title: Characterization of yield stress and slip behaviour of skin/hair care gels using steady flow and LAOS measurements and their correlation with sensorial attributes.
abstract: Gels made with three different polymers widely used as rheology modifiers in cosmetic formulations (cross-linked poly(acrylic acid), cross-linked poly(maleic acid-alt-methyl vinyl ether) copolymer and cross-linked poly(acrylic acid-co-vinyl pyrrolidone) copolymer) were characterized by rheological and sensory evaluation methods to determine the relationship between sensorial perception and corresponding rheological parameters. Both conventional rheological characterization methods and a more recent method, Fourier Transform Rheology with Large Amplitude Oscillatory Flow data (LAOS), were utilized to characterize the material with and without wall slip. Sensorial analyses were implemented in vivo to evaluate the perceived ease of initial and rub-out spreadability, cushion, pick-up and slipperiness attributes of the gels. Results were statistically analysed by both variance (ANOVA) and principle component analysis (PCA). Sensorial panel testing characteristics discriminated the three materials, and PCA analyses revealed that sensory attributes could be well predicted by rheological methods. Rheological experiments, without wall slip, revealed that gel strength in the linear viscoelastic region (LVR) and yield stress of these materials are similar, but exhibit significantly different wall slip and thixotropy behaviour in the low shear rate region under wall slip conditions. Above the critical shear rate, which corresponds to the yield stress, all tested materials did not slip and behaved as conventional, shear thinning polymeric fluids. In particular, the rheological parameters and sensorial perception of the 1% cross-linked vinyl pyrrolidone/acrylic acid copolymer were significantly affected by wall slip and/or thixotropy-related shear banding phenomena.
authors.affiliation: Materials Science Group, Global R&D, Ashland Specialty Ingredients, 1361 Alps Road, Wayne, NJ 07470, USA. sozkan@ashland.com
authors.forename: S
authors.initials: S
authors.lastname: Ozkan
authors.forename: T W
authors.initials: TW
authors.lastname: Gillece
authors.forename: L
authors.initials: L
authors.lastname: Senak
authors.forename: D J
authors.initials: DJ
authors.lastname: Moore
mesh_terms: D003358:Cosmetics; D005583:Fourier Analysis; D005782:Gels; D006197:Hair; D006801:Humans; D025341:Principal Component Analysis; D012212:Rheology; D012867:Skin
chemical_list: D003358:Cosmetics; D005782:Gels