Self-Assembly Properties of Cationic Gemini Surfactants with Biodegradable Groups in the Spacer

: Self-assembly properties of cationic gemini surfactants with biodegradable amide or ester groups in the spacer were investigated utilising time-resolved fluorescence quenching, dynamic light scattering and zeta potential measurements. A correlation between aggregation parameters such as micelle aggregation number, micelle size and zeta potential with the structure of gemini molecules was made. For gemini molecules with medium spacer lengths, micelle aggregation number does not change much with the surfactant concentration. When the spacer is extended, a stronger aggregation tendency is observed for gemini surfactant molecules with two ester groups in the spacer and the aggregation number increases. The assumption of stronger aggregation of ester-based gemini molecules at larger spacer number values is also documented by measurements of the size and zeta potential of ester-based micelles. The explanation of the difference in aggregation ability of amide-based and ester-based gemini molecules is related to the structural features of gemini molecules, notably to the larger flexibility and denser arrangement of ester-based gemini molecules in a micelle. To support this assumption, optimised 3D models of the studied gemini molecules were constructed. Correspondingly, the calculations show smaller size and interfacial area for ester-based gemini conformers.

Evidence of pre-micellar aggregates in aqueous solution of amphiphilic PDMS–PEO block copolymer

The decrease in the PEO chain hydration favours the increase in the PDMS–PEO micelle aggregation number with the increase in temperature.

Determination of micelle aggregation numbers of alkyltrimethylammonium bromide and sodium dodecyl sulfate surfactants using time-resolved fluorescence quenching

The time-resolved fluorescence quenching method was applied to determine the micelle aggregation number of cationic single-chain surfactants dodecyltrimethylammonium bromide (DTAB), cetyltrimethylammonium bromide (CTAB) and anionic surfactant sodium dodecyl sulfate (SDS). The concentration dependence of micelle aggregation number was found to be linear for all investigated surfactants in the concentration range 2‒15 × the value of critical micelle concentration of the respective surfactant. The values of micelle aggregation number were found in the range 30‒77. Different trends in the linear concentration dependence of micelle aggregation number were observed for cationic surfactants and for the anionic surfactant SDS. A small slope value was found for cationic surfactants, while the SDS micelle aggregation number concentration dependence showed significantly a larger slope value. The aggregation number increase with the increasing SDS concentration results in the micellar growth. Results from a simple analysis based on computer models of cationic and anionic surfactant molecules with dodecyl chains supports, the formation of intramicellar hydrogen bonding between surfactant molecules in SDS micelle shell.

Studies on the Hydrodynamic Diameter and Aggregation Number of Nonionic Switchable Surfactant

An Investigation of the micelle aggregation number (N) and hydrodynamic diameter (Dh) is conducted on nonionic switchable surfactant 11-ferrocenylundecyl polyoxyethylene ether (FPEG), the micelle aggregation number of FPEG solution is determined by steady-state fluorescence probe, the results show that the micelle aggregation number (N) increase linearly with the concentration range from 5 to 12 times CMC of FPEG solutions. The critical micelle aggregation number Nmwhich means that the aggregation number of surfactant at the concentration of CMC is calculated to be 66. The hydrodynamic diameter (Dh) of FPEG micelle is determined by dynamic light scattering (DLS), the measurement angle is fixed at 90°and the wavelength is 532nm, the distribution data analyses by NNLS (non-negatively constrained least square) algorithm, the results reveal that the mean value of Dhat the concentration of 0.5 mmolL-1is 7.8nm. the POLY value, which used to explain the micelle polydispersity in the aqueous solution, is measured and the results show that the POLY values are slightly different, this indicates that the micelle aggregation morphology of FPEG is polydispersity in the aqueous solution.

Study on Aggregation Behaviour of Mixture of Alkylbenzene Sulfonate Gemini Surfactant Ib and Nonionic Surfactant Triton X-100

The interaction between the anionic Gemini surfactant Ib and the conventional nonionic surfactant Triton X-100 was investigated. The critical micelle concentrations (cmc) of different mixtures were measured by surface tension measurement at 298 K. The results showed that the cmc of different mixtures at any mole ratio was lower than that of either pure Ib or Triton X-100, indicating synergetic behavior. And the interaction parameter ß values for the mixed micelles were negative, showing attractive interaction between these surfactant molecules. Besides, the micelle aggregation number (N) was measured using a steady state fluorescence quenching method. The N values of the mixed surfactant system were larger than that of pure Ib but lower than pure Triton X-100 at any ratio.