Effect of Counterions and Headgroup Hydrophobicity on Properties of Micelles Formed by Alkylpyridinium Surfactants. 2. Microcalorimetry

Abstract

Citation for published version (APA): Bijma, K., Blandamer, M. J., & Engberts, J. B. F. N. (1998). Effect of counterions and headgroup hydrophobicity on properties of micelles formed by alkylpyridinium surfactants. 2. Microcalorimetry. Langmuir, 14(1), 79 -83. DOI: 10.1021/la970216n Copyright Other than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. We report the influence of counterions and headgroup hydrophobicity on the enthalpies and heat capacities of micelle formation by 1-alkyl-4-n-dodecylpyridinium surfactants in aqueous solution. For micelle-forming 1-alkyl-4-n-dodecylpyridinium iodide surfactants (alkyl ) C1-C3), enthalpies of micelle formation show no trend with respect to 1-alkyl chain length. Changes in molecular architecture of the counterion, however, have a large influence on the thermodynamics of micelle formation. It is shown that next to solvation, London dispersion interactions, counterion (substituent)-water interactions, and the microenvironment of counterions adsorbed to micellar surfaces play an important role in determining the exothermicities of micelle formation. Isobaric heat capacities of micelle formation show that the formation of wormlike micelles for salicylate-containing cationic surfactants is due to a favorable microenvironment for salicylate counterions in the Stern layer of micelles.

A Titration Microcalorimetric Study of the Effects of Halide Counterions on Vesicle-Forming Aggregation in Aqueous Solution of Branched-Chain Alkylpyridinium Surfactants

“…The sample cell was stirred (350 rpm) to ensure complete mixing. It had been shown previously (13) that the stirring speed has no effect on the recorded enthalpograms for the deaggregation of micelles. We confirmed this observation by repeating a number of experiments using a stirring speed of 800 rpm.…”

“…The effect of counterions is not completely clear. While Johnson and Olofsson (12) found a trend for aromatic counterions between the position of the counterions with respect to the headgroup area and the heat capacities, no such trend was observed by Bijma et al (13). The large negative isobaric heat capacities for vesicle formation are a consequence of the fact that the aggregates are formed through overlap of the thermally labile hydrophobic hydration shells (2).…”

Rheology of Wormlike Micelles: Equilibrium Properties and Shear Banding Transitions

“…Contrary to simple salts (class A), a large proportion of these counterions (∼80%) is assumed to be incorporated into the micelles. It was found that in CPCl-NaSal, long wormlike micelles are immediately formed at the cmc (0.04 wt.%), without passing through an intermediate spherical morphology [68,69,71].…”

Effect of Counterion Structure on Micellar Growth of Alkylpyridinium Surfactants in Aqueous Solution

“…The difference in enthalpy of dilution below and above the CMC was taken as the enthalpy of micelle formation (21).…”