All solvents and reagents, unless otherwise indicated, were purchased from commercial sources and used directly as supplied. Tyvek^® polyethylene nonwoven fabric was obtained from E. I. du Pont de Nemours and Company, Wilmington, DE, and Kolon^® gsm70 spun-bonded polyester fabric was obtained from Korea Vilene, Inc. ¹H and ¹⁹F NMR spectra were recorded on a Bruker DRX 400 or 500 spectrometer. Chemical shifts are reported in ppm relative to an internal reference (CDCl₃, CFCl₃ or TMS). All melting points reported are uncorrected. Contact angle (CA) measurements for both water and hexadecane on a surface were performed according to procedures in the manufacturer’s manual using a Ramé-Hart Standard Automated Goniometer Model 200 employing DROP image standard software and equipped with an automated dispensing system with a 250 µL syringe and an illuminated specimen stage assembly. 2H,2H,3H,3H-perfluorononoyl chloride, 2H,2H,3H,3H-perfluoroheptanoyl chloride, 1H,1H,2H,2H-perfluorooctyl isocyanateand 1H,1H,2H,2H-perfluorohexyl isocyanate were synthesized from the corresponding perfluoroalkylethyl iodides [34].

A four-neck reactor fitted with a stirrer, thermocouple, nitrogen purge, addition funnel and jacketed condenser was purged with nitrogen and charged with magnesium turnings (4.86 g, 202.5 mmol) and anhydrous ether (300 mL). To this suspension was slowly added a solution of 1H,1H,2H,2H-perfluorooctyl iodide (94.8 g, 200 mmol) in ether (100 mL) over a 2 h period. After the addition of about 10 mL of iodide, the mixture was heated to 35 °C, and when the reaction was initiated the rest of the iodide was added, keeping the temperature below 35 °C. The mixture was stirred for 2 h at room temperature (RT) and cooled to 5–10 °C. Excess dry ice (~15 g) was added in small portions with constant stirring. After 15 min, the mixture was quenched with H₂SO₄ (25%) and the ether phase was separated. The aqueous phase was extracted with ether (2 × 100 mL). Combined ether phases were washed with NaOH solution (25%, 3 × 75 mL). The combined alkaline phases were heated at 100 °C for 10 min and neutralized using H₂SO₄ (50%) after cooling to ice temperature. The precipitate formed was filtered and washed with water to obtain 2H,2H,3H,3H-perfluorononoic acid as a white crystalline solid (56.5 g, 14.1 mmol, 72%). mp. 61–63 °C.

The 2H,2H,3H,3H-perfluorononoic acid (44.4 g, 113.2 mmol) was heated with PCl₅ (35.4 g, 169.8 mmol) at 110 °C for 3 h and the resulting mixture fractionally distilled to obtain 2H,2H,3H,3H-perfluorononoyl chloride as a colorless liquid (44.5 g, 107.5 mmol, 95%). bp. 129 °C @ 85 mm Hg.

A 3-necked flask fitted with a stirrer, an addition funnel and a condenser with N₂ purge was charged with freshly distilled 2H,2H,3H,3H-perfluorononoyl chloride (16.26 g, 39.6 mmol). Trimethylsilyl azide (TMSN₃, 4.57 g, 39.61 g) was added dropwise via the addition funnel, keeping the temperature about 5–10 °C. The mixture was then stirred at 10 °C for 30 min and heated at 75 °C for 1.5 h. After the reaction was complete (GC analysis), trimethylsilyl chloride was distilled off at atmospheric pressure and then the product was fractionally distilled under vacuum to produce 1H,1H,2H,2H-perfluorooctyl isocyanate as a colorless liquid (11.9 g, 30.6 mmol, 77%) bp.100–103 °C @ 30 mm Hg.

Using a similar procedure as described above, reaction of 1H,1H,2H,2H-perfluorohexyl iodide (74.8 g, 200 mmol) with Mg (4.86 g, 202.5 mmol) and dry-ice (~15 g) produced 2H,2H,3H,3H-perfluoroheptanoic acid as a white crystalline solid (43 g, 145.7 mmol). Reaction of 2H,2H,3H,3H-perfluoroheptanoic acid (30.0 g, 102.7 mmol, mp. 44 °C) with PCl₅, followed by distillation, produced 2H,2H,3H,3H-perfluoroheptanoyl chloride as a colorless liquid (18.0 g, 61.8 mmol, 60%, bp. 27 °C @ 3 mm Hg. The 2H,2H,3H,3H-perfluoroheptanoyl chloride (4.30 g, 10.5 mmol) upon reaction with TMSN₃ (1.45 g, 12.6 mmol), followed by fractional distillation, produced 1H,1H,2H,2H-perfluorohexyl isocyanate as a colorless liquid (2.5 g, 6.42 mmol, 61%). bp.101–103 °C @ 50 mm Hg.

A mixture of dichloromethane (350 mL), N-Boc-β-alanine (8.50 g, 45.0 mmol), 1-[3-(dimethylamino)propyl]-3-ethylcarbodiimide hydrochloride (EDCl) (8.6 g, 45.0 mmol) and 4-(dimethylamino)pyridine (5.49 g, 45.0 mmol) were stirred for 10 min at RT, followed by addition of octylamine (5.71 g, 45.0 mmol). The mixture was stirred for 12 h at RT. The mixture was washed with 5% HCl (2 × 100 mL), saturated NaHCO₃ solution (1 × 100 mL) and brine (1 × 50 mL). The resulting organic layer was dried (MgSO₄) and concentrated to provide N-Boc-β-ala-octylamide (1) as a white crystalline solid (11.6 g, 38.6 mmol, 86%): mp. 67.5–68.4 °C; ¹H NMR (methanol-d4): δ 3.18 (t, J = 7.0 Hz, 2H), 2.90 (t, J = 6.5 Hz, 2H), 2.35 (t, J = 6.5 Hz, 2H), 1.51 (quintet, J = 7.0 Hz, 2H), 1.34 (m, 10H), 0.93 (t, distorted, J = 6.5 Hz, 3H):

A suspension of 1 (10.5 g, 35.0 mmol) in dichloromethane (40 mL) was stirred with trifluoroacetic acid (TFA) (31.9 g, 280.0 mmol) at RT for 3 h. Chloroform (100 mL) was added and the bulk of the solvents and TFA evaporated under vacuum. The resulting trifluoroacetate salt was suspended in dichloromethane (50 mL) and stirred with dropwise addition of saturated NaHCO₃ solution (200 mL) and the solid formed was filtered. The residue was washed several times with cold water and dried under vacuum to provide compound 2 as a white solid (6.5 g, 32.5 mmol, 93%): mp. 142–143.5 °C. ¹H NMR (methanol-d4): δ 3.46 (t, J = 7.2 Hz, 2H), 3.17 (t, J = 7.0 Hz, 2H), 2.58 (m, 2H), 2.40 (t, J = 6.5 Hz, 4H), 1.50 (quintet, J = 7.0 Hz, 2H), 1.34 (m, 10H), 0.93 (t, distorted, 3H): ¹⁹F NMR (methanol d4): δ −82.8 (m, 3F), −115.9 (m, 2F), −123.3 (s, 2F), −124.3 (s, 2F), −125.0 (m, 2F), −127.7 (m, 2F).

Using a similar procedure as described for the synthesis of compound 1, reaction of N-Boc-L-aspartic acid (10.0 g, 43.1 mmol) with n-octylamine (11.1 g, 86.2 mmol) 1-[3-(dimethylamino)propyl]-3-ethylcarbodiimide hydrochloride (EDCl) (16.5 g, 86.2 mmol) and 4-(dimethylamino)pyridine (5.25 g, 43.1 mmol) in dichloromethane (300 mL) provided N-Boc-L-Asp-dioctylamide 3 (18.8 g, 41.3 mmol, 92%). mp. 112–113 °C.

Using a similar procedure as described for the synthesis of compound 2, reaction of 3 (18.6 g, 41.0 mmol) with trifluoroacetic acid (46.7 g, 410 mmol) in dichloromethane (50.0 mL) provided compound 4 (13.4 g, 96%) as a white solid. mp. 120.5–122 °C. ¹H NMR (acetone-d6) δ 7.14 (bs, 2H), 4.35 (dd, J = 8.8, 4.6 Hz, 1H), 3.18 (m, 4H), 2.66 (dd, J = 14.0, 4.0 Hz, 1H), 2.35 (dd, J = 14.0, 8.0 Hz, 1H), 1.90 (bm, 2H), 1.50 (m, 4H), 1.31 (m, 10H), 0.90 (t, J = 6.8 Hz, 3H).

To a mixture of 2 (1.0 g, 5.0 mmol), dichloromethane (20 mL) and triethylamine (0.526 g, 0.52 mmol) under a N₂ purge was added 2H,2H,3H,3H-perfluorononoyl chloride (2.13 g, 5.2 mmol) and the mixture stirred for 5 h at RT. The bulk of the dichloromethane was evaporated and the solid obtained was taken in ethyl acetate (60 mL) and then washed with 2% HCl (2 × 30 mL), water (1 × 30 mL) and brine (1 × 30 mL). The resulting organic layer was dried (MgSO₄) and concentrated to provide 5a as a white solid (2.46 g, 4.29 mmol, 86%): ¹H NMR (methanol-d4): δ 3.46 (t, J = 7.2 Hz, 2H), 3.17 (t, J = 7.0 Hz, 2H), 2.58 (m, 2H), 2.40 (t, J = 6.5 Hz, 4H), 1.50 (quintet, J = 7.0 Hz, 2H), 1.34 (m, 10H), 0.93 (t, distorted, 3H): ¹⁹F NMR (methanol-d4): δ −82.8 (m, 3F), −115.9 (m, 2F), −123.3 (s, 2F), −124.3 (s, 2F), −125.0 (m, 2F), −127.7 (m, 2F).

Using a similar procedure as described for the synthesis of compound 5a, reaction of 2 (1.37 g, 6.85 mmol) with 2H,2H,3H,3H-perfluoroheptanoyl chloride (2.13 g, 6.85 mmol) and triethylamine (0.69 g, 6.85 mmol) provided 5b as a white solid (2.8 g, 5.90 mmol, 86%): mp. 99–102 °C; ¹H NMR (CDCl₃): δ 6.78 (bs, 1H), 5.81 (bs, 1H), 3.56 (q, J = 6.4 Hz, 2H), 3.25 (q, J = 7.2 Hz, 2H), 2.47 (m, 2H), 2.43 (t, J = 5.6 Hz, 4H), 1.51 (quintet, J = 7.0 Hz, 2H), 1.30 (m, 10H), 0.901 (t, J = 7.5 Hz, 3H); ¹⁹F NMR (CDCl₃): δ −81.6 (m, 3F), −115.3 (m, 2F), −125.0 (m, 2F), −126.6 (m, 2F).

Using a similar procedure as described for the synthesis of compound 5a, reaction of 2 (1.37 g, 6.85 mmol) with pentafluorobenzoyl chloride (1.57 g, 6.85 mmol) and triethylamine (0.69 g, 6.85 mmol) provided 5c as a white solid (2.2 g, 5.58 mmol, 82%): mp. 154–155 °C; ¹H NMR (methanol-d4): δ 3.65 (t, J = 6.8 Hz, 2H), 3.19 (t, J = 7.2 Hz, 2H), 2.53 (t, J = 5.6 Hz, 2H), 1.52 (quintet, J = 7.0 Hz, 2H), 1.34 (m, 10H), 0.92 (t, distorted, 3H); ¹⁹F NMR (methanol-d4): δ −144.3 (m, 2F), −155.8 (m, 1F), −164.3 (m, 2F).

Using a similar procedure as described for the synthesis of compound 5a, reaction of 4 (1.775 g, 5.0 mmol) with 2H,2H,3H,3H-perfluorononoyl chloride (0.438 g, 2.7 mmol) provided 6a as a white solid (2.8 g, 77%): mp. 178–180 °C; ¹H NMR (acetone-d6) δ 7.52 (bs, 1H), 7.17 (bs, 1H), 7.06 (bs, 1H), 4.55 (m, 1H), 3.02 (bs, 4H), 2.55-2.40 (m, 6H), 1.27 (m, 4H), 1.16 (bs, 20 H), 0.75 (bs, 6H); ¹⁹F NMR (acetone-d6): δ −82.1 (s, 3F), −115.2 (s, 2F), −122.8 (s, 2F), −123.8 (s, 2F), −124.4 (s, 2F), −127.1 (s, 2F).

Using a similar procedure as described for the synthesis of compound 5a, reaction of 4 (1.77 g, 5.0 mmol) with 2H,2H,3H,3H-perfluoroheptanoyl chloride (1.55 g, 5.0 mmol) provided 6b as a white solid (1.92 g, 61%): mp. 163.5–165.5 °C; ¹H NMR (DMF-d7): δ 8.80 (bs, 1H), 8.0 (bs, 1H), 7.96 (bs, 1H), 4.91 (q, J = 6.0 Hz, 1H), 3.32 (m, 4H), 2.87–2.70 (m, 4H), 1.63 (m, 4H), 1.45 (bs, 20 H), 0.75 (t, distorted, 6H); ¹⁹F NMR (DMF-d7): δ −81.8 (m, 3F), −114.9 (m, 2F), −125.9 (m, 2F), −126.6 (m, 2F).

Using a similar procedure as described for the synthesis of compound 5a, reaction of 4 (1.77 g, 5.0 mmol) with pentafluorobenzoyl chloride (1.15 g, 5.0 mmol) provided 6c as a white solid (1.8 g, 66%): mp. 172–183.5 °C; ¹H NMR (DMF-d7): δ 9.11 (d, J = 8.0 Hz, 1H), 7.88 (m 2H), 4.96 (q, J = 6.8 Hz, 1H), 3.19 (m, 4H), 2.78–2.70 (m, 2H). 1.48 (m, 4H), 1.29 (bs, 20 H), 0.89 (t, distorted, 6H); ¹⁹F NMR (DMF-d7): δ −143.0 (m, 2F), −155.5 (t, J = 21.6 Hz, 1F), −163.9 (m, 2F).

To a mixture of 2 (0.822 g, 4.11 mmol), dichloromethane (20 mL) and triethylamine (0.02 g, 0.2 mmol) under a N₂ purge was added 1H,1H,2H,2H-perfluorooctyl ioscyanate (1.75 g, 4.52 mmol), and the mixture stirred for 5 h at RT. The solid product was filtered and washed with cold hexanes (2 × 5 mL) to provide 7a as a white solid (1.8 g, 3.05 mmol, 74%): mp. 132–136 °C; ¹H NMR (methanol-d4): δ 3.46 (t, J = 7.2 Hz, 2H), 3.39 (t, J = 6.4 Hz, 2H), 2.94 (m, 2H), 2.60 (t, J = 6.0 Hz, 2H), 2.39 (m, 2H), 1.53 (m, 2H), 1.34 (bs, 10H), 0.92 (t, distorted, 3H); ¹⁹F NMR (methanol-d4): δ −82.8 (m, 3F), −115.6 (m, 2F), −123.2 (s, 2F), −124.2 (s, 2F), −125.0 (m, 2F), −127.7 (m, 2F).

Using a similar procedure as described for the synthesis of compound 7a, reaction of 2 (0.629 g, 3.14 mmol) with 1H,1H,2H,2H-perfluorohexyl isocyanate (1.2 g, 4.15 mmol) provided 7b (1.08 g, 67%): ¹H NMR (methanol-d4): δ 3.46 (t, J = 7.2 Hz, 2H), 3.39 (t, J = 6.4 Hz, 2H), 3.19 (m, 2H), 2.61 (t, J = 6.0 Hz, 2H), 2.39 (m, 2H), 1.53 (m, 2H), 1.34 (bs, 10H), 0.92 (t, distorted, 3H); ¹⁹F NMR (methanol-d4): δ −83.0 (m, 3F), −115.8 (m, 2F), −126.1 (m, 2F), −127.6 (m, 2F).

Using a similar procedure as described for the synthesis of compound 7a, reaction of 2 (1.0 g, 5.0 mmol) with pentafluorophenyl isocyanate (1.04 g, 5.0 mmol) provided 7c as a white solid (1.72 g, 84%): mp. 175–176 °C; ¹H NMR (methanol-d4): δ 3.48 (t, J = 6.8 Hz, 2H), 3.20 (t, J = 7.2 Hz, 2H), 2.45 (t, J = 5.6 Hz, 2H), 1.52 (quintet, J = 7.0 Hz, 2H), 1.33 (m, 10H), 0.91 (t, J = 7.5 Hz, 3H); ¹⁹F NMR (methanol-d4): δ −149.4 (m, 2F), −162.8 (t, J = 20.6 Hz, 1F), −167.3 (m, 2F).

Using a similar procedure as described for the synthesis of compound 7a, reaction of 4 (0.912 g, 2.57 mmol) with 1H,1H,2H,2H-perfluorooctyl isocyanate (1.16 g, 3.0 mmol) provided 8a as a white solid (1.1 g, 1.47 mmol, 58%): ¹H NMR (methanol-d4): δ 4.54 (t, J = 6.8 Hz, 1H), 3.46 (t, J = 6.8 Hz, 2H), 3.21 (m, 4H), 2.60 (m, 2H), 2.40 (m, 2H), 1.53 (m, 4H), 1.33 (bs, 20H), 0.922 (t, distorted, 6H); ¹⁹F NMR (methanol-d4): δ −82.8 (m, 3F), −115.6 (s, 2F), −123.2 (s, 2F), −124.2 (s, 2F), −125.0 (s, 2F), −127.6 (m, 2F).

Using a similar procedure as described for the synthesis of compound 7a, reaction of 4 (0.79 g, 2.24 mmol) with 1H,1H,2H,2H-perfluorohexyl isocyanate (1.0 g, 3.26 mmol) provided 8b as a white solid (1.51 g, 71%) ¹H NMR (methanol-d4): δ 4.54 (t, J = 6.8 Hz, 1H), 3.46 (t, J = 6.8 Hz, 2H), 3.22 (m, 4H), 2.61 (m, 2H), 2.41 (m, 2H), 1.51 (m, 4H), 1.33 (bs, 20H), 0.922 (t, distorted, 6H); ¹⁹F NMR (methanol-d4): δ −83.0 (m, 3F), −115.8 (m, 2F), −126.0 (m, 2F), −127.6 (m, 2F).

Using a similar procedure as described for the synthesis of compound 7a, reaction of 4 (1.77 g, 5.0 mmol) with pentafluorophenyl isocyanate (1.04 g, 5.0 mmol) provided 8c as a white solid (2.0 g, 3.45 mmol, 71%): ¹H NMR (DMF-d7, 100 °C): δ 8.74 (m, 1H), 7.57 (bs, 2H), 7.17 (bs, 1H), 4.74 (q, J = 6.8 Hz, 1H), 3.35 (m, 4H), 2.86 (dd, J = 15.2, 6.0 Hz, 1H), 2.78 (dd, J = 15.2, 6.0 Hz, 1H), 1.65 (m, 4H), 1.47 (bs, 20 H), 1.03 (t, distorted, 6H); ¹⁹F NMR (DMF-d7): δ −147.8 (m, 2F), −163.2 (t, J = 22.0 Hz, 1F), −168.3 (m, 2F).

Using a similar procedure as described for the synthesis of 1, reaction of N-Boc-β-alanine (8.5 g, 45.0 mmol) with n-octanol (5.85 g, 45.0 mmol), 1-[3-(dimethylamino)propyl]-3-ethylcarbodiimide hydrochloride (8.62 g, 45.0 mmol) and 4-(dimethylamino)pyridine (5.49 g, 45.0 mmol) in dichloromethane (350 mL) provided n-octyl-N-Boc-β-alanine (12.75 g, 42.3 mmol, 94%). Using a similar procedure as described for the synthesis of 2, n-octyl-N-Boc-β-alanine (12.0 g, 39.87 mmol) was deprotected with trifluoroacetic acid to obtain n-octyl-β-alanine (6.8 g, 33.8 mmol, 85%). Reaction of n-octyl-β-alanine (0.573 g, 2.85 mmol) with 1H,1H,2H,2H-perfluorooctyl isocyanate (1.1 g, 2.85 mmol) provided 9 as a pale yellow oil (1.95 g, 62%): ¹H NMR (CDCl₃): δ 4.06 (t, J = 7.2 Hz, 2H), 3.53 (t, J = 6.4 Hz, 2H), 3.26 (m, 2H), 2.30 (m, 2H), 1.55 (m, 2H), 1.20 (bs, 10H), 0.81 (t, distorted, 3H); ¹⁹F NMR (CDCl₃): δ −81.2 (m, 3F), −114.4 (m, 2F), −122.2 (s, 2F), −123.2 (m, 2F), −124.0 (m, 2F), −126.5 (m, 2F).

Using a similar procedure as described for the synthesis of 1, reaction of N-Boc-L-aspartic acid (10.0 g, 43.1 mmol) with n-octanol (11.2 g, 86.2 mmol) provided N-Boc-dioctylaspartate as an oil (19.0 g, 41.5 mmol, 96%): ¹H NMR (CDCl₃): δ 5.49 (d, J = 8 Hz, 1H), 4. 53 (m, 1H), 4.14 (m, 2H), 4.06 (t, J = 7.2 Hz, 2H), 2.95 (dd, J = 17.2, 4.4 Hz, 1H), 2.78 (dd, J = 17.8, 5.2 Hz, 1H), 1.60 (quintet, J = 7.2 Hz, 4 H), 1.29 (bm, 10H), 1.44 (s, 9H) 0.87 t, J = 7.8 Hz, 6H).

Using a similar procedure as described for the synthesis of 2, N-Boc-dioctylaspartate (19.0 g, 41.5 mmol) was deprotected using trifluoroacetic acid to obtain dioctylaspartate as a viscous oil which solidified in the freezer (12.1 g, 34.0 mmol, 82%).¹H NMR (CDCl₃): δ 4.16 (m, 4H), 3.82 (dd, J = 7.2, 5.3 Hz, 1H), 2.95 (dd, J = 17.6, 4.6 Hz, 1H), 2.71 (dd, J = 17.6, 4.5 Hz, 1H), 1.80 (bs, 2H), 1.62 (m, 4H), 1.31 (m, 10 H), 0.90 (t, J = 6.8 Hz, 6H). Using a similar procedure as described for the synthesis of 7a, reaction of octyldiaspartate (0.629 g, 3.14 mmol) with 1H,1H,2H,2H-perfluorohexyl isocyanate (1.21 g, 4.21 mmol) provided 10 as an oil (1.12 g, 67%): 1H NMR (CDCl3): δ. 5.70 (bs, 1H), 5.39 (bs, 1H), 4.75 (m, 1H), 4.15-3.4.0 (m, 4H), 3.55 (t, J = 6.4 Hz, 2H), 2.97 (dd, J = 16.8, 4.8 Hz, 1H), 2.78 (dd, J = 16.8, 4.8 Hz, 1H), 2.34 (m, 2H), 1.60 (m, 4H), 1.26 (m, 16H), 0.93 (t, J = 6.8 Hz, 6H); 19F NMR (CDCl3): δ. −81.5 (m, 3F), −114.5 (m, 2F), −122.4 (s, 2F), −123.5 (s, 2F), −124.4 (s, 2F), −126.7 (m, 2F).

Typically, 1–4 mg/mL of a gelator in an organic solvent in a closed vial was heated in a reactor block equipped to heat multiple vials. The vials were heated to 5–10 °C below the boiling point of the solvent until a clear solution was obtained, and then were allowed to cool to RT either by switching off the heat or by transferring the vials to a constant temperature water bath kept at 25 °C. The state of the solution was evaluated after 2–12 h. Stability of the gel was tested by inverting the vial, and gel samples for which the whole mass remains a single phase (no phase separation between solid and liquid phase) are considered stable.

Nonwoven fabrics (Tyvek^® polyethylene nonwoven fabric and Kolon^® spun-bonded polyester fabric (about 3.0 cm × 3.0 cm) were immersed in a suspension of amide or urea-amide gelator (1–3 mg/mL) in organic solvent kept in closed reaction flask equipped with a stir bar and temperature controller. The mixtures were heated to 5 °C below the boiling point of the solvent for 1–2 h until clear solutions formed. The flasks were then either rapidly cooled to RT by removing the oil bath or slowly cooled to RT by switching off the heat. Gel formation was usually observed in about 0.5–6 h, and the gels were allowed to age for an additional 6 h. The gelator-impregnated samples were removed and dried in a vacuum oven at RT overnight. The dried samples were weighed and used for contact angle measurements.

Several new partially fluorinated organogelators were designed via careful manipulation of hydrogen bonding functionalities (urea and amide) and hydrophobic functionalities (fluorocarbon and hydrocarbon) in the molecule to promote gelation. Boc-protected amino acids, N-Boc-β-alanine and N-Boc-L-aspartic acid were chosen as the building blocks. First N-Boc-β-alanine and N-Boc-L-aspartic acid were transformed to the corresponding N-Boc-octylamides (1 and 3) by reacting with octylamine (Scheme 1). The resulting amides were deprotected to obtain the corresponding free amide-amine derivatives (2 and 4), the primary building blocks for partially fluorinated amide or urea-amide derivatives.

The majority of these newly synthesized amide and urea-amide derivatives showed gelation properties in organic solvents during their work-up or isolation. A systematic study was then performed to examine the gelation behavior of these partially fluorinated amide or urea-amide derivatives in various organic solvents. A methodology was developed where gelation was attempted with varying amounts of organogelator with a matching a solvent system. A suitable solvent system selection is based on initial solubility experiments. In general, a gelator that is too soluble in an organic solvent will stay dissolved without forming a gel, even at high concentrations. If the gelator is not soluble in an organic solvent, and partially or fully dissolves at high temperature, it may precipitate again as the temperature is lowered. Ideally, the organogelators should dissolve in a solvent at a temperature close to its boiling point and assemble into a network upon cooling, leading to a single gel phase that does not move upon shaking or inverting the vial.

In a typical screening experiment, 0.5–4 mg/mL slurries of the organogelators in various organic solvents were prepared and heated with stirring at a temperature 5 °C below the boiling point of the solvent to induce full dissolution. Gelation occurred upon cooling, as was evident by significant increase in viscosity and/or the formation of a translucent-to-opaque appearance, without the formation of precipitate. The majority of the partially fluorinated amide and urea-amide derivatives showed gelation properties in a variety of organic solvents at remarkably low concentrations, ranging from 0.5 to 4 mg/mL. The partially fluorinated amide derivative 5a showed gelation properties in acetone (2–3 mg/mL) and n-butanol (3–4 mg/mL) leading to partial gels. The corresponding perfluorobutyl derivative (5b) showed gelation in acetone at 3–4 mg/mL and was a clear solution in n-butanol at various concentrations. Both 5a and 5b existed either as clear solutions or slurries in THF, dichloromethane, methanol and toluene at various concentrations (0.5–4 mg/mL), and did not show any signs of gelation. Compound 5c did not gel under any conditions tested, indicating that a long-chain perfluoroalkyl group is probably needed to induce gelation of these bis-amide systems. We then examined the tris-amide systems 6a–c for their gelation abilities at various concentrations in a variety of organic solvents. Compound 6a gelled in acetone (2 mg/mL) and in n-butanol (4 mg/mL) to form opaque gels which were stable for several weeks at room temperature. Similarly, compound 6b formed stable hazy gels in acetone at (3 mg/mL) and in dichloromethane (2 mg/mL). Compound 6c formed gels in acetone at (1–2 mg/mL) and in methanol (2 mg/mL), indicating gelation could be induced on this tris-amide system even though it comprises a pentafluorophenyl group.

Gelation of urea-amide derivatives (7a–c and 8a–c) was then attempted in a variety of organic solvents under varying concentrations. Compound 7a gelled in THF (2 mg/mL) and acetone (2 mg/mL) forming stable gels, and partially gelled in n-butanol (3 mg/mL). Compound 7b gelled in acetone and THF (3 mg/mL), leading to stable gels. The pentafluorophenyl urea-amide derivative 7c remained as slurry or solution in many organic solvents, although partial gel formation was observed in dichloromethane (2 mg/mL). The urea-bis-amide derivatives 8a–c showed excellent gelation properties in a variety of organic solvents. Compound 8a gelled in both acetone and dichloromethane at 2–3 mg/mL concentrations. Compound 8a also showed partial gelation in THF and n-butanol at 2–4 mg/mL concentrations. Compound 8b gelled in dichloromethane (2 mg/mL) and acetone (3 mg/mL), leading to stable gels. Compound 8c showed excellent gelation behavior with a variety of organic solvents (toluene, THF, acetone, dichloromethane, n-butanol and methanol) at concentrations ranging from 0.5–3 mg/mL, and formed stable gels in several instances. Table 1 summarizes some of the best conditions for gel formation, and the minimum concentration of gelator where stable gels were obtained.

In general, we conclude that the partially fluorinated urea-amide derivatives (7a–c and 8a–c) are better gelators than the corresponding amide systems (5a–c and 6a–c), possibly due to the ability of the urea moieties to form directional hydrogen bonds. In order to further understand the influence of amide groups in the gelation ability of these urea-amide systems, we synthesized the corresponding urea-ester derivatives, which in general did not show any gelation properties under the same gelation conditions as the urea-amide systems. For example, urea-ester derivatives 9 and 10 (comparable to urea-amides 7a and 8b) were synthesized via the esterification of N-Boc-β-alanine and N-Boc-L-aspartic acid with n-octanol, followed by deprotection and reaction of the amine with 1H,1H,2H,2H-perfluorooctyl isocyanate (Figure 3). Both 9 and 10 were oils and failed to gel in common organic solvents, indicating amide functionalities are desired in addition to the urea group in the backbone of these partially fluorinated compounds to obtain good gelation properties.

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^® polyethylene nonwoven fabric and Kolon^® 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^® and Kolon^® 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^® and Kolon^® 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^® and Kolon^® fabrics [31]. Figure 4 shows SEMs at 2,000× and 10,000× magnification of the Kolon^® fabric surface-treated with gelator 7a with an average fiber diameter of 142 nm.

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^® and Kolon^® 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^® fabric surface treated with gelator 7a, with an advancing contact angle of 140°. 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°). 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. Surprisingly, the pentafluorophenyl-derived urea-amide derivative 8c, which showed excellent gelation characteristics, also showed excellent water advancing and receding contact angles (superhydrophobic), but extremely poor oil repellency, as hexadecane penetrated into the substrate within a few seconds. This observation is consistent with the need for long-chain perfluoroalkyl groups with terminal CF₃ groups in the gelator molecule in order to provide oil repellency [35]. Surface structure created by the gelator and pentafluorophenyl groups or hydrocarbon alkyl groups in the gelator backbone are not sufficient for imparting oil repellency to the treated composites.