Synthesis and characterization of polyacrylonitrile nanoparticles by dispersion/emulsion polymerization process

Polyacrylonitrile nanoparticles in sizes ranging from approximately 35 to 270 nm were prepared by dispersion/emulsion polymerization of acrylonitrile in a continuous aqueous phase in the presence of potassium persulfate as initiator and various alkyl-sulfate and sulfonate surfactants. The influence of various polymerization parameters (e.g., concentration of monomer and initiator, type and concentration of surfactant, temperature and time of polymerization, ionic strength, pH and co-solvent concentration) on the properties (e.g., size and size distribution, yield, stability, etc.) of the particles has been investigated. The polymerization of acrylonitrile may occur in two major locations: in the aqueous continuous phase (dispersion polymerization) and/or within the surfactant micelles (emulsion polymerization). A discussion concerning the role of these two mechanisms under different conditions, including comparison with previous literature, is also presented. Surface and bulk characterizations of the particles were performed by methods such as transmission and scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, zeta potential, and gravimetric measurements.     

Properties of oil1/water/oil2 double emulsions containing lipophilic acrylic polymer

Stable oil₁/water/oil₂ (o₁/w/o₂) double emulsions (DEs) containing glyceryl monooleate as a promoter of skin permeability in internal ultradispersed phase o1 (heptane) and an acrylic polymer as a pressuresensitive adhesive in external dispersion medium o₂ (ethyl acetate) are obtained. The aqueous interlayer of the DEs contains Tween 80, hydroxypropyl cellulose, and sometimes lysozyme. The phase ratio in the emulsions is constant. The effect of polyacrylate concentration on the stability, microstructure, and rheological properties of DEs is studied. Factors of DE stability, with the viscoelastic properties of the external dispersion medium being of the most importance, are analyzed. The DEs are used to produce ultradisperse films, which exhibit long-term release of lysozyme at a constant rate with its enzymatic activity retained preserved. The diffusion coefficient of the protein in the polymer matrix is determined.     

Interfacial rheology of protein–surfactant mixtures

The distribution of proteins and surfactants at fluid interfaces (air–water and oil–water) is determined by the competitive adsorption between the two types of emulsifiers and by the nature of the protein–surfactant interactions, both at the interface and in the bulk phase, with a pronounced impact on the interfacial rheological properties of these systems. Therefore, the interfacial rheology is of practical importance for food dispersion (emulsion or foam) formulation, texture, and stability. In this review, the existence of protein–surfactant interactions, the mechanical behaviour and/or the composition of emulsifiers at the interface are indirectly determined by interfacial rheology of the mixed films. The effect on the interfacial rheology of protein–surfactant mixed films of the protein, the surfactant, the interface and bulk compositions, the method of formation of the interfacial film, the interactions between film forming components, and the displacement of protein by surfactant have been analysed. The last section tries to understand the role of interfacial rheology of protein–surfactant mixed films on food dispersion formation and stability. The emphasis of the present review is on the interfacial dilatational rheology.     

Investigation of structure, stability, phase composition and magnetic ordering in ultrathin iron/nickel films

By thermal and chemical treatment of Langmuir-Blodgett (LB) films, oxidic and metallic Fe and Ni layers can be prepared. The films are characterised, where differences e.g. in the lateral homogeneity are found. The metallic Fe containing samples show a higher corrosion stability as compared with films prepared by other coating techniques. Mixed Fe/Ni oxidic and metallic layers, respectively, are prepared, where the Ni concentration in the oxidic films can be determined as a function of the ratio of initially transferred numbers of LB layers. The phase composition of the metallic Fe changes systematically with the Ni concentration.In partial fulfilment of his thesis     

Compatibility of binary systems of poly(methyl methacrylate), poly(vinyl chloride) and poly(vinyl acetate)

The influence of the thermal treatment on the stability in time of the dispersion degree of films containing binary polymer mixtures, poly(vinyl chloride)/poly(methyl methacrylate), poly(vinyl chloride)/poly(vinyl acetate) and poly(vinyl acetate)/poly(methyl methacrylate), was studied by thermogravimetry and optical microscopy with phase contrast. The dispersion degree depends particularly on the composition of the polymer mixture and can be improved by thermal treatment at temperatures above the glass temperatures of both homopolymers. It seems that this thermal treatment yields exclusively metastable structures with a general tendency to phase separation in a short time after thermal treatment, the heterogeneity mixtures (as film) being more pronounced.     

Hydrophobic bacteria at the hexadecane-water interface: examination of micrometre-scale interfacial properties

Hydrophobic bacteria, like colloidal solids, can spontaneously adsorb onto fluid-fluid interfaces and modify their mechanical properties. In this study, two strains of bacteria--Acinetobacter venetianus RAG-1 and Rhodococcus erythropolis 20S-E1-c--were prepared in their stationary (i.e. non-dividing) phase in the absence of biosurfactants; the cells were then used as emulsifiers to stabilize n-hexadecane droplets in aqueous environments. Using the micropipette technique, colloidal stability of the bacteria-coated droplets was examined through direct-contact experiments. Both types of bacteria were seen to function as effective stabilizers, although the Acinetobacter venetianus RAG-1 film provided stronger resistance to droplet-droplet coalescence. In addition to creating steric barriers, the adsorbed bacteria also interacted with one another at the interface, giving rise to higher order rheological properties. A technique of directly probing the mechanical properties of the emulsion drop surfaces (i.e. the adsorbed films) on the micrometre-scale revealed that (a) the films behaved as purely elastic sheets, and (b) with a reduction in cell concentration in the aqueous phase, less oil was emulsified, but the elastic moduli of the adsorbed films remained unchanged (suggesting an "all or none" adsorption process). These results are in contrast to a previous macroscopic (i.e. millimetre-scale) study, which showed that the absorbed films were viscoelastic, with the apparent elastic moduli depending strongly on cell concentration. The rheological properties of these bacteria-adsorbed interfaces appeared therefore to be length scale-dependent.     

Ethanol-assisted graphene oxide-based thin film formation at pentane-water interface

Graphene oxide (GO) can be viewed as an amphiphilic soft material, which form thin films at organic solvent-water interfaces. However, organic solvent evaporation provides little driving force, which results in slow GO transfer in aqueous phase, thus dawdling GO film formation processes for various potential applications. We present an ethanol-assisted self-assembly method for the quick formation of GO or GO-based composite thin films with tunable composition, transmittance, and surface resistivity at pentane-water interface. The thickness of pure GO and reduced GO (rGO) films ranging from ~1 nm to more than 10 nm can be controlled by the concentration of GO in bulk solution. The transmittance of rGO films can be tuned from 72% to 97% at 550 nm while the surface resistivity changes from 8.3 to 464.6 kΩ sq(-1). Ethanol is essential for achieving quick formation of GO thin films. When ethanol is injected into GO aqueous dispersion, it serves as a nonsolvent, compromising the stability of GO and providing driving force to allow GO sheets aggregate at the water-pentane interface. On the other hand, neither the evaporation of pentane nor the mixing between ethanol and water provides sufficient driving forces to allow noteworthy amount of GO sheets to migrate from the bulk aqueous phase to the interface. This method can also be extended to prepare GO-based composites thin films with tunable composition, such as GO/single walled carbon nanotube (SWCNT) composite thin films investigated in this work. Reduced GO/SWCNT composite films show much lower surface resistivity compared to pure rGO thin films. This ethanol-assisted self-assembly method opens opportunities to design and fabricate new functional GO-based hybrid materials for various potential applications.     

THE INFLUENCE OF COLLOIDAL STABILITY ON CRITICAL PIGMENT VOLUME CONCENTRATION (CPVC)

The level of colloidal stability of a latex coating formulation is governed by the hydrodynamic size of the pigment particle and its aggregates, along with the electrolyte concentration of the coating formulation. Model latex coating films were developed to investigate the effects of pigment aggregate size and the electrolyte concentration in the latex coating formulation on the critical pigment volume concentration (CPVC), as determined by mechanical optical and permeability properties.

The poly(styrene) pigment and poly(styrene-butadiene) (60:40) binder particles were characterized for their relative sizes, the surfactant surface coverage and the critical coagulation concentration, in dilute (1.8% solids) and concentrated (42% solids) dispersions, for sodium chloride and calcium chloride. The hydrodynamic diameter of the strong pigment aggregates formed as a function of aging time, after adjusting the electrolyte concentration of the pigment dispersion to the c.c.c. level were characterized by capillary chromatography technique.

The Increasing size of the pigment aggregates and the increasing electrolyte concentration of the latex coating formulation were shown to sharply decrease the CPVC values determined by mechanical and optical properties such as tensile strength and contrast ratio of the coating. Their influence on the permeability property of the films such as porosity was limited by the availability of the binder to form smooth surface below 35-40% PVC.

The morphological studies of the coating films showed that aggregates cause an increase in the degree of non-uniform distribution of the binder and pigment in the latex coating film     

Facile way of dynamically tailoring microporous structures in polyvinylidene fluoride films prepared by thermally induced phase separation

Polyvinylidene fluoride (PVDF) films were prepared via thermally induced phase separation (TIPS) using diphenyl carbonate as the diluter in an attempt to disclose the competitive relationship between crystal growth and droplet growth during phase separation process. By varying the quenching temperature different temperature gradient fields were established, which were theoretically evaluated via enthalpy transformation method. The effects of polymer concentration and quenching temperature on evolution of hierarchical morphologies in TIPS films were systematically investigated. According to the morphological characteristics, the cross-sectional morphology of the films with lower polymer concentration (Φ_P = 25%) could be divided into three layers; while that of higher polymer concentration counterpart (Φ_P = 55%) only presented a bi-layered structure. The reason for this could be ascribed to the effect of cooling rate on both crystal growth and droplet growth during TIPS process, which further determined the formation of the hierarchical structure in microporous films. With an increasing quenching temperature, both pore size and porosity of PVDF films increased, accompanied by an improvement on both thermal stability and dynamic mechanical thermal property. The present study could insightfully supply a facile route to fabricate structure-controllable microporous films of crystalline polymers via an appropriate regulation of the TIPS quenching parameters.     

Selection of surfactants for stable paraffin-in-water dispersions, undergoing solid-liquid transition of the dispersed particles

A new experimental procedure is proposed for express evaluation of the coalescence stability of dispersions, in which the dispersed particles undergo solid-liquid phase transition. The procedure includes centrifugation of the dispersion concurrently with the phase transition of the particles and allows precise quantification of dispersion stability in terms of a critical pressure, at which the coalescence between the dispersed particles/drops takes place. The method is applied for studying the effects of surfactant type and concentration on the stability of paraffin-in-water dispersions, which have potential application in energy storage and transportation systems. Several types of water-soluble surfactants (anionic, nonionic, and polymeric) are compared, whereas hexadecane or tetradecane is used as a dispersed phase. Most of the studied individual surfactants are found to be inefficient stabilizers (except for the nonionic Tween 40 and Tween 60). However, the dispersion stability increases significantly after the addition of appropriate cosurfactants, such as hexadecanol, Brij 52, or cocoamidopropyl betaine. Surfactants and cosurfactants with longer hydrophobic tails are better stabilizers than those with shorter tails. The obtained results are discussed from the viewpoint of the mechanisms of particle/drop coalescence during the solid-liquid-phase transition. The consistency and the undercooling temperatures of the studied dispersions are also discussed, because these properties are important for their practical applications. The proposed procedure for evaluation of dispersion stability and some of the conclusions could be relevant to food emulsions, in which dispersed fat particles undergo solid-liquid-phase transition of similar type.     

Dispersing different nanoparticles in paraffin wax as enhanced phase change materials

Highly conductive nanoparticles were proposed to be dispersed into phase change materials (PCMs) such as paraffin wax for heat transfer enhancement. The mixture, often referred to as nanoparticle-enhanced phase change material (NePCM), has been studied extensively for latent heat energy storage but with conflicting results. This study attempts to understand this problem by investigating the stability of NePCMs under multiple thermal (melting–solidification) cycles, which has not been well explained in previous studies. We believe that stability of a NePCM is prerequisite for any experimental investigation of its thermal properties or application. In this study, paraffin wax was chosen as the base material. Three different types of nanoparticles were tested, i.e., multi-walled carbon nanotubes, graphene nanoplatelets, and aluminum oxide nanoparticles (Al₂O₃). The nanoparticles were dispersed into paraffin wax at varying mass fractions using mechanical dispersion methods (sonication, stirring) with and without different surfactants. Stability of different mixtures was investigated after consecutive thermal cycles performed in an environmental chamber. Significant coagulation and deposition of nanoparticles were found after a few thermal cycles regardless of the nanoparticle type, concentration, or dispersion method. Different boundary conditions in heating were also examined for their effects. None of these methods led to long-term stable NePCMs. The “negative” results from this study indicate that long-term stability of NePCM (at least for the paraffin wax and nanoparticles tested) remains a major challenge and requires further research with a multidisciplinary approach.

     

Original Preparation of PEKK Dispersion for Coating by Transfer from a Chloroform Stable Dispersion to an Aqueous Stable Dispersion,by Emulsion/Solvent Evaporation

In this work, aqueous dispersions of PolyEtherKetoneKetone (PEKK) oligomers were obtained by an emulsion/dispersion solvent evaporation technique. The PEKK oligomers were synthesized by a Friedel–Crafts acylation with a number average degree of polymerization of 4. The synthesized PEKK oligomers had very good thermal stability and spontaneously formed a stable dispersion of swollen micrometric fibers in chloroform. After sonication of the chloroform dispersion in water in the presence of sodium dodecyl sulfate (SDS) and evaporation, we obtained aggregated particles with a mean diameter between 120 and 160 nm, decreasing linearly with the PEKK concentration. The most stable dispersions were obtained with 0.5% wt of surfactant and, at a fixed concentration of SDS, the stability decreased when the PEKK concentration was increased. The different dispersions of PEKK in water were very stable and, after water evaporation, formed homogeneous films for high-performance coating.     

中空纤维分散液膜富集稀土元素

采用2-乙基己基膦酸单-2-乙基己基酯(HEHEHP)-正庚烷为萃取剂,盐酸为反萃取剂,中空纤维膜作支撑膜,研究中空纤维分散液膜技术富集稀土镱(Yb~(3+))离子。考察了体系物性:反萃分散相中反萃剂浓度、萃取剂浓度、萃取剂与反萃剂体积比、料液相p H值、稀土离子浓度;流体流动状态:反萃分散相与料液相流速变化等因素对富集稀土离子的影响。中空纤维分散液膜富集Yb~(3+)的最佳条件为:萃取剂浓度为0.25 mol/L,反萃取剂HCl浓度为4.00 mol/L,萃取剂与反萃剂体积比为10∶40,料液相p H=2.80,稀土离子浓度为0.025 mol/L。反萃分散相体积流量和料液相体积流量较小时,萃取率随流量的增加呈现逐渐增大的趋势。若两相体积流量过大,反萃过程进行不完全,萃取率反而下降。研究结果表明,中空纤维分散液膜技术可实现稀土离子的有效富集。     

Some new aspects of and conclusions on theory of stability of colloids and their experimental verification

This paper considers three aspects of colloid stability theory: phase stability, the stability of disperse composition and aggregative stability in relation to the merits of a direct operational determination of the disjoining pressure. Four components of the disjoining pressure are treated: the dispersion, ion/electrostatic, adsorption and structural terms. The simplest and most general way to derive the second and third components of disjoining pressure is to use the Gibbs-Duhem equation generalized by inclusion of terms corresponding to the electric work of charging the particle interface. The theory of the adsorption component of disjoining pressure explains the stability of free films of some binary solutions demonstrated experimentally by Sheludko and Ekerova.

With regard to other aspects of colloid stability we note that flow-ultramicroscopic measurements of the concentration of colloid particles are free from the shortcomings of other methods. This makes accessible the kinetics of slow coagulation of sols (e.g., gold sols) and reveals the role of disaggregation here and in the establishment of aggregative quasi-equilibrium. The measurements of molecular attraction between crossed metal wires as a function of gap width are presented.     

Preparation of a stable double emulsion (W1/O/W2): role of the interfacial films on the stability of the system

This paper presents new protocols enabling preparation of W1/O/W2 double emulsions: one, using soybean oil as the O phase, that yields edible emulsions with industrial applications, and a second that yields emulsions with a previously unattainable concentration 15% (w/w) of surfactants in the external phase (the 15% target was chosen to meet the typical industry standard). Preparation of a stable W1/O emulsion was found to be critical for the stability of the system as a whole. Of the various low HLB primary surfactants tested, only cethyl dimethicone copolyol (Abil EM90), A-B-A block copolymer (Arlacel P135), and polyglycerol ester of ricinoleic acid (Grinstead PGR-90) yielded a stable W/O emulsion. Investigation of the surface properties of those surfactants using the monolayer technique found two significant similarities: (1) stable, compressible, and reversibly expandable monolayers; and (2) high elasticity and surface potential. The high degree of elasticity of the interfacial film between W1 and O makes it highly resilient under stress; its failure to break contributes to the stability of the emulsion. The high surface potential values observed suggest that the surfactant molecules lie flat at the O/W interfaces. In particular, in the case of PGR-90, the hydroxyl (-OH) groups on the fatty acid chains serve as anchors at the O/W interfaces and are responsible for the high surface potential. The long-term stability of the double emulsion requires a balance between the Laplace and osmotic pressures (between W1 droplets in O and between W1 droplets and the external aqueous phase W2). The presence of a thickener in the outer phase is necessary in order to reach a viscosity ratio (preferably approximately 1) between the W1/O and W2 phases, allowing dispersion of the viscous primary emulsion into the W2 aqueous phase. The thickener, which also serves as a dispersant and consequently prevents phase separation due to its thixotropic properties, must be compatible with the surfactants. Finally, the interactions between the low and high HLB emulsifiers at the O/W2 interface should not destabilize the films. It was observed that such destructive interaction for the system could be prevented by the use of two high HLB surfactants in the outer aqueous phase: an amphoteric surfactant, Betaine, and an anionic surfactant, sodium lauryl ether sulfate. The combination of such pairs of surfactants was found to contribute to the films' stability.     

铂粒子修饰单壁碳纳米管/聚苯胺复合膜对甲醛的电催化氧化

在溶有单壁碳纳米管(SWNTs)的苯胺溶液中, 通过电化学共聚合法成功制备了单壁碳纳米管(SWNT)/聚苯胺(PANI)复合膜. 用电沉积法将铂沉积到SWNT/PANI复合膜上. 样品的成分和形貌分别用XRD和SEM表征. 四探针和电化学交流阻抗的研究表明被PANI包裹的SWNTs整齐地排列在复合膜中, 从而提高了复合膜的电导率, 促进了电荷转移. 循环伏安(CV)说明Pt修饰的SWNT/PANI复合膜对于甲醛氧化具有良好的电催化活性及稳定性. 研究结果表明SWNT/PANI复合膜是一种非常好的催化剂载体, 有着广泛的应用前景.     

Polarisation switching and molecular relaxation behaviour of anthraquinone dye-dispersed polymer-stabilised ferroelectric liquid crystal composites

Guest–host polymer-stabilised ferroelectric liquid crystal (GH-PSFLC) composite films have been prepared with dispersion of small concentration (0.1, 0.25 and 0.5 wt%) of anthraquinone blue dye in PSFLC host matrix via a polymerisation-induced phase separation (PIPS) process. The variation in alignment and size of twisted fibril has been observed in the optical textures of the guest–host composites with different wt/wt ratio of anthraquinone dye. The electrical and dielectric properties of PSFLC mixture and its guest–host derivatives are studied. Our results showed that an optimum amount of dye concentration (0.1 wt%) enhances the dielectric permittivity as well as the spontaneous polarisation of the GH-PSFLC material in the SmC* phase.     

Charge transport and contact resistance in coplanar devices based on colloidal polyaniline dispersion

The charge transport properties of thin films prepared from colloidal dispersion of polyaniline stabilized by poly(N‐vinylpyrrolidone) (PANI/PVP) have been investigated. The electrical characterization of coplanar device comprising of gold electrodes and PANI/PVP film deposited by spin coating served to gain insights into the contact and bulk resistance. The films prepared from PANI/PVP colloidal dispersion show high stability over a large temperature range. Temperature dependent measurements in the range from 90 to 350 K reveal that the charge transport can be described by a three‐dimensional variable‐range hopping mechanism as the dominant mode in the films. The stability of the films cast from dispersion within a large temperature range opens the possibility of the application as a polymer semiconductor layer in sensors and charge‐transport interlayer in organic solar cells. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1710–1716     

Synthesis and characterization of new flame-retardant microspheres by dispersion polymerization of pentabromobenzyl acrylate

New flame-retardant nano/micro particles of sizes ranging between 0.06 ± 0.01 and 1.70 ± 0.23 μm were formed by dispersion polymerization of the pentabromobenzyl acrylate monomer (PBBA) in methyl ethyl ketone as a continuous phase. The effect of various polymerization parameters, e.g., monomer concentration, initiator type and concentration, stabilizer concentration and crosslinker monomer concentration, on the size, size distribution and polymerization yield of the produced poly(pentabromobenzyl acrylate) particles has been elucidated. Poly(pentabromobenzyl acrylate)/polystyrene (PPBBA/PS) nano/micro blends of the contents of different PPBBA particles were prepared by mixing the PPBBA particles with a PS solution in methylene chloride, followed by evaporation of the methylene chloride from the mixture. The thermal stability of these blends was also studied.     

Nano-architectural silica thin films with two-dimensionally connected cagelike pores synthesized from vapor phase

Novel mesostructured silica thin films were prepared on a Si substrate by a vapor-phase synthesis. Vapor of tetraethoxysilane (TEOS) was infiltrated into a surfactant film consisting of a poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer. Nanophase transition from a lamellar structure to a two-dimensional cage structure of a silica-surfactant nanocomposite was found under vapor infiltration. The rearrangement into the cage structure implies high mobility of the silica-surfactant composites in solid phase. The silica thin films have two-dimensionally connected cagelike mesopores and are isotropic parallel to the film surface. The structure of pores of the films is advantageous for next-generation low-k films. The mesoporous structure has a large lattice parameter d of approximately 102 A, silica layer thickness of approximately 58 A, pillar diameter in the middle of approximately 60 A, pore size of approximately 72 A, BET surface area of approximately 729 m(2)/g, and pore volume of approximately 1.19 cm(3)/g. The films synthesized by the vapor infiltration show a lower concentration of residual Si-OH groups compared to the films prepared by a conventional sol-gel method. The films show high thermal stability up to 900 degrees C and high hydrothermal stability. This method is a simpler process than conventional sol-gel techniques and attractive for mass production of a variety of organic-inorganic composite materials and inorganic porous films.