Preparation of heterogeneous film from core-shell composite polymer particles produced by the stepwise heterocoagulation method with heat treatment

Characterization of Heterocoagulation with Oppositely Charged Polymer Colloid Particles through Online Tracking of Light Transmittance

Heterocoagulation of colloid particles with opposite surface charge has been used for the preparation of composite microspheres with specifically designed suprastructure, such as those with raspberry-like surface morphology and core-shell microspheres, which are difficult to achieve through other techniques. Here we report our investigation on the heterocoagulation of cationic polystyrene (PS) particles with anionic poly(methyl methacrylate) (PMMA) particles by a novel technique, i.e., by following online the evolution of the light transmittance in the process with practically no disturbance of the dispersion and no post-treatment for the samples. Different heterocoagulations were conducted with PS and PMMA latexes with different latex mixing regimes and different particle sizes for both latexes. The evolution of the light transmittance in all of these processes, mainly with addition of anionic latex to cationic latex, was followed online. By combining TEM to detect the morphology of the composite microspheres formed and light scattering to follow the size evolution in the heterocoagulation, this work gives a clear picture of the heterocoagulation process. In addition, a set of mathematical equations are established in order to estimate the number ratio of the particles with opposite charge and the surface coverage percent of the large primary particle with the small ones. Results show that the particle size plays a key role in the process. The mechanism of the heterocoagulation process is discussed.

Preparation of raspberry-like polymer particles by a heterocoagulation technique utilizing hydrogen bonding interactions between steric stabilizers

Large polystyrene particles stabilized by poly(acrylic acid) (PAA) (L-PS(PAA)) (as the core) and small polystyrene particles stabilized by poly(vinyl pyrrolidone) (PVP) (S-PS(PVP)) (as the corona) were successfully used to prepare raspberry-like particles by a heterocoagulation technique utilizing the hydrogen bonding interaction between PAA and PVP. The coverage of L-PS(PAA) by S-PS(PVP) could be controlled by adding PVP homopolymer to the L-PS(PAA) dispersion and by changing the molecular weight of the stabilizers. Moreover, the heterocoagulation of large poly(methyl methacrylate) particles stabilized by PAA (L-PMMA(PAA)) and S-PS(PVP) particles was also accomplished, resulting in the formation of L-PMMA(PAA)-core/S-PS(PVP)-corona raspberry-like composite particles. These results suggested that the raspberry-like particles composed of various polymer particles could be formed by the heterocoagulation technique utilizing the hydrogen bonding interaction.

Macroporous ZrO2 ceramics prepared from colloidally stable nanoparticles building blocks and organic templates

ZrO2 macroporous materials with well-ordered structures were prepared using nano-ZrO2 particles as the building materials and polystyrene spheres as the organic templates. A well-dispersed nano-ZrO2 suspension with a narrow particle size distribution was prepared by deagglomeration of as-received nano-ZrO2 powders via ultrasonication, and then centrifugation was performed to remove agglomerated bigger particles. Negatively charged polystyrene spheres were uniformly coated with positively charged nano-ZrO2 particles by means of electrostatic attraction at pH 4. Green samples were prepared by slip casting from colloidally stable suspension of nano-ZrO2 coated polystyrene spheres. ZrO2 macroporous materials with well-ordered microstructure derived from the nano-ZrO2 coated polystyrene spheres.