Controlling the optimum surfactants concentrations for dispersing carbon nanofibers in aqueous solution

As a new nano-scale functional material, it is necessary to achieve a uniform distribution in the composites for gaining the CNFs’ excellent reinforcing effect. In this paper, CNFs were purified by the method of high temperature annealing treatment. Six surfactants, methylcellulose (MC), hydroxypropyl methylcellulose (HPMC), sodium dodecyl sulfate (SDS), dodecylamine (DDA), N, N-dimethyl formamide (DMF) and cetyltrimethyl ammonium bromide (CTAB) were used individually and combinatorially in a certain concentration to disperse the CNFs in aqueous solution. To achieve a good dispersion of the CNFs, a method utilizing ultrasonic processing was employed. The CNFs treated by the method of high temperature annealing treatment were characterized by differential thermal analysis (DTA) and thermogravimetry analysis (TGA), and the ultrasonication-driven dispersion of CNFs in aqueous solutions were monitored by UVvis spectroscopy and transmission electron microscopy (TEM). The experiments reveal that the method of high temperature annealing treatment purified the CNFs and the maximum achievable dispersion of CNFs corresponds to the maximum UV absorbance of the solution. All results show that the surfactants mixture of MC and SDS in a certain concentration of 0.4 and 2.0 g/L has the maximum dispersion effect on CNFs in aqueous solution, the optimum concentration ratio of MC, SDS, and CNFs was 2: 10: 1.     

聚羧酸系高效减水剂合成工艺的优化研究

以甲基烯丙基聚氧乙烯醚(HPEG)和丙烯酸(AA)为单体,以过氧化氢-抗坏血酸(H2 O2-Vc)为氧化还原引发体系,以巯基丙酸(MPA)为链转移剂,共聚合成了HPEGAA型聚羧酸减水剂.研究了合成温度、酸醚比及引发剂用量对聚羧酸减水剂分散性能的影响.结果表明,聚羧酸减水剂的最佳合成工艺为:n(AA):n(HPEG)=...     

Dispergation and modification of multi-walled carbon nanotubes in aqueous solution

Multi-walled carbon nanotubes (MWCNTs) are widely applied in development of composite materials. However, their properties are directly influenced by the degree of uniformity of dispersion of MWCNTs in the material’s matrix. In this paper, the dispersing of raw MWCNTs (R-MWCNTs) and decorated MWCNTs (D-MWCNTs) was studied in aqueous solution. The D-MWCNTs were obtained by chemical modification method by treatment of initial MWCNTs with the mixture of concentrated nitric and sulfuric acids (3: 1 vol/vol). To achieve a good dispersion of the MWCNTs, a method utilizing ultrasonic processing and surfactant (polyvinylpyrrolidone, PVP) was employed. MWCNTs were characterized by Fourier transform infrared spectroscopy (FT–IR) and X-ray diffraction (XRD). The prepared MWCNTs suspensions were investigated by UV spectroscopy, zeta potential measurements, surface tension and transmission electron microscopy (TEM). The D-MWCNTs have better dispersibility in aqueous solution; this attributed to the functional groups formed on their surface during chemical modification. The PVP surfactant in a certain concentration of 0.6 g/L has the maximum dispersing effect on MWCNTs in aqueous solution, the optimum concentration ratio of PVP and MWCNTs was 3: 1.     

Zeta potential time dependence reveals the swelling dynamics of wood cellulose nanofibrils

In this paper, we present the swelling dynamics of individual wood cellulose nanofibrils (CNFs) following solvent substitution into various organic solvents and drying, by employing the time dependence of the zeta potential (ζ). We succeeded in smoothly redispersing the coaggregating CNFs dried in solvents, including acetone, acetonitrile, DMSO, ethanol, and t-butanol into water. ζ-t plots of the redispersed CNFs measured in a 1 mM KCl solution indicated different values of Δζ (volume fraction of hydration capacity), corresponding to the dielectric constant of the substituted solvents. Differential scanning calorimetry confirmed that the redispersed CNFs swell to different degrees, corresponding to Δζ. This swelling behavior is characterized by expansion of hemicelluloses, the amorphous polysaccharides located on the CNF surface, with a different degree of aggregation during drying. The specific swelling ratio, radius, and diameter of the CNFs in water were calculated using the values of ζ(0) and ζ(∞) by introducing surface chemical analysis. The calculated diameters of the CNFs at t = 0 coincided well with the median diameters measured directly by transmission electron microscope. Swellability of hemicelluloses exponentially increased with the decrease in dielectric constant of solvent during drying. The analysis method combining zeta potential time dependence and a surface chemical approach proved useful for specifically evaluating the swelling dynamics of polymers on a bulk surface.     

聚羧酸盐和聚萘磺酸盐分散剂在高浓度水悬浮剂中的应用

研究了聚羧酸盐分散剂(SD-819)和聚萘磺酸盐分散剂(SD-661)在水溶液中的表面性能;同时考察了分散剂添加量对500 g/L扑草净水悬浮剂(SC)中的吸附、Zeta电势和流变性能等的影响.结果表明,与分散剂SD-661相比,分散剂SD-819水溶液中的表面张力(γcmc)小,临界胶束浓度(cmc)和胶束生成自由能(ΔGmic)低,吸附量大,制备出的扑草净SC黏度低,流动性好,触变性优良.结果表明,聚羧酸盐分散剂更适用于高浓度扑草净SC的制备.     

Preparation,application and water reducing mechanism of a novel fluorescent superplasticizer with improved flow retaining ability and clay tolerance

Abstract

Novel fluorescent polycarboxylate superplasticizer modified by anhydride naphthalene groups was prepared, and characterized by ^1?H NMR and FTIR. Fluidity behaviors of cement suspensions mixed with the polycarboxylate indicated that the superplasticizer not only exhibited good fluidity maintaining properties but also demonstrated stable performance in the coexistence of clay. The addition of quaternary ammonium salt polymer can inhibit the water absorption and expansion of clay. Adsorption amounts, adsorption layer thickness and zeta potential were determined to elucidate the water reducing mechanism. The adsorbed layer thickness was linked to the steric hindrance, deciding the dispersing ability and dispersing retention ability.     

Lattice Poisson-Boltzmann simulations of electro-osmotic flows in microchannels

This paper presents the numerical results of electro-osmotic flows in micro- and nanofluidics using a lattice Poisson-Boltzmann method (LPBM) which combines a potential evolution method on discrete lattices to solve the nonlinear Poisson equation (lattice Poisson method) with a density evolution method on discrete lattices to solve the Boltzmann-BGK equation (lattice Boltzmann method). In an electrically driven osmotic flow field, the flow velocity increases with both the external electrical field strength and the surface zeta potential for flows in a homogeneous channel. However, for a given electrical field strength and zeta potential, electrically driven flows have an optimal ionic concentration and an optimum width that maximize the flow velocity. For pressure-driven flows, the electro-viscosity effect increases with the surface zeta potential, but has an ionic concentration that yields the largest electro-viscosity effect. The zeta potential arrangement has little effect on the electro-viscosity for heterogeneous channels. For flows driven by both an electrical force and a pressure gradient, various zeta potential arrangements were considered for maximize the mixing enhancement with a less energy dissipation.     

聚羧酸类超塑化剂分子结构对石膏分散性能的影响

研究了甲基丙烯酸-甲氧基聚乙二醇甲基丙烯酸酯(MAA-MPEGMA)、甲基丙烯酸-烯丙基聚乙二醇醚(MAA-APEG)、丙烯酸-烯丙基聚乙二醇醚(AA-APEG)三类梳形聚羧酸类接枝共聚物以及丙烯酸均聚物(PAA)对石膏粉体分散性能和凝结时间的影响.聚合物侧链长度越短、分子量越小、电荷密度越高对石膏的分散性能越好,同时...     

Physicochemical properties of structured phosphatidylcholine in drug carrier lipid emulsions for drug delivery systems

Drug carrier emulsions were prepared with structured phosphatidylcholine (PC-LM) which has both a long hydrocarbon chain and a medium hydrocarbon chain, and the characteristics of PC-LM as an emulsifier were investigated by measuring the creaming ratio, the surface tension of the emulsion system, and the mean particle size and zeta potential of the oil droplets in emulsions. The emulsion prepared with PC-LM as an emulsifier kept the condition and the ratio of separation was lower than those with purified egg yolk lecithin (PEL). The mean particle size of the emulsion prepared with PC-LM was smaller than that with PEL when using only sonication, approximately 250 nm. When using a high-pressure homogenizer after sonication, the mean emulsion size with PC-LM was also smaller than with PEL, approximately 150 nm. The surface tension of the various emulsions and the zeta potential of the emulsion droplets were measured to investigate the stability of the systems. In emulsions with PC-LM or PEL, the surface tension as an index of stability increased as the pressure of the homogenizer increased. Moreover, the zeta potential of the emulsion droplets prepared with PC-LM also increased with an increase in pressure of the homogenizer. As a result, it was found that the drug carrier emulsion prepared with PC-LM had significant advantages in terms of stability and mean diameter. We considered it could be used for the preparations of nanoparticle dispersion systems in drug delivery systems.     

Influence of polyvinyl pyrrolidone on the dispersion of multi-walled carbon nanotubes in aqueous solution

The sonication-driven suspensions of multi-walled carbon nanotubes (MWNTs) were prepared using the polyvinyl pyrrolidone as a dispersant. UV-visible absorbency, surface tension, zeta potential, adsorption isotherm and transmission electron microscopy, were used to characterize the homogeneity and stability of MWNTs suspensions with different concentrations of polyvinyl pyrrolidone. All results show that the optimum concentration of polyvinyl pyrrolidone in suspension is 0.5 g/L.     

USING ELECTROPHORESIS TO DETERMINE ZETA POTENTIAL OF MICELLES AND CRITICAL MICELLE CONCENTRATION

A heterodyne laser Doppler electrophoresis method for measuring the zeta potential of a surfactant micelle has been developed. Details of the method and results obtained will be presented in this paper. In comparison with the tracer electrophoresis method used in determining the zeta potential of a surfactant micelle, this method is much time saving and less laborious. The zeta potential values of one anionic and three cationic surfactant micelles have been determined by using this method. From the zeta potential versus concentration curve, one can determine the micellar dissociation concentration and the critical mi cellar concentration of a surfactant. The values obtained agree quite well with the surface tension measurement. The surfactant systems were studied in the presence and absence of NaCI. The zeta potential appears to decrease with the increase of NaCI concentration.     

Adsorbing behavior of polycarboxylate superplasticizer in the presence of the ester group in side chain

The effect of the ester group in side chain on adsorbing behavior and dispersion of polycarboxylate superplasticizer (PC) was studied by comparing the performance of two types of PC. The fluidity of cement paste was tested to discuss the dispersing ability and dispersing retention ability of PC. The total organic carbon analyzer was used to measure the adsorption amount, and the adsorption layer was obtained by x-ray photoelectron spectroscopy. Fourier-transform infrared spectroscopy, nuclear magnetic resonance, and pH value were used to verify the stability of the ester group, and the electrokinetic properties of cement particle were confirmed using the zeta potential measurement. The results show that the ester group in side chain reduces the initial dispersing ability while it increases the dispersing retention ability. The dispersing retention ability depends on the increase of adsorption amount and adsorption layer in 5–60 minutes, and the greater increase leads to the better dispersing retention ability. The ester group can be decomposed to release carboxyl group to enhance the adsorbing ability of PC under the condition of cement hydration, which is the main reason for the greater increase of adsorption amount and adsorption layer and the improvement in dispersing retention ability. It suggests that grafting the ester group is a good way to enhance the dispersing retention ability.     

Wettability interpretation of oxygen plasma modified poly(methyl methacrylate)

Poly(methyl methacrylate) (PMMA) has been modified via a dc pulsed oxygen plasma for different treatment times. The modified surfaces were characterized by X-ray photoelectron spectroscopy (XPS), optical profilometer, zeta potential, and advancing contact angle measurements. The measured advancing contact angles of water decreased considerably as a function of discharge. Several oxygen-based functionalities (carbonyl, carboxyl, carbonate, etc.) were detected by XPS, while zeta potential measurements confirmed an increase in negative charge for the treated PMMA surface. Evaluating the correlation between the concentration of polar chemical species and zeta potential, we found that increase in surface hydrophilicity results from the coeffect due to incorporation of oxygen functional groups and creation of charge states. The electrical double layer (EDL) effect was also considered in contact angle interpretation by introducing an additional surface tension term into Young's equation. We also found that EDL contribution to the solid-liquid interfacial tension is negligible and can be safely ignored for the systems considered here.     

Research on synthesis and action mechanism of polycarboxylate superplasticizer

The relationship between the structure and performance of polycarboxylate superplasticizer was analyzed. The respective functions of the structure units of the main and branched chains were discussed. The progress of synthesis and molecular structure design and synthesis of polycarboxylate superplasticizer were reviewed according to the difference in the structure unit of the main chain. Results indicated that their performance is related to the structure unit of the main and branched chains, as well as the position and species of functional groups. The polycarboxylate superplasticizer, which had suitable graft and block polymers of polyethylene glycol or polyoxyethylene, and a suitable sulfonic group, had small slump loss besides high water-reducing performance. On the other hand, the hydroxyl group at the end of the chain causes gelation easily. On the basis of the items mentioned above, as well as the source and cost of raw materials, esterification of polyethylene glycol and acrylic acid were first adopted using para-toluene sulfonic acid as catalyst, then polymerized with sodium sulfonate methacrylate. A certain amount of acrylic was added in order to regulate both the polymerization degree of the main chain and the ratio of carboxyl and sulfonic groups in the branched chain. As a result, the high performance superplasticizer has been synthesized (was obtained). The divergence of the cement plasma is about 200 mm when the addition amount of superplasticizer is 0.16%–0.20% of cement weight, and the ratio of the water and cement is 0.29. Translated from Journal of Wuhan Uniwersity of Technology, 2006, 28(9): 18–20 [译自: 武汉理工大学学报]     

Effects of Sequence Structure of Polycarboxylate Superplasticizers on the Dispersion Behavior of Cement Paste

Different AA-OEGMA copolymers with random and block distributions were synthesized using free radical polymerization and reversible addition-fragmentation chain transfer polymerization, respectively. Studies on the dispersion ability, adsorption isotherm, adsorption conformation, and zeta potential revealed that the random and block architecture behaved differently. Sequence structure of polycarboxylate polymers (PCPs) had a significant influence on its performance. Both monomer ratio and sequence structure had influences on the dispersion of cement paste. Compared with random PCPs, PCPs with block distribution adsorbed faster on cement particle surfaces because of the higher density of exposed carboxylic groups. For random PCPs, the adsorption was a thermodynamic spontaneous process and driven by entropy, while it was driven by Gibbs free energy for block PCPs. Besides, the hydrodynamic radius of random PCPs in solution was larger than the block PCPs. However, the adsorbed layer thickness of random PCPs was close to that of block PCPs. Furthermore, the zeta potential illustrated that the PCPs with block distribution may adopt a more extended conformation compared with random PCPs. All these findings found from the differences between random PCPs and block PCPs will help the researchers to explore high-performance PCPs.     

Organization of amphiphiles: XII. Evidence in favor of formation of hydrophobic complexes in aqueous solution

The effects of nonionic surfactants OP-10 and OP-30 (polyoxyethylated octyl phenols with 10 and 30 oxyethylene groups, respectively) in surfactant mixtures with ionic surfactants hexadecyltrimethylammonium bromide (CTAB) and sodium dodecyl sulphate (SDS) have been investigated by a conductometric method in conjunction with fluorescence, surface tension, zeta potential, and DLS measurements. The interactions are found to be antagonistic in nature for each of the systems; i.e., micellization of CTAB as well as SDS is hindered on addition of the nonionic surfactants. The antagonism is found to be more prominent in the presence of OP-10 compared to that of OP-30. Two types of mechanistic paths, path A operating below the critical micellar concentration and path B operating beyond the critical micellar concentration of nonionic surfactants, have been suggested. In path A, the retardation in micellization has been attributed to a decrease in monomeric concentration of the ionic surfactants from solution as a result of the formation of a hydrophobic complex between nonionic and ionic surfactants. In path B, the decrease in monomer concentration is due to the solubilization of the ionic surfactant in micelles of the nonionic surfactants in a 1:1 stoichiometric ratio. A theoretical treatment to the interaction in each ionic-nonionic pair yields a positive value of the interaction parameter supporting the concept of antagonism. The formation of the hydrophobic complex is supported by fluorescence and surface tension measurements. A schematic representation of the stabilization of these hydrophobic complexes has been suggested. The association of ionic surfactants by nonionic micelles is suggested by zeta potential and DLS studies.     

Non-aqueous dispersion properties of pure barium titanate for tape casting

The dispersion properties of concentrated (25.0 and 50.0 vol.%) dispersions of high purity barium titanate powder dispersed in a methyl ethyl ketone (MEK) -ethanol solvent of moderate dielectric constant were studied in an effort to improve the uniformity of tape cast and sintered bodies. An amphoteric phosphate ester surfactant was found to be an effective dispersant. The dispersion properties of the phosphate ester were subsequently investigated by rheological, adsorption, conductivity, and electrophoretic mobility methods in order to evaluate a dispersion mechanism.Optimum dispersion occurred at an azeotrope solution of MEK and ethanol. The barium titanate particles dispersed in dry solvents exhibited a greater degree of dispersion than particles dispersed in hydrated solvents. The adsorption isotherm for the adsorption of the phosphate ester onto barium titanate particle surfaces using dry solvents exhibited a well-defined plateau corresponding to monolayer surface coverage. The plateau was less well defined for particles dispersed in hydrated solvents. Polymer coverage remained essentially constant with varying solvent composition. Optimum dispersion and maximum zeta potential occurred at a concentration of phosphate ester which corresponded to initial monolayer coverage. A maximum in the zeta potential also occurred at the azeotrope solution of MEK-ethanol and again coincided with optimum dispersion.Conductivity data indicate a dynamic adsorption-desorption dissociation mechanism for the ionic phosphate ester at the solid/liquid interface. The adsorption and conductivity data indicate the mechanism of dispersion stability is a combination of electrostatic and steric phenomena.     

Microcapsules with compact wall from hydrocarbon/fluorocarbon composite surfactants for electrophoretic display

The components and their concentration ratio of surfactant mixture in aqueous solution of gelatin and sodium carboxymethylcellulose (NaCMC) are very important during the preparation of stable microcapsules for electrophoretic display.In this work,hydrocarbon/fluorocarbon composite surfactant was introduced for the first time into the capsule wall to improve the chemical resistance and barrier property of the microcapsules.By investigating surface tension and zeta potential of NaCMC with the mixture of sodiu...     

Topochemistry of cellulose nanofibers resulting from molecular and polymer grafting

The aim of this study was to synthesize hydrophobic cellulose nanofibers (CNFs) using different chemical treatments including polymer and molecular grafting. For polymer grafting, immobilizing poly (butyl acrylate) (PBA) and poly (methyl methacrylate) (PMMA) on CNFs were implemented by the free radical method. Also, acetyl groups were introduced directly onto the CNFs surface by acetic anhydride for molecular grafting. The gravimetric and X-ray photoelectron spectroscopy analysis showed the high grafting density of PMMA on the surface of CNFs. AFM results revealed that molecular grafting created non-uniformity on the CNFs surface, as compared to polymer brushes. In addition, thermodynamic work of adhesion and work of cohesion for the modified CNFs were reduced in water and diiodomethane solvents. Dispersion factor was studied to indicate the dispersibility of CNFs in polar and non-polar media. Dispersion energy was reduced after modification as a result of decreasing interfacial tension and the dispersibility of modified CNFs was improved in diiodomethane.     

Synthesis of Mg–Al–Fe–NO3 layered double hydroxides via a mechano-hydrothermal route

Mg–Al–Fe–NO₃ layered double hydroxides (LDHs) with a constant Mg²⁺/(Al³⁺ + Fe³⁺) molar ratio but varying Al³⁺/Fe³⁺ molar ratios were successfully synthesized by a mechano-hydrothermal (MHT) method from Mg(OH)₂, Al(OH)₃ and Fe(NO₃)₃·9H₂O or Mg(NO₃)₂·6H₂O as starting materials. The resulting LDHs (MHT-LDHs) were characterized by XRD, TEM, SEM, FT-IR, and zeta potential, size distribution and specific surface area analyses. It was found that pre-milling played a key role in the LDH formation during subsequent hydrothermal treatment. The MHT route is advantageous in terms of low reaction temperature compared with the conventional hydrothermal method, and the target products are of high crystallinity and good dispersion compared with the conventional mechanochemical (MC) method. The MHT-LDHs had higher specific surface area and zeta potential, and lower hydrodynamic diameter than LDHs obtained by MC method (MC-LDHs). Furthermore, the removal of Cr(VI) from aqueous solutions using the LDHs was examined, showing that the MHT-LDHs are of higher removal efficiency than MC-LDHs for the heavy metal pollutant.