BUBBLE BATH WITH ALOE VERA GEL

  

 

 
A bubble bath containing aloe vera gel, sodium laureth sulfate, glycol distearate, and cocamide DEA was measured under oscillatory flow for a range of strains at a frequency of 2 Hz and at 22°C. The plot of the viscous and elastic stress versus the shear strain reveals a fluid with a critical strain=1.2 and an elastic yield stress of 50 Pa. Based on these values, a microstructure relaxation time can be calculated [1],

Tm = 1/(critical strain · 2 pi · frequency) = 0.066 sec.

A critical strain near one indicates that Tm is in the midrange of the spectrum of relaxation times of this material. Yielding occurs when the oscillatory flow-induced structure cannot recover during the period of oscillation [2].

Measurements of the viscosity and elasticity also were made over a range of frequencies from 0.1 to 40 Hz while holding the stress constant at 1 Pascal. A Maxwell relaxation time TM is given by

TM = elasticity / (2 pi · frequency · viscosity).

When calculated at 0.1, 1, 10 Hz, this gives TM = 0.118, 0.097, 0.058 sec. This is a material with a narrow range of relaxation times.

 

[1] Thurston, G. B., Stress-strain relations for viscoelastic liquids, in Theoretical and Applied Rheology, ed. by P. Moldenaers and R. Keunings (Elsevier Science Publishers B. V. Belgium) 112- 114 (1992).
[2] Thurston, G. B., Non-Newtonian viscosity of human blood: Flow-induced changes in microstructure, Biorheology, 31, 179-192 (1994).

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