Amphiphilic block copolymers composed of a poly(3-hexylthiophene) (P3HT) segment and a sulfonated polystyrene (PS-stat-PSS) sequence with well-defined and easily tunable structure were synthesized through Grignard metathesis polymerization (GRIM), RAFT polymerization and sulfonation of PS. Because of the hydrophilic nature and ionic conductivity of the PSS segment, such copolymer shows good solubility in water and high conductivity∼1 S/m in form of dryfilm. Conductivity can be further enhanced with the addition of single-walled nanotubes (SWNTs). The present amphiphilic block copolymer enables efficient unbundling and stabilization of SWNTs in water. With the help of an original microfluidic technique referred to asmicrofluidic pervaporation, we investigated the concentration process of SWNT/copolymer suspensions up to dry films and obtained a complete phase diagram which reveals the aggregation of SWNTs during the concentration process in agiven concentration range. High conductivity of about 370 S/m is achieved for SWNT/copolymer nanocomposites at high concentration of SWNTs. The microfluidic pervaporation method is also shown to provide a direct determination of the CNT percolation threshold.