新疆褐煤疏水改性提高其成浆性能

针对新疆褐煤具有较高内水的问题,制备了阴离子AKD改性剂和非离子AKD改性剂,对褐煤颗粒进行疏水改性。研究了改性前后煤粒表面化学成分、孔隙分布、亲疏水性和Zeta电位等煤粒表面特性,并结合NSF分散剂在改性前后煤粒表面吸附量大小,探讨了改性前后褐煤水煤浆的成浆性、流变性和稳定性。结果表明,改性后煤粒孔隙结构降低,煤粒表面碳的相对含量增加,氧的相对含量降低,煤水界面接触角增加,煤粒疏水性能增强。NSF分散剂在改性煤表面吸附量增加,煤粒表面负电性增强。由阴离子AKD改性煤、非离子AKD改性煤制备的水煤浆最大成浆质量分数从原煤56.6%分别增加至61.0%、62.5%,浆体析水率从原煤13.97%分别降低至7.45%、7.89%,同时改性后煤粒制备的浆体均表现出剪切变稀的假塑性流体。因此,改性煤粒更容易制备高浓度、低黏度、高稳定性且易于储存和运输的水煤浆。     

Spontaneous formation of super water-repellent fractal surfaces in mixed wax systems

Alkylketene dimers (AKDs) and triglyceride waxes form fractal surfaces spontaneously and show super water-repellent property. Spontaneous formation of fractal structures on their surfaces takes place when the meta-stable crystalline phase of the waxes transforms to the thermodynamically stable form of crystal. The triglyceride waxes form the meta-stable alpha-phase in whole specimen when solidified from their melt. In the case of AKD, on the other hand, only a small portion of the specimen solidifies in the meta-stable form of crystal. The surface of the AKD, however, becomes fractal in the whole part. We have, thus, examined the fractal structure formation in the mixed wax systems in which one wax forms fractal surfaces and the other one does not. In the stearic acid/tristearin mixed system as a typical one, the super water-repellent fractal surfaces form in the higher composition region of tristearin than that of the eutectic point in their mixture.     

Nitrogen Sorption Studies of Silica Particles Obtained in Emulsion and Microemulsion Media

The internal surface structures of silica aerogel particles synthesized using different catalysts in emulsion and microemulsion media have been investigated by means of N(2) adsorption and desorption isotherms. Surface fractal dimensions have been computed using different methods: Frankel-Halsey-Hill plots of the adsorption isotherms, the thermodynamic fractal isotherm equation, and a modification of the thermodynamic fractal isotherm equation. Silica aerogels synthesized in emulsion media with an acidic catalyst have a high specific surface area without micropores and show two separate ranges of scales where the surface fractal dimensions are different and constant. Silica aerogels synthesized in emulsion media with a basic catalyst have a moderate specific surface area with a high percentage of micropores and show constant surface fractal dimensions over a larger range. Silica aerogels synthesized in microemulsion media with a basic catalyst have a low specific surface area with a moderate percentage of micropores and show a moderate range of scales over which the surface fractal dimension is constant. Analyses by both the thermodynamic and modified thermodynamic methods give similar ranges of the surface fractal dimensions of the silica particles. Copyright 2000 Academic Press.     

Effect of surfactants on wetting of super-hydrophobic surfaces

The effect of surfactants on wetting behavior of super-hydrophobic surfaces was investigated. Super-hydrophobic surfaces were prepared of alkylketene dimer (AKD) by casting the AKD melt in a specially designed mold. Time-dependent studies were carried out, using the axisymmetric drop shape analysis method for contact angle measurement of pure water on AKD surfaces. The results show that both advancing and receding contact angles of water on the AKD surfaces increase over time ( approximately 3 days) and reach the values of about 164 and 147 degrees , respectively. The increase of contact angles is due to the development of a prickly structure on the surface (verified by scanning electron microscopy), which is responsible for its super-hydrophobicity. Aqueous solutions of sodium acetate, sodium dodecyl sulfate, hexadecyltrimethylammonium bromide, and n-decanoyl-n-methylglucamine were used to investigate the wetting of AKD surfaces. Advancing and receding contact angles for various concentrations of different surfactant solutions were measured. The contact angle results were compared to those of a number of pure liquids with surface tensions similar to those of surfactant solutions. It was found that although the surface tensions of pure liquids and surfactant solutions at high concentrations are similar, the contact angles are very different. Furthermore, the usual behavior of super-hydrophobic surfaces that turn super-hydrophilic when the intrinsic contact angle of liquid on a smooth surface (of identical material) is below 90 degrees was not observed in the presence of surfactants. The difference in the results for pure liquids and surfactant solutions is explained using an adsorption hypothesis.     

Characterization of fractal particles using acoustics, electroacoustics, light scattering, image analysis, and conductivity

Fractals are aggregates of primary particles organized with a certain symmetry defined essentially by one parameter-a fractal dimension. We have developed a model for the interpretation of acoustic data with respect to particle structure in aggregated fractal particles. We apply this model to the characterization of various properties of a fumed silica, being but one example of a fractal structure. Importantly, our model assumes that there is no liquid flow within the aggregates (no advection). For fractal dimensions of less than 2.5, we find that the size and density of aggregates, computed from the measured acoustic attenuation spectra, are quite independent of the assumed fractal dimension. This aggregate size agrees well with light-scattering measurements. We applied this model to the interpretation of electroacoustic data as well. A combination of electroacoustic and conductivity measurements yields sufficient data for comparing the fractal model of the particle organization with a simple model of the separate primary particles. Conductivity measurements provide information on particle surface conductivity reflected in terms of the Dukhin number (Du). Supporting information for the zeta potential and Du can also be provided by electroacoustic measurements assuming thin double-layer theory. In comparing values of Du from these two measurements, we find that the model of separate solid particles provides much more consistent results than a fractal model with zero advection. To explain this, we first need to explain an apparent contradiction in the acoustic and electroacoustic data for porous particles. Although not important for interpreting acoustic data, advection within the aggregate does turn out to be essential for interpreting electrokinetic and electroacoustic phenomena in dispersions of porous particles.     

Spontaneous formation of fractal structures on triglyceride surfaces with reference to their super water-repellent properties

Alkylketene dimer (AKD), a kind of wax, has been known to form fractal surfaces spontaneously and show super water-repellency. Such formation of water-repellent and fractal surfaces was also found in this work for triglycerides. Since the crystal phase transitions of these waxes were well studied, we studied the formation of their fractal surfaces through contact angle measurements, differential scanning calorimetry (DSC), and X-ray diffraction (XRD). From time-dependent contact angle measurements, it was found that the formation of super water-repellent surfaces with fractal structures occurred spontaneously also on the triglyceride surfaces at different temperatures. The freshly solidified triglyceride surfaces were almost transparent, and their initial contact angles of water were close to 110 degrees. The surfaces then became rough and clouded after being incubated for a certain time at a specified temperature. The super water-repellent surfaces were quite rough and showed fractal structures with the dimension of ca. 2.2 calculated from the scanning electron microscopic (SEM) images by the box-counting method. The phase transformation from a metastable state to a stable cystalline one after the solidification from the melt of triglycerides was clearly observed by DSC and XRD measurements. The fractal crystalline structures and the super water-repellency resulted from this phase transformation and the crystal growth. Ensuring the initial sample solidified into the metastable state and curing the surface at an appropriate temperature are key factors for the successful preparation of fractal triglyceride surfaces by the solidification method.     

A stable AKD-in-water emulsion: Stabilized by MSG-modified laponite nanoparticle

Alkyl ketene dimmer (AKD) is widely used in papermaking industry, which is applied in form of o/w emulsion to increase paper water-resistance. In this paper, AKD-in-water emulsions were prepared by monosodium glutamate (MSG)-modified laponite. The aggregation, surface charge, and hydrophobicity of the laponite particles in aqueous dispersion were changed by the MSG and the properties of the as-prepared emulsions were varied correspondingly. When the MSG concentration is 2?mmol/g, AKD emulsion with small droplet size, high storage stability, and high sizing efficiency is obtained. The morphology, droplet diameter and distribution, storage stability and sizing efficiency of the AKD-in-water emulsion were investigated.     

Structure of peptides on metal oxide surfaces probed by NMR

Peptides that bind inorganic surfaces and template the formation of nanometer-sized inorganic particles are of great interest for the self- or directed assembly of nanomaterials for sensors and diagnostic applications. These surface-recognizing peptides can be identified from combinatorial phage-display peptide libraries, but little experimental information is available for understanding the relationship between the peptide sequence, structure at the nanoparticle surface, and function. We have developed NMR methods to determine the structures of peptides bound to inorganic nanoparticles and report on the structure of three peptides bound to silica and titania surfaces. Samples were prepared under conditions leading to rapid peptide exchange at the surface such that solution-based nuclear Overhauser experiments can be used to determine the three-dimensional structure of the bound peptide. The binding motif is defined by a compact "C"-shaped structure for the first six amino acids in the 12-mer. The orientation of the peptide on the nanoparticle surface was determined by magnetization transfer from the nanoparticle surface to the nearby peptide protons. These methods can be applied to a wide variety of abiotic interfaces to provide an insight into the relationship between the primary sequence of peptides and their functionality at the interface.     

Preparation and application of hollow molecularly imprinted polymers with a super‐high selectivity to the template protein

Protein‐imprinted polymers with hollow cores that have a super‐high imprinting factor were prepared by etching the core of the surface‐imprinted polymers that used silica particles as the support. Lysozyme as template was modified onto the surface of silica particles by a covalent method, and after polymerization and the removal of template molecules, channels through the polymer layer were formed, which allowed a single‐protein molecule to come into the hollow core and attach to the binding sites inside the polymer layer. The adsorption experiments demonstrated that the hollow imprinted polymers had an extremely high binding capacity and selectivity, and thus a super‐high imprinting factor was obtained. The as‐prepared imprinted polymers were used to separate the template lysozyme from egg white successfully, indicating its high selectivity and potential application in the field of separation of protein from real samples.     

Nanostructured films from phthalocyanine and carbon nanotubes: surface morphology and electrical characterization

We report on the investigation of the surface morphology and DC conductivity of nanostructured layer-by-layer (LbL) films from nickel tetrasulfonated phthalocyanine (NiTsPc) alternated with either multi-walled carbon nanotubes (MWNTs/NiTsPc) or multi-walled carbon nanotubes dispersed in chitosan (MWNTs+Ch/NiTsPc). We have explored the surface morphology of the films by using fractal concepts and dynamic scale laws. The MWNTs/NiTsPc LbL films were found to have a fractal dimension of ca. 2, indicating a quasi Euclidean surface. MWNTs+Ch/NiTsPc LbL films are described by the Lai-Das Sarma-Villain (LDV) model, which predicts the deposition of particles and their subsequent relaxation. An increase in the wetting contact angle of MWNTs+Ch/NiTsPc LbL films was observed, as compared with MWNTs/NiTsPc LbL films, which presented an increase in the fractal dimension of the first system. Room temperature conductivities were found be ca. 0.45 S/cm for MWNTs/NiTsPc and 1.35 S/cm for MWNTs+Ch/NiTsPc.     

A bidimensional simulation of particle-cluster aggregation with variable active sites particles

 In this work a simple program has been developed which simulates the process of particle– cluster aggregation limited by diffusion. All the simulation have been carried out using 2d square lattices with square “particles” having a variable number of active inter-action sites (from 3 to 8) for each particle in order to analyze the effect of such limitation on the fractal dimension of the aggregates. The fractal dimension of such aggregates was calculated by the so-called “box counting” method. It has been shown that there is no change in the value of the fractal dimension (1.70) as the active site number is increased. Instead it appears that there is an average number of active sites of about 2.3 for all the structures no matter how many active interaction sites the particles have. This appears as an interesting result in connection with the aggregation of particles such as renneted casein micelles, which could present differences in the surface density of active sites. Received: 11 February 1997 Accepted: 8 January 1998     

Dry,hydrophobic microfibrillated cellulose powder obtained in a simple procedure using alkyl ketene dimer

In order to produce dry and hydrophobic microfibrillated cellulose (MFC) in a simple procedure, its modification with alkyl ketene dimer (AKD) was performed. For this purpose, MFC was solvent-exchanged to ethyl acetate and mixed with AKD dissolved in the same solvent. Curing at 130 °C for 20 h under the catalysis of 1-methylimidazole yielded a dry powder. Scanning electron microscopy of the powder indicated loss in nanofibrillar structure due to aggregation, but discrete microfibrillar structures were still present. Water contact angle measurements of films produced from modified and unmodified MFC showed high hydrophobicity after AKD treatment, which persisted even after extraction with THF for 8 h. The hydrophobized MFC was characterized by Fourier transform infrared spectroscopy, nuclear magnetic resonance and X-ray analysis. In summary, strong indications for the presence of AKD on the surface of MFC before and after extraction with solvent were found, but only a very small amount of covalent β-ketoester linkages between the modification agent and cellulose was revealed.     

铅铬黄粒子的微胶囊化及其表面形貌的表征

研究了铅铬黄粒子的微胶囊化及其机理；探讨了对粒子表面形貌的量化表征方法．结果表明，在油包水（Ｗ／Ｏ）乳液中对铅铬黄粒子进行无机微胶囊化是一提高其耐酸、碱性的有效方法．颜料粒子的表面形貌可用其表面分形维数（Ｄ）量化表征．     

Chemical composition of “AKD vapour” and its implication to AKD vapour sizing

Alkyl ketene dimer (AKD) sizing of paper involves the redistribution of the wax over the fibre surface upon heating. The two major mechanisms widely studied so far are the spreading of an autophobic precursor of molten AKD and AKD vapour transport and re-deposition on the fibre surface. All previous work assumed that the transport of AKD vapour could be expressed by the change of water contact angle with substrates that were exposed to the vapour. Information regarding the chemical composition of the vapour phase above the AKD wax has not been found in the literature. In this work, a simple method for analysing the chemical composition of the vapour is established. Our preliminary results indicated that the chemical composition of AKD vapour in the temperature range of 75–80 °C is dominantly fatty acids. This suggests that the sizing effect by actual AKD molecules via the vapour deposition mechanism is likely to be insignificant in this temperature range. This also implies that fatty acids play a positive role in AKD sizing. The chemical stability of AKD in this temperature range is also studied.     

Extraction of tributyltin by magnetic molecularly imprinted polymers

We have prepared core-shell magnetic molecularly imprinted polymer nanoparticles for recognition and extraction of tributyl tin (TBT). The use of particles strongly improves the imprinting effect and leads to fast adsorption kinetics and high adsorption capacities. The functional monomer acrylamide was grafted to the surface of Fe₃O₄ nanospheres in two steps, and MIP layers were then formed on the surface by creating a MIP layer on the surface consisting of poly(ethyleneglycol dimethacrylate) with a TBT template. The particles were characterized in terms of morphological, magnetic, adsorption, and recognition properties. We then have developed a method for the extraction of TBT from spiked mussel (Mytilidae), and its determination by liquid chromatography-tandem mass spectrometry. The method has a limit of detection of 1.0 ng?g^?1 (n?=?5) of TBT, with a linear response between 5.0 and 1,000 ng?g^?1. The proposed method was successfully applied to the determination of trace TBT in marine food samples with recoveries in the range of 78.3–95.6 %.

Poly(phenylsilsesquioxane)s: Structural and morphological characterization

Poly(phenylsilsesquioxane) (PPSQ) polymers that were obtained from different synthetic routes were comparatively studied. The polymers were characterized by infrared and solid‐state ²⁹Si NMR spectroscopies. According to the results of X‐ray diffraction and thermogravimetric analyses, the materials richest in silanol showed a less organized network and lower weight loss temperature. The morphology of the products was influenced by the preparation conditions. PPSQ, with a morphology rich in spherical particles, was achieved with an n‐hexadecyltrimethylammonium bromide template in the reaction medium, whereas the morphology of this polymer obtained in the absence of the template was featureless. Small‐angle X‐ray scattering analyses revealed that the PPSQ samples showed a predominance of surface‐fractal behavior. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1580–1589, 2000     

Numerical computations of molecular reactions in associated systems caused by the formation of fractal structures

The interaction between particles in a system containing fractal clusters has been computationally simulated. The fractal structure of the system has been demonstrated to determine the kinetic characteristics of particle interaction. If a system in an N-dimensional space (N = 2, 3, 4) contains fractal clusters with the fractal dimension D > N-1, the rate of interaction of a free particle with particles belonging to clusters depends on their concentration according to the power law. The exponent gamma of this power law formally corresponds to the kinetic order of the reaction with respect to the concentration of particles belonging to the clusters. Its value is determined by the free surface of the clusters and depends on its fractal dimension D. The results of simulation qualitatively agree with the data on high, non-integral orders of many liquid phase molecular reactions characterized by self-organization of the medium via weak intermolecular interactions, such as hydrogen bonds.     

Mechanical properties and structure of particle coated interfaces: influence of particle size and bidisperse 2D suspensions

We report surface pressure-area (Pi-A) isotherms of bidisperse mixtures of anionic polystyrene latex particles at a water/n-decane interface as well as optical photographs of the interface for various compressions and mixture ratios. In the case of mixtures of 3 and 5 mum particles, we observe crystalline layers at high or low concentration ratios, where the "impurity" particles concentrate at the grain boundaries of the crystalline structure. At intermediate ratios, the layers become highly disordered. However, in both cases, we show that the shape of the isotherms remains unchanged. In the case of the mixtures of 9 mum particles with either 3 or 5 mum particles, the smaller particles aggregate around the larger particles through capillary interaction resulting in the formation of large fractal aggregates. At high compression, these layers contain holes that seem very compressible. As a result, the surface pressure isotherms show a smaller surface pressure jump than for other mixtures.