- Super water-repellent surfaces resulting from fractal structure
-
Super water-repellent surfaces showing a contact angle of 174° for water droplets have been made of alkylketene dimer (AKD). Water droplets roll around without attachment on the super water-repellent surfaces when tilted slightly. The AKD is a kind of wax and forms spontaneously a fractal structure in its surfaces by solidification from the melt. The fractal surfaces of AKD repel a water droplet completely and show a contact angle larger than 170° without any fluorination treatments. Theoretical prediction of the wettability of the fractal surfaces has been given in the previous paper.3 The relationship between the contact angle of the flat surface θ and that of the fractal surface θf is expressed by the equation cos θf = (L/l)D-2 cos θ where (L/l)D-2 is the surface area magnification factor. The fractal dimension of the solid AKD surface was determined to be D ≈ 2.3 applying the box-counting method to the SEM images of the AKD cross section. L and l, which are the largest and the smallest size limits of the fractal behavior of the surface, are also estimated from the box-counting method. The contact angles of some water/1,4-dioxane mixtures on the fractal and the flat AKD surfaces were determined, and the values of cos θf were plotted against cos θ. The plot of cos θf against cos θ agrees well with the theoretical prediction. It has been demonstrated by this work that the fractal concept is a powerful tool to develop some novel functional materials.
- Shibuichi, Satoshi,Onda, Tomohiro,Satoh, Naoki,Tsujii, Kaoru
-
-
Read Online
- Synthesis of mycolic acid biosurfactants and their physical and surface-active properties
-
Five mycolic acids [2-alkyl-3-hydroxy FA: R 1C*H(OH)C*HR2COOH] were synthesized using acyl chlorides with alkyl chains of different lengths (total carbon numbers of mycolic acids, 12, 16, 20, 24, 36). The relationship between the chemical structures of the mycolic acids and their surface-active properties was determined. The acids were synthesized in three steps: (i) dimerization of acyl chloride into alkyl ketene dimer, (ii) selective reduction of C=C to C-C by hydrogenation, and (iii) βlactone ring cleavage under alkaline conditions. The yields of C12-, C16-, C20-, C 24-, and C36-mycolic acid were 72, 73, 73, 73, and 73%, respectively. The critical micelle concentrations (CMC) of C12-, C16-, and C20-mycolic acid were 2.2 × 10 -4, 1.36 × 10-4, and 7.4 × 10-5 M, respectively. As the carbon number increased, the surface tension at the CMC value was also lower; the values for C12-, C16-, and C20-mycolic acid were 46.54, 43.59, and 41.57 dyn/cm, respectively. The emulsifying activities of mycolic acids were determined for n-tetradecane, n-hexadecane, cyclohexane, and diesel oil. The results showed that C 12-mycolic acid was the best emulsifier for diesel oil, C 16-mycolic acid was the best emulsifier for n-tetradecane and n-hexadecane, and C20-mycolic acid was the best emulsifier for cyclohexane. This study showed that mycolic acids having surface-active properties can be chemically synthesized for potential applications in the detergent/cleaning material industries, for example, in oil spill cleanup, oil recovery, textiles, pharmaceuticals, and cosmetics. Copyright
- Lee, Myungjin,Gwak, Hyung Sub,Park, Byeong Deog,Lee, Sung-Taik
-
p. 181 - 188
(2007/10/03)
-