Polystyrene-grafted Silica Nanoparticles Research Articles

Meso–Microscale Study of Glycerol/Dodecanol Pickering Emulsions Stabilized by Polystyrene-Grafted Silica Nanoparticles for Interfacial Catalysis

In this study, we report a combined meso–microscale computational study of Pickering emulsions stabilized by sulfonated polystyrene-grafted silica nanoparticles for the glycerol/dodecanol system using dissipative particle dynamics. Different glycerol/dodecanol emulsification regimes could be ascertained as a function of the length of polystyrene brushes as well as the surface density, sulfonation degree, and distribution of sulfonic acid groups in the brushes, matching experimental results. Local nanomixing effects between glycerol and dodecanol could be clearly identified in the vicinity of the catalytic sulfonic acid groups, unraveling potential reactivity zones for etherification.

Polystyrene-Grafted Silica Nanoparticles: Investigating the Molecular Weight Dependence of Glass Transition and Fragility Behavior

Polymer-tethered nanoparticles provide a strategy to improve particle dispersion in polymer nanocomposites and as materials themselves can exhibit self-healing behavior and enhanced mechanical properties. The few studies that previously characterized the glass transition temperature (Tg) behavior of neat polymer-grafted nanoparticles in the absence of a polymer matrix largely focused on average Tg response. We synthesized polystyrene-grafted silica nanoparticles (Si-PS) via ARGET ATRP, achieving the densely grafted state. Using differential scanning calorimetry, we investigated the brush molecular weight (MW) dependence of Tg, Tg breadth, heat capacity jump (ΔCp), and fragility from 12 to 98 kg/mol. Compared with free PS chains of the same MW, brush Tg increases by 1–2 °C, brush Tg breadth remains unchanged within error down to 36 kg/mol and increases by 3–4 °C at brush MWs of 12 and 13 kg/mol, and brush ΔCp and fragility remain unchanged within error down to 52 kg/mol and then decrease with decreasing MW...

Dynamical crossover between hyperdiffusion and subdiffusion of polymer-grafted nanoparticles in a polymer matrix

The dynamical behavior of polystyrene-grafted silica nanoparticles dispersed in an atactic polystyrene matrix was studied using x-ray photon correlation spectroscopy. The time-autocorrelation functions were subjected to fitting analyses based on continuous-time random walk models. The nanoparticles exhibited non-Brownian behavior, and as the temperature increased, the crossover from hyperdiffusion to subdiffusion occurred at 1.25T_{g}, where T_{g} is the glass transition temperature of the matrix polystyrene. Hyperdiffusive behavior is caused by the dynamical heterogeneity of the polymer matrix associated with the glass transition. When the temperature was higher than 1.25T_{g}, the interaction of the grafted polymers with the polymer matrix became relatively significant, and caused a dramatic change in the dynamical behavior of the nanoparticles.

Polymeric nanocapsules with controllable crosslinking degree via combination of surface‐initiated atom transfer radical polymerisation and photocrosslinking techniques

The crosslinked polystyrene nanocapsules with controllable crosslinking degree have been prepared by the ultraviolet (UV)-induced photocrosslinking of the polystyrene grafted silica nanoparticles (SN-PS), which was obtained by the surface-initiated atom transfer radical polymerisation of styrene from the modified silica nanoparticle templates, after the silica templates were etched with hydrofluoric acid. The effect of the UV-irradiating time on the inner diameter of the nanocapsules, and the degree of crosslinking and the thickness of the shells was investigated. The dynamic light scattering results showed that the degree of crosslinking of the obtained nanocapsules increased with the prolongation of the UV-irradiation time, therefore the inner diameter of the nanocapsules increased. However, the percentage of grafting of the crosslinked polymer shells decreased with increasing the UV-irradiation time because of the photodecomposition of the polystyrene grafted during the UV-irradiated crosslinking process, according to the thermogravimetric analysis.

Enhancing the fraction of grafted polystyrene on silica hybrid nanoparticles

Polymer-grafted inorganic nanoparticles are being developed for a diverse array of applications, ranging from drug delivery to multifunctional composites. In many instances, performance of these core-shell hybrids is limited by relatively broad distributions of size and composition, as well as the presence of impurities, such as unattached polymer chains. Herein, further synthetic improvements, and associated characterization techniques, to enhance the fraction of the grafted polystyrene shell on silica hybrid nanoparticles are discussed. We found that during surface-initiated atom transfer radical polymerization (SI-ATRP) from the silica nanoparticles, thermal self-initiation of styrene produces unattached polymer chains. Size exclusion chromatography afforded a facile approach to quantify the mass of the unattached polymer, and provide a substantial refinement to estimates of chain graft density beyond traditionally-used approaches, such as thermogravimetry. This fraction of unattached polymer is still present even after post-polymerization work-up via precipitation and re-dissolution. Removal necessitates additional procedures, such as high speed centrifugation. Selection of a lower polymerization temperature, in concert with a more reactive Cu complex, significantly reduces the amount of unattached polystyrene impurity. The improved polymerization conditions and post-polymerization purification provide more refined polystyrene-grafted silica nanoparticles to clarify structure-property relationships of these core-shell hybrids.

Controlled grafting of polystyrene on silicananoparticles using NMP: a new route without free initiator to tune the grafted chain length

We synthesized well-defined polystyrene-grafted silica nanoparticles by adapting our previous synthesis process without using free initiator. We were able to obtain a more versatile system in which we can tune the masses of the grafted chains while controlling the polymerization, the colloidal stability and avoid the formation of free polymer chains. The final grafted objects were characterized in a refined way using SANS and the contrast matching method.

Facile Preparation of Crosslinked Polymeric Nanocapsules via Combination of Surface-Initiated Atom Transfer Radical Polymerization and Ultraviolet Irradiated Crosslinking Techniques

A facile approach for the preparation of crosslinked polymeric nanocapsules was developed by the combination of the surface-initiated atom transfer radical polymerization and ultraviolet irradiation crosslinking techniques. The well-defined polystyrene grafted silica nanoparticles were prepared via the SI-ATRP of styrene from functionalized silica nanoparticles. Then the grafted polystyrene chains were crosslinked with ultraviolet irradiation. The cross-linked polystyrene nanocapsules with diameter of 20–50 nm were achieved after the etching of the silica nanoparticle templates with hydrofluoric acid. The strategy developed was confirmed with Fourier transform infrared, thermogravimetric analysis, and transmission electron microscopy.

Self-Assembly of Poly(9,9‘-dihexylfluorene) to Form Highly Ordered Isoporous Films via Blending

Highly ordered hexagonal arrays of isoporous films prepared from poly(9,9'-dihexylfluorene) and polystyrene-grafted silica nanoparticles (Si-graft-PS) are presented. These close-packed arrays were formed in areas of many square millimeters. The pore size varied from 3.6 to 8.5 microm, depending on the concentration of Si-graft-PS and the processing conditions. Solid-state photoluminescence resulted in a significant red shift of up to 30 nm in these films compared to that in conventional processing techniques. These differences are attributed to enhanced aggregation of the polymers caused by polymer-solvent interactions. These highly ordered polymer films may find use in microelectronic and biological and/or chemical sensor applications.

Preparation of Comb‐like Styrene Grafted Silica Nanoparticles

Comb‐like polystyrene grafted silica nanoparticles (c‐PS‐SNs) were prepared by the following steps: (a) methacryloxypropyl silica nanoparticles (MPSNs) were used as macromonomer and free radical copolymerized with 4‐vinyl benzyl chloride (VBC) by a solution polymerization method; (b) the product of (A), poly(4‐vinyl benzyl chloride) grafted silica nanoparticle (PVBC‐SN) was separated and then used as a macroinitiator for the surface‐initiated atom transfer radical polymerization (SI‐ATRP) of styrene catalyzed by the complex of Cu(I)Br and 2,2′‐bipyridyl (bipy) in toluene solutions. The structurally well‐defined polymer chains were grown from the nanoparticle surfaces to yield particles composed of a silica core and a well defined, densely grafted outer comb‐like PS layer. A percentage of grafting (PG%) (the weight ratio of the PS grafted with that of the silica charged) of more than 80% was achieved after a polymerizing time of 5 hr.

Preparation of polystyrene grafted silica nanoparticles by two-steps UV induced reaction

Polystyrene grafted silica nanoparticles (PSSNs) were prepared by the followed two steps: methacryloxypropyl silica nanoparticles (MPSNs) were modified with the monomer-iniferter, 4-vinylbenzyl N, N-diethyldithiocarbamate (VBDC) under UV irradiation. Then the VBDC modified silica nanoparticles (VBDCSNs) were used as iniferter for the surface-initiated (SI) controlled/“living” radical polymerization of styrene. A percentage of grafting (PG%) of 315.7% was achieved with a conversion of styrene of about 35% after 18 h UV irradiation.

In situ radical transfer addition polymerization of styrene from silica nanoparticles

The in situ radical transfer addition polymerization of styrene from silica nanoparticles was carried out by the free radical polymerized of styrene in the presence of mercaptopropyl-modified silica nanoparticles as chain-transfer agent. The effects of the amount of the initiator, polymerizing temperature and polymerizing time on the convention of styrene (C) and the percentage of grafting were investigated. Results of elemental analysis, IR, X-ray photoelectron spectrometer and transmission electron microscope demonstrated that the desired polymer chains have been covalently bonded to the surface of the silica nanoparticles. A C of 42.56% and a PG of 38.10% could be achieved with the optimal condition. The polystyrene grafted silica nanoparticles could be separated and used as nanofiller for polymers.