Binary mixtures of rod-like colloids

In this work we investigate the shear induced instabilities occurring in colloidal binary mixtures of rigid anisotropic particles. To this end, we derive a theoretical framework including equilibrium and non-equilibrium methods. The equilibrium description is derived on the basis of microscopic density functionals in the Parsons-Lee and Ramakrishnan-Youssuf approximations. The result is a mesoscopic free energy given in terms of a set of orientational order parameter tensors (one for each component of the mixture) and their gradients. In this regard, our theory may be seen as an extension of the Landau-de Gennes theory to mixtures. However, our theory incorporates microscopic information, particularly the aspect ratios and number densities characterizing the components of the mixture. Specializing to binary mixtures of rod-like particles, these functionals are then used to explore the stability of isotropic and nematic equilibrium phases in terms of composition and rod lengths. We extend the description to consider non-equilibrium phenomena by combining our equilibrium theory with the theory of irreversible processes. Thus, extending the Doi-Hess approach to the study of binary mixtures under shear. As a result, we obtain a set of hydrodynamic equations which take into account the competition between flow-induced effects on the alignment and the relaxation of the entire system towards equilibrium. Based on these hydrodynamic equations we turn to the study of shear induced phenomena under planar Couette flow geometry. These investigations are divided in two parts. First, we focus on a one-component system and study the underlying relation existing between shear and stress. We observed that disregarding the equilibrium (un-sheared) state of the system (close to the isotropic-nematic transition or deep in its nematic phase), we find several new types of shear banded states characterized by regions with regular oscillatory orientational dynamics. Finally we concentrate on binary mixtures. Here, after exploring a vast range of parameters, we observe several dynamical states appearing in the system. These dynamical states include the synchronization of of in-and out-of-the shear plane oscillatory states of the two components. Interestingly, for a specific set of parameters, we observe the appearance of symmetry breaking behavior where both components of the mixture display different in-phase oscillatory states.

Author dc:creator

• Lugo-Frías, Rodrigo

Advisor dc:contributor.advisor

• Klapp, Sabine

Licence dc:rights.uri

• https://creativecommons.org/licenses/by/4.0/

Language dc:language.iso

en

Identifier URI

http://dx.doi.org/10.14279/depositonce-5535

OAI identifier oai:identifier

oai:depositonce.tu-berlin.de:11303/5948