The Controllability Of Mixed Cationic/anionic Surfactant Vesicle Systems And Their Applications In The Preparation Of Nanomaterials

The aqueous mixed SDS/DTAB/alkali metal chloride vesicle systems with SDS in excess have been investigated. The vesicles and hollow polymethyl methacrylate (PMMA) microspheres prepared by the vesicle templates have been characterized by the DLS, TEM, SEM and AFM measurements. The controllability for the particle size, degree of dispersion, and micromorphology has been investigated. The main contents of this study include the following three sections:First, the effect of salt type, salt concentration and the surfactant concentration on the phase region of vesicles has been investigated. The experimental results indicated that:1. At 303.15 K, the phase region of vesicles becomes wider with the increase of the radius of the alkali metal cations. The reason is that the increase of the radius of the alkali metal cations leads to higher degree of counterion binding, thus weakens the electrostatic attraction between the oppositely charged headgroups and the electrostatic repulsion between the headgroups with the same charges, it is beneficial for the formation of vesicles in a wider region. At 343.15K, the vesicle phase region becomes narrower. It is related to the breakdown of vesicles due to some factors such as the faster thermal motions at higher temperature.2. The effect of salt concentration and surfactant concentration on the aqueous mixed SDS/DTAB/NaCl vesicle systems:(a) When the salt concentration increased from 22 mmol·L-1 to 60 mmol·L-1, the vesicle phase region becomes wider and shifts to the region with higher SDS content at 303.15 K; 44 mmol·L-1 NaCl aqueous solution is more beneficial for the formation of vesicles at 343.15 K, it is related to the best salt concentration for the formation of vesicles, (b) The change of vesicle phase region is unobvious with the increase of the total surfactant concentration within certain concentration range. But at very low concentration, the vesicle phase region shifts obviously to the region with higher SDS content. Because micelles or precipitations are easily form as the difference between the content of SDS and the content of DTAB is not large, the increase of SDS content will change the critical packing parameter to values suitable for the formation of vesicles. At 343.15 K, the mass fraction of the total surfactant 1%is close to the saturated concentration for formation of vesicles, the further increase of the total surfactant will result in the breakdown of vesicles.The second, the controllability for the vesicle size and degree of dispersion was performed by changing the preparation conditions of vesicles based on vesicle phase region investigation, TEM and DLS measurements.1. The time factor. Prepared after a certain time (about a week), vesicles will become stable. However, the further increase of the storage time will result in the fusion of the vesicles, the vesicles diameter increases significantly and becomes more polydispersed. The fused vesicles are in high-energy unstable states, rearrangement of the microstructure occurs after certain storage time, and finally the fused vesicles will rearrange to smaller vesicles in lower-energy state.2. The ratio factor. For the studied system, the vesicles become more polydispersed with the increase of the molar ratio between SDS and DTAB. The reason is that the change of molar ratio results in the change of the ionic headgroups and thus the change of the curvature of the formed aggregates.3. The effect of salt concentration. For those more uniform size and smaller vesicles, the vesicle size decreases with the increase of salt concentration, and their dispersibility will be more excellent.4. The effect of total surfactant concentration. The effect of surfactant concentration on vesicles is weak.The third, the controllability of the particle size and dispersibility for the hollow PMMA microspheres has been investigated. The experimental results indicated that for those stable single-phase vesicle systems existed both at 303.15 K and 343.15 K, when the vesicles were used as templates for the preparation of PMMA, their sizes become smaller and the dispersibility becomes more excellent after polymerization. For those monodispersed vesicles stable existed at 303.15 K but unstable at 343.15K, their sizes become slightly larger and the dispersibility decreases slightly after polymerization. The results of DLS, TEM, SEM and AFM experiments indicated that the characteristic and morphology of vesicles are unchanged after the polymerization of the MMA monomers inside the vesicles. In addition, hollow PMMA microspheres have also been prepared by 12-3-12/AS/H2O aqueous two-phase systems in which vesicles are their typical microstructures. It illustrates that other vesicles can be used as templates to prepare hollow PMMA nanomaterials.Based on the controllability results and economical consideration, hollow PMMA microspheres with relatively uniform particle sizes can be prepared by using aqueous mixed SDS/DTAB/44 mmol·L-1 NaCl vesicle systems with the total surfactant mass fraction 1%and molar ratio range 2.3 to 2.5 as templates. These vesicle systems used as templates have good application prospect in the preparation of nanomaterials.