Nanocomposites of Polydiacetylene and Rare Earth Ions with Reversible Thermochromism

We report a facile approach to water-dispersible polydiacetylene/rare earth ions nanocomposites with reversible thermochromism. The nanocomposites were prepared by doping rare earth ions Dy^3＋ or Sin^3＋ into layer-structured 10,12-pentacosadiynoic acid （PCDA） nanopar- ticles to obtain PCDA/rare earth ions nanocomposites （PCDA-RE） and subsequently annealing PCDA-RE at the temperature slightly higher than the melting point of pure PCDA crystals, followed by topochemically polymerizing the annealed PCDA-RE. The polymerized PCDA-RE, i.e. poly（10,12-pentacosadiynoic acid）/rare earth ions nanocomposites （PDARE： PDA-Dy or PDA-Sm）, are largely reversible （PDA-Sm） or even completely reversible （PDA-Dy） in the thermochromism, while, without the doping, pure PDA is completely irreversible. It is confirmed that, PDA-RE are also layer-structured with a d-spacing of 5.4 nm, higher than the d-spacing of pure PDA （4.7 nm）. In PDA-RE, the rare earth ions form a layer in-between and interact strongly with the PDA bilayers, being responsible for the high degree or even the complete reversibility. This is the first example to make PDA completely reversible through the doping of rare earth ions; the annealing process is essential for the complete reversibility since it removes any defects in the structure.

Fabrication of Melamine/Tb^3+-Intercalated Polydiacetylene Nanosheets and Their Thermochromic Reversibility

Polydiacetylene(PDA)is one kind of the conjugated polymer with layered structure,which can serve as a host to accommodate the guest components through intercalation.In these intercalated PDAs,some of them were reported to have a nearly perfect organized structure and perform completely reversible thermochromism.Till now,these reported intercalated PDAs were made by only introducing a single component for intercalation.Here,we chose 10,12-pentacosadiynoic acid(PCDA)as the monomer,of which the carboxyl-terminal groups can interact with either Tb^3+ ions or melamines(MAs).When the feeding molar ratio of PCDA,MA,and Tb^3+ ion was 3:267:1,only Tb^3+ ions were intercalated though excess MAs existed.Such Tb^3+- intercalated poly-PCDA exhibited completely reversible thermochromism,where almost all the carboxyl groups interacted with Tb^3+ ions to form the nearly perfect structure.When the feeding molar ratio of PCDA,MA,and Tb^3+ ion was 3:267:0.6,both Tb^3+ ions and MAs were intercalated.There existed some defects in the imperfect MA-intercalated domains and at the domain boundaries.The MA/Tb^3+- intercalated poly-PCDA exhibits partially reversible thermochromism,where the backbones near the defects are hard to return the initial conformation,while the rest,those at nearly perfect organized domains,are still able to restore the initial conformation.

Facile and Large-scale Fabrication of Biodegradable Thermochromic Fibers Based on Poly(lactic acid)

To investigate the feasibility of developing biobased and biodegradable thermochromic fibers,poly(lactic acid)(PLA)fibers with visual temperature indicator functionality were fabricated using a scalable melt spinning technique(spinning speed 800 m/min),where PLA and thermochromic microcapsules were used as fiber-forming polymers and color indicators,respectively.The effect of thermochromic microcapsules on the mechanical properties and reversible color-changing function of PLA fibers was systematically investigated to achieve high tenacity and sensitive color-changing function.The difference in the fiber performance was connected to changes in the multilayer structure.The results show that PLA fibers exhibit excellent tenacity of 3.7-4.7 cN/dtex and reversible and stable thermochromic behavior over 31℃.The high fraction of mesophase within TPLA-1 fiber plays an important role in its tenacity.Meanwhile,the low-concentration of microcapsules(~1 wt%)with good dispersion could act as a nucleating agent inside the PLA matrix and contribute to the formation of microcrystals in the amorphous between primary lamellae,which is also beneficial to maintain the tenacity of the fibers.The agglomeration of high-concentration microcapsules within PLA fibers hampered the formation of mesophase,resulting in a decrease in fiber tenacity.Aside from the content of microcapsules,the agglomeration of high-concentration microcapsules(>5 wt%)is the main reason that limits the substantial increase in fiber color depth.This study opens up new possibilities for degradable thermochromic fibers produced using standard industrial spinning technology.