Production of submicron-sized multihollow polymer particles by alkali/cooling method

Role of Osmotic Pressure for the Formation of Sub-micrometer-Sized, Hollow Polystyrene Particles by Heat Treatment in Aqueous Dispersed Systems †

In a previous article, it was reported that a rather amount of sulfate end-groups as initiator fragment were buried in the inside of polystyrene (PS) particles, which were synthesized by emulsion polymerization with potassium persulfate initiator and nonionic emulsifier and operated to absorb water from the aqueous medium, resulting in hollow particles, when the PS emulsion was treated at higher temperature than the glass transition temperature of PS. In this article, it was clarified that the water absorption is based on the osmotic pressure between the outside (aqueous medium) and inside of the PS particles due to the buried sulfate end-groups.

Formation of cagelike sulfonated polystyrene microspheres via swelling-osmosis process and loading of CdS nanoparticles

In this report, we studied the formation mechanism of cagelike polymer microspheres fabricated conveniently and efficiently through a swelling-osmosis process of sulfonated polystyrene (SPS) microspheres in a ternary mixed solvent (water/ethanol/heptane). The scanning electron microscopy and transmission electron microscopy observations indicated that the morphology of the final cagelike SPS microspheres is mainly controlled by the composition of the mixed solvent and the swelling temperature. Considering the solubility parameters of related reagents and the low interface tension of heptane and the aqueous solution of ethanol (only 6.9 mN/m), we confirm that the porogen procedure starts from the swelling of SPS microspheres by heptane, followed by the osmosis process of water molecules into the swollen SPS microspheres forced by the strong hydrophilicity of -SO3H group. The water molecules permeated into SPS microspheres will aggregate into water pools, which form the pores after the microspheres are dried. These prepared cagelike SPS microspheres are further served as the scaffold for the in situ generated CdS nanoparticles under γ-ray radiation. The CdS/SPS composite microspheres show good fluorescence performance. This work shows that the cagelike SPS microspheres have a wide industrial application prospect due to their economical and efficient preparation and loading nanoparticles.

A facile approach to synthesize SiO2 · Re2O3 (Re = Y, Eu, La, Sm, Tb, Pr) hollow sphere and its application in drug release

Multifunctional SiO2 · Re2O3 (Re = Y, Eu, La, Sm, Tb, Pr) hollow spheres (HSs) have been fabricated using an acidic Re3+ ion solution. Under ultraviolet radiation, functional HSs emit different colors of light according to the different rare-earth ions embedded into the shell of SiO2 hollow spheres. The as-prepared hollow capsules were characterized by X-ray diffraction, transmission electron microscopy, high-resolution transmission electron microscopy, Brunauer-Emmett-Teller method, scanning electron microscopy, and energy-dispersive spectrometry. Drug loading and release experiments have been carried out using SiO2 · Eu2O3 HSs that acted as drug carriers. The results demonstrate that the multifunctional HSs exhibit a high storage capacity and the ability of retaining drug stability and activity, which indicates that the as-synthesized fluorescent hollow capsules are a potential candidate as drug delivery materials.

Incorporation of disodium alkyl polyoxyethylene ether sulfosuccinate inside styrene droplets: mechanism and its application for preparation of multihollow polymer spheres

Emulsion polymerization of styrene was carried out using two kinds of alkyl polyoxyethylene ether sulfosuccinates as surfactant: disodium cetyl polyoxyethylene (25) ether sulfosuccinate (CPS) and octyl-phenol polyoxyethylene (10) ether sulfosuccinate (OPS). In experiments, the incorporation of CPS or OPS inside styrene droplets and polystyrene particles was clearly observed. Based on this phenomenon, multihollow polymer spheres are prepared in a one-step reaction and this strongly supports the proposed incorporation mechanism. CPS is more effective than OPS during the preparation of multiporous spheres. This difference between the two surfactants mainly contributes to the difference of the length of the EO (polyoxyethylene) group, which can determine the affinity among surfactant, styrene, and water molecules.

Preparation of multihollow polymer particles by seeded emulsion polymerization using seed particles with incorporated nonionic emulsifier

Emulsion polymerizations of styrene using poly(oxyethylene) nonylphenyl ether nonionic emulsifier were carried out at different emulsifier and initiator (potassium persulfate, KPS) concentrations to prepare polystyrene (PS) seed particles with incorporated nonionic emulsifier. Seeded emulsion polymerizations of styrene using the PS seed particles with different amounts of incorporated emulsifier were carried out to develop a novel method for the preparation of multihollow particles. When seed particles with a small amount of incorporated emulsifier were used, non-hollow spherical particles were prepared. However, multihollow particles were obtained in the case of seed particles with a large amount of incorporated emulsifier. Moreover, the higher the initiator concentration in the preparation of seed particles, the more effectively were hollow particles prepared. On the basis of the above results, a mechanism for the formation of multihollow structure was suggested.

Incorporation of nonionic emulsifiers inside particles in emulsion polymerization: mechanism and methods of suppression

Emulsion polymerizations of styrene were carried out using two kinds of polyoxyethylene lauryl ether nonionic emulsifiers having different hydrophilic-lipophilic balances (HLB): Emulgen 109P (HLB 13.6); and Emulgen 150 (HLB 18.3). In both cases, incorporation of emulsifier inside polystyrene (PS) particles was clearly observed, as previously reported for the emulsion polymerization of styrene and methacrylic acid using polyoxyethylene nonyl phenyl ether (Emulgen 911, HLB 13.7) nonionic emulsifier. The generality of the incorporation phenomenon of nonionic emulsifier inside polymer particles in emulsion polymerization was clarified. In the case of Emulgen 109P, which is more hydrophobic than Emulgen 150, about 30% of the total amount was incorporated inside the PS particles, higher than for Emulgen 150 (15%). The difference seemed to be ascribed to the difference in the affinities between the nonionic emulsifiers and styrene, which cause the incorporation of emulsifier. On the basis of this idea, suppression of the incorporation was achieved by decreasing the polymerization temperature and the monomer-feed rate. This strongly supports the proposed incorporation mechanism.