380 JOURNAL OF COSMETIC SCIENCE UTILIZING RHEOLOGICAL PARAMETERS TO PREDICT CONSUMER-PERCEIVED SENSORY ATTRIBUTES OF COSMETIC CREAMS Penny Anderson, Julie Harrison, Deb O'Toole and Angie Hendrickson Artistry Center for Skin Health Research, Amway Corporation, Ada, MI Introduction: Rheology is the study of flow and defmmation of liquid to semi-solid materials [l]. This complex technology has numerous practical applications to the development, manufacture, quality assurance and end-use of consumer products. During the product development cycle, rheological measurements can be used to characterize formulation prototypes, differentiate processing changes, and simulate shear flows imparted during material transformations. Moreover, rheological methodologies can be employed to mimic the sensory perception experienced by consumers upon dispensing a lotion from a bottle, or rubbing a cream into the skin. Recently, significant correlations have been established between rheometer-generated properties and consumer-perceived attributes collected from trained, dermatosensory panelists. Subjective descriptions of cosmetic cream attributes such as "firmness, and stickiness" were related to quantitative instrumental measurements of elastic modulus and negative normal force (upon extension) respectively. These correlations provide the potential to aid product developers in the prediction of targeted consumer sensory attributes, thereby reducing the need to conduct elaborate, expensive panel testing (for selected properties) while simultaneously accelerating the product development cycle. Measurements and Methods: Commercially available prestige-positioned, anti-aging creams and developmental formulation prototypes were evaluated for sensory descriptive ratings by dermatosensory panelists [2]. Replicate prototypes and products were characterized utilizing a TA Instruments AR-I000 Rheometer equipped with a parallel plate geometry for generation of various oscillatory and flow properties. Comparison ofDermatosensory "Firmness" Rating vs. Elastic (Storage) Modulus A dynamic rheological measurement technique [3, 4] was devised, which involved gently probing the samples by applying a "back and forth" motion (wobbling) in a sinusoidal pattern of deformation. Rheometer stress ramps were imparted via small amplitude oscillatory stress at a constant frequency = 0.5 radians/second to determine the linear regime of the viscoelastic spectrum for various prototypes [Figure 1]. The data generated from the rheometer was then resolved into elastic and viscous components (G'= Storage Modulus, G"- Loss Modulus) which represent the solid-like (stored) and liquid-like (dissipated) energies of the creams respectively [Figure 2]. Fig 11 re I: Illustration of!ypic_al!�()_111eter (}s�!!lation _l\l e � o� Figure 2: Resolution of Viscoelastic Moduli for Cream 800 :" I 300 I -200 C -700 ·1200 Graphical Interpretation of Applied Stress C!lan� -c.t,opol Copoljm,rsystem In an Oaclllatlon Stress Ramp d. 11Xll t-------�-�-'-+-o ..... .....­ Frequency• 111111 (wt) . · ·······..:-.. 10 o.lll■-onln■tp1]1tw•D.&t1dl11C 100 Replicate testing was conducted on each product and/or prototype applying the above rheological method to determine the following average values of Elastic Modulus, G'. This data was then compared to "firmness" ratings achieved from the Dermatosensory panel in Table I and Figure 3 below. A statistically significant linear correlation was established revealing a strong proportional relationship between the instrumental values and human descriptive ratings.

2008 ANNUAL SCIENTIFIC SEMINAR 381 T able I. Averue G 'and Fi 1rmnm tinllJ or anous Ra' fi V ' C reams Sample F'""- 0-rlndna Rada. NiaitCmA 42.8 l"lnfiml, Moitr\R c.rime Atv1A 41.7 NillitCrmn A."-113 JS.I Davtime Moisture Creme AMB 33.7 Bodv Cream AMA 32.9 Ni_.Crmn AMC 33.1 Niilm C'.rima 8 31.9 Ni,hCmC 32 001'9109-82 32.8 001'9109-84 31.8 001'91119-86 30.8 G' IPal 2191 2439 892 876 642 S38 349 806 974 S42 606 3000. I 2500-t--"�,---==-=---:-=-:::::-=---....,..,.--:---�--1 i�2000--------""--------:tuo...-R'···.;.._.?,'y•1S1�-- '8- � i 1500+----------------- 1 ! � 3 1000+------,.----,.------'-...P-'----'--.,,.---t r-= s = !?. 500 -1,-..-,....,.:,,._---"--"-'--._.....:. c...:,t!III!,-. __ �__.� 0 10 20 30 -40 � Flnm-Aallng 50 Comparison of Dermatosensory "Stickiness" Rating vs. Negative Normal Force upon Extension In addition to the oscillatory rheometer measurement technique, an extensional mode of deformation (pulling flow) was also imparted onto the various cosmetic prototypes. During execution of this test, a rapid tension deformation (upward motion of the sampling geometry) of user-defined velocity [um/sec] was applied to the sample over a specified distance. The corresponding change in the Normal force (this reads as a negative force or pulling force from the sensor in the bottom of Peltier plate of the instrument) was measured by the rheometer. The resulting measurement values can further be related to the stringiness, stickiness, and cohesiveness of the sample as perceived by many consumers. Table 2 and Figure 4 exhibit the linear relationship established between dermatosensory descriptive ratings for "stickiness" and the C?rresponding negative normal force values. Table 2. Avenn - Normal Fon:e Valuavs.StickinessRatinpforVariousCosmeticCreams Sample Stickiocss Neptive Description Jbti122 Normal Fortt INI Ni_ditCmneA 31.6 0.1986 l'illlltCmneB 37.6 0.4517 Nidrt a-c:me C 28.6 0.1602 Nil!bt Cream AMB 31.3 0,2449 Daytime Moistw"e Creme AMB 29.S 0.1538 IBodv Cream AMA 28.9 0.1217 NidU Cream AMC 29.0 0.0897 DOT9109-82 30.0 0.1186 DOT9109-34 28.S 0.1281 DOT9109-86 30.0 0.1260 Conclusions Fi&ure 4. Com:latioo of Dmnatosensory Stickinas Attribute to Normll Force After Tmsioo 0.5 .,...._,...,... __________....,...___ i 0. 45 �.,...._ .. ,@ 0.3 +-------..--,-_;.-..,...._.:,..'-------- 6 zo.25 +-----,---------,-----,......-.--........--------_,.......,.... .- ' 0.2 0.15 +-_:_..,....,.:.._:....,,..,,;-'-���--���..,,..,.:.,.._._-- Z I 0.1 -t----'--,...-,---..,;,._..-..,;_ __ ...,.:..�-'-"-'�-----....... 0.05 +----.....,.,--,.;,-.-,....,....,,....,..,.... ______ ____ 0 +-�--...,....-'-'---...,.:..----'----"----- 0 10 20 30 Stic:klnau Rlltlng 40 Rheological methodologies can be successfully leveraged to objectively and quantitatively d cribe aesthetic attributes of cosmetic products. This informative tool provides a m aningful, sensitive, and instrumental approach towards describing cream into consumer-perceived terminology which can further assist cosmetic chemists in pinpointing the desired, targeted properties of developmental prototypes. References I. Barnes, Hutton, Walters, "An Introduction to Rheology," pg 159-169, 1989 2. Carlone, Sensory Spectrum, Inc, Dermatosensory Panel Testing, December 5th 2005 3. Barnes, "A Handbook of Elementary Rheology", pg 27-76, 2000 4. Macosko, "Rheology Principles, Measurements, and Applications", pg 117-126, 237-255, 1994