LAUSR

In this paper, the influence of clobetasol propionate and sodium dodecyl sulfate on the viscoelastic modules and gelation transition of aqueous solutions of poloxamer 407 are investigated experimentally. The influence of the polymer volume fraction is also examined. The experimental investigations are carried out with eight different samples of solutions. Four of them are free of additives varying just on macromolecule volume fraction. The other four samples are produced from the previous ones by addition of clobetasol and a surfactant (sodium dodecyl sulfate) in a volume fraction compatible with commercial applications. All samples are sheared in a high-performance rheometer of parallel disks with an automatic control of gap and temperature. The first set of tests are carried out under the condition of steady shear. From these tests, we obtain results for the apparent viscosity of the solutions of shear rate for two different temperatures, 6 ∘ C and 36 ∘ C. While a shear-thinning behavior is verified for the temperature of 36 ∘ C, the viscosity is observed to have a non-shear rate dependence at 6 ∘ C for all samples. The second tests deal with non-isotherm trials under a regime of small amplitude oscillatory shear, in a temperature range from 3.5 to 50 ∘ C. The viscoelastic moduli of storage and loss of energy are obtained as a function of the temperature for fixed values of frequency and angular deflection. The gelation transition of the polymer solution is characterized as a sudden change in the viscoelastic modulus. This interesting finding is directly associated with microstructure transitions induced by increase of the temperature. We show results of the temperature of micellization and the gelation temperature as a function of the polymer volume fraction for a suspension in the absence of additives and with a certain volume fraction of SDS (surfactant) and clobetasol propionate. The presence of additives reinforces the link of micelles making the structure more stable and resistant to breakup. The effect of SDS or clobetasol propionate on gelation is seen to be very important, and there is a lack of systematic research about additives. We also present a result for the shear elastic modulus of the solution as a function of the polymer volume fraction for 6 ∘ C. This shows that the micelles-like chain formation at a given temperature leads to a solid characteristic of the polymer that can be interpreted as a yield stress even at low temperatures. The presence of SDS and clobetasol propionate produces new rheological response of the poloxamer.