Isotropic-nematic phase transition in suspensions of filamentous virus and the neutral polymer Dextran

Dogic, Zvonimir; Purdy, Kirstin; Grelet, Éric; Adams, Marie; Fraden, Seth

doi:10.1103/physreve.69.051702

Cited by 131 publications

(159 citation statements)

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“…Under high-salt conditions, hard-core repulsive interactions dominate the behavior of fd/polymer mixtures, and consequently all phase transitions in this system are entropically driven (8). Similar mixtures have been used to explore the influence of attractive interactions on the isotropic-nematic phase transition and kinetics of various liquid crystalline phase transitions (9)(10)(11). In these studies, the qualitative observation of 2D membrane-like structures was reported.…”

Section: Resultsmentioning

confidence: 99%

Entropy driven self-assembly of nonamphiphilic colloidal membranes

Barry

Dogic

2010

Proc. Natl. Acad. Sci. U.S.A.

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We demonstrate that homogeneous monodisperse rods in the presence of attractive interactions assemble into equilibrium 2D fluid-like membranes composed of a one-rod length thick monolayer of aligned rods. Unique features of our system allow us to simultaneously investigate properties of these membranes at both continuum and molecular lengthscales. Analysis of thermal fluctuations at continuum lengthscales yields the membranes' lateral compressibility and bending rigidity and demonstrates that the properties of colloidal membranes are comparable to those of traditional lipid bilayers. Fluctuations at molecular lengthscales, in which single rods protrude from the membrane surface, are directly measured by comparing the positions of individual fluorescently labeled rods within a membrane to that of the membrane's continuum conformation. As two membranes approach each other in suspension, protrusion fluctuations are suppressed leading to effective repulsive interactions. Motivated by these observations, we propose an entropic mechanism that explains the stability of colloidal membranes and offers a general design principle for the self-assembly of 2D nanostructured materials from rod-like molecules.colloids | liquid crystals | nanorods | depletion interaction I n hard-body fluids, interactions between individual particles are described by a steep repulsive potential that imposes an infinite energetic penalty for any overlapping particles. It follows that any accessible state of a hard particle fluid has no internal energy and that minimizing the free energy of such a system is equivalent to maximizing its entropy. Hard particles have served as essential model systems for our understanding of the liquid and solid state, demonstrating the existence of nematic and smectic phases in hard rods (1, 2) and a 3D crystalline phase in hard spheres (3). These results exemplify the counterintuitive yet well established notion that entropy alone can drive the self-assembly of ordered structures. In this paper, we extend these ideas of entropic self-assembly to a equilibrium structure, a colloidal membrane. We demonstrate that in the presence of attractive (depletion) interactions mediated by nonadsorbing polymer, monodisperse rod-like colloids (filamentous viruses) spontaneously assemble into 2D membranes. In contrast to the previous examples of entropic self-assembly, in which the constituent molecules assemble into 3D structures, the self-assembly of homogeneous rods into colloidal membranes is self-limited to two dimensions, similar to what is observed for the assembly of amphiphilic lipids into ubiquitous biological membranes (4). However, unlike amphiphilic molecules that have a heterogeneous molecular structure, all the molecules involved in assembly of colloidal membranes are homogeneous, suggesting that geometry as well as chemical heterogeneity can be used to design pathways for self-assembly of various molecular species (5).In what follows, we utilize two unique features of our model experimental virus/polymer system t...

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Section: Resultsmentioning

confidence: 99%

Entropy driven self-assembly of nonamphiphilic colloidal membranes

Barry

Dogic

2010

Proc. Natl. Acad. Sci. U.S.A.

Self Cite

135

186

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“…They found an increase of the entropy of the polymer spheres when the hard particles were moved together, leading to an effective attraction between the particles. Depletion forces have been observed and analyzed theoretically in a variety of systems, including mixtures of large and small colloidal particles, both with spheres and rods, mixtures of colloidal particles and polymers, and mixtures of proteins and polymers, inducing either or both particle aggregation and phase separation (21,24). Depletion forces also are credited as being responsible for the formation of protein crystals in mixtures of proteins and polymers such as PEG (17).…”

Section: Entropy and Energy Combine To Drive The Ndna Phase Separationmentioning

confidence: 99%

Phase separation and liquid crystallization of complementary sequences in mixtures of nanoDNA oligomers

Zanchetta

Nakata

Buscaglia

et al. 2008

Proc. Natl. Acad. Sci. U.S.A.

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Using optical microscopy, we have studied the phase behavior of mixtures of 12-to 22-bp-long nanoDNA oligomers. The mixtures are chosen such that only a fraction of the sample is composed of mutually complementary sequences, and hence the solutions are effectively mixtures of single-stranded and double-stranded (duplex) oligomers. When the concentrations are large enough, such mixtures phase-separate via the nucleation of duplex-rich liquid crystalline domains from an isotropic background rich in single strands. We find that the phase separation is approximately complete, thus corresponding to a spontaneous purification of duplexes from the single-strand oligos. We interpret this behavior as the combined result of the energy gain from the end-to-end stacking of duplexes and of depletion-type attractive interactions favoring the segregation of the more rigid duplexes from the flexible single strands. This form of spontaneous partitioning of complementary nDNA offers a route to purification of short duplex oligomers and, if in the presence of ligation, could provide a mode of positive feedback for the preferential synthesis of longer complementary oligomers, a mechanism of possible relevance in prebiotic environments.condensation ͉ nucleation ͉ depletion ͉ prebiotic ͉ PEG M olecular crowding of cellular interior is known to play a role in the spontaneous organization of biological macromolecules (1). Several biochemical and physiological processes are found to be influenced by strong packing constraints (2, 3), and complex ordered arrangements, such as liquid-crystalline mesophases, have been shown to arise from highly packed biomolecules (4). Of particular interest is the ordering of highly concentrated DNA in cell nuclei, which can lead to a variety of mesophases in vivo (5). However, whether such ordering caused by packing constraints had represented an evolutionary advantage remains an open question.Concentrated solutions of fully hybridized nanoDNA (nDNA) exhibit various liquid crystalline forms of supramolecular ordering, promoted by end-to-end adhesion of the paired bases at the terminals of the duplexes. This behavior has been reported recently for a wide set of self-complementary (SC) 6-to 20-bp nDNA sequences and for mutually complementary sequences in the same length range (6). Here we explore the phase behavior of mixtures of nDNA in which only some of the sequences are complementary, thus able to pair in double strands (DSs), and part of the sequences are not, and thus always remain in the solution as single strands (SSs). We have found that in concentrated mixtures of duplex and SS nDNA, the system phaseseparates into duplex-rich liquid crystal (LC) domains coexisting with a duplex-poor isotropic phase, leading to the physical segregation of 4-to 6-nm-long complementary chains from noncomplementary ones. This phase separation is a collective effect of the duplex and SS nDNA because the duplexes alone would not form LCs in such solutions, their concentration being well below that required for LC forma...

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“…We use the fd -virus, which is an excellent model liquid crystal system for both static and dynamic behaviour [13][14][15][16]. The virus' contour length and diameter are 0.88 µm and 6.6 nm, respectively.…”

Section: Pacs Numbersmentioning

confidence: 99%

“…We introduce a new method for estimating elastic constants suitable to colloidal and biological systems, as an alternative to previous methods using magnetic fields [11] or light scattering [12]. Specifically, we determine the transition from a splay to a bend director field, with increasing wedge angle.We use the fd -virus, which is an excellent model liquid crystal system for both static and dynamic behaviour [13][14][15][16]. The virus' contour length and diameter are 0.88 µm and 6.6 nm, respectively.…”

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confidence: 99%

Confinement Induced Splay-to-Bend Transition of Colloidal Rods

et al. 2012

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We study the nematic phase of rodlike fd -virus particles confined to channels with wedgestructured walls. Using laser scanning confocal microscopy we observe a splay-to-bend transition at the single particle level as a function of the wedge opening angle. Lattice Boltzmann simulations reveal the underlying origin of the transition and its dependence on nematic elasticity and wedge geometry. Our combined work provides a simple method to obtain the splay-to-bend elasticity ratios and offers a way to control the position of defects through the confining boundary conditions. PACS numbers:Packing and confinement problems emerge in fields ranging from biology to engineering. In biological systems the organization of the cell is determined, among other things, by the packing of fibril-like particles (actin filaments, DNA) [1,2]. An example of the subtlety of packing phenomena is the plethora of liquid crystalline phases that can be found in arrangements of anisotropic particles by increasing concentration [3,4]. Confinement of liquid crystals adds to the complexity, since the interactions of the particles with the walls may lead to structures that compete with those formed in the bulk [5,6]. Many of the next generation liquid crystal display devices exploit this interplay by using structured or patterned surfaces as an essential element of their design [7,8]. Very recently, the ordering at sawtoothed structures has been studied theoretically within a Landau-De Gennes framework [9,10], with a focus on the wetting behaviour. In this Letter, in a combined experimental and theoretical effort, we show the rich phenomenology that emerges when confining a nematic liquid crystal to a microfluidic channel with a wedge structured wall. We seek to disentangle how the wedge geometry and elasticity of the fd -virus' nematic phase determine the adopted deformation in the wedge. We introduce a new method for estimating elastic constants suitable to colloidal and biological systems, as an alternative to previous methods using magnetic fields [11] or light scattering [12]. Specifically, we determine the transition from a splay to a bend director field, with increasing wedge angle.We use the fd -virus, which is an excellent model liquid crystal system for both static and dynamic behaviour [13][14][15][16]. The virus' contour length and diameter are 0.88 µm and 6.6 nm, respectively. These dimensions allow for the 3D determination of the position and orientation of individual particles by means of laser scanning confocal microscopy (LSCM). Thus we obtain detailed mechanistic insights on a single particle level of the director field. Moreover, due to the relatively large size of the particles, we can study effects of wall structures that are, when translated to the scale of thermotropic liquid crystals, very small and inaccessible. The particles were grown following standard protocols [17] and dispersed in 20 mM tris buffer at pH 8.15 with 100 mM NaCl and 15% EtOH. The ethanol was added to prevent the growth of bacteria. The virus concent...

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Isotropic-nematic phase transition in suspensions of filamentous virus and the neutral polymer Dextran

Cited by 131 publications

References 46 publications

Entropy driven self-assembly of nonamphiphilic colloidal membranes

Entropy driven self-assembly of nonamphiphilic colloidal membranes

Phase separation and liquid crystallization of complementary sequences in mixtures of nanoDNA oligomers

Confinement Induced Splay-to-Bend Transition of Colloidal Rods

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