Controlling the Localization of Liquid Droplets in Polymer Matrices by Evaporative Lithography

Localized inclusions of liquids provide solid materials with many functions, such as self‐healing, secretion, and tunable mechanical properties, in a spatially controlled mode. However, a strategy to control the distribution of liquid droplets in solid matrices directly obtained from a homogeneous solution has not been reported thus far. Herein, we describe an approach to selectively localize liquid droplets in a supramolecular gel directly obtained from its solution by using evaporative lithography. In this process, the formation of droplet‐embedded domains occurs in regions of free evaporation where the non‐volatile liquid is concentrated and undergoes a phase separation to create liquid droplets prior to gelation, while a homogeneous gel matrix is formed in the regions of hindered evaporation. The different regions of a coating with droplet embedment patterns display different secretion abilities, enabling the control of the directional movement of water droplets.     

Emulsifying potency of new amino acid-type surfactant (II): stable water-in-oil (W/O) emulsions containing 85 wt% inner water phase

The ternary phase diagram for N-[3-lauryloxy-2-hydroxypropyl]-L-arginine L-glutamate (C12HEA-Glu), a new amino acid-type surfactant, /oleic acid (OA)/water system was established. The liquid crystal and gel complex formations between C12HEA-Glu and OA were applied to a preparation of water-in-oil (W/O) emulsions. Stable W/O emulsions containing liquid paraffin (LP) as the oil and a mixture of C12HEA-Glu and OA as the emulsifier were formed. The preparation of stable W/O emulsions containing 85 wt% water phase was also possible, in which water droplets would be polygonally transformed and closely packed, since the maximum percentage of inner phase is 74% assuming uniformly spherical droplets. Water droplets would be taken into the liquid crystalline phase (or the gel complex) and the immovable water droplets would stabilize the W/O emulsion system. The viscosity of emulsions abruptly increased above the 75 wt% water phase (dispersed phase). The stability of W/O emulsions with a lower weight ratio of OA to C12HEA-Glu and a higher ratio of water phase was greater. This unusual phenomenon may be related to the formation of a liquid crystalline phase between C12HEA-Glu and OA, and the stability of the liquid crystal at a lower ratio of oil (continuous phase). W/O and oil-in-water (O/W) emulsions containing LP were selectively prepared using a mixture of C12HEA-Glu and OA since the desirable hydrophile-lipophile balance (HLB) number for the emulsification was obtainable by mixing the two emulsifiers.     

Thermotropic liquid crystals embedded in a high water gel system

An emulsion was formed when the thermotropic liquid crystal (LC) mixture E5 was added to an aqueous polyvinylalcohol (pva) solution and shaken. This emulsion was gelled by addition of an aqueous borax solution. The pva polymer functioned not only as the gelling agent but also appeared to act as a polymeric surfactant which stabilised the LC droplets. This high water gel-liquid crystal (HWG-LC) system contained nearly 80 wt % water and more LC wt % than polymer. The system was thermally reversible, undergoing a gel to sol transition upon heating to 70°C and reforming a gel upon cooling. The HWG-LC showed electrooptical behaviour dependent upon a switched electric field when constrained between transparent electrodes. The pressure required to form a thin film between these electrodes induced a structural emulsion in the dispersion causing LC droplet disruption and the formation of an LC network in the gel.     

Atomic Force Microscopy Study of the Adhesion of Saccharomyces cerevisiae

The influence of the liquid properties and the operating variables on the intrinsic volumetric flow rate, q(0), of the droplets at the liquid-atmosphere interface in nonfoaming adsorptive bubble separation and that, W(f0), of the liquid in foam at the liquid-foam interface in foam separation was studied to estimate the enrichment ratio of surface-active substance in the two techniques. Each intrinsic flow rate was determined by the extrapolation method, which the authors proposed previously, and was mainly influenced by superficial gas velocity, liquid viscosity, and surface tension. Although the changes in the surface tension and the liquid viscosity were small, they greatly affected the intrinsic flow rates for both the droplets and the liquid in foam. The experimental results were applied to a dimensional analysis. Dimensionless volumetric flow rates, q(0)/Q and W(f0)/Q, were successfully correlated with a dimensionless number (Ohnesorge number, Z=&mgr;(L)/(rho(L)sigmad(b))(0.5)). q(0)/Q=6.66 Z(1.46) and W(f0)/Q=2.53Z(0.533) were obtained for the nonfoaming and the foaming regions within errors of 30 and 35%, respectively. The enrichment ratio of surface-active substance in the droplets and the liquid in foam to the bulk liquid was derived by using these correlations for the nonfoaming and the foaming regions, respectively. A good agreement of the experimental enrichment ratio and the calculated ones was obtained by using the correlations for nonfoaming and foaming. Copyright 2001 Academic Press.     

Dye-dependent studies on droplet pattern and electro-optic behaviour of polymer dispersed liquid crystal

In order to study the droplet pattern and electro-optic (EO) behaviour of polymer dispersed liquid crystal (PDLC) with the addition of dye, dichroic polymer dispersed liquid crystal (DPDLC) films were prepared using a nematic liquid crystal (NLC), photo-curable polymer (NOA 65) and anthraquinone blue dichroic dye (B2), in equal ratio (1:1) of polymer and liquid crystal (LC) by polymerisation induced phase separation (PIPS) technique. Dichroic dye was taken in different concentration (wt./wt. ratio) as 0.0625%, 0.125%, 0.25%, 0.5% and 1% of the LC mixture in DPDLC films. Initially, in an open circuit when there is no proviso for external electric field (0 V), LC droplets in polymer matrix exhibited bipolar pattern, though on closing the circuit with the increase of electric field pattern of droplets starts changing, LC molecules align along the direction of applied electric field and aligned completely relatively at higher field (30 V), which illustrate vertical radial pattern. Further, results show that the DPDLC film containing 0.0625% dye concentration with consistent average droplet size ~4.30 μm, exhibits the best transmission at lower operating voltage.     

Boosting the stability of protein emulsions by the synergistic use of proteins and clays

The preparation and the properties of high-pressure emulsions based on five different proteins are reported. As proteins, we used the well-studied bovine serum albumin (BSA), a biotechnical produced hydrophobin called H Star Protein B? (HPB), a protein isolate from soybeans, a wheat protein isolate (Plantasol W), and a commercially available yeast extract. All emulsions were characterized by visual appearance, light microscopy, conductivity, and rheological measurements. Beside the emulsion based on soy protein isolate, all other samples showed phase separation under the used conditions (0.5 wt.% protein; 50 wt.% oil). Plantasol W and yeast extract formed the most unstable emulsions showing typical instability processes like coalescence. Gel-like properties have been observed for emulsions based on BSA, soy protein isolate, and HPB. The same proteins were also used to stabilize emulsions after their adsorption on clay particles. Interestingly, all emulsions had gel-like properties with a yield stress value and were stable to the used conditions. It is concluded that the gel character results from the stickiness of the protein covered oil droplets and is independent from the used protein type. The proteins which are adsorbed on the oil droplets can still interact and bind to proteins on other oil droplets.     

Gas-Phase Silicon Alkoxide Reactivity vs. Na-Alginate Droplets for Conjugation of Alginate and Sol-Gel Technologies

Solutions with Na-alginate concentrations ranging from 0.5 to 2.5% w/v are processed to prepare Ca-alginate beads using a nozzle ejector under constant He-flow. Beads were spherical in shape and their size distributions were determined; in all samples the average diameter fell in the 120–140 μm interval. Volumetric yields were found to be linearly dependent of the original Na-alginate load whereas the bead diameters were almost constant, according to a constant hindrance of Ca-alginate macromolecular units in the final Ca-alginate gel. The rheology of Na-alginate solutions was studied, with determination of intrinsic viscosity; experimental evidence of microsphere formation, even at the lowest Na-alginate concentrations, indicated that ejection processing changes the rheological parameters controlling bead formation in ordinary dropping processing. Gaseous silicon alkoxides – Si(OEt)₄ and MeSi(OEt)₃ – carried by a He flow were deposited on Na-alginate droplets during ejection. The process was studied by continuous mass spectrometry analysis before and after Na-alginate ejection during the 5-min treatment; in all cases results indicated a deposition yield of 58%. Traces of alcohol in the mass spectrometry analysis of the out-flow gas excluded instantaneous formation of sol-gel silica on the Na-alginate droplets during their residence in the gas phase. For various Na-alginate concentrations, ethanol released by silica gel formation is constant as well as the amount of deposited SiO₂; a siliceous layer ranging from 0.08 to 0.17 μm thick on the surface of the Ca-alginate beads was calculated.     

Effect of Emulsifier Type on the Crystallization Kinetics of Oil-in-Water Emulsions Containing a Mixture of Solid and Liquid Droplets

Measurements of the ultrasonic velocity as a function of time (at 6.0°C) have been used to monitor the kinetics of crystallization of oil droplets in n -hexadecane-in-water emulsions containing a mixture of solid and liquid droplets. Crystallization is induced in liquid droplets when solid droplets are present. Induced crystallization is probably caused by crystals, protruding from solid droplets, penetrating into liquid droplets during collisions and thus acting as nucleation sites for crystal growth. The rate of induced crystallization depends strongly on the type of emulsifier used to stabilize the emulsion droplets. For the series of emulsifiers used in this study the rate decreased in the following order: Tween 20 > SDS > β-lactoglobulin > β-casein. Differences in rate can be explained by considering the influence the emulsifiers have on the interactions between droplets.     

Morphological transformations of native petroleum emulsions. I. Viscosity studies

Emulsions of water in as-recovered native crude oils of diverse geographical origin evidently possess some common morphological features. At low volume fractions varphi of water, the viscosity behavior of emulsions is governed by the presence of flocculated clusters of water droplets, whereas characteristic tight gels, composed of visually monodisperse small droplets, are responsible for the viscosity anomaly at varphi approximately 0.4-0.5. Once formed, small-droplet gel domains apparently retain their structural integrity at higher varphi, incorporating/stabilizing new portions of water as larger-sized droplets. The maximum hold-up of disperse water evidently is the close-packing limit of varphi approximately 0.74. At higher water contents (up to varphi approximately 0.83), no inversion to O/W morphology takes place, but additional water emerges as a separate phase. The onset of stratified flow (W/O emulsion gel + free water) is the cause of the observed viscosity decrease, contrary to the conventional interpretation of the viscosity maximum as a reliable indicator of the emulsion inversion point.     

Development of molecularly imprinted-solid phase extraction combined with dispersive liquid–liquid microextraction for selective extraction and preconcentration of triazine herbicides from aqueous samples

In this study, a sensitive and developed method based on the use of molecularly imprinted-solid phase extraction along with dispersive liquid–liquid microextraction has been reported for selective extraction and pre-concentration of triazine pesticides from aqueous samples. Molecularly imprinted microspheres (template, atrazine) were synthesized using precipitation polymerization and used as sorbent in SPE procedure. A model solution containing the studied pesticides was slowly passed through the atrazine-MIP cartridge. The adsorbed analytes were eluted with methanol, mixed with carbon tetrachloride (as extraction solvent) and rapidly injected into deionized water. In this process, the analytes were extracted into fine droplets of carbon tetrachloride and the fine droplets were sedimented in bottom of the conical test tube by centrifugation. Finally, GC-FID was used for the separation and determination of analytes in the sedimented phase. Some important parameters affecting the performance of developed method were completely investigated. The linear ranges of calibration curves were wide and limits of detection and limits of quantification were between 0.2–7 and 0.5–20 ng mL^?1, respectively. The relative standard deviation obtained for six repeated experiments of atrazine (10 ng mL^?1) was 3.1 %. The relative recoveries obtained for the atrazine in the spiked samples were within in the range of 92–98 %.     

Dispersive liquid–liquid microextraction and spectrophotometric determination of cobalt in water samples

A new simple and rapid dispersive liquid–liquid microextraction has been applied to preconcentrate trace levels of cobalt as a prior step to its determination by spectrophotometric detection. In this method a small amount of chloroform as the extraction solvent was dissolved in pure ethanol as the disperser solvent, then the binary solution was rapidly injected by a syringe into the water sample containing cobalt ions complexed by 1-(2-pyridylazo)-2-naphthol (PAN). This forms a cloudy solution. The cloudy state was the result of chloroform fine droplets formation, which has been dispersed in bulk aqueous sample. Therefore, Co-PAN complex was extracted into the fine chloroform droplets. After centrifugation (2 min at 5000 rpm) these droplets were sedimented at the bottom of conical test tube (about 100 µL) and then the whole of complex enriched extracted phase was determined by a spectrophotometer at 577 nm. Complex formation and extraction are usually affected by some parameters, such as the types and volumes of extraction solvent and disperser solvent, salt effect, pH and the concentration of chelating agent, which have been optimised for the presented method. Under optimum conditions, the enhancement factor (as the ratio of slope of preconcentrated sample to that obtained without preconcentration) of 125 was obtained from 50 mL of water sample, and the limit of detection (LOD) of the method was 0.5 µg L^?1and the relative standard deviation (RSD, n = 5) for 50 µg L^?1 of cobalt was 2.5%. The method was applied to the determination of cobalt in tap and river water samples.     

The electro-optical response of nematic emulsions

Switchable nematic emulsions are micron-sized droplets of nematic liquid crystal, floating in isotropic fluid matrices. Such droplets can be switched from an opaque (off) to a transparent (on) state by application of very low electric fields. It is known that the electro-optical properties of liquid crystal dispersions are affected by several parameters, including the liquid crystal loading. The electro-optical response of nematic emulsions has been investigated as a function of liquid crystal weight percentage. Almost transparent films with a reduced contrast ratio are obtained with lower liquid crystal contents. A macroscopic phase separation is observed when liquid crystal content exceeds 45 wt %. On the contrary, large contrast ratios and very low switching fields can be obtained if liquid crystal ranges from 25 to 35 wt %. Consequently, nematic emulsions prepared in this liquid crystal range can be used as promising systems for electro-optical applications. In addition to technological developments, these results can help computational and basic studies of phase separation in novel multiphase liquid crystalline materials.     

Preparation of uniformly sized alginate microspheres using the novel combined methods of microchannel emulsification and external gelation

The purpose of this study was to prepare alginate (ALG) microspheres with narrow size distribution using a combination of microchannel (MC) emulsification technique and external gelation method. ALG solution was dispersed as water-in-oil (W/O) emulsion droplets in iso-octane containing 5 wt% Span 85 as the immiscible continuous phase via MC emulsification technique using hydrophobic MC array. The MC array used in this experiment is a grooved-type MC consisting of 1070 channels fabricated on a 25 mm × 28 mm silicon microchip. The monodisperse W/O emulsion droplets generated from the MCs were in the mean particle diameter (d_av) range of 18–22 μm and coefficient of variation (CV) of 5–26% at the ALG concentrations of 0.5–3.0 wt% and flow rates of 0.05–0.4 mL/h. The d_av of the emulsion droplets hardly changed below a dispersed phase threshold flow rate of 0.2 mL/h but gradually became smaller when the dispersed phase concentration was increased. The resulting emulsion droplets were then congealed to form rigid ALG gel particles by reacting them with calcium chloride (CaCl₂) solution. Gelation of the ALG droplets by calcium ion (Ca²⁺) resulted in shrinkage of its d_av, forming uniformly sized ALG microspheres with an average diameter of 6.2 μm and a CV of below 10% at the ALG concentration of 3 wt%.     

Stable and Oriented Liquid Crystal Droplets Stabilized by Imidazolium Ionic Liquids

Liquid crystals represent a fascinating intermediate state of matter, with dynamic yet organized molecular features and untapped opportunities in sensing. Several works report the use of liquid crystal droplets formed by microfluidics and stabilized by surfactants such as sodium dodecyl sulfate (SDS). In this work, we explore, for the first time, the potential of surface-active ionic liquids of the imidazolium family as surfactants to generate in high yield, stable and oriented liquid crystal droplets. Our results show that [C₁₂MIM][Cl], in particular, yields stable, uniform and monodisperse droplets (diameter 74 ± 6 µm; PDI = 8%) with the liquid crystal in a radial configuration, even when compared with the standard SDS surfactant. These findings reveal an additional application for ionic liquids in the field of soft matter.     

Highly concentrated (gel) emulsions,versatile reaction media

Highly concentrated (gel) emulsions are characterised by dispersed phase volume fractions exceeding 0.74, the critical value for the most compact packing of monodispersed undistorted spheres. Their structure consists of polyhedral droplets separated by thin films of continuous phase, a structure resembling gas–liquid foams. Their rheological properties vary from elastic to viscoelastic having a gel appearance. One of the most promising applications is their use as reaction media. The recent advances in the preparation of low-density polymeric materials (solid foams, aerogels) are reviewed and new applications are described. These include the preparation of dual meso/macroporous inorganic oxide materials and the use of gel emulsions as alternative to conventional solvent media in chemical and enzyme-catalysed reactions.     

Hollow spheres of aromatic polyamide prepared by reaction‐induced phase separation

Hollow spheres of aromatic polyamide are obtained by the reaction‐induced phase separation during polymerization of 5‐hydroxyisophthalic acid and 1,4‐phenylene diamine in an aromatic solvent at a concentration of 1–2% at 320 °C without stirring. The hollow sphere has a dimple hole and the diameters of the hollow spheres are 3–4 μm. The droplets are initially generated via liquid–liquid phase separation and then rigid cross‐linked network structure formed the rigid skin layer on the surface of the droplets. The solidification of the droplets occurred owing to the further polymerization in them with maintaining the morphology to form the hollow spheres. The hollow spheres exhibit outstanding thermal stability. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Heterochromatin Protein HP1α Gelation Dynamics Revealed by Solid‐State NMR Spectroscopy

Heterochromatin protein 1α (HP1α) undergoes liquid–liquid phase separation (LLPS) and forms liquid droplets and gels in vitro, properties that also appear to be central to its biological function in heterochromatin compaction and regulation. Here we use solid‐state NMR spectroscopy to track the conformational dynamics of phosphorylated HP1α during its transformation from the liquid to the gel state. Using experiments designed to probe distinct dynamic modes, we identify regions with varying mobilities within HP1α molecules and show that specific serine residues uniquely contribute to gel formation. The addition of chromatin disturbs the gelation process while preserving the conformational dynamics within individual bulk HP1α molecules. Our study provides a glimpse into the dynamic architecture of dense HP1α phases and showcases the potential of solid‐state NMR to detect an elusive biophysical regime of phase separating biomolecules.     

Preconcentration Ultra Trace of Cd(II) in Water Samples Using Dispersive Liquid‐Liquid Microextraction with Salen(N,N′‐Bis(Salicylidene)‐Ethylenediamine) and Determination Graphite Furnace Atomic Absorption Spectrometry

Dispersive liquid–liquid microextraction (DLLME) technique was successfully used as a sample preparation method for graphite furnace atomic absorption spectrometry (GF AAS). In this extraction method, 500 μL methanol (disperser solvent) containing 34 μL carbon tetrachloride (extraction solvent) and 0.00010 g Salen(N,N′‐bis(salicylidene)ethylenediamine) (chelating agent) was rapidly injected by syringe into the water sample containing cadmium ions (interest analyte). Thereby, a cloudy solution formed. The cloudy state resulted from the formation of fine droplets of carbon tetrachloride, which have been dispersed, in bulk aqueous sample. At this stage, cadmium reacts with Salen(N,N′‐bis(salicylidene)‐ethylenediamine), and therefore, hydrophobic complex forms which is extracted into the fine droplets of carbon tetrachloride. After centrifugation (2 min at 5000 rpm), these droplets were sedimented at the bottom of the conical test tube (25 ± 1 μL). Then a 20 μL of sedimented phase containing enriched analyte was determined by GF AAS. Some effective parameters on extraction and complex formation, such as extraction and disperser solvent type and their volume, extraction time, salt effect, pH and concentration of the chelating agent have been optimized. Under the optimum conditions, the enrichment factor 122 was obtained from only 5.00 mL of water sample. The calibration graph was linear in the range of 2‐21 ng L^?1 with a detection limit of 0.5 ng L^?1. The relative standard deviation (R.S.D._s) for ten replicate measurements of 20 ng L^?1 of cadmium was 2.9%. The relative recoveries of cadmium in tap, sea and rain water samples at a spiking level of 5 and 10 ng L^?1 are 99, 94, 97 and 96%, respectively. The characteristics of the proposed method have been compared with cloud point extraction (CPE), on‐line liquid‐liquid extraction, single drop microextraction (SDME), on‐line solid phase extraction (SPE) and co‐precipitation based on bibliographic data. Therefore, DLLME combined with GF AAS is a very simple, rapid and sensitive method, which requires low volume of sample (5.00 mL).     

Interaction of non-ionic hydrogels with weak aromatic acids

Measurements are reported of the swelling behaviour at 20°C of poly (N isopropylacrylamide) (PNIPA) gels in aqueous solutions of two weak aromatic acids, phenol and resorcinol. For solute concentrations below 45 mmol/l the uptake of these solutions is similar. Due to selective solvation phenol exhibits an excess equilibrium concentration inside the gel of 5% over that in the surrounding bath, while for resorcinol, the excess is found to be 12%. At 50 mmol/l solute concentration, both systems display a volume transition accompanied by expulsion of the solvent. The solubility limits in water of these aromatic compounds, which are significantly different from each other (870 mmol/l and 9080 mmol/l respectively), are far above this critical concentration. In the collapsed condition the expelled liquid spreads on the surface of the phenol treated gel, while an ordered arrangement of separate droplets is generated in the case of resorcinol. In the latter case an acute contact angle was observed. It is also shown by acid-base titration that the PNIPA/water system may exhibit a slight ion exchanging character.     

Route to stable non-spherical emulsion droplets

A route to the production of stable non-spherical emulsion droplets has been developed by pushing millimeter-sized liquid droplets stabilized by an excess amount of solid Pickering particles through a narrow capillary. This excess amount allows for the full coverage of the newly created droplets’ interface during deformation. Upon exiting the capillary the adhered particles wedge, or “jam”, on the surface preserving the non-spherical shape. Stable millimeter-sized non-spherical liquid droplets with aspect ratios exceeding 10 and cross-sections in line with capillary dimensions are easily obtained. Post-modification can be performed in conventional reactors. The ability to fabricate non-spherical droplets creates exciting opportunities in areas such as self-healing polymer composites.