title: Interfacial rheology of polymer/carbon nanotube films co-assembled at the oil/water interface.
abstract: At appropriate conditions, water-dispersed acid-functionalized single-walled carbon nanotubes (SWCNTs) co-assemble at the oil/water interface with toluene-dissolved amine-terminated polystyrene (PS-NH2) to form composite thin films displaying pronounced interfacial viscoelasticity. To probe this viscoelasticity, the films were examined under dilatational deformations of pendant drop tensiometry/rheometry, with storage and loss moduli recorded against frequency ω (0.003 < ω < 3 Hz) and time-dependent relaxation modulus recorded against time t (0.2 < t < 2000 s). Without the SWCNTs, PS-NH2-decorated interfaces have little dilatational stiffness, i.e., low storage modulus, but their stiffness grows as SWCNTs are added, reaching 50-100 mN m-1at large ω. Two characteristic relaxation processes are identified in the composite films: a fast process (ω ∼ 0.1-0.2 Hz) attributable to local structural relaxation of confined PS-NH2and a slow process (t ∼ 300-2000 s) attributable to component adsorption/desorption (or attachment/detachment). Among the variables that affect positions and strengths of these relaxations are SWCNT and PS-NH2bulk concentrations as well as water phase pH. In frequency or timescale ranges intermediate between the two relaxations, the co-assembled films display "soft-glass" behavior, with the storage and loss moduli characterized by nearly equal power-law exponents. The relaxation modulus, better able to probe terminal behavior, eventually decays to zero, revealing that the films are fundamentally fluid-like due to the slow relaxation, and in support of this conclusion, large strain compression-induced film wrinkles disappear at large t.
authors.affiliation: Polymer Science and Engineering Department, University of Massachusetts Amherst, Amherst, 01003, USA. hoagland@mail.pse.umass.edu russell@mail.pse.umass.edu.
authors.forename: Tao
authors.initials: T
authors.lastname: Feng
authors.affiliation: Polymer Science and Engineering Department, University of Massachusetts Amherst, Amherst, 01003, USA. hoagland@mail.pse.umass.edu russell@mail.pse.umass.edu.
authors.forename: David A
authors.initials: DA
authors.lastname: Hoagland
authors.affiliation: Polymer Science and Engineering Department, University of Massachusetts Amherst, Amherst, 01003, USA. hoagland@mail.pse.umass.edu russell@mail.pse.umass.edu and Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA and WPI-Advanced Institute for Materials Research (WPI-AIMR), Tohoku University, 2-1-1 Katahira, Aoba, Sendai 980-8577, Japan.
authors.forename: Thomas P
authors.initials: TP
authors.lastname: Russell