Structure and "Surfactochromic" Properties of Conjugated Polyelectrolyte (CPE): Surfactant Complexes between a Cationic Polythiophene and SDS in Water

Knaapila, Matti and Evans, Rachel C. and Garamus, V. M. and Almásy, László and Székely, Noémi Kinga (2010) Structure and "Surfactochromic" Properties of Conjugated Polyelectrolyte (CPE): Surfactant Complexes between a Cationic Polythiophene and SDS in Water. LANGMUIR, 26 (19). pp. 15634-15643. ISSN 0743-7463

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Abstract

We report on the phase transitions, solution structure, and consequent effect on the photophysical properties of poly[3-(6-trimethylammoniumhexyl)thiophene] bromide (P3TMAHT) in aqueous sodium dodecylsulfate (SDS). Polythiophene was mixed with SDS or deuterated SDS to form P3TMAHT(SDS)(x) complex (x = the molar ratio of surfactant over monomer units) in D2O and studied by small-angle neutron and X-ray scattering (SANS/SAXS) and optical spectroscopy. At room temperature, P3TMAHT forms charged aggregates with interparticle order. The addition of SDS eliminates the interparticle order and leads to rod-like (x = 1/5) or sheet-like polymer-SDS aggregates (x = 1/2 to 1) containing rod-like (x = 1/5 to 1/2) or sheet-like (x = 1/2 to 1) polymer associations. Partial precipitation occurs at the charge compensation point (x = 1). Ellipsoidal particles without interparticle order, reminiscent of SDS micelles modified by separated polymer chains, occur for x = 2 to 5. Free SDS micelles dominate for x = 20. Structural transitions lead to a concomitant variation in the solution color from red (P3TMAHT) to violet (x = 1/5 to 1) to yellow (x > 2). The photoluminescence fingerprint changes progressively from a broad featureless band (x = 0) through the band narrowing and appearance of vibronic structure (x = 1/5 to 1) to the return to it blue-shifted broad emission band (x = 5). The polymer stiffness reaches a maximum for x = 1, which leads to minimization of the Stokes shift (0.08 eV). This work gives fundamental information upon how surfactant complexation can influence both the solution structure and photophysical properties of a water-soluble polythiophene.

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