64 JOURNAL OF COSMETIC SCIENCE by the ring of plate method for a hairspray formulation) on a hairspray before it contacts the hair. Therefore, a hairspray formulator must be concerned with non-equilibrium surface tension as well. Bubble pressure non-equilibrium surface tensiometry involves blowing bubbles of gas into a liquid and measuring the maximum pressure necessary to form each bubble. That pressure is directly proportional to surface tension. By blowing bubbles at different rates, non-equilibrium surface tension values can be determined at surface ages as low as 5 milliseconds. Drop volume tensiometry is an equivalent method for non-equilibrium interfacial tension. It involves measuring interfacial tension (liquid/liquid) by dispensing one liquid drop-wise into another liquid from a well defined capillary tip, and observing the balance of forces that exists between the adhesion force the drop has for the capillary tip and the buoyancy force the drop feels. Drop volume tensiometry is a non- equilibrium technique, because the drop can be formed and measured for interlhcial tension at various rates. Minimum measurable interface age is typically about 0.5 second. A major use of non-equilibrium interfacial tension is to study diffusion and adsorption rates of emulsifiers to liquid/liquid interfaces. This has great application to the formulation of emulsified products like sunscreens and lotions. Commercial instruments are also readily available for the study of non-equilibrium surface and interfacial tension, though manufacturers don't abound, as in the case for equilibrium surface and interfacial tension. Newly Developed Surface Science Methods The Pendant Drop Technique for Both Equilibrium and Non-Equilibrium Surface and Interfacial Tension It has long been known that either surface or interfacial tension can be determined simply by analyzing the shape of drop of liquid (or bubble of gas) that is pendant (attached to) to a capillary tip. The overriding principles are the Laplace equation (which equates the curvature of a liquid/gas or liquid/liquid interface to the tension that exists between the two phases) and buoyancy forces which cause a pendant drop to elongate due to the density difference between the two phases. However, despite the relative ease with which one might capture an image of a pendant drop for analysis (either photographically or digitally), this method was virtually unused by surface scientists until approximately 15 years ago. This was because the processing of an image into surface or interfacial tension data (i.e. the robust solution of the Laplace equation) was tedious. However, in the age of high-speed personal computers and high-speed digital image capture, that has changed. The method is now widely used for both surface and interfacial tension determinations. Non-equilibrium tensions are possible as per the rapid formation of a pendant drop and subsequent high-speed imagining. The pendant drop method is perhaps the most flexible of all surface and interfacial tension methods in terms of temperature, and even pressure, control. It is also one of the easiest techniques to keep free of contamination. Commercial instruments are readily available. The Oscillating Pendant Drop Technique for the Study of Surface and Interfacial Rheology Even more recently (within the last 5 years), a major breakthrough has made for surface scientists. A computer controlled oscillating pendant drop tensiometer has been commercialized which allows not only for determination surface and interfacial tension as a function of time as an interface equilibrates, but also enables the experimenter to controllably perturb a pre-equilibrated interface and monitor its response to the perturbation. This represents a radical departure from previous non-equilibrium surface and interfacial science techniques, which only focused on monitoring the progression of an interface toward equilibrium. Such "2-dimensional" rheological properties as: Gibbs' modulus, interfacial elasticity, surface elasticity, interfacial viscosity, and surface viscosity can be determined. The droplet's surface area is controlled by a precision pump and can be made to oscillate sinusoidally, linearly, step-wise, and/or by feedback control with respect to the real-time data. The ability to study what happens when an interface or surface at equilibrium is perturbed is critically important to the advancement of our uf•derstanding of emulsion stability and foam persistence. Yet, previously such measurements where not possilSle with commercial instrumentation (except in the case of Langmuir trough studies with insoluble monolayer systems). Oscillating Drop Tensiometers have been commercially available in the United States for approximately 1 year. Data directly related to emulsion stability and foam persistence will be discussed.

1999 ANNUAL SCIENTIFIC MEETING 65 SPECIAL PRESENTATION BARRIER FUNCTION AND AGING SKIN: CURRENT AND NEW THERAPEUTIC STRATEGIES Linda D. Rhein, Ph.D. SmithKline Beecham Consumer Healthcare, Parsippany, NJ 07054 Aging skin often has associated with it a variety of problems. Dryness, winter xerosis and even ichthyosis are common occurrences and are often associated with extreme itching. Photodamage resulting from chronic exposure to the sun leads to the appearance of wrinkles and fine lines. Other lesions that appear frequently are lentigens or age spots which are areas of hyperpigmentation. In the worst cases of photodamage patients often end up with skin cancers such as squamous or basal cell carcinomas and melanoma. The cosmetic industry is obligated to provide treatments for all these age-associated indications except skin cancer. Physical Chemical Strategies to Enhance Aging Skin Barrier Treatments for dry skin and winter xerosis involve a variety of therapeutic strategies based on the structure and function of stratum comeum. The cells of this horny layer are constantly being worn away and replaced by newly keratinised cells, in a continual cycle. This cycle of keratinisation, cell loss and replacement is important because a variety of skin problems, including ichthyosis, psoriasis, and eczema, involve disturbances of the normal sequence. The cycle may be disturbed by a variety of factors, including exposure to substances such as surfactants and emulsifiers often in cosmetics, low relative humidity, cold weather, vitamin A, alpha hydroxy acids, or drugs, as well as chemical messengers produced by the cells themselves such as in disease states, e.g. psoriasis which is characterised by accelerated cell formation. Stratum corneum is composed of lipids and proteins. Since treatments for dryness often are lipidoidal in nature and interact with the hydrophobic part of the membrane, a brief discussion of the lipids found in the stratum corneum is in order. Lipids in stratum corneum originate from the lameliar bodies. Lameliar bodies are formed on the Golgi. The lameliar body attaches to the cell membrane of the keratinocytes and their lipid contents are extruded into the intercellular spaces around the corneocytes. They are then modified by enzymes present in the intercellular spaces to produce the intercellular lipids found in the upper layers of the stratum comeum (see review by Abraham, W., in Surfactants in Cosmetics, Surfactant Science Series Vol. 68, Edited by Rhein and Reiger, 1997). Lipids in the upper layers contain predominantly cholesterol, ceramides and free fatty acids in a ratio of25:50:15 as weight percent. They are unique in that they do not contain phospholipids which are typically found in other biological membranes. During the process of modification to produce these lipids, phospholipids present in the lamellar body secretions are completely abolished converting them to free fatty acids glucosylceramides also present in the secretions are converted to ceramides.