Polyelectrolyte Templated Polymerization in Langmuir Films: Nanoscopic Control of Polymer Chain Organization

Abstract

Polyelectrolytes introduced in the aqueous subphase are shown to have a profound impact on the kinetics of polymerization of N-octadecylaniline at the air/water interface. This can be attributed to changes effected in molecular organization and reorientation behavior in the Langmuir film. The polyelectrolyte templates lead to considerable modification of the morphology of the monomer and polymer Langmuir films. Polyelectrolyte complexation is found to be an elegant and efficient methodology to achieve enhanced alignment of the polyaniline chains in the transferred Langmuir-Blodgett (Langmuir-Schafer) film.

Poly(N‐octadecylaniline) Synthesized at the Air‐Water Interface: Aligned Nanofibers and Gold Nanocomposite Assembly via the Langmuir‐Blodgett Technique

“…Further experiments therefore addressed NOA polymerization in Langmuir films formed in an LB trough. NOA does not form a stable monolayer on pure water as shown by negligible surface pressure increase upon compression; however, sulfuric acid in the subphase lends some stability as revealed by the π‐A isotherm (Figure ). This may be attributed to the protonation of the amine group and stabilization of the cationic amphiphiles by electrostatic interaction with the sulfate ions.…”

“…Growth and alignment of the polymer chains and nanofibers clearly follow the direction of the applied mechanical force, demonstrating that the LB methodology and polymerization at the air‐solution interface provides a simple route to oriented polymer chain organization; this observation may be contrasted with the randomly oriented and thicker microfibers obtained in the films obtained in the petri‐dish experiment, shown in Figure . We had shown earlier the utility of polyelectrolyte templating to achieve polymer organization; however, we find now that a reduced temperature and oxidizer:monomer ratio, and higher surface pressure at which the polymerization and film transfer are carried out, can achieve similar or even better chain organization.…”

“…Electrochemical polymerization of aniline has been carried out in a Langmuir trough in presence of exfoliated graphene oxide, to yield polyaniline with preferential orientation . We have explored earlier, the polymerization of N‐octadecylaniline (NOA) in Langmuir films to form poly(N‐octadecylaniline) (PNOA), focusing on the impact of polyelectrolyte templating . PNOA has been synthesized by alkylation of PANI, and LB films of pre‐formed PNOA have been reported .…”

Mechanical Control of Molecular Aggregation and Fluorescence Switching/Enhancement in an Ultrathin Film

“…5−8 Such a technique can also be exploited to grow oriented nanostructures of conjugated polymers at the air−water interface. 9 The LB technique is a unique approach for the assembly of molecules into ultrathin films. Organization of molecules in LB films can be tailored through various protocols, including mixing the desired molecules with amphiphiles like fatty acids and lipids 10,11 and the formation of multilayer structures.…”

“…Selective formation of the polar form of a molecular crystal could be induced by growing it on noncentrosymmetric inorganic crystals . Aggregation of the chromophore head groups in Langmuir–Blodgett (LB) films can be effectively suppressed through the complexation with polyelectrolytes introduced from the subphase, leading to enhanced optical and nonlinear optical responses. − Such a technique can also be exploited to grow oriented nanostructures of conjugated polymers at the air–water interface …”