Liquid crystal nanoparticles prepared as miniemulsions

Strongly Chiral Liquid Crystals in Nanoemulsions

Liquid crystal (LC) emulsions represent a class of confined soft matter that exhibit exotic internal organizations and size-dependent properties, including responses to chemical and physical stimuli. Past studies have explored micrometer-scale LC emulsion droplets but little is known about LC ordering within submicrometer-sized droplets. This paper reports experiments and simulations that unmask the consequences of confinement in nanoemulsions on strongly chiral LCs that form bulk cholesteric and blue phases (BPs). A method based on light scattering is developed to characterize phase transitions of LCs within the nanodroplets. For droplets with a radius to the pitch ratio (R_v /p₀ ) as small as 2/3, the BP-to-cholesteric transition is substantially suppressed, leading to a threefold increase of the BP temperature interval relative to bulk behavior. Complementary simulations align with experimental findings and reveal the dominant role of chiral elastic energy. For R_v /p₀  ≈ 1/3, a single LC phase forms below the clearing point, with simulations revealing the new configuration to contain a τ^-1/2 disclination that extends across the nanodroplet. These findings are discussed in the context of mechanisms by which polymer networks stabilize BPs and, more broadly, for the design of nanoconfined soft matter.

Effects of droplet size and surfactants on anchoring in liquid crystal nanodroplets

Liquid crystal (LC) droplets attract scientific attention for many advanced applications, including, but not limited to optical and sensing devices. To aid experimental advancements, theoretical calculations have been conducted to quantify molecular driving forces responsible for the collective behaviour of LC molecules within micrometer-size spherical droplets. To quantify the LC molecular anchoring within spherical physical constraints, molecular simulations at atomistic resolution would be useful. In an attempt to bridge the gap between computational capabilities and experimental interest, coarse-grained simulations are used here to study nematic LC nanodroplets dispersed in water. A LC phase diagram is generated as a function of droplet size and temperature. The effect of adding surfactants on LC anchoring was quantified, considering surfactants of different molecular features. When few surfactants are present, they self-assemble at the droplet boojums regardless of their molecular features. All surfactants tested shifted LC orientation from bipolar to uniaxial. When the surfactants have a hydrophobic tail of sufficient length, they cause deviations from the spherical symmetry of LC droplets. Increasing the concentration of these surfactants enhances such phenomenon. Simulations were also conducted to assess the ability of the surfactants to prevent the agglomeration between two LC droplets. The results showed that coalescence was inevitable at all conditions and suggested that large enough surfactant concentrations can delay the phenomenon. The results presented could be helpful for designing novel surface-active compounds to develop optical and/or sensing devices at conditions in which mutual solubility between water and LCs is low.

Application of Solid Lipid Nanoparticles to Improve the Efficiency of Anticancer Drugs

Drug delivery systems have opened new avenues to improve the therapeutic effects of already-efficient molecules. Particularly, Solid Lipid Nanoparticles (SLNs) have emerged as promising nanocarriers in cancer therapy. SLNs offer remarkable advantages such as low toxicity, high bioavailability of drugs, versatility of incorporation of hydrophilic and lipophilic drugs, and feasibility of large-scale production. Their molecular structure is crucial to obtain high quality SLN preparations and it is determined by the relationship between the composition and preparation method. Additionally, SLNs allow overcoming several physiological barriers that hinder drug delivery to tumors and are also able to escape multidrug resistance mechanisms, characteristic of cancer cells. Focusing on cell delivery, SLNs can improve drug delivery to target cells by different mechanisms, such as passive mechanisms that take advantage of the tumor microenvironment, active mechanisms by surface modification of SLNs, and codelivery mechanisms. SLNs can incorporate many different drugs and have proven to be effective in different types of tumors (i.e., breast, lung, colon, liver, and brain), corroborating their potential. Finally, it has to be taken into account that there are still some challenges to face in the application of SLNs in anticancer treatments but their possibilities seem to be high.

Liquid crystals in micron-scale droplets, shells and fibers

The extraordinary responsiveness and large diversity of self-assembled structures of liquid crystals are well documented and they have been extensively used in devices like displays. For long, this application route strongly influenced academic research, which frequently focused on the performance of liquid crystals in display-like geometries, typically between flat, rigid substrates of glass or similar solids. Today a new trend is clearly visible, where liquid crystals confined within curved, often soft and flexible, interfaces are in focus. Innovation in microfluidic technology has opened for high-throughput production of liquid crystal droplets or shells with exquisite monodispersity, and modern characterization methods allow detailed analysis of complex director arrangements. The introduction of electrospinning in liquid crystal research has enabled encapsulation in optically transparent polymeric cylinders with very small radius, allowing studies of confinement effects that were not easily accessible before. It also opened the prospect of functionalizing textile fibers with liquid crystals in the core, triggering activities that target wearable devices with true textile form factor for seamless integration in clothing. Together, these developments have brought issues center stage that might previously have been considered esoteric, like the interaction of topological defects on spherical surfaces, saddle-splay curvature-induced spontaneous chiral symmetry breaking, or the non-trivial shape changes of curved liquid crystal elastomers with non-uniform director fields that undergo a phase transition to an isotropic state. The new research thrusts are motivated equally by the intriguing soft matter physics showcased by liquid crystals in these unconventional geometries, and by the many novel application opportunities that arise when we can reproducibly manufacture these systems on a commercial scale. This review attempts to summarize the current understanding of liquid crystals in spherical and cylindrical geometry, the state of the art of producing such samples, as well as the perspectives for innovative applications that have been put forward.

Slide cover glass immobilized liquid crystal microdroplets for sensitive detection of an IgG antigen

Slide cover glass immobilized AIgG conjugated LC microdroplets for optical detection of rabbit IgG antigen through interfacial antibody–antigen interactions.

Dynamics of ethyl cellulose nanoparticle self-assembly at the interface of a nematic liquid crystal droplet

A general methodology for the assessment of nanoparticle adsorption at the liquid crystal–water interfaces.

Liquid crystal nanoparticle formulation as an oral drug delivery system for liver-specific distribution

Liquid crystal nanoparticles have been utilized as an efficient tool for drug delivery with enhanced bioavailability, drug stability, and targeted drug delivery. However, the high energy requirements and the high cost of the liquid crystal preparation have been obstacles to their widespread use in the pharmaceutical industry. In this study, we prepared liquid crystal nanoparticles using a phase-inversion temperature method, which is a uniquely low energy process. Particles prepared with the above method were estimated to be ~100 nm in size and exhibited a lamellar liquid crystal structure with orthorhombic lateral packing. Pharmacokinetic and tissue distribution studies of a hydrophobic peptide-based drug candidate formulated with the liquid crystal nanoparticles showed a five-fold enhancement of bioavailability, sustained release, and liver-specific drug delivery compared to a host-guest complex formulation.

Anti-IgG-anchored liquid crystal microdroplets for label free detection of IgG

AIgG anchored LC microdroplets showing configurational transition from radial (a) to bipolar (b) upon interaction with IgG.

The role of ligand–receptor interactions in visual detection of HepG2 cells using a liquid crystal microdroplet-based biosensor

Optical (a) and polarized (b) micrographs showing orientational transition in a LC microdroplet on contacting with a HepG2 cell in PBS solution.

A new pathway for the formation of radial nematic droplets within a lipid-laden aqueous-liquid crystal interface

A new pathway for the formation of liquid crystal (LC) droplets with radial LC ordering is reported for the first time in the presence of surfactants and lipids. Interactions of an enzyme with the topological defects in the LC mediate the response of these droplets and thus provide new designs for stimuli-responsive soft materials.

Detecting proteins in microfluidic channels decorated with liquid crystal sensing dots

In this paper, we report the integration of liquid crystal (LC) dots on microfluidic channels as microscopic protein sensors. Flexibility of patterning LC dots on a surface to fit small microfluidic channels is achieved by using inkjet printing technology. These LC dots (1 pL) remain stable when they are subjected to flowing buffer solution at a high flow velocity (v ≥ 0.198 cm/s). When the buffer solution contains protein, such as bovine serum albumin (BSA), it causes a change in the orientational ordering of the LC dots as indicated by a distinct dark-to-bright transition in the optical appearance of the LC dots. Moreover, we are able estimate the concentration of BSA by simply counting the number of bright LC dot sections. This microscopic protein sensor has potential applications in the real-time detection and quantification of proteins in aqueous solutions. This detection method is advantageous because protein labeling and complex instrumentation are not required.

Inkjet printing and release of monodisperse liquid crystal droplets from solid surfaces

Recently, liquid crystal (LC) droplets in aqueous solutions have become a new platform for chemical and biological sensing applications. In this work, we present a two-step method to generate monodisperse LC droplets in aqueous solutions for sensing applications. In the first step, we exploit inkjet printing to dispense uniform LC droplets on a solid surface. Uniform LC droplets, ranging from 35 to 136 μm in diameter, can be prepared by printing multiple times on the same spot. In the second step, we flush the LC droplets with a stream of aqueous solution in an open rectangular channel. Factors that determine the polydispersity of the LC droplets include flow rates and surface wettability. Under appropriate experimental conditions (i.e., when the surface is glass and the flow rate is sufficiently high), the LC droplets can be lifted off completely and carried away by the solution, forming free LC droplets (15-62 μm in diameter). These free LC droplets can respond to a chemical reaction and change their optical textures uniformly.

Liquid crystal droplets as a hosting and sensing platform for developing immunoassays

In this paper, we report an immunoassay in which probe proteins are immobilized on the surface of liquid crystal (LC) droplets rather than on solid surfaces. The advantage of this immunoassay is that the binding of antibodies to the probe proteins can be transduced by the LC droplets directly without the need for additional steps. For example, when we incubate the LC droplets decorated with immunoglobulin G (IgG) in a solution containing anti-IgG (AIgG), these droplets change their orientations from radial to bipolar configuration. In contrast, when we incubate the IgG-LC droplets in a solution containing anti-human serum albumin (AHSA), no changes are observed. The change of orientational configuration indicates the formation of the antigen-antibody immunocomplex on the surface of the LC droplets. Using LC droplet immunoassays, we successfully detect antibody concentrations as low as 0.01 μg/mL for AIgG and 0.02 μg/mL for AHSA. Because the immunoassay using LC droplets is label-free and gives a unique optical response, it has the potential to be further developed as a portable and low-cost immunoassay.

Director configuration of liquid-crystal droplets encapsulated by polyelectrolytes

Liquid-crystal 4-n-pentyl-4'-cyanobiphenyl (5CB) droplets dispersed in aqueous solution are prepared by the assembly of poly(styrenesulfonic acid) (PSSH) and poly(styrenesulfonate sodium) (PSSNa) at the 5CB/water interface. The micrometer sized PSSH-coated 5CB droplets in the space confinement formed by two parallel glass slides break up into submicrometer sized droplets under evaporation-induced flow. We find that the size reduction of the PSSH-coated droplets is accompanied by the bipolar-to-radial configuration transition of the 5CB in the droplets, while the PSSNa-coated 5CB droplets show no size-dependent configuration transition in the same size range. Our results suggest that the size-dependent director configuration of liquid-crystal droplets encapsulated by polyelectrolytes can be modulated by changing the interface conditions, which is important in designing liquid-crystal droplets for optical and biological applications.

Spectral tuning of organic nanocolloids by controlled molecular interactions

The controlled self-assembly of molecules and interactions between them remain a challenge in creating tunable and functional organic nanostructures. One class of molecular systems that has proven useful for incorporating tunable functionality at different length scales is liquid crystals (LCs) due to its ability to inherently self-organize. Here we present a novel approach to utilize the self-assembly of polymerizable liquid crystals to control the molecular aggregation of stable fluorescent chromophores and create a unique class of organic fluorescent nanocolloids. By adjusting the ratio between the dye and LC molecules inside the nanocolloids, we demonstrate the ability to control the molecular interactions and tune the fluorescent emission spectra of nanocolloid populations under single wavelength excitation. The single absorption spectrum and multiple emission spectra are highly desirable and reminiscent of the spectroscopic signature of quantum dots. These novel fluorescent nanocolloids have broad potential applications in fluorescent imaging and biological labeling.

Phase behavior of Phytantriol/water bicontinuous cubic Pn3m cubosomes stabilized by Laponite disc-like particles

The present article reports on the specific effects of temperature on Phytantriol-based cubosomes stabilized by inorganic stabilizers as opposed to organic stabilizers. The ability of Laponite to stabilize Phytantriol-based parent bulk phase is first demonstrated. The sub-micron-sized Laponite-stabilized particles were found to be both physically and chemically stable over time. The temperature-induced behavior, both in heating and cooling directions, of these lipid-based cubosomes has been investigated and compared with their polymer-stabilized counterparts (Pluronic F127). This allows us to extract the particular influence of each stabilizer. Whereas an increased hydration of the cubic structure was evidenced at high pH values, this effect was eliminated to compare the specific influence of both stabilizers on these Phytantriol-based cubosomes. Evidence of differences in the relaxation rates of the internal structures with temperature was found for the two stabilizers, in particular in the cooling direction whilst in the heating direction the two stabilizers could be considered as undisruptive. The origin of this difference is discussed.

Macromolecular surfactants for miniemulsion polymerization

The use of polymeric surfactants as stabilizers in miniemulsion polymerization was reviewed. The structural characteristics of reported polymeric surfactants were detailed and compared. The concept of multi-functional polymeric surfactants was evidenced. The specificities brought by polymeric surfactants in the process of miniemulsion polymerization in comparison to molecular surfactants were analysed for the stability of the initial monomer emulsion, polymerization kinetics and characteristics of the obtained latexes. The contribution of polymeric surfactants to the control of the characteristics of the obtained nanoparticles was detailed with regard to the nature of the core material and to the surface coverage. Polymeric surfactants can be seen as powerful tools for the design of original nanoparticles. On the basis of the available data, possible research topics are suggested.

Miniemulsion polymerization and the structure of polymer and hybrid nanoparticles

The miniemulsion process allows the formation of complex structured polymeric nanoparticles and the encapsulation of a solid or liquid, an inorganic or organic, or a hydrophobic or hydrophilic material into a polymer shell. Many different materials, ranging from organic and inorganic pigments, magnetite, or other solid nanoparticles, to hydrophobic and hydrophilic liquids, such as fragrances, drugs, or photoinitators, can be encapsulated. Functionalization of the nanoparticles can also be easily obtained. Compared to polymerization processes in organic solvents, polymerization to obtain polymeric nanoparticles can be performed in environmentally friendly solvents, usually water.

Ultrasmall liquid droplets on solid surfaces: production, imaging, and relevance for current wetting research

The investigation of micro- and nanoscale droplets on solid surfaces offers a wide range of research opportunities both at a fundamental and an applied level. On the fundamental side, advances in the techniques for production and imaging of such ultrasmall droplets will allow wetting theories to be tested down to the nanometer scale, where they predict the significant influence of phenomena such as the contact line tension or evaporation, which can be neglected in the case of macroscopic droplets. On the applied side, these advances will pave the way for characterizing a diverse set of industrially important materials such as textile or biomedical micro- and nanofibers, powdered solids, and topographically or chemically nanopatterned surfaces, as well as micro-and nanoscale devices, with relevance in diverse industries from biomedical to petroleum engineering. Here, the basic principles of wetting at the micro- and nanoscales are presented, and the essential characteristics of the main experimental techniques available for producing and imaging these droplets are described. In addition, the main fundamental and applied results are reviewed. The most problematic aspects of studying such ultrasmall droplets, and the developments that are in progress that are thought to circumvent them in the coming years, are highlighted.

Role of surfactant in the stability of liquid crystal-based nanocolloids

We examine the dependence of liquid crystalline nanocolloid formation and stability on surfactant. Nanocolloids composed of polymerizable liquid crystal mesogens and cross-linking agents and capped with either ionic or nonionic surfactants are prepared via the miniemulsion technique. Colloids synthesized with anionic surfactant were stable and displayed 2D hexagonal packing when deposited via slow vertical pulling of the silicon substrate from an aqueous suspension. Liquid crystal nanocolloids stabilized with the nonionic, polar polymer polyvinyl alcohol (PVA) were stable in aqueous environments but coalesced upon drying to form relatively large, well-defined crystal-like structures with uniform birefringence. SEM images reveal that the coalesced structures have mesalike features. Polarized light, atomic force, and polarized Raman microscopy of these structures indicate that the liquid crystal molecules are arranged with their long molecular axis slightly tilted with respect to the surface normal. A mechanism is proposed to explain the formation of the mesalike structures from the nanocolloids. These studies provide fundamental insight into the incorporation and stabilization of polymerizable liquid crystal molecules into nanovolumes and open up opportunities for the incorporation of functionality and anisotropy into isotropically shaped nanocolloids.

A computer simulation study of the formation of liquid crystal nanodroplets from a homogeneous solution

The aggregation of liquid crystal nanodroplets from a homogeneous solution is an important but not well understood step in the preparation of various advanced photonic materials. Here, the authors performed molecular dynamics computer simulations of the formation of liquid crystalline nanodroplets, starting from an isotropic and uniform binary solution of spherical Lennard-Jones (solvent) and elongated ellipsoidal Gay-Berne (solute) rigid particles in low (<10%) concentration. They studied the dynamics of demixing and the mesogen ordering process and characterized the resulting nanodroplets assessing the effect of temperature, composition, and specific solute-solvent interaction on the morphology, structure, and anisotropy. They find that the specific solute-solvent interaction, composition, and temperature can be adjusted to tune the nanodroplet growth and size.