Stimuli-Responsive Pyrrolidone Based Surfactants

A fundamental characteristic of surfactants is their tendency to adsorb at gas/water interface in an oriented fashion and form aggregates at bulk phase due to their amphiphilic structure of surfactant molecules. Stimuli-responsive surfactants, which mean their properties can be controlled by environmental factors such as light, electron, magnetic, temperature, pH, organic and inorganic addictive agents, have attracted much attention in the development of personal care, advance materials, biotechnology, oil recovery, environmental management and daily-life products. N-alkyl2-pyrrolidones (CnP) are well-known solvents with low vapor pressure and toxicity. They have wide industrial applications such as flocculation of particles, skin permeation enhancers, shampoo and cosmetics. It was established that when the alkyl chain length is exceeded6, CnP could reduce the air-water surface tension, but was hard to form micelles in aqueous which limits their further applications. Thus, developing pyrrolidone surfactants is extremely interesting. At the same time chemical combination of some stimuli-responsive groups in the new surfactant molecule could enable its specific functionalities.In the present dissertation, three series of pyrrolidone based surfactants, N-ethyl-2-pyrrolidone N-alkyl amine (CnNP, where n=8,10,12,14,16,18), N, N'-dialky1-N,N'-di(ethyl-2-pyrrolidone) ethylenediamine (Di-CnP, where n=6,8,10,12), N,N'-dialkyl-N,N'-di(ethyl-isoindolinone) ethylenediamine (Di-CnI, where n=6,8,10,12), were designed and synthesized. The adsorption, aggregation and emulsion properties of these surfactants were characterized by various techniques such as equilibrium surface tension, fluorescence, static and dynamic light scattering (SLS and DLS), UV-vis spectroscopy, rheology, nuclear magnetic resonance spectroscopy (NMR), cryogenic or negative stained transmission electron microscopy (Cryo-TEM or Negative stained-TEM) and Zetasizer in detail. The main findings are following.(1) Three series of pyrrolidone based surfactants, CnNP (n=8,10,12,14,16,18), Di-CnP (n=6,8,10,12), Di-CnI (n=6,8,10,12), were synthesizedand characterized by employing1HNMR,13CNMR, ESI-MS and Elemental analysis,showing that all objective products were obtained with high purity.(2) The adsorption properties of CnNP aqueous solutions at pH3.5and10.5were investigated by employing surface tension measurement. It can be found that all CnNP possess surface activity, however, C8NP could only reduce the air-water surface tension without micelles formation in aqueous, further increase in concentration resulted in phase separation. Compared the surface activity parameters of CnP and CmN2N, the surface activity of CnNP is higher than CnP, but lower than CmN2N. The aggregation behavior of CnNP in aqueous were characterized by rheology, SLS, DLS, NMR, cryo-TEM and negative stained-TEM techniques in detail. It can be found that the pH-dependent micelle to vesicle transitions of CnNP was universally observed in the bulk phase. More interestingly, the other stimuli factors like CO2, CuCl2and surfactant concentration also could induce the aggregates transition, the detail transition process was shown in Figure Al.(3) The surface activity and micellization behavior of Di-CnP at acidic, neutral and basic conditions were characterized by equilibrium surface tension and fluorescence techniques. It was found that the surface activity of Di-CnP depends on the pH of aqueous solutions due to the protonation state of surfactant molecules when pH was varied. The new compounds have superior surface activity in comparison with that ofpyrolidone-based single-tailed surfactants CnNP, m-2-m type conventional cationic Gemini surfactants and gluconamide-type nonionic Gemini surfactants.The self-assembly of Di-CnP, were studied systematically by employing UV-vis spectroscopy, fluorescence spectroscopy, NMR, DLS, cryo-TEM and negative stained-TEM measurements. pH induced spherical micelle to vesicle transitions (MVTs) were observed in all diluted Di-CnP aqueous solutions. Apart from the pH induced MVTs, concentration induced MVTs were also observed in the protonated Di-CnP aqueous solutions due to counterion binding, indicating the presence of a second critical vesicle concentration (cvc) for ionic type Di-CnP. Furthermore, the cvc is decreased linearly with the number of carbon atoms n in the hydrophobic tail, following the well-known Stauff-Klevens rule, in the given protonation states. (4) We used equilibrium surface tension techniques to study the adsorption behavior of Di-CI aqueous solutions at pH2.5,7.0and11.0. It was found that the surface activity of Di-CnI depends on the aqueous solution pH due to the protonation state of surfactant molecules when pH was varied. The new compounds have lower cmc, but higher ?Cmc in comparison with that of pyrrolidone-based pH sensitive Gemini surfactant Di-CnP.The self-assembly of Di-CnI, were studied by employing UV-vis spectroscopy, DLS and negative stained-TEM measurements. Theconcentration induced MVTs were observed in the protonated Di-CnI aqueous solutions, suggesting the presence of a second critical vesicle concentration (cvc) for ionic type Di-CnP. Moreover, the cvc is decreased linearly with the number of carbon atoms n in the hydrophobic tail, following the well-known Stauff-Klevens rule, in the given protonation states.(5) The emulsion behavior of kerosene/water system was studied by employing IKA T25disperser, zetasizer (Mastersizer-2000), zeta potential, fluorescence and polarization microscope, in which CnNP, Di-CnP, Di-CnI were used as emulsifier. It was found that the stability of the O/W emulsion was dependent on aqueous pH, the structure of hydrophilic head group, the length of hydrophobic tail and the type of surfactants strongly. The O/W emulsion system could achieve the best stability when we used Di-C12I at pH2.5as emulsifier, indicating that the introduction of benzen in hydrophilic head group could improve the emulsifying properties of kerosene/water system.The present dissertation was focused on the relationship of surfactants structure-properties to design and synthesis three type pyrrolidone-based surfactants and investigated their surface activity, aggregation behaviors and emulsifying properties. Additionally, the novel pyrrolidone-based surfactants was also attempted to application in controlled drug release, gene transfer and nano-material preparation et al. Those uncompleted work may receive attentions and interest from colloid and interface researchers, and the work may be continued.