Joseph Jojo P, Miglani Chirag, Singh Ashmeet, Gupta Deepika, Pal Asish
Institute of Nano Science and Technology, Phase 10, Sector 64, Mohali, Punjab-160062, India.
Soft Matter. 2020 Mar 11;16(10):2506-2515. doi: 10.1039/d0sm00033g.
Synthetic systems mimicking the natural self-folding process are attractive to impart multiple structural control over polymer crosslinking and the subsequent alteration of their macroscopic self-healing properties. In that regard, polymers P1-P5 containing pendant photo-crosslinkable moieties were designed and underwent intra- or interchain collapse to form diverse nanostructures. The shape and dimension of the nanostructures could be efficiently controlled by the concentration, solvent compatibility and characteristics of the polymers. Photodimerization of the coumarin moieties transformed the extended coiled chain of the polymer to uniform sized nanoparticles in a dilute condition, while in the crowded macromolecular concentration regime, the polymer folded into nanostructures with polydisperse topologies that were far from a condensed globule or partially swollen globule conformation. Scaling law exponents for polymer chain compaction suggested an interchain collapse with rigid compact segments connected by flexible polymer chains that draws an analogy with elastomers. Such a hardening of the rigid segment as a consequence of photodimerization rendered a significant increase in the glass transition temperature (Tg), which could be reversibly controlled upon decrosslinking. Lastly, the structural variation of this class of polymers over self-healing was explored and the crosslinked polymers showed phototriggered non-autonomic and intrinsic self-healing behaviour under ambient conditions. This is an interesting approach to access a photomodulated self-healing system with low Tg polymers that shows the coexistence of autonomic and nonautonomic self-healing pathways and that may find application in designing smart coatings for photovoltaic devices.
模仿自然自折叠过程的合成系统对于在聚合物交联及其宏观自修复性能的后续改变方面施加多种结构控制具有吸引力。在这方面，设计了含有侧基光可交联部分的聚合物P1 - P5，它们经历链内或链间塌陷以形成各种纳米结构。纳米结构的形状和尺寸可以通过聚合物的浓度、溶剂相容性和特性来有效控制。香豆素部分的光二聚作用在稀溶液中将聚合物的伸展卷曲链转变为尺寸均匀的纳米颗粒，而在大分子浓度较高的情况下，聚合物折叠成具有多分散拓扑结构的纳米结构，这些拓扑结构远离凝聚球或部分溶胀球构象。聚合物链压实的标度律指数表明存在链间塌陷，其中刚性紧密段由柔性聚合物链连接，这与弹性体有相似之处。光二聚作用导致的刚性段硬化使得玻璃化转变温度（Tg）显著升高，脱交联后该温度可被可逆控制。最后，探索了这类聚合物在自修复过程中的结构变化，交联聚合物在环境条件下表现出光触发的非自主和固有自修复行为。这是一种获得具有低Tg聚合物的光调制自修复系统的有趣方法，该系统展示了自主和非自主自修复途径的共存，并且可能在设计用于光伏器件的智能涂层中得到应用。
