Multihollow Structures Research Articles

Transport features of topological corner states in honeycomb lattice with multihollow structure

Higher-order topological phase in 2-dimensional (2D) systems is characterized by in-gap corner states, which are hard to detect and utilize. We numerically investigate transport properties of topological corner states in 2D honeycomb lattice, where the second-order topological phase is induced by an in-plane Zeeman field in the conventional Kane-Mele model. Through engineering multihollow structures with appropriate boundaries in honeycomb lattice, multiple corner states emerge, which greatly increases the probability to observe them. A typical two-probe setup is built to study the transport features of a diamond-shaped system with multihollow structures. Numerical results reveal the existence of global resonant states in bulk insulator, which corresponds to the resonant tunneling of multiple corner states and occupies the entire scattering region. Furthermore, based on the well separated energy levels of multiple corner states, a single-electron source is constructed.

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.

Dual-template magnetic molecularly imprinted particles with multi-hollow structure for the detection of dicofol and chlorpyrifos-methyl.

In this work, a novel dual-template magnetic molecularly imprinted polymer particle for dicofol and chlorpyrifos-methyl was prepared through oil-in-water emulsifier-free emulsion technology. The resulting magnetic particles were characterized with electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction. It was found that as-prepared particles were well-shaped spheres with multi-hollow structures and of a size around 125 μm. Meanwhile it showed a good magnetic sensitivity. The results testified that multi-hollow magnetic molecularly imprinted polymers possessed excellent recognition capacity and fast kinetic binding behavior to the objective molecules. The maximum binding amounts toward dicofol and chlorpyrifos-methyl were 31.46 and 25.23 mg/g, respectively. The feasibility of the use of the particles as a solid-phase extraction sorbent was evaluated. Satisfactory recoveries ranging from 90.62 to 111.47 and 91.07 to 94.03% were obtained for dicofol and chlorpyrifos-methyl, respectively, spiked at three concentration levels from real samples. The Langmuir isotherm equation provided an excellent fit to the equilibrium sorption data of either dicofol or chlorpyrifos-methyl. It provided a novel way to advise dual-template magnetic molecularly imprinted polymer particles to adsorb pesticides with high selectivity.

Fabrication of Tunable Janus Microspheres with Dual Anisotropy of Porosity and Magnetism

This work presents a facile approach to produce a novel type of Janus microspheres with dual anisotropy of porosity and magnetism based on Pickering-type double emulsion templates. A stable aqueous Fe3O4 dispersion-in-oil-in-water (WF/O/W) double Pickering emulsion is first generated by using hydrophobic silica and hydrophilic mesoporous silica particles as stabilizers. Janus microspheres with multihollow structure possessing magnetite nanoparticles concentrated on one side of the microspheres are obtained after polymerization of the middle oil phase of the double emulsion under a magnetic field. The resultant Janus microspheres are characterized by optical microscopy, scanning electron microscopy (SEM), and energy-dispersive X-ray analysis (EDX). Moreover, we have systematically investigated the influences of Fe3O4 particle concentration, hydrophobic silica particle content, and volume ratio of the inner water phase to middle oil phase (WF/O) on the double emulsion formation and consequently on the structure of the resulting Janus microspheres. Our results show that the distribution of the multihollow structures within the prepared microspheres can be accurately tailored by adjusting the ratio of WF/O. In addition, the obtained Janus microsphere can be fairly orientated under a magnetic field, making them a potential candidate for synthesizing Janus membrane.

The Mechanism of the Formation of Multihollow Polymer Spheres through Sulfonated Polystyrene Particles

Multihollow poly(methyl methacrylate) (PMMA) particles were successfully fabricated simply by gamma-ray radiating emulsions consisting of MMA monomers, sulfonated polystyrene (SP) particles, and water. The mechanism on the formation of the holes was studied in detail. It was found that there were two routes to achieve two different multihollow structures dependent on the initial location of SP particles before emulsification. If SP particles first located in the water phase, cage-like hollow PMMA particles were obtained through the formation of a Pickering emulsion. Otherwise, if SP particles first located in the oil (MMA) phase, a different multihollow structure would be produced via the formation of a multiple emulsion. This work provides a simple method to fabricate two different structured multihollow particles using the same conditions.

Multihollow structured poly(methyl methacrylate)/silver nanocomposite microspheres prepared by suspension polymerization in the presence of dual dispersion agents

Poly(methyl methacrylate) (PMMA)/silver nanocomposite microspheres with unique multihollow structures were prepared by suspension polymerization in the presence of dual dispersion agents. The addition of a lipophilic emulsifier, polyethylene glycol (30EO) dipolyhydroxystearate (Arlacel P135), not only stabilized water-in-oil (W/O) emulsion, but also converted silver nanoparticles from hydrophilic to lipophilic. When a suspension polymerization dispersion agent, poly(vinyl alcohol), was added to the above W/O emulsion system, a water-in-oil-in-water suspension was formed with silver nanoparticles dispersed in the oil phase. The suspension polymerization was carried out at low temperature with 2,2’-azobis(2,4-dimethylvaleronitrile) as the initiator. When modified silver nanoparticles were added, the rate of polymerization increased slightly. High monomer conversion (about 85%) was obtained in spite of low polymerization temperature of 30 °C. Under controlled conditions, PMMA/silver microspheres with various hollow structures were synthesized. The PMMA/silver microspheres with multihollow structure showed high antibacterial ability.

Preparation of multihollow P(St–MAA) particles by sequence soap-free/soap emulsion polymerization and followed by stepwise alkali/acid posttreatment

The effects of ionic emulsifier, sodium dodecylbenzene sulfate (SDBS), on the formation of the multihollow structures in sub-micron sized polymer particles produced by alkali/acid posttreatment were investigated. The original latex particles with narrow size distribution were synthesized by a new sequence emulsifier-free/emulsifier emulsion copolymerization of styrene (St) and methacrylic acid (MAA). Results indicated that the pore size decreased and the pore number increased with the increase of SDBS amount, and the morphology of the posttreated latex particles was also significantly influenced by the introducing time of SDBS in the preparation of the original latex particles, and a suitable introducing time was 3 h of polymerization.

Multihollow polymer microcapsules by water-in-oil-in-water emulsion polymerization: morphological study and entrapment characteristics

Multihollow cross-linked poly(methyl methacrylate) (PMMA) microcapsules were produced by water-in-oil-in-water emulsion polymerization and their applicability to encapsulate water-soluble ingredients was evaluated. In the microscopic analysis, all the PMMA microcapsules showed multihollow structures. In order to evaluate the entrapment efficacy, continuously, a water-soluble ingredient (monosodium phosphate, MSP) was incorporated into the inner voids of the microcapsules, and then its releasing profiles were measured with the storage conditions in pure water. In the releasing test, it was observed that the degree of cross-linking of PMMA had a significant influence on the migration of MSP through the polymer phase. At a sufficient degree of cross-linking of the polymer phase, the leakage of MSP out of the microcapsules was stopped successfully. It is believed that the extremely small network size and the mechanically strong network structure hindered effectively the water flow caused by the concentration gradient between water-soluble ingredients.

Evaporation behavior of water from aqueous dispersions of multihollow particles prepared by the stepwise alkali/acid method

In order to clarify the formation mechanism of multihollow structures inside styrene–methacrylic acid copolymer particles prepared by the stepwise alkali/acid method, which we proposed in 1990, the evaporation behavior of water from aqueous dispersions of the original carboxylated particles and those after the alkali treatment and the stepwise alkali/acid treatments was examined. It is concluded that the particle after the alkali treatment had a number of small water pools inside.

Effect of nonionic emulsifier on the production of multihollow polymer particles by the stepwise acid/alkali method

The effects of nonionic emulsifier on the formation of multihollow structures formed within sub-micron-sized polymer particles by the “acid/alkali method” proposed by the authors were examined. The original acid-swellable particles were produced by seeded emulsion terpolymerization of styrene, butyl acrylate, and dimethylaminoethyl methacrylate. The results indicate that the nonionic emulsifier had a great effect on the formation of multihollow particles.

Effect of polymer composition on the production of cationic multihollow polymer particles by the stepwise acid/alkali method

The effect of the polymer composition on the formation of multihollow structures formed within submicron-sized styrene–butyl acrylate–dimethylaminoethyl methacrylate terpolymer particles by the “acid/alkali method” proposed by the authors was examined. The cationic particles were produced by seeded emulsion terpolymerization with 2,2′-azobis(2-amidinopropane) hydrochloride initiator. The dimethylaminoethyl methacrylate content and the glass-transition temperature of the terpolymer greatly affected the formation of the multihollow structure.

Synthesis and characterization of hollow polymer latex particles

Latex particles with a multihollow structure were prepared by seeded emulsion polymerizatoin. Thus seed latexes Sn, consisting of styrene(St) and methyl methacrylate (MMA) copolymer, and Sa, consisting of St–MMA–AA (acrylic acid) copolymers, were first prepared, then a series of core–shell composite latexes SnCa, SnCn, SaCa and SaCn were synthesized with or without AA in the absence of emulsifiers in the second step. Final latexes were then treated by alkali and acid subsequently at 90°C for 3 h. TEM observation showed that only SnCa and SaCa (prepared with AA in the second polymerization, suffix Ra" means with AA, Rn" means without AA) produced multihollow structures in the particles, and their particle volumes increased 42% for SnCa and 23% for SaCa after the treatment in comparison with original latex particles. No hollows were observed for SnCn and SaCn particles prepared without AA and new particles were formed for the SaCn latex in the second step polymerization. © 1997 John Wiley & Sons, Ltd.

Formation of multihollow structures in crosslinked composite polymer particles

Micron-size monodisperse polymer particles having multihollow structures were prepared as follows. First, micron-size monodisperse polystyrene/poly(styrene-divinylbenzene) (PS/P(S-DVB)) composite particles were produced by seeded copolymerization of S and DVB with 2,2′-azobisisobutyronitrile as an initiator in the ethanol/water (76/24, weight ratio) medium in the presence of 2.37 μm-size monodisperse PS seed particles produced by dispersion polymerization. The molar ratio of S/DVB was changed in the range of 1/1∼10/1. The uncrosslinked polymer within the composite particles was extracted with toluene under reflux. For the highest DVB content (S/DVB=1/1, molar ratio), one large hollow was observed in a part of the composite particles after the extraction. For the middle DVB content (S/DVB=4/1, molar ratio), multihollow structure was observed in all the particles. For the lowest DVB content (S/DVB=10/1, molar ratio), fine multihollow structure was observed in all the particles.