纳米颗粒在Polymer网络中扩散的双弹簧模型
A Double-Spring Model for Nanoparticle Diffusion in a Polymer Network
摘要：
纳米粒子在聚合物网络中的输运作为描述生命系统中各种结构的典型简化模型，在生物医学工程和纳米技术中具有重要意义。预测有序网络中NP分子的有效扩散系数一直是这一前沿领域的研究热点。本文采用单粒子耗散粒子动力学（DPD）方法，研究了不同纳米粒子半径和网络刚度条件下纳米粒子在非缠结聚合物网络中的扩散。研究发现，由于结偏离引起的形变对纳米粒子跳跃过程中克服的势垒$U$有显著的贡献，对于较大的纳米粒子和较低的网络刚度，它的作用超过了环拉伸引起的应变能.基于连续介质力学理论的分析表明，这种变形能与结偏之间的关系可以用非线性弹簧来描述。考虑到环路拉伸和结偏离的影响，提出了一个双弹簧模型来描述有序网络中纳米粒子的扩散率。理论预测与我们的数值模拟是一致的，并与现有的调查定性一致。该模型有助于提高我们对纳米粒子在复杂生物环境中的动力学行为的理解，并为设计生物医学应用提供理论指导。
英文摘要：
The transport of nanoparticles (NPs) in polymer networks, as a typical simplified model describing various structures in living systems, is profoundly important in biomedical engineering and nanotechnology. Predicting the effective diffusivity of NP confined in an ordered network has been an intriguing focus in this frontier field. In the present study, the diffusion of NPs in an unentangled polymer network for different NP radii and network stiffness is numerically investigated by single particle dissipative particle dynamics (DPD). It is found that, the deformation due to the junction deviation contributes significantly to the the potential barrier $U$ for the NP to overcome during hopping, and it is dominated over the strain energy induced by loop stretching for larger NPs and lower network rigidity. Analyses based on the theory of continuum mechanics reveal that the relation between this deformed energy and the junction deviation can be described by a non-linear spring. Taking into account both effects of the loop stretching and junction deviation, a double-spring model is proposed to characterize the diffusivity of the NPs in the ordered network. The theoretical prediction is in good agreement with our numerical simulations, and qualitatively consistent with the investigations available. This model is helpful to improve our understanding on the dynamic behavior of nanoparticle in complex biological environment, and provide theoretical guidance in designing biomedical applications.
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