Yoo Pil J, Zacharia Nicole S, Doh Junsang, Nam Ki Tae, Belcher Angela M, Hammond Paula T
Department of Chemical Engineering and SKKU Advanced Institute of Nanotechnology, Sungkyunkwan University, Suwon 440-746, Republic of Korea.
ACS Nano. 2008 Mar;2(3):561-71. doi: 10.1021/nn700404y.
The phenomenon of interdiffusion of polyelectrolytes during electrostatic layer-by-layer assembly has been extensively investigated in the past few years owing to the intriguing scientific questions that it poses and the technological impact of interdiffusion on the promising area of electrostatic assembly processes. In particular, interdiffusion can greatly affect the final morphology and structure of the desired thin films, including the efficacy and function of thin film devices created using these techniques. Although there have been several studies on the mechanism of film growth, little is known about the origin and controlling factors of interdiffusion phenomena. Here, we demonstrate a simple but robust method of observing the process of polyelectrolyte interdiffusion by adsorbing charged viruses onto the surface of polyelectrolyte multilayers. The surface mobility of the underlying polycation enables the close-packing of viruses adsorbed electrostatically to the film so as to achieve a highly packed structure. The ordering of viruses can be controlled by the manipulation of the deposition pH of the underlying polyelectrolyte multilayers, which ultimately controls the thickness of each layer, effective ionic cross-link density of the film, and the surface charge density of the top surface. Characterization of the films assembled at different pH values were carried out to confirm that increased quantities of the mobile polycation LPEI incorporated at higher pH adsorption conditions are responsible for the ordered assembly of viruses. The surface mobility of viruses atop the underlying polyelectrolyte multilayers was determined using fluorescence recovery after photobleaching technique, which leads to estimate of the diffusion coefficient on the order of 0.1 microm(2)/sec for FITC-labeled viruses assembled on polyelectrolyte multilayers.
在过去几年中，由于聚电解质在静电逐层组装过程中相互扩散现象引发了有趣的科学问题，且这种相互扩散对静电组装工艺这一前景广阔的领域具有技术影响，因此该现象受到了广泛研究。特别是，相互扩散会极大地影响所需薄膜的最终形态和结构，包括使用这些技术制造的薄膜器件的功效和功能。尽管已经有几项关于薄膜生长机制的研究，但对于相互扩散现象的起源和控制因素却知之甚少。在这里，我们展示了一种简单而可靠的方法，即通过将带电病毒吸附到聚电解质多层膜表面来观察聚电解质相互扩散的过程。底层聚阳离子的表面迁移率使得静电吸附到薄膜上的病毒能够紧密堆积，从而形成高度致密的结构。病毒的排列可以通过控制底层聚电解质多层膜的沉积pH值来实现，这最终控制了每层的厚度、薄膜的有效离子交联密度以及顶层的表面电荷密度。对在不同pH值下组装的薄膜进行表征，以确认在较高pH吸附条件下掺入的可移动聚阳离子LPEI数量的增加是病毒有序组装的原因。使用光漂白后荧光恢复技术测定了底层聚电解质多层膜上病毒的表面迁移率，这使得能够估计在聚电解质多层膜上组装的FITC标记病毒的扩散系数约为0.1平方微米/秒。
