Transport dynamics of complex fluids

Sanggeun Song, Seong Jun Park, Minjung Kim, Jun Soo Kim, Bong June Sung, Sangyoub Lee, Ji Hyun Kim, Jaeyoung Sung

Research output: Contribution to journalArticlepeer-review

33 Scopus citations


Thermal motion in complex fluids is a complicated stochastic process but ubiquitously exhibits initial ballistic, intermediate subdiffusive, and long-time diffusive motion, unless interrupted. Despite its relevance to numerous dynamical processes of interest in modern science, a unified, quantitative understanding of thermal motion in complex fluids remains a challenging problem. Here, we present a transport equation and its solutions, which yield a unified quantitative explanation of the mean-square displacement (MSD), the non-Gaussian parameter (NGP), and the displacement distribution of complex fluids. In our approach, the environment-coupled diffusion kernel and its time correlation function (TCF) are the essential quantities that determine transport dynamics and characterize mobility fluctuation of complex fluids; their time profiles are directly extractable from a model-free analysis of the MSD and NGP or, with greater computational expense, from the two-point and four-point velocity autocorrelation functions. We construct a general, explicit model of the diffusion kernel, comprising one unbound-mode and multiple bound-mode components, which provides an excellent approximate description of transport dynamics of various complex fluidic systems such as supercooled water, colloidal beads diffusing on lipid tubes, and dense hard disk fluid. We also introduce the concepts of intrinsic disorder and extrinsic disorder that have distinct effects on transport dynamics and different dependencies on temperature and density. This work presents an unexplored direction for quantitative understanding of transport and transport-coupled processes in complex disordered media.

Original languageEnglish
Pages (from-to)12733-12742
Number of pages10
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number26
StatePublished - 2019

Bibliographical note

Publisher Copyright:
© 2019 National Academy of Sciences. All rights reserved.


  • Colloidal particles on lipid tube
  • Complex fluids
  • Diffusion kernel correlation
  • Supercooled
  • Thermal motion
  • Water


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