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Introduction |
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Janus particles
are microscopic species comprised of two or more regions of physical, or more
commonly, chemical difference. Many potential uses exist for such species
ranging from solar cells to new anti cancer treatments, and the ability to
better control drug delivery with selective regions on the particle[]. The simplest
Janus particle that one can synthesize is a sphere with chemically or
physically differing hemispheres. More complicated anisotropic shaped Janus
particles are possible though; one of interest is the Janus Rod. The simplest
scenario for modeling a Janus Rod is a Rigid Tangent Bead model as shown in
figure 1.
Figure 1. –
Four site rigid rod tangent bead model of a Janus Particles where green sites
are attractive and red sites repulsive and no interaction other than Hard
sphere repulsion between dissimilar sites. Previous
studies by Mukta Tripathy and Kenneth S. Schweizer on the system described in
figure 1 were conducted using the Reference Interaction Site Model (RISM).
RISM is an integral equation theory which is an extension of the traditional Ornstein
Zernike (OZ) equation to particles with multiple sites. For this simple
model, short range attractive Square Well and repulsive step potentials were
used to describe the different sites. Microphase separation was observed and
based off of the radial distribution function, g(r) and the static structure factor, S(k), probable structures were predicted and one example can be
seen in figure 2.
Figure 2. –
Microphase separated Janus rods predicted based off of previous RISM
analysis. II. – Present Work RISM is a
powerful, computationally inexpensive, and well supported approach to liquid
state theory; however, there is no direct visualization of the structures. In
an effort to support or refute the proposed microphase separated structures,
Monte Carlo simulations of the same system were carried out. |
