JOURNAL OF COSMETIC SCIENCE 92 While there is a great amount of formulation knowledge on how to achieve water resistance and rub-off resistance, our industry has fewer technical advances in oil/sebum resistance (1–4). Previously, we developed a set of simple, semiquantitative, yet highly relevant nonhuman test methods for understanding color cosmetics’ oil resistance. Those test methods not only enabled us to make comprehensive assessments of makeup formu- lations’ lasting performance when exposed to oil (grease or sebum), but also helped reveal each ingredient’s subtle impact to a fi nish formulation’s oil resistance effi cacy (4). Based on our learnings, we propose here a “Soft” + “Hard” formulation strategy toward long wear and sebum/oil resistance. For illustration, we apply here the “Soft” + “Hard” formu- lation strategy to silicone-based makeup formulations. MATERIALS AND METHODS “SOFT” + “HARD” FORMULATION STRATEGY FOR SILICONE-BASED FORMULATIONS To apply the “Soft” + “Hard” strategy to silicone-based formulation chassis, we created a con- ceptual map of silicone materials’ “hardness” and charted several types of silicone materials, including polydimethylsiloxanes, silicone resins, silicone polyethers (SPEs), silicone crosspolymers, alkylmethylsiloxanes, silicone acrylates, and silica silicate (Scheme 1). The per- ceived “hardness” is largely based on materials’ glass transition temperature or soften- ing temperature. For instance, low-viscosity silicone fl uids would be considered very “Soft,” while materials like commercial MQ resins with a glass transition temperature over 200°C would be at the very “Hard” end of the conceptual map. MATERIALS An important type of “Soft” components we investigated are SPE fl uids used for creating W/Si or W/O formulations. With typical Tg values well below -100°C, most silicone emulsifi ers were placed on the “soft” end of the conceptual “hardness” map. SPEs in this study include a block copolymer with an INCI name of “Bis-Isobutyl PEG/PPG-10/7/ Dimethicone Copolymer,” two random copolymers with INCI names of “PEG/PPG- 19/19 Dimethicone” and “Lauryl PEG-10 Tris(trimethylsiloxy)silylethyl Dimethicone.” A silicone acrylate (SiAc) copolymer (INCI name: “Acrylates/Polytrimethylsiloxymethacrylate Copolymer”) was selected to illustrate a type of “Hard” silicone components. The silicone acrylate technology is currently used for long-lasting lip products and durable liquid foundations with comfortable wear. The particular silicone acrylate (Acrylates/ Polytrimethylsiloxymethacrylate Copolymer) referred to throughout this study is a brittle Scheme 1. A conceptual map of silicone materials’ “hardness,” charting several types of silicone materials.

LONG-WEAR SEBUM-RESISTANT COSMETICS 93 solid at room temperature and has a distinct melting transition with onset of ~75°C and peak at ~90°C based on differential scanning calorimetry (DSC) study. Blends of silicone acrylate and SPE at various ratios were prepared by mixing and evaporating volatile sol- vent. We prepared and tested two sets of simple makeup prototypes to further illustrate our “Soft” + “Hard” strategy for achieving sebum resistance. In our study, artifi cial se- bum, a mixture of organic oils, was used (4). METHODS AND RESULTS Visual assessment and cross-section transmission electron microscopy (TEM) were per- formed to help understand compatibility between and silicone acrylate and different SPEs. After removing volatile carrier fl uids, silicone acrylate and “PEG/PPG-19/19 Di- methicone” blended at 7:3 ratio formed an optically transparent plastic material. The compatibility between silicone acrylate and “PEG/ PPG-19/19 Dimethicone” in the blend was further suggested by cross-section TEM (Figure 1A). No distinct phase domain was observed at 5-nm scale and above. On the contrary, silicone acrylate and “Lauryl PEG-10 Tris(trimethylsiloxy)silylethyl Dimethicone” blended at a 7:3 ratio formed an opaque solid. Distinct phase domains, sized from several nanometers to over 100 nm, were observed under cross-section TEM (Figure 1B). All indicate incompatibility be- tween the two materials. Viscoelastic properties of compatible silicone acrylate/SPE blends were further investi- gated. Shown in Figure 2A are temperature sweep measurements of elastic modulus (G’) of silicone acrylate (SiAc) and “PEG/PPG-19/19 Dimethicone” (an SPE) blends at differ- ent ratios. Figure 2B shows damping factor of related blends. G’ level of SiAc/SPE at a 7:3 ratio was lower than that of neat silicone acrylate at the entire temperature range tested. Also, the addition of SPE shifted the damping factor peak to a lower temperature, which is indicative that thermal transition occurred at a lower temperature. At room temperature, the blend of SiAc/SPE at a 7:3 ratio showed a signifi cantly higher dumping factor (more “viscous”) than neat silicone acrylate. Clearly, more pronounced effects were observed from the SiAc/SPE (6:4) blend. These systematic changes signify that this par- ticular SPE worked as an effective plasticizer in the blends. DSC study (data not shown) Figure 1. Cross-section TEM images of blends. (A) A blend of silicone acrylate and “PEG/PPG-19/19 Dimethicone” at 7:3 ratio. (B) A blend of silicone acrylate and “Lauryl PEG-10 Tris(trimethylsiloxy)silylethyl Dimethicone” at 7:3 ratio.