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 uncover 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. We find the
wavevector-dependent fluctuation rates in the liquid phase are suppressed
relative to those in the colloidal phase and relative to observations 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. Using coarse-grained
simulations, we find that the extracted shape and strength of the interparticle
potential 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 complex fluids
and other nanoscale soft matter, such as densely packed proteins and
non-equilibrium self-assembly processes, in addition to designing microscopic
strategies to avert gelation.
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