Tunable distribution of silica nanoparticles in water-borne coatings via strawberry supracolloidal dispersions

HYPOTHESIS

Water-borne coatings are rapidly expanding as sustainable alternatives to organic solvent-borne systems. Inorganic colloids are often added to aqueous polymer dispersions to enhance the performance of water-borne coatings. However, these bimodal dispersions have many interfaces which can result in unstable colloids and undesirable phase separation. The covalent bonding between individual colloids, on a polymer-inorganic core-corona supracolloidal assembly, could reduce or suppress instability and phase separation during drying of coatings, advancing its mechanical and optical properties.

METHODS

Aqueous polymer-silica supracolloids with a core-corona strawberry configuration were used to precisely control the silica nanoparticles distribution within the coating. The interaction between polymer and silica particles was fine-tuned to obtain covalently bound or physically adsorbed supracolloids. Coatings were prepared by drying the supracolloidal dispersions at room temperature, and their morphology and mechanical properties were interconnected.

FINDINGS

Covalently bound supracolloids provided transparent coatings with a homogeneous 3D percolating silica nanonetwork. Supracolloids having physical adsorption only, resulted in coatings with a stratified silica layer at interfaces. The well-arranged silica nanonetworks strongly improve the storage moduli and water resistance of the coatings. These supracolloidal dispersions offer a new paradigm for preparing water-borne coatings with enhanced mechanical properties and other functionalities, like structural color.

Emerging trends in the delivery of nanoformulated oxytocin across Blood-Brain barrier

Neurological diseases are related to the central nervous system disorders and considered as serious cases. Several drugs are used to treat neurological diseases; however, to date the main issue is to design a therapeutic model which can cross the blood-brain-barrier (BBB) easily. The delivery of neuropeptides into the brain lays as one of the important routes for treating neurological disorders. Neuropeptides have been demonstrated as potential therapeutics for neurological disorders. Among numerous neuropeptides, the oxytocin (OT) hormone is of particular interest as it serves as a neurotransmitter in the brain as well as its role as a hormone. OT has a wide-range of activities in the brain and has a key role in cognitive, neuroendocrine, and social functions. However, OT does not cross the BBB readily coupled with its half-life in the blood being too short. The current literature reveals that the delivery of OT by nanoparticle-based drug delivery system (DDS) improves its efficacy. Nanoparticle based DDS are considered important tools for the targeted delivery of drugs to the brain as they lower toxicity of the drug and improve the drug efficacy. Nanoparticles are advantageous candidates for biomedical applications due to their distinctive characteristics such as quantum effects, large surface area and their ability to carry and transport the drug to its target site. OT can be delivered through oral and intranasal routes, but the bioavailability of OT inside the brain can further be enhanced by the delivery using nanoparticles. The application of nano-based delivery system not only improves the penetration of OT inside brain but also increases its half-life by the application of encapsulation and extended release. The aim of current review is to provide an overview of nanoparticle-based drug-delivery systems for the delivery of OT inside brain.

An extensive case study on the dispersion parameters of HI-assisted reduced graphene oxide and its graphene oxide precursor

The formation of highly concentrated and stable graphene derivatives dispersions remains a challenge towards their exploitation in various applications, including flexible optoelectronics, photovoltaics, 3D-printing, and biomedicine. Here, we demonstrate our extensive investigation on the dispersibility of graphene oxide (GO) and reduced graphene oxide (RGO) in 25 different solvents, without the use of any surfactant or stabilizer. Although there is a significant amount of work covering the general field, this is the first report on the dispersibility of: a) RGO prepared by a HI/AcOH assisted reduction process, the method which yields RGO of higher graphitization degree than the other well-known reductants met in the literature, b) both GO and RGO, explored in such a great range of solvents, with some of them not previously reported. In addition, through calculation of their Hansen Solubility Parameters (HSP), we confirmed their dispersibility behavior in each solvent, while we indirectly validated the most advanced graphitization degree of the studied RGO compared to other reported RGOs, since its HSPs exhibit the highest similarity with the respective ones of pure graphene. Finally, high concentrations of up to 189 μg mL^-1 for GO and ~ 87.5 μg mL^-1 for RGO were achieved, in deionized water and o-Dichlorobenzene respectively, followed by flakes size distribution and polydispersity indices estimation, through dynamic light scattering as a quality control of the effect of a solvent's nature on the dispersion behavior of these graphene-based materials.

High-concentration graphene dispersion stabilized by block copolymers in ethanol

This article describes a comprehensive study for the preparation of graphene dispersions by liquid-phase exfoliation using amphiphilic diblock copolymers; poly(ethylene oxide)-block-poly(styrene) (PEO-b-PS), poly(ethylene oxide)-block-poly(4-vinylpyridine) (PEO-b-PVP), and poly(ethylene oxide)-block-poly(pyrenemethyl methacrylate) (PEO-b-PPy) with similar block lengths. Block copolymers were prepared from PEO using the Steglich coupling reaction followed by reversible addition-fragmentation chain transfer (RAFT) polymerization. Graphite platelets (G) and reduced graphene oxide (rGO) were used as graphene sources. The dispersion stability of graphene in ethanol was comparatively investigated by on-line turbidity, and the graphene concentration in the dispersions was determined gravimetrically. Our results revealed that the graphene dispersions with PEO-b-PVP were much more stable and included graphene with fewer defects than that with PEO-b-PS or PEO-b-PPy, as confirmed by turbidity and Raman analyses. Gravimetry confirmed that graphene concentrations up to 1.7 and 1.8mg/mL could be obtained from G and rGO dispersions, respectively, using PEO-b-PVP after one week. Distinctions in adhesion forces of PS, VP, PPy block units with graphene surface and the variation in solubility of the block copolymers in ethanol medium significantly affected the stability of the graphene dispersion.

Production and Biotransformation of Phytosterol Microdispersions to Produce 4-Androstene-3,17-Dione

The current state of knowledge regarding phytosterols biotransformation to produce the steroid intermediate 4-androstene-3,17-dione (AD) shows different technologies. However, the initial concentration of phytosterols in batch cultures is limited due to its low solubility in aqueous media, causing serious difficulties for scaling up because of the low mass transfer. In this chapter, we describe a fermentation method of a phytosterol microdispersion with Mycobacterium sp. B3805 in the context of an integral technology for AD production. The microdispersion generation is based on a patent application that claims the production of an aqueous phytosterol microdispersion with an average size particle of 370 nm, and high stability and solubility in water at high phytosterols concentrations (Harting et al., 2012/US0046254). Our results indicate that up to 20 g/L phytosterols can be biotransformed with this technology allowing a good dispersion and stability of reactants in the fermentation broth.

Effect of low frequency ultrasound on the surface properties of natural aluminosilicates

Structural and surface properties of different natural aluminosilicates (layered, chain and framework structural types) exposed of 20 kHz ultrasound irradiation (0-120 min) in aqueous and 35 wt%. aqueous H2O2 dispersions were studied by X-ray diffraction (XRD), dynamic light scattering (DLS), nitrogen adsorption-desorption, thermal analysis, and Fourier transform infrared spectroscopy (FTIR) techniques. It was confirmed that sonication caused slight changes in the structure of investigated minerals whereas their textural properties were significantly affected. The aqueous dispersions of montmorillonite (Mt), clinoptilolite (Zlt), glauconite (Glt) and palygorskite (Pal) were represented by several particles size fractions according to DLS-study. Ultrasound irradiation produced a decrease of the average particle diameter by 4-6 times in water and by 1.3-5 times in H2O2 dispersions except for Pal, which underwent strong agglomeration. A significant increase of total pore volume and pore diameter was observed for Glt sonicated in H2O2 dispersions whereas for Pal mainly micropore volume sharply increased in both aqueous and H2O2 dispersions.

PVP-b-PEO block copolymers for stable aqueous and ethanolic graphene dispersions

The ability to disperse pristine (unfunctionalized) graphene is important for various applications, coating, nanocomposites, and energy related systems. Herein we report that amphiphilic copolymers of poly(4-vinyl pyridine)-block-poly(ethylene oxide) (PVP-b-PEO) are able to disperse graphene with high concentrations about 2.6mg/mL via sonication and centrifugation. Ethanolic and aqueous highly-ordered pyrolytic graphite (HOPG) dispersions with block copolymers were prepared and they were compared with the dispersions stabilized by P-123 Pluronic® (P123) and poly(styrene)-block-poly(ethylene oxide) (PS-b-PEO) synthesized. Transmission electron microscopy, scanning electron microscopy, atomic force microscopy, X-ray diffraction, Raman and UV-visible spectroscopic studies confirmed that PVP-b-PEO block copolymers are better stabilizers for HOPG graphene than P123 and PS-b-PEO. X-ray photoelectron spectroscopy and force-distance (F-d) curve analyses revealed that the nitrogen of vinyl pyridine plays a vital role in better attractive interaction with surface of graphene sheet. Thermogravimetric analysis showed that larger amount of PVP-b-PEO was adsorbed onto graphene with longer poly(4-vinyl pyridine) (PVP) block length and in aqueous medium, respectively, and which was consistent with electrical conductivity decreases. This study presents the dispersion efficiency of graphene using PVP-b-PEO varies substantially depending on the lengths of their hydrophobic (PVP) domains.

Biodegradation of dispersed Macondo oil in seawater at low temperature and different oil droplet sizes

During the Deepwater Horizon (DWH) accident in 2010 a dispersant (Corexit 9500) was applied at the wellhead to disperse the Macondo oil and reduce the formation of surface slicks. A subsurface plume of small oil droplets was generated near the leaking well at 900-1300 m depth. A novel laboratory system was established to investigate biodegradation of small droplet oil dispersions (10 μm or 30 μm droplet sizes) of the Macondo oil premixed with Corexit 9500, using coastal Norwegian seawater at a temperature similar to the DWH plume (4-5°C). Biotransformation of volatile and semivolatile hydrocarbons and oil compound groups was generally faster in the 10 μm than in the 30 μm dispersions, showing the importance of oil droplet size for biodegradation. These data therefore indicated that dispersant treatment to reduce the oil droplet size may increase the biodegradation rates of oil compounds in the deepwater oil droplets.