Journal of Photochemistry and Photobiology A: Chemistry 147 (2002) 45–54 Characterization of non-ionic surfactant aggregates by fluorometric techniques Marian Wolszczak a,∗ , Jacek Miller b a Institute of Applied Radiation Chemistry, Technical University, Wroblewskiego 15, 93-590 Lodz, Poland b Faculty of Process and Environmental Engineering, Wolczanska 213/215, 93-005 Lodz, Poland Received 28 September 2001; accepted 4 October 2001 Abstract Steady-state and nanosecond time-resolved studies have been carried out on the fluorescence quenching of excited pyrene by N,N- dibutylaniline in an aqueous solution of non-ionic micelles of the six Tritons, (oxyethylene) m -p-(1,1,3,3-tetramethylbutyl)phenyl ethers with m ranging from 8 to 70. The aggregation numbers and the rate constants of intramicellar quenching have been determined. The critical micelle concentrations of investigated Tritons were determined using the dependence of the fluorescence spectrum of pyrene on the microenvironment. The local polarity was obtained from the intensity ratio of the first to the third peak (I 1 /I 3 ) in the fluorescence spectrum of pyrene. The microviscosity of the micellar core was estimated to be about 200 cP at ambient temperature on the basis of fluorescence spectra of 1,3-bis(1-pyrene)propane, from the excimer to the monomer emission intensity ratio using the calibration curve determined for a number of solvents of known viscosities. © 2002 Elsevier Science B.V. All rights reserved. Keywords: Fluorescence quenching; Tritons micelles; Pyrene; Aggregation number 1. Introduction Non-ionic surfactants belonging to polyethylene oxide family are widely used in industrial and domestic applica- tions. The structure and dynamical properties of the surfac- tant micelles play an important role in their applications. Triton X-100 is one of the non-ionic surfactants widely used and extensively studied. Techniques such as light scattering, NMR viscometry, small-angle X-ray scattering, ultrasonic absorption, rheological measurements and spectrometry have delivered substantial data on the TX-100 micelle. The results of these investigations show that the non-polar hy- drocarbon chains are packed in the interior micellar core, whereas the hydrophilic polyoxyethylene chains stay out- side the core forming a larger shell with a certain number of water molecules included. However, the details of micel- lar properties such as a degree of packing of hydrophobic chains in micellar core or even the shape of micelle are controversial [1–4]. The literature concerning other Tritons is rather scarce. The aim of this work was to obtain the parameters for characterization of micellar properties of six polyoxyethylene-p-(1,1,3,3-tetramethylbutyl)phenyl ethers distinguished by the length of their polyoxyethylene chains. Steady-state and time-resolved fluorescence techniques ∗ Corresponding author. E-mail address: marianwo@mitr.p.lodz.pl (M. Wolszczak). have been used by us to determine aggregation numbers, N, critical micelle concentration (CMC), microviscosity (microfluidity) and micropolarity of the micellar interior. 2. Experimental 2.1. Reagents The six studied polyoxyethylene-p-(1,1,3,3-tetramethyl- butyl)phenyl ethers of the general formula belong to popular family of non-ionic surfactants known as Tritons ® . The specification of used materials is shown in Table 1. Each Triton is a mixture of homologues, which differ in the hydrophilic chain length, so m is the average value. Experiments were carried out with pyrene (99% Fluka) and 1,3-bis(1-pyrene)propane (P3P) (Molecular Probes, USA) as a fluorescent probes. P3P was used without additional purification. Pyrene was purified by column chro- matography [5]. The quencher N,N-dibutylaniline (DBA) 1010-6030/02/$ – see front matter © 2002 Elsevier Science B.V. All rights reserved. PII:S1010-6030(01)00611-6