Rheology of a cellulose graft copolymer. Comparison with other closely packed gel thickeners

Hydrolyzed cellulose–polyacrylonitrile graft copolymer is a polyelectrolyte gel suspension with a high viscosity in water. It is a closely packed swollen gel particle suspension in the appropriate concentration range and has similar rheological properties to other thickeners of this type. Viscosities η in either water or salt solution are reduced to a single master curve by use of the reduced viscosity function η/cQ, where c is weight fraction of polymer and Q is swelling volume in excess solvent of the same ionic strength. The effective molecular weight between crosslinks, M_c, determined from shear modulus, corresponds to M_c values for other closely packed gel thickners of similar η/cQ. Among all examples of this class of thickener, the plateau values of η/cQ, which occur at cQ > 2, are approximately inversely proportional to M_c.     

Elastic modulus of viscoelastic magnetic silicone gel body

This paper describes various viscoelastic magnetic silicone gel bodies developed to create a new type of viscoelastic magnetic material. This material is capable of undergoing substantial changes in mechanical properties due to the large deformation caused by magnetic traction force under the application of a moderate strength magnetic field. This study performed tensile tests for various viscoelastic magnetic silicone gel bodies under a uniform steady magnetic field. The elastic moduli of the gel bodies were measured under different controlled experimental conditions. The experimental results showed that, under the applied magnetic field, the elastic moduli of the viscoelastic magnetic silicone gel bodies increased and were largely dependent upon the magnetic properties of the magnetic particles. The magnetic particle size and the material properties of the dispersant and the silicone gel also had significant effects on the moduli of the gel bodies. This paper also discusses the most appropriate combination of the materials used in this study from the standpoint of gaining a large magnetic traction force. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers     

Shear rate dependent viscosity of suspensions in newtonian and non-newtonian liquids

Viscosity measurements in a wide shear rate range, on suspensions of six Newtonian and non-Newtonian liquids, are reported.The shear rate dependency of suspensions in non-Newtonian liquids is compared with that of suspensions in Newtonian ones and an extension to the former of the Krieger—Dougherty theory, which holds for the latter, is attempted. Although some success is obtained, an alternative explanation of the observed behavior of the suspensions of non-Newtonian liquids is discussed.     

Tailoring closely packed gel–particle systems for use as thickening agents

When used as a thickening agent in aqueous suspension, hydrolyzed starch–polyacrylonitrile graft copolymer (H-SPAN) has broadly variable rheological properties, such as viscosity, storage modulus, and stress overshoot characteristics. A series of H-SPAN preparations with variable swelling ratio Q were made by pretreating portions of stock material. As 1% suspensions in water, they had viscosities η that were non-Newtonian. At a constant shear rate, η of the suspensions depended on Q and had a sharp maximum in the midrange of Q. In terms of reduced concentration cQ, where c is weight fraction of polymer, the highest η occurred when cQ was approximately 2. With isoionic dilution, each suspension had a constant reduced viscosity function, η/cQ, provided cQ > 2. The value of η/cQ fell rapidly when cQ approached 1. All thickeners of the closely packed gel–particle type so far examined have this relation of the reduced variables. The shear modulus calculated from measurements of primary normal force and corrected for solvent swelling, according to theory for rubber for elasticity, was essentially constant for each suspension measured during isoionic dilution to cQ = 2. The density of crosslinks calculated from the modulus was extremely low for all samples. The variable rheological properties of the preparations resulted primarily from differences in their low effective crosslink densities.     

Temperature dependence of time-resolved photoluminescence in closely packed alignment of Si nanodisks with SiC barriers

We study the temperature dependence of time-resolved photoluminescence (PL) in closely packed alignment of Si nanodisks (NDs) with SiC barriers, fabricated by neutral beam etching using bio-nano-templates. The PL time profile indicates three decaying components with different decay times. The PL intensities in the two slower decaying components depend strongly on temperature. These temperature dependences of the PL intensity can be quantitatively explained by a three-level model with thermal activation energies of 410 and 490 meV, depending on the PL components. The activation energies explain PL quenching due to thermal escape of electrons from individual NDs. This thermal escape affects the PL decay times above 250 K. Dark states of photo-excited carriers originating from the separate localization of electron and hole into different NDs are elucidated with the localization energies of 70 and 90 meV. In contrast, the dynamics of the fastest PL decaying component is dominated by electron tunneling among NDs, where the PL intensity and decay time are constant for temperature.     

Functional correction to the classical expression for the average flow velocity in a closely packed granular bed

The new capillary model of pores in a granular bed derived from the model of fractional cells for the bed is used to show that there is a need for correcting the classical relation between the average actual flow velocity in the pores and the formal filtration velocity when the value of the bed porosity is less than the porosity of the bed with a cubic grain packing. Separate values of the corresponding correction are found and it is written as a power-law function of the bed porosity. A corrected relation between the actual and formal velocities for actual packed beds is proposed. This relation makes it possible to avoid a tangible systematic error of 6 to 10%.     

Effect of spatial gel inhomogeneity on the elastic modulus of strong polyelectrolyte hydrogels

Summary The effect of spatial inhomogeneity on the elastic modulus of ionic poly(acrylamide) (PAAm) hydrogels has been investigated with the static light scattering measurements. The gels were prepared by free-radical crosslinking copolymerization of acrylamide and 2-acrylamido-2-methylpropane sulfonic acid sodium salt (AMPS) monomers and N,N’-methylenebis(acrylamide) crosslinker. The crosslinker concentration of the hydrogels was fixed in our experiments while the mole fraction of AMPS in the comonomer feed (x_i) was varied over a wide range. Elasticity measurements show that the modulus of elasticity of gels increases with increasing x_i from 0 to 0.2. The excess scattering of gels, that is, the degree of spatial gel inhomogeneity rapidly decreases with increasing x_i and approaches to zero at x_i=0.05. Debye-Bueche analysis of the light scattering data indicates frozen concentration fluctuations in gel; the size of the static structures increases while the extent of concentration fluctuations reduces with increasing x_i. It was shown that the macroscopic elastic properties of PAAm gels are mainly controlled by the microscopic gel structure determined by the scattering measurements.     

Adhesion between high strength and high modulus polyethylene fibers by use of polyethylene gel as an adhesive

The use of polyethylene gels to adhere high strength and high modulus polyethylene fibers together has been investigated. It was found that the joint strength obtained using high density polyethylene (HDPE) gel in decalin or tetralin depended on the heating temperature and time of the gel. When heated at 100°C for 30 min, the gel showed such a high joint strength that polyethylene fibers were torn, and this should be enough for practical uses. The results of the present study demonstrate that utilization of the polyethylene gel as an adhesive is an extremely effective method when polyethylene fibers are used in composite materials.     

On flooding in packed columns

A mechanism for flooding in packed columns, based on interactions between holdup and pressure gradient is proposed and is shown to be consistent with experimental observations. The differences in the flooding mechanism between wetted wall columns and packed columns are considered also.     

Lattice modulus and crystallite thickness measurements in ultra-high modulus linear polyethylene

Measurements have been made of the apparent Young's modulus of the crystalline part of a number of ultra-high modulus polyethylene drawn tapes by observing the change in Bragg angle of the 002 X-ray reflection when the tapes are placed under stress. The variation with temperature has been measured and it is argued that the common limiting value of modulus reached by all samples at low temperature represents the true crystalline modulus and that the room temperature value, which is some 40% lower, is strongly suggestive of a morphology in which a considerable fraction of the material is non-crystalline and is located, from the mechanical point of view, essentially in parallel with the crystalline fraction. Accurate measurements of the linewidths of the 200, 020 and 002 X-ray reflections have been made in order to deduce the mean thickness of the crystalline elements in the three principal directions. The ‘a’ and ‘b’ thicknesses vary very little with draw ratio but the ‘c’ thickness increases at high draw ratios to a value more than twice as great as the (constant) long period determined from small-angle scattering.     

Recent developments in packed columns

Highlights of a recently concluded four year experimental program on random packings are presented. They include (a) a revised definition of loading to achieve better reproducibility; (b) discussion of the erratic behavior near the “flood” point which helps explain the scatter in the published “flood” data; (c) new data showing that with proper distribution, efficiency is stable over a broad range; and (d) controlled maldistribution studies leading to guidelines for distributor design, fabrication and installation. The need to precisely define commonly used terms is emphasized.     

Viscous dissipation in packed beds

Factors affecting the magnitude of viscous dissipation in packed beds under conditions used in high pressure liquid chromatography are investigated. The free surface model is employed to characterize packed beds, to evaluate the flow field and to derive the appropriate similitude criterion for the effect of viscous dissipation. Equations for the calculation of radial temperature profiles due to internal heat generation in beds with axially uniform and non-uniform wall temperatures are given and the results are illustrated for typical cases. The evaluation of the temperature profiles in beds with non-uniform wall temperature is based on experimentally measured wall temperatures.     

Axial dispersion in packed beds

Behaviour of axial dispersion in packed beds is made clear from the properties of the equation of continuity. New dispersion data are added to relate liquid data with gas data in the Stokes flow regime. A special device to send a plane impulse of tracer liquor was developed. A correlation has been given for a wide range of flow and dispersion in packed beds.     

Absorption in packed bubble columns

The mass transfer characteristics of packed bubble columns were studied by employing various packings of different sizes and shapes in 10–38·5 cm i.d. columns. The theory of absorption accompanied by pseudo-mth order reaction was used to obtain the values of effective interfacial area. The values of liquid side mass transfer coefficient were obtained by using the theory of absorption accompanied by slow chemical reaction. The superficial gas velocity was varied from 5 to 25 cm/sec. The packed bubble columns showed a considerable improvement in the performance over empty bubble columns. A criterion for the scale-up of these columns has been suggested.     

Gas distribution in large-diameter packed columns

The aim of the present work was to determine the extent of gas maldistribution in large-diameter columns containing corrugated-sheet structured packings. A large-diameter column simulator has been designed for this purpose (cross section, 3 m × 0.5 m; packed bed height, 4.4 m) with 15 independent inlets for gas, allowing the introduction of diverse initial distribution profiles. The gas velocity profiles leaving the top of the packed bed are discussed in terms of lateral spreading and observed effects of gas load, liquid load and the height of the packed bed.