Aggregation Behaviors Of Differently Structured Block Polyethers And The Dispersing Ability Of Single-Walled Carbon Nanotubes

PEO-PPO-PEO block polyethers are typical nonionic polymeric surfactants, with the characters of strong interfacial absorption ability, good biocompatibility, and environment friendly. PEO-PPO-PEO block polyethers have many applications in the fields of enhanced oil recovery, cosmetics, wastewater treatment, paper making, fluid modification, controlled drug release, and synthesis of micro and nano materials, etc. Moreover, these applications of block polyether closely relate with the aggregation behaviors of block polyether at different interfaces and in various solvents. Thus, the aggregation behaviors and the physicochemical properties of the complex systems consisted of block polyether and polymers have attracted increasing attentions.In the past decades, a number of studies have focused on the physicochemical properties of PEO-PPO-PEO block polyethers, which can not only form a wealth of aggregates in bulk solution, but also at the air/water interface. PEO-PPO-PEO block polyethers dissolve in the form of single molecules in bulk solution at lower temperature and concentration. Once the concentration is higher than the critical micellization concentration (cmc) or the temperature is higher than the critical micellization temperature (cmt), block polyether molecules may aggregate. The adsorbed layers at the air/water interface draw more and more attentions, block polyether molecules can aggregate and form "brush" or "loop and tail" structures at the air/water interface. With the emphasis on environmental protection, more and more attention has been paid to the investigations about the mild surfactants. Thus, the researches of the theory and application of block polyethers have been numerously reported; however, the studies on the block polyethers with branched structure are rarely published. Recently, the investigations show that introductions of some other groups in the block polyethers can greatly improve the characteristic of polyethers and achieve the functions of multiple responses. Based on our previous researches, we synthesize the block polyethers with branched structure and benzene ring. Meanwhile, we investigate the aggregation behaviors of block polyethers with different structures, the dispersion effects on single-walled carbon nanotubes, and improvements on the rheology behavior of polymers, such as hydrolyzed polyacrylamide (HPAM) and hydrophobic modified hydrolyzed polyacrylamide (HMPAM). This thesis is divided into six parts:In the first section, the properties and the aggregation behaviors in bulk solution, at the air/water interface, liquid/liquid interface, and liquid/solid interface of block polyethers are summarized. Moreover, the interactions between block polyethers and polymers and the applications of block polyethers in different areas are discussed.The second section is divided into two parts. In part one, the aggregation behaviors at the air/water interface of three block polyethers TEPA[(PO)36(EO)100]7, TEPA[(PO)36(EO)100(PO)36]7 and TEPA[(PO)36(EO)100(PO)56]7 are investigated by the methods of equilibrium surface tension, dynamic surface tension, and interfacial dilational rheology. The results show that the hydrophobicity of block polyether is stronger, the surface tension of water solution is lower, and the efficiency and effectiveness to lower surface tension are stronger as the numbers of PO groups at the end of polyether branch increase. The results of dynamic surface tension show that the molecular change of block polyethers can influence the diffusion process greatly. At the initial stage of diffusion, the diffusion rate of TEPA[(PO)36(EO)100]7 is the fastest and that of TEPA[(PO)36(EO)100(PO)36]7 is the lowest among the three polyethers;at the diffusion anaphase, the diffusion rate is influenced significantly by the concentration of block polyethers. The results of interfacial dilational rheology show that the molecular change of polyethers can influence the aggregation behavior at the air/water interface;meanwhile, concentration is another important effect on the dilational viscoelasticity. In second part, compared with the linear block polyether P123, the aggregation behaviors of block polyethers with benzene ring (BPE and BEP) are investigated by surface tension and interfacial rheology. The conformational change of block polyethers with benzene ring is deduced and proved by the methods of the whole atom dynamic simulation. The results of surface tension show that the introduction of benzene ring can enhance the adsorption ability of polyether molecules at air/water interface and improve the efficiency of lowering surface tension; the aggregation behavior is different as the variation of the block order of polyether. The efficiency of BPE molecules is higher than that of BEP. The results of interfacial rheology show that the introduction of benzene ring increases the viscoelasticity and the viscoelasticity changes with the variation of block polyether, which is because that the introduction of benzene ring can make the change of molecular conformation, which is also proved by full atom dynamic simulations.In the third section, the comparisons of aggregation behaviors between branched block polyether T1107 and linear block polyether (EO)60(PO)40(EO)60 in aqueous solution are studied by MesoDyn simulation methods. The results show that T1107 and linear block polyethers can form spherical, rod-like, worm-like micelles, and micellar clusters. T1107 molecules can form micelles at lower concentration than that of (EO)60(PO)40(EO)60 and the aggregation number of T1107 micelles is lower than that of (EO)6o(PO)4o(EO)6o. According to the information provided by MesoDyn simulation about micellar changes with time evolution, the micelles of both polyethers vary with time evolution, polyether structure, concentration, and shearing effect. When shear rate is 1×105s-1, the shear can induce the micelles of both polyether changing from sphere to rod. When shear rate is lower than 1×105s-1, the influence of shear on the aggregation is different, T1107 molecules can form huge micelles and micellar clusters under the effect of shearing, while the linear block polyether can firstly form huge micelles and then the huge micelles disaggregate.In the forth section, the effects of different salt sodium benzoate and NaCl on the aggregation behavior of block polyethers with benzene ring are investigated by surface tension, interfacial dilational rheology, steady-state fluorescence and dynamic light scattering measurements. The results of surface tension show that sodium benzoate can influence the surface tension of block polyether aqueous solution more greatly than NaCl within the concentration range studied. When the concentration of block polyether is lower than its cmc, sodium benzoate molecules can adsorb at the air/water interface together with polyether molecules, which lead to the decrease of surface tension; when the concentration of polyether is higher than its cmc, sodium benzoate has little effect on the decrease of surface tension. The results of interfacial dilational rheology show that the effect of sodium benzoate on the dilational modulus of block polyether with benzene ring is different from that of NaCl. The dilational modulus with sodium benzoate is higher than that with NaCl. The interfacial tension relaxation measurement show that the molecular conformation changes with the addition of different salt. The steady-state fluorescence measurements show that the addition of sodium benzoate can decrease the hydrophobic index of BPE solutions, but increase that of BEP solutions. The influence of NaCl on the hydrophobic index of both BPE and BEP solutions is little, indicating that the interactions between sodium benzoate and polyethers are present in bulk solutions. However, the variation of hydrophobic index of BPE/sodium benzoate system is different from that of BEP/sodium benzoate system, which is due to the different polyether structure. The results of dynamic light scattering show that the hydrodynamic radius of aggregation of block polyethers and sodium benzoate system is larger than that of block polyether and NaCl system, indicating that sodium benzoate can participate in the formation of aggregate.In the fifth section, the ability of dispersing single-walled carbon nanotubes (SWNTs) in aqueous solutions of block polyethers with the different structures of branch and benzene ring is investigated in detail by UV-vis-NIR, Raman spectra, HRTEM observations. The dispersion limit and efficiency are used to demonstrate the dispersion ability of SWNTs in polyether aqueous solutions. It can be concluded that the increase branch number can enhance the dispersion ability of block polyethers. In the branched block polyethers, AE82 is a better dispersant with larger dispersion limit and efficiency though the defect density of SWNTs in AE82 solution is higher than that in AE83 solutions. The polyether BPE containing benzene rings has a slightly lower dispersion limit on SWNTs than AE82, but its concentration at the dispersion limit point is lower and the dispersion efficiency is much larger than AE82, while the molecular weight of BPE is just a half of AE82. Moreover, the density of defective SWNTs dispersed in the solutions of AE83 and BEP with PEO-PPO structure is lower than that in AE82 and BPE, while the dispersion efficiency of AE83 and BEP is lower. Based on the comprehensive consideration of the effect of dispersion and costs, BPE is the most effective dispersant on SWNTsIn the sixth section, the effects of block polyethers with benzene ring on the rheology characteristic of HPAM and HMPAM systems are investigated. The results show that the polyethers BPE and BEP can enhance the viscosity of HPAM systems, but decrease that of HMPAM. As increase of polyether concentration, the viscosities of the complex systems increase firstly and then decrease. When the polymer and polyether concentrations are 0.12 and 0.2 wt%, respectively, the viscosity of the complex system is the highest among the concentrations range studied here. Meanwhile, the heat resistance and salt tolerance of polymer systems can be enhanced when polyethers with benzene ring is added to the systems.