Charging of unfunctionalized graphene in organic solvents

Unfunctionalized graphene is positively or negatively charged when it is dispersed in organic solvents. The charging is negative in solvents with high electron donor numbers and positive in those with low donor numbers. We suggest that the charging originates from electron transfer between graphene surfaces and solvent molecules, and the stable dispersion of unfunctionalized graphene in organic solvents is mainly controlled by electrostatic repulsion between the charged graphene surfaces.     

Electrochemical reduction of graphene oxide in organic solvents

Graphene oxide (GO) cast on conductive substrates was electrochemically reduced in some organic solvents. The amount of electricity required for the almost complete reduction of GO was 2.0 C for 1 mg GO, corresponding to attaching of a one-electron reducible species to each benzene ring in graphene. The electrochemically reduced GO film gave an electrical conductivity of about 3 S cm⁻¹ and exhibited a relatively high specific capacitance of 147.2 F g⁻¹ in propylene carbonate. The electrochemical reduction of GO was feasible on Al foils as well.     

Selection of coalescing solvents for coatings derived from polyurethane dispersions utilizing high throughput research methods

Reduction of volatile organic compounds (VOCs) in coatings is being driven by regulation and consumer preference. Development of binders that are capable of delivering expected performance at low VOC is a major thrust of coatings research and development. Toward this end, polyurethane dispersions (PUDs) from natural oil polyester polyols (NOPs) have been developed. These hydrophobic NOP-based PUD coatings exhibit exceptional early water resistance and hydrolytic stability, excellent acid resistance, and good toughness & abrasion resistance. Most high performance PUDs require large amounts of solvent to form crack-free films with good properties. However, with the right choice of process and solvent parameters, PUDs have been shown to require reduced amounts of coalescing solvents to yield the desirable array of end-user properties with ambient temperature drying. High-throughput research (HTR) was used as a means to accelerate formulation and product development of PUDs. Rapid formulation and testing allows for probing of interactions between variables in greater depth and breadth than conventional formulation techniques, leading to rapid development of robust products and formulations. The HTR methods for coatings applications include the use of specially designed experiments, robotic formulation, coating, and characterization tools as well as informatics for data visualization, extraction, and modeling. This paper details the use of HTR capability to explore the effect of cosolvents on end-use properties of NOP based PUD coatings as well as the proposed mechanisms of film formation in NOP-PUDs. The results provide a basis for guidelines for selection of cosolvents for PUD coatings with high performance and low VOC (<100 g/L VOC).     

The production of concentrated dispersions of few-layer graphene by the direct exfoliation of graphite in organosilanes

We report the formation and characterization of graphene dispersions in two organosilanes, 3-glycidoxypropyl trimethoxysilane (GPTMS) and phenyl triethoxysilane (PhTES) as new reactive solvents. The preparation method was mild and easy and does not produce any chemical modification. The dispersions, which exhibit the Tyndall effect, were characterized by TEM and Raman spectroscopy to confirm the presence of few-layer graphene. Concentrations as high as 0.66 and 8.00 mg/ml were found for PhTES and GPTMS, respectively. The latter is one of the highest values reported for a dispersion of graphene obtained by any method. This finding paves the way for the direct synthesis of polymer nanofiller-containing composites consisting of graphene and reactive silanes to be used in sol–gel synthesis, without any need for solvent removal, thus preventing graphene reaggregation to form graphite flakes.     

Using a glowing wire generator for production of charged, uniformly sized nanoparticles at high concentrations

The glowing wire represents a clean method of producing particles from a few nanometers to some tens of nanometers in diameter. An empirical rule is derived, identifying the materials, for which the method is applicable. A fraction of the particles is already charged at an efficiency comparable to radioactive chargers. This allows the direct use for mobility size classification and deposition without any further charging step. By applying a potential difference to the wire with respect to the housing, the charged particle yield can be increased by almost two orders of magnitude. Downstream of a mobility classifier a maximum concentration as high as was reached. The generator shows excellent long-term stability.     

Solubilities of the fatty acids in organic solvents at low temperatures

Summary A considerable series of pure fatty acids has been prepared and their solubilities have been determined at temperatures down to −70° in acetone, methanol and Skellysolve B. Solubility ratios have also been determined for oleic to palmitic acid and linoleic to oleic acid in a number of additional solvents at certain temperatures. Submitted in partial fulfillment of the requirements for the Ph.D. degree in the Graduate School.     

Preparation of a graphene nanosheet/polyaniline composite with high specific capacitance

A graphene nanosheet (GNS)/polyaniline (PANI) composite was synthesized using in situ polymerization. The morphology and microstructure of samples were examined by scanning electron microscopy (SEM), transition electron microscopy (TEM), X-ray diffraction (XRD) and Raman spectroscopy. Electrochemical properties were characterized by cyclic voltammetry (CV) and galvanostatic charge/discharge. GNS as a support material could provide more active sites for nucleation of PANI as well as excellent electron transfer path. The GNS was homogeneously coated on both surfaces with PANI nanoparticles (∼2 nm), and a high specific capacitance of 1046 F g⁻¹ (based on GNS/PANI composite) was obtained at a scan rate of 1 mV s⁻¹ compared to 115 F g⁻¹ for pure PANI. In addition, the energy density of GNS/PANI composite could reach 39 W h kg⁻¹ at a power density of 70 kW kg⁻¹.     

Synthesis of graphene/vitamin C template-controlled polyaniline nanotubes composite for high performance supercapacitor electrode

A graphene nanosheet/polyaniline nanotube (GPNT) composite is prepared for the first time by in-situ chemical oxidative polymerization of aniline using vitamin C as a structure directing agent. The vitamin C molecules lead to the synthesis of polyaniline (PANI) nanotubes through the development of rod-like assembly by H-bonding in an aqueous medium. The initially synthesized graphene oxide/polyaniline nanotubes composite is reduced to graphene using hydrazine monohydrate followed by re-oxidation and protonation of the PANI to produce the GPNT nanocomposite. This novel composite showed a high specific capacitance of 534.37 F/g and an excellent energy density of 74.27 Wh/kg at a constant current of 0.5 mA. Besides, the GPNT composite exhibited excellent cycle life with 91.4% specific capacitance retained after 500 charge-discharge cycles. The excellent performance is due to the synergistic combination of graphene which provides good electrical conductivity and mechanical stability, and PANI nanofiber which deals with good redox activity.     

Swelling of lignites in organic solvents

Data on the swelling of Turkish lignites can be summarized using linear multiparameter equations that take into account various properties of solvents. Factors responsible for the amounts of absorbed solvents are the basicity and cohesion energy density of the solvents.     

Si3N4-Al2O3-CaO系材料烧结性能及反应过程研究

以氮化硅、活性氧化铝微粉和纯铝酸钙水泥为原料,研究了在焦炭保护情况下,Si3N4-Al2O3-CaO系材料经1500℃、1600℃和1650℃烧成时的烧结性能和物相变化,同时借助SEM、EDX和XRD等手段对其显微结构和反应过程进行了观察和分析.结果表明,该体系材料的烧结性能与试样的组成和烧成温度有关温度由1500℃升至1600℃,试样体积密度增加,显气孔率降低,但升至1650℃时,试样的体积密度反而下降,显气孔率增加;在同一温度下,试样中Si3N4含量增加,体积密度下降.同时,试样在烧成过程中存在质量变化现象1500℃烧成试样均表现为质量增加,当温度升至1600℃和1650℃时,试样质量又由增加变为减小.根据热力学分析推测,试样烧成过程中存在复杂的化学反应,低于1500℃时,反应Si3N4(s)+3/2CO(g)=3/2Si2N2O(s)+1/2N2(g)+3/2C(s)是试样质量增加的主要机理;高于1500℃时,反应Si3N4(s)+3/2CO(g)=3/2SiC(s)+3/2SiO(g)+2N2(g)是引起质量损失的主要机理.XRD分析显示,烧后试样中除存在刚玉和Si3N4相外,在烧成过程中还发生了物相变化1500℃时出现了钙黄长石相,1600℃时钙黄长石又消失,出现了Ca-α-Sia-lon和β-Sialon,温度升至1650℃时,Ca-α-Sialon又消失,β-Sialon却大量出现于部分试样中.因此可以认为,钙黄长石是铝酸钙水泥中CaO与Si3N4表面的SiO2和Al2O3反应形成的,温度升高时,其与Si3N4进一步反应形成Ca-α-Sialon,1650℃时Ca-α-Sialon消失,可能是在该温度下,试样内部的化学反应导致试样组成偏离Ca-α-Sialon相区;而β-Sialon是Si3N4固溶Al2O3反应形成的,其含量取决于试样中Al2O3、Si3N4的含量及烧成温度.     

Experimental study of drop size distributions at high phase ratio in liquid-liquid dispersions

An experimental investigation has been carried out in order to analyse the drop size distributions of a liquid-liquid dispersion in a stirred vessel at high phase ratio. Two liquid-liquid systems have been investigated: one at low and one at high coalescence rate. A sampling technique has been developed in order to measure the drop size distributions in the mixer with the help of a laser granulometer. A statistical approach has been attempted to derive the most probable drop size distribution in the mixer and the results have been compared with the experimental primary distributions. The comparison suggests that the energy dissipation cannot be considered as uniformly distributed in the mixer. The mean diameter of the distribution has been correlated to the global mechanical input power and to the volume phase fraction (phase ratio) for both systems in the frame of the classical Hinze-Kolmogorov theory. The results show that for each volume fraction studied, the mean diameter of the dispersion is a decreasing power law of the Weber number with an exponent equal to −0.6 at low phase ratio. However, it appears that for both systems studied this exponent is a decreasing function of the phase ratio. This result reveals the existence of a more complex breakup mechanism with high phase ratio than that assumed in the theory which has to be discriminated from dampening effect of the dispersed phase upon the turbulent energy of the bulk phase. The study of the secondary distributions mean diameter seems to be in good agreement with the numerical predictions of Stone (Annu. Rev. Fluid Mech. 26 (1994) 65). The ratio between the mean diameter of the primary distribution to the satellite drop mean diameter is a growing function of the viscosity ratio.     

Determination and correlation of diffusion coefficients of some dyes in organic solvents of high viscosity

Diffusion coefficients of three dyes at low concentrations in a range of liquids of different viscosities have been measured by a capillary method, and the validity of various empirical equations for predicting diffusion coefficients has been assessed. The inverse relationship between diffusion coefficient and viscosity was found to apply only in mobile liquids, the product Dη being greater in viscous liquids. For a given viscosity, the difference between predicted and experimental values was greatest for hydrogen-bonded liquids. Comparison with other results suggests that the diffusivity varies inversely as some power of the molar volume of the solute, the exponent varying from about 0.7 for mobile liquids, through 1.1 to 1.4 for viscous liquids, to a literature value of 1.7 for solid rubber.     

Synthesis of cobalt ferrite in organic solvents

The possibility of synthesizing the nanosized CoFe₂O₄ particles in organic solvents, such as glycerol and diphenyl oxide, at 250°C and atmospheric pressure under conditions of distillation of the formed water was studied. In the case of glycerol, we obtained the adduct of the latter with cobalt ferrite. The reaction in diphenyl oxide resulted in the formation of ferrite particles sized 8–10 nm.     

Diffusion of organic solvents in isobutylene-based polymers

Diffusion behavior of several organic solvents in polyisobutylene (PIB) and in poly(p-methylstyrene-co-iso-butylene) (PMS-BR) with different monomer ratios has been studied. The experiments have been conducted over a temperature range of 50 to 100°C using a conventional gravimetric Sorption technique. The PMS-BR copolymers contained 2, 7, and 15 weight percent p-methylstyrene, respectively. Although employing temperatures were far above the glass transition temperatures of polymers, the diffusion coefficients are correlated well with the Vrentas-Duda free-volume theory. For all the solvents, the PIB shows the highest diffusivity while the copolymer with the 15% p-methylstyrene gives the lowest value. This behavior can be explained by the amount of fractional free-volume present in a system.     

Fabrication of insulated metal substrates with organic ceramic composite films for high thermal conductivity

Insulated metal substrates (IMSs) were fabricated and characterized using an organic ceramic composite as a coating mixture. Organic‐inorganic sol solutions were prepared by a sol‐gel process using TEOS (tetraethylorthosilicate), MTMS (methyltrimethoxysilane) and PhTMS (phenyltrimethoxysilane). Ceramic fillers were composed of aluminum oxide (1 and 4 µm) and silicon nitride. The optimal ratio of ceramic filler in the coating mixture was found to be 70 wt%. A thermal conductivity of 3.16 W/mK and a breakdown voltage of 4 kV with a leakage current of 0.17 mA/cm² were obtained for the 122 µm-thick film. A well-networked microstructure between the sol resin and filler in the organic ceramic composite films enhanced the properties of the IMS, such as thermal conductivity and electric insulation.     

Hindered settling of organic pigment dispersions in hydrocarbon liquids

A modified Steinour hindered settling method has been developed for the study of dispersed organic pigment species containing a large proportion of associated immobile liquid. These species are termed flow units with effective volumes and densities different from those of the pigment itself. The effective volume and density are calculated from the final sediment volume fraction after correction (if practicable) by an appropriate packing factor. The mean flow unit diameter (or a size parameter) can then be estimated. The present method has been satisfactorily tested using formalin-fixed yeast cells as model flow units which can be sized readily by optical microscopy. Data for organic pigment dispersions compare well with their appearance under the optical microscope. Various uses of simplified versions of the present technique in studies of dispersibility and dispersion stability of organic pigments are described and exemplified using mainly copper phthalocyanine pigments in hydrocarbon solvents.     

Hindered settling of organic pigment dispersions in hydrocarbon liquids

A modified Steinour hindered settling method has been developed for the study of dispersed organic pigment species containing a large proportion of associated immobile liquid. These species are termed flow units with effective volumes and densities different from those of the pigment itself. The effective volume and density are calculated from the final sediment volume fraction after correction (if practicable) by an appropriate packing factor. The mean flow unit diameter (or a size parameter) can then be estimated. The present method has been satisfactorily tested using formalin-fixed yeast cells as model flow units which can be sized readily by optical microscopy. Data for organic pigment dispersions compare well with their appearance under the optical microscope. Various uses of simplified versions of the present technique in studies of dispersibility and dispersion stability of organic pigments are described and exemplified using mainly copper phthalocyanine pigments in hydrocarbon solvents.