Surface chemical functionalization of cylindrical nanopores derived from a polystyrene-poly(methylmethacrylate)
1Department of Chemistry, Kansas State University, Manhattan, Kansas 66506, USA.
Abstract:
This paper demonstrated covalent functionalization of surface -COOH groups on cylindrical nanopores derived from a polystyrene-poly(methylmethacrylate) diblock copolymer (PS- b-PMMA) via amidation mediated by 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC). The surface functionalization led to conversion of the surface charge of the nanopores and also to the shrinkage of effective pore radius, as verified using cyclic voltammetry for PS- b-PMMA-derived nanoporous films immobilized on gold substrates. For native PS- b-PMMA-derived nanoporous films, the redox current of anionic Fe(CN) 6 (3-) decreased with increasing solution pH due to the deprotonation of the surface -COOH groups, whereas those of cationic Ru(NH 3) 6 3+ and uncharged 1,1'-ferrocenedimethanol (Fc(CH 2OH) 2) were similar regardless of pH. In contrast, upon EDC-mediated amidation of the nanopore surface with ethylenediamine, the redox current of Ru(NH 3) 6 3+ decreased with decreasing pH and those of Fe(CN) 6 (3-) and Fc(CH 2OH) 2 were independent of pH. The decrease in redox current of Ru(NH 3) 6 3+ at acidic pH was consistent with the presence of -NH 2 groups on the nanopore surface as a result of the covalent immobilization of ethylenediamine. Furthermore, the redox current of Fc(CH 2OH) 2 decreased upon amidation of the nanopores with tetraethyleneglycol monoamine ((PEO) 4NH 2), reflecting the shrinkage of the effective pore radius. The control of the surface charge and effective radius of the nanopores via EDC-mediated amidation will provide a simple means for controlling the selectivity of molecular mass transport through PS- b-PMMA-derived nanopores.
