Chiral Droplets Research Articles

Chiral Liquid Crystal Microdroplets for Sensing Phospholipid Amphiphiles.

Designing simple, sensitive, fast, and inexpensive readout devices to detect biological molecules and biomarkers is crucial for early diagnosis and treatments. Here, we have studied the interaction of the chiral liquid crystal (CLC) and biomolecules at the liquid crystal (LC)-droplet interface. CLC droplets with high and low chirality were prepared using a microfluidic device. We explored the reconfiguration of the CLC molecules confined in droplets in the presence of 1,2-diauroyl-sn-glycero3-phosphatidylcholine (DLPC) phospholipid. Cross-polarized optical microscopy and spectrometry techniques were employed to monitor the effect of droplet size and DLPC concentration on the structural reorganization of the CLC molecules. Our results showed that in the presence of DLPC, the chiral LC droplets transition from planar to homeotropic ordering through a multistage molecular reorientation. However, this reconfiguration process in the low-chirality droplets happened three times faster than in high-chirality ones. Applying spectrometry and image analysis, we found that the change in the chiral droplets’ Bragg reflection can be correlated with the CLC–DLPC interactions.

Thermal generation of droplet soliton in chiral magnet

Controlled creation of localized magnetic textures beyond conventional $\ensuremath{\pi}$-skyrmions is an important problem in the field of magnetism. Here, by means of spin dynamics simulations, Monte Carlo simulations, and harmonic transition state theory we demonstrate that an elementary chiral magnetic soliton with zero topological charge---the chiral droplet---can be created by thermal fluctuations in the presence of the tilted magnetic field. The proposed protocol relies on an unusual kinetics combining the effects of the entropic stabilization and low-energy barrier for the nucleation of a topologically trivial state. Following this protocol by varying temperature and the tilt of the external magnetic field, one can selectively generate chiral droplets or $\ensuremath{\pi}$-skyrmions in a single system. The coexistence of two distinct magnetic solitons establishes a basis for a rich magnetization dynamics and opens up the possibility for the construction of more complex magnetic textures such as skyrmion bags and skyrmions with chiral kinks.

Programmable Rainbow-Colored Optofluidic Fiber Laser Encoded with Topologically Structured Chiral Droplets.

Optofluidic lasers are emerging building blocks with immense potential in the development of miniaturized light sources, integrated photonics, and sensors. The capability of on-demand lasing output with programmable and continuous wavelength tunability over a broad spectral range enables key functionalities in wavelength-division multiplexing and manipulation of light-matter interactions. However, the ability to control multicolor lasing characteristics within a small mode volume with high reconfigurability remains challenging. The color gamut is also restricted by the number of dyes and emission wavelength of existing materials. In this study, we introduce a fully programmable multicolor laser by encapsulating organic-dye-doped cholesteric liquid crystal microdroplet lasers in an optofluidic fiber. A mechanism for tuning laser emission wavelengths was proposed by manipulating the topologically induced nanoshell structures in microdroplets with different chiral dopant concentrations. Precision control of distinctive lasing wavelengths and colors covering the entire visible spectra was achieved, including monochromatic lasing, dual-color lasing, tri-color lasing, and white colored lasing with tunable color temperatures. Our findings revealed a CIE color map with 145% more perceptible colors than the standard RGB space, shedding light on the development of programmable lasers, multiplexed encoding, and biomedical detection.

Chiral droplets and current-driven motion in ferromagnets

We find numerically skyrmionic textures with skyrmion number $Q=0$ in ferromagnets with the Dzyaloshinskii-Moriya interaction, perpendicular anisotropy, and the magnetostatic field. These have a skyrmion part and an antiskyrmion part, and they may be called chiral droplets. They are stable in an infinite film as well as in disk-shaped magnetic elements. Droplets are found in films for values of the parameters close to the transition from the ferromagnetic to the spiral phase. Under spin-transfer torque, they move in the direction of the spin flow and behave as solitary waves of Newtonian character, in stark contrast to the Hall dynamics of the standard $Q=1$ skyrmion.

Chaotic and periodical dynamics of active chiral droplets

The interplay between the chirality of many biological molecules and the energy injected at small length-scales as the result of biological processes is at the base of the life of the cells. With the aim of unveiling the connection between these two features, here we analyze by means of lattice Boltzmann simulations the behavior of an active droplet of cholesteric liquid crystal under the effect of intense active doping, within the framework of active gel theory. We find that a droplet of chiral liquid crystal, fueled by active force dipoles, develops defect loops (closed disclination lines) that pierce the interior of the droplet, leading the droplet to develop an erratic motility mode. When the droplet is fueled by in-warding active torque dipoles, three different dynamical regimes develops at varying both the thermodynamic chirality and the strength of active energy injection: a stable rotational state at low activity, an intermittent disclination dance regime, and a turbulent state where closed disclination lines formation is inhibited and new pairs of oppositely charged surface defects leads to the development of chaotic rotational motion. Finally, we show that out-warding torque dipoles are able to sustain a periodical dynamics at higher chirality characterized by the nucleation/annihilation of pairs of disclination rings.

Prolate and oblate chiral liquid crystal spheroids.

Liquid crystals are known to exhibit intriguing textures and color patterns, with applications in display and optical technologies. This work focuses on chiral materials and examines the palette of morphologies that arises when microdroplets are deformed into nonspherical shapes in a controllable manner. Specifically, geometrical confinement and mechanical strain are used to manipulate orientational order, phase transitions, and topological defects that arise in chiral liquid crystal droplets. Inspired by processes encountered in nature, where insects and animals often rely on strain and temperature to alter the optical appearance of dispersed liquid crystalline elements, chiral droplets are dispersed in polymer films and deformation induced by uniaxial or biaxial stretching. Our measurements are interpreted by resorting to simulations of the corresponding systems, thereby providing an in-depth understanding of the morphologies that arise in these materials. The reported structures and assemblies offer potential for applications in smart coatings, smart fabrics, and wearable sensors.

Reorientation behavior in the helical motility of light-responsive spiral droplets

The physico-chemical processes supporting life’s purposeful movement remain essentially unknown. Self-propelling chiral droplets offer a minimalistic model of swimming cells and, in surfactant-rich water, droplets of chiral nematic liquid crystals follow the threads of a screw. We demonstrate that the geometry of their trajectory is determined by both the number of turns in, and the handedness of, their spiral organization. Using molecular motors as photo-invertible chiral dopants allows converting between right-handed and left-handed trajectories dynamically, and droplets subjected to such an inversion reorient in a direction that is also encoded by the number of spiral turns. This motile behavior stems from dynamic transmission of chirality, from the artificial molecular motors to the liquid crystal in confinement and eventually to the helical trajectory, in analogy with the chirality-operated motion and reorientation of swimming cells and unicellular organisms.

Rotation and propulsion in 3D active chiral droplets

Chirality is a recurrent theme in the study of biological systems, in which active processes are driven by the internal conversion of chemical energy into work. Bacterial flagella, actomyosin filaments, and microtubule bundles are active systems that are also intrinsically chiral. Despite some exploratory attempt to capture the relations between chirality and motility, many features of intrinsically chiral systems still need to be explored and explained. To address this gap in knowledge, here we study the effects of internal active forces and torques on a 3-dimensional (3D) droplet of cholesteric liquid crystal (CLC) embedded in an isotropic liquid. We consider tangential anchoring of the liquid crystal director at the droplet surface. Contrary to what happens in nematics, where moderate extensile activity leads to droplet rotation, cholesteric active droplets exhibit more complex and variegated behaviors. We find that extensile force dipole activity stabilizes complex defect configurations, in which orbiting dynamics couples to thermodynamic chirality to propel screw-like droplet motion. Instead, dipolar torque activity may either tighten or unwind the cholesteric helix and if tuned, can power rotations with an oscillatory angular velocity of 0 mean.

Mixed emulsion of liquid crystal microresonators: towards white laser systems.

Microdroplet systems have attracted great interest because of their wide range of applications, easiness in processing and handling, feasibility in developing miniaturized devices with high performances and large flexibility. In this study, a stable emulsion based on different dye-doped chiral liquid crystal droplets has been engineered in order to achieve simultaneous omnidirectional lasing at different wavelengths. To obtain the mixed emulsion of dye doped Bragg onion-type microresonators the twofold action, as a surfactant and a droplet stabilizer, of the polyvinyl alcohol dissolved in water has been exploited. Multiple wavelengths lasing in all directions around the mixed emulsion is demonstrated. By water evaporation, a plastic sheet including different types of chiral droplets is also obtained, retaining all the emission characteristic of the precursor emulsion. A relevant feature is the large flexibility of the preparation method that enables an easy and full control of the lasing spectrum addressing white laser systems. However, the simplicity of the procedure based on a single-step process as well as the high stability of the mixed emulsion is a relevant result, envisaging strong potentiality for developing easy and friendly technologies useful in the field of identification, sensing, imaging, coating and lab-on-a-chip architectures.