2001 ANNUAL SCIENTIFIC SEMINAR 413 transmitted through the combined sunscreen and substrate and E is the effective UV dose transmitted through the sunscreen only, computed as E = SPFs *Ess. Eo, Ess, and E are irradiance values integrated over time, and expressed in multiples of the MEI} (0.02 effective joules/cm2), which is the UV dose required to produce minimally perceptible erythema (sunburn). Measured values of Eo are plotted against computed values of E, and the SPF of the sunscreen at any given time is Eo / E. The SPF measured in the in vivo SPF test is the value of Eo when E reaches one IVIED. The value of SPF measured in vitro must be approximately equal to the SPF measured using the in vivo test for the assessment of photostability and UVA protection to be valid. A power curve fit equation, E =ctEo I•, may then be computed using a least squares curve fitting method, as shown below for a typical broad spectrum sunscreen product with an SPF of 26: 3 E = 0'0098Eø"4's4 • •= R 2 = 0.99 • g • SPF 0 10 20 30 40 50 60 Eo (Effective UV Dose Applied, MED) Since a value of 1 for [3 represents a linear relationship between E and Eo, and a constant SPF, a sunscreen may be considered photostable if the value of I• is near 1. In the example shown above, I• = 1.4184, and the sunscreen is not considered photostable. We have set a proposed limit of 1.1 for It. Thus, if [• 1.1, a sunscreen may be labeled as photostable. The UVA protection factor, APF, represents the UVA component of SPF. APF may be calculated in the same manner as SPF, for the wavelength range from 320 to 400 nm There is general agreement that the contribution of UVA to the acute effects of sunlight is about 20%. Therefore, if the ratio of APF to SPF is at least 20 percent, we propose that the sunscreen may be labeled "Broad Spectrum."

414 JOURNAL OF COSMETIC SCIENCE GEMINI SURFACTANTS FOR SUNSCREENS Klaus Kwetkat, Ph.D. Sasol Olefins & Surfactants GrnbH, Marl, Germany Gemini Surfactants Gemini surfactants, i.e. two surfactant moieties (a hydrophilic group and a hydrophobic chain) joined by a spacer, have attracted a lot of attention in recent years. Their main characteristics are superior interfacial activity, high electrolyte tolerance, mildness and high flexibility when compared to their conventional counterparts. Most gemini surfactants show low diffusion velocities and there is evidence that exchange rates between bulk phase and aggregates (e.g. micelies) are considerably slower than for conventional surfactants. In other words gemini surfactants tend to form more stable aggregates. Translating the unique properties of gemini surfactants into applications has been the main hurdle to commercialization so far. A simple, one to one exchange with conventional surfactants gives mediocre results at best. CERALUTION TM H - gel network emulsions When gemini surfactants are incorporated into a well balanced matrix of cosmetic raw materials their unique properties can be exploited in formulations. CERALUTION TM H (behenyl alcohol, glyceryl stearate, glyceryl stearate citrate, sodium dicocoylethylenediamine PEG-15 sulfate) is such a matrix that can be used as a building block in personal care formulations. It has been designed as liquid crystalline lameliar gel network O/W emulsifier. As this system is based on a gemini surfactant it can form stable liquid crystalline gel networks very efficiently and under a wide range of circumstances, i.e. oil loads and polarities, pH values (4 to 12) and electrolyte concentrations. The gel network helps to form and stabilize emulsions mainly in three ways. It's formation leads to extremely low interfacial tension which allows the formation of very small droplets - CERALUTION TM H is very efficient in this aspect (at 2.5 wt % with 0.1 wt% of a hydrocolloid stable nano-emulsions are formed). The third phase, the gel network, separates oil droplets and water phase. Moreover the lameliar gel network increases the viscosity of the emulsion. Usually the gel network emulsifiers are designed to increase viscosity even at low concentrations. The viscosity helps to stabilize the emulsion against creaming or sedimentation. The CERALUTION TM H gel network has a critical temperature (at which the lamellar gel network starts to disintegrate) of 65 øC. The higher the critical gel network temperature the better the temperature stability of the emulsion. Nonionic surfactants which are added to an emulsion on top of the gel network emulsifier will usually be incorporated into the network and will lower the viscosity. More important, they will also lower the critical gel network temperature and will thus destabilize the whole system. The critical gel network temperature also influences water resistance of a gel network emulsion as the temperature at which a dried gel network can be re-wetted follows the critical gel network temperature. Consequently water resistance is also compromised as soon as nonionic surfactants are added on top of the optimized gel network emulsifier. CERALUTION TM H gel network emulsions are very electrolyte tolerant. The comparison of two identical emulsions, one with CERALUTION TM H the other with a nonionic system shows that at a sodium chloride concentration of 4 wt % the emulsion with the nonionic emulsifier system is about to separate whereas the CERALUTION TM H based emulsion does not show any effect. The gemini surfactant blend, CERALUTION TM H, can also be used as a dispersant. At concentrations of approx. 1 to 2 wt %, titanium dioxide, be it with a hydrophilic or hydrophobic coating, is as efficiently dispersed as in commercially available titanium dioxide dispersions. The lamellar gel network formed by CERALUTION TM H adds protection against oxidation to, e.g. a sunscreen. Tests in which the level of lipid peroxides (monitored by the squalene / squalene peroxide ratio) was checked before and after the irradiation with UV light (10 J / cm 2) showed an effect comparable to a lotion which contained free tocopherol. We still do not know the mechanism but have proved that the effect is reproducible and not dependent on a special formulation. CERALUTION TM based sprayable emulsions As explained above a gel network emulsifier imparts viscosity to an emulsion. Thus its effect on an emulsion which needs to have very low viscosity (comparable to water) would be detrimental. CERALUTION TM H can be modified by the addtion of another gemini surfactant based blend, C ERALUTION TM F (sodium lauroyi iactylate, sodium dicocoylethylenediamine PEG-15 sulfate). The latter blend was developed as a building block for hair and skin cleansing and can also be used to switch off the gel network formation when added to CERALUTION TM H. Contrary to lotions or creams