Fluorocarbon and Hydrocarbon Short-Chain Nonionic Amphiphiles:  A Comparative Study of Their Behavior in Aqueous Medium

Abstract

The aqueous solution properties and the micellar structure of two short-chain nonionic surfactants containing a hydrocarbon tail, 1,2-hexanediol (HD), and a perfluorinated tail, 3,3,4,4,5,5,6,6,6-nonafluoro-1,2-hexanediol (PFHD), have been compared by using various techniques such as pyrene fluorescence spectroscopy, vapor pressure osmometry, tensiometry, and dye solubilization. The aggregational behavior of both systems in aqueous medium has been evidenced by the polarity decrease of the pyrene microenvironment with increasing surfactant concentration. The binding coefficient of pyrene with the aggregates was calculated by application of the phase-separation model to the pyrene fluorescence results. The aggregation numbers of the HD (N H) and PFHD (N PF) micelles have been evaluated by application of the phase-separation and the mass-action law models to the osmotic coefficients measurements. The N H value (26 ± 8), which is in good accordance with previous experimental results (30 ± 10), is higher than N PF (15 ± 1). Both compounds exhibit surface-active properties with a maximum surface tension lowering of 42 and 57 mN m-1 for HD and its perfluorinated homologous compound, respectively. Their solubilizing power toward Orange OT was compared. Critical micelle concentrations (CMCs) have been determined in the temperature range 20−50 °C (30−50 °C for PFHD insoluble below 30 °C), and thermodynamic parameters such as standard enthalpy and entropy changes for micellization have been calculated.

Perfluorooctanoate in Aqueous Urea Solutions: Micelle Formation, Structure, and Microenvironment

“…The changes in the microenvironment characteristics of APFO micelles with urea addition can be assessed by observing the I1/I3 ratio as a function of urea concentration. There are no uniform criteria for obtaining CMC values from I1/I3 vs. surfactant concentration plots, and different authors follow different methods: The first turning point in the I1/I3 vs. surfactant concentration curve [58]; the inflection point in the ratio of peak intensities of fine structure (I1/I3, I3/I1, or I5/I1) vs. surfactant concentration curve [74,75]; the intersection of straight lines fitted to the first plateau region below CMC and the linear part of the I1/I3 decrease region (near the inflection point) or the linear part of I1/I3 decrease region (near the inflection point) and second linear plateau region above CMC (not observed in the case of our APFO system) in I1/I3 vs. surfactant concentration curve [75]. For the fluorinated surfactants lithium perfluorononanoate (LiPFN) and sodium perfluorononanoate (NaPFN), the CMC has been determined from the concentration corresponding to maximal changes that is obtained from the derivative of d(I1/I3)/d(surfactant concentration) plots [76].…”

Thermodynamic Investigation of the Micellization and the Adsorption of Short Perfluoroalkylated Diols via Fluorescence Spectroscopy and Tensiometry

“…Such a difference in polarity, apparently inconsistent with the increase of the perfluorinated chain, is attributed to an increase in the rigidity of the hydrophobic tail, which enables the penetration of solvent molecules in the aggregates or which makes difficult the incorporation of the probes, as was already evoked in Ref. (13) about the polarity sensed by pyrene in hydrocarbon and fluorinated aggregates. Therefore the system tFOD (with the higher tail length)/DMAPhC becomes more sensitive with the presence of methanol; the sharp increase in CMC with the methanol content is observed at methanol contents smaller than those determined by tensiometry.…”

“…Hence the microenvironment polarity sensed by pyrene is comprised between those of methanol and ethanol in the case of nFHD micelles, and that of tFOD is very close to that of low-methanol-contents aqueous solutions. This can be attributed to the low flexibility of the perfluorinated chain, in comparison with the hydrocarbon ones (13), which favors water penetration in the micellar core and thus leads to a higher polarity sensed by pyrene. It can also be attributed to the inhibition of pyrene penetration induced by the aliphatic tail rigidity and/or caused by the steric hindrance of pyrene.…”

“…Comparing the E T (30) values obtained from pyrene with those obtained from DMAPhC in the case of nFHD systems, we can notice a polarity sensed by DMAPhC lower than that of pyrene. Given that pyrene is mainly partitioned in the aggregates (13) and slightly in the bulk phase and assuming the same for DMAPhC, this difference in polarity is mainly due to a difference in the polarity of the probe in the aggregates. Hence, despite its polar functions, DMAPhC is probably located more inside the hydrophobic core of the micellar aggregate than pyrene.…”

Conformational preferences and antimicrobial activities of alkanediols

“…It were interpreted that amphipathic alkanediols could easily penetrate into phospholipid membrane bilayers and might disrupt the membrane structure [11], as inhibitions of substrate transport by lipophilic acids [46,47]. In particular, the formation of micelle-like structure of 1,2-hexanediol measured in aqueous solution [48][49][50][51][52] may support this interpretation. In particular, the small-angle neutron scattering study of hexanediols in aqueous solution exhibited the stronger aggregation of 1,2-hexanediol than 1,6-hexanediol [52].…”