Electrostatic heterocoagulation of carbon nanotubes and LiCoO2 particles for a high-performance Li-ion cell

Nanotubes were coated on the surface of active LiCoO₂ particles using electrostatic heterocoagulation to enhance the electrochemical properties of a Li-ion battery. Only 0.5 wt% of multiwalled carbon nanotubes (MWCNTs) was added as a conducting agent into the LiCoO₂ cathode, which had a density of 4.0 g cm⁻³. We found that our electrode that was prepared using heterocoagulation with 0.5 wt% of thin MWCNTs maintained a volumetric capacitance of 403 mAh cm⁻¹ after 40 cycles from the initial 624 mAh cm⁻¹, compared with previous result of 310 mAh cm⁻¹ obtained from simple mixing with 3 wt% MWCNTs. The high volumetric capacity with smaller swelling using less amount of MWCNTs was attributed to the self-assembled nanotube network formed between active particles during coagulation, which was maintained with volume expansion during cycle testing.     

Colloidal poly(styrene-co-butyl acrylate)/multi-walled carbon nanotubes nanocomposite by heterocoagulation in aqueous media

Colloidal nanocomposite particles were prepared by heterocoagulation of carbon nanotubes (CNTs) dispersion stabilized by cationic hexadecyltrimethylammonium bromide (CTAB) and negatively charged poly(styrene-co-butyl acrylate), P(St-co-BA), latex prepared by conventional emulsion polymerization in aqueous medium with the aid of a flocculant, polyaluminium chloride (PAC), at elevated temperature above the T_g of P(St-co-BA). The hybrid nanocomposite particles were prepared by a simple procedure consisting of mixing two dispersions, particle growth, and stabilization steps. The effects of the surface properties of CNTs, molecular weight of latex polymer, types of flocculants and its optimum concentration were investigated. At a well-controlled condition, the spherical or potato-like particles in the size range of 10-100 μm were achieved. After film formation of the nanocomposite particles, it was able to confirm that CNTs were uniformly distributed without agglomeration in the matrix, resulting in the percolation at a low concentration of CNTs.     

The effects of multiwalled carbon nanotubes on the hot-pressed 3 mol% yttria stabilized zirconia ceramics

The bulk composites of 3 mol% yttria stabilized zirconia ceramics reinforced by multiwalled carbon nanotubes were prepared by ball milling, spray-drying and hot-pressing processes. The effects of MWCNTs’ contents and heterocoagulation pretreatment on the mechanical properties of 3Y–ZrO₂/MWCNTs’ composites were investigated at room temperature. Experimental results showed that the heterocoagulation pretreatment played a vital role in homogeneous dispersion of MWCNTs in the ceramic matrix. The flexural strength of 989.8 ± 20.0 MPa and fracture toughness of 5.77 ± 0.06 MPa M^1/2 were obtained for the composite with 1.0 wt.% of MWCNTs’ content, which were 135.3 MPa (or 8.4%) higher in flexural strength and 0.92 MPa M^1/2 (or 21.1%) higher in fracture toughness than those of blank 3Y–ZrO₂, respectively. The mechanisms of strengthening and toughening of the composites could be attributed to the synergic effects of bridging, pulling out of MWCNTs and their promotive effects on the phase transformation of the ceramics.     

Construction of composite particles with monolayered poly(styrene-co-acrylic acid) spheres on gold surface via heterocoagulation

Composite particles are successfully fabricated in a shape of bead-on-bead through a heterocoagulation. Submicron poly(styrene-co-acrylic acid) (PSAA) spheres are prepared and used as guest materials of composite particles. The spheres adsorb on the gold surface of a host material in perfect monolayered form and the pH dependence of the adsorption degree is also investigated. At strong acidic condition, the spheres are effectively adsorbed on the host materials, while the adsorption efficiency dramatically decreases with increasing pH due to the deprotonation of carboxyl groups at the surface of the spheres. Even though the composite particles are immersed in good solvents of PSAA for 12 h, the particles exhibit excellent adsorption stability.     

Processing alumina spheres by a colloidal route using silica-polystyrene hybrid nanoparticles

Colloidal granulation of alumina is an original shaping process leading to spherical granules directly in suspension from a diluted system. It is based on a heterocoagulation mechanism where silica added in small amount acts as a binding agent. The role of a submicronic latex of polystyrene was investigated, free, or as a hybrid object covered by silica nanoparticles synthesized by a Pickering emulsion polymerization method. Latex particles were not able to form primary agglomerates despite a high negative zêta potential. An addition of latex in combination with silica improved the state and homogeneity of the final microstructure which could be attributed to a decrease of the internal strains during the processing. Hybrid nanoparticles, by combining the binding agent (silica) and the organic phase, were able to form primary agglomerates, and to finally obtain alumina spheres exhibiting both a spherical morphology and a greater homogeneous microstructure.     

Composite natural rubber based latex particles: a novel approach

The oil resistance of natural rubber (NR) film could be effectively improved by using the heterocoagulation of large NR particle with small polychloroprene (CR) particles. In the preparation of NR/CR composite particle with a core-shell structure, a nonionic surfactant whose molecule bears poly(ethylene oxide) (PEO) was adsorbed on CR particles and allowed to form complexes between PEO and indigenous surfactant (protein-lipid) on the NR particle surface. Composite latex particle obtained was characterised by particle size, zeta potential and glass transition temperature measurements and the data indicated the presence of CR on the outer layer of composite particle. Better oil resistance of film casted from heterocoagulated latex when compared to that of NR film confirmed the NR/CR core-shell structure. The epoxidised natural rubber (ENR), crosslinked ENR and/or skim latex particles were investigated in order to replace the use of CR in the heterocoagulation process.     

Classification of submicron Ni particles by heterocoagulation

In this work, the size classification of a mixture of submicron and micron size Ni particles dispersed in aqueous solution was investigated. The suspension of Ni particles was allowed to flow, under laminar condition, through a burette filled with an adhesion medium (i.e. substrate). The difference between zeta potentials of larger particles and adhesion medium created a base for the heterocoagulation. Thus, the larger particles move towards the medium assisted by the Saffman lift force and are attracted to its surface. The finer particles, on the other hand, flow off the burette and were collected as a separate fraction. This phenomenon was then explained by numerical simulating the particle's motion and showing that a stronger Saffman lift force will act in the direction of the substrate only for large particles, leaving the smaller ones unaffected as they sediment out.     

Bottom-up synthesis of PS-CNF nanocomposites

Polystyrene-carbon nanofiber (CNF) nanocomposites have been synthesized by a ‘bottom-up’ method through electrostatic assembly. First, a cationic polystyrene (PS) latex was synthesized by conventional emulsion polymerization. The latex was mixed with an aqueous suspension of oxidized CNF. PS-CNF nanocomposites were obtained by heterocoagulation due to the electrostatic interaction between cationic PS latex and anionic CNF. Thermal properties were characterized by DSC and TGA, while morphologies of the nanocomposites were studied by SEM. Electrical resistivity results showed that the percolation threshold in our PS-CNF nanocomposites was below 2 wt% (1 vol%). This low percolation threshold is related to the dispersion, and thus a superior network formation of CNF in PS matrix.