Adsorption Behavior Of Dye-polyether Derivatives At The Interface Of Its Parent Dye Particle

Dispersants play a crucial role in the dye commercialization and application of disperse and vat dye. To make stable dye dispersions and improve dye adsorption and diffusion into fiber during the dyeing process at high temperatures, a great deal of effort has been spent on developing methodologies for specifying and reasoning about the selection or design of dispersants. The adsorption of dispersant on dye surface is mainly determined by three factors:the interaction of the dispersant with the dye surface, the hydrophobicity of the dispersant and the adsorbed thickness layer. Based on the above considerations, a series of dye-polyether derivatives was synthesized and applied to disperse its hydrophobic parent dye in our previous work. In order to understand the dispersion mechanism of dye-polyether derivatives, its characterization in aqueous solutions, the dispersing efficiency to its parent dye and the adsorption behavior on dye surface were studied in this paper. By means of the scaling theory and dispersion stability theory, the relationship among molecular structure of dye-polyether derivatives, dispersion stability and adsorption behavior is constructed. Also the adsorption behavior of dye-polyether derivatives and polyethers on dye surface was simulated by utilizing a variety of computer simulation techniques from microscopic and mesoscopic aspects. And these results can provide some guidance on the design and optimization of hydro-dispersant. The main contents and conclusions are summarized as follows:Based on structural characteristics of hyper-dispersant, another dye-polyether derivative, in which the dye molecule (C.I. Disperse Red60) is bonded onto polyether via a triazine ring, was synthesized and characterized by FTIR,1H NMR and elemental analysis. This dispersant exhibits unique dispersing performance for C.I. Disperse Red60. The dyeing performance of the prepared dye dispersions on polyester fabrics also was comparing with that of commercial dye. The dyed fabrics showed very good to excellent fastness to washing and rubbing while the dyeing effluent was colorless. Also the reduction clearing is not necessary in the dyeing process of the prepared dye dispersions, and this can save large amounts of energy, water and chemicals. It is indicated that this dispersant has excellent solubilization effect to C.I. Disperse Red60and can increase the apparent solubility of disperse dye effectively during the dyeing process at high temperatures.The characterization of dye-polyether derivatives and polyethers in aqueous solutions was studied by the measurement of surface tension, steady-state fluorescence, and dynamic light scattering. For polyethers, the plots of surface tension exhibit two breaks as a characteristic for polymers with high percent of PEO:the first break at low concentration originates from a structural transformation in the polymer molecule resulting in a more compact polymer layer at the surface while the second one corresponds to the critical micelle concentration (cmc) and signifies the formation of polymolecular micelles. However, these polymers are all unlike common surfactants and do not exhibit a clear cmc, which is consistent with the possibility that the aggregation structures are more complicated than conventional micelles. In comparison, the surface tension curves of dye-polyether derivatives are more like those of ordinary surfactants. The cmc values of dye-polyether derivatives are less than that of their polyethers counterparts. Polyethers fail to form stable aggregates in the aqueous solutions even at concentration above2g/L due to the lacking hydrophobicity of PPO. The introduction of aromatic dye molecule into the highly hydrophilic polyethers promotes their aggregation in solution. And when the concentration of dye-polyether derivatives is greater than0.5g/L, they can form stable, larger aggregates with a hydrodynamic diameter in the range of50-150nm in aqueous solutions, and the speculated micelle structure is loose packing and highly swollen by large amount of water penetrating inside its core.The adsorption behavior of polyethers and dye-polyether derivatives on dye surface was studied by experimental measurements. The results showed that adsorption isotherms of these polymers on the dye surface are the Langmuir type. The saturation adsorbed amounts of polymers occur after the critical micelle concentration (cmc) has been reached and are increased with molecular weight and hydrophobicity. For dye-polyether derivatives, the saturation adsorbed amounts are about2times of those of their polyethers counterparts. It is indicated that the introduction of parent dye molecule into the polyethers structure increases their molecular hydrophobicity due to the existence of π electrons present in the structure, and results an additional adsorption driving forces, the strong π-π stacking between the polymer and the dye surface. It is speculated that these polymers are adsorbed on the dye surface in a brush-like monolayer conformation. The calculated values of average distance between two neighboring chains are less than the values of Flory radius indicates the brush conformation is formed. Good correspondence of values of adlayer thickness is observed between prediction by the adsorption model and calculation from the Zeta potential experiments. And the introduction of dye molecule into the polyethers increases the adlayer thickness by about2nm.The total potential energy between two dye particles under saturated adsorption was calculated according to the related literatures. The results showed that all the polymers lead to strong steric barriers against agglomeration under saturation coverage, because of the overlap of molecules adsorbed at the two approaching particle surfaces. However, a shallow attractive well is observed in all the potential energy curves, which might lead to the formation of relatively weak particle agglomerates. As it shows, the total interaction energy is a strong function of the adsorbed layer thickness. When the adlayer thickness increases from5.1to16.7nm, and the magnitude of the attractive well decreases from approximately2.4to0.3kT. This relatively weak attractive potential was observed to have some impact on the dispersion stability of dye dispersions. For the dispersions with dye-polyether derivatives, the magnitude of the total potential energy is much higher than that of their polyethers counterparts obviously. The good coincidence between theory prediction and experiment data suggests that dye-polyether derivatives improve the dispersion stability by increasing adlayer thickness and chain density. For the effect of polyethers chains, however, the potential energy curves appear to be greatly influence by adlayer thickness or molecular weight. In disagreement with theoretical expectations, the dispersion stability is significantly related to the adsorption energy as well. Because of the high percent of PEO, the strong polymer-water interaction is so powerful that it is greater than the anchoring energy, thus, as the particles approach each other, the polymers are desorbed and squeezed out of the space between them, allowing particles to flocculate or coagulate. Good dispersion stability requires a large hydrophobic anchor to provide high adsorption energy. It also can be informed that both equilibrium and dynamic considerations should be taken into account for designing or selecting of dispersants. The above results indicated that the dispersion stability could be enhanced by increasing the adlayer thickness or adsorption energy.The interaction energy and adsorption energy between polymers and dye surface, the adsorption behavior of L207and RL207on dye surface (002) were simulated using molecular dynamics and Metropolis Monte Carlo method. The conformation of polymers on dye surface and the change in the energy of the systems were also explored. The results showed that the magnitude of interaction energy and adsorption energy of dye-polyether derivatives are larger than those of their polyethers counterparts, and the adsorption conformation of two polymers is different. L207is almost not adsorbed on dye surface and exit in aqueous solution. Because the longer PEO chains of L207, the strong polymer-water interaction is so powerful that it is greater than the interaction between PPO chains and dye surface and make it not adsorb onto the dye surface. For RL207, the dye molecule segment and PPO chains can adsorb onto the dye surface because of strong π-π stacking between dye molecule segment of RL207and dye surface, while the PEO chains interact favorably with the aqueous medium and stretch into the solution, so as to achieve the purpose of stabilizing the dye particles.The aggregation behavior of dye-polyether derivatives and polyethers in aqueous solution was investigated by MesoDyn simulation, and the influences of molecular structure and concentration of dye-polyether derivatives on their microphase behavior were discussed. In the aqueous solution, dye-polyether derivatives can form different morphologies at different volume fractions and three aggregation types were observed:spherical micelle, worm-like micelle and micellar cluster. The structure of the spherical micelle and worm-like micelle consists of a core of the Dye and PO beads surrounded by a solvent-swollen corona of the EO beads, while a very few water molecules remaining in its core. Due to the coalescence among micelles, bigger and irregular shape micellar clusters are formed at the certain concentration. In this situation, the Dye and PO beads still form the micellar core, while the EO beads wrap multiple micellar cores in the form of continuous phase. The formation of micelle can be divided into four stages:the induction stage, pre-formation stage, evolution stage and the final equilibrium stage. The increase of the initial concentration of dye-polyether derivatives can shorten the induction time and increase the order parameter after equilibrium stage.The adsorption behavior of dye-polyether derivatives and polyethers on dye surface was simulated by dissipative particle dynamics method. The results showed that the adsorbed amounts of polyethers on dye surface are low and most polymers are still exit as single chain in aqueous solution. This is because the PPO chains are short and not sufficiently hydrophobic. However, the introduction of parent dye molecule into the polyethers structure increases their molecular hydrophobicity, and the adsorption behavior of dye-polyether derivatives on dye surface (Wall) shows big difference compared to their polyethers counterparts. The adsorption of dye-polyether derivatives on dye surface (Wall) is in a brush-like monolayer conformation. The above simulated results are consistent with the experimental conclusions.