摘要:

Rheological data are reported for dispersions of crosslinked polystyrene beads (170 nm diameter) in a 0.15 weight fraction solution of polystyrene(Mw=410,000)in either of two solvents: tritolylphosphate (TCP) or 1,2‐di(2‐ethyl hexyl)phthalate (DOP). With these solvents, for fixed polymer concentration, the osmotic pressure is larger in solutions in TCP. Experiments include creep, recovery, stress‐growth at constant strain rate, and strain sinusoidal in time. Dispersions were studied, with 0.05, 0.10, 0.15, and 0.20 weight fractionwBof the beads. The dispersions exhibited solidlike behavior provided the strain did not exceed about 0.02, with an equilibrium modulus proportional to the square of the bead concentration. For larger strain, the behavior with slow deformation rates can be described by a pseudolinear constitutive equation, with a viscosity that decreases with increasing shear rate κ. The yield stress, as obtained from creep measurements, marking the transition from solidlike to fluidlike behavior is of the magnitude expected for a bead suprastructure stabilized by osmotic pressure effects related to depletion of the polymer concentration near the bead surfaces. In steady‐state flow at larger κ, the viscosity approaches a plateau valueηpindependent of κ, and the recoverable strain following cessation of steady flow is also independent of κ. This behavior is interpreted in terms of remnants of the suprastructure (flocculated suspension) responsible for solidlike behavior at small strain, with the remnants increasing in number but decreasing in size with increasing κ, while their volume fractions remains about constant. It is found thatln(ηp/η0)is proportional towBwith a temperature‐independent proportionality constant which is larger for the dispersions in TCP solution. This is consistent with the larger osmotic pressure of solutions of polystyrene in TCP in comparison with those in DOP, inasmuch as the remnants of the bead suprastructure are stabilized by osmotic effects. Hereη0is the viscosity of the polystyrene solution.

ISSN:0148-6055    

DOI:10.1122/1.549998

出版商:The Society of Rheology    

年代:1988

数据来源: AIP

摘要:

The constitutive equation for the “elastic flexible reptating rope” model is derived. In this model the macromolecule is represented by a continuous flexible elastic rope, confined in a tube along its contour and performing a reptation motion. The analytical expressions for the relative extension and the one‐ and two‐segment distribution functions are derived. This enables the determination of the explicit form of the constitutive equation. Due to the elasticity of the rope, fast internal relaxation modes appear in the theory as well as long reptation times. It is expected that fast deformation processes can therefore be described accurately by this constitutive equation.

ISSN:0148-6055    

DOI:10.1122/1.549969

出版商:The Society of Rheology    

年代:1988

数据来源: AIP

摘要:

A rheological model for liquid‐filled capsules made of biomaterials was formulated, wherein theoretical equations for capsule pressure‐deflection, relaxation and creep, allow parametric fitting to experimentally obtained curves. The line taken establishes a realistic link between the theoretical model and the experimental data. Special apparatus and computer programs were developed for measuring and recording rheological properties of small capsules made of biomaterials, such as caviar or liquid encapsulated by Chitosan. The technique may be used for improving texture design and simulation of imitation caviar, or serve as a rapid means for commercial classification of caviar and caviar substitutes. The methodology may also serve for quantifying rheological properties of liquid drugs encapsulated in Chitosan, as a vehicle for continuous controlled drug apportioning. It may also be utilized for measuring rheological properties of similar capsular structures found in other living organisms.

ISSN:0148-6055    

DOI:10.1122/1.549975

出版商:The Society of Rheology    

年代:1988

数据来源: AIP

摘要:

Solutions are obtained for steady‐state low Reynolds number flow of viscoplastic materials in systems with recirculating eddies using the finite‐element method. The reattachment length and eddy intensity in planar and axisymmetric abrupt expansions are correlated with Reynolds number and dimensionless yield stress for Bingham and Casson materials. Flow in a stenosis is examined using Newtonian and Casson constitutive relationships. The separation zones in a 180 degree planar bifurcation with straight and bent inlets are compared for Bingham and Newtonian fluids. The results show that the size and strength of recirculation is reduced for viscoplastic materials.

ISSN:0148-6055    

DOI:10.1122/1.549976

出版商:The Society of Rheology    

年代:1988

数据来源: AIP

ISSN:0148-6055    

DOI:10.1122/1.549994

出版商:The Society of Rheology    

年代:1988

数据来源: AIP