Inspired by the tunability of coordination mode of natural zinc proteins, this paper describes a new type of polymer micelle, whose coordination mode may be finely tuned simply via adjusting the solution media. To this end, a well-defined poly [N-(6-(3,5-di-tert-butyl-2-hydroxybenzylideneamino)hexyl)methacrylamide]-block-poly(2-hydroxyethyl methacrylate) (PDBHHMA-b-PHEMA) amphiphilic block copolymer was synthesized via rapid and well-controlled visible light activating RAFT polymerization at 25 °C and subsequently directly reacted with 3,5-di-tert-butyl-2-hydroxybenzaldehyde. 1 H NMR and GPC analyses indicate the intact structure, well-defined molecular weight, and narrow distribution of PDBHHMA 32 -b-PHEMA 120 . PDBHHMA 32 -b-PHEMA 120 may self-assembles into small PDBHHMAcore micelles in methanol or large inversed PDBHHMA-shell micelles in dichloromethane. Cobalt ions coordinate with the functionalities of PDBHHMA blocks in whole micellar shells or cores. The coordination of DBHHMA units in micellar shells proceeds much more rapidly than in micellar cores. The addition of small amount of DMF may significantly accelerate the coordination process in micellar cores. Although this coordination has a negligible effect on the sizes of both types of spherical micelles, coordination in micellar cores leads to a linear increase of light scattering intensity up to a critical feed molar ratio of [Co 2þ ] 0 /[DBHHMA] 0 = 0.4, whereas coordination in micellar shells does not influence light scattering intensity, even large excess of cobalt ions added, e.g., [Co 2þ ] 0 /[DBHHMA] 0 = 0.7. In micellar cores, cobalt ions tend to coordinate with DBHHMA units in interchain mode; N,N-dimethylformamide (DMF) cosolvent may accelerate this coordination process but increase the tendency of intrachain coordination. On the contrary, coordination in micellar shells occurs predominantly in intrachain mode. These media-tunable coordination modes finely tune the stability of micelles in their nonselective good solvent DMF.
Porous carbon/carbon composites were infiltrated by mixed Si-Mo-Ti powder with different Ti content below 1600℃ to produce an ablative C f /C-(Mo,Ti)Si 2-SiC composite. Microstructure, mechanical properties and ablation properties of the infiltrated composites were investigated. Results show that composites infiltrated by mixed powders with 14%wt Ti content have dense gradient structure and good mechanical properties. Three different kinds of typical morphologies can be distinguished on the surface of infiltrated composites according to the distribution of MoSiTi solid solutions. Formation mechanisms of the three kinds of typical morphologies are also analyzed. Ablation resistance improvement is attributed to the dense and continuity ceramic phases which distribute from inside to surface of the composites. Composites infiltrated with 14%wt Ti have the best ablation resistance due to the protective oxide layer formed by type I and type III morphologies during the ablation process. Linear and mass ablation rates of such composites are 0.002mm/s and 0.01mg/s, respectively.
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