The vibrational density of states of a disordered gel model

Abstract

We investigate the vibrational density of states (vDOS) in harmonic approximation of a binary mixture of colloidal patchy particles with two and three patches for different relative compositions $x_2$. At low temperature, this system forms a thermo-reversible gel, i.e. a fully bonded network of chains of two-patches particles, in which the branching points are provided by three-patches particles. For all the compositions we find in the vDOS a pronounced peak at low frequency whose height grows on increasing the fraction of two-functional particles, or equivalently with the average length of the chains. To identify the various spectral features, we compare the vDOS of the whole system with the one of small representative structures of the network and with the vDOS of a long linear chain of two-patches particles and we find that these structures are indeed able to rationalize the various peaks in the vDOS of the full system. At large $x_2$ the vDOS of the gel and of the long chain show remarkable similarities. Analyzing the dispersion relations and the spectrum of the linear chain we show that the excess of low frequency modes, the analog of the boson peak in glassy disordered systems, arises from the strong coupling between rotations and translations.

19 pages, 8 figures

References in corpus (5)

• Phase diagram of patchy colloids: towards empty liquids
• Colloidal Gels: Equilibrium and Non-Equilibrium Routes
• Theoretical and numerical study of the phase diagram of patchy colloids: ordered and disordered patch arrangements
• Structural Relaxation of a Gel Modeled by Three Body Interactions
• Randomness-Induced Redistribution of Vibrational Frequencies in Amorphous Solids

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• Computing the phase diagram of binary mixtures: a patchy particle case study
• On the normal modes of weak colloidal gels
• Structure and elasticity of model disordered, polydisperse and defect-free polymer networks
• Structural, mechanical, and vibrational properties of particulate physical gels