Study Of Sodium Oleate-based CO 2 Stimuli-responsive Surfactant Micelles

The surfactant molecular self-assembly to form different microstructure driven by the noncovalent interactions.Nowaday,CO₂-responsive surfactant micelles are a special stimulating responsive micelle,which can adjust the pH value of mixed systems and achieve the system structure and performance changes.And,NaOA is a convenient surfactant,which is contribute to form different micelles duo to its structure.Thus,we prepare various kinds of CO₂-responsive surfactant micelles based on NaOA to study the property of CO₂-responsive surfactant micelles.Firstly,there was a CO₂-responsive surfactant micelles prepared based on NaOA and PMDPTA,which was to explore the effect of tertiary amine on the CO₂-responsive surfactant micelles transformation.The results showed that with CO₂ bubbling into the solution,the microstructure of the solution was transformed from spherical micelles to worm-like micelles,finally to micelles disappearance.The appearance of the phase behavior was transformed from transparen and water-like to transparent and viscous,finally to water-like and distrurb.Because of PMDPTA ionized to form PMDPTAH+ by CO₂,the electrostatic interaction was changed from electrostatic repulsion to electrostatic action,which could shield the electrostatic repulsion between the head of surfactant and made the distance decrease.Finally,it leaded to micelles transformation to form worm-like.When CO₂ bubbling into the solution to adjust pH<9.00,the OA-was ionized to form HOA,which couldn't work with PMDPTAH+ because of HOA dissolved in the solution.Thus,with OA-decreasing in solution,the electrostatic action was gradually reduced to disappear,which lead to worm-like micelle disappearance.It can be explained that the electrostatic interaction from electrostatic attraction to electrostatic repulsion can affect the micellar transformation of the surfactant.Thus,after CO₂ bubbling,the tertiary amine was transformed into quaternary ammonium salt,which could lead to micelles transformation.Then,we prepared two kinds of CO₂-responsive surfactant micelles Based on N-Butyldiethanolamine-Sodium oleate?BDEA-NaOA?and N,N-Diethyl butylamine-Sodium oleatey?DEBA-NaOA?.With CO₂ bubbling into solutions,the microstructure of BDEA-NaOA mixed solution and the DEBA-NaOA mixed solution both could form worm-like micelles at 8.00<pH<9.00 However,it was found that the worm-like micelles of the BDEA-NaOA mixed solution at room temperature were denser and more closely wound than of the mixed solution of DEBA-NaOA.The mixed BDEA-NaOA formed worm-like micelles was obviously different from DEBA-NaOA,which resulted from the effect of the substituted hydroxyl group in BDEA.Hydroxyl groups were easily utilized to form hydrogen bonding.Based on hydrogen bonding and the electrostatic attraction between the cation and the cation,the worm-like micelles was more denser and closer.And the appearance of the solution was more viscosity.It can be shown that because of the different groups of tertiary amines,it could result in different micelle formed.Finally,we prepared three kinds of CO₂-responsive surfactant micelles based on DMAPA-NaOA DEAPA-NaOA and DBAPA-NaOA.By comparing the properties of DMAPA-NaOA mixed solution and DEAPA-NaOA mixed solution and DBAPA-NaOA mixture,it was to explore the effect of electrostatic interaction on the CO₂-responsive surfactant micelles.The result showed that with CO₂ bubbling to the solution,the micelles of DBAPA-NaOA was directly transformed from spherical micelles to vesicles.And,with the CO₂ bubbling into the DMAPA-NaOA solution,the microstructure was transformed to worm-like micelles at 9.90>pH>9.50,and it formed coexsted with worm-like micelles and vesicles at 9.50>pH>9.50.Finally,microstructure of solution was completely transformed into vesicles at 9.10>pH>9.00.While the DEAPA-NaOA mixed solution formed worm-like micelles at 10.2>pH>9.6,and it formed two-phase system at 9.60>pH>9.10.And when at 9.10>pH>9.00,the microstructure is completely transformed into vesicles.The comparison of these two mixed solutions shows that DEAPA-NaOA is more likely to form micelles than DMAPA-NaOA in the formation of micelles.This is due to the carbon chain increasing,the hydrophobicity of the tertiary amine is also increasing,when the CO₂ into the mixed solution,the tertiary amine is protonated to form a quaternary ammonium salt.it accelerated the transformation of micelles based on electrostatic interaction and hydrophobic interaction.Therefore,for the CO₂-responsive surfactant micelles,with the increase of alkyl chains of tertiary amines,it could accelerate the micellar transformation in solution.