Image time-correlation, dynamic light scattering, and birefringence for the study of the response of anisometric colloids to external fields

Kang, Kyongok

doi:10.1063/1.3589856

Cited by 25 publications

(40 citation statements)

References 30 publications

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“…1(a). Equilibration times and the texture dynamics after equilibration are quantified by means of image time-correlation spectroscopy [35,36]. From time traces of the transmitted intensity as recorded by the CCD camera, we compute intensity correlation functions, which we will refer to as ''image timecorrelation functions'' C V ðtÞ (the index ''V'' stands for video).…”

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confidence: 99%

Glass Transition in Suspensions of Charged Rods: Structural Arrest and Texture Dynamics

Kang

Dhont

2013

Phys. Rev. Lett.

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We report on the observation of a glass transition in suspensions of very long and thin, highly charged colloidal rods (fd-virus particles). Structural particle arrest is found to occur at a low ionic strength due to caging of the charged rods in the potential setup by their neighbors through long-ranged electrostatic interactions. The relaxation time of density fluctuations as probed by dynamic light scattering is found to diverge within a small concentration range. The rod concentration where structural particle arrest occurs is well within the full chiral-nematic state, far beyond the two-phase isotropic-nematic coexistence region. The morphology of the suspensions thus consists of nematic domains with various orientations. We quantify the dynamics of the resulting texture with image-time correlation spectroscopy. Interestingly, the decay times of image correlation functions are found to diverge in a discontinuous fashion at the same concentration of charged rods where structural particle arrest is observed. At the glass-transition concentration, we thus find both structural arrest and freezing of the texture dynamics.

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confidence: 99%

Glass Transition in Suspensions of Charged Rods: Structural Arrest and Texture Dynamics

Kang

Dhont

2013

Phys. Rev. Lett.

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“…The time-scale is the time interval during which melting and forming of nematic domains occurs, while the length-scale is the maximum size of the domains. Detailed measurements of the characteristic time for melting and domain formation are performed through image-time correlation spectroscopy, where transmitted-light correlation functions are constructed from time-resolved CCD images [27] the principle of which is explained in Figure 2. Constructing correlation functions from CCD microscopy images of transmitted light has been proposed and used to study the dynamics of slow dynamical modes in colloidal systems and foams in Cerbino and Trappe [28], Duri et al [29].…”

Section: Electric-field Induced Phase/state Diagram Of Suspensions Ofmentioning

confidence: 99%

“…Away from the transition line there is a fast dynamical state D f that is indicated with a blue point. To probe the dynamics of the melting and reforming nematic domains, image-time correlation functions are construction from time-resolved CCD images [27]. The construction of correlation functions from CCD images of transmitted light has also been proposed in Cerbino and Trappe [28], Duri et al [29].…”

Section: Image-time Correlation Spectroscopy In Low-frequency Inducedmentioning

confidence: 99%

“…Then the decay rate of correlation functions is used to characterize the dynamics of textures. For data acquisition, a time binning (or time interval), a total number of frames, and the region of interest are optimized [27]. Image-time correlation functions are shown in Figure 2C, together with fits to a stretched exponential.…”

Section: Image-time Correlation Spectroscopy In Low-frequency Inducedmentioning

confidence: 99%

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Electric-field induced microdynamics of charged rods

Kang

2014

Front. Phys.

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Electric-field induced phase/state transitions are observed in AC electric fields with small amplitudes and low frequencies in suspensions of charged fibrous viruses (fd), which are model systems for highly charged rod-like colloids. Texture-and particle-dynamics in these field-induced states, and on crossing transition lines, are explored by image time-correlation and dynamic light scattering, respectively. At relatively low frequencies, starting from a system within the isotropic-nematic coexistence region, a transition from a nematic to a chiral nematic is observed, as well as a dynamical state where nematic domains melt and reform. These transitions are preliminary due to field-induced dissociation/association of condensed ions. At higher frequencies a uniform state is formed that is stabilized by hydrodynamic interactions through field-induced electro-osmotic flow where the rods align along the field direction. There is a point in the field-amplitude vs. frequency plane where various transition lines meet. This point can be identified as a "non-equilibrium critical point," in the sense that a length scale and a time scale diverge on approach of that point. The microscopic dynamics exhibits discontinuities on crossing transition lines that were identified independently by means of image and signal correlation spectroscopy.

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“…The electrical cell consists of two optical, flat ITO electrodes, with a spacing of typically 1.5 mm. The several phases and states are characterized by means of various experimental methods, such as the image-time correlation, dynamic light scattering, and electric birefringence [9] [10]. The various phases and states are shown in Figure 2, in the applied field amplitude versus frequency plane.…”

Section: Electric Phase/state Diagrammentioning

confidence: 99%

Charged Colloidal Rods Out of Equilibrium

Kang¹

2015

ACES

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This article is a comprehensive overview of the ongoing research of the author on charged colloidal rods out of equilibrium, under external electric fields and at high concentrations around the glass transition. The suspensions of fd-virus particles are used as a model system for charged colloidal rods, which exhibit several disorder-order (and liquid-crystalline) phase transitions. When a low AC electric field is applied to suspensions in isotropic-nematic coexistence concentration, with frequencies that are sufficiently low to polarize the electric double layer and the layer of condensed ions, various phases/states are induced: a chiral nematic, a dynamical state where nematic domains persistently melt and form, and a uniform homeotropic phase. A point in the field-amplitude versus frequency diagram, where various transitions lines meet, can be identified as a non-equilibrium critical point. Without an electric field, at high concentrations of charged fd-rods, various self-assembled orientation textures are found beyond the isotropic-nematic coexistence regions, and a glass transition is observed on approach and within the glass state that are probed. The presented system exhibits transient behaviors of repulsive glasses and slow dynamics out of equilibrium.

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Image time-correlation, dynamic light scattering, and birefringence for the study of the response of anisometric colloids to external fields

Cited by 25 publications

References 30 publications

Glass Transition in Suspensions of Charged Rods: Structural Arrest and Texture Dynamics

Glass Transition in Suspensions of Charged Rods: Structural Arrest and Texture Dynamics

Electric-field induced microdynamics of charged rods

Charged Colloidal Rods Out of Equilibrium

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