Tubular crystals, two-dimensional lattices wrapped into cylindrical topologies, arise in many con... more Tubular crystals, two-dimensional lattices wrapped into cylindrical topologies, arise in many contexts, including botany and biofilaments, and in physical systems such as carbon nanotubes. The geometrical principles of botanical phyllotaxis, describing the spiral packings on cylinders commonly found in nature, have found application in all these systems. Several recent studies have examined defects in tubular crystals associated with crystalline packings that must accommodate a fixed tube radius. Here we study the mechanics of tubular crystals with variable tube radius, with dislocations interposed between regions of different phyllotactic packings. Unbinding and separation of dislocation pairs with equal and opposite Burgers vectors allow the growth of one phyllotactic domain at the expense of another. In particular, glide separation of dislocations offers a low-energy mode for plastic deformations of solid tubes in response to external stresses, reconfiguring the lattice step by s...
We study colloids suspended in nematic liquid crystal in grooves with homeotropic anchoring. We o... more We study colloids suspended in nematic liquid crystal in grooves with homeotropic anchoring. We observe "eyelashes", topological dipole chains that follow the local, curved director field. These beget wires that connect the groove corners to topographical features on the cell lid to yield oriented, curvilinear colloidal wires spanning the cell, formed in a nonsingular director field. As the groove aspect ratio changes, we find different ground states and corroborate our observation with numerics. Our results rely upon on the scale of topographical features, the sharpness of edges, and the colloid-sourced distortions; all these elements can be exploited to guide the formation of reconfigurable structures in nematics.
Controlling the molecular alignment of liquid crystal monomers (LCMs) within nano- and microstruc... more Controlling the molecular alignment of liquid crystal monomers (LCMs) within nano- and microstructures is essential in manipulating the actuation behavior of nematic liquid crystal elastomers (NLCEs). Here, we study how to induce uniformly vertical alignment of nematic LCMs within a micropillar array to maximize the macroscopic shape change using surface chemistry. Landau-de Gennes numerical modeling suggests that it is difficult to perfectly align LCMs vertically in every pore within a poly(dimethylsiloxane) (PDMS) mold with porous channels during soft lithography. In an untreated PDMS mold that provides homeotropic anchoring of LCMs, a radially escaped configuration of LCMs is observed. Vertically aligned LCMs, a preferred configuration for actuation, are only observed when using a PDMS mold with planar anchoring. Guided by the numerical modeling, we coat the PDMS mold with a thin layer of poly(2-hydroxyethyl methacrylate) (PHEMA), leading to planar anchoring of LCM. Confirmed by ...
Filamentous bacteriophages such as the fd virus have long been used as ideal model systems to inv... more Filamentous bacteriophages such as the fd virus have long been used as ideal model systems to investigate the phase behavior of suspensions of rodlike particles. We study the structure and phase behavior of a mutant, fd Y21M, and compare them to the properties of conventional fd wild-type (wt). These two viruses exhibit dramatically different phase behavior despite differing only by a single amino acid of the major coat protein pVIII. We find that this is attributable to significant differences in the flexibility of the viruses. Using the more rigid fd Y21M, we are able for the first time to quantitatively test the Onsager description of the isotropic-nematic phase transition of rigid rods. Even more surprising are the differences in the behavior of the cholesteric phase of fd Y21M and fd wt. While fd wt forms a cholesteric pitch with a left-handed helix, fd Y21M forms a cholesteric pitch with the opposite handedness. In addition, the magnitude of the cholesteric pitch changes by almost fivefold. Using mixtures of the two viruses, we are able to create liquid crystal systems with tunable control over the macroscopic chiral behavior.
ABSTRACT The use of micropost arrays is explored as a means for controlling self-assembly and dir... more ABSTRACT The use of micropost arrays is explored as a means for controlling self-assembly and director alignment in nematic chromonic liquid crystal (CLC) films. Experiment and numerical solutions reveal that the micropost arrays induce bistable director alignment in the film, along either diagonal of a square micropost lattice. We demonstrate stabilization of large domains of a single director orientation by rubbing the substrate surface along a single diagonal, a procedure which biases planar CLC director alignment in the film. Additionally, by varying the rubbing angle we investigate the competition between alignment via micropost patterns versus substrate rubbing, and we find the resulting assemblies to be largely controlled by micropost geometry. Variation of micropost layout, spacing and dimensions leads to further interesting self-assembled patterns and defect geometries.
We report synergistic co-assembly between smectic A liquid crystal (SmA LC) and planar anchoring ... more We report synergistic co-assembly between smectic A liquid crystal (SmA LC) and planar anchoring fluorosilane functionalized silica (F-SiO2) nanoparticles (NPs). Both scanning electron microscope (SEM) images and grazing incidence X-ray diffraction (GIXD) patterns show that when cooled from the isotropic phase to SmA phase, F-SiO2 NPs (100-500 nm in diameter) migrate from the bottom to the top of the LC film through the central cusp defects of toric focal conic domains (TFCDs). When the NPs form a monolayer on top, replacing the LC/air interface, vertically aligned SmA layers are formed between the top and bottom planar surfaces. When F-SiO2 NP diameter is small (<500 nm), we observe a weak-anchoring regime, where NPs do not cause appreciable layer curvature and NP migration is driven by surface energy. When F-SiO2 particle diameter > 500 nm, strong distortions occur in the smectic layers, and the particle is found suspended at the TFCD defect core. The knowledge of the interm...
When immiscible fluids are advected by an externally applied chaotic flow field, a nonequilibrium... more When immiscible fluids are advected by an externally applied chaotic flow field, a nonequilibrium steady state arises from the competition between coarsening and the chaotic ripping-apart of domains. We simulate a two-dimensional binary fluid system advected by two different flow fields: a periodic alternating vortex flow and a periodic alternating sine flow. For each case, we examine the local degree of chaos in the flow field by computing finite-backward-time Lyapunov exponent values at each point in the system. We find that this Lyapunov exponent field is correlated with the advected fluids' local free energy density, which is inversely related to the local time-averaged size of phase-separated domains in the steady state. This raises the possibility of making universal predictions of steady-state characteristics based on Lyapunov analysis of the flow field.
New image (MOC, THEMIS, HRSC and HiRISE) and topography (MOLA) data now available allow for a re-... more New image (MOC, THEMIS, HRSC and HiRISE) and topography (MOLA) data now available allow for a re-examination of the aureoles. Spatial, geographic and topographic relations have been examined.
We consider a system of two immiscible fluids advected by a chaotic flow field. A nonequilibrium ... more We consider a system of two immiscible fluids advected by a chaotic flow field. A nonequilibrium steady state arises from the competition between the coarsening of the immiscible fluids and the domain bursting caused by the chaotic flow. It has been established that the average domain size in this steady state scales as a inverse power of the Lyapunov exponent. We examine the issue of local structure and look for correlations between the local domain size and the finite-time Lyapunov exponent (FTLE) field. For a variety of chaotic flows, we consistently find the domains to be smallest in regions where the FTLE field is maximal. This raises the possibility of making universal predictions of steady-state characteristics based on Lyapunov analysis of the flow field.
In this work, we exploit well defined boundary conditions to control the formation of defects in ... more In this work, we exploit well defined boundary conditions to control the formation of defects in nematic liquid crystal (NLC) 5CB. When supported between micropost arrays, disclination lines form and bear the signature of the micropost shape owing to the elasticity of the medium. The existence of these disclination lines can be tuned due to the thermotropic nature of the material simply by varying temperature thereby providing an element of control not present in typical isotropic fluids. When colloids are introduced to a nematic liquid crystal, elastic distortions arise that have an associated Frank free energy cost. This excess energy is reduced by interacting with the micropost induced disclination lines and subsequent colloid-micropost attractions arise. We consider both isotropic particles (spheres) and more complex anisotropic particles. Further, we observe these effects 5CB-air interfaces as well as in bulk 5CB. This work is experimental and supplemented with analysis to supp...
While the physics of spherical colloids confined in a nematic slab has been thoroughly investigat... more While the physics of spherical colloids confined in a nematic slab has been thoroughly investigated (see, e.g. [1-3]), interactions between anisotropic particles are less well studied [4-6]. Here, we report the behavior of micro-rods confined in a nematic cell. The anchoring conditions on the particles and on the bounding walls of the cell are well defined. Depending on the type of anchoring, cylinders spontaneously form 1D structures, chains parallel to the director, and 2D ordered structures, crystals with hexagonal symmetry. These latter structures are not observed for isotropic particles. By application of an external field, the anchoring conditions on the bounding walls can be dynamically controlled, and transitions between the different structures can be generated. Recent progress in understanding the particle self-assembly process is presented. [1] P. Poulin and D. Weitz, Physical Review E, 57, 626 (1998). [2] M. Škarabot and el., Physical Review E, 77, 031705 (2008). [3] I. ...
We exploit the long-ranged elastic fields inherent to confined nematic liquid crystals to assembl... more We exploit the long-ranged elastic fields inherent to confined nematic liquid crystals to assemble colloidal particles trapped at the liquid crystal interface into reconfigurable structures with complex symmetries and packings. Spherical colloids with homeotropic anchoring trapped at the interface between air and the nematic liquid crystal 5CB create quadrupolar distortions in the director field causing particles to repel and consequently form close-packed assemblies with a triangular habit. Here we report on complex, open structures organized via interactions with defects in the bulk. Specifically, by confining the nematic liquid crystal in an array of microposts with homeotropic anchoring conditions, we cause defect rings to form at well-defined locations in the bulk of the sample. These defects source elastic deformations that direct the assembly of the interfacially-trapped colloids into ring-like assemblies, which recapitulate the defect geometry even when the microposts are co...
Focal conic domains (FCDs) in smectic-A liquid crystals have drawn much attention, both for their... more Focal conic domains (FCDs) in smectic-A liquid crystals have drawn much attention, both for their exquisitely structured internal form and for their ability to direct the assembly of micromaterials and nanomaterials in a variety of patterns. A key to directing FCD assembly is control over the eccentricity of the domain. Here, we demonstrate a new paradigm for creating spatially varying FCD eccentricity by confining a hybrid-aligned smectic with curved interfaces. In particular, we manipulate interface behavior with colloidal particles in order to experimentally produce two examples of what has recently been dubbed the flower texture [C. Meyer et al., Focal Conic Stacking in Smectic A Liquid Crystals: Smectic Flower and Apollonius Tiling, Materials 2, 499, 2009], where the focal hyperbolæ diverge radially outward from the center of the texture, rather than inward as in the canonical éventail or fan texture. We explain how this unconventional assembly can arise from appropriately curv...
Colloidal particles organize spontaneously at fluid interfaces owing to a variety of interactions... more Colloidal particles organize spontaneously at fluid interfaces owing to a variety of interactions to form well organized structures that can be exploited to synthesize advanced materials. While the physics of colloidal assembly at isotropic interfaces is well understood, the mechanisms that govern interactions between particles at liquid crystal interfaces are not yet clearly established. In particular, smectic liquid crystal films offer important degrees of freedom that can be used to direct particles into new structures. In this work, we report the behavior of solid micrometric beads with homeotropic anchoring confined at interfaces of thin smectic films. We study the interactions and self-assembly of these particles in both supported and free standing films. When particles are captured in thin membranes, they induce distortions of the smectic interface to satisfy wetting properties at particle boundaries, leading to capillary interactions. These forces compete with elastic ones i...
ABSTRACT The use of micropost arrays is explored as a means for controlling self-assembly and dir... more ABSTRACT The use of micropost arrays is explored as a means for controlling self-assembly and director alignment in nematic chromonic liquid crystal (CLC) films. Experiment and numerical solutions reveal that the micropost arrays induce bistable director alignment in the film, along either diagonal of a square micropost lattice. We demonstrate stabilization of large domains of a single director orientation by rubbing the substrate surface along a single diagonal, a procedure which biases planar CLC director alignment in the film. Additionally, by varying the rubbing angle we investigate the competition between alignment via micropost patterns versus substrate rubbing, and we find the resulting assemblies to be largely controlled by micropost geometry. Variation of micropost layout, spacing and dimensions leads to further interesting self-assembled patterns and defect geometries.
ABSTRACT We compare the phase behavior of a mutant filamentous virus, fd Y21M, to that of a conve... more ABSTRACT We compare the phase behavior of a mutant filamentous virus, fd Y21M, to that of a conventional fd wild-type (wt). We find significantly different macroscopic phase behavior despite the only microscopic difference between the two viruses being in a single amino acid of the major coat proteinpVIII. Compared to fd wt, the location of the isotropic–cholesteric phase transition for fd Y21M shifts to lower densities. This is attributable to a significant difference in the flexibility of the two viruses. The persistence length of fd wt is 2.8 ± 0.7 µm, whereas the persistence length of fd Y21M is 9.9 ± 1.6 µm. The large persistence length of fd Y21M makes it an essentially rigid rod, thus allowing for the first time a quantitative test of the Onsager theory for the isotropic–nematic phase transition. Even more striking, is the difference in the chiral phase behavior of the two viruses. Both viruses form cholesteric phases, with the fd wt forming a left-handed cholesteric helix, and the fd Y21M forming a right-handed one. At a given density, the magnitude of the cholesteric pitch between the two systems is different by fivefold. Using mixtures of the two viruses, we create a liquid crystalline system with a tunable control over its macroscopic chirality.
Tubular crystals, two-dimensional lattices wrapped into cylindrical topologies, arise in many con... more Tubular crystals, two-dimensional lattices wrapped into cylindrical topologies, arise in many contexts, including botany and biofilaments, and in physical systems such as carbon nanotubes. The geometrical principles of botanical phyllotaxis, describing the spiral packings on cylinders commonly found in nature, have found application in all these systems. Several recent studies have examined defects in tubular crystals associated with crystalline packings that must accommodate a fixed tube radius. Here we study the mechanics of tubular crystals with variable tube radius, with dislocations interposed between regions of different phyllotactic packings. Unbinding and separation of dislocation pairs with equal and opposite Burgers vectors allow the growth of one phyllotactic domain at the expense of another. In particular, glide separation of dislocations offers a low-energy mode for plastic deformations of solid tubes in response to external stresses, reconfiguring the lattice step by s...
We study colloids suspended in nematic liquid crystal in grooves with homeotropic anchoring. We o... more We study colloids suspended in nematic liquid crystal in grooves with homeotropic anchoring. We observe "eyelashes", topological dipole chains that follow the local, curved director field. These beget wires that connect the groove corners to topographical features on the cell lid to yield oriented, curvilinear colloidal wires spanning the cell, formed in a nonsingular director field. As the groove aspect ratio changes, we find different ground states and corroborate our observation with numerics. Our results rely upon on the scale of topographical features, the sharpness of edges, and the colloid-sourced distortions; all these elements can be exploited to guide the formation of reconfigurable structures in nematics.
Controlling the molecular alignment of liquid crystal monomers (LCMs) within nano- and microstruc... more Controlling the molecular alignment of liquid crystal monomers (LCMs) within nano- and microstructures is essential in manipulating the actuation behavior of nematic liquid crystal elastomers (NLCEs). Here, we study how to induce uniformly vertical alignment of nematic LCMs within a micropillar array to maximize the macroscopic shape change using surface chemistry. Landau-de Gennes numerical modeling suggests that it is difficult to perfectly align LCMs vertically in every pore within a poly(dimethylsiloxane) (PDMS) mold with porous channels during soft lithography. In an untreated PDMS mold that provides homeotropic anchoring of LCMs, a radially escaped configuration of LCMs is observed. Vertically aligned LCMs, a preferred configuration for actuation, are only observed when using a PDMS mold with planar anchoring. Guided by the numerical modeling, we coat the PDMS mold with a thin layer of poly(2-hydroxyethyl methacrylate) (PHEMA), leading to planar anchoring of LCM. Confirmed by ...
Filamentous bacteriophages such as the fd virus have long been used as ideal model systems to inv... more Filamentous bacteriophages such as the fd virus have long been used as ideal model systems to investigate the phase behavior of suspensions of rodlike particles. We study the structure and phase behavior of a mutant, fd Y21M, and compare them to the properties of conventional fd wild-type (wt). These two viruses exhibit dramatically different phase behavior despite differing only by a single amino acid of the major coat protein pVIII. We find that this is attributable to significant differences in the flexibility of the viruses. Using the more rigid fd Y21M, we are able for the first time to quantitatively test the Onsager description of the isotropic-nematic phase transition of rigid rods. Even more surprising are the differences in the behavior of the cholesteric phase of fd Y21M and fd wt. While fd wt forms a cholesteric pitch with a left-handed helix, fd Y21M forms a cholesteric pitch with the opposite handedness. In addition, the magnitude of the cholesteric pitch changes by almost fivefold. Using mixtures of the two viruses, we are able to create liquid crystal systems with tunable control over the macroscopic chiral behavior.
ABSTRACT The use of micropost arrays is explored as a means for controlling self-assembly and dir... more ABSTRACT The use of micropost arrays is explored as a means for controlling self-assembly and director alignment in nematic chromonic liquid crystal (CLC) films. Experiment and numerical solutions reveal that the micropost arrays induce bistable director alignment in the film, along either diagonal of a square micropost lattice. We demonstrate stabilization of large domains of a single director orientation by rubbing the substrate surface along a single diagonal, a procedure which biases planar CLC director alignment in the film. Additionally, by varying the rubbing angle we investigate the competition between alignment via micropost patterns versus substrate rubbing, and we find the resulting assemblies to be largely controlled by micropost geometry. Variation of micropost layout, spacing and dimensions leads to further interesting self-assembled patterns and defect geometries.
We report synergistic co-assembly between smectic A liquid crystal (SmA LC) and planar anchoring ... more We report synergistic co-assembly between smectic A liquid crystal (SmA LC) and planar anchoring fluorosilane functionalized silica (F-SiO2) nanoparticles (NPs). Both scanning electron microscope (SEM) images and grazing incidence X-ray diffraction (GIXD) patterns show that when cooled from the isotropic phase to SmA phase, F-SiO2 NPs (100-500 nm in diameter) migrate from the bottom to the top of the LC film through the central cusp defects of toric focal conic domains (TFCDs). When the NPs form a monolayer on top, replacing the LC/air interface, vertically aligned SmA layers are formed between the top and bottom planar surfaces. When F-SiO2 NP diameter is small (<500 nm), we observe a weak-anchoring regime, where NPs do not cause appreciable layer curvature and NP migration is driven by surface energy. When F-SiO2 particle diameter > 500 nm, strong distortions occur in the smectic layers, and the particle is found suspended at the TFCD defect core. The knowledge of the interm...
When immiscible fluids are advected by an externally applied chaotic flow field, a nonequilibrium... more When immiscible fluids are advected by an externally applied chaotic flow field, a nonequilibrium steady state arises from the competition between coarsening and the chaotic ripping-apart of domains. We simulate a two-dimensional binary fluid system advected by two different flow fields: a periodic alternating vortex flow and a periodic alternating sine flow. For each case, we examine the local degree of chaos in the flow field by computing finite-backward-time Lyapunov exponent values at each point in the system. We find that this Lyapunov exponent field is correlated with the advected fluids' local free energy density, which is inversely related to the local time-averaged size of phase-separated domains in the steady state. This raises the possibility of making universal predictions of steady-state characteristics based on Lyapunov analysis of the flow field.
New image (MOC, THEMIS, HRSC and HiRISE) and topography (MOLA) data now available allow for a re-... more New image (MOC, THEMIS, HRSC and HiRISE) and topography (MOLA) data now available allow for a re-examination of the aureoles. Spatial, geographic and topographic relations have been examined.
We consider a system of two immiscible fluids advected by a chaotic flow field. A nonequilibrium ... more We consider a system of two immiscible fluids advected by a chaotic flow field. A nonequilibrium steady state arises from the competition between the coarsening of the immiscible fluids and the domain bursting caused by the chaotic flow. It has been established that the average domain size in this steady state scales as a inverse power of the Lyapunov exponent. We examine the issue of local structure and look for correlations between the local domain size and the finite-time Lyapunov exponent (FTLE) field. For a variety of chaotic flows, we consistently find the domains to be smallest in regions where the FTLE field is maximal. This raises the possibility of making universal predictions of steady-state characteristics based on Lyapunov analysis of the flow field.
In this work, we exploit well defined boundary conditions to control the formation of defects in ... more In this work, we exploit well defined boundary conditions to control the formation of defects in nematic liquid crystal (NLC) 5CB. When supported between micropost arrays, disclination lines form and bear the signature of the micropost shape owing to the elasticity of the medium. The existence of these disclination lines can be tuned due to the thermotropic nature of the material simply by varying temperature thereby providing an element of control not present in typical isotropic fluids. When colloids are introduced to a nematic liquid crystal, elastic distortions arise that have an associated Frank free energy cost. This excess energy is reduced by interacting with the micropost induced disclination lines and subsequent colloid-micropost attractions arise. We consider both isotropic particles (spheres) and more complex anisotropic particles. Further, we observe these effects 5CB-air interfaces as well as in bulk 5CB. This work is experimental and supplemented with analysis to supp...
While the physics of spherical colloids confined in a nematic slab has been thoroughly investigat... more While the physics of spherical colloids confined in a nematic slab has been thoroughly investigated (see, e.g. [1-3]), interactions between anisotropic particles are less well studied [4-6]. Here, we report the behavior of micro-rods confined in a nematic cell. The anchoring conditions on the particles and on the bounding walls of the cell are well defined. Depending on the type of anchoring, cylinders spontaneously form 1D structures, chains parallel to the director, and 2D ordered structures, crystals with hexagonal symmetry. These latter structures are not observed for isotropic particles. By application of an external field, the anchoring conditions on the bounding walls can be dynamically controlled, and transitions between the different structures can be generated. Recent progress in understanding the particle self-assembly process is presented. [1] P. Poulin and D. Weitz, Physical Review E, 57, 626 (1998). [2] M. Škarabot and el., Physical Review E, 77, 031705 (2008). [3] I. ...
We exploit the long-ranged elastic fields inherent to confined nematic liquid crystals to assembl... more We exploit the long-ranged elastic fields inherent to confined nematic liquid crystals to assemble colloidal particles trapped at the liquid crystal interface into reconfigurable structures with complex symmetries and packings. Spherical colloids with homeotropic anchoring trapped at the interface between air and the nematic liquid crystal 5CB create quadrupolar distortions in the director field causing particles to repel and consequently form close-packed assemblies with a triangular habit. Here we report on complex, open structures organized via interactions with defects in the bulk. Specifically, by confining the nematic liquid crystal in an array of microposts with homeotropic anchoring conditions, we cause defect rings to form at well-defined locations in the bulk of the sample. These defects source elastic deformations that direct the assembly of the interfacially-trapped colloids into ring-like assemblies, which recapitulate the defect geometry even when the microposts are co...
Focal conic domains (FCDs) in smectic-A liquid crystals have drawn much attention, both for their... more Focal conic domains (FCDs) in smectic-A liquid crystals have drawn much attention, both for their exquisitely structured internal form and for their ability to direct the assembly of micromaterials and nanomaterials in a variety of patterns. A key to directing FCD assembly is control over the eccentricity of the domain. Here, we demonstrate a new paradigm for creating spatially varying FCD eccentricity by confining a hybrid-aligned smectic with curved interfaces. In particular, we manipulate interface behavior with colloidal particles in order to experimentally produce two examples of what has recently been dubbed the flower texture [C. Meyer et al., Focal Conic Stacking in Smectic A Liquid Crystals: Smectic Flower and Apollonius Tiling, Materials 2, 499, 2009], where the focal hyperbolæ diverge radially outward from the center of the texture, rather than inward as in the canonical éventail or fan texture. We explain how this unconventional assembly can arise from appropriately curv...
Colloidal particles organize spontaneously at fluid interfaces owing to a variety of interactions... more Colloidal particles organize spontaneously at fluid interfaces owing to a variety of interactions to form well organized structures that can be exploited to synthesize advanced materials. While the physics of colloidal assembly at isotropic interfaces is well understood, the mechanisms that govern interactions between particles at liquid crystal interfaces are not yet clearly established. In particular, smectic liquid crystal films offer important degrees of freedom that can be used to direct particles into new structures. In this work, we report the behavior of solid micrometric beads with homeotropic anchoring confined at interfaces of thin smectic films. We study the interactions and self-assembly of these particles in both supported and free standing films. When particles are captured in thin membranes, they induce distortions of the smectic interface to satisfy wetting properties at particle boundaries, leading to capillary interactions. These forces compete with elastic ones i...
ABSTRACT The use of micropost arrays is explored as a means for controlling self-assembly and dir... more ABSTRACT The use of micropost arrays is explored as a means for controlling self-assembly and director alignment in nematic chromonic liquid crystal (CLC) films. Experiment and numerical solutions reveal that the micropost arrays induce bistable director alignment in the film, along either diagonal of a square micropost lattice. We demonstrate stabilization of large domains of a single director orientation by rubbing the substrate surface along a single diagonal, a procedure which biases planar CLC director alignment in the film. Additionally, by varying the rubbing angle we investigate the competition between alignment via micropost patterns versus substrate rubbing, and we find the resulting assemblies to be largely controlled by micropost geometry. Variation of micropost layout, spacing and dimensions leads to further interesting self-assembled patterns and defect geometries.
ABSTRACT We compare the phase behavior of a mutant filamentous virus, fd Y21M, to that of a conve... more ABSTRACT We compare the phase behavior of a mutant filamentous virus, fd Y21M, to that of a conventional fd wild-type (wt). We find significantly different macroscopic phase behavior despite the only microscopic difference between the two viruses being in a single amino acid of the major coat proteinpVIII. Compared to fd wt, the location of the isotropic–cholesteric phase transition for fd Y21M shifts to lower densities. This is attributable to a significant difference in the flexibility of the two viruses. The persistence length of fd wt is 2.8 ± 0.7 µm, whereas the persistence length of fd Y21M is 9.9 ± 1.6 µm. The large persistence length of fd Y21M makes it an essentially rigid rod, thus allowing for the first time a quantitative test of the Onsager theory for the isotropic–nematic phase transition. Even more striking, is the difference in the chiral phase behavior of the two viruses. Both viruses form cholesteric phases, with the fd wt forming a left-handed cholesteric helix, and the fd Y21M forming a right-handed one. At a given density, the magnitude of the cholesteric pitch between the two systems is different by fivefold. Using mixtures of the two viruses, we create a liquid crystalline system with a tunable control over its macroscopic chirality.
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