Tuning Molecular Orientation Responses of Microfluidic Liquid Crystal Dispersions to Colloid and Polymer Flows.

An important approach to molecular diagnostics is integrating organized substances that provide complex molecular level responses to introduced chemical and biological agents with conditions that optimize and distinguish such responses. In this respect, liquid crystal dispersions are attractive components of molecular diagnostic tools. This paper analyzes a colloid system, containing a nematic liquid crystal as a dispersed phase, and aqueous surfactant and polymer solutions as the continuous phases. We applied a microfluidic approach for tuning orientation of liquid crystal molecules in picoliter droplets immobilized on microchannel walls. Introduction of surfactant to the aqueous phase was found to proportionally increase the order parameter of liquid crystal molecules in microdroplets. Infusion of polymer solutions into surfactant-mediated microfluidic liquid crystal dispersions increased the order parameter at much lower surfactant concentrations, while further infusion of surfactant solutions randomized the orientation of liquid crystal molecules. These effects were correlated with the adsorption of surfactant molecules on surfaces of microdroplets, stabilizing the effect of a polymer matrix on bound surfactant ions and the formation of insoluble polymer-colloid aggregates, respectively. The revealed molecular behavior of liquid crystal dispersions may contribute to optimized synthesis of responsive liquid crystal dispersions for in-flow molecular diagnostics of polymers and colloids, and the development of functional laboratory-on-chip prototypes.

Alginate/chitosan hydrogels as perspective transport systems for cefotaxime.

This work reports synthesis of pH-responsive alginate/chitosan hydrogel spheres with the average diameter of 2.0 ± 0.05 mm, which contain cefotaxime that is an antibiotic of the cefalosporine group. The spheres provided the cefotaxime encapsulation efficiency of 95 ± 1%. An in vitro release of cefotaxime from the spheres in the media that simulate human biological fluids in peroral delivery conditions was found to be a pH-dependent process. The analysis of cefotaxime release kinetics by the Korsmeyer-Peppas model revealed a non-Fickian mechanism of its diffusion, which may be related to intermolecular interactions occurring between the antibiotic and chitosan. Conductometry, UV spectroscopy, and IR spectroscopy were used to study complexation of chitosan with cefotaxime in aqueous media with varied pH, characterize the composition of the complexes, and calculate their stability constants. The composition of the cefotaxime-chitosan complexes was found to correspond to the 1.0:4.0 and 1.0:2.0 molar ratios of the components at pH 2.0 and 5.6, respectively. Quantum chemical modeling was used to evaluate energy characteristics of chitosan-cefotaxime complexation considering the influence of a solvent.

Dynamic Flow Control over Optical Properties of Liquid Crystal-Quantum Dot Hybrids in Microfluidic Devices.

In this paper, we report developing approaches to tuning the optical behavior of microfluidic devices by infusing smart hybrids of liquid crystal and quantum dots into microchannel confinement. We characterize the optical responses of liquid crystal-quantum dot composites to polarized and UV light in single-phase microflows. In the range of flow velocities up to 10 mm/s, the flow modes of microfluidic devices were found to correlate with the orientation of liquid crystals, dispersion of quantum dots in homogeneous microflows and the resulting luminescence response of these dynamic systems to UV excitation. We developed a Matlab algorithm and script to quantify this correlation by performing an automated analysis of microscopy images. Such systems may have application potential as optically responsive sensing microdevices with integrated smart nanostructural components, parts of lab-on-a-chip logic circuits, or diagnostic tools for biomedical instruments.

Tuning Properties of Polyelectrolyte-Surfactant Associates in Two-Phase Microfluidic Flows.

This work focuses on identifying and prioritizing factors that allow control of the properties of polyelectrolyte-surfactant complexes in two-phase microfluidic confinement and provide advantages over synthesis of such complexes in macroscopic conditions. We characterize the impact of polymer and surfactant aqueous flow conditions on the formation of microscale droplets and fluid threads in the presence of an immiscible organic solvent. We perform an experimental and selected numerical analysis of fast supramolecular reactions in droplets and threads. The work offers a quantitative control over properties of polyelectrolyte-surfactant complexes produced in two-phase confinement by varying capillary numbers and the ratio of aqueous and organic flowrates. We propose a combined thread-droplet mode to synthesize polyelectrolyte-surfactant complexes. This mode allows the production of complexes in a broader size range of R ≈ 70-200 nm, as compared with synthesis in macroscopic conditions and the respective sizes R ≈ 100-120 nm. Due to a minimized impact of undesirable post-chip reactions and ordered microfluidic confinement conditions, the dispersity of microfluidic aggregates (PDI = 0.2-0.25) is lower than that of their analogs synthesized in bulk (PDI = 0.3-0.4). The proposed approach can be used for tailored synthesis of target drug delivery polyelectrolyte-surfactant systems in lab-on-chip devices for biomedical applications.

On-Chip Control over Polyelectrolyte-Surfactant Complexation in Nonequilibrium Microfluidic Confinement.

The goal of this work is to classify and quantify the factors that govern polyelectrolyte-surfactant complexation in microfluidic confinement and optimize the designs and operating modes of microfluidic reactors to offer additional advantages over the macroscopic synthesis of such complexes. We analyze and solve a system of governing convection-diffusion-reaction equations to conveniently represent these factors or their combinations as dimensionless similarity criteria. We discuss how these factors contribute to the on-chip control of the reaction initiation, the complex product distribution in a microfluidic device, and the phase behavior of the confined reacting flows and experimentally verify the results in microchips. This approach allows for designing microfluidic devices and setting their operating modes to avoid undesirable clogging by reaction products, control the initiation of the complexation reaction, and produce polyelectrolyte-surfactant aggregates with a broader size range and reduced dispersity.

Activation and Switching of Supramolecular Chemical Signals in Multi-Output Microfluidic Devices.

In this study, we report on the developing of a continuous microfluidic reaction device that allows selective activation of polyelectrolyte-surfactant chemical signals in microflows and switches them between multiple outputs. A numerical model was developed for convection-diffusion reaction processes in reactive polymer-colloid microfluidic flows. Matlab scripts and scaling laws were developed for this model to predict reaction initiation and completion conditions in microfluidic devices and the location of the reaction front. The model allows the optimization of microfluidic device geometry and the setting of operation modes that provide release of the reaction product through specific outputs. Representing a chemical signal, polyelectrolyte-surfactant reaction products create various logic gate states at microfluidic chip outputs. Such systems may have potential as biochemical signal transmitters in organ-on-chip applications or chemical logic gates in cascaded microfluidic devices.

Optical and structural characteristics of PMMA films doped with a new anisometric EuIII complex.

A new film material capable of transforming UV radiation into visible light was obtained from a highly anisometric EuIII complex with organic ligands in a polymethylmethacrylate (PMMA) matrix and then structurally characterized. An important advantage of the synthesized complex is its good solubility in organic solvents such as dichloromethane, chloroform, THF, toluene, etc. The ligand environment (flexible alkyl and cyclohexyl substituents) of the EuIII complex was selected to prevent crystallization, to inhibit the formation of defects in the structure of films and to provide its uniform distribution in the polymer during polymerization. As a result we obtain an EuIII complex of the film with remarkable thermal behavior: the complex melts to isotropic liquid without decomposition, it supercools at ambient temperature and it forms a stable amorphous material at low (up to -30°C) temperatures. The films were prepared by two methods: bulk polymerization and spin coating. A comparison of the differences of luminescent and optical characteristics of micro- and nanosized PMMA films doped with the anisometric EuIII complex is given. Based on X-ray powder diffraction and small-angle scattering data, it has been supposed that the association of EuIII complex molecules occurs in the voids of the PMMA matrix and is accompanied by the formation of a nanocrystalline phase. For films obtained by spin coating, a deeper microphase separation is demonstrated than by bulk polymerization. The dimensional characteristics of the nano-associates were determined and a correlation between the method of preparation and the type of distribution of the EuIII complex in the PMMA matrix is established.

Ab initio study of energy transfer pathways in dinuclear lanthanide complex of europium(III) and terbium(III) ions.

An ab initio XMCQDPT2/CASSCF study of energy transfer processes in the dinuclear lanthanide complex [(Acac)3Eu(µ-Bpym)Tb(Acac)3] (Acac is acetylacetonate, and Bpym is 2,2'-bipyrimidine) and a corresponding computational procedure are presented. Because ligands in lanthanide complexes weakly interact with each other, the large dinuclear complex bearing seven organic ligands is divided into fragments that reproduce the electrostatic effects of the ions on the electronic and geometrical structure of the ligands. The multireference XMCQDPT2/CASSCF approach is directly applied to these relatively small fragments with reasonable computational cost. The calculated energies of the singlet and triplet excited states agree well with the experiment. Based on the calculated energies, the energy level diagrams of the complex are constructed and intramolecular energy transfer channels are determined.

Spin crossover star-shaped metallomesogens of iron(II).

Three new types of spin crossover (SCO) metallomesogens of Fe(II) based on symmetric tripod ligands and their magnetic and structural properties are reported here. These were obtained by condensation of tris(2-aminoethyl)amin (tren) with the aldehyde derived from 3-alkoxy-6-methylpyridine (mpyN, N (number of carbon atoms in n-alkyl chains) = 8, 18), 1-alkyl-1H-imidazole (imN, N = 4, 16, 18, 20, 22), or 1-alkyl-1H-benzimidazole (bimN, N = 6, 14, 16, 18, 20). A complex derived from 1-octadecyl-1H-naphtho[2,3-d]imidazole (nim18) retains the high spin state at any temperature. Single crystals of the short-chain complexes were investigated by a combination of X-ray crystallography, magnetic measurements and Mössbauer spectroscopy. Generally, in comparison with the short-chain complexes the long-chain complexes display more gradual SCO and undergo a phase transition crystal-liquid crystal that is reflected in their magnetic properties. Characterization by X-ray powder diffractometry and differential calorimetry reveal formation of a smectic mesophase upon melting.

Luminescent complexes of terbium ion for molecular recognition of ibuprofen.

The complexation behavior and luminescent properties of terbium (Tb(3+) ) complexes containing bi-dental ligands were studied: nitrogen - 1,10-phenanthroline, and oxygen - trifluoroacetylacetone as well as acetylacetone ligands with ibuprofen (Ibu; a non-steroidal anti-inflammatory drug). Aqueous and aqueous alcohol microheterogeneous solutions were used as media. The effects of solubilization by various micellar solutions, pH and ligand type on luminescent properties of Tb(3+) complexes were investigated. Sensitized luminescence of mixed ligand complex Tb(1,10-phenanthroline)-Ibu and dynamic quenching effect in complex Tb(trifluoroacetylacetone)3 -Ibu allow Ibu determination with the limit of detection 5.3 × 10(-8) mol/L and 1.26 × 10(-6) mol/L, respectively.

N,N-dimethyldodecylamine oxide self-organization in the presence of lanthanide ions in aqueous and aqueous-decanol solutions.

The article represents the results of research in self-organization of new lanthanide systems in water-decanol medium. The systems are based on N,N-dimethyldodecylamine oxide, a zwitterionic surfactant. The study covers the complex formation of lanthanide ions with C12DMAO molecules and the influence of Ln(III) ions and medium composition on surfactant association in diluted solutions. The analysis of adsorption isotherms was carried out on the basis of the combination of Gibbs and Langmuir adsorption equations. The results were used to determine physicochemical properties and parameters of a monomolecular adsorption layer. The research objects were various lanthanide ions with identical coordination centers. A number of spectroscopic methods (UV, NMR self-diffusion, EPR, dynamic light scattering (DLS), and fluorescent analysis) were involved in the research for comparative estimations of molecular dynamics, critical micellization concentration, geometry, sizes, and aggregation numbers of micellar aggregates. Micelle structure simulation revealed good agreement between experimental data and quantum chemical calculations.

Mesogenic and luminescent properties of lyotropic liquid crystals containing Eu(III) and Tb(III) ions.

Lyotropic metallomesogens containing trivalent rare-earth metal ions have unique attractive behavior due to the combination of some specific properties of the lanthanide ions with anisotropic supramolecular organization liquid crystal and provide new promises in biochemistry and materials science. In this article, we have studied the liquid crystal and luminescence properties of lyotropic systems containing Eu(III) and Tb(III) ions based on nonionic surfactants. The type, the structural parameters of the mesophases, and the structure of a liquid crystal complex have been investigated using polarized optical microscopy (POM), X-ray diffraction, and Fourier transform infrared. In addition, on the basis of the luminescence lifetime, the structure of the first coordination sphere was determined. The results obtained based on time-resolved spectroscopy data are discussed in the light of the influence ligand environment, ion type, and the type of supramolecular organization on the luminescence efficiency of lyotropic lanthanide containing systems. The first time was reported for Eu(III) complexes increasing the luminescence efficiency in the hexagonal phase compared to the lamellar mesophase.

Magnetic alignment study of rare-earth-containing liquid crystals.

The liquid-crystalline rare-earth complexes of the type [Ln(LH)3(DOS)3]-where Ln is Tb, Dy, Ho, Er, Tm, or Yb; LH is the Schiff base N-octadecyl-4-tetradecyloxysalicylaldimine; and DOS is dodecylsulfate-exhibit a smectic A phase. Because of the presence of rare-earth ions with a large magnetic anisotropy, the smectic A phase of these liquid crystals can be easier aligned in an external magnetic field than smectic A phases of conventional liquid crystals. The magnetic anisotropy of the [Ln(LH)3(DOS)3] complexes was determined by measurement of the temperature-dependence of the magnetic susceptibility using a Faraday balance. The highest value for the magnetic anisotropy was found for the dysprosium(III) complex. The magnetic alignment of these liquid crystals was studied by time-resolved synchrotron small-angle X-ray scattering experiments. Depending on the sign of the magnetic anisotropy, the director of the liquid-crystalline molecules was aligned parallel or perpendicular to the magnetic field lines. A positive value of the magnetic anisotropy (and parallel alignment) was found for the thulium(III) and the ytterbium(III) complexes, whereas a negative value of the magnetic anisotropy (and perpendicular alignment) was observed for the terbium(III) and dysprosium(III) complexes.

First Example of Coexistence of Thermal Spin Transition and Liquid-Crystal Properties.

The rodlike FeIII complex of an N-alkyloxysalicylidenyl-N'-ethyl-N-ethylenediamine ligand, shown as a computer model in the picture, is the first compound in which spin-crossover (SC) and liquid-crystalline (LC) properties coexist. This synergy should allow the magnetic and optical properties of SC compounds to be combined with the sensitivity of the LC state to electromagnetic fields.