JOURNAL OF COSMETIC SCIENCE 138 The impact of temperature is a factor to consider as the jar temperature normally varies from that of the skin surface. Figures 3 and 6A suggest that temperature (25° versus 32°C) only slightly affects the high-rate, shear-thinning behavior however, although hidden in the scale of the overlay, this slight difference in total stress is accessible in G’L/G’M, Chebyshev elasticity index (e3/e1) and σmax (Table II). Figure 7 maps the elastic component of the total stress (σ’) as a function of shear rate. At the chosen isotherms us- ing smooth surfaces, the effect of temperature on the apparent dynamic elasticity near the LVR is notable, but the difference is minimal at the highest shear rates, where mid-to-late spreadability is rated hence, for smooth surfaces, the elastic contributions to the Sun- screen Gel SPF-50 sensory profi le are expected to be similar at both 25° and 32°C iso- therms. Note that shear banding and wall slip confound the physical meaning of the magnitude of σ and, therefore, σ’, σ”, σ0, and σ’0. Nevertheless, wall slip is an integral part of the sensorial experience, and the apparent σ’ is potentially more important to tex- ture profi ling than accurately gauging the true material property (i.e., slip or shear band- ing clouds the interpretation of the instrumental stress response). The Refreshing Gel Cream. The Lissajous plots in Figures 4B, 5B, and 6B summarize the smooth, rough, and thermal data. The Lissajous trajectory of the Refreshing Gel Cream (Figure 4B) shows a smooth transition from a viscoelastic gel to a structured fl uid, as judged by its nearly circular center loops and its thin Lissajous tail. Thermally speaking, the standard rheology (see Figure 3) of the Refreshing Gel Cream, including the apparent yield stress, was not affected by raising the temperature from 25° to 32°C however, there was a decrease in the ZSV at the warmer temperature, indicating that the fl ow and associ- ated molecular interactions at near-zero shear rate are slightly affected by heat. This is echoed in Figure 6B, which shows a very slight change (earlier stress plateauing) in the Figure 6. Effect of temperature and/or surface roughness on the contours of the shear rate plots for (A) Sun- screen Gel SPF-50, (B) Refreshing Gel Cream, (C) Buttery Cream, and (D) Cushion Cream SPF-15.

LARGE AMPLITUDE OSCILLATORY SHEAR 139 32°C Lissajous profi le. Chebyshev and DFT analyses show that e3/e1 remains the same, but that there is a modest change in the nonlinear moduli ratio (G’L/G’M Table II). The G’L/G’M ratio is very sensitive to slight changes in the tail shapes of the Lissajous curve hence, the slightly lower stress plateauing in the 32°C stress curve (Figure 6B) is partially a function of changes in strain-induced stored energy as a function of temperature and shear. Similar to the Sunscreen Gel SPF-50, the Lissajous profi le of the Refreshing Gel Cream (Figure 4B) describes a sigmoidal total stress versus shear rate profi le, implying a transition from a soft solid to a structured fl uid however, relative to the Sunscreen Gel SPF-50, the mag- nitude of the maximum oscillatory stress at the highest shear is 130 Pa greater for the Refreshing Gel Cream further, although the Sunscreen Gel SPF-50 is viscoelastic, the system trends toward a Newtonian fl uid at ~300 s-1, whereas (as evidenced by the larger area of the Lissajous tail in Figure 4B and the slightly larger area in Figure 7A) at higher shear rates, the Refreshing Gel Cream maintains a more appreciable degree of elasticity. Comparing the slopes of the inner ellipses of each system, which correlate with lower-shear texture properties, the microstructure of the Refreshing Gel Cream appears stiffer and more viscous with a longer LVR than the softer Sunscreen Gel SPF-50 (Figure 4A vs. 4B). The trend is inferred from the hurried deformation of circular trajectories of the Sunscreen Gel SPF-50, relative to the Refreshing Gel Cream technology, as observed at strain rates less than 4 s-1 (Figure 5, roughened surfaces data). Undoubtedly, there is not only a transition from circular to elliptical shape, but also a clockwise rotation of the loops (Figure 4A), implying softening of the Sunscreen Gel SPF-50 at relatively low de- formation amplitudes—in a region where the Refreshing Gel Cream is nearer to its LVR. Finally, the apparent yield results from high shear rate LAOS (25°C, smooth surface plates) are 230/160 Pa (σ0/σ’0), which are higher than the Sunscreen Gel SPF-50 σ0 data by Table II Summary of Nonlinear Rheology Data for 25°/32°C (Smooth Surface) Formulation G’L/G’M 25/32°C at 185 s-1 (±3.9%) (e3/e1) 25/32°C at 185 s-1 (±0.01) σ’max, γ = 600% 25/32°C (±2 Pa) Sunscreen Gel SPF-50™ 4.80/2.45 (−43%) +0.31/+0.23 (−26%) 177/126 (−29%) Cushion Cream SPF-15 2.87/2.70 (−5.9%) +0.24/+0.24 (0.0%) 400/336 (−16%) Refreshing Gel Cream 3.52/2.57 (−27%) +0.23/+0.23 (0.0%) 191/180 (−5.8%) Buttery Cream 2.17/1.30 (−40%) +0.26/+0.13 (−50%) 358/146 (−59%) Figure 7. Plot of apparent elastic stress versus shear rate for (A) 25°C versus (B) 32°C for Sunscreen Gel SPF-50, Refreshing Gel Cream, Buttery Cream, and Cushion Cream SPF-15 (smooth plates). Note that wall slip and thixotropy are integral participants in the instrumental data as well as the sensorial ratings (12). Also, in 7B, note the diminished apparent elasisticity for the Buttery Cream.