PVA membranes with a surface layer of magnetically-patterned cobalt-containing multiwall carbon nanotubes

Composite membranes 15 to 40 µm thick are prepared by mixing aqueous solutions of polyvinyl alcohol (PVA) with dimethyl sulfoxide solutions of multiwall carbon nanotubes (MWNT) at various concentrations. MWNT are synthesized with a microwave-assisted technique from graphite and cobalt acetate powders and exhibit residual Co nanoparticles of less than 100 nm inside MWNTs and at MWNT tip terminations (MWNT-Co). Due to attached Co nanoparticles, MWNT-Co can be pulled by an external magnetic field gradient which induces segregation and clustering in the composite with PVA producing self-organized stripe (or laning) MWNT-Co density pattern along the direction of an applied magnetic field as low as 2.5 mT. These patterns occur within concentrations in the 0.15 to 0.30 wt% range of MWNT-Co in the PVA matrix. Membranes with preserved magnetically-induced MWNT-Co patterns are obtained by curing the solutions under an applied magnetic field. For all assayed concentrations and due to magnetophoretic diffusive segregation effects, the MWNT-Co emerge in the composite membranes as an upper surface layer of MWNT-Co covered only by a thin skin of PVA. This particular arrangement of MWNT-Co makes these membranes good candidates as active elements in devices with applications in many fields. We study structural, optical, and electrical properties of both disordered and magnetically-patterned MWNT-Co/PVA membranes.