Structures And Properties Of Fluorinated Surfactants

Cationic fluorine surfactants occupied a very important position in fluorinesurfactants’ whole productions and applications. At present, the basic rawmaterials of most widely used cationic fluorine surfactants was mainlyelectrolysis fluorination products perfluoroalkylsulfonyl fluorine (C_nF_2n+1COF),and perfluoroalkylacyl fluorine (C_nF_2n+1COF). They could respectively reactwith the N,N-dimethyl propylene amine [NH₂（CH₂）₃N（CH₃）₂] to synthesize twokinds of intermediates, CnF2n+1SO2NH（CH2）3N（CH3）2andC_nF_2n+1SO₂NH（CH₂）N（CH₃）₂. Finally two types of cationic fluorine surfactantamine salts and quaternary ammonium salts was obtained through theacidification or quaternization to introduce hydrophilic groups. Because thestarting material perfluorooctanesulfonyl fluoride costs much less, amine saltsand quaternary ammonium salts derived from C8F7SO2NH（CH2）3N（CH3）2havebecome the most widely used two kinds of cationic fluorine surfactants. Thiskind of cationic fluorine surfactants was so widely applied in industry that themajor reports were patents and publicly published research paper is not much.The research of the relationship between the structures and properties about it iswanted. In this paper cationic fluorine surfactants which wereN-[γ-（dialkylamino）alkyl]perfluorooctanesulfonamides’ derivative products (fourhydrochloride salts [C₈F₁₇SO₂NH（CH₂）_nNHR₂Cl^-] and four quaternaryammonium salts [C₈F₁₇SO₂NH（CH₂）_nN⁺R₂（CH₃）I^-]) were synthesized on thebasis of perfluoroalkylsulfonyl fluorine. These cationic fluorine surfactants’solubility in aqueous solution, surface activity, wetting abilities and foamproperties were studied through the determination of solubility, surface tension,contact angle in the paraffin’s surface, foaming force and foam stability,C₈F₁₇SO₂NH（CH₂）₂N（CH₃）₂HCl and C₈F₁₇SO₂NH（CH₂）₂N（CH₃）₃I’s poorsolubility resulting in bad surface activity, wetting ability in the paraffin’s surface and foaming ability. The results of the research showed that, these cationicfluorine surfactants’ cmc and γ_cmcwere both very low suggested its surfaceactivity were very high, in a certain range changes in the length of linker（hydrocarbon spacer） and the size of hydrophilic group, could significantlyinfluence the solubility of surfactants but insignificantly influence their surfaceactivity, their wetting ability and foaming ability appeared similar laws. Thereason may be due to perfluorineoctyl’s strong hydrophobicity, its ability andefficiency to lower the surface tension depended on the length of the fluorinecarbon chain, which overwhelming upon the influence from the length of linker（hydrocarbon spacer） and the size of hydrophilic group. Therefore, whenchoosing this kind of cationic fluorine surfactants, those which having bettersolubility, more mature synthesis technology and low cost can be preferred inindustrial application without regard to the influences of the terminal groups’subtle changes in the properties.Then anionic fluorine surfactant p-perfluorononenyloxy benzene sulfonate(C₉F₁₇OC₆H₄SO₃Na, OBS) derived from hexafluoropropene trimer was mixedwith different cationic hydrogenated surfactants C_nNR [C_nH_2n+1N（CH₃）₃Br andC_nH_2n+1N（CH₂CH₃）₃Br, n=8,10,12, abbr. C_nNM and C_nNE, respectively]. Itshowed that, after mixed with C_nNR, both the cmc and γ_cmcof OBS were greatlylowered, i.e. the efficiency was totally enhanced. Among those different molarratios between OBS and C₈NE, the molar ratio of1:1showed the best surfaceactivity, i.e. it showed the lowest cmc and γ_cmc. Meanwhile, when the molar ratiowas apart from equimolar, the cmc of OBS-excess systems were smaller thanthat of C₈NE-excess systems, however, with the γ_cmcnot significantly changed.Compared with single surfactant systems, the Γt mfor the mixtures of OBS–C₈NEwas significantly increased while the Aminwas significantly decreased. WhenOBS was mixed with C_nNE with different alkyl chain length, the sequence ofcmc for the mixtures: C₈NE> C₁₀NE> C12NE. It suggested that the increase ofhydrophobic chain length of C_nNE would induce the decrease of cmc. When theheadgroup size of C_nNR （n=8,10） was changed in the mixture, i.e., from–triethylammonium to–trimethylammonium, the surface activity for both werealmost the same. In other words, the change of the headgroup size of C_nNRshowed no significant influence on the surface activity of the mixtures.