title: Length-controlled rodlike self-assemblies in binary mixed langmuir-blodgett monolayers on mica.
abstract: In this paper, atomic force microscopy (AFM) has been used to investigate the morphology of monolayers of the amphiphilic rod-coil diblock molecule (EO7OPV) containing oligo(phenylene vinylene) dimer (OPV) and poly(ethylene oxide) (PEO) as well as the morphology of mixed monolayers of EO7OPV and palmitic acid (PA) deposited onto mica by the Langmuir-Blodgett technique. At surface pressures higher than 3 mN/m, EO7OPV forms regular-shaped aggregates with a monomolecular layer structure, where the hydrophilic PEO blocks are adsorbed onto the mica substrate and the hydrophobic OPV blocks form an ordered crystalline OPV layer on the top of the PEO layer through the strong pi-pi stacking interaction. In the mixed LB monolayers of EO7OPV and PA, the phase separation occurs. At a certain mixed ratio, EO7OPV molecules form rodlike domains with regular shape and uniform size at surface pressures higher than 3 mN/m. With the increase of the molar fraction of PA, the rodlike domains consisting of EO7OPV are elongated. The length of the rodlike domains can be tuned easily in a large range by altering the molar ratio of EO7OPV and PA. In addition, the rodlike domains are oriented to specific directions, corresponding to the directions of the potassium ion array on the mica surface having 6-fold symmetry. We demonstrate the possible formation mechanism and the elongation origin of rodlike domains in mixed LB monolayers and propose the two-step formation process of oriented rodlike domains deposited onto the mica substrate.
authors.affiliation: Key Laboratory for Supramolecular Structure and Materials of Ministry of Education, Jilin University, Changchun, 130012, PRC.
authors.forename: Hongbo
authors.initials: H
authors.lastname: Li
authors.forename: Qingtao
authors.initials: Q
authors.lastname: Liu
authors.forename: Miao
authors.initials: M
authors.lastname: Xu
authors.forename: Weifeng
authors.initials: W
authors.lastname: Bu
authors.forename: Xiankun
authors.initials: X
authors.lastname: Lin
authors.forename: Lixin
authors.initials: L
authors.lastname: Wu
authors.forename: Jiacong
authors.initials: J
authors.lastname: Shen