Formation of anomalous particles during the emulsifier-free polymerization of styrene

Synthesis of dimpled polymer particles and polymer particles with protrusions - Past, present, and future

Since the development of emulsion polymerization techniques, polymer particles have become the epitome of standard colloids due to the exceptional control over size, size distribution, and composition the synthesis methods allow reaching. The exploration of different variations of the synthesis methods has led to the discovery of more advanced techniques, enabling control over their composition and shape. Many early investigations focused on forming particles with protrusions (with one protrusion, called dumbbell particles) and particles with concavities, also called dimpled particles. This paper reviews the literature covering the synthesis, functionalization, and applications of both types of particles. The focus has been on the rationalization of the various approaches used to prepare such particles and on the discussion of the mechanisms of formation not just from the experimental viewpoint but also from the standpoint of thermodynamics. The primary motivation to combine in a single review the preparation of both types of particles has been the observation of similarities among some of the methods developed to prepare dimpled particles, which sometimes include the formation of particles with protrusions and vice versa. The most common applications of these particles have been discussed as well. By looking at the different approaches developed in the literature under one general perspective, we hope to stimulate a more ample use of these particles and promote the development of even more effective synthetic protocols.

Shape engineering of polystyrene particles from spherical to raspberry-like to hollow flower-like via one-step non-surfactant self-templating polymerization of styrene in ethanol-water mixtures

We report a facile method for preparation of polystyrene (PS) particles with spherical, raspberry-like, and hollow flower-like structures by single-step non-surfactant self-templating polymerization of styrene in ethanol–water mixtures. PS particles with diverse morphologies could be easily obtained by simply adjusting the volume ratios of the styrene/water/ethanol mixture and initiator-ethanol–water mixture. By decreasing this ratio, the particles with spherical, raspberry-like, and hollow flower-like structures were obtained in sequence. The wettability of the coatings changing from hydrophilicity to hydrophobicity was easily tuned by the PS particles with different roughnesses. A competitive mechanism of interfacial polymerization and exudation was proposed to interpret the formation of PS particles with diverse morphologies.

We report a facile method for preparation of polystyrene (PS) particles with spherical, raspberry-like, and hollow flower-like structures by single-step non-surfactant self-templating polymerization of styrene in ethanol–water mixtures.

HIC1 and RassF1A Methylation Attenuates Tubulin Expression and Cell Stiffness in Cancer

Cell stiffness is a potential biomarker for monitoring cellular transformation, metastasis, and drug resistance development. Environmental factors relayed into the cell may result in formation of inheritable markers (e.g., DNA methylation), which provide selectable advantages (e.g., tumor development-favoring changes in cell stiffness). We previously demonstrated that targeted methylation of two tumor suppressor genes, hypermethylated in cancer 1 (HIC1) and Ras-association domain family member 1A (RassF1A), transformed mesenchymal stem cells (MSCs). Here, transformation-associated cytoskeleton and cell stiffness changes were evaluated. Atomic force microscopy (AFM) was used to detect cell stiffness, and immunostaining was used to measure cytoskeleton expression and distribution in cultured cells as well as in vivo. HIC1 and RassF1A methylation (me_HR)-transformed MSCs developed into tumors that clonally expanded in vivo. In me_HR-transformed MSCs, cell stiffness was lost, tubulin expression decreased, and F-actin was disorganized; DNA methylation inhibitor treatment suppressed their tumor progression, but did not fully restore their F-actin organization and stiffness. Thus, me_HR-induced cell transformation was accompanied by the loss of cellular stiffness, suggesting that somatic epigenetic changes provide inheritable selection markers during tumor propagation, but inhibition of oncogenic aberrant DNA methylation cannot restore cellular stiffness fully. Therefore, cell stiffness is a candidate biomarker for cells' physiological status.

One-Step Synthesis of Hollow Dimpled Polystyrene Microparticles by Dispersion Polymerization

The design and preparation of hollow nonspherical microparticles are of great significance for their potential applications, but the development of a facile synthetic method using only one production step remains a great challenge. In the current work, a new template-free method based on dispersion polymerization was successfully developed to produce anisotropic hollow polystyrene (PS) microparticles in a single step. In the synthesis, ammonium persulfate (APS) played a critical role in the formation and growth of highly uniform and stable hollow PS microparticles. By varying the concentration of APS and that of the stabilizer used, polyvinylpyrrolidone, we were able to control the average size of the PS particles and their degree of concavity. Based on our results and observations, a plausible mechanism for formation of these unusually shaped PS microparticles was proposed.

Easy-to-fill asymmetric polymeric micro-reservoirs

Thermoplastic, asymmetrical, micrometric reservoirs filled with a desired host molecule are achieved by gas foaming and subsequent filling. This method paves the way to a breakthrough in the vibrant micro- and nanoparticle area.

Effect of interfacial free energy on the formation of polymer microcapsules by emulsification/freeze-drying

Hollow polymer microparticles with a single opening on the surface were formed by freeze-drying aqueous polymer colloids swollen with solvent. The results show that the particle morphology is due to phase separation in the polymer emulsion droplets upon freezing in liquid nitrogen, and that morphological changes are driven largely by lowering interfacial free energy. The effects of added surfactant, volume fraction of solvent, type of solvent, and processing conditions on the particle morphology were examined and compared to theoretical predictions. The dried hollow particles were resuspended in a dispersing media and exposed to a second swelling solvent to close the surface opening and form microcapsules. The interfacial free energy difference between the inside and outside surfaces is the driving force for closing the hole on the surface. The emulsification/freeze-drying technique can be used to encapsulate hydrophilic additives in the core of the microcapsules, demonstrating the potential of the technique in controlled-release applications.

Microscale fish bowls: a new class of latex particles with hollow interiors and engineered porous structures in their surfaces

Microscale fish bowls, hollow particles with engineered holes in their surfaces, were prepared using two different methods. In the first method, commercial latex beads suspended in water were swollen with a good solvent of the polymer, followed by freezing with liquid nitrogen and evaporation of the solvent below 0 degrees C. While one big hole was generated when the amount of solvent used for the swelling was relatively low, small holes could be produced in the outer surface of each bowl by increasing the degree of swelling. The porosity and pore structure show a similar dependence on the degree of swelling for both amorphous and semicrystalline polymers even though they are supposed to exhibit different phase behaviors during the freezing and solvent evaporation processes. In the second method, a polymer emulsion in water was prepared and then frozen with liquid nitrogen, followed by solvent evaporation below 0 degrees C. The porosity and pore structure could be controlled by adjusting the concentration of the polymer solution used to prepare the emulsion. As for encapsulation, the bowl-shaped particles could be transformed back into solid beads via thermal annealing at a temperature near the glass transition temperature of the polymer or by adding a good solvent of the polymer to the colloidal suspension. In a proof-of-concept experiment, microscale fish bowls were fabricated from poly(caprolactone), quickly loaded with a fluorescent dye, and sealed through thermal annealing. The encapsulated dye could then be slowly released in a phosphate buffered saline, suggesting their potential use as a new class of microscale capsules for drug delivery.

The cleaning of polymer colloids

The current state of knowledge of the cleaning of polymer colloids is reviewed with regard to a wide range of cleaning and characterisation techniques. The type, level and quantity of impurities involved with different polymer latex formulations varies widely. Even for similar formulations, differences in the nature and number of functional groups reported are often a consequence of sometimes subtle differences in the cleaning procedures employed. Not only may surface functionality be affected but also monomer and oligomer extraction procedures may lead to morphological changes in the particles. No single technique alone is likely to be able to remove all impurities. Care is needed to avoid the introduction of new impurities from the equipment, materials and water used as well as possible contamination from atmospheric carbon dioxide, bacteria and fungi. These factors also need to be considered in the storage of latex particle standards.