SHAMPOO:

RHEOLOGICAL ASSESSMENT UNDER CONDITIONS OF PRACTICAL USAGE

To correlate a consumer's sensory assessment to the product's rheology, it is important to measure the rheological properties under conditions which mimic the consumers interaction with the product[1]. Shampoo is placed on wet hair and is diluted by the subsequent manipulation of the shampoo through the wet hair. It has been found that consumers generally move the shampoo on the hair with strokes of approximately 0.5 sec duration. For these reasons, three samples of shampoo* were measured for a range of shear rates and at a frequency of 2 Hz: 1) without dilution, 2) diluted 50% and 3) diluted 75% with distilled water. The undiluted shampoo was viscoelastic with a high elasticity. The shampoo diluted 50% with water was viscoelastic but the viscosity decreased by a factor of 600 and the elasticity by 14,000. Diluting the shampoo 75% reduces the viscosity by 3000; this mixture shows no measurable elasticity. Therefore, as the rheology changes from initial application to subsequent dilution, the consumer's perception of the product's "feel" will change. However, the development of foam may quickly change this perception.

*Ingredients: deionized water, sodium lauryl sulfate, lauramide DEA, sodium laureth sulfate, hydrolyzed wheat protein, hydrolized collagen, hydrolyzed wheat starch, cocamidopropyl betaine, panthenol, tocpheryl acetate, retinyl palmitate, hydroxypropyl methylcellulose, extract of ginger, cherry bark and hops, PVP, lecithin, beta-carotene, trisodium EDTA, sodium chloride, citric acid, DMDM hydantoin, fragrance and dyes.

[1] Miner, P. E., "Emulsion Rheology: Creams and Lotions", in Rheological Properties of Cosmetics and Toiletries, edited by D. Laba (Marcel Dekker, Inc., New York) 55-152 (1993).

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