Preparation of Monodisperse Bio-Based Polymer Particles via Dispersion Polymerization.

Monodisperse bio-based polymer particles were successfully prepared through the dispersion polymerization of tulip-derived α-methylene-γ-butyrolactone (MBL) in N,N-dimethylformamide/ethanol (7/3, w/w) at 65 °C with poly(vinylpyrrolidone) (PVP) as a colloidal stabilizer. The diameter of the polymer particles was well controlled by changing the composition of the reaction medium or PVP concentration. Furthermore, 100% bio-based poly(MBL) (PMBL) particles were prepared via the dispersion polymerization of MBL in water using hydrolyzed PMBL as a colloidal stabilizer, which was synthesized by hydrolysis of PMBL.

Preparation of Salt-Responsive Hollow Hydrophilic Polymer Particles by Inverse Suspension Polymerization.

Hydrophilic polymer particles with a hollow structure have potential applications such as carriers for hydrophilic drugs. However, there are few reports on preparation and morphology control of such particles via a simple method. In this study, hollow hydrophilic polymer particles were prepared by inverse suspension polymerization for water droplets containing 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) anions, 1-vinylimidazole (VIm) cations, oligo(ethylene glycol) diacrylate (OEGDA), dextran, and an initiator via the self-assembling phase-separated polymer (SaPSeP) method developed in our lab. The inner morphology of the particle could be controlled (as single- or multi-hollow structures) by changing the concentrations of the OEGDA and the dextran. The obtained hollow particles could encapsulate a hydrophilic fluorescent substance in their hollow region when the substance was added to the primary droplets before polymerization. In addition, the poly(AMPS-co-VIm-co-OEGDA) shell of the particles exhibited an ionic cross-linked structure, which could be stimulated by salt. The poly(AMPS-co-VIm-co-OEGDA) hollow particles with the encapsulated substance released the substance when salt was added to the dispersion. These results indicated that the applicability of the SaPSeP method can be broadened for morphology control of the hydrophilic polymer particles encapsulating water-soluble materials.

Monodispersed Nitrogen-Containing Carbon Capsules Fabricated from Conjugated Polymer-Coated Particles via Light Irradiation.

Near-infrared (NIR) light irradiation induced the transformation of polypyrrole (PPy) to nitrogen-containing carbon (NCC) material due to its light-to-heat photothermal property. The temperature of the PPy increased over 700 °C within a few seconds by the NIR laser irradiation, and elemental microanalysis confirmed the decreases of hydrogen and chloride contents and increases of carbon and nitrogen contents. Monodispersed polystyrene (PS)-core/PPy shell particles (PS/PPy particles) synthesized by aqueous chemical oxidative seeded polymerization were utilized as a precursor toward monodispersed NCC capsules. When the NIR laser was irradiated to the PS/PPy particles, the temperature rose to approximately 300 °C and smoke was generated, indicating that the PS component forming the core was thermally decomposed and vaporized. Scanning electron microscopy studies revealed the successful formation of spherical and highly monodispersed capsules, and Fourier transform infrared spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy studies confirmed the capsules consisted of NCC materials. Furthermore, sunlight was also demonstrated to work as a light source to fabricate NCC capsules. The size and thickness of the capsules can be controlled between 1 and 80 µm and 146 and 231 nm, respectively, by tuning the size of the original PS/PPy particles and PPy shell thickness.

Preparation of Cellulose Particles with a Hollow Structure.

In this study, we report the preparation of hollow cellulose particles via a solvent-releasing method with the ionic liquid 1-ethyl-3-methylimidazolium acetate ([Emim]Ac). A dispersion comprising [Emim]Ac droplets with dissolved cellulose and a hexane medium containing a stabilizer was poured into a large amount of acetone (precipitant), resulting in the precipitation of cellulose and the formation of solid cellulose particles with a hollow structure. We found that the formation of the hollow structure resulted from the equilibrium phase separation. Porous structures were also obtained using ethanol or t-butanol as a precipitant, where cellulose immediately precipitated (i.e., exhibited non-equilibrium phase separation). In the case where acetone was used as the precipitant, the diffusion rate of [Emim]Ac from the droplets into the precipitant was relatively low; that is, the precipitation of cellulose was delayed, which allowed the cellulose to be phase-separated into a thermodynamically stable structure (equilibrium phase separation), resulting in the formation of the hollow structure.

Morphology Control of Porous Cellulose Particles by Tuning the Surface Tension of Media during Drying.

We previously reported the preparation of cellulose particles by the solvent releasing method (SRM). The obtained cellulose particles had a porous structure filled with a surrounding medium. However, the structure was fragile and easily collapsed because of the capillary pressure as the medium evaporated, resulting in dense cellulose particles. To control the morphology of the cellulose particles in a dry state, we focused our study on the influence of the surface tension of the surrounding medium on the structure of cellulose particles because the capillary pressure is proportional to the surface tension. Different media such as toluene, acetone, and pentane were investigated. The morphologies of the resulting cellulose particles were estimated by volume changes, specific surface areas, and compressive strengths. From these results, as the surface tension of the media filling the particles was lowered, the particle's specific surface area increased, resulting in the formation of softer particles.

Preparation of Cellulose/Silver Composite Particles Having a Recyclable Catalytic Property.

We reported the preparation of porous cellulose particles by the solvent-releasing method, in which a solution of cellulose, dissolved in 1-butyl-3-methylimidazolium chloride and N,N'-dimethylformamide, was dropped into a large amount of 1-butanol using a syringe. The obtained particles had a high specific area because of their porous structure. Herein, to functionalize the cellulose particles, carboxylate groups are introduced into their porous structure by 2,2,6,6-tetramethylpiperidine-1-oxyl-mediated oxidation and ion exchange of carboxylate groups to Ag cations is conducted. Composite cellulose/Ag particles were synthesized by the reduction reaction using the carboxylate groups as a scaffold without free silver nanoparticles in the medium. The obtained composite particles exhibited a high catalytic ability, which was evaluated by examining the reduction of 4-nitrophenol. Moreover, we determined that the catalytic efficiency was maintained for at least three cycles by immobilizing Ag on cellulose particles.

Ambient-Temperature Waterborne Polymer/rGO Nanocomposite Films: Effect of rGO Distribution on Electrical Conductivity.

Electrically conductive polymer/rGO (reduced graphene oxide) films based on styrene and n-butyl acrylate are prepared by a variety of aqueous latex based routes involving ambient temperature film formation. Techniques based on miniemulsion polymerization using GO as surfactant and "physical mixing" approaches (i.e., mixing an aqueous polymer latex with an aqueous GO dispersion) are employed, followed by heat treatment of the films to convert GO to rGO. The distribution of GO sheets and the electrical conductivity depend strongly on the preparation method, with electrical conductivities in the range 9 × 10-4 to 3.4 × 102 S/m. Higher electrical conductivities are obtained using physical mixing compared to miniemulsion polymerization, which is attributed to the former providing a higher level of self-alignment of rGO into larger linear domains. The present results illustrate how the distribution of GO sheets within these hybrid materials can to some extent be controlled by judicious choice of preparation method, thereby providing an attractive means of nanoengineering for specific potential applications.

Encapsulation of Either Hydrophilic or Hydrophobic Substances in Spongy Cellulose Particles.

We have reported cellulose particles with a spongy structure that we prepared by the solvent releasing method (SRM) from cellulose droplets composed of cellulose, 1-butyl-3-methylimidazoliumchrolide ([Bmim]Cl), and N,N-dimethylformamide (DMF). The spongy structure collapsed as the medium evaporated, resulting in dense cellulose particles. In this study, we encapsulated the hydrophilic and hydrophobic fluorescent substances in these particles to investigate the use of such particles in potential applications that require encapsulating of substances (e.g., drug delivery). Wet cellulose particles retained their spongy structure in both hydrophobic and hydrophilic media. When the spongy cellulose particles were dispersed in a solution containing nonvolatile solutes, these solutes were driven into the cellulose particles as media evaporated. Subsequently, the cellulose particles collapsed and encapsulated the nonvolatile solutes. Regardless of whether the solute was hydrophilic or hydrophobic, the encapsulation efficiency exceeds 80%. The maximum loading reflected the saturated solubility of solute in solution that filled the cellulose beads. Moreover, the encapsulated solute was released by dispersing the cellulose beads in the solvent, and the rate of release of the encapsulated solute could be controlled by coating the cellulose beads with a conventional polymer.