Yanhui Huang

Core-shell structured hyperbranched aromatic polyamide/BaTiO3 hybrid filler for poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) nanocomposites with the dielectric constant comparable to that of percolative composites.

Polymer nanocomposites with the dielectric constant comparable to that of percolative composites are successfully prepared by using core-shell structured hyperbranched aromatic polyamide grafted barium titanate (BT-HBP) hybrid nanofiller. Poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) (PVDF-TrFE-CFE) was used as the polymer matrix because of its high intrinsic dielectric constant and easy processability. The BT-HBP hybrid nanofiller were prepared by a solution polymerization of diaminobenzoic acid on the surface of amino-funcationalized BT nanoparticles. Nuclear magnetic resonance ((1)H NMR) and transmission electron microscopy (TEM) were used to verify the chemical structure of the hyperbranched aromatic polyamide and core-shell structure of the hybrid filler, respectively. It was found that the nanocomposite with 40 vol % BaTiO3-HBP had a dielectric constant of 1485.5 at 1000 Hz, whereas the corresponding nanocomposite sample with untreated BaTiO3 only showed a dielectric constant of 206.3. Compared with classic percolative composites, the advantage of the PVDF-TrFE-CFE/BaTiO3-HBP nanocomposites is that the composites show high enough breakdown strength and high dielectric constant simultaneously. An enhanced interfacial polarization mechanism between the BT-HBP and the polymer matrix was suggested for understanding the observed unusually high dielectric constant.

Core@Double-Shell Structured Nanocomposites: A Route to High Dielectric Constant and Low Loss Material

This work reports the advances of utilizing a core@double-shell nanostructure to enhance the electrical energy storage capability and suppress the dielectric loss of polymer nanocomposites. Two types of core@double-shell barium titanate (BaTiO3) matrix-free nanocomposites were prepared using a surface initiated atom transfer radical polymerization (ATRP) method to graft a poly(2-hydroxylethyle methacrylate)-block-poly(methyl methacrylate) and sodium polyacrylate-block-poly(2-hydroxylethyle methacrylate) block copolymer from BaTiO3 nanoparticles. The inner shell polymer is chosen to have either high dielectric constant or high electrical conductivity to provide large polarization, while the encapsulating outer shell polymer is chosen to be more insulating as to maintain a large resistivity and low loss. Finite element modeling was conducted to investigate the dielectric properties of the fabricated nanocomposites and the relaxation behavior of the grafted polymer. It demonstrates that confinement of the more conductive (lossy) phase in this multishell nanostructure is the key to achieving a high dielectric constant and maintaining a low loss. This promising multishell strategy could be generalized to a variety of polymers to develop novel nanocomposites.

Toward the development of a quantitative tool for predicting dispersion of nanocomposites under non-equilibrium processing conditions

Developing process-structure relationships that predict the impact of the filler-matrix interfacial thermodynamics is crucial to nanocomposite design. This work focuses on developing quantitative relationships between the filler-matrix interfacial energy, the processing conditions, and the nanoparticle dispersion in polymer nanocomposites. We use a database of nanocomposites made of polypropylene, polystyrene, and poly(methyl methacrylate) with three different surface-modified silica nanoparticles under controlled processing conditions. The silica surface was modified with three different monofunctional silanes: octyldimethylmethoxysilane, chloropropyldimethylethoxysilane, and aminopropyldimethylethoxysilane. Three descriptors were used to establish the relationship between interfacial energy, processing conditions, and final nanoparticle dispersion. The ratio of the work of adhesion between filler and polymer to the work of adhesion between filler to filler (descriptor:

Enhanced charge trapping in bimodal brush functionalized silica-epoxy nanocomposite dielectrics

W_{\text{PF}} /W_{\text{FF}}

Free volume in nanodielectrics

WPF/WFF) and the mixing energy for the production of the nanocomposites (descriptor: Eγ) are used to determine the final dispersion state of the nanoparticles. The dispersion state is described using a descriptor that characterizes the amount of interfacial area from TEM images (descriptor:

Predicting the breakdown strength and lifetime of nanocomposites using a multi-scale modeling approach

\bar{I}_{\text{filler}}