New Brush Copolymers as an Effective Dispersant for Stabilizing Concentrated Suspensions of Silver Nanoparticles.

Silver nanopowders (nano-Ag) have extremely high surface energy and are generally difficult to have an effective dispersant for their dispersion stabilization. This study proposes two brush copolymers that show a strong preference for adsorption on the nano-Ag surface via their backbone, while their side chains extend into the dispersion solvent for particle stabilization. After adding only 5 wt % (based on the mass of nano-Ag) of the proposed dispersants, the nano-Ag particles can be stably suspended without settling for at least 2 months. Besides, 5 wt % of these dispersants can well stabilize at least 40 wt % nano-Ag dispersed in di(ethylene glycol) ethyl ether, which is a common solvent for conductive inks and pastes. For applications, a thin film cast using the dispersed nano-Ag shows greatly improved surface flatness as compared to that made without the dispersant, and a low electrical resistivity of 2 × 10-5 Ω cm is obtained after the film is annealed at 170 °C for 20 min.

New Approach for the Synthesis of Nanozirconia Fortified Microcapsules.

Robust poly(urea-formaldehyde) (PUF) microcapsules with composite shells comprising zirconia (ZrO2) nanopowder incorporated in PUF were fabricated via a novel and facile one-pot synthesis. ZrO2 nanopowder was chosen because it owns one of the highest mechanical strengths among ceramics. The nanopowder was predispersed in the core material to combine encapsulation and fortification into a single process. In the core, the well-dispersed nanopowder migrated to the interface, where PUF polymerization took place. The mechanical strength of the microcapsule with nano-ZrO2 incorporated in the shell (42% by weight) is three times greater than that of the microcapsule without ZrO2. In a preliminary application wherein the microcapsules were embedded in a model of poly(vinyl alcohol) (PVA) membrane, the PVA specimen exhibited a higher ultimate tensile strength when fortified microcapsules were embedded than when unfortified microcapsules were used.

Preparation of highly dispersed and concentrated aqueous suspensions of nanodiamonds using novel diblock dispersants.

HYPOTHESIS: Finding an efficient dispersant for obtaining a good dispersion of 5-nm detonation nanodiamond (DND) is always a challenge. Two newly designed diblock copolymers, both poly(ammonium methacrylate)-block-poly(2-phenoxyethyl acrylate) (PMA-b-PBEA) but with different molar ratios of PMA to PBEA, were proposed to be efficient dispersants in stabilizing the concentrated aqueous suspensions of DND. EXPERIMENTS: The dispersion efficiency of dispersants for DND in aqueous suspensions was studied by the measurements of particle size, sedimentation property, and rheological behavior. The interactions between the added dispersants and DND were identified by the zeta potential and adsorption analyses. Calculations based on Derjaguin-Landau-Verwey-Overbeek (DLVO) theory were conducted for clarifying the dominant parameters relating to the dispersion efficiency of dispersants. FINDINGS: Compared with the commercially popular dispersant ammonium polyacrylate, these two diblock dispersants exhibited superior efficiency in the stabilization of DND suspensions. Using the diblock copolymers as dispersants, good dispersion stability in a DND suspension with an extremely high solid content of 30 wt% was achieved. According to experimental analyses and based on DLVO calculations, a low number of accompanied counter-ions, high adsorption capability, and thick PMA-b-PBEA adsorption layer are the main reasons for the extremely high dispersion efficiency of the two new dispersants.

Newly designed diblock dispersant for powder stabilization in water-based suspensions.

A newly designed dispersant for water-based suspensions, ammonium poly(methacrylate)-block-poly(2-phenoxyethyl acrylate) (PMA-b-PBEA), is proposed in this study. According to the results of rheological analysis, the dispersion efficiency of this new dispersant is superior to that of the commercially available ammonium polyacrylate (PAA-NH4). The diblock structure of PMA-b-PBEA, which simultaneously contains a low-polar anchoring head group and a water-dissociable stabilizing moiety, is the main cause for its extremely high efficiency for powder dispersion. The unique structure not only results in effective adsorption approximately double that of PAA-NH4, but also produces a low number of counter-ions that compress the electrical double layer and ruin powder stabilization. Based on Derjaquin-Landau-Verwey-Overbeek calculations, the large adsorbance of PMA-b-PBEA gives the powder, titania (TiO2) in this study, a high steric stabilization energy. In addition, PMA-b-PBEA provides TiO2 with a remarkably high electrostatic energy because it generates fewer counter-ions. This energy provides excellent dispersity of powder in the suspensions with a high solid content of 60wt% without showing any rheological hysteresis.

Hansen solubility parameter analysis on the dispersion of zirconia nanocrystals.

Nanoparticle dispersible in a broad range of solvents is desirable when preparing an organic/inorganic nanocomposite. In this report, the dispersion behavior of carboxylate-grafted zirconia nanoparticle in 25 solvents covering a wide range of polarity was analyzed based on their Hansen solubility parameters (HSP). Particles grafted with alkyl-chain longer than four carbons could only be dispersed in non-polar solvents, while that grafted with acetic acid was dispersible in polar ones. However, particle modified with methacrylic acid (MA) was compatible with both types of solvents, which was rather unexpected. Further NMR analysis showed that the carboxylate-grafted samples contained a trace amount of triethanolamine (TEA) due to the particular ZrO2 synthesis process employed. The combination of the hydrophilic TEA ligand with the short hydrophobic tail of methacrylate broadened the range of compatible solvents from benzene to methanol. Such an extended solvent compatibility was observed previously only for nanoparticles covered with large polymer surfactants having both hydrophilic and hydrophobic groups. Achieving this with two small molecules having separate functional groups is crucial when one needs to maximize the inorganic content in a composite.

Decoration of multi-walled carbon nanotubes by polymer wrapping and its application in MWCNT/polyethylene composites.

We dispersed the non-covalent functionalization of multi-walled carbon nanotubes (CNTs) with a polymer dispersant and obtained a powder of polymer-wrapped CNTs. The UV-vis absorption spectrum was used to investigate the optimal weight ratio of the CNTs and polymer dispersant. The powder of polymer-wrapped CNTs had improved the drawbacks of CNTs of being lightweight and difficult to process, and it can re-disperse in a solvent. Then, we blended the polymer-wrapped CNTs and polyethylene (PE) by melt-mixing and produced a conductive masterbatch and CNT/PE composites. The polymer-wrapped CNTs showed lower surface resistivity in composites than the raw CNTs. The scanning electron microscopy images also showed that the polymer-wrapped CNTs can disperse well in composites than the raw CNTs.

An efficient approach to derive hydroxyl groups on the surface of barium titanate nanoparticles to improve its chemical modification ability.

Highly hydroxylated barium titanate (BaTiO(3)) nanoparticles have been prepared via an easy and gentle approach which oxidizes BaTiO(3) nanoparticles using an aqueous solution of hydrogen peroxide (H(2)O(2)). The hydroxylated BaTiO(3) surface reacts with sodium oleate (SOA) to form oleophilic layers that greatly enhance the dispersion of BaTiO(3) nanoparticles in organic solvents such as tetrahydrofuran, toluene, and n-octane. The results of Fourier transform infrared spectroscopy confirmed that the major functional groups on the surface of H(2)O(2)-treated BaTiO(3) nanoparticles are hydroxyl groups which are chemically active, favoring chemical bonding with SOA. The results of transmission electron microscopy of SOA-modified BaTiO(3) nanoparticles suggested that the oleate molecules were bonded to the surfaces of nanoparticles and formed a homogeneous layer having a thickness of about 2 nm. Furthermore, the improved dispersion capability of the modified BaTiO(3) nanoparticles in organic solvents was verified through analytic results of its settling and rheological behaviors.

Synthesis of acrylic copolymers consisting of multiple amine pendants for dispersing pigment.

A class of acrylic copolymers with narrow molecular weight distribution from butyl methacrylate and glycidyl methacrylate comonomers via atom transfer radical polymerization was synthesized. Various types of polarities including hydroxyl-amines, glycols, and carboxylic acids were then grafted onto the oxirane side groups. The resultant comb-like copolymers with different polar pendants were tested for homogenizing a representative Yellow pigment in 1,6-hexanediol diacrylate medium. Specifically, the polyacrylates with 1,3-diamine pendants (7-10 multiplicity on each polymer strain) enabled to homogeneously disperse the pigment than the analogous copolymers with hydroxyl or carboxylic acid groups. Ultimately, the pigment dispersion with an average size of ca. 20 nm in diameter, high transmittance and low viscosity was achieved. Furthermore, the pigment dispersion was allowed to UV-cure into a film, and for the first time, the primary structures of the pigment particles (ca. 50 nm in diameter) were observed by transmission electronic microscope.