Neutral Polymer With Non-ionic Surfactant Tx-100 Molecules Orderly Combination Of Interaction

Various molecular assemblies, such as micelles, vesicles, microemulsion and lyotropic liquid crystals, form spontaneously for the special hydrophilic and hydrophobic amphiphile properties of surfactant. They have been widely applied in biology, material synthesis, energy, and various modern science and technology because of their special polar and nonpolar microenvironment and of the nanometer scale in at least one dimension. The mixtures of surfactant and macromolecules, especially water soluble polymer, possess particular properties, which can be adjusted by the designation and modification of the molecular structure of polymer. So far, the mixtures of surfactant and polymer have been used in oil extraction, cosmetic, material synthesis, pharmaceutical etc. The investigation of the interaction between surfactant and polymer has been attracted much attention. They spread widely and go deep into the level of molecular and sub-molecular.In the present work, the interaction mechanism between water soluble polymer poly(ethylene glycol)s (PEG),pluronic copolymer (poly(ethylene oxide)- poly(propylene oxide)- poly(ethylene oxide)) and various surfactant molecular assemblies such as micelles, lamellar liquid crystals and reverse micelles were investigated. We focus our attention on the interaction model of complex between polymer and surfactant assemblies, and the effect of polymer chain length, composition and temperature on the topology of the complex. The main results are listed as follows:1. The microstructure of Triton X-100 (TX-100)/poly (ethylene glycol) (PEG) complex has been investigated by fluorescence resonance energy transfer (FRET), dynamic light scatter (DLS), freeze-fractured transmission electron microscopy (FF-TEM) and 1H NMR technology. The nonionic surfactant TX-100 and pyrene are employed as energy donor and acceptor respectively, and the average distance between them is calculated quantitatively in the systems of TX-100/PEG with different molecular weights (MW). The results of FRET study indicate that the presence of PEG leads to the separation of donor and acceptor in TX-100 micelles, suggesting that PEG chains insert into TX-100 micelles making the microstructure of PEG-bound TX-100 aggregates looser than that of free micelles, which is independent of the MW of PEG. However, FF-TEM, DLS and 1H NMR studies show that the morphology of the complex of TX-100/PEG depends on the MW of the polymer. PEG with shorter chain (MW <2000 Dalton) insert into and wrap around TX-100 micelles and form sphere-like complex, while that with longer chain (MW >2000 Dalton) would interact with numbers of TX-100 micelles and form coral-shaped clusters. In addition, higher temperature facilitate complex formation, while alcohols do not effect the interaction of TX-100 and PEG.2. Formation and structure transition of the complex composed of triblock copolymer F127 and nonionic surfactant TX-100 have been investigated by 1H NMR spectroscopy, dynamic light scattering (DLS) and isothermal titration calorimetry (ITC). Three TX-100 concentration regions are identified, within which TX-100/20 mg/mL F127 complex undergoes different temperature-induced structure transitions: In low concentration region (<9.42 mM), F127 single molecular species (unimers) wrap around TX-100 micelles forming F127/TX-100 complex with TX-100 micelle as the skeleton at a lower temperature (5 oC), and the skeleton transfers to F127 micelle at higher temperature (40 oC); in intermediate TX-100 concentration region (9.42-94.85 mM), the skeleton of F127/TX-100 complex transfers from TX-100 micelle successively into F127 micelle and TX-100 micelle again upon heating; the interaction of F127 with TX-100 is saturated in high TX-100 concentration region (>157.57 mM), and free TX-100 micelles coexist with larger clusters of F127/TX-100 complexes. In addition, TX-100-induced F127/TX-100 complex formation and structure transition are also investigated at constant temperatures. The results show that: Within 5-10 oC, F127 unimers mainly adsorb on the surface of TX-100 micelles just like normal water soluble polymers; in the temperature region of 15-25 oC, TX-100 micelles prompts F127 micelle formation; within 30-40 oC, TX-100 inserts into F127 micelles leading to the breakdown of F127 aggregates at higher TX-100 concentrations, and the obtained unimers thread through TX-100 micelles forming complex with TX-100 micelle as skeleton.3. Dynamic light scattering (DLS), 1H NMR, fluorescence and FT-IR are employed to investigated the effect of poly (ethylene glycol)s (PEG) with different molecular weight (MW) on the reverse micelles in the system of TX-100/cyclohexane/H2O. The results show that TX-100 forms non-spherical reverse micelles in cyclohexane, which transfer to small spherical ones at higher temperature. PEG400 is solubilized in the polar core of reverse micelles, and interacts with EO chains of TX-100 replacing binding water. Larger clusters of reverse micelles induced by PEG are observed at higher temperatures and PEG concentration. The efficiency to induce cluster formation increases with PEG molecular weight.4. Lamellar-to-isotropic phase transition is observed in the system of TX-100/n-C8H17OH/H2O induced by neutral water soluble polymer poly (ethylene glycol) (PEG) with molecular weight ranging from 400 to 20000. The location of PEG in the lamellar liquid crystal and the microstructure change of the lamellar phase during phase transition are investigated by means of 2H NMR, small angle X-ray diffraction (SXRD), rheology, polarized optical microscopy (POM) and freeze-fractured transmission electron microscopy (FF-TEM). Calculations based on the"Swelling Model"show that 0.92-2.58 wt% PEG2000 penetrates into the amphiphile layer, and the rest resolve in water layer. Both of these two kinds of locations induce the lamellar-to isotropic phase transition. The longer the chain length of PEG, the higher the efficiency is. In addition, a critical molecular weight of PEG is observed before phase transition occurs, with which the disturbance of PEG on the microstructure of lamellar liquid crystal is most prominent. And the critical molecular weight of PEG is independent of the thickness of water layer. The value is 2000 for the system of TX-100/n-C8H17OH/H2O.5. 2H NMR, small angle X-ray diffraction (SXRD), rheology, and polarized optical microscopy (POM) are employed to investigated interaction of triblock copolymer F127 (PEG4000-PPG4000-PEG4000) with lamellar liquid crystal in the system of TX-100/n-C8H17OH/H2O. The results are compared with P123 (PEG1000-PPG4000-PEG1000), PPG4000, and the mixture of PPG4000 and PEG4000 to study the effect of composition and conformation of polymer chain on the interaction between polymer and lamellar liquid crystal. Lamellar to isotropic phase transition induced by polymer is observed. The hydrophobic blocks of copolymer penetrate into the the surfactant amphiphile bilayer. Random coils of longer hydrophilic chain of F127 in the water layer cause the bend of amphiphile bilayer, while shorter hydrophilic chains of P123 penetrate into the hydrophilic layer of amphiphile bilayer. Both the hydrophobic and hydrophiphilic chain of copolymer contribute to the microstructure change of lamellar liquid crystal and subsequently phase separation. In addition, the phase separation occurs easily induced by PEG than copolymer.