Intermicellar interactions and micelle size distribution in aqueous solutions of polyoxyethylene surfactants

Abstract

Mutual diffusion coefficients (D) and self-diffusion coefficients (D') in D,Osolutions of n-dodecylpolyoxyethylene surfactants [C,,H,,(OC,H,),OH, m = 5 and 81 have been measured by dynamic light scattering and pulsedgradient F.t.n.m.r., respectively. On the basis of the ratio DID', micelle size distribution and intermicellar interactions have been discussed. The results have been compared with those for the C12E, system reported previously. Below ca. T,-30 "C (T, is the lower critical solution temperature) size distribution is narrow and intermicellar interactions are weak; this is consistent with the existence of spherical micelles. In the temperature range T, -30-T, -15 "C, the excluded volume effects are dominant and increase in magnitude with increasing temperature. At the same time, the size distribution becomes broad. These results originate from elongation of micelles. Above ca. T,-15 "C, the results can be explained by the decrease in the excluded volume effects and/or rapid increase in attractive interactions with increasing temperature. At still higher temperatures (T, -4 "C-T,), attractive interactions become dominant. Proton n.m.r. linewidths and viscosities have also been measured.

Interactions between surfactants and {1,4-phenylene-[9,9-bis(4-phenoxy-butylsulfonate)]fluorene-2,7-diyl}

“…This has been confirmed by dynamic light scattering [34] and small angle neutron scattering [35]. NMR studies in such systems are expected to show considerable line broadening due to slow tumbling [36].…”

“…From 1 H NMR spectra, self-diffusion and proton relaxation studies, it has been shown that with increasing surfactant concentration C 12 E 5 forms elongated rod-like micelles [33,34]. This has been confirmed by dynamic light scattering [34] and small angle neutron scattering [35].…”

Effects of 1-hexanol on C12E10 micelles: a molecular simulations and light scattering study

“…The data shows that R H of pure C 12 E 10 solutions remain nearly constant upto ∼35 • C, after which R H starts to increase due to the temperature increase. This response is typical of C i E j surfactants, and the measured apparent R H increase has been attributed to the onset of intermicellar attraction 47,[60][61][62] resulting from dehydration of the ethoxylate chains. Samples con- taining hexanol show similar overall behaviour to pure C 12 E 10 solution, but the onset of temperature induced increase in R H shifts to progressively lower temperatures (see Electronic Supplementary Information Figure S1).…”

A Thermodynamic Model for Micellar Growth on the Basis of Light Scattering Intensities from Extremely Dilute Solutions of Nonionic Surfactant

“…[2], [A10], previous studies (10,11) at around the critical composition, it was shown that repulsive interactions (excluded volume effects) are dominant (k 2 ú 0) below about T c 0 4 K. Above this temperature, intermicellar interactions are dominated by attraction (k 2 õ 0). This conclusion is supported by direct measurements of the surface force on the C 12 E 5 system (40) and precise measurements of static and dynamic light scattering at the critical composition on the C 12 E 6 system (38).…”

“…Most of nonionic surfactant aggregation number), N A is Avogadro's number, M 1 is the systems have the lower critical solution temperature (T c ) molecular weight of the surfactant monomer, N w is the and the problem concerning attractive interactions between weight averaged aggregation number of micelles (see Eq. micelles or the critical effects led to debate on micellar [A12]), and c and c 1 are the weight concentrations in g growth with increasing temperature (10,11,(37)(38)(39). In our cm 03 ) of total surfactant molecules and surfactant monomers, respectively.…”