Controlled Phase Separation Research Articles

Can adding oil control domain formation in binary amphiphile bilayers?

Bilayers formed of two species of amphiphile of different chain lengths may segregate into thinner and thicker domains composed predominantly of the respective species. Using a coarse-grained mean-field model, we investigate how mixing oil with the amphiphiles affects the structure and thickness of the bilayer at and on either side of the boundary between two neighbouring domains. In particular, we find that oil molecules whose chain length is close to that of the shorter amphiphiles segregate to the thicker domain. This smooths the surface of the hydrophobic bilayer core on this side of the boundary, reducing its area and curvature and their associated free-energy penalties. The smoothing effect is weaker for oil molecules that are shorter or longer than this optimum value: short molecules spread evenly through the bilayer, while long molecules swell the thicker domain, increasing the surface area and curvature of the bilayer core in the interfacial region. Our results show that adding an appropriate oil could make the formation of domain boundaries more or less favourable, raising the possibility of controlling the domain size distribution.

On Demand Control of Lipid Composition in Individual Bilayers

Lipid phase behavior affects a diverse range of cellular processes including virus entry, protein partitioning and signaling. Phase coexistence can be generated using ternary lipid mixtures in model membranes. In particular fluorescence imaging of Giant Unilamellar Vesicles (GUVs) has been used as a model system with which to understand such membrane phenomena. By creating GUVs with a range of lipid compositions a phase diagram can be mapped out. However poor equilibration of lipid mixtures has been implicated as a potential pitfall of such experiments, resulting in a heterogeneous population of GUV compositions. In order to overcome this potential problem we use Total Internal Reflection Fluorescence imaging of Droplet Interface Bilayers, generating ternary lipid mixtures within a single bilayer, where the composition of the bilayer can be titrated in situ, and the effects on phase coexistence examined. Droplet Interface Bilayers are formed by the contact of a lipid-coated water droplet and a hydrogel substrate immersed in a solution of lipids in oil to form a bilayer. Access to the oil phase enables us to vary the lipid composition of a single bilayer, and control phase separation.

Anomalous phase separation behavior in dynamically asymmetric LCST polymer blends

The interplay of thermodynamic forces and self-generated stresses induced in different compositions, and at different quench depths on the phase behavior of dynamically asymmetric PS/PVME blends are studied. The thermodynamic phase diagram is obtained from dynamic temperature sweep experiments. Phase contrast optical microscopy and rheological measurements including linear viscoelastic behavior and the stress growth behavior are employed to investigate the time evolution of the different phase-separating morphologies. At an intermediate quench depth of 14 °C, in addition to thermodynamically controlled phase separation mechanisms (nucleation and growth, NG, and spinodal decomposition, SD), three different kinds of phase separation behavior are induced by transient gel formation due to self-induced stresses in the early stage of phase separation: (i) conventional viscoelastic phase separation (VPS), (ii) nucleation of aggregate-like PS-rich phase and subsequent formation of a percolated network by coalescence, and (iii) nucleation of an aggregate-like PS-rich phase while the dispersed-matrix morphology is preserved in the later stages of phase separation. While it is generally accepted that VPS occurs at deep quench depths, we observe the VPS mechanism at shallow quench depths which is attributed to dynamic heterogeneity in the phase-separated domains. A dynamic phase diagram which shows the effect of dynamic asymmetry on phase behavior is proposed.

A family of oxide–carbide–carbon and oxide–nitride–carbon nanocomposites

This paper describes a powerful and versatile approach that combines the benefits of sol-gel processing with controlled phase separation to yield oxide-carbide-carbon or oxide-nitride-carbon nanocomposites.

Morphological Control of Multihollow Polymer Latex Particles through a Controlled Phase Separation in the Seeded Emulsion Polymerization

In this work, we first reported that the phase separation can take place both inside and outside of a multihollow-structured cross-linked seed microspheres swollen by styrene monomers in water during the radiation-induced seeded emulsion polymerization. The phase separation process in these two opposite directions will determine the morphology of final latex particles. First, sulfonated cross-linked polystyrene (SCPS) seed microspheres were swollen by styrene in water. Water will permeate into the SCPS seed microspheres during the swelling process, forced by the osmotic pressure produced by the strong hydrophilicity of the sulfonic acid groups. New aqueous phases are created and stabilized by the hydrophilic -SO3H groups, resulting in a multihollow structure of swollen SCPS seed microspheres. When the polymerization of styrene is induced by (60)Co γ-ray radiation, the phase separation of newly formed polystyrene phase will occur at the seed microsphere-water interface inside and/or outside of the SCPS seed microspheres through adjusting the diameter of seed microsphere, the content of cross-link agent, and the sulfonation degree of SCPS seed microspheres. As a result, SCPS latex particles with a variety of special morphologies, such as spherical multihollow, plum-like, and walnut-like latex particles were obtained. The results of this study provide not only a simple and interesting way to design and synthesize multihollow polymer latex particles with controllable surface morphologies but also a better understanding on phase separation mechanism during the swelling and polymerization of monomers in cross-linked amphiphilic polymer networks.

Formation behavior and performance studies of novel antifouling EVAL/PEO–PPO–PEO blend membranes for oil/water separation

Novel anti-fouling poly (ethylene-co-vinyl alcohol)/polyethylene oxide-polypropylene oxide-polyethylene oxide (EVAL/PEO–PPO–PEO) blend membranes were prepared by immersion precipitation method with different EVAL/PEO–PPO–PEO ratios. Thermodynamic and kinetic parameters which govern the formation of membrane were studied by viscosity and precipitation kinetics. Polyethylene oxide–polypropylene oxide–polyethylene oxide (PEO–PPO–PEO) content in the membrane solution controls phase separation by thermodynamic enhancement and kinetic hindrance. The addition of PEO–PPO–PEO is favorable for the formation of spongy like pores and higher porosity surface, which results in larger water flux and higher oil rejection rate through the membrane. Improved hydrophilicity and fouling resistance which have great significance in oil/water separation field were observed by the presence of PEO–PPO–PEO in the membrane. Fourier transform infrared spectroscopy results proved the residual PEO–PPO–PEO in the blend membranes.

Anisotropic particles from a one-pot double emulsion induced by partial wetting and their triggered release.

A family of anisotropic particles is synthesized via a facile, scalable, and versatile method based on a conventional double emulsion, which is very well suited for practical production and applications. Partial wetting theory is well established as a powerful instrument to elucidate the controlled phase separation within the double emulsion. This theory is employed to assist the manipulation of the phase separation process for the formation of well-defined nonspherical particles as well as their triggered release.

Tailored Hydrogel Membranes for Efficient Protein Crystallization

Crystallization still represents the bottleneck in the process of protein structure determination at high resolution, despite high‐throughput structural genomics programs requiring optimized crystallization strategies regarding crystal quality, time, success rate, reproducibility, and used protein amount. On the other hand, the development of suitable materials for controlled heterogeneous nucleation might facilitate biomacromolecular crystallization in a variety of experimental conditions which are not conventionally fruitful. Here, the possibility to fabricate hydrogel membranes displaying controlled chemical composition and nanostructure and to use them as heterogeneous supports for biomacromolecular crystallization is demonstrated. Diverse gel morphologies are obtained by controlling phase separation kinetics during gel layer formation on membrane support. These composite materials are found to increase the efficiency of the crystallization process so that crystals with enhanced diffraction properties are produced at lower protein concentration than conventional technique, thus affording the possibility to improve current approaches to protein crystallization and to be adapted to specific targets.

Hierarchical porous titania/carbon nanotube nanocomposite photoanode synthesized by controlled phase separation for dye sensitized solar cell

Incorporation of carbon nanotubes (CNT) in titania photoanode of dye sensitized solar cell (DSC) with hierarchical porous structure synthesized by controlled phase separation was studied. The hierarchical porous composite photoanode contained mesopores of 15nm and macropores of 280nm with surface roughness of about 15.4nm. The Raman spectroscopy confirmed the presence of CNTs beside titania anatase phase. Also, the transmission electron microscopy revealed that a very thin titania layer was formed on CNTs after impregnation with titania sol. The I–V characteristics of the DSCs with and without CNTs showed that incorporation of CNTs in photoanode led to an increase in current density and efficiency, which was due to the increase in surface area and hence dye adsorption, increase in density of states in titania and charge injection, and increase in charge collection and electron lifetime. The electrochemical impedance spectroscopy exhibited lower series resistance, lower charge injection resistance, and higher electron lifetime in DSCs containing CNTs. Addition of CNTs in photoanode also affected the critical thickness of porous layer with which the maximum efficiency could be obtained. Furthermore, the open circuit voltage and fill factor of the DSCs was independent of thickness when TiO2/CNT composite was used. The optimum amount of CNTs was found to be 0.32wt%, which led to the short circuit current density of 10.12mA/cm2, open circuit voltage of 680mV, fill factor of 56%, and efficiency of 3.85%.

Porous Polymers by Controlling Phase Separation during Vapor Deposition Polymerization

A template-free method is described to fabricate continuous-phase, porous polymer films by simultaneous phase separation during vapor deposition polymerization. The technique involves concurrent polymerization, crosslinking, and phase separation of condensed species and reaction products. Deposited films form open-cell, macroporous structures consisting of crosslinked and glassy poly(glycidyl methacrylate). By limiting phase separation during vapor phase deposition, spatially dependent morphologies, such as layered morphologies, can be grown. Results show that combining vapor deposition polymerization with phase separation establishes morphological control, which may be applied to applications including cellular scaffolds, thin cushions and vibration dampers, and membranes for separations.

Hierarchical sol–gel derived porous titania/carbon nanotube films prepared by controlled phase separation

Titania/carbon nanotube (CNT) composite films containing hierarchical interconnected porous structure have the advantages of high surface area of mesoporous structure and micro-channels of titania as well as high conductivity and charge separation properties of CNTs. In this research, the composites were prepared with controlled phase separation of titania sol. The main parameters to control the phase separation and macroporous morphology of the films including water content, stabilizer content, polyethylene glycol content, sol concentration, and deposition speed were investigated. X-ray diffraction and Raman spectroscopy confirmed the presence of CNTs together with anatase titania phase. Transmission electron microscopy showed that a very thin layer of titania was formed on CNT surface which improved interface of TiO2/CNT. It was found that macropores grew either with increasing water or polyethylene glycol content. However, stabilizer content and deposition speed had an inverse effect on macropores formation. Furthermore, sol concentration caused binodal decomposition and hence widened the pore size distribution. Although CNTs were ineffective in macropores formation, they strongly affected the transparency and charge separation of the composite films.

Oil-filled hydrogel particles for reduced-fat food applications: Fabrication, characterization, and properties

The food industry needs effective strategies to develop reduced calorie products with desirable sensory attributes. This study utilizes controlled phase separation of biopolymer mixtures to form oil-filled hydrogel particles suitable for use in food products. Filled hydrogel particles were fabricated from fat droplets (0 to 1%), sodium caseinate (1.5 to 3%) and high-methoxy pectin (1.5 to 3%) mixtures (pH 5) using two different approaches: multistep and simple methods. The multistep method involved inducing segregative phase separation of the mixed biopolymers at pH 7 (due to electrostatic repulsion), and then reducing to pH 5 to promote aggregative phase separation (due to electrostatic attraction). The simple method involved mixing all the components together at pH 7 and then adjusting to pH 5. The oil-filled hydrogel particles were spheroid in shape, with mean particle diameters (d43) around 10 μm. They consisted of fat droplets trapped within caseinate-rich hydrogel particles that were dispersed within a pectin-rich phase. The hydrogel particles increased the lightness and viscosity of aqueous solutions, and may therefore be suitable to replace fat droplets or starch granules in reduced calorie products. The food industry needs effective strategies to develop reduced calorie products with desirable sensory attributes. This study utilizes controlled phase separation of biopolymer mixtures to form oil-filled hydrogel particles suitable for use in food products. They consisted of fat droplets trapped within caseinate-rich hydrogel particles dispersed within a pectin-rich phase. The hydrogel particles increased the lightness and viscosity of aqueous solutions, and may be suitable to replace fat droplets or starch granules within reduced calorie products.

Anisotropic janus magnetic polymeric nanoparticles prepared via miniemulsion polymerization

Anisotropic Janus magnetic polymeric nanoparticles are prepared via the miniemulsion polymerization of styrene and acrylic acid monomers in the presence of oleic acid-coated magnetic nanoparticles (MNPs). The controllable phase separation between the polymer matrix and the encapsulated MNPs is a key success factor to produce Janus morphology. The effects of MNPs, 2,2′-azobis(2-isobutyronitrile) and sodium dodecyl sulfate contents, on the morphology, chemical composition and colloidal stability of the prepared Janus hybrid particles are investigated. Besides the determination of polymerization conversion, zeta potential, size analysis, TGA, and TEM are applied for characterization of the anisotropic particles. The results show the stable spherical Janus particles containing MNPs (15 wt % magnetic content) located on one side of each polymer particle. The anisotropic submicron Janus magnetic polymeric particles (250 nm) can be easily separated by an external magnet. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4779–4785

Controlled biopolymer phase separation in complex food matrices containing fat droplets, starch granules, and hydrocolloids

New strategies are needed to create high-quality reduced-calorie foods designed to combat the recent rise in overweight and obesity. In this study, we examined the influence of controlled phase separation and gelation of mixed biopolymer systems on the physical properties of model food matrices containing fat droplets, starch granules, and hydrocolloids. Phase separation of pectin–caseinate mixtures was induced through thermodynamic incompatibility (pH7) followed by electrostatic complexation (pH5), and then gelation was induced by adding calcium ions. The resulting model food matrices consisted of fat droplets, starch granules, and a phase separated biopolymer matrix. Confocal microscopy showed that the fat droplets were located within caseinate-rich hydrogel particles, which were present in the interstitial region around the swollen starch granules. All systems exhibited shear-thinning behavior and had yield stresses that increased with increasing biopolymer and calcium concentration. Swollen starch granules had a greater influence on the rheology of the mixed systems than other components due to their relatively high effective volume fractions, whereas fat droplets had a greater influence on the optical properties due to their stronger light scattering efficiency. Calcium ions increased the apparent viscosity of mixed systems, which was attributed to charge screening and ion-bridging effects. These findings suggest that controlled phase separation and gelation of mixed biopolymer systems have potential to create reduced calorie emulsion-based foods, or products with novel textural characteristics.

Fabrication and Characterization of a Nitric Oxide-Releasing Nanofibrous Gelatin Matrix

Nitric oxide (NO) plays an important role in cardiovascular homeostasis, immune responses, and wound repair. The pro-angiogenic and antimicrobial properties of NO has stimulated the development of NO-releasing materials for wound dressings. Gelatin, an abundant natural biodegradable polymer derived from collagen, is able to promote wound repair. S-Nitroso-N-acetylpenicillamine (SNAP) can release NO under physiological conditions and when exposed to light. The objective of this project was to fabricate a NO-releasing gelatin-based nanofibrous matrix with precise light-controllable ability. Results showed that under controlled phase separation fabrication conditions, the gelatin formed a highly porous matrix with the nanofiber diameter ranging from 50 to 500 nm. Importantly, the removal of the trace amount of divalent metal ions within gelatin generated a more stable nanofibrous structure. N-acetyl-D-penicillamine (NAP) was functionalized onto the matrix and nitrosated with t-butyl nitrite, yielding a SNAP-gelatin matrix. Analysis of the photoinitiated NO-release showed that the SNAP-gelatin matrices released NO in a highly controllable manner. Application of increasing light intensities yielded increased NO flux from the matrices. In addition, the dried matrices stored in dark at 4 °C maintained stable NO storage capacity, and the purified (ion-removed) gelatin preserved higher NO-releasing capacity than nonpurified gelatin. The antibacterial effect from the SNAP-gelatin matrices was demonstrated by exposing Staphylococcus aureus ( S. aureus ) to a light-triggered NO flux. This controllable NO-releasing scaffold provides a potential antibacterial therapeutic approach to combat drug resistant bacteria.

Accelerating the Phase Separation in Aqueous Poly(N-isopropylacrylamide) Solutions by Slight Modification of the Polymer Stereoregularity: A Single Molecule Fluorescence Study

We discovered for aqueous thermoresponsive polymer solutions that only a slight change in stereoregularity of the polymer can drastically accelerate phase separation. Single molecule fluorescence tracking (SMT) for an isotactic-slight-rich (meso-diad-rich) polymer sample solution revealed an interpolymer nanonetwork even before phase separation, and also revealed a novel phase in which translational molecular motion was frozen after phase separation. For such systems, fluorescence correlation spectroscopy (FCS) provided quantitative information on molecular diffusion. The results on FCS well agreed with the interpolymer nanonetwork model that was proposed on the basis of SMT measurement. We demonstrate such a novel method to control phase separation dynamics and also the interpolymer nanonetwork model.

The Effect of Additive on the Performance and Phase Separation of Benzo[1,2‐b:3,4‐b′]dithiophene‐Based Polymer Heterojunction Photovoltaic Devices

AbstractAn alternating copolymer (PBDTC10DBT) of benzo[1,2‐b:3,4‐b′]dithiophene (BDT) as donor and 4,7‐di(3‐decylthiophen‐2‐yl)‐2,1,3‐benzothiadiazole (C10DBT) as acceptor is designed and synthesized. In order to investigate the effect of the 1,8‐diiodooctane (DIO) additive on the morphology and photovoltaic performance, polymer solar cells (PSCs) based on PBDTC10DBT:[6,6]‐phenyl‐C61‐butyric acid methyl ester (PC61BM) are fabricated. The morphology of blend films and the interpenetrating network between the donor and the acceptor is examined using atomic force microscopy and scanning electron microscopy. This work shows that the PBDTC10DBT:PC61BM blend films with added DIO (3%, v/v) have improved absorption and controlled phase separation. Morphology with a domain size of 20–30 nm that forms in the DIO system is proposed to facilitate charge transport and minimize charge carrier recombination, which are the main reasons why the power conversion efficiency of the PSCs is improved from 1.93% (without DIO) to 2.23% (with DIO).magnified image

One-step preparation of magnetic Janus particles using controlled phase separation of polymer blends and nanoparticles

We present a simple method with the aid of a microfluidic droplet-generation technique to fabricate magnetic Janus particles by utilizing a solvent evaporation-induced phase separation and preferential partitioning of magnetic nanoparticles in the polymer blends. Non-aqueous emulsion droplets of the polymer blends and nanoparticles solution are produced to become Janus particles after the evaporation of the solvent. The stabilizing polymer of the nanoparticles, which is compatible only with one of the polymer blends to be phase-separated, plays a key role in the anisotropic positioning of the nanoparticles in the Janus particles. Using this phase separation-based method and microfluidics, excellent control over the size, size distribution, and morphology of the particles is achieved. Especially, we could control the morphology of the Janus particles easily by varying the volume ratio of the polymers. However, with an analysis of the shapes of resulting Janus particles, we found that non-equilibrium aspects of the evaporation-induced phase separation play a major role in determining the particle morphology. We expect that the versatility of this method in the choice of polymer blends and functional nanoparticles will enable the fabrication of colloids with various functionality and desired morphology.

Janus Anisotropic Hybrid Particles with Tunable Size from Patchy Composite Spheres

We have developed a facile approach to synthesize anisotropic Janus hybrid particles by selective modification of bulgy patches on the composite spheres, which are in situ grown by phase separation during seeded emulsion polymerization. Janus particles are achieved by dissolution of the seed polymer particles. It is the key to control phase separation to form multiple bulges and tune their size by pH and monomer fraction. The size of the Janus particles is continuously tunable from submicrometer to nanometer scale. They can be massively synthesized since many bulges are derived from one seed sphere.

Preparation of a Diblock Supramolecular Copolymer via Self-Sorting Organization

By incorporating a bis(crown ether) into an otherwise immiscible supramolecular polymer blend prepared from self-sorting organization of two heteroditopic AB-type monomers, a compatible AB diblock supramolecular copolymer was formed. The formation of the supramolecular copolymer was characterized by various techniques including 1H NMR, DOSY, specific viscosity, and SEM. Because of the existence of the glue-like bis(crown ether), newly formed supramolecular copolymer shows quite different properties from those of the immiscible supramolecular polymer blend in solution, in gel, and in the solid state. The evolution between the blend and the copolymer can be realized reversibly by adding or removing the bis(crown ether). This study provides an efficient and convenient strategy to control phase separation and morphology in supramolecular polymers and to prepare complex and highly ordered supramolecular structures.