FILM PROPERTIES OF POLYMERS USED IN ANHYDROUS SUNSCREEN FORMULATIONS 209 Formulation C, which contained a sunscreen phase, but no polymer, appears to have cov- ered the entire surface of the corneocytes with a sunscreen fi lm. The fi lm entirely covered the surface, as evident in the SEM micrographs. The individual corneocytes were less apparent as the fi lm entirely covered the surface. There are many similarities between Fig ure 3. SEM micrographs of various sun care formulations deposited (sprayed) onto layers of stratum corneum cells (magnifi cation = 500–×1,000). (A) Formulation A, (B) Formulation B, (C) Formulation C, (D) Formulation D, (E) Formulation E, and (F) Formulation F.

JOURNAL OF COSMETIC SCIENCE 210 Figures 2A and C and 3A and C due to the absence of the fi lm former which typically appears on the surface of the corneocytes and is not present in these formulations. This confi rms the fact that the sunscreen phase blends well with the corneocytes. Formulation D represents a typical sun care spray formulation, which contained a sun- screen phase and a relatively low level (1% w/w) of fi lm former. As expected, the sun- screen phase formed a continuous fi lm over the corneocytes. The fi lm former did not form the same type of network that we observed when the polymer was used alone (Figure 3B) but rather formed discrete blotches on the surface of the sunscreen fi lm. This behavior confi rms that there is an interaction between the sunscreen phase and the fi lm former, which indicates that portions of the fi lm former intercalate the sunscreen fi lm, whereas the remaining portion of the fi lm former creates a fi lm over the sunscreen layer. In Formulations E and F, two distinct polymers were added at low concentrations to study the interaction of composite fi lm formers on the surface characteristics of the fi lms created. Specifi cally, acrylates/dimethicone copolymer and hydroxypropyl cellulose, re- spectively, were added to Formulations E and F. By examination of the surface topography of the fi lms created, we observed that the surface properties of the two fi lms were com- pletely different. In the case of acrylates/dimethicone copolymer, there was no interaction of this polymer with the existing VA/butyl maleate/isobornyl acrylate copolymer. In fact, it appeared that acrylates/dimethicone copolymer formed discrete particles on the surface of the fi lm. On the other hand, the addition of hydroxypropyl cellulose to the existing polymer (VA/butyl maleate/isoburnyl acrylate copolymer) created a very defi ned network of the two polymers on the surface of the sunscreen fi lm. In an effort to study the applicability of this methodology to other formulations, we ex- amined the fi lm morphology of an SPF 30 commercial sunscreen containing VA/butyl maleate/isobornyl acrylate copolymer as a polymeric fi lm former. The micrographs of the commercial sunscreen and Formulation D are displayed in Figure 4. Examination of the two micrographs indicates a number of similarities between the two fi lms created. In both instances, the polymer formed a fi lm over the sunscreen fi lm, and the polymeric fi lm is made up of discrete particles rather than a network. The behavior of the fi lm former was Figure 4. SEM micrographs of a commercial sun care product containing VA/butyl maleate/isobornyl acrylate copolymer deposited (sprayed) onto layers of stratum corneum cells (magnifi cation = ×300).