The
significant size distribution of as-synthesized nanomaterials
presents a challenge for reproducable and reliable applications. In
this paper, we report a fluidic-assisted sorted assembly method in
which nanomaterial sorting and enhanced assembly can be achieved simultaneously.
As a proof of concept, a two-dimensional (2D) graphene flake, with
a large size variation, was chosen as the target nanomaterial system.
This study synergizes a novel fluidic assembly design, suspending
a rotating disk over a polydimethylsiloxane (PDMS) substrate, and
a computational fluid dynamics (CFD) model using Ansys CFX to disclose
the mechanism of sorted assembly. By controlling the rotating speed
and the gap between the disk and the substrate, the flow field is
altered. In contrast to centrifugal sorting, where larger particles
move outward, in this study, the size of assembled graphene flake
(average lateral size, X
c) reduces significantly
from the center (X
c = 3 μm) to the
edge of the disk (X
c = 2 μm). The
particle sorting process is dictated by the fluid shear-stress, with
higher shear-stress leading to smaller particles, while the assembly
process is mainly dominated by the pressure field with higher pressure
magnitude leading to better assembly. Near the edge of the disk, enhanced
particle sorting is coupled with an enhanced assembly where a continuous
graphene film with smaller X
c can be formed.
To prove the potential application of this method, an ultrasensitive
strain sensor with one of the lowest detection limits, 0.02%, is demonstrated.
This research presents a novel route toward large-scale and cost-effective
manufacturing of nanomaterial-based flexible electronics.