Vorticity banding in rodlike virus suspensions

Harvard University, Cambridge, Massachusetts, United States
Physical Review E (Impact Factor: 2.33). 09/2006; 74(2 Pt 2):026307. DOI: 10.1103/PhysRevE.74.026307
Source: PubMed

ABSTRACT Vorticity banding under steady shear flow is observed in a suspension of semiflexible colloidal rods (fd virus particles) within a part of the paranematic-nematic biphasic region. Banding occurs uniformly throughout the cell gap within a shear-rate interval (.gamma-, .gamma+) , which depends on the fd concentration. For shear rates below the lower-border shear rate .gamma- only shear elongation of inhomogeneities, which are formed due to paranematic-nematic phase separation, is observed. Within a small region just above the upper-border shear rate .gamma+ , banding occurs heterogeneously. An essential difference in the kinetics of vorticity banding is observed, depending on the morphology of inhomogeneities formed during the initial stages of the paranematic-nematic phase separation. Particle tracking and polarization experiments indicate that the vorticity bands are in a weak rolling flow, superimposed on the applied shear flow. We propose a mechanism for the origin of the banding instability and the transient stability of the banded states. This mechanism is related to the normal stresses generated by inhomogeneities formed due to the underlying paranematic-nematic phase transition.

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Star polymers with tunable number and size of arms, and thus interactions, represent ideal model systems for exploring the regime of soft material behaviour that interpolates between hard spheres and polymeric coils. This regime is characterized by a rich variety of properties that reflect the combination of polymeric and colloidal features. In this review we discuss some of these properties, and in particular the host of kinetic frustration phenomena encountered with such ultrasoft particles. They include soft colloidal glass-like transitions (a kind of jamming), induced upon increasing volume fraction (by heating or increasing the mass concentration), and the glass melting upon application of thermal (depletion) forces.
  • [Show abstract] [Hide abstract]
    ABSTRACT: We review the effect of shear flow on the phase behavior and structure of colloidal dispersions with increasing degree of complexity. We discuss dispersions of colloidal rods, stiff living polymers like wormlike micelles, and colloidal platelets. In addition, a review is presented on sheared binary dispersions. For all cases we discuss the interplay between thermodynamic instabilities and hydrodynamic instabilities.
    The European Physical Journal Special Topics 11/2013; 222(11):2739-2755. DOI:10.1140/epjst/e2013-02055-2 · 1.76 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Carboxymethylcellulose (CMC) and xanthan gum were studied as dispersants for microfibrillated cellulose (MFC) suspension using a rotational rheometer and imaging methods. The imaging was a combination of photography and optical coherence tomography (OCT). Both polymers dispersed MFC fibers, although CMC was more effective than xanthan gum. The negatively charged polymer chains increased the viscosity of the suspending medium and acted as buffers in between the negatively charged fibers. This behavior decreased the number and strength of contacts between the fibers and subsequently dispersed the flocs. The stronger separation of the fibers was reflected in the frequency sweep where the MFC/polymer suspensions had lower gel strength than pure MFC suspension. Dispersing effect was also observed in the flow measurements, where the floc size was more uniform with polymers in the decelerating flow and after long, slow constant shear, which normally induces a heterogeneous structure with large flocs into the MFC suspension.
    06/2014; 106:283-92. DOI:10.1016/j.carbpol.2014.02.032

Full-text (3 Sources)

Available from
Aug 22, 2014