Colloidal System To Explore Structural and Dynamical Transitions in Rod Networks, Gels, and Glasses

Wilkins, Georgina M. H.; Spicer, Patrick T.; Solomon, Michael J.

doi:10.1021/la9004196

Cited by 44 publications

(57 citation statements)

References 61 publications

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“…There are three possible scenarios: (i) the formation of bundles of average size N ; (ii) chain formation, where N aligned nanotubes overlap minimally at their ends; and (iii) the formation of a heterogeneous network of fractal aggregates. 57,62,67 In our system, all three effects presumably exist. Bundle formation reduces the aspect ratio to λ ′ = λ/ √ N in Eq.…”

Section: B Scaling Electronic Type and Film Durabilitymentioning

confidence: 87%

Empirical evaluation of attractive van der Waals potentials for type-purified single-walled carbon nanotubes

et al. 2012

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Van der Waals forces play a critical role in the structure and stability of single-wall carbon nanotube (SWCNT) materials. Thin films assembled from SWCNTs purified by electronic type show particular promise for flexible electronics applications, but mechanical durability remains an unresolved issue. Using transition resonances determined from spectroscopic measurements of typepurified SWCNTs deposited on quartz, coupled with analogous spectroscopic characterization of polydimethylsiloxane (PDMS) substrates, we use the Lifshitz theory of van der Waals dispersion interactions developed by Rajter and co-workers [R. F. Rajter et. al., Phys. Rev. B 76, 045417 (2007)] to examine the influence of electronic type on van der Waals contact potentials in polymer supported nanotube networks. Our results suggest a significantly stronger nanotube-nanotube and nanotube-polymer attraction for the semiconducting SWCNT fractions, consistent with recent measurements of the electronic durability of flexible transparent SWCNT coatings.PACS numbers: 61.48. De, 78.67.Ch, 82.35.Np, 78.20.Bh 2 I. INTRODUCTIONVan der Waals (vdW) forces play a significant role in the structural stability of matter across a broad range of chemistry, physics, and biology. 1-6 They also play a particularly important role in nanotechnology, where they dominate the short-range attraction between nanoparticles and can hinder their dispersion and manipulation. [7][8][9][10][11] For particles lacking a permanent dipole moment, vdW dispersion forces arise solely from small fluctuations in the electromagnetic field -or more precisely, the dielectric permittivity -across the space between the particles, 12,13 which is dominated by the zero-point energy of quantum vacuum fluctuations. The quantum-field nature of such a mundane, ubiquitous and sometimes macroscopic force is quite remarkable, if on occasion not fully appreciated.Single-wall carbon nanotubes (SWCNTs) are nanometer thick tubes of graphene 100 nm to 100 µm in length. They can be either metallic or semiconducting, depending on the chiral vector (n, m) that characterizes the symmetry of rolling a 2D graphene sheet into a hollow tube. 14 They are one of the most studied materials within the realm of modern nanotechnology, with exceptional physical properties that herald the possibility of significant technological potential. 15 The importance of vdW forces in SWCNT materials cannot be overstated. The high aspect ratio and strong anisotropy create potential wells thousands of k B T in depth, but SWCNTs have yet to realize their full potential as mechanical reinforcing agents. This is primarily due to the mechanical failure of interfacial contacts, which are largely governed by vdW forces. Although chemical crosslinking can help mitigate such effects, this often occurs at the expense of the intrinsic SWCNT properties of interest, 16 which can limit the potential impact of applications.Raw nanotube materials typically contain a broad distribution of lengths and a mixture of the two distinct electronic species...

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Section: B Scaling Electronic Type and Film Durabilitymentioning

confidence: 87%

Empirical evaluation of attractive van der Waals potentials for type-purified single-walled carbon nanotubes

et al. 2012

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“…However, although networks of anisotropic particles are important, e.g. in shiny paper coatings, systematic experimental studies of the effect of anisotropy in systems with attractions are limited: attractions between colloidal platelets can lead to stacking [10,11], gels of colloidal rods form bundles [12] and due to their patchy interactions, clay platelets form low density colloidal 'liquids' [13].Here we introduce an anisotropic colloidal system of faceted polyhedra, or 'rocks', with tuneable interactions, amenable to 3D single-particle level analysis with confocal microscopy. Unlike gels of spherical particles where phase separation is suppressed by slow dynamics due to the high local colloid density of the 'arms', we show that the polyhedral nature of the rocks leads to bonds which do not rotate and thus rigid structures and networks of low fractal dimension are formed.…”

mentioning

confidence: 99%

Polyhedral colloidal ‘rocks’: low-dimensional networks

2012

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We introduce a model system of anisotropic colloidal 'rocks'. Due to their shape, the bonding introduced via non-absorbing polymers is profoundly different from spherical particles: bonds between rocks are rigid against rotation, leading to strong frustration. We develop a geometric model which captures the essence of the rocks. Experiments and simulations show that the colloid geometry leads to structures of low fractal dimension. This is in stark contrast to gels of spheres, whose rigidity results from locally dense regions. At high density the rocks form a quasi one-component glass. PACS numbers: 82.70.Dd;64.60.Cn Dispersions of mesoscopic colloidal particles are important for several reasons. They model atomic and molecular systems, yet single particle level imaging reveals local phenomena, such as pinpointing mechanisms of dynamic arrest [1,2], which are inaccessible in conventional systems. Furthermore, colloidal and nanoparticle systems are important materials. Colloidal gels stabilize a range of industrial and consumer products from pesticides to cosmetics. Underlying both is the tuneability of interactions between colloids which are theoretically well understood and hence enable design of self-assembled structures at small lengthscales. Recently, anisotropic interactions using a number of sticky patches per particle have been introduced, opening new routes of self-assembly. Reducing the number of patches per particle leads to networks of low fractal dimension [3].Here we consider depletion induced gels of anisotropic particles. The addition of polymer mediates an effective attraction between the colloids due to excluded volume effects -see Fig 1(b). The depth of this attraction is proportional to the polymer concentration c p and the range is set by the polymer size. At sufficient strengths of the depletion attraction, spinodal phase separation leads to colloid-rich (polymer-poor) 'colloidal liquid' and colloidpoor (polymer-rich) 'colloidal gas' phases. Decreasing the range of the depletion interaction by reducing the size of the polymer relative to the colloid leads to a higher density colloidal liquid. If the packing fraction of the colloidal liquid is high enough (φ ≈ 0.58) phase separation is arrested. The resulting network of voids combined with 'arms' of high local colloid density, is termed a gel [4].A range of anisotropic particles has been synthesized [5,6], and systems with hard interactions have recieved considerable attention very recently: rods form the expected liquid crystalline phases [7], anisotropy suppresses long-ranged order close to a wall [8] and at high density, colloidal dumbells show multiple relaxation pathways [9]. However, although networks of anisotropic particles are important, e.g. in shiny paper coatings, systematic experimental studies of the effect of anisotropy in systems with attractions are limited: attractions between colloidal platelets can lead to stacking [10,11], gels of colloidal rods form bundles [12] and due to their patchy interactions, clay platelets for...

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“…Control and understanding of the various structures has technological relevance, particularly as rod-like particles can affect rheological properties of solutions at much lower volume fractions than spherical particles. 1 Significant interest in the polymorphism of solutions of rods is derived from biology: rod-like biofilaments, such as actin, microtubules, and intermediate filaments, define the structure and mechanics of the cell and its organelles. Prior work has investigated the physics of in vitro solutions of filamentous biopolymers.…”

Section: Introductionmentioning

confidence: 99%

Electrostatics and depletion determine competition between 2D nematic and 3D bundled phases of rod-like DNA nanotubes

2016

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Rod-like particles form solutions of technological and biological importance. In particular, biofilaments such as actin and microtubules are known to form a variety of phases, both in vivo and in vitro, whose appearance can be controlled by depletion, confinement, and electrostatic interactions. Here, we utilize DNA nanotubes to undertake a comprehensive study of the effects of those interactions on two particular rod-like phases: a 2D nematic phase consisting of aligned rods pressed against a glass surface, and a 3D bundled network phase. We experimentally measure the stability of these two phases over a range of depletant concentrations and ionic strengths, finding that the 2D phase is slightly more stable than the 3D phase. We formulate a quantitative model of phase stability based on consideration of pairwise rod-rod and rod-surface interactions; notably, we include a careful accounting of solution electrostatics interactions using an effective-charge strategy. The model is relatively simple and contains no free parameters, yet predicts phase boundaries in good agreement with the experiment. Our results indicate that electrostatic interactions, rather than depletion, are largely responsible for the enhanced stability of the 2D phase. This work provides insight into the polymorphism of rod-like solutions, indicating why certain phases appear, and providing a means (and a predictive model) for controlling those phases.

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Colloidal System To Explore Structural and Dynamical Transitions in Rod Networks, Gels, and Glasses

Cited by 44 publications

References 61 publications

Empirical evaluation of attractive van der Waals potentials for type-purified single-walled carbon nanotubes

Empirical evaluation of attractive van der Waals potentials for type-purified single-walled carbon nanotubes

Polyhedral colloidal ‘rocks’: low-dimensional networks

Electrostatics and depletion determine competition between 2D nematic and 3D bundled phases of rod-like DNA nanotubes

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