7,395 research outputs found
Effect of silica colloids on the rheology of viscoelastic gels formed by the surfactant cetyl trimethylammonium tosylate
The effects of the addition of sub-micrometer sized colloidal silica spheres
on the linear and nonlinear rheology of semi-dilute solutions of a viscoelastic
gel are studied. For a 1.4 wt.% solution of the surfactant CTAT, a peak in the
zero shear rate viscosity is observed at approximately equal
weight percents of silica and CTAT. This peak shifts to lower silica
concentrations on increasing either the CTAT concentration or the surface
charge on silica and disappears when the CTAT concentration is increased to
2.6wt%. The increases in and the high frequency plateau modulus
G on the introduction of SiO are explained by considering the
increasingly entangled wormlike micelles that are formed due to the enhanced
screening of the electrostatic interactions. The observed decrease in the
values of G and at higher concentrations of silica
particles is explained in terms of the formation of surfactant bilayers due to
the adsorption of the positively charged cetyl trimethylammonium to the
negatively charged silica.Comment: 28 pages, includes 8 eps and 2 png figures; accepted for publication
in Jl. Colloid Interface Sc
Dynamical Behaviour in the Nonlinear Rheology of Surfactant Solutions
Several surfactant molecules self-assemble in solution to form long, flexible
wormlike micelles which get entangled with each other, leading to viscoelastic
gel phases. We discuss our recent work on the rheology of such a gel formed in
the dilute aqueous solutions of a surfactant CTAT. In the linear rheology
regime, the storage modulus and loss modulus
have been measured over a wide frequency range. In
the nonlinear regime, the shear stress shows a plateau as a function
of the shear rate above a certain cutoff shear rate
. Under controlled shear rate conditions in the plateau regime,
the shear stress and the first normal stress difference show oscillatory
time-dependence. The analysis of the measured time series of shear stress and
normal stress has been done using several methods incorporating state space
reconstruction by embedding of time delay vectors.The analysis shows the
existence of a finite correlation dimension and a positive Lyapunov exponent,
unambiguously implying that the dynamics of the observed mechanical instability
can be described by that of a dynamical system with a strange attractor of
dimension varying from 2.4 to 2.9.Comment: 12 pages, includes 7 eps figure
Experimental study of nonlinear dust acoustic solitary waves in a dusty plasma
The excitation and propagation of finite amplitude low frequency solitary
waves are investigated in an Argon plasma impregnated with kaolin dust
particles. A nonlinear longitudinal dust acoustic solitary wave is excited by
pulse modulating the discharge voltage with a negative potential. It is found
that the velocity of the solitary wave increases and the width decreases with
the increase of the modulating voltage, but the product of the solitary wave
amplitude and the square of the width remains nearly constant. The experimental
findings are compared with analytic soliton solutions of a model Kortweg-de
Vries equation.Comment: The manuscripts includes six figure
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