“配位耦合”玻璃化转变体系的焓弛豫特征及能量耗散机理研究

In this proposal, we present a new solution possible for enhancing the polymeric damping property and decoupling height and width of the damping peak by tuning the activation free energy of segmental cooperative rearrangement from entropic to enthalpic-dominated mode so as to independently mediate the dynamic fragility (m) and glass transition temperature (Tg). To testify the idea, model polymers are copolymerized to components with side groups capable of hydrogen bonding (HB) and ionic coordination. HB donors and ionic counterparts with high cohesive energy density are introduced to create so-called “ligand-coupled” glass-forming polymers which provide an intriguing temperature-sensitive 3D-coupled structure. Enthalpy relaxation accompanying segmental cooperative rearrangement will be tested to correlate the most basic relaxation mode with the “ligand-coupled” enthalpy change. Meanwhile, by comparing with results of broadband dielectric measurements and molecular dynamics simulations, we will go forward to investigate systematically the effects of stiffness and symmetry of the side groups, species and number of HBs, and the coordination structure of ionomers on the coupling parameter of structure relaxation, the ratio of Tg/m and the recovered enthalpy. Analysis and discussion will focus on the relationships between multi-scaled relaxation-induced energy consumption and their coupling parameters, and on the correlation of the irreversible internal friction to the reversible recovered enthalpy. It is expected that our results are not only theoretically and practically important for clarifying the molecular origin of the energy dissipation from both dynamic and thermodynamic viewpoints, and thus providing a new molecular design criterion for developing high-quality damping materials, but also devoted to identifying the thermodynamic origin of the kinetic fragility in the glass-forming polymers.

针对高分子阻尼材料内耗与模量、峰高与峰宽相互受限，本项目认为，解决问题的关键在于如何将玻璃化协同转变的激活自由能由熵变调整为焓变主导，实现Tg和脆度m独立调控。为了验证新设想，我们在模型共聚物中引入具有氢键化和离子化功能的侧基，通过与具有高内聚能密度的氢键供体和反离子配体“配位耦合”形成温度敏感的三维强耦合结构。拟从协同重排运动的焓弛豫特征入手，将最基本弛豫形式与“配位耦合”焓变关联，结合宽频介电谱测试和分子动力学模拟，系统考察侧基刚性和对称性、氢键种类和数量以及离聚体配位结构对弛豫耦合因子、Tg/m和弛豫焓的影响规律，探讨多尺度能量耗散与耦合因子、不可逆内耗与可逆弛豫焓的内在关联。研究成果不仅有助于从热力学和动力学两个方面明确能量耗散分子机理，为开发高性能减振吸音材料提供分子设计新思路，而且对于剖析协同重排动力学的热力学根源，深入理解聚合物的玻璃化转变本质具有很好的学术价值。

本项目在模型聚合物中引入具有氢键化和离子化功能的侧基，系统考察了侧基刚性和对称性、氢键种类和数量以及离聚体配位结构对玻璃化转变温度Tg、动力学脆度m和弛豫焓ΔHR的影响规律，探讨多尺度能量耗散与耦合因子、不可逆内耗与可逆弛豫焓的内在关联。主要成果包括以下五个方面：.（1）实验证实，小分子桥接“氢键耦合”和金属离子“配位耦合”有可能在提高体系Tg的同时，有效降低m，从而突破WLF方程关于所有聚合物Tg/m保持恒定这一基本规律。改变Tg/m比值关键在于调控氢键强度和金属离子配位强度，降低刚性分子链间的耦合因子。.（2）实验证实，提高聚合物体系的Tg/m值有助于增大阻尼峰面积TA，为突破内耗与模量、峰高与峰宽相互受限，开发高性能减振吸音材料提供新的分子设计思路。.（3）首次发现，小分子桥接“氢键耦合”体系的阻尼衰减速度与聚合物基体的玻璃化转变温度及玻璃化转变相关的α松弛及βJG松弛过程无关，与小分子种类和含量也没有直接的关系，但是与快次级松弛（βfast）时间直接关联，说明杂化材料阻尼性能衰减取决于分子间氢键断裂，与小分子自发凝聚的长程迁移没有直接关系。该研究成果不仅为厘清阻尼增效机理提供了“配位耦合”与分子内耗关联的直接证据，而且为快速检测阻尼材料的使用寿命提供了一种全新的方法。.（4）首次发现弛豫焓ΔHR与协同重排过剩熵ΔSex,α(Tg)之间存在ΔHR=0.05Tg˙ΔSex,α(Tg)，为非晶聚合物测算α弛豫过剩熵提供了新方法。进一步研究发现，利用ΔHR与协同重排过剩熵ΔSex,α(Tg)之间关联式，动力学脆度m与热容差ΔCp和弛豫焓ΔHR等热力学参数的关联符合Adam-Gibbs理论预测。玻璃化转变的本质是动力学过程，但是其热力学根源争议不断。我们的实验结果不仅为玻璃化转变的热力学根源提供了新证据，而且还有可能将不可逆的摩擦耗能与可逆的弛豫焓ΔHR建立关联，阐明内耗调控机制提供理论依据。.（5）长侧链的PnAMA、含金属离子团簇体的离聚物和纳米粒子界面层存在ΔHR值异常偏低现象，导致动力学脆度m和热力学参数Tg·ΔCp/ΔHR无法关联偏离Adam-Gibbs理论预测。研究发现，ΔHR值异常偏低源于纳米相分离，而且只有当纳米微区尺寸与本体Tg处CRR尺寸相当时ΔHR才会异常降低。.