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Bulk blue phase structures. Snapshots of the states obtained after dispersing a suspension of colloidal nanoparticles within a cholesteric liquid crystal in the BPI-forming region. a–d correspond to the case of a dispersion of particles in a pre-equilibrated BPI phase; e–h are obtained by dispersing colloids in an isotropic phase and then quenching into the range where BPI is stable, leading to the formation of an amorphous, BPIII-like, disclination network. Structures correspond to (a) and (e) w=0.23 and ϕ=1%; (b) and (f) w=0.23 and ϕ=5%; (c) and (g) w=2.3 and ϕ=1%; (d) and (h) w=2.3 and ϕ=5%. The anchoring of the director field to the colloidal surface is normal. (For the full parameter list used to generate Figs 1, 2, 3 see Supplementary Notes.) For clarity, only a portion of the simulation box is shown its linear extent being (one-eighth of the total volume); the full structures are shown in Supplementary Figs 2 and 3.
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Colloidal particles dispersed in liquid crystals can form new materials with tunable elastic and electro-optic properties. In a periodic 'blue phase' host, particles should template into colloidal crystals with potential uses in photonics, metamaterials and transformational optics. Here we show by computer simulation that colloid/cholesteric mixtur...
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... 1: Free energy parameters used in the simulations. Bulk BPI corre- spond to Fig. 1 (A-D), bulk quench to Fig. 1 (E-H); confined geometries are shown in Fig. 2; and the external field case is relevant for Fig. 3. ...
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... the electric field is then switched off, and the system quickly relaxes to a metastable state which shows a resid- ual anisotropy in the colloidal distribution. The total length of this final relaxation phase is 1 × 10 6 LB time steps. Table 1: Free energy parameters used in the simulations. Bulk BPI corre- spond to Fig. 1 (A-D), bulk quench to Fig. 1 (E-H); confined geometries are shown in Fig. 2; and the external field case is relevant for Fig. ...
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... length scale can be set by mapping the half pitch to a realistic blue phase unit cell size, which is in the 100-500 nm range [1]. For bulk simulations ( Fig. 1 and Fig. 3 in the main text), a suitable choice is one where one simulation unit (lattice site) corresponds to 10 nm. Therefore the colloidal size in Figs. 1 and 3 corresponds to ∼ 50 nm. ...
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... length scale can be set by mapping the half pitch to a realistic blue phase unit cell size, which is in the 100-500 nm range [1]. For bulk simulations ( Fig. 1 and Fig. 3 in the main text), a suitable choice is one where one simulation unit (lattice site) corresponds to 10 nm. Therefore the colloidal size in Figs. 1 and 3 corresponds to ∼ 50 ...
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... obtain an energy scale, it is possible to choose A 0 10 6 Pa, which is reasonable following Ref. [1] (this is also the choice in Ref. [12]). This choice leads to a simulation unit of free energy (or stress) equal to 10 8 Pa in Figs. 1 and 3. From the energy and length scales one can map elastic constants to physical units: for instance, the simulation in Fig. 1 corresponds to a liquid crystal with splay, bend and twist (Frank) elastic constants equal to 35 pN (or equivalently K = 70 ...
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... energy scale, it is possible to choose A 0 10 6 Pa, which is reasonable following Ref. [1] (this is also the choice in Ref. [12]). This choice leads to a simulation unit of free energy (or stress) equal to 10 8 Pa in Figs. 1 and 3. From the energy and length scales one can map elastic constants to physical units: for instance, the simulation in Fig. 1 corresponds to a liquid crystal with splay, bend and twist (Frank) elastic constants equal to 35 pN (or equivalently K = 70 ...
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... relates the rotational viscosity γ 1 to the ordering strength q and the order parameter mobility Γ. In the present simulations, Γ = 0.5 and the value of γ for the simulation in Fig. 1 leads to q = 1/2. For real liquid crystalline materials, γ 1 usually lies in range 10 −2 −1 Pa s [2]; for definiteness say γ 1 = 1 Pa s (equivalently 10 poise). Given the previous mapping for free energy (or stress) units, this leads to a simulation unit of time equal to 10 −8 ...
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... in practice as the Reynolds number = ρV Λ/η (where V is a typical velocity, in our simulations around 21 cell) remains small enough [13]. To summarize, the simulations represent BP-forming materials, with the interpretation of the simulation units for length, time, and energy density being close to 10 nm, 10 ns, and 100 MPa respectively. Fig. 1 A-D (with liquid crystal order parameter initialised to equilibrium blue phase I structure), but for the entire simulation system of 128 3 lattice sites. (A) solid volume fraction 1% and weak anchoring; (B) 4% solid volume fraction and weak anchoring; (C) 1% solid volume fraction and strong anchoring; (D) 4% solid volume fraction and ...
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... 1% and weak anchoring; (B) 4% solid volume fraction and weak anchoring; (C) 1% solid volume fraction and strong anchoring; (D) 4% solid volume fraction and strong anchoring. The view direction in the main figure is from the left here. There is a reference particle at the bottom left in each panel which does not take part in the simulation. Fig. 1 E-H (initialised via a "quench" to generate a disordered network), but for the entire simulation system of 128 3 lattice sites. (E) solid volume fraction 1% and weak anchoring; (F) 4% solid volume fraction and weak anchoring; (G) 1% solid volume fraction and strong anchoring; (H) 4% solid volume fraction and strong anchoring. Again, ...
Citations
... The organic electrochemical transistors (OECTs) that make use of ion injection from an electrolyte to modulate its organic semiconductor channel, have been widely applied in biological interfacing, printed logic circuitry, chemical sensors, neuromorphic devices, and many more. [41,[129][130][131] The doping state of the organic channel could be modulated by the gate voltage-controlled ion injection from the electrolyte dielectric, leading to a conductivity change of the channel. An OECT generally has a very high transconductance than other types of transistors due to the extremely large equivalent capacitance per unit area (typically as high as 100 μF cm −2 , two magnitudes higher than electric-doublelayer (EDL) capacitance) rendered by the ion injection. ...
Brain‐computer interfaces (BCIs) that enable human‐machine interaction have immense potential in restoring or augmenting human capabilities. Traditional BCIs are realized based on complementary metal‐oxide‐semiconductor (CMOS) technologies with complex, bulky, and low biocompatible circuits, and suffer with the low energy efficiency of the von Neumann architecture. The brain‐neuromorphics interface (BNI) would offer a promising solution to advance the BCI technologies and shape our interactions with machineries. Neuromorphic devices and systems are able to provide substantial computation power with extremely high energy‐efficiency by implementing in‐materia computing such as in situ vector‐matrix multiplication (VMM) and physical reservoir computing. Recent progresses on integrating neuromorphic components with sensing and/or actuating modules, give birth to the neuromorphic afferent nerve, efferent nerve, sensorimotor loop, and so on, which has advanced the technologies for future neurorobotics by achieving sophisticated sensorimotor capabilities as the biological system. With the development on the compact artificial spiking neuron and bioelectronic interfaces, the seamless communication between a BNI and a bioentity is reasonably expectable. In this review, the upcoming BNIs are profiled by introducing the brief history of neuromorphics, reviewing the recent progresses on related areas, and discussing the future advances and challenges that lie ahead.
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... This has spurred a number of studies that investigate their emergence in several natural systems [4,[6][7][8][9][10][11][12][13][14][15]. Furthermore, helical motifs in synthetic molecules have been explored for their key technological ramifications [16] such as the synthesis of NEMs devices [17][18][19][20][21][22], piezoelectric devices [23] and other optical materials [24][25][26]. For these applications, helical molecules are typically designed using techniques such as vapour deposition which rely on specific interactions between the constituent monomers. ...
Helical motifs are ubiquitious in macromolecular systems. The mechanism of spontaneous emergence of helicity is unknown, especially in cases where torsional interactions are absent. Emergence of helical order needs coordinated organization over long distances in polymeric macromolecules. We establish a very generic mechanism to obtain spontaneous helicity by inducing screened Coulomb interactions between monomers in a semiflexible heteropolymer. Due to changes in solvent conditions, different segments (monomers) of a polymeric chain can get locally charged with charges of differing polarities and magnitudes along the chain contour. This in turn leads to spontaneous emergence of transient helical structures along the chain contour for a wide range of Debye-lengths. We have avoided using torsional potentials to obtain helical structures and rely only on radially symmetric interactions. Lastly, transient helices can be made long-lived when they are subjected to geometric confinement, which can emerge in experimental realizations through a variety of conditions.
... (2.8) and (2.9) by a standard lattice Boltzmann method [45]. We incidentally note that, although a hybrid LB machinery has been already successfully employed to study binary [52] and ternary fluids [49], active gels [53][54][55] and liquid crystals, such as nematics [56,57] and cholesterics [30,31,[58][59][60][61], in this work the applicability of the method has been further extended to study liquid crystal emulsions in the presence of a surfactant whose dynamics is explicitly solved. ...
We numerically study the dynamics of quasi-two dimensional cholesteric liquid crystal droplets in the presence of a time-dependent electric field, rotating at constant angular velocity. A surfactant sitting at the droplet interface is also intro- duced to prevent droplet coalescence. The dynamics is modeled following a hybrid numerical approach, where a standard lattice Boltzmann technique solves the Navier- Stokes equation and a finite difference scheme integrates the evolution equations of liquid crystal and surfactant. Our results show that, once the field is turned on, the liq- uid crystal rotates coherently triggering a concurrent orbital motion of both droplets around each other, an effect due to the momentum transfer to the surrounding fluid. In addition the topological defects, resulting from the conflict orientation of the liq- uid crystal within the drops, exhibit a chaotic-like motion in cholesterics with a high pitch, in contrast with a regular one occurring along circular trajectories observed in nematics drops. Such behavior is found to depend on magnitude and frequency of the applied field as well as on the anchoring of the liquid crystal at the droplet interface. These findings are quantitatively evaluated by measuring the angular velocity of fluid and drops for various frequencies of the applied field.
... (16)(17)(18)(19)(20)(21)(22)(23) The large birefringence combined with versatile driving methods for switching make LC-NP composites an attractive material system for reconfigurable active plasmonic devices. (24) The switching of such composites was recently experimentally demonstrated for Ag and Au NPs where structural changes of the LC-NP composite were induced by a thermal stimulus and led to a tunable plasmonic response. (25,26) A number of studies report on the successful co-assembly of NPs by LCs into geometries that mimic the mesogen arrangement. ...
The arrangement of nanoscale building blocks into patterns with microscale periodicity is challenging to achieve via self-assembly processes. Here, we report on the phase transition-driven collective assembly of gold nanoparticles in a thermotropic liquid crystal. A temperature-induced transition from the isotropic to the nematic phase leads to the assembly of individual nanometre-sized particles into arrays of micrometre-sized aggregates, whose size and characteristic spacing can be tuned by varying the cooling rate. This fully reversible process offers hierarchical control over structural order on the molecular, nanoscopic, and microscopic level and is an interesting model system for the programmable patterning of nanocomposites with access to micrometre-sized periodicities.
... (8) and (9) by a standard lattice Boltzmann method [45]. We incidentally note that, although a hybrid LB machinery has been already successfully employed to study binary [52] and ternary fluids [49], active gels [53][54][55] and liquid crystals, such as nematics [56,57] and cholesterics [30,31,[58][59][60][61], in this work the applicability of the method has been further extended to study liquid crystal emulsions in the presence of a surfactant whose dynamics is explicitly solved. ...
We numerically study the dynamics of quasi-two dimensional cholesteric liquid crystal droplets in the presence of a time-dependent electric field, rotating at constant angular velocity. A surfactant sitting at droplet interface is also introduced to prevent droplet coalescence. The dynamics is modeled following a hybrid numerical approach, where a standard lattice Boltzmann technique solves the Navier-Stokes equation and a finite difference scheme integrates the evolution equations of liquid crystal and surfactant. Our results show that, once the field is turned on, the liquid crystal rotates coherently triggering a concurrent orbital motion of both droplets around each other, an effect due to the momentum transfer to the surrounding fluid. In addition the topological defects, resulting from the conflict orientation of the liquid crystal within the drops, exhibit a chaotic-like motion in cholesterics with a high pitch, in contrast with a regular one occurring along circular trajectories observed in nematics drops. Such behavior is found to depend on magnitude and frequency of the applied field as well as on the anchoring of the liquid crystal at the droplet interface. These findings are quantitatively evaluated by measuring of the angular velocity of fluid and drops for various frequencies of the applied field.
... Theoretical works also suggest that BPLCs are effective templates of micron-sized colloids to form tunable photonic crystals [20,21]. A new application of BPLCs as templates to control the spatial distribution of nanomaterials was demonstrated by Gharbi et al., who studied gold spherical nanoparticles functionalized with mesogenic ligands in BPLCs [22]. ...
Ethylene oxide oligomers and polymers, free and tethered to gold nanoparticles, were dispersed in blue phase liquid crystals (BPLC). Gold nanospheres (AuNPs) and nanorods (AuNRs) were functionalized with thiolated ethylene oxide ligands with molecular weights ranging from 200 to 5000 g/mol. The BPLC mixture (ΔTBP ~6 °C) was based on the mesogenic acid heterodimers, n-hexylbenzoic acid (6BA) and n-trans-butylcyclohexylcarboxylic acid (4-BCHA) with the chiral dopant (R)-2-octyl 4-[4-(hexyloxy)benzoyloxy]benzoate. The lowest molecular weight oligomer lowered and widened the BP range but adding AuNPs functionalized with the same ligand had little effect. Higher concentrations or molecular weights of the ligands, free or tethered to the AuNPs, completely destabilized the BP. Mini-AuNRs functionalized with the same ligands lowered and widened the BP temperature range with longer mini-AuNRs having a larger effect. In contrast to the AuNPs, the mini-AuNRs with the higher molecular weight ligands widened rather than destabilized the BP, though the lowest MW ligand yielded the largest BP range, (ΔTBP > 13 °C). The different effects on the BP may be due to the AuNPs accumulating at singular defect sites whereas the mini-AuNRs, with diameters smaller than that of the disclination lines, can more efficiently fill in the BP defects.
... [17][18][19][20][21][22][23][24] The large birefringence combined with versatile driving methods for switching make LC-NP composites an attractive material system for reconfigurable active plasmonic devices. 25 The switching of such composites was recently experimentally demonstrated for Ag and Au NPs where structural changes of the LC-NP composite were induced by a thermal stimulus and led to a tunable plasmonic response. 26,27 A number of studies report on the successful co-assembly of NPs by LCs into geometries that mimic the mesogen arrangement. ...
The arrangement of nanoscale building blocks into patterns with microscale periodicity is challenging to achieve via self-assembly processes. Here, we report on the phase transition-driven collective assembly of gold nanoparticles in a thermotropic liquid crystal. A temperature-induced transition from the isotropic to the nematic phase leads to the assembly of individual nanometre-sized particles into arrays of micrometre-sized aggregates, whose size and characteristic spacing can be tuned by varying the cooling rate. This fully reversible process offers hierarchical control over structural order on the molecular, nanoscopic, and microscopic level and is an interesting model system for the programmable patterning of nanocomposites with access to micrometre-sized periodicities.
... Therefore, BPLCs are considered one of the most promising candidates for the highly efficient production of 3D photonic crystals. [89][90][91][92][93] According to Bragg's law, the reflective wavelength (λ) of BP nanostructures can be determined by the following equation [94] λ ...
3D photonic nanostructures with intrinsic chirality have recently entered the research limelight due to their fundamental importance and potential technological applications. Blue‐phase liquid crystals (BPLCs) with chiral cubic nanostructures are an inventive example of 3D chiral photonic nanostructures. The inherently self‐organized 3D chiral nanostructures give rise to a complete photonic bandgap, which results in the selective reflection of circularly polarized light in all three dimensions. Herein, a comprehensive review of the state‐of‐the‐art of BPLCs and their potential applications is presented. First, the history and fundamentals of BPLCs are introduced. Then, the recent endeavors in the design, synthesis, and properties of BPLCs such as lattice orientation control with different techniques, photonic bandgap tuning with external fields, and fabrication of free‐standing BPLC polymer films are summarized. Finally, a discussion of the future challenges and potential applications of BPLCs is provided. It is believed that this review would stimulate innovative ideas for the design and engineering of novel chiral nanostructured materials for advanced photonic systems with tailorable functionalities. 3D chiral photonic nanostructures are of great significance due to the presence of a complete photonic bandgap and omnidirectional selective reflection of circularly polarized light. Herein, an account on the state‐of‐the‐art in blue‐phase liquid crystals with chiral cubic nanostructures and their potential applications is provided. In addition, perspectives for future scope, challenges, and opportunities for such a multidisciplinary topic are presented.
... Much research has been devoted to three-dimensional (3D) self-assembly [25], though a two-dimensional (2D) variant continues to be of interest from an exploratory perspective [47][48][49][50][51][52][53][54][55] as well as in applied technologies [1,56]. Optimal function is achieved via slab geometry in many devices, including optoelectronic/photonic materials [57][58][59][60][61], sensors [60,[62][63][64][65][66][67][68], display technologies [69][70][71], smart glass [72,73], spatial light modulators [74][75][76][77], and tunable filters [78][79][80][81]. However, dimensionality plays an essential role in the type and extent of structural order that a condensed phase can maintain [52,[82][83][84][85][86][87][88]. ...
A bidimensional (2D) thermotropic liquid crystal (LC) is investigated with Molecular Dynamics (MD) simulations. The Gay-Berne mesogen with parameterization GB(3, 5, 2, 1) is used to model a calamitic system. Spatial orientation of the LC samples is probed with the nematic order parameter: a sharp isotropic-smectic (I-Sm) transition is observed at lower pressures. At higher pressures, the I-Sm transition involves an intermediate nematic phase. Topology of the orthobaric phase diagram for the 2D case differs from the 3D case in two important respects: 1) the nematic region appears at lower temperatures and slightly lower densities, and 2) the critical point occurs at lower temperature and slightly higher density. The 2D calamitic model is used to probe the structural behavior of LC samples under strong confinement when either planar or homeotropic anchoring prevails. Samples subjected to circular, square, and triangular boundaries are gradually cooled to study how orientational order emerges. Depending on anchoring mode and confining geometry, characteristic topological defects emerge. Textures in these systems are similar to those observed in experiments and simulations of lyotropic LCs.
... [29][30][31][32][33][34][35] One of the key research goals is to develop a means for controlling such nematic colloidal behavior by external stimuli, which could potentially also lead to technological applications. [36][37][38][39][40][41][42][43][44][45][46][47][48][49] However, while shapes and topology of colloidal inclusions were shown to be capable of defining formation of topological defects and inter-particle colloidal interactions, 8,16,23 so far only theoretical studies considered the possibility of transformations of shape and topological characteristics like genus within such colloidal systems. 50 Similar to nematic LC colloids, controllable actuation of components within composite mesostructured materials are needed in photonic crystals and other microstructures, but progress is limited so far. ...
Control of physical behaviors of nematic colloids and colloidal crystals has been demonstrated by tuning particle shape, topology, chirality and surface charging. However, the capability of altering physical behaviors of such soft matter systems by changing particle shape and the ensuing responses to external stimuli has remained elusive. We fabricated genus-one nematic elastomeric colloidal ring-shaped particles and various microstructures using two-photon photopolymerization. Nematic ordering within both the nano-printed particle and the surrounding medium leads to anisotropic responses and actuation when heated. With the thermal control, elastomeric microstructures are capable of changing from genus-one to genus-zero surface topology. Using these particles as building blocks, we investigated elastomeric colloidal crystals immersed within a liquid crystal fluid, which exhibit crystallographic symmetry transformations. Our findings may lead to colloidal crystals responsive to a large variety of external stimuli, including electric fields and light. Pre-designed response of elastomeric nematic colloids, including changes of colloidal surface topology and lattice symmetry, are of interest for both fundamental research and applications.
