The Aggregation Behavior Of Water Soluble Macromolecular Surfactant

Macromolecular surfactant consists of hydrophobic group and hydrophiphilic group, whose molecular weight is about 10³ï½ž10⁶g/mol. It has been widely used in bioinspired morphosynthesis strategy, nonmaterial synthesis, and medicine delivery. Several kinds of amphiphilic polyether copolymers and cationic macromolecular surfactant have been synthesized in our laboratory, and the properties such as aggregation behavior and interfacial properties have been investigated by experimental methods. Above the former works, dissipative particle dynamics (DPD) and mesoscale dynamics (MesoDyn) simulation methods are used to investigate the aggregation morphology and the aggregation process of the macromolecular surfactants and oxyethylated nonionic surfactants in aqueous solution, to offer mesoscale information for the application in biomedicine, nanomaterials, and etc. In details, the main results are summarized as follows:I . Aggregation behaviors of linear amphiphilic polyether copolymersAmphiphilic polyether copolymer is an important class of surfactants, which has been widely used in detergency. cosmetic, lubrication, bioprocess, and others. In this chapter, the aggregation behaviors of three polyether copolymers (EO)₁₆(PO)₁₈, (EO)₈(PO)₁₈(EO)₈ and (PO)₉(EO)₁₆(PO)₉ in aqueous solutions are studied by DPD simulation method. The simulation results indicate that the architecture and concentration of copolymer influenced the aggregate shape and size. All the three block copolymers would form spherical micelles at low concentration. However, with the concentration increasing, triblock (EO)₈(PO)₁₈(EO)₈ take cylindrical micelles and lamellar phase, diblock (EO)₁₆(PO)₁₈ tend to form cylindrical micelles, intercluster micelles, and lamellar phase, and triblock (PO)₉(EO)₁₆(PO)₉ tend to form intercluster aggregates and gels. Different from the traditional aggregates formed by low molecular weight surfactants, aggregates formed by the three studied copolymers include a large amount of water. For diblock copolymer (EO)₁₆(PO)₁₈, intercluster micelles form because that different aggregates share the hydrated shell. For triblock copolymer (PO)₉(EO)₁₆(PO)₉, intercluster micelles form for two reasons: different aggregates share the hydrated shell and the hydrophilic block act as a bridge. In comparison with block copolymer (PO)₉(EO)₁₆(PO)₉, the other two copolymers adopt more extendible conformation in aqueous solution. The results calculated by density functional theory (DFT) at B3LYP/6-31G(d) level show that the negative charges of oxygen in oxyethylene group is more than that in propylene group, which made polypropylene oxide more hydrophobic than polyethylene oxide in aqueous solution.II. Aggregation behavior of star-like amphiphilic polyether copolymerIt has been found that star amphiphilic polyether copolymers have many advantages in practical application according to their molecular structure. The phase behaviors of a star-like amphiphilic polyether copolymer (denoted as Polyetherl) are studied using the DPD simulation method in the absence and presence of shear. The influence of concentration and shear on the phase separation is discussed.In the absence of shear, spherical micelle, multicompartment wormlike micelle, and gel can be found in Polyetherl aqueous solution with the concentration increasing. The influence of shear on the rheological behavior of spherical and wormlike micellar solutions show that both shear thickening and thinning can occur. For spherical micellar solution, the first shear thickening comes from the elongate of the micelle to cylindrical micelle, and the followed shear thinning consists of two steps: the orientation of the elongated micelles (aligned along the shear flow direction) and the fission of some elongated micelles into smaller micelles. Again a slight shear thickening occurs due to the elongate of small micelles. For wormlike micelle, the first shear thinning comes from the orientation of the micelles (aligned along the shear flow direction) and the followed shear thickening occurs due to the elongate of micelles. The end-to-end point distance of Polyetherl increase with the concentration and shear rate increasing.III. Aggregation behaviors of oxyethlatd nonionic surfactants Nowadays, Oxyethlated nonionic surfactants get more and more attention for their low toxicity and easily biologically discomposed. They are widely used in emulsion, solubilization, and separation. In this chapter, the phase behaviors of C₁₆E_n(n=5, 10, 15, 20), SDS, and C₁₆E₅/SDS in aqueous solutions are simulated using the DPD simulation method. The simulation results show that C₁₆E₅ can form spherical micelle, wormlike micelle, lamellar phase, and reverse micelle in aqueous solution, while the other three surfactants can form hexagonal phase besides the above structures. The wormlike micelles are flexible. Both the increasing of concentration and number of EO can result in C₁₆E_n chains extendible. Spherical micelle, hexagonal phase, and lamellar phase can be found in SDS aqueous solution with the concentration increasing. For C₁₆E₅/SDS complex, aggregates containing several hydrophobic regions are formed by the hydrophobic interaction between SDS and C₁₆E₅ aggregates.IV. Aggregation behavior of cationic macromolecular surfactant MTAC-BA-AMA kind of cationic macromolecular surfactants Methacryloxyethyl Trimethyl Ammonium Chloride-Butyl Acrylate-Acrylamide (denoted as P2) is synthesized by emulsion polymerization. The characters of P2 are investigated by light scattering, element analysis, surface tension, viscosity, steady state fluorescence, and mesoscale dynamics (MesoDyn) methods. The results of surface tension measurement show that the polymer is surface activity and has two transition breaks on the surface tension isotherm. The viscometric study indicates that P2 shows typical polyelectrolyte behavior in aqueous solution. Hydrophobic regions are formed by P2 in aqueous solution, which is deduced from the results of fluorescence. MesoDyn simulation shows that spherical micelles, cylindrical micelles, and network structures form in the solution with the concentration increasing, which makes the apparent viscosity of the solution firstly decrease and then increase. The addition of SDS into the solution of P2 can decrease the viscosity and cmc because of the interaction between SDS and P2. The novelty of the thesis(1) For the first time, it is found that cylindrical micelle can be formed by PPO-PEO-PPO in a narrow range of concentration in aqueous solution. The main driven force for cylindrical micelle formation is hydrophobic interaction, which is obtained from the time evolution of cylindrical micelle formation.(2) For the first time, DPD simulation method was used to study the aqueous solution of star copolymer, which has five arms. The study reveals a new morphology named wormlike multicompartment micelle that has not been observed before and also provides a direct visualization of the evolution of wormlike multicompartment micelle. The simulation results give the information about the process of aggregation and the reasons causing complicate rheological behavior in mesoscale sence.(3) MesoDyn simulation and experiment methods are used together to study cationic macromolecular surfactant for the first time, which made the properties of the cationic macromolecular surfactant can be easily understood.