A microstructure-based approach to modeling electrostriction that accounts for variability in spatial locations of domains
A microstructure-based approach to modeling electrostriction that accounts for variability in spatial locations of domains
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一种基于微结构的电致伸缩建模方法，可解释域空间位置的变化
DOI：
10.1016/j.jmps.2018.09.024
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发表时间：
2019
影响因子：
5.3
通讯作者：
von Lockette, Paris
中科院分区：
文献类型：
--
作者：
Erol, Anil;Ahmed, Saad;Ounaies, Zoubeida;von Lockette, Paris
基于聚偏氟乙烯（PVDF）的弛豫铁电聚合物家族的发现由于其高的电致伸缩应变和相对低的磁滞损耗而引起了人们的关注。这些RFE聚合物表现出复杂的微观结构，包含结晶域和无定形域;结晶域的相互作用驱动这些EAP的电致伸缩行为，而无定形域决定材料的机械行为。此外，结晶域在空间上和取向上分布在无定形介质上，进一步使RFE聚合物的形态复杂化。虽然一些研究都集中在实验和计算调查不同的结晶相之间的相互作用，这个家庭的RFE，电致伸缩模型，代表双相RFE聚合物的微观结构的变异性是缺乏的。所提出的模型的目的是链接到所观察到的机电耦合的半结晶微结构。能量密度函数被构造用于EAP的代表性体积元（RVE），包括用于每个相、结晶和非晶的项。晶畴之间的相互作用是基于一对偶极子之间的库仑相互作用能。非晶畴的响应是由一个修改的超弹性应力拉伸八链模型预测。然后根据等温机电变形的本构关系分析总自由能，以确定RVE中产生的应力。应变与电场的关系，即电致伸缩，从柯西应力的自平衡条件计算。材料的微观结构是考虑到通过施加偶极能量的半结晶网络模型，其中一个偶极子，代表一个结晶域是由一个无定形介质包围。半结晶RVE经历与相邻微晶的相互作用，这驱动材料的电致伸缩。半结晶网络模型的两个基本情况下，探索研究的结晶域的位置相对于彼此的空间变化的影响。此外，更高保真度的空间位置的描述，通过添加一个概率密度函数（PDF）的偶极子周围的中心偶极子。将该模型与文献中的实验结果进行比较，可以最佳拟合地确定描述PDF的模型参数，例如微观结构本身的方面。这些结果与实验数据吻合得很好，这意味着该模型有能力通过用单个可调参数拟合偶极子分布来推断材料微观结构的关键信息。该模型是独特的，因为它的结晶域的描述是服从光谱散射技术的直接测量。因此，在模型中的可调参数被链接到可量化的物理特性，如偶极矩和空间分布参数的大小，该模型也可以用来阐明网络形态的最佳拟合这些物理意义的可调参数的实验数据，可能提供了一个处理之间的联系，为未来的研究人员的结构性质的关系。
The discovery of polyvinylidene fluoride (PVDF) based family of relaxor ferroelectric (RFE) polymers has attracted attention due to their high electrostrictive strain and relatively low hysteresis loss. These RFE polymers exhibit complex microstructures containing both crystalline domains and amorphous domains; the interactions of the crystalline domains drive the electrostrictive behavior of these EAPs, while the amorphous domains dictate the mechanical behavior of the materials. Furthermore, the crystalline domains are spatially and orientationally distributed across the amorphous medium, further complicating the morphology of RFE polymers. Although a number of studies have focused on experimental and computational investigation of the interaction among different crystalline phases of this family of RFE, electrostriction models that represent the variabilities in the microstructure of biphasic RFE polymers are lacking. The proposed model aims to link the semicrystalline microstructure to the observed electromechanical coupling. An energy density function is constructed for a representative volume element (RVE) of the EAP, including a term for each phase, crystalline and amorphous. The interaction of the crystalline domains is based on the Coulomb interaction energy between a pair of dipoles. The responses of the amorphous domains are predicted by a modified hyperelastic stress–stretch eight-chain model. The total free energy is then analyzed under constitutive laws for an isothermal electromechanical deformation to determine the stresses generated in the RVE. The strain versus electric field, i.e. the electrostriction, relationship is calculated from a self-equilibrium condition of the Cauchy stress. The microstructure of the material is taken into account by applying the dipolar energy to a semicrystalline network model, in which a dipole that represents a crystalline domain is surrounded by an amorphous medium. The semicrystalline RVE experiences interactions with neighboring crystallites, which drives the electrostriction of the material. Two basic cases of the semicrystalline network model are explored to study the effects of spatial variation of crystalline domain locations relative to each other. Furthermore, higher fidelity descriptions of spatial location are introduced through the addition of a probability density function (PDF) of dipoles around a central dipole. Comparing the model to experimental results from the literature allows best-fit determination of the model parameters describing the PDF, e.g. aspects of microstructure, itself. These results, which agree well with experimental data, imply that the model has an ability to infer key information about the microstructure of the material by fitting the distribution of dipoles with a single adjustable parameter. The model is unique in that its descriptions of the crystalline domains is amenable to direct measurement by spectroscopic scattering techniques. Consequently, adjustable parameters in the model are linked to physical characteristics that are quantifiable, such as magnitudes of dipole moments and spatial distribution parameters.The model may also be used to elucidate aspects of network morphology using best fit of these physically meaningful adjustable parameters to experimental data, possibly providing a link between processing-structure-property relationships for future researchers.
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