title: Structure and Dynamics of Bimodal Colloidal Dispersions in a Low-Molecular-Weight Polymer Solution.
abstract: We present an experimental study of the structural and dynamical properties of bimodal, micrometer-sized colloidal dispersions (size ratio ≈ 2) in an aqueous solution of low-molecular-weight polymer (polyethylene glycol 2000) using synchrotron ultra-small angle X-ray scattering (USAXS) and USAXS-based X-ray photon correlation spectroscopy. We fixed the volume fraction of the large particles at 5% and systematically increased the volume fraction of the small particles from 0 to 5% to evaluate their effects on the structure and dynamics. The bimodal dispersions were homogenous through the investigated parameter space. We found that the partial structure factors can be satisfactorily retrieved for the bimodal colloidal dispersions using a Percus-Yevick hard-sphere potential when the size distributions of the particles were taken into account. We also found that the partial structure factor between the large particles did not exhibit a significant variation with increasing volume fraction of the small particles, whereas the isothermal compressibility of the binary mixture was found to decrease with increasing volume fraction of the small particles. The dynamics of single-component large-particle dispersion obey the principles of de Gennes narrowing, where the wave vector dependence of the interparticle diffusion coefficient is inversely proportional to the interparticle structure factor. The dynamics of the bimodal dispersions demonstrate a strong dependence on the fraction of small particles. We also made a comparison between the experimental effective dynamic viscosity of the bimodal dispersion with the theoretical predictions, which suggest that the complex mutual interactions between the large and small particles have a strong effect on the dynamic behaviors of bimodal dispersions.
authors.affiliation: Material Measurement Laboratory, National Institute of Standards and Technology , Gaithersburg, Maryland 20899, United States.
authors.forename: Fan
authors.identifier: 0000-0003-1248-0278
authors.initials: F
authors.lastname: Zhang
authors.affiliation: Material Measurement Laboratory, National Institute of Standards and Technology , Gaithersburg, Maryland 20899, United States.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Allen
authors.affiliation: Material Measurement Laboratory, National Institute of Standards and Technology , Gaithersburg, Maryland 20899, United States.
authors.forename: Lyle E
authors.initials: LE
authors.lastname: Levine
authors.affiliation: Department of Chemical Engineering, National Tsing Hua University , Hsinchu, Taiwan 30013, Republic of China.
authors.forename: De-Hao
authors.initials: DH
authors.lastname: Tsai
authors.affiliation: X-ray Science Division, Advanced Photon Source, Argonne National Laboratory , Argonne, Illinois 60439, United States.
authors.forename: Jan
authors.initials: J
authors.lastname: Ilavsky