CATIONIC TREATMENT OF IRON OXIDES 619 of 240,000 g/mol and a charge density of 6.2, had one cationic group in each monomer unit. Artifi cial eyelashes (Echo’s Eyelash® Taeil, Republic of Korea) were manufactured, using untreated human hair, to measure the volume effects by mascara application. The eyelashes were designed to achieve an average length of 7.0 mm and a thickness of 72.0 μm by referring to the results of a previous study (9). SURFACE TREATMENT The surface of iron oxide was treated with cationic polymers by a wet process well known to those in the industry (2). This method has been used to treat pigments with a hydro- philic surface (such as clay minerals), inorganic materials (such as silica or titanium dioxide), and polymeric materials (such as polymethyl methacrylate). Iron oxide was dispersed in deionized water in a ratio of 1:2. The cationic polymers were agi- tated in a separate tank to reach transparency in deionized water at 50°C. The aqueous poly- mer slurry was added to the pigment to form a colloidal dispersion of the coating materials. Following agitation for 1 hr, the mixture was fi ltered to form a paste and dried under heat. The pigment was then ground using an atomizer (BRA-15 Baro Engineering, Republic of Korea) and fi nally screened with a polarizer (CSTS-601 Chang Sung Hitech, Republic of Korea). MEASUREMENT OF ZETA POTENTIAL AND PARTICLE CLUSTER SIZE The zeta potential values and particle cluster sizes of the coated pigments were measured using a zeta potential spectrophotometer (ELS-8000 Otsuka Electronics Co. Ltd., Japan). All measurements were made at pH 7 to simulate mascara application. The samples were diluted 1,000-fold in 0.1 M NaCl solution or deionized water for zeta potential or par- ticle cluster size, respectively, and sonicated 5 min prior to measurement. The measure- ments were repeated three times. MASCARA FORMULATION Mascara bulks were prepared employing a basic mascara formula using coated and uncoated iron oxides. The formula included: water (to 100%), acrylates copolymer (20%), paraffi n (10%), iron oxides (10%), beeswax (5.0%), carnauba wax (3.0%), stearic acid (3.5%), palmitic acid (1.5%), polybutene (1.0%), triethanolamine (1.0%), butylene glycol (1.0%), and hydroxyethylcellulose (0.2%) with necessary chelating agents and preservatives. Mascara weight measurement. Mascara weight was defi ned as the weight difference of artifi - cial eyelashes before and after twelve mascara applications. Twelve applications is defi ned as dividing the eyelashes into three sections (i.e., left, middle, right) and applying mas- cara in each section twice from the top and twice from the bottom. The experiments were repeated three times. Sensory test. Sensory tests were conducted by a trained panel of thirty Korean women in the age range of 20-35 regularly using mascara every day. Volume and spreadability scores were marked in the range of 0-14.

JOURNAL OF COSMETIC SCIENCE 620 Table I Effect of Cationic Polymer Treatment on Particle Cluster Size and Zeta Potential of Iron Oxides Coating material Particle cluster size (nm) Zeta potential (mV) Weight difference (mg) Type Concentration (%) None 0 4396.7 ± 74.6 -12.033 ± 0.605 7.673 ± 0.111 PQ-6 3 2934.0 ± 74.1 25.273 ± 1.222 8.973 ± 0.068 5 1562.4 ± 29.3 52.483 ± 0.468 15.123 ± 0.136 10 1099.3 ± 84.6 63.437 ± 1.217 15.843 ± 0.060 GHC 3 1514.3 ± 41.2 43.927 ± 0.612 11.350 ± 0.461 5 1290.6 ± 8.54 45.677 ± 0.389 11.913 ± 0.178 10 1215.0 ± 36.7 47.693 ± 0.441 12.517 ± 0.333 PQ-10 3 3579.8 ± 21.0 28.080 ± 0.896 9.090 ± 0.187 5 2372.2 ± 10.5 33.763 ± 1.293 10.573 ± 0.095 10 2057.4 ± 29.9 40.553 ± 0.338 11.230 ± 0.099 Data presented as mean ± SD (n = 3). PQ-6: polyquaternium-6. GHC: guar hydroxypropyl trimonium chlo- ride. PQ-10: polyquaterium-10. DATA ANALYSIS Data were presented as mean ± SD, and all statistical analyses were performed using MINITAB 15 software (Minitab Inc., Pennsylvania). RESULTS AND DISCUSSION EFFECT OF TYPE AND CONCENTRATION OF CATIONIC POLYMERS ON ZETA POTENTIAL AND PARTICLE CLUSTER SIZE OF TREATED IRON OXIDES Iron oxide, naturally having a negative surface charge, was coated with cationic polymers in an effort to improve its adhesion to the eyelashes. The type and concentration of the coating polymers were shown to signifi cantly modify the zeta potential and particle clus- ter size of the treated iron oxides by using two-way ANOVA (p 0.05). The zeta potential of iron oxide was relatively affected more by the type of polymer used than its concentration. PQ-6 and GHC especially resulted in a higher positive zeta poten- tial value than PQ-10 treatment. The concentration of coating polymers was in direct proportion to the surface zeta potential in all three types. The type of cationic polymer also showed a stronger effect on the particle cluster size compared to its coating concentration. The data indicated that treatment by any of the three polymers tested resulted in a smaller-sized particle cluster of iron oxide. The rela- tively low difference in particle cluster size by means of GHC concentration strongly suggests that cationic treatment itself has more infl uence than the concentration of the polymers (Table I). RELATIONSHIP BETWEEN SURFACE ZETA POTENTIAL AND PARTICLE CLUSTER SIZE OF TREATED IRON OXIDES The relationship between the surface zeta potential and particle cluster size of treated iron oxides was evaluated by general linear model (GLM) analysis. Figure 2 describes