This correlation is described using the shear rate. This means that the viscosity is not a constant value, but depends on the shear intensity. Ĭosmetic creams and lotions generally show shear-thinning behavior. Thereby it is assumed that the sample can be spread easier at a low viscosity value. The flow behavior of creams can be evaluated using viscosity measurements. This is an intended property as the product should be easily applicable on the skin and not drip off. It is surprising that even lotions – which seem quite fluid – show gel-like behavior. The measurement shows that the values for storage and loss modulus of the lotion are clearly lower than the values for the cream (see table 1).
The measurement reflects what can be felt immediately: The cream has a higher structural strength. This means that the sample will only start to flow when influenced by additional external forces.įigure 1 shows two measurements on a lotion and a skin cream. 1), the sample shows gel-like behavior at the preset frequency. If G′ is above G″ in the linear viscoelastic range* (LVE range, see fig. Whereas the parameter G′ (storage modulus) describes the elastic behavior of a sample, G″ (loss modulus) represents the viscous portion. The structural strength of a sample can be determined with an oscillation measurement in the form of an amplitude sweep. The structure is also significant for processing and when planning the production plant. pressed out of a tube) and for the skin feel. The structure is an important parameter for the evaluation of the skin cream’s behavior when it is extracted (e.g.
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