Aggregation Behavior Of Poly(Dimethylsiloxane)-ethoxylate/propoxylate At Interface

Polyether-modified silicone surfactant is a novel family of amphiphilic molecules consisted of a hydrophobic Si-O-Si chain with high surface activity. It is a high efficient surfactant which can decrease surface tension remarkable to about 21 mN·m^-1, and has high surface activity in both water and organic solvent. In addition, it is low poisonous, antioxygenic, anti-ultraviolet, biocompatible and no environmental pollution. Thus, it is used in a wide range of industrial and technological applications, including textile softening, cosmetics, and drug delivery, etc. As many new products of this family come forth ceaselessly, it has been attached importance to the studies on their physical-chemical properties.The effect of temperature and inorganic salt on the aggregation behavior of poly(dimethylsiloxane)ethoxylate/propoxylate (PSEP) at air/water interface was investigated by surface tension and dilational surface viscoelasticity measurements. The aggregation behaviors of different carbon hydrogen surfactants at air/water interface were also investigated to contrast with that of PSEP. Fluorescence spectrum measurement was used to study the effect of carbon hydrogen surfactants on the aggregation behavior of PSEP in bulk phase. Furthermore, the dispersing carbon nanotubes (CNTs) in aqueous solution with PSEP were investigated by Raman spectra and high resolution transmission electron microscopy (HR-TEM) measurements, that is the aggregation behavior of PSEP on the solid/liquid interface. There are four parts in this dissertation.The research significance of silicone surfactants was clarified in the first section of the dissertation, and the aggregation behaviors of silicone surfactant on the interface and in bulk phase were also summarized in this part.In the second section, the aggregation behavior of PSEP on the air/water interface and the effect of temperature and inorganic salt were studied by cloud point, surface tension and dilational surface viscoelasticity measurements, etc. NaCl, NaBr and CaCl₂ could decrease the cloud point of PSEP, which indicated they had salting-out effect on PSEP, and their ability of decreasing PSEP's cloud point was NaCl > NaBr > CaCl₂. NaCl, NaBr and CaCl₂ had little influence on the minimum surface tension (γ_cmc) of PSEP, while they showed significant effect on the critical micelle concentration (cmc) of PSEP, and Cl^- had stronger influence on cmc than Br^- did. The micellization of PSEP in different media was an entropy-driven. And the effect of entropy on the micellization became weak as the temperature of system increased, while the effect of entropy increased with the temperature in the system with inorganic salt. The results also showed that dilatational frequency, concentration of surfactant and inorganic salt affected the interfacial viscoelasticity of PSEP solution. Dilatational modulus increased with the dilatational frequency, implying that stable surface film was favorable to form. In addition, the dilatational modulus increased initially and then decreased with the increasing of PSEP concentration.Cloud point, surface tension, dilational surface viscoelasticity and fluorescence spectrum measurements were employed to investigate the interactions between PSEP and carbon hydrogen surfactants and the effect of the complex formulation's ratio in the third section. Adding SDS,DTAB or C₁₂E₈ into PSEP aqueous solution could rise the cloud point in different degree, and their ability of affectting the PSEP's cloud point is SDS >DTAB > C₁₂E₈. Theγ_cmc and cmc of PSEP/ SDS,PSEP/DTAB and PSEP/C₁₂E₈ systems were between the two single aqueous solution of surfactants, which expressed that there are interactions between the two components and they preferred to form mixed micelles. However, the cmc of PSEP/C₁₂E₈ was higher than that of every single component and this phenomenon should be further studied. The dilational frequency had little effect on dilational modulus as the concentration of PSEP was low in the compounded system, and the dilational modulus was affected by dilational frequency with the concentration of PSEP increasing. As the molar ratio of the compounded system was fixed, the dilational modulus of each compounded system increased firstly and then decreased with the concentration of PSEP. Moreover, the results of fluorescence spectrum indicated that the mixed micelles with close structure were formed in PSEP/ SDS and PSEP/C₁₂E₈ system, while the micellar structure in PSEP/DTAB system was loose.In the fourth section, dispersing CNTs in aqueous media with PSEP was investigated by UV-vis-NIR adsorption spectrum, HR-TEM and Raman spectrum measurements, etc. It was shown that PSEP was a good dispersant for CNTs, which could disperse CNTs at low concentration. However, the dispersing ability was affected by the concentration of PSEP, i.e. the dispersing effect enhanced initially and then weakened with the increasing of PSEP concentration. Because PSEP molecules had great steric hindrance effect, they could disperse CNTs well at low concentration. While CNTs tended to coagulate due to bridging action of PSEP molecules at higher concentration.