液晶相位过渡诱导了多电解质两复合体中的旋转交叉
Yves Bodenthin1, Guntram Schwarz, Zbigniew Tomkowicz
1University Siegen, FB7 Solid State Physics, D-57068 Siegen, Germany.
Journal of the American Chemical Society
|February 12, 2009
概括
铁和金属的高分子聚合物形成液晶. 加热Fe-PAC会带来不可逆转的旋转交叉 (SCO) 与颜色变化,而Ni-PAC没有SCO. 溶解恢复了原来的状态.
科学领域:
- 协调化学 协调化学
- 材料科学 材料科学 材料科学
- 超分子化学 超分子化学
背景情况:
- 金属上分子协调聚电解质 (MEPE) 是由金属离子和连接体的自我组装形成的.
- 结合像二甲基酸盐 (DHP) 这样的两性质,可以产生具有液晶性质的多电解质两性质复合物 (PAC).
研究的目的:
- 为了研究Fe-PAC和Ni-PAC系统中的旋转交叉 (SCO) 行为.
- 了解结构变化,热性质和磁过渡之间的关系.
- 为了比较PAC中的SCO行为与整洁的MEPE.
主要方法:
- 铁 (II) 或尼 (II) 离子与6,6',6''-bis(2-pyridyl) -2,2':4',4'':2'',2'''-四氧化 (btpy) 自组合,形成MEPE.
- 与二甲基酸盐 (DHP) 进行序列组装,以形成PAC.
- 热分析 (热重力测量分析,差分扫描热量计) 和磁性测量.
主要成果:
- 在加热时,Fe-PAC呈现出不可逆转的,几乎完全 (95%) 的自旋交叉,从低自旋到高自旋状态,伴随着颜色变化.
- 在Fe-PAC中的SCO与两矩阵的融化和相关的结构变化有关.
- 在冷却时,Fe-PAC不会重新组装,但可以通过溶解回收;Ni-PAC显示了类似的结构变化,但没有SCO.
结论:
- 在Fe-PAC中的液晶矩阵对于实现完全和不可逆转的SCO.至关重要.
- 相比之下,Fe-MEPE的固态架构限制了结构变化,导致不完整的SCO取决于样本历史和溶剂含量.
- 这项研究突出了两矩阵在控制金属超分子材料中SCO特性中的作用.
相关概念视频
Polymer Classification: Crystallinity
Unlike ionic or small covalent molecules, polymers do not form crystalline solids due to the diffusion limitations of their long-chain structures. However, polymers contain microscopic crystalline domains separated by amorphous domains.
Crystalline domains are the regions where polymer chains are aligned in an orderly manner and held together in proximity by intermolecular forces. For example, chains in the crystalline domains of polyethylene and nylon are bound together by van der Waals...
Crystalline domains are the regions where polymer chains are aligned in an orderly manner and held together in proximity by intermolecular forces. For example, chains in the crystalline domains of polyethylene and nylon are bound together by van der Waals...
Cationic Chain-Growth Polymerization: Mechanism
The cationic polymerization mechanism consists of three steps: initiation, propagation, and termination. In the initiation step of the polymerization process, the π bond of a monomer gets protonated by the Lewis acid catalyst, which is formed from boron trifluoride and water. The protonation of the π bond generates a carbocation stabilized by the electron‐donating group. In the propagation step, the π bond of the second monomer acts as a nucleophile and attacks the generated carbocation,...
Phase Transitions: Melting and Freezing
Heating a crystalline solid increases the average energy of its atoms, molecules, or ions, and the solid gets hotter. At some point, the added energy becomes large enough to partially overcome the forces holding the molecules or ions of the solid in their fixed positions, and the solid begins the process of transitioning to the liquid state or melting. At this point, the temperature of the solid stops rising, despite the continual input of heat, and it remains constant until all of the solid is...
Phase Transitions
Whether solid, liquid, or gas, a substance's state depends on the order and arrangement of its particles (atoms, molecules, or ions). Particles in the solid pack closely together, generally in a pattern. The particles vibrate about their fixed positions but do not move or squeeze past their neighbors. In liquids, although the particles are closely spaced, they are randomly arranged. The position of the particles are not fixed—that is, they are free to move past their neighbors to occupy...
Phase Transitions
A phase transition is the process in which a substance changes from one state of matter to another, like from a solid to a liquid, liquid to gas, or vice versa, at a specific temperature and under given pressure conditions. This change is spontaneous and is affected by alterations in temperature and pressure. These parameters impact the strength of the forces between molecules (intermolecular forces) in the substance.During a phase transition, both the initial and final phases of the substance...
Anionic Chain-Growth Polymerization: Mechanism
The mechanism for anionic chain-growth polymerization involves initiation, propagation, and termination steps. In the initiation step, a nucleophilic anion, such as butyl lithium, initiates the polymerization process by attacking the π bond of the vinylic monomer. As a result, a carbanion, stabilized by the electron‐withdrawing group, is generated. The resulting carbanion acts as a Michael donor in the propagation step and attacks the second vinylic monomer, which acts as a Michael acceptor.


