Cellulose acetate-poly{[9,9-bis(6′-N,N,N-trimethylammonium)hexyl]fluorene-phenylene} bromide blends: Preparation, characterization and transport properties

Abstract

The preparation of cellulose acetate-poly-(9,9-bis(6′-N,N,N-trimethylammonium)-hexyl-fluorene phenylene) bromide (HTMA-PFP) blend films by solvent casting from a dispersion is reported. Films were characterized by UV–visible spectroscopy, SEM, electrical conductivity, TGA and DSC. It was found that morphological and physical chemical properties of blends were dependent both on the solvent and the degree of polymerization of cellulose acetate. The fluorescence properties of different blends were evaluated by fluorescence microscopy and it was shown that they are dependent on the structural properties of the blend as well as the aggregation level of the polyfluorene. Release kinetics of HTMA-PFP, incorporated into blend films, in SDS aqueous solutions have been studied and are discussed on the basis of the Korsmeyer–Peppas equation.

Introduction

Ionic conjugated polyelectrolytes (CPs) are important materials as a consequence of their impact in the development of areas related to chemical [1], [2] and biological [3], [4] sensors, charge injection and transport layers [5]. They also demonstrate potential in areas including photovoltaic systems and light emitting diodes (LEDs) [5], [6], [7]. These ionic conjugated polymers are also relevant for applications in self-assembly [8] and for film preparation using solvent based methodologies, such as inkjet and screen printing [9]. Fluorene-based polymers show particular potential for these applications because of their blue emission and high luminescence yields [10], and, in addition, they have rigid rod structures which provide the possibility of forming nematic liquid crystalline phases [11]. However, conjugated polyelectrolytes containing the fluorene moiety tend to aggregate in aqueous solutions, leading to inter-chain interactions which greatly reduce luminescence yields [12]. Further, the solubility of polyfluorene based systems in water is poor. An interesting approach which has been used to increase solubility in water and, consequently, to find out the fluorescent and conductance properties of CPs is through the addition of ionic or non-ionic surfactants [13], [14], [15].

An alternative approach is the use of CPs as polymer blend films. The use of conjugated polymers in solid matrices based on cellulose has been reported for optoelectronic and sensing purposes [16], [17]. In the present work, we report the preparation and characterization of films of cellulose acetate and poly-(9,9-bis(6′-N,N,N-trimethylammonium)-hexyl-fluorene phenylene) bromide (HTMA-PFP) blends. Cellulose acetate is a well-known polymer derived from cellulose, with neutral properties and high capacity for transparent film formation. Applications include optical devices [18], [19] and membrane separation [20], [21], [22]. Cellulose acetate produces porous structures [23] and its properties are dependent on the acetylation degree. This affects a number of key structural properties, such as the polymer crystallinity, and solubility in various solvents [24], [25].

In this paper, the immobilization of a cationic poly(fluorene-phenylene), poly{[9,9-bis(6′-N,N,N-trimethylammonium) hexyl]fluorene-phenylene} bromide (HTMA-PFP), into a cellulose acetate film has been carried out. The effect of the acetylation degree, molecular weight and solvent on the morphological, thermal, optical and conductivity properties of the blends is discussed. The desorption kinetics of the HTMA-PFP, from the blend film in the presence of sodium dodecyl sulfate are also evaluated and discussed.