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Hyper-branched hydrocarbon surfactants give fluorocarbon-like low surface energies

Abstract : Two series of Aerosol-OT-analogue surfactants (sulfosuccinate-type di-BCnSS and sulfoglutarate-type di-BCnSG) with hyper-branched alkyl double tails (so called "hedgehog" groups, carbon number n = 6, 9, 12, and 18) have been synthesized and shown to demonstrate interfacial properties comparable to those seen for related fluorocarbon (FC) systems. Critical micelle concentration (CMC), surface tension at the CMC (γCMC) and minimum area per molecule (Amin) were obtained from surface tension measurements of aqueous surfactant solutions. The results were examined for relationships between the structure of the hedgehog group and packing density at the interface. To evaluate A and B-values in the Klevens equation for these hedgehog surfactants, Log(CMC) was plotted as a function of the total carbon number in the surfactant double-tail. A linear relationship was observed, producing B-values of 0.20-0.25 for di-BCnSS and di-BCnSG, compared to a value of 0.31 for standard double-straight-tail sulfosuccinate surfactants. The lower B-values of these hedgehog surfactants highlights their lower hydrophobicity compared to double-straight-tail surfactants. To clarify how hydrocarbon density in the surfactant-tail layer (ρlayer) affects γCMC, the ρlayer of each double-tail surfactant was calculated and the relationship between γCMC and ρlayer examined. As expected for the design of low surface energy surfactant layers, ρlayer was identified as an important property for controlling γCMC with higher ρlayer leading to a lower γCMC. Interestingly, surfactants with BC9 and BC12-tails achieved much lower γCMC, even at low ρlayer values of < 0.55 g cm−3. The lowest surface energy surfactant studied here was di-BC6SS which had a γCMC of only 23.8 mN m−1. Such a low γCMC is comparable to those obtained with short FC-tail surfactants (eg. 22.0 mN m−1 for the sulfosuccinate-type FC-surfactant with R=F(CF2)6CH2CH2-).
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Submitted on : Friday, May 16, 2014 - 9:46:34 PM
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Masanobu Sagisaka, Tsuyoshi Narumi, Misaki Niwase, Shioki Narita, Atsushi Ohata, et al.. Hyper-branched hydrocarbon surfactants give fluorocarbon-like low surface energies. Langmuir, American Chemical Society, 2014, 30, pp.6057-6063. ⟨10.1021/la501328s⟩. ⟨hal-00992364⟩



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