Coherent X-ray scattering reveals nature of dynamical transitions in nanoparticle-polymer suspensions

POLYMER

卷:105

Article

Chandran, Sivasurender^1,2  Begam, N.¹  Sprung, M.³  Basu, J. K.¹ 

[1] Indian Inst Sci, Dept Phys, Bangalore 560012, Karnataka, India

[2] Albert Ludwigs Univ Freiburg, Inst Phys, D-79104 Freiburg, Germany

[3] Deutsch Elektronen Synchrotron DESY, Notkestresse 85, D-22607 Hamburg, Germany

关键词: Dynamics;    Rheology;    Suspensions;    Nanoparticle-polymer mixtures;    X-ray photon correlation spectroscopy;    Diffusing wave spectroscopy;   

DOI  :  10.1016/j.polymer.2016.07.048

来源: Elsevier

【 摘 要 】

We report the microrheological behavior and dynamics of the suspensions of polystyrene-grafted gold nanoparticles (PGNPs) mixed with linear polystyrene (PS) as a function of the PS concentration and size asymmetry parameter, xi (=M-g/M-m, with M-g and M-m being the grafted and free chain molecular weights, respectively) = 2.76 and 0.14. Diffusive wave spectroscopy (DWS) is used for measuring the frequency dependent micro-rheology parameter, the loss modulus G ''(omega)(similar to omega(alpha)). For suspensions with xi = 0.14 a transition of a, from similar to 1 to similar to 1.6, is observed at a critical fraction of added polymers. On the other hand, a is always similar to 1 for the suspensions with xi = 2.76. Corresponding x-ray photon correlation spectroscopy (XPCS) data on the same samples reveals a sharp transition in the nature of dynamics of PGNPs, from exponential to logarithmic, in suspensions with x = 0.14, while for suspensions with xi = 2.76 this dynamical transition is not observed. Interestingly, the dynamical transition in xi = 0.14 based samples occurs at the same fraction of added polymers, where the transition of a from similar to 1 to similar to 1.6 was observed, thus providing a clear correlation between microscopic dynamics and micro-rheology. The conformational transitions of the grafted polymers is found to be the reason behind the observed differences in the dynamic behavior of the two systems. The important role of advanced x-ray scattering techniques in unravelling subtle aspects of nanoscale complex polymer and soft colloidal dynamics is thus revealed. (C) 2016 Elsevier Ltd. All rights reserved.

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