NIR-Photocontrolled Aqueous RAFT Polymerization with Polymerizable Water-Soluble Zinc Phthalocyanine as Photocatalyst.

In order to give an answer for the challenges of long wavelength-photocontrolled radical polymerization in aqueous solutions and to address the shortcomings of conventional near-infrared (NIR) photocatalysts (PCs) that are difficult to subject to post-treatment, we designed and synthesized a series of ß-tetra-substituted water-soluble zinc phthalocyanines (ß-TS-Zns) as the NIR PCs for reversible addition-fragmentation chain transfer (RAFT) polymerization successfully under irradiation with NIR (λmax = 730 nm) light at room temperature. Importantly, the NIR PCs can also be designed as polymerizable monomers and covalently loaded on the polymer chains, which are endowed with permanent NIR photocatalysis of the resultant polymers. Moreover, the polymerization can not only be carried out in water but also in phosphate buffer saline (PBS) solution, yielding polymers with controlled molar mass and narrow dispersities (D = 1.03-1.25). Therefore, this NIR-photocontrolled aqueous RAFT polymerization system may provide a charming strategy for possible applications in tissue engineering biomaterial in situ benefiting from the high penetration ability of NIR light.

Simultaneous melting and solidification of a columnar dendritic microstructure in a temperature gradient: Numerical modeling and experiments⋆.

The microstructural evolution of a SCN-ACE alloy in a temperature gradient is studied by cellular automaton (CA) modeling and in situ experiments. The initially columnar dendrites gradually evolve to a completely solid region with a planar solid/liquid interface. The CA simulations and in situ observations present the migration of secondary dendrite arms and liquid pockets due to temperature gradient zone melting (TGZM), and the movement of the interface between a mushy zone and a fully liquid zone. The CA simulations show that the interface movement toward the lower temperature region is caused by the increasing concentration of the fully liquid region. Through updating the concentration in the fully liquid zone to the initial concentration in the CA simulation for mimicking the efficient stirring in liquid, the movement of the interface between the mushy zone and the fully liquid zone is hindered. The simulated liquid fractions and mean concentrations throughout the mushy zone decrease with time, which agree well with the analytical predictions. The simulated concentrations in the resolidified mushy zone are not higher than the temperature-dependent solidus concentrations, implying that no supersaturation remains after the mushy zone fully solidifies.