Kavli Affiliate: Naomi S. Ginsberg
| First 5 Authors: Christian P. N. Tanner, Vivian R. K. Wall, Mumtaz Gababa, Joshua Portner, Ahhyun Jeong
| Summary:
The ability to understand and ultimately control the transformations and
properties of various nanoscale systems, from proteins to synthetic
nanomaterial assemblies, hinges on the ability to directly elucidate their
dynamics on their characteristic length and time scales. Here, we use MHz X-ray
photon correlation spectroscopy (XPCS) to directly elucidate the characteristic
microsecond-dynamics of density fluctuations of semiconductor nanocrystals
(NCs), not only in a colloidal dispersion but also in a liquid phase consisting
of densely packed, yet mobile, NCs with no long-range order. By carefully
disentangling X-ray induced effects, we find the wavevector-dependent
fluctuation rates in the liquid phase are suppressed relative to those in the
colloidal phase and to those in experiments and hydrodynamic theories of
densely packed repulsive particles. We show that the suppressed rates are due
to a substantial decrease in the self-diffusion of NCs in the liquid phase,
which we attribute to explicit attractive interactions. Via comparison with
simulations, we find that the extracted strength of the attractions explains
the stability of the liquid phase, in contrast to the gelation observed via
XPCS in many other charged colloidal systems. This work opens the door to
elucidating fast, condensed phase dynamics in a variety of complex fluids and
other nanoscale soft matter systems, such as densely packed proteins and
non-equilibrium self-assembly processes.
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