Fluorosurfactants at Structural Extremes:  Adsorption and Aggregation

Abstract

Fluorosurfactants with several structural modifications have been synthesized, and the air/water interface and bulk aggregation properties investigated. The compounds were fluorinated ethylene oxide (EO) nonionics where the number and position of the hydrophilic group(s) has been radically altered to generate linear, bolaform, and Y-shaped analogues. A noticeable structure-interfacial packing relationship was observed via both tensiometric measurements and neutron reflection studies: the limiting molecular areas, a(cmc), and surface excesses, gamma(cmc), are strongly dependent on the number and position of the EO headgroups. Differing bulk aqueous properties were also observed. Small-angle neutron scattering shows an evolution of micelle structure from cylindrical to disk-like aggregates on changing from Y-shaped to bolaform molecular structure.

Effect of double quaternary ammonium groups on micelle formation of partially fluorinated surfactant

“…However, it is difficult to estimate the effect of the hydrophilic group on surface tension because of both electric charge and volume effects in the present ionic surfactant. For a nonionic fluorinated surfactant, the length of the polyoxyethylene hydrophilic group seems to influence the surface tension to some extent [19,20].…”

Small-angle X-ray scattering (SAXS) study on nonionic fluorinated micelles in aqueous system

“…Recently, Eastoe et al [37] have shown the formation of cylindrical or planar nonionic fluorinated micelles depending on the number and position of hydrophilic head group per surfactant molecule by small-angle neutron scattering (SANS) study. As for example, the Y-shape fluorinated surfactant (CF 3 (CF 2 ) 5 (CH 2 ) 2 N[(CH 2 CH 2 O) 3 H] 2 ), where both head groups are at the same end of the hydrophobic group presents cylindrical micelles with average length of ∼12 nm.…”

A new oligo(hexafluoropropylene oxide)-b-oligo(ethylene oxide) diblock surfactant obtained by radical reactions

“…Using similar conditions to those of section 2.1.1, for the radical addition of C 6 F 13 I onto an allyl-O-PEG-OCH 3 , a striking difference was noted between the three initiators ( Table 1). 43 This can be easily identified by mass spectrometry with m/z fragments at 126, 252, and 522 m/z assigned to PhCF 2 +, I-Ph-CF 2 +, and the molecular weight of C 6 F 13 PhI fragments, respectively (Fig. However, TBPPI enabled the reaction to achieve the highest yield of C 6 F 13 -CH 2 CHICH 2 -O-PEG-OCH 3 .…”

“…19 In addition, PFCs bioaccumulate in the food chains and have long half-lives in human blood: 16 3.6, 5.4, 20-22 and 8.5 years for PFOA, PFOS and perfluorohexane sulfonate, respectively. [37][38][39] Various strategies to synthesize potentially non-bio accumulable alternatives to PFOA have been reported: 40 (1) chemicals bearing either a CF 3 O or (CF 3 ) 2 N end-group, 41 (2) compounds produced from small perfluorinated chains with non-ionic oligoethylene oxide or carbohydrate, 36,42 (3) carboxylate gemini surfactants, 43,44 (4) vinylidene fluoride (VDF) telomers with short 1-iodoperfluoroalkane where methylene groups may act as "weak" degradable points, 45,46 (5) 3,3,3-trifluoropropene (TFP) telomers from either 1-iodoperfluoroalkanes or other chain transfer agents, 47 (6) VDF and TFP cotelomers, 48 and (7) compounds derived from oligo(hexafluoropropylene oxide), oligo(HFPO). 24 PFOS itself is quite stable in the environment, with no known natural mechanism of degradation.…”