Surface Of Polymer Microspheres Research Articles

Fabrication of depth-controlled dimples on polymer microsphere and capturing of nano-sized objects

Polymer microspheres containing submicron-sized surface dimples were prepared through the acid-dissolving removal of silica nanoparticles as templates from the surface of core-shell microspheres, which were prepared by modified suspension polymerization of a silica nanoparticle-dispersed polymerizable monomer mixture (methyl methacrylate and divinylbenzene dispersing). We demonstrated depth control of the dimples on the surface of polymer microspheres and evaluated their capturing properties. The depth of the dimples could be facilely controlled by changing the surface polarity of silica nanoparticles (1 µm) as templates during the synthesis of the core-shell microspheres. The depth of the prepared dimples ranged from 250 to 810 nm, and the gate diameter of the dimple was related to its depth owing to the spherical shape of the template. The inner surfaces of the dimples were evaluated based on the adsorption of cationic and anionic fluorescent dyes. Confocal laser microscopy observations indicated that the inner surfaces of the dimples were densely stained with both fluorescent dyes, whereas the outer surfaces of the microspheres were not stained, suggesting that the inner surfaces of the dimples were more hydrophobic. Silica particles smaller than the gate diameter of the dimple were crammed (or jammed) into the inner space of the dimple, and the captured silica particles did not drop off even after washing with water more than five times. Because the larger silica nanoparticles could not be trapped, the dimples could selectively capture the nanosized objects in their inner space.

Synthesis and evaluation of phenolic capsaicin-derived self-polymers for antibacterial activity

Capsaicin, as a low-toxic antibacterial bioactive substance, is recognized as an environmentally friendly antifouling agent. To obtain a naturally derived antifouling agent with stronger antibacterial ability, capsaicin-derived self-polymers (labeled POHABA, PPHABA, PAHMA, and PAMTHBA) containing phenols (catechol, hydroquinone, resorcinol, phloroglucinol) and N-hydroxymethyl acrylamide were synthesized by precipitation polymerization, which was uniform spheroids with folded surfaces (diameter 0.6–1.6 µm, except PAMTHBA diameter 200–400 nm). The antibacterial activity assay showed that they had a significant inhibitory effect on E. coli and S. aureus (MIC: 0.4 mg/mL against E. coli and 0.8 mg/mL against S. aureus; antibacterial rate: 99.99 % for E. coli and 98.18 % for S. aureus), which was related to the content of phenolic hydroxyl on the surface of the microspheres by comparison with the semi-quantitative analysis of EDS and XPS spectra. The antibacterial activity of self-polymers was significantly higher than that of the monomers, mainly because there were more and more uniform hydroxyl groups on the surface of polymer microspheres. These results provide a theoretical basis for capsaicin-derived self-polymers to be applied to environmentally friendly antifouling agents.

Facile fabrication and SERS performance of polymer/Ag core-shell microspheres via the reverse breath figure accompanied by in situ reduction

A new facile fabrication process of the polymer/Ag core-shell microspheres is demonstrated via the reverse breath figure method accompanied by in situ reduction. In contrast to traditional approaches, which require the prior preparation of polymer microspheres, the star-shaped polyhedral oligomeric silsesquioxane (POSS) amphiphilic block copolymers solution containing AgNO3 is cast under ethanol vapor for the formation of polymer/AgNO3 core-shell microspheres in one step. The influence of polymer molecular structures, solvent, non-solvent and metal salt on the morphology of polymer microspheres was analyzed. Then the AgNO3 can be reduced in situ to form Ag nanoparticles on the surface of polymer microspheres, which resulted in the formation of polymer/Ag core-shell microspheres. The reduced Ag nanoparticles were homogeneously deposited on the surfaces of polymer microspheres, which can exhibit good performance in the surface-enhanced Raman scattering (SERS). The polymer/Ag core-shell microspheres substrate showed a high detection sensitivity (enhancement factor 2.49 × 106) with excellent uniformity and reproducibility for Rhodamine 6G (R6G) (relative standard deviation of the intensity at 612 cm−1 was 6.19%＜20%). The proposed strategy is facile to implement and thus a promising new method for the preparation of polymer/metal core-shell microspheres.

Selective reflection enhancement by controlling of surface-layering structure of inorganic nanoparticles on polymer microspheres

Polymeric materials generally transmit or absorb UV light while weakly reflecting visible light. Treating the surface of a polymer material can increase reflectivity in the visible region. Inorganic nanoparticles, including silica and alumina, exhibit high reflectivity and light scattering at visible and UV wavelengths. Therefore, the possibility exists to absorb UV light and selectively reflect visible light by immobilizing a single layer of inorganic nanoparticles on the surface of polymer microspheres. Core-shell microspheres containing a layered shell of inorganic nanoparticles were prepared by a modified suspension polymerization method. The surface morphology of the microspheres was altered by changing the type, size, and amount of inorganic nanoparticles. The reflectivity of the microspheres was investigated via UV-Vis-NIR spectrophotometry. The packing density of the shell layer was controlled by changing the quantity of nanoparticles added. UV–visible spectroscopy indicates that the core-shell microspheres absorb UV light at wavelengths less than 380 nm and selectively reflect visible light at wavelengths greater than 400 nm. The reflectance of visible light is enhanced by changing the type and concentration of inorganic nanoparticles, and reflectance is increased by 26% relative to bare polymer microspheres. Thus, the core-shell microspheres absorb UV light and selectively reflect visible light.

Functional polymer microspheres as “turn-off” chemosensors for detection of copper cations

Functional polymer microspheres with fluorescent carbazole unit and various functional groups, such as amide, pyridyl, and imidazole, were prepared by distillation precipitation copolymerization of divinylbenzene (DVB) as a crosslinker, N-vinylcarbazole (NVCz), together with acrylamide (AAm), 4-vinylpyridine (VPy), and 1-vinylimidazole ((VIM) as functional monomers in acetonitrile in the absence of any stabilizer. The resultant polymer microspheres were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), UV-Vis spectroscopy, photoluminescent spectroscopy, inductively coupled plasma (ICP), and X-ray photoelectron microscopy (XPS). The functional polymer microspheres acted as a “turn-off” chemical sensor with excellent stability for determination of copper cation (Cu2+) in methanol via the quenching effect of fluorescence after adsorption of Cu2+ from the solution through the capture ability of functional groups, such as pyridyl, imidazole, and amide on the surface of polymer microspheres. A good linear relationship was set up between the photoluminescence intensity at the emission peak of 352 nm and the Cu2+ concentrations ranging from 0 to 1.0 μM with the presence of pyridyl group as a ligand. The effects of the functional groups were investigated on the fluorescent response for the microspheres as chemical sensors.

Preparation and characterization of film-forming raspberry-like polymer/silica nanocomposites via soap-free emulsion polymerization and the sol–gel process

Herein, we report on the synthesis of film-forming poly(styrene-co-butyl acrylate-co-acrylic acid)/SiO2 [P(St-BA-AA)/SiO2] nanocomposites by in situ formation of SiO2 nanoparticles from TEOS via sol–gel process in the presence of poly(acrylic acid) (PAA)-functionalized poly(styrene-co-butyl acrylate) [P(St-BA)] particles fabricated by soap-free emulsion polymerization. The formed silica particles could be absorbed by polyacrylate chains on the surface of PAA-functionalized P(St-BA) particles; thus, raspberry-like polymer/silica nanocomposites would be obtained. Transmission electron microscopy, Fourier transform infrared spectroscopy, attenuated total reflectance infrared spectrum, ultraviolet–visible transmittance spectra, and thermogravimetric analysis were used to characterize the resulting composites. The results showed that the hybrid polymer/silica had a raspberry-like structure with silica nanoparticles anchored on the surface of polymer microspheres. The thermal, fire retardant, and mechanical properties and water resistance of the film were improved by incorporating silica nanoparticles, while the optical transmittance was seldom affected due to nanosized silica particles uniformly dispersed in the film.

Raspberry-like nanocomposite microsphere via Double In situ miniemulsion polymerization using interfacial redox initiator system

Inorganic/polymer nanocomposites have drawn a lot of attention due to their wide applications in medicine, coating, cosmetics, catalysis, biology, and so on. Many techniques have been adopted to the fabrication and morphology control of nanocomposite particles, such as aqueous dispersion polymerization, surfactant free polymerization, heterophase polymerization, Pickering emulsion polymerization, miniemulsion polymerization, and so forth. Such nanocomposite microspheres have been examined in a wide range of applications, ranging from new synthetic mimics for understanding the behavior of micro-meteorites, to stimulus responsive Pickering emulsifiers to tough, transparent, scratch-resistant coatings for either timber or housing exteriors. However, to control the dispersion of nanoparticles into polymer matrices is a significant challenge and it is often difficult to achieve this goal as inorganic particles are typically immiscible with polymer phase. Among the above methods miniemulsion polymerization has been proved to be a powerful and versatile process in the fabrication of inorganic/polymer microspheres. However, colloidal nanocomposite microspheres are most synthesized by in situ the polymerization of organic monomer in the presence of pre-formed inorganic colloidal particles. In order to obtain high encapsulation efficiencies, the silica particles had to be well dispersed within the monomer phase prior to miniemulsification. The most difficulty in the preparation of nanocomposites is to avoid the aggregation of nanoparticles in the polymer matrix. According to Steven P. Armes’ opinion, raspberry-like nanocomposite microspheres satisfy the basic demands. That is, the nanoparticles not only closely pack on the surface of polymer microspheres, but distribute homogeneously throughout the polymer microspheres. In order to obtain raspberry-like microspheres, auxiliary monomers were required to enhance the interaction between hydroxyl groups (acidic) on silica surfaces and amino groups (basic) during the formation of nanocomposite particles. 4-Vinylpyridine (4-VP), 1-vinylimidazole (1-VID), and 2-(methacryloyl) ethyltrimethylammonium chloride (MTC) have been used to successfully prepare PMMA/SiO2 organic-inorganic microspheres. Following the above synthesis route, Armes prepared a series of conducting polymer-silica nanocomposite microspheres based on either polyaniline, polypyrrole or poly(3,4-ethylenedioxythiophene). Stefan A. F. Bon prepared armored nanocomposite polymer microspheres by soap-free emulsion polymerizations in the presence of silica nanoparticles. Furthermore more complex multilayered nanocomposite polymer colloids were obtained by using a second conventional seeded emulsion polymerization step. Based on our previous works, silica/polymer hybrid particles have been fabricated successfully via double in situ miniemulsion polymerization by taking full advantage of phase separation between inorganic component and the growing polymer. Inspired by these interesting and valuable results, we investigated the feasibility of fabrication of nanocomposite microspheres with nanosilica distributing homogeneously throughout the polymer microspheres. Herein we report a novel and flexible technique to fabricate raspberry-like silica/polystyrene microspheres via interfacial initiated miniemulsion polymerization. The nanocompostite microspheres were fabricated via double in situ miniemulsion polymerization by taking full advantage of phase separation between inorganic component and the growing polymer. Nanosilica particles are formed throughout the polymer microspheres. This method can be expected to produce large quantity of submicrometer sized nanocomposite microspheres with high silica content towards biomimetic nanocomposites.

Facile Fabrication of Hybrid Hollow Microspheres via in Situ Pickering Miniemulsion Polymerization

Abstract Hybrid hollow microspheres have been fabricated successfully via miniemulsion polymerization using the in situ formed and modified nanosilica particles as Pickering emulsifier. The hydrolysis and condensation reactions of tetraethoxysilane (TEOS) take place to form nanosilica particles which are then partially modified by oil-soluble 3-(trimethoxysilyl)propyl methacrylate (MPS) at the oil/water interface under basic conditions. After the miniemulsification process, Pickering miniemulsions were stabilized by the in situ nanosilica particles. Hybrid hollow microspheres are obtained with silica nanoparticles closely packed on the surface of polymer microspheres. The results showed that both the weight ratios of TEOS/styrene and MPS/TEOS have great effects on the production of stable Pickering emulsion and then the morphologies of the obtained hybrid microspheres.

Locating carbon nanotubes (CNTs) at the surface of polymer microspheres using poly(vinyl alcohol) grafted CNTs as dispersion co-stabilizers

In this communication, we prepared carbon nanotubes (CNTs) modified by poly(vinyl alcohol) that are used as co-stabilizers for the dispersion polymerization of methyl methacrylate. Poly(methyl methacrylate) microspheres with CNTs selectively located at their surface are formed. This specific localization is a way to enhance the electrical conductivity of the nanocomposite.

A Simple Route for Formation of Continuous Ni Nanoshells on Polymer Microspheres

Abstract Continuous Ni nanoshells of 1.2 nm-thick were successfully fabricated on polymer microspheres via a simple one-step process. The preferential coating of Ni on the surface of polymer microspheres was attributed to the use of ethylene glycol as a solvent and appropriate reaction temperature.

A new approach to hybrid nanocomposite materials with periodic structures.

Hybrid core-shell polymer-semiconductor or polymer-metal microspheres were used in the "bottom-top" approach to production of nanocomposite materials with periodic structures. In the first step CdS and Ag nanocrystals were synthesized in situ on the surface of polymer microspheres using ion exchange between the counter ions in the electrical double layer of latex beads and ions in the liquid medium. In the second step a low-Tg polymeric shell was synthesized on the surface of hybrid particles, which upon annealing of the periodic array of three-layer microbeads formed a matrix. The proposed strategy employing hybrid microspheres as the functional structural blocks shows a new way to produce optically responsive materials with periodicity commensurable with the wavelength of light, an intrinsic property of photonic crystals.

Capacitance–voltage property of composite microsphere monolayer with polymer/Fe 2O 3/ polymer structure

Inorganic nanoparticles Fe 2O 3 3–5 nm in diameter were assembled on the surface of polymer microspheres and then encapsulated in the polymer to form a trilayer composite structure. The capacitance–voltage ( C– V) curve of the composite microsphere monolayer shows the presence of a plateau. The electron transportation process in the special structure was investigated combining with the energy band model. The results show that Fe 2O 3 layer acts as a charge trap between polymer layers which are regarded as potential barriers.