Interactions and film formation in polyethylenimine-cetyltrimethylammonium bromide aqueous mixtures at low surfactant concentration

H Comas-Rojas, E Aluicio-Sarduy, S Rodriguez-Calvo, A Perez-Gramatges, S J Roser, K J Edler

Research output: Contribution to journalArticle

21 Citations (Scopus)

Abstract

The interactions involved in aqueous mixtures of polyethyleneimine (PEI) and cetyltrimethylammonium bromide ( CTAB) were studied under dilute conditions. The phase diagram of this polyelectrolyte - surfactant system of similar charge was constructed by determining the CAC and CMC* values at different PEI concentrations, using surface-tension and conductivity measurements, respectively. Formation of thin films at the air - solution interface was detected at concentrations belonging to the interaction region of the phase diagram, using Brewster angle microscopy. These films were formed at low polymer and surfactant concentrations, 0.01% w/ v PEI and 0.1 mmol dm(-3) CTAB. Results from SAXS determinations indicate that, under these conditions, mesostructure formation occurs exclusively at the surface. The effect of PEI on surfactant micellisation is determined by the polyelectrolyte nature of the polymer. The presence of the polymer in the aggregate significantly affects free micelle formation, even when hydrophobic interactions are mainly determined by the surfactant structure. The films obtained at low surfactant concentration are mesostructured, composed of five layers, each one 49.7 angstrom thick, as was determined using specular X-ray reflectometry. These results indicate that mesostructured film formation is achievable under more economical and environmentally friendly conditions, suggesting novel routes for surfactant templating in mixed polyelectrolyte systems of similar charge.
Original languageEnglish
Pages (from-to)747-753
Number of pages7
JournalSoft Matter
Volume3
Issue number6
DOIs
Publication statusPublished - 2007

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