具有吸引力的胶体复合物的超导导电性
Tunneling conductivity in composites of attractive colloids
摘要：
在导体-绝缘体纳米复合材料中，导电填料分散在绝缘基体中，通过粒子间隧穿或跳跃过程建立电连接。这些系统本质上是非重复性的，并且导电性$σ$对填料性质的功能依赖性的连贯描述，特别是导体-绝缘体转变，需要通过放松固定连接距离的约束来超越通常的连续渗流方法。在这篇文章中，我们考虑分散体的导电球形粒子连接到所有其他的隧穿电导，并受到一个有效的吸引方阱势。我们发现，在低含量的导电填料的$ϕ$的导体-绝缘体转变不确定的行为$σ$在较大的浓度，在显着的对比是由逾渗理论预测。特别是，我们发现，在低$ϕ$的电导率几乎完全由粘性的吸引力，而在较大的$ϕ$值$σ$主要取决于势阱的深度。因此，通过改变电位的范围和深度，同时保持粘性固定，具有类似导体-绝缘体转变的复合材料可以在中间和大的$ϕ$值下显示几个数量级的电导率变化。通过使用最近开发的有效介质理论和临界路径近似，我们解释这种行为的主导隧穿过程，其中涉及粒子间的距离跨越不同区域的方阱流体结构作为$ϕ$是不同的。我们的预测可以在实验中通过改变聚合物纳米复合材料中不同的耗尽剂的电位分布来测试。
英文摘要：
In conductor-insulator nanocomposites in which conducting fillers are dispersed in an insulating matrix the electrical connectedness is established by interparticle tunneling or hopping processes. These systems are intrinsically non-percolative and a coherent description of the functional dependence of the conductivity $σ$ on the filler properties, and in particular of the conductor-insulator transition, requires going beyond the usual continuum percolation approach by relaxing the constraint of a fixed connectivity distance. In this article we consider dispersions of conducting spherical particles which are connected to all others by tunneling conductances and which are subjected to an effective attractive square well potential. We show that the conductor-insulator transition at low contents $ϕ$ of the conducting fillers does not determine the behavior of $σ$ at larger concentrations, in striking contrast to what is predicted by percolation theory. In particular, we find that at low $ϕ$ the conductivity is governed almost entirely by the stickiness of the attraction, while at larger $ϕ$ values $σ$ depends mainly on the depth of the potential well. As a consequence, by varying the range and depth of the potential while keeping the stickiness fixed, composites with similar conductor-insulator transitions may display conductivity variations of several orders of magnitude at intermediate and large $ϕ$ values. By using a recently developed effective medium theory and the critical path approximation we explain this behavior in terms of dominant tunneling processes which involve interparticle distances spanning different regions of the square-well fluid structure as $ϕ$ is varied. Our predictions could be tested in experiments by changing the potential profile with different depletants in polymer nanocomposites.
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