arXiv subjects

Matthew A. Glaser

Publications and source records attributed to Matthew A. Glaser.

At least 19 recordsLinked to original sources

arXiv2025

Fully-chromophoric ferroelectric nematics for electronic electro-optics

Electronic electro-optic (EEO) phase modulation is a key emerging technology for the chip-scale inter-conversion of signals between the electronic and photonic domains. The recent discovery of the ferroelectric nematic ($N_F$) liquid crystal phase, a three dimensional fluid of rod-shaped organic molecules having near-perfect equilibrium polar molecular orientational order, offers attractive opportunities for the creation of second-order nonlinear optical materials for EEO. Here we propose and realize a design motif for $N_F$ EEO molecules in which few-nanometer-long molecular rods are functionalized both for electro-static end-to-end association, facilitating $N_F$ phase formation, and for chromophoric optical nonlinearity, enabling high EEO efficiency, a combination enabling an active second-order nonlinear EEO medium that is 100% chromophoric.

cond-mat.soft↗

arXiv2024

An active hydroelastic liquid crystal phase of a fluttering ferroelectric nematic

Polarization flutter, produced by an applied AC electric field drives an equilibrium ferroelectric nematic ($\mathrm{N_F}$) liquid crystal (LC) through a transition into a dissipative active ferroelectric nematic state exhibiting strong elasto-hydrodynamic intermolecular interaction. In such a fluttering ferroelectric, the typical equilibrium $\mathrm{N_F}$ textural features adopted to reduce electrostatic energy, such as preferences for director bend, and alignment of polarization parallel to LC/air interfaces, are overcome, giving way to nonequilibrium conjugate structures in which director splay, and alignment of polarization normal to $\mathrm{N_F}$/air interfaces are preferred. Viewing the latter textures as those of an active nematic phase reveals that self-organization to reduce effective viscosity and resulting dissipation generates a flow-driven apparent nematic elasticity and interface structuring that dominates equilibrium LC elastic and surface forces.

cond-mat.soft↗

arXiv2024

Freely Suspended Nematic and Smectic Films and Free-Standing Smectic Filaments in the Ferroelectric Nematic Realm

We show that stable, freely suspended liquid crystal films can be made from the ferroelectric nematic ($\mathrm{N_F}$) phase and from the recently discovered polar, lamellar $\mathrm{SmZ_A}$ and $\mathrm{SmA_F}$ phases. The $\mathrm{N_F}$ films display two-dimensional, smectic-like parabolic focal conic textures comprising director/polarization bend that are a manifestation of the electrostatic suppression of director splay in the film plane. In the $\mathrm{SmZ_A}$ and $\mathrm{SmA_F}$ phases, the smectic layers orient preferentially normal to the film surfaces, a condition never found in typical thermotropic or lyotropic lamellar LC phases, with the $\mathrm{SmZ_A}$ films exhibiting focal-conic fan textures mimicking the appearance of typical smectics in glass cells when the layers are oriented normal to the plates, and the $\mathrm{SmA_F}$ films showing a texture of plaquettes of uniform in-plane orientation where both bend and splay are suppressed, separated by grain boundaries. The $\mathrm{SmA_F}$ phase can also be drawn into thin filaments, in which X-ray scattering reveals that the smectic layer planes are normal to the filament axis. Remarkably, the filaments are mechanically stable even if they break, forming free-standing, fluid filaments supported only at one end. The unique architectures of these films and filaments are stabilized by the electrostatic self-interaction of the liquid crystal polarization field, which enables the formation of confined, fluid structures that are fundamentally different from those of their counterparts made using previously known liquid crystal phases.

cond-mat.soft↗

arXiv2024

Thermotropic reentrant isotropy and antiferroelectricity in the ferroelectric nematic realm: Comparing RM734 and DIO

The current intense study of ferroelectric nematic liquid crystals was initiated by the observation of the same ferroelectric nematic phase in two independently discovered organic rod-shaped mesogenic compounds, RM734 and DIO. We recently reported that the compound RM734 also exhibits a monotropic, low-temperature, antiferroelectric phase having reentrant isotropic symmetry (the $I_A$ phase), the formation of which is facilitated to a remarkable degree by doping with small (below $1\%$) amounts of the ionic liquid ${\rm BMIM-PF}_6$. Here we report similar phenomenology in DIO, showing that this reentrant isotropic behavior is not only a property of RM734 but is rather a more general, material-independent feature of ferroelectric nematic mesogens. We find that the reentrant isotropic phases observed in RM734 and DIO are similar but not identical, adding two new phases to the ferroelectric nematic realm. The two $I_A$ phases exhibit similar, strongly peaked, diffuse x-ray scattering in the WAXS range $(1<q<2 \, Å^{-1})$ indicative of a distinctive mode of short-ranged, side-by-side molecular packing. The scattering of the $I_A$ phases at small $q$ is quite different in the two materials, however, with RM734 exhibiting a strong, single, diffuse peak at $q \sim 0.08 \,Å^{-1}$ indicating mesoscale modulation with $\sim 80 \,Å$ periodicity, and DIO a sharper diffuse peak at $q \sim 0.27 \,Å^{-1} \sim (2π/{\rm molecular length})$, with second and third harmonics, indicating that in the $I_A$ phase of DIO, short-ranged molecular positional correlation is smectic layer-like.

cond-mat.soft↗

arXiv2023

Dielectric spectroscopy of ferroelectric nematic liquid crystals: Measuring the capacitance of insulating interfacial layers

Numerous measurements of the dielectric constant $ε$ of the recently discovered ferroelectric nematic ($N_F$) liquid crystal (LC) phase report extraordinarily large values of $ε^\prime$ (up to ~30,000). We show that what is in fact being measured in such experiments is the high capacitance of the non-ferroelectric, interfacial, insulating layers of nanoscale thickness that bound the $N_F$ material in typical cells. We analyze a parallel-plate cell filled with $N_F$ material of high-polarization $\mathbf{P}$, oriented parallel to the plates at zero applied voltage. Minimization of the dominant electrostatic energy renders $\mathbf{P}$ spatially uniform and orients it to make the electric field in the $N_F$ as small as possible, a condition under which the voltage applied to the cell appears almost entirely across the high-capacity interfacial layers. This coupling of orientation and charge creates a combined polarization-external capacitance (PCG) Goldstone reorientation mode requiring applied voltages orders of magnitude smaller than that of the $N_F$ layer alone to effectively transport charge across the $N_F$ layer. The $N_F$ layer acts as a low-value resistor and the interfacial capacitors as reversible energy storage reservoirs, lowering the restoring force (mass) of the PCG mode and producing strong reactive dielectric behavior. Analysis of data from several experiments on ferroelectric liquid crystals (chiral smectics C, bent-core smectics, and the $N_F$ phase supports the PCG model, showing that deriving dielectric constants from electrical impedance measurements of high-polarization ferroelectric LCs, without properly accounting for the self-screening effects of polarization charge and the capacitive contributions of interfacial layers, can result in overestimation of the $ε^\prime$ values of the LC by many orders of magnitude.

cond-mat.soft↗

arXiv2023

Thermotropic reentrant isotropy and antiferroelectricity in the ferroelectric nematic material RM734

We report a transition from the ferroelectric nematic liquid crystal ($N_F$) phase to a lower-temperature, antiferroelectric fluid phase having reentrant isotropic symmetry ($I_A$), in the liquid crystal compound RM734 doped with small concentrations of the ionic liquids BMIM or EMIM. Even a trace amount of ionic liquid dopant facilitates the kinetic pathway for the transition from the $N_F$ to the $I_A$, enabling simple cooling to produce this isotropic fluid phase rather than resulting in crystallization. The $I_A$ was also obtained in the absence of specific ionic liquid doping by appropriate temperature cycling in three distinct, as-synthesized-and-purified batches of RM734, two commercial and one from our laboratory. An additional birefringent, lamellar-modulated, antiferroelectric phase with the director parallel to the layers, resembling the smectic $Z_A$, is found between the paraelectric and ferroelectric nematic phases in RM734/BMIM mixtures.

cond-mat.soft↗

arXiv2022

Observation of a uniaxial ferroelectric smectic A phase

We report the smectic $A_F$, a new liquid crystal phase of the ferroelectric nematic realm. The smectic $A_F$ is a phase of small polar, rod-shaped molecules which form two-dimensional fluid layers spaced by approximately the mean molecular length. The phase is uniaxial, with the molecular director, the local average long-axis orientation, normal to the layer planes, and ferroelectric, with a spontaneous electric polarization parallel to the director. Polarization measurements indicate almost complete polar ordering of the $\sim 10$ Debye longitudinal molecular dipoles, and hysteretic polarization reversal with a coercive field of about $2 \times 10^5$ V/m is observed. The smectic $A_F$ phase appears upon cooling in two binary mixtures of partially fluorinated mesogens: 2N/DIO, exhibiting a nematic ($N$) -- smectic $Z_A$ (Sm$Z_A$) -- ferroelectric nematic ($N_F$) -- smectic $A_F$ (Sm$A_F$) phase sequence; and 7N/DIO, exhibiting an $N$ -- Sm$Z_A$ -- Sm$A_F$ phase sequence. The latter presents an opportunity to study a transition between two smectic phases having orthogonal systems of layers.

cond-mat.soft↗

arXiv2022

Towards the cellular-scale simulation of motor-driven cytoskeletal assemblies

The cytoskeleton -- a collection of polymeric filaments, molecular motors, and crosslinkers -- is a foundational example of active matter, and in the cell assembles into organelles that guide basic biological functions. Simulation of cytoskeletal assemblies is an important tool for modeling cellular processes and understanding their surprising material properties. Here we present aLENS, a novel computational framework to surmount the limits of conventional simulation methods. We model molecular motors with crosslinking kinetics that adhere to a thermodynamic energy landscape, and integrate the system dynamics while efficiently and stably enforcing hard-body repulsion between filaments -- molecular potentials are entirely avoided in imposing steric constraints. Utilizing parallel computing, we simulate different mixtures of tens to hundreds of thousands of cytoskeletal filaments and crosslinking motors, recapitulating self-emergent phenomena such as bundle formation and buckling, and elucidating how motor type, thermal fluctuations, internal stresses, and confinement determine the evolution of active matter aggregates.

cond-mat.soft↗

arXiv2021

Antiferroelectric Smectic Ordering as a Prelude to the Ferroelectric Nematic:Introducing the Smectic $Z_A$ Phase

We have structurally characterized the liquid crystal phase that appears as an intermediate state when a dielectric nematic, having polar disorder of its molecular dipoles, transitions to the almost perfectly polar-ordered ferroelectric nematic. This intermediate phase, which fills a 100-year-old void in the taxonomy of smectics and which we term the "smectic $Z_A$", is antiferroelectric, with the nematic director and polarization oriented parallel to smectic layer planes, and the polarization alternating in sign from layer to layer. The period of this polarization wave ($\sim$180 A) is mesoscopic, corresponding to $\sim$40 molecules side-by-side, indicating that this lamellar structure is collectively stabilized. A Landau free energy, originally formulated to model incommensurate antiferroelectricity in crystals, describes the key features of the nematic-Sm$Z_A$-ferroelectric nematic phase sequence.

cond-mat.soft↗

arXiv2021

Ideal Mixing of Paraelectric and Ferroelectric Nematic Phases in Liquid Crystals of Distinct Molecular Species

The organic mesogens RM734 and DIO are members of separate molecular families featuring distinct molecular structures. These families, at the present time, are the only ones known to exhibit a ferroelectric nematic liquid crystal (LC) phase. Here we present an experimental investigation of the phase diagram and electro-optics of binary mixtures of RM734 and DIO. We observe paraelectric nematic (N) and ferroelectric nematic (NF) phases in both materials, each of which exhibits complete miscibility across the phase diagram, showing that the paraelectric and ferroelectric are the same phases in RM734 as in DIO. Remarkably, these molecules form ideal mixtures with respect to both the paraelectric-ferroelectric nematic phase behavior and the ferroelectric polarization density of the mixtures, the principal order parameter of the transition. Ideal mixing is also manifested in the orientational viscosity, and the onset of glassy dynamics at low temperature. This behavior is attributable in part to the similarity of their overall molecular shape and net longitudinal dipole moment (~ 11 Debye), and to a common tendency for head-to-tail molecular association. In contrast, the significant difference in molecular structures leads to poor solubility in the crystal phases, enhancing the stability of the ferroelectric nematic phase at low temperature in the mixtures and making possible room temperature electro-optic effects. In the mixtures with excess DIO, an intermediate phase appears via an ultraweak, first-order transition from the N phase, in a narrow temperature range between the paraelectric and ferroelectric nematics.

cond-mat.soft↗

arXiv2021

Polar In-Plane Surface Orientation of a Ferroelectric Nematic Liquid Crystal: Polar Monodomains and Twisted State Electro-Optics

We show that surface interactions can vectorially structure the three-dimensional polariza-tion field of a ferroelectric fluid. The contact between a ferroelectric nematic liquid crystal and a surface with in-plane polarity generates a preferred in-plane orientation of the polarization field at that interface. This is a route to the formation of fluid or glassy monodomains of high polarization without the need for electric field poling. For example, unidirectional buffing of polyimide films on planar surfaces to give quadrupolar in-plane anisotropy also induces mac-roscopic in-plane polar order at the surfaces, enabling the formation of a variety of azimuthal polar director structures in the cell interior, including uniform and twisted states. In a π-twist cell, obtained with antiparallel, unidirectional buffing on opposing surfaces, we demonstrate three distinct modes of ferroelectric nematic electro-optic response: intrinsic, viscosity-limited, field-induced molecular reorientation; field-induced motion of domain walls separating twist-ed states of opposite chirality; and propagation of polarization reorientation solitons from the cell plates to the cell center upon field reversal. Chirally doped ferroelectric nematics in anti-parallel-rubbed cells produce Grandjean textures of helical twist that can be unwound via field-induced polar surface reorientation transitions. Fields required are in the 3 V/mm range, indicating an in-plane polar anchoring energy of wP ~ 3x10-3 J/m2.

cond-mat.soft↗

arXiv2021

Comparison of explicit and mean-field models of cytoskeletal filaments with crosslinking motors

In cells, cytoskeletal filament networks are responsible for cell movement, growth, and division. Filaments in the cytoskeleton are driven and organized by crosslinking molecular motors. In reconstituted cytoskeletal systems, motor activity is responsible for far-from-equilibrium phenomena such as active stress, self-organized flow, and spontaneous nematic defect generation. How microscopic interactions between motors and filaments lead to larger-scale dynamics remains incompletely understood. To build from motor-filament interactions to predict bulk behavior of cytoskeletal systems, more computationally efficient techniques for modeling motor-filament interactions are needed. Here we derive a coarse-graining hierarchy of explicit and continuum models for crosslinking motors that bind to and walk on filament pairs. We compare the steady-state motor distribution and motor-induced filament motion for the different models and analyze their computational cost. All three models agree well in the limit of fast motor binding kinetics. Evolving a truncated moment expansion of motor density speeds the computation by $10^3$--$10^6$ compared to the explicit or continuous-density simulations, suggesting an approach for more efficient simulation of large networks. These tools facilitate further study of motor-filament networks on micrometer to millimeter length scales.

physics.bio-ph↗

arXiv2020

Chiral self-sorting of active semiflexible filaments with intrinsic curvature

Many-body interactions in systems of active matter can cause particles to move collectively and self-organize into dynamic structures with long-range order. In cells, the self-assembly of cytoskeletal filaments is critical for cellular motility, structure, intracellular transport, and division. Semiflexible cytoskeletal filaments driven by polymerization or motor-protein interactions on a two-dimensional substrate, such as the cell cortex, can induce filament bending and curvature leading to interesting collective behavior. For example, the bacterial cell-division filament FtsZ is known to have intrinsic curvature that causes it to self-organize into rings and vortices, and recent experiments reconstituting the collective motion of microtubules driven by motor proteins on a surface have observed chiral symmetry breaking of the collective behavior due to motor-induced curvature of the filaments. Previous work on the self-organization of driven filament systems have not studied the effects of curvature and filament structure on collective behavior. In this work, we present Brownian dynamics simulation results of driven semiflexible filaments with intrinsic curvature and investigate how the interplay between filament rigidity and radius of curvature can tune the self-organization behavior in homochiral systems and heterochiral mixtures. We find a curvature-induced phase transition from polar flocks to self-sorted chiral clusters, which is modified by filament flexibility. This phase transition changes filament transport from ballistic to diffusive at long timescales.

cond-mat.soft↗

arXiv2020

Collective motion of driven semiflexible filaments tuned by soft repulsion and stiffness

In active matter systems, self-propelled particles can self-organize to undergo collective motion, leading to persistent dynamical behavior out of equilibrium. In cells, cytoskeletal filaments and motor proteins self-organize into complex structures important for cell mechanics, motility, and division. Collective dynamics of cytoskeletal systems can be reconstituted using filament gliding experiments, in which cytoskeletal filaments are propelled by surface-bound motor proteins. These experiments have observed diverse dynamical states, including flocks, polar streams, and single-filament spirals. Recent experiments with microtubules and kinesin motor proteins found that the collective behavior of filaments can be tuned by altering the concentration of the crowding macromolecule methylcellulose in solution. Increasing the methycellulose concentration reduced filament crossing, promoted alignment, and led to a transition from active, isotropically oriented filaments to locally aligned polar streams. This emergence of collective motion is typically explained as an increase in alignment interactions by Vicsek-type models of active polar particles. However, it is not yet understood how steric interactions and bending stiffness modify the collective behavior of active filaments. We use simulations of driven filaments with tunable soft repulsion and rigidity in order to better understand how the interplay between filament flexibility and steric effects can lead to different active dynamic states. We find that increasing filament stiffness decreases the probability of filament alignment, yet increases collective motion and long-range order, in contrast to the assumptions of a Vicsek-type model. In addition to repulsion and driving, tuning filament stiffness can promote collective behavior, and controls the transition between active isotropic filaments, locally aligned flocks, and polar streams.

cond-mat.soft↗

arXiv2018

Experimental Studies of Two-dimensional Laminar Jet Flows in Freely Suspended Liquid Crystal Films

Two dimensional (2D) laminar jet-----a stream of fluid that projected into a surrounding medium with the flow confined in 2D-----has both theoretical and experimental significance. We carried out 2D laminar jet experiments in freely suspended liquid crystal films (FSLCFs) of nanometers thick and centimeters in size, in which individual molecules are confined to single layers thus enable film flows with two degrees of freedom. The experimental observations are found in good agreement with the classic 2D laminar jet theory of ideal cases that assume no external coupling effects, even in fact there exist strong coupling force from the ambient air. We further investigated this air coupling effect in computer simulations, with the results indicated air has little influence on the velocity maps of flow near the nozzle. This astonishing results could be intuitively understood by considering 2D incompressibility of the films. This experiment, together with a series of our previous experiments, show for a wide range of Reynolds number, FSLCFs are excellent testing beds for 2D hydrodynamics.

cond-mat.soft↗

arXiv2017

Realization of hydrodynamic experiments on quasi-2D liquid crystal films in microgravity

Freely suspended films of smectic liquid crystals are unique examples of quasi two-dimensional fluids. Mechanically stable and with quantized thickness of the order of only a few molecular layers, smectic films are ideal systems for studying fundamental fluid physics, such as collective molecular ordering, defect and fluctuation phenomena, hydrodynamics, and nonequilibrium behavior in two dimensions (2D), including serving as models of complex biological membranes. Smectic films can be drawn across openings in planar supports resulting in thin, meniscus-bounded membranes, and can also be prepared as bubbles, either supported on an inflation tube or floating freely. The quantized layering renders smectic films uniquely useful in 2D fluid physics. The OASIS team has pursued a variety of ground-based and microgravity applications of thin liquid crystal films to fluid structure and hydrodynamic problems in 2D and quasi-2D systems. Parabolic flights and sounding rocket experiments were carried out in order to explore the shape evolution of free floating smectic bubbles, and to probe Marangoni effects in flat films. The dynamics of emulsions of smectic islands (thicker regions on thin background films) and of microdroplet inclusions in spherical films, as well as thermocapillary effects, were studied over extended periods within the OASIS (Observation and Analysis of Smectic Islands in Space) project on the International Space Station. We summarize the technical details of the OASIS hardware and give preliminary examples of key observations.

cond-mat.soft↗

arXiv2017

Double-Helical Tiled Chain Structure of the Twist-Bend Liquid Crystal phase in CB7CB

The twist-bend nematic liquid crystal phase is a three-dimensional fluid in which achiral bent molecules spontaneously form an orientationally ordered macroscopically chiral heliconical winding of molecular scale pitch, in absence of positional ordering. Here we characterize the structure of the ground state of the twist-bend phase of the bent dimer CB7CB and its mixtures with 5CB over a wide range of concentrations and temperatures, showing that the contour length along the molecular direction for a single turn of the helix is approximately equal to 2πRmol, where Rmol is the radius of bend curvature of a single all-trans CB7CB molecule. This relation emerges from a model which simply relates the macroscopic characteristics of the helical structure, which is mostly biaxial twist and has little bend, to the bent molecular shape. This connection comes about through the presence in the fluid of self-assembled oligomer-like correlations of interlocking molecules, arising from the nanosegregation of rigid and flexible molecular subcomponents, forming a brickwork tiling of pairs of molecular strands into a duplex double-helical chain.

cond-mat.soft↗

arXiv2016

Contributions of microtubule dynamic instability and rotational diffusion to kinetochore capture

Microtubule dynamic instability allows search and capture of kinetochores during spindle formation, an important process for accurate chromosome segregation during cell division. Recent work has found that microtubule rotational diffusion about minus-end attachment points contributes to kinetochore capture in fission yeast, but the relative contributions of dynamic instability and rotational diffusion are not well understood. We have developed a biophysical model of kinetochore capture in small fission-yeast nuclei using hybrid Brownian dynamics/kinetic Monte Carlo simulation techniques. With this model, we have studied the importance of dynamic instability and microtubule rotational diffusion for kinetochore capture, both to the lateral surface of a microtubule and at or near its end. Over a range of biologically relevant parameters, microtubule rotational diffusion decreased capture time, but made a relatively small contribution compared to dynamic instability. At most, rotational diffusion reduced capture time by 25%. Our results suggest that while microtubule rotational diffusion can speed up kinetochore capture, it is unlikely to be the dominant physical mechanism. In addition, we found that when microtubules undergo dynamic instability, lateral captures predominate even in the absence of rotational diffusion. Counterintuitively, adding rotational diffusion to a dynamic microtubule increases the probability of end-on capture.

physics.bio-ph↗