276 JOURNAL OF COSMETIC SCIENCE copy (ESEM) can be exploited to this end. These techniques have the advantage over many indirect and macroscopic tests that give little information on hair morphology and the presence of specific adsorbates such as polymers. Quaternized cationic polymers have a high affinity for the hair's surface due to the hair's negative charge at normal pH and are typically used as conditioners due to their high cationic charge density. Generally, hair conditioning involves some interfacial alteration in the protein matrix of the hair. There is a wealth of literature covering electron microscopy studies of hair (1). Studies include ESEM, which, unlike traditional SEM, does not require a high vacuum and can allow the hair to be studied in an ambient and hydrated environment (2). More recently, attention has been paid to hair structure and morphology using scanning probe and atomic force microscopy (SPM and AFM), allowing the hair to be imaged at varying pH and hydration levels (3-6). SPM has also been instrumental in detecting cationic poly- mer adsorption onto hair, these polymers adsorbing strongly at normal pH due to high cationic charge density, an essential property for hair conditioning (7,8). There is little literature on spectroscopic studies of hair however, electron energy loss spectroscopy (EELS) has been used to map the sulfur distribution in human hair, giving information on the distribution and abundance of keratin bonds (9). In addition, SIMS imaging has recently been proposed by Gillen et •l. as a promising technique for mapping distributions of certain ions in hair such as Ba +, K +, and C2H3 + after doping hair in various inorganic and organic solutions. Their recent work gives some good examples (10). With the emphasis on cosmetics, this paper shows how a variety of techniques can be used to investigate the presence of adsorbed species onto biological materials such as hair. MATERIALS AND METHODS GENERAL HAIR TREATMENT Bleached hair samples were purchased from DeMeo Brothers, New York. The bleached hair was studied both untreated, by simply rinsing the sample in distilled water and allowing to dry naturally, and treated, as outlined below. Treatment was carried out using polyquaternium-6, a cationic conditioning polymer, [poly(dimethyldiallyl ammonium chloride), Merquat©-100, 40% active, Calgon Corpo- ration, for polymer composition (see Figure l a)] by soaking in a 0.1% w/w aqueous solution (18Mf• deionized water) for two hours and then rinsing in running deionized water for two minutes. The tress was then left to dry naturally for 24 hours. To enable clearer detection of the polymer adsorption, and to differentiate the polymer from the hair with greater distinction, some tresses were treated with a phosphorus- labeled polyquat-6 derivative. This phosphorus-labeled Merquat © 100 was prepared by polymerizing dimethyldiallylammonium chloride in the presence of hypophosphorous acid as a chain regulator. The structure is given in Figure lb. For distinction, the commercially available Merquat©-100 will be referred to as N-Merquat©-100, and the synthesized phosphorus-labeled as P-Merquat- 100.

ADSORPTION OF POLYMER ONTO HAIR 277 (a) . H:C CH: n (b) Figure 1. a: Structure of the polyquaternium-6 polymer. b: Structure of the phosphorus-labeled polyquater- nium-6 polymer. The molar ratio of n:m is approximately 99:1. For polymer synthesis see text. INSTRUMENTATION Environmental SEM. Environmental SEM (ESEM) permits high-resolution imaging of fully hydrated materials. ESEM offers all the capabilities of conventional SEM, but a differential pumping system enables specimens to be maintained in a gaseous environ- ment to around 20-torr pressure (11). Secondary electron imaging exploits the ionized gas in the chamber by using proportional gas amplification of the SE signal (12). The ionized chamber gas also dissipates charge buildup on the specimen. Water vapor is a convenient and efficient imaging gas. By balancing chamber pressure and specimen temperature along the 100% RH isobar, specimens may be maintained in a fully