Linear viscoelasticity of emulsions : I. The effect of an interfacial film on the dynamic viscosity of nondilute emulsions

The dynamic viscosity of nondilute monodisperse emulsions is calculated by using a cell model. Two possibilities for describing the mechanical properties of the interfacial film between the internal and the external phase are considered: (A) the film is assigned a two-dimensional linear viscoelastic behavior and (B) the film is treated as a shell with finite thickness containing a Newtonian liquid. The resulting expressions for the dynamic viscosity show that model B has two relaxation times and model A has at least two or more. If a Voigt-Kelvin model is used to describe the interfacial rheology, model A will also have just two relaxation times. The results obtained may be used to interpret measurements on emulsions in terms of microscopic parameters of these emulsions

Effective viscosity of dispersions approached by a statistical continuum method

The problem of the determination of the effective viscosity of disperse systems (emulsions, suspensions) is considered. On the basis of the formal solution of the equations governing creeping flow in a statistically homogeneous dispersion, the effective viscosity is expressed in a series expansion in terms of correlation functions. The contribution of the interfacial tension to the effective viscosity is also considered and finally bounds for the effective viscosity are indicated

Linear viscoelasticity of emulsions : II. Measurements of the linear viscoelastic behavior of emulsions in the kilohertz range

Linear viscoelasticity of emulsions in shear deformation in the kilohertz range is demonstrated experimentally. In order to avoid complications due to inertia effects, emulsions with small droplet sizes are studied. The preliminary measurements are interpreted as being the result of droplet deformations. If this interpretation is correct, measurements of the dynamic viscosity of emulsions may be used to obtain information about the mechanical properties of the interfacial layer between droplets and the continuous phase. In particular, the evaluation of the interfacial tension of emulsion droplets from bulk properties might be possible using this technique

Frequency dependent linear viscoelastic properties of ordered polystyrene latices

An experimental investigation of linear rheological properties of monodisperse ordered latex dispersions has been carried out. Measurements of the dynamic shear modulus and the dynamic viscosity in the frequency range between 0.04 Hz and 2500 Hz are reported. The volume fraction and the electrolyte concentration were variables in the experiment. The results show that a description of the rheological behaviour with a simple linear phenomenological equation is not possible. The measured dynamic moduli can only be described with a great number of relaxation times

Hard sphere colloidal dispersions: Mechanical relaxation pertaining to thermodynamic forces

The complex viscosity of sterically stabilized (hard) silica spheres in cyclohexane has been measured between 80 Hz and 170 kHz with torsion pendulums and a nickel tube resonator. The observed relaxation behaviour can be attributed to the interplay of hydrodynamic and thermodynamic forces. The validity of the Cox-Merz rule is checked

An ellipsometric study of protein adsorption at the saliva-air interface

At the liquid-air interface of human saliva a protein layer is adsorbed. From ellipsometric measurements it was found that the thickness of the surface layer ranged from 400 to 3600 Å and the amount of protein material adsorbed was 9–340 mg/m2. Based on the concentration of protein in the layer the samples could be classified into two groups: a low concentration (ca. 0.15 g/ml) and a high concentration (0.7–1.1 g/ml). In the low concentration group the surface layers appeared to be thin (500–600 Å) while those in the high concentration group appeared to be much thicker (1000–3500 Å). A correlation between the bulk pH and the thickness of the surface layer could be established

Where's the Doughnut? LBV bubbles and Aspherical Fast Winds

In this paper we address the issue of the origin of LBV bipolar bubbles. Previous studies have explained the shapes of LBV nebulae, such as $\eta$ Car, by invoking the interaction of an isotropic fast wind with a previously deposited, slow aspherical wind (a ``slow torus''). In this paper we focus on the opposite scenario where an aspherical fast wind expands into a previously deposited isotropic slow wind. Using high resolution hydrodynamic simulations, which include the effects of radiative cooling, we have completed a series of numerical experiments to test if and how aspherical fast winds effect wind blown bubble morphologies. Our experiments explore a variety of models for the latitudinal variations of fast wind flow parameters. The simulations demonstrate that aspherical fast winds can produce strongly bipolar outflows. In addition the properties of outflows recover some important aspects of LBV bubbles which the previous "slow torus" models can not.Comment: 23 pages, 6 figures, to appear the Astrophysical Journa

Rheological properties of human saliva

From measurements with a Couette-type viscometer provided with a guard ring it was shown that at the saliva-air interface a protein layer is adsorbed. Measurements of the surface shear modulus of this layer on saliva of 7 healthy subjects were performed at a frequency of about 70 Hz and a temperature of 25 °C. For a surface age of about 1.5 h the surface shear modulus and the surface viscosity were in the order of 1 Nm−1 and 10−3 Nm−1 s, respectively. From ellipsometric measurements it was found that the thickness of the protein layer was approx. 100nm and, using this value, it could be concluded that the shear modulus and the dynamic viscosity were in the order of 107 Pa and 104 Pa s, respectively. The layer appeared to be fragile. Even shear deformation amplitudes of 4 × 10−5 are too high to assure linearity. The complex viscosity (η = η′ − iη′′) of the bulk liquid of human submandibular saliva below the absorbed layer was measured in the frequency range 70 Hz–200 kHz with 3 torsional resonators, each for a different frequency, and a Ni-tube resonator. It was concluded, that the real part of the complex viscosity (η′) decreases from 1.1 mPa s at 70 Hz to a value of 0.95 mPa s at high frequencies. Except at the lowest frequency (70 Hz), the value of η′′ was too small to be detected