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Durham University

Department of Engineering

Staff Profile

Publication details for Professor Michael Petty

Knaapila, M, Almasy, L, Garamus, VM, Pearson, C, Pradhan, S, Petty, MC, Scherf, U, Burrows, HD & Monkman, AP (2006). Solubilization of polyelectrolytic hairy-rod polyfluorene in aqueous solutions of nonionic surfactant. Journal Of Physical Chemistry B 110(21): 10248-10257.

Author(s) from Durham

Abstract

We report on the solubilization, phase behavior, and self-organized colloidal structure of a ternary water-polyfluorene-surfactant (amphiphile) system comprised of polyelectrolytic poly {1,4-phenylene[9,9-bis(4-phenoxybutylsulfonate)] fluorene-2,7-diyl} (PBS-PFP) in nonionic pentaethylene glycol monododecyl ether (C12E5) at 20 degrees C. We show in particular how a high amount ( milligrams per milliliter) of polyfluorene can be solubilized by aqueous C12E5 via aggregate formation. The PBS-PFP and C12E5 concentrations of 0.31 x 10(-4)- 5 x 10(-4) M and 2.5 x 10(-4)- 75 x 10(-4) M, respectively, were used. Under the studied conditions, the photoluminescence (PL), surface tension, static contact angle, and (pi-A) isotherm measurements imply that D2O-PBS-PFP(C12E5)(x) realizes three phase regimes with an increasing molar ratio of surfactant over monomer unit (x). First, for x <= 0.5, the mixture is cloudy. In this regime polymer is only partially dissolved. Second, for 1 <= x <= 2, the solution is homogeneous. In this regime polymer is dissolved down to the colloidal level. Small-angle neutron scattering (SANS) patterns indicate rigid elongated (polymer-surfactant) aggregates with a diameter of 30 angstrom and mean length of similar to 900 angstrom. The ratio between contour length and persistence length is less than 3. Third, for x >= 4, the solution is homogeneous and there is cooperative binding between polymer and surfactant. Surface tension, contact angle, and surface pressure remain essentially constant with increasing x. A PL spectrum characteristic of single separated polyfluorene molecules is observed. SANS curves show an interference maximum at q similar to 0.015 angstrom(-1), indicating an ordered phase. This ordering is suggested to be due to the electrostatic repulsion between polymer molecules adsorbed on or incorporated into the C12E5 aggregates ( micelles). On dilution the distance between micelles increases via 3-dimensional packing. In this regime the polymer is potentially dissolved down to the molecular level. We show further that the aggregates (x = 2) form a floating layer at the air-water interface and can be transferred onto hydrophilic substrates.