate concentration was the major factor affecting mechanical properties of texturized pieces with higher strength as the gelling agent concentration increased. Furthermore, gel strength and thermostability generally increased as calcium and glucono-δ-lactone concentrations, and/or heat treatment duration increased. As large quantities of sweetened pulp were used, texturized pieces with high dry matter content and good flavor qualities were obtained.     

Ovalbumin thermal Gelation Prediction by Application of Temperature-Time History

A model for characterizing changes in viscosity of soy protein during extrusion was adapted to predict apparent viscosity ratio of gelling ovalbumin. For ovalbumin (87% purity) the temperature time histories of 3,5, and 7% gel formation were determined at 85, 90 and 95°C. A back-extrusion method was used to determine apparent viscosity ratios during gelation. Activation energy for denaturation/gelation was estimated at 159 kJ/mol. The model parameter a (degree of molecular entanglement) was 0.75, 0.75, and 1.0 for 3, 5, and 7% gels, respectively. Reaction rate constants were similar for samples with different protein concentrations. Maximum apparent viscosity ratio increased as protein concentrations increased. The mathematical model was verified by determining apparent viscosity ratios at 86 and 93°C and water holding at 90°C, resulting in R²-0.93. This model may be useful in predicting ovalbumin thermal gelation apparent viscosity ratios.     

Small‐angle neutron scattering of poly(styrene)/poly(acrylic acid–ethyl acrylate) copolymers: The effect of the degree of hydrolysis of the poly(acrylic acid–ethyl acrylate) block

We report the results of systems based on polystyrene‐poly(ethyl acrylate) (PEA) diblocks, which self‐assemble in aqueous solutions to form spherical micelles. Previous work has shown that the rheological properties of these solutions, in particular the gel–liquid transition, can be tuned through the use of a simple hydrolysis reaction to convert PEA to poly(acrylic acid) (PAA). We studied the effect of the extent of hydrolysis on the self‐assembly and micellar interactions. Small‐angle neutron scattering (SANS) spectra were fit with a variety of models to determine the micelle structure. As more PEA was converted to PAA (i.e., as the corona became more charged and more hydrophilic), the micellar aggregation number decreased, analogous to observations of other polymeric micelles. This effect could impact the gel–liquid transition and rheology in this system and in similar micellar block copolymer gels. Finally, our SANS spectra qualitatively agreed with predictions for attractive colloidal glasses, confirming the idea that the elasticity of these gels arises from the jamming of micelles. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 490–497, 2004     

Effects of solvent adsorption on solution properties of poly(vinyl alcohol)/dimethylsulfoxide/water ternary systems

In this study, the solvent adsorption phenomena of poly(vinyl alcohol) (PVA) in cosolvent mixtures of dimethylsulfoxide (DMSO; solvent 1) and water (solvent 2) were investigated. Typically, this cosolvent mixture could form hydrogen‐bonded DMSO/(water)₂ complexes, involving one DMSO and two water molecules. Because of the complex formation in the cosolvent mixtures, PVA chains preferentially adsorb water molecules at DMSO mole fraction X₁ < 0.33, but preferentially adsorb DMSO molecules at X₁ > 0.33. The preferential adsorption of DMSO (a good solvent for PVA) could cause the relatively extended conformation of PVA chains in solutions because of the increase in excluded volume effect. Because of various interactions between PVA chains and cosolvent mixtures, the aggregation and gelation behaviors of PVA solutions were significantly affected by the composition of cosolvent mixture. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3211–3217, 2004     

Viscoelastic behavior of thermosetting epoxy mixtures modified with syndiotactic polystyrene during network formation

The rheological behavior of thermosetting epoxy mixtures modified with thermoplastic syndiotactic polystyrene (sPS) was monitored during the curing of the epoxy resin. The selected thermosetting system was diglycidyl ether of bisphenol A cured with 4,4′‐methylene bis(3‐chloro‐2,6‐diethylaniline) in the presence of various compositions of sPS (from 2.5 to 12.5 wt %). The storage and loss shear moduli of the systems were monitored during network formation. The validity of the Winter–Chambon criterion for the accurate determination at the gelation point from rheological data was demonstrated. The influence of the sPS concentration on the dynamic rheological properties of the samples was investigated. The experimental data showed that at sPS concentrations lower than 7.5 wt %, phase separation induced a quick increase in the viscosity, which was related to a crystallization‐induced phase separation of sPS. For sPS concentrations higher than 7.5 wt %, near the phase‐inversion composition, the rheological behavior of the mixtures was characteristic of a cocontinuous structure. After the viscosity jumped at the onset of phase separation, a decrease in the viscosity was found, and later on, the viscosity increased again because of gelation. Additionally, the influence of the cure temperature on the rheological properties was studied. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2348–2355, 2006     

Effect of milk solids concentration on the gels formed by the acidification of heated pH-adjusted skim milk

Reconstituted skim milk of 10–25% total solids was adjusted to pH values between about 6.2 and 7.1 and heated at 80 °C for 30 min. Gels were formed from the heated milks by slow acidification to pH 4.2 and the gelation process and final gels were analyzed for their rheological properties. At each milk concentration, the final acid gel firmness (final G′) and breaking stress could be changed markedly by manipulation of the pH during heating. The final gel firmness and breaking stress could also be modified by changing the concentration of the milk solids prior to heating and acidification. The results indicated that similar gel firmness and breaking stress could be achieved over a range of milk concentrations by control of the pH of the milk during heating. When expressed as a percentage change in final G′ or breaking stress relative to that obtained at the natural pH, plots of the change in final G′ or breaking stress versus pH fell close to a single curve, indicating that the same mechanism may influence the gelation properties at all milk concentrations. The final G′ and breaking stress were related to the denaturation and interaction of the whey proteins with the casein micelles, and the formation of non-sedimentable casein when the milk was heated.