Abstract:

The effects of temperature ranging from 0 to 40 ℃ on the physicochemical properties, including surface activity, spreading behavior, and foaming performance, of three betaine-type short-chain fluorocarbon surfactants with different hydrophilic groups, namely C₄F₉SO₂NH（CH₂） ₃N⁺（CH₃） ₂CH₂COO^-（C4-Ac）, C₄F₉SO₂NH（CH₂） ₃N⁺（CH₃） ₂CH₂CH₂SO₃^-（C4-sa） and C₄F₉SO₂NH（CH₂） ₃N⁺（CH₃） ₂CH₂CH₂PO（OH）O^-（C4-pa）, were investigated. The results indicated that, the critical micelle concentration （cmc） of fluorocarbon surfactants slightly increased with temperature, while the minimum surface tension （γ_cmc） decreased. Among the three, the C4-sa solution showed the best surface activity with the cmc of 2.21 mmol/L and γ_cmc of 16.28 mN/m. The spreading coefficients of the surfactants first increased with temperature, and then began to level off at 20 ℃. Notably, the C4-sa exhibited the highest spreading ability, which was consistent with the trend of surface tension. The foam expansion ratio increased with temperature, but the growth became insignificant after reaching 20 ℃. The foam properties of the three surfactants were all poor at low temperature but were significantly improved when the temperature was slightly increased. At the same temperature, the foam expansion ratio of C4-sa was the highest among the three, which could reach 6.9 at 20 ℃. In conclusion, temperature did have a certain influence on the physicochemical properties of betaine-type short-chain fluorocarbon surfactants, especially at low temperature. If applied in actual low temperature environment, formulation would be needed to improve the performance. This work could provide a theoretical basis for application of this series of surfactants at different ambient temperatures.

Key words: fluorocarbon surfactant, surface tension, temperature, foaming ability, spreading ability