Search results for " Viscosity"

1996

Developing an artificial oxygen carrier for use in humans, we polymerize native haemoglobin and myoglobin, using bifunctional, amino group specific cross-linkers, to soluble, so-called hyperpolymers. These polymers, like other polymerized globular proteins, are members of a new class of macromolecues which consist of macromolecular base units. They all have, due to the mechanisms of the chemical reaction, broad distributions of molecular weights. Fractions of hyperpolymers of human haemoglobin were obtained by employing preparative gel-permeation (size-exclusion) chromatography. The calibration curve of analytical gel-permeation chromatography (GPC) for haemoglobin hyperpolymers was determi…

Aqueous Laponite Clay Dispersions in the Presence of Poly(ethylene oxide) or Poly(propylene oxide) Oligomers and their Triblock Copolymers

2008

The effect of polyethylene oxide (PEO) or polypropylene oxide (PPO) oligomers of various molecular weight (Mw) as well as of triblock copolymers, based on PEO and PPO blocks, on aqueous laponite RD suspensions was studied with small-angle neutron scattering (SANS). The radius of gyration (RG) increases for low Mw whereas the opposite occurs for larger Mw. This behavior is explained on the-basis that an effective RG is given by two contributions: (1) the size of the particles coated with the polymer and (2) the interactions between the laponite RD particles which are attractive for small and repulsive for large polymers. The SANS curves in the whole Q-range are well described by a model of n…

Polyelectrolytes Revisited: Reliable Determination of Intrinsic Viscosities

2007

The linear extrapolation of (hh0)/(h0c) towards c !0 constitutes the basis of traditional methods to determine intrinsic viscosities (h), where h is the viscosity of polymer solutions of concentration c and h0 is the viscosity of the pure solvent. With uncharged macromolecules this procedure works well; for polyelectrolytes it fails because of the pronounced non-linearity of the above dependence at high dilution resulting from the increasing electrostatic inter- actions. This contribution presents a new method for the determination of (h). It rests upon the application of the laws of phenomenological thermodynamics to the viscosity of polymer solutions and introduces a generalized intrinsic…

1985

Viscosity measurements were carried out as a function of pressure and temperature with solutions of 8 wt.-% PVC (Mw ≈ 75 000) in ten thermodynamically good solvents by means of a Searle-type viscometer. A rollingxyhball viscometer was used for the investigation of the pure solvents. In all cases the viscosity increases in a more or less exponential manner when the pressure is raised. The viscosity ratio f1000 = η1000 bar/η1bar can be varied by the choice of the solvent from ca. 2 (tetrahydrofuran) to 3,0 (cyclohexanone) at 40°C. For a constant temperature of 40°C, the volumes of activation for the viscous flow of the solutions, V≠, or f1000 exceed that of the pure solvent, by typically 25%.…

Viscometric study on the compatibility of polymer–polymer mixtures in solution

1999

Abstract The viscosity behaviour of mixtures formed by two uncharged polymers in dilute solution has been studied at 25°C. The ternary systems assayed, and denoted solvent (1)/ polymer (2)/ polymer (3), have in common the poly(ether sulphone) (PES) as polymer 2, and poly(vinylidene fluoride) (PVDF), poly(methyl methacrylate) (PMMA) or poly(styrene) (PS) as polymer 3. The intrinsic viscosity and the viscometric interaction parameters have been experimentally measured for the binary (solvent/polymer) as well as for the ternary systems, and also theoretically evaluated for the latter. The estimation of the compatibility degree of the above polymer pairs have been done by means of three criteri…

Viscometric behaviour of polymer blends based on poly (vinylidene fluoride)

1994

The viscosity behaviour of dilute dimethylformamide solutions of poly(vinylidene fluoride)-poly (methyl methacrylate) and poly(vinylidene fluoride)-polystyrene has been studied at 25°C. The polymer concentration ranges are such that neither phase separation nor microgel formation occurs, although we are very close to theta conditions. The intrinsic viscosity and viscosity interaction parameter of the ternary mixtures have been calculated. The estimation of the compatibility of the above polymer pairs has been studied based on: a) specific viscosities; b) viscosity interaction parameters, according to Krigbaum and Wall formalism, and c) viscosity interaction parameters of a system formed by …

Correlation between transport and equilibrium properties through the ternary interaction parameter for cosolvent and cononsolvent polymeric systems

1992

A study of the ternary polymer systems dimethyl formamide-ethyl acetate-polystyrene, chloroform-1,4 dioxane-polystyrene and tetrahydrofuran-chloroform-polystyrene was carried out by viscosity and light scattering at 298 K. A good correlation has been found between the excess intrinsic viscosity, unperturbed polymer dimensions, second virial coefficient and the excess Gibbs free energy by using a ternary interaction parameter, dependent on molecular weight. This modification enables the conversion between transport and equilibrium properties.

1979

Pressure influences on the viscosity of polymer solutions

1982

Of all physico-chemical quantities characterizing the behavior of liquids, the viscosity coefficient η is normally most sensitive to pressure. Early measurements of η(p) date back almost 100 years [1] but they were carried out with very different objectives [2]. Currently, one is particularly interested in polymer solutions, for instance because of the additives to motor oils and of oil recovery. The present paper reports on measurements with polystyrenes of high molecular uniformity in eight different solvents. It confines itself to zero-shear viscosities and discusses the possibilities of discovering the influence of pressure via the molecular structure of the solvent and via its thermody…

An investigation on using pre-treated tyre rubber as a replacement of synthetic polymers for bitumen modification

2015

Rubberized bitumen obtained through a swelling process, has widely proven to be a successful technology for asphalt pavement applications and a solution to reduce the dismantling of tyre rubber on landfills. However, this technology presents two main operative issues which needs the adoption of costly special equipment. Firstly, significant high value of High Temperature Viscosity (HTV) which imposes mixing and compaction difficulties and leads to increased energy consumption and emissions. Furthermore, during the hot storage period, phase separation between rubber particles and the base bitumen could occur. Developing Recycled Tyre Rubber Modified Bitumen (RTR-MBs) with improved storage st…