## 3 Results and Discussion
### Surface Modification of Nonwoven Supports in Organic Solvents  
The concept of fabricating low surface energy surfaces via surface modification of nonwoven substrates using self-assembly of partially fluorinated urea or amide gelators has been described in our earlier reports [29, 31]. The gelators self-assemble into fiber-like morphologies in solution, which grow sufficiently long and become entangled with one another, forming a gel with their solvent medium. In the presence of a solid or fibrous substrate, the gelation occurs on the surface of the substrate, creating a composite with an altered surface topology. Removal of the solvent from the gel composite leaves behind a network of assembled gelator fibers on the substrate, thus producing a composite surface with high surface area and roughness, which are desirable for superior hydrophobic/oleophobic properties. A few of the partially fluorinated amide and urea-amide gelators that showed good gelation properties were gel-impregnated on nonwoven supports (Tyvek(r) polyethylene nonwoven fabric and Kolon(r) polyester fabric) in a suitable organic solvent. The nonwoven supports were then dried in a vacuum oven at room temperature to produce a composite of xerogel coated on the substrate. These surface-modified composites were then evaluated for hydrophobic and oleophobic properties. The tris-amide gelators (**6a** and **6b**) were impregnated on the Tyvek(r) and Kolon(r) fabrics in acetone and dichloromethane, respectively, leading to the corresponding gel-impregnated composites. Similarly, the partially fluorinated urea-amide gelators (**7a** and **8c**) that showed excellent gelation behavior were gel impregnated on both Tyvek(r) and Kolon(r) fabrics in acetone, leading to the corresponding surface-modified composites. Examination of these composites by SEM showed a nanofibrous network of gelators impregnated on the fabric surface, vastly different from the micro structured surfaces of Tyvek(r) and Kolon(r) fabrics [31]. Figure 4 shows SEMs at 2,000\(\times\) and 10,000\(\times\) magnification of the Kolon(r) fabric surface-treated with gelator **7a** with an average fiber diameter of 142 nm. Figure 4: SEMs of composite prepared by impregnation of gelator **7a** on Kolon® fabric at 2,000\(\times\) (left) and 10,000\(\times\) (right) magnifications. Figure 3: Urea-ester derivatives from \(N\)-Boc-\(\beta\)-alanine and \(N\)-Boc-L-aspartic acid. The composites produced by gel-impregnation of fluorinated organogelators were evaluated for water/oil repellency via dynamic contact angle measurement for water and hexadecane. Table 2 summarizes the results of contact angle measurements for the composites and those for untreated controls (Tyvek(r) and Kolon(r) fabrics). The results indicate that the composite materials produced by the gel impregnation of fluorinated gelators **6a**, **6b**, **7a**, **8a** and **8c** exhibit significantly higher water advancing contact angles than the untreated controls. The higher water contact angles observed for these surfaces suggest increased surface roughness in addition to the incorporation of hydrophobic alkyl or fluoroalkyl functionalities. The inset in Figure 4 shows a water droplet sitting on the Kolon(r) fabric surface treated with gelator **7a**, with an advancing contact angle of 140\({}^{\circ}\). The effect of surface structure created by gel-impregnation is particularly important as clear solutions (no gel with solvents chosen) of urea-amide gelators dip-coated on nonwoven substrates showed relatively inferior performance (water advancing contact angle \(<\)117\({}^{\circ}\)). The treated composites derived from gelators **6a**, **6b** and **7a** (comprising perfluoroalkyl chains) also showed a high advancing contact angle for hexadecane, indicating excellent oil repellency.