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.     

Polymeric homogeneous composite membranes for separations in organic solvents

A new generation of organic solvent nanofiltration (NF) composite membranes was prepared combining a support layer with a selective layer made both from the same polymeric material (P84 copolyimide). These membranes, homogeneous in composition, but composite in structure, were defined as polymeric homogeneous composite (PHC) membranes. The composite membranes have the advantage over the asymmetric ones that each layer can be optimized independently. Moreover, the use of the same material for the preparation of both, the selective and the support layer, ensures a high affinity between the two layers and increases the long‐term stability of the composite membranes, reducing the possibility of delamination phenomena. In the design of the PHC membranes, a great attention was devoted to the support layer development. The effects of the composition of the casting solutions on the structure of porous P84 copolyimide membranes were investigated allowing to identify the conditions for the preparation of highly permeable, chemically, and mechanically stable P84 sponge like porous membranes. PHC membranes were prepared by coating and controlled solvent evaporation of a P84 solution on the optimized support crosslinked by reaction with a diamine (1,5‐diamino‐2‐methylpentane). Pure solvent permeation test and rejection experiments were carried out on the P84 supports and the corresponding PHC membranes in aggressive organic solvents like N‐methyl‐2‐pyrrolidone and N,N‐dimethyformamide, in which the original polymer was soluble. The PHC membrane resulted completely stable over long times (>96 h). © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Anhydrous organic dispersions of highly reduced chemically converted graphene

A straightforward, systematic approach to the reduction of graphene oxide (GO) that affords dispersions of chemically converted graphene (CCG) in anhydrous organic solvents with decreasing basal plane defects is reported. The extent of reduction can be controlled and optimized, resulting in highly reduced dispersible chemically converted graphene (hrCCG) having an O_1S/C_1S ratio of 0.06, which approaches that of graphite. The hrCCG dispersion in anhydrous dimethylformamide (DMF) was stable for several months at a concentration of 0.5–0.6 mg mL⁻¹. This process was found to be easily scalable and could be exploited for the large scale production of hrCCG in DMF and its dispersion in other anhydrous organic solvents. This study demonstrates that the stability of the graphene dispersion is critically dependent on the exfoliation process. The improved elimination of basal defects and the restoration of aromaticity, while maintaining dispersion stability on a large scale in an anhydrous organic solvent, greatly increase the potential of this material for a wide variety of applications.     

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).     

氧化石墨烯增强有机硅橡胶复合泡沫材料的性能

以甲基乙烯基硅橡胶（MVQ）为基质,以氧化石墨烯（GO）为增强剂和阻燃剂,制备了有机硅橡胶复合泡沫材料,考察了GO用量对复合泡沫材料力学性能及阻燃性能的影响。结果表明,随着GO用量的增加,有机硅橡胶复合泡沫材料的密度增大,拉伸性能和压缩性能提高,极限氧指数（LOI）增大,熔滴现象和发烟现象减弱。当GO用量为5份时,与纯MVQ相比,复合泡沫材料的拉伸强度提高了6.6倍,撕裂强度提高了4.7倍,压缩强度（50%形变）提高了12.3倍,LOI由22.3%提高至26.5%,且未发生熔滴和发烟现象,阻燃性能显著提高。     

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.     

Hollow tremella-like graphene sphere/SnO2 composite for high performance Li-ion battery anodes

A hollow tremella-like graphene sphere/tin dioxide (HTGS/SnO₂) composite was successfully prepared by simple emulsification and impregnation followed by calcination. In this material, tin dioxide adheres to the folds on the surface of the hollow tremella-like graphene spheres. Hollow tremella-like graphene spheres as the matrix of SnO₂ not only provide a space of volumetric expansion for the tin oxide particles, relieve the internal stress of the tin dioxide, but also effectively avoid aggregation of the tin dioxide and increase the electrical conductivity. As an anode electrode material for batteries, the initial discharge/charge capacities of HTGS/SnO₂ are 1762.4 mAh g^-1 and 1169.4 mAh g^-1, and the Coulomb efficiency is 96.9%. After 50 cycles, capacity remains 80.4% of reversible capacity. The excellent electrochemical stability is attributed to the extraordinary structure of HTGS/SnO₂. The hollow structure of graphene sphere allows simultaneous insertion of lithium ions from the inner and outer surfaces. Meanwhile, the tin dioxide particles are uniformly dispersed by the wrinkles on the surface of the graphene, thereby enlarging the space for the volume expansion of tin dioxide in order to avoid contact with the electrolyte.     

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.     

Effects of polymers and clay concentrations on the viscosities of organo-smectite dispersions under high pressure

The viscosities of organo-smectite dispersions in mineral oil with and without the addition of a high molecular weight copolymer of sodium acrylate and acrylamide, were measured at elevated pressures by using a falling-body type viscometer. The increase in viscosity of the organo-smectites as a function of clay concentration under pressure generally follows the Arrhenius equation. The viscosities of mineral oil and organo-smectites in the presence and absence of the polymer increase exponentially with pressure. At the lower concentrations of clay the increase in viscosity in these systems can be placed in the order: mineral oil < dimethyldioctadecylammonium (DMDO)-montmorillonite ∼ dimethylodioctadecylammonium (DMDO)-hectorite ∼ dimethyloctadecylbenzylammonium (DMOB)-montmorillonite < DMDO montmorillonite + polymer ∼ DMDO-hectorite + polymer < DMOB-montmorillonite + polymer.     

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.     

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.     

Influence of aqueous dispersions in place of organic solvents during the synthesis of shape memory polyurethanes on their structure and properties

In this work, the effect of synthesizing shape memory polyurethanes in aqueous dispersions instead of in organic solvents on the structure and properties of the obtained polymers was investigated. Shape memory polyurethanes based on polycaprolactone diol and isophorone diisocyanate were synthesized by two routes: (1) aqueous dispersion (PU/SM_WATER) and (2) dissolution in THF (PU/SM_THF). The samples were analyzed by infrared spectroscopy (FTIR), X‐ray diffraction (XRD), static light scattering (SLS), atomic force microscopy (AFM), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and mechanical tests. The aqueous dispersion method led to the production of polyurethanes with a higher degree of phase separation and a higher degree of crystallinity. The morphology of the obtained polyurethanes demonstrated that PU/SM_WATER displays a structure with better defined phase separated domains. The polyurethanes exhibited similar average molar masses, soft segment glass transitions (T_gs) and mechanical properties. The lower degrees of phase separation and crystallinity of the PU/SM_THF led to lower values for the shape memory properties (shape recovery ratio (R_r)). The observed changes in the structure of the polyurethanes due to the replacement of organic solvent by an aqueous dispersion during their syntheses confirmed the preparation of shape memory polyurethanes with enhanced shape memory properties. POLYM. ENG. SCI., 57:432–440, 2017. © 2016 Society of Plastics Engineers     

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.