Microstructural regimes of colloidal rod suspensions, gels, and glasses

Solomon, Michael J.; Spicer, Patrick T.

doi:10.1039/b918281k

Cited by 259 publications

(257 citation statements)

References 126 publications

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“…In glassy dispersions of colloidal spheres, there is no long-range order but particle caging hinders free diffusion: breaking and reformation of cages dominates the dynamics [3]. The situation is more complex for elongated colloidal particles such as DNA, actin filaments, and filamentous viruses because of the additional orientational degree of freedom [4,5]. This gives rise to a sequence of mesophases with increasing packing fraction, from the (chiral) nematic where there is only orientational ordering to smectic and (hexatic) columnar liquid-crystalline phases characterized by one-and two-dimensional positional order [6,7].…”

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confidence: 99%

Fractional Hoppinglike Motion in Columnar Mesophases of Semiflexible Rodlike Particles

et al. 2013

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We report on single-particle dynamics of strongly interacting filamentous fd virus particles in the liquidcrystalline columnar state in aqueous solution. From fluorescence microscopy, we find that rare, discrete events take place, in which individual particles engage in sudden, jumplike motion along the main rod axis. The jump length distribution is bimodal and centered at half-and full-particle lengths. Our Brownian dynamics simulations of hard semiflexible particles mimic our experiments and indicate that full-length jumps must be due to collective dynamics in which particles move in stringlike fashion in and between neighboring columns, while half jumps arise as a result of particles moving into defects. We find that the finite domain structure of the columnar phase strongly influences the observed dynamics. The interplay between ordering, fluctuations, and mobility of particles is a key ingredient in our current understanding of soft matter. The Lindemann criterium for crystal melting purports that a crystal can only be stable provided that fluctuations of the particles away from the equilibrium positions are less than about 1=8 of the lattice distance [1], which indeed is observed in real space in crystalline dispersions of spherical colloids [2]. In glassy dispersions of colloidal spheres, there is no long-range order but particle caging hinders free diffusion: breaking and reformation of cages dominates the dynamics [3]. The situation is more complex for elongated colloidal particles such as DNA, actin filaments, and filamentous viruses because of the additional orientational degree of freedom [4,5]. This gives rise to a sequence of mesophases with increasing packing fraction, from the (chiral) nematic where there is only orientational ordering to smectic and (hexatic) columnar liquid-crystalline phases characterized by one-and two-dimensional positional order [6,7].While self-diffusion in nematic [8,9] and smectic [10-14] phases has been investigated theoretically and experimentally, little is known about dynamics in the dense columnar phase, where particles are stacked into liquidlike columns that are organized in a hexagonal array. Perfect hexagonal ordering is frustrated for the chiral fd virus by the helical twist of the particles, spawning dislocations. This breaks long-range hexagonal translational order, giving rise to a hexatic columnar phase [7]. In this Letter, we report on the intriguing motion of particles in this highly viscous hexatic phase, using particle tracking of fluorescently labeled fd viruses. We observe rare and discrete jump events along the director, predominantly of half a particle length, while a significant fraction of events involves full-length jumps. A small fraction of the particles reorients during the jump, hinting at the presence of structural defects, such as dislocations or grain boundaries.Hoppinglike diffusion processes of one rod length have been observed before in the smectic of an fd virus [11,12]. It stems from the underlying lamellar structure of the smectic th...

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Fractional Hoppinglike Motion in Columnar Mesophases of Semiflexible Rodlike Particles

et al. 2013

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“…), ceramic bulk powders, catalyst pellets, and reinforcing fibers in industry. [1][2][3][4][5][6] On the sub-micron length scale anisometric colloids such as rods and platelets form dense random packings and glasses, 4,[7][8][9][10][11][12][13] while protein filaments may randomly pack in animal cells.…”

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Isochoric ideality in jammed random packings of non-spherical granular matter

et al. 2011

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Randomly packed particles in granular matter, ubiquitous in nature and industry, usually defy simple predictions for the optimal amorphous packing density because jammed granules are strongly correlated. While mixing different granular shapes seems to be a further complication, we discovered in simulations that binary rodsphere mixtures harbor a surprisingly simple dependence of packing volume fraction on mixture composition. This isochoric ideality covers the entire composition range and is experimentally validated by mixtures of sphero-cylindrical TicTac sweets and spherical beads: their joint random packing volume is indeed independent of the segregation state. Isochoric ideality occurs in a rod-shape range that includes the unique aspect ratio, which universally maximizes rod-sphere packing densities and suggests a novel amorphous analog of a plastic crystal, namely rod-sphere mixtures with completely uncorrelated particle orientations.The puzzle of dense amorphous particle packings has caught the close attention of mathematicians and scientists from many different disciplines. In particular, non-spherical particles and their mixtures, jammed into random packings, are abundant and occur on widely different length scales. Macroscopic instances of anisotropic granular matter, among many others, are the grains in solidifying igneous rocks, various grains in food (rice, pasta's, TicTac sweets, etc.), ceramic bulk powders, catalyst pellets, and reinforcing fibers in industry.1-6 On the sub-micron length scale anisometric colloids such as rods and platelets form dense random packings and glasses, 4,7-13 while protein filaments may randomly pack in animal cells.14 Essential questions are how tight one can pack particles in jammed amorphous packings and how to optimize the corresponding random close packing (RCP) density. In quest of the optimal or densest random packing, particle non-sphericity has proven to be an effective means to maximize the RCP density. Recent studies on random packing of sphero-cylinders 15 and ellipsoids 16,17 revealed an intriguing non-monotonic dependence of the RCP density on the particle elongation. Starting from the Bernal random sphere packing, the RCP density first raises to a maximum for nearly spherical particles and only beyond this maximum the random packing density monotonically decreases with particle aspect ratio. So far, this peculiar maximum has only been observed for monodisperse granules 15-17 and colloids. 9 As polydispersity in size and shape is often unavoidable, one important question is how to optimize packing densities of granular mixtures, which ideally could be predicted from densities of the monodisperse components. It is therefore of fundamental and practical interest to investigate for such mixtures the existence of a density maximum and the universality, if any, in its location or magnitude.We uncover the universality in jamming of rather short spherocylinders of length L (including two hemi-spherical caps at both ends) and diameter D by investigating the RCP of...

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“…Polymer gels are found in many applications ranging from foods (Ross-Murphy, 1995;Tunick, 2010) and drug delivery (Andrews & Jones, 2006) to adhesives (Creton, 2003) and consumer products (Solomon & Spicer, 2010). By manipulating the gel's microstructure, a wide variety of physical properties can be achieved ranging from hard rubbery plastics to soft hydrogels.…”

Section: Introductionmentioning

confidence: 99%

“…The crosslinks are permanent and cannot be reformed if broken. Weak gels contain crosslinks which can be broken and reformed such as colloidal gels and some biopolymer gels (Spicer & Solomon, 2010;Richter, 2007). Entangled polymer systems are sometimes referred to as pseudo gels because, over a range of time scales, physical entanglements between polymer chains mimic chemical crosslinks giving these materials gel-like properties (Kavanagh & Ross-Murphy, 1998).…”

Section: Introductionmentioning

confidence: 99%