Materials and Reagents. Alumina NPs (Aeroxide-Alu), perfluorotetradecanoic
acid, 9H-hexadecafluorononanoic acid, stearic acid,
2-propanol, and ethanol were purchased from Sigma-Aldrich and used
as received. Isostearyl acids were obtained from Nissan Chemical
Industries and used without further purification. Distilled water
(Millipore, 15 MΩ cm) was used throughout the experimental process
Synthesis of Carboxylate Functionalized Nanoparticles. In a
modification to the reported procedures in the literature,25,31 the alumina
NPs were refluxed overnight in toluene (100 mL) with the appropriate
carboxylic acid: isostearyl acids, fluorinated carboxylic acids, and stearic
acid. The functionalized particles were then centrifuged for 30 min and
then re-dispersed in 2-propanol (2 × 30 mL) and ethanol (1 × 30 mL)
and then centrifuged again in order to remove unreacted carboxylic acid.
Finally particles were oven-dried at 80 °C overnight