The effects of confinement on glass transition temperature (Tg) and physical aging are measured in polystyrene (PS), poly(methyl methacrylate) (PMMA), and poly(2-vinyl pyridine) (P2VP) nanocomposites containing 10- to 15-nm-diameter silica nanospheres or 47-nm-diameter alumina nanospheres. Nanocomposites are made by spin coating films from sonicated solutions of polymer, nanofiller, and dye. The Tgs and physical aging rates are measured by fluorescence of trace levels of dye in the films. At 0.1–10 vol % nanofiller, Tg values can be enhanced or depressed relative to neat, bulk Tg (Tg,bulk) or invariant with nanofiller content. For alumina nanocomposites, Tg increases relative to Tg,bulk by as much as 16 K in P2VP, decreases by as much as 5 K in PMMA, and is invariant in PS. By analogy with thin polymer films, these results are explained by wetted P2VP–nanofiller interfaces with attractive interactions, nonwetted PMMA–nanofiller interfaces (free space at the interface), and wetted PS–nanofiller interfaces lacking attractive interactions, respectively. The presence of wetted or nonwetted interfaces is controlled by choice of solvent. For example, 0.1–0.6 vol % silica/PMMA nanocomposites exhibit Tg enhancements as large as 5 K or Tg reductions as large as 17 K relative to Tg,bulk when films are made from methyl ethyl ketone or acetic acid solutions, respectively. A factor of 17 reduction of physical aging rate relative to that of neat, bulk P2VP is demonstrated in a 4 vol % alumina/P2VP nanocomposite. This suggests that a strategy for achieving nonequilibrium, glassy polymeric systems that are stable or nearly stable to physical aging is to incorporate well-dispersed nanoparticles possessing attractive interfacial interactions with the polymer. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2935–2943, 2006

http://absimage.aps.org/image/MAR06/MWS_MAR06-2005-001949.pdf

Polymer-Nanoparticle Interfacial Interactions in Polymer Nanocomposites: Confinement Effects on Glass Transition Temperature and Suppression of Physical Aging.

Functionalized glass fibers cloth/spherical BN fillers/epoxy laminated composites with excellent thermal conductivities and electrical insulation properties

Magnolol-based bio-epoxy resin with acceptable glass transition temperature, processability and flame retardancy

Glass fibers (GFs)/epoxy laminated composites always present weak interlaminar shear strength (ILSS) and low cross-plane thermal conductivity coefficient (λ⊥). In this work, silica-sol, synthesized from tetraethyl orthosilicate (TEOS) and KH-560 via sol-gel method, was employed to functionalize the surface of GFs (Si-GFs). Together with a spherical boron nitride (BNN-30), the thermally conductive BNN-30/Si-GFs/epoxy laminated composites were then fabricated. Results demonstrate that Si-sol is beneficial to the improvement of mechanical properties for epoxy laminated composites (especially for ILSS). The BNN-30/Si-GFs/epoxy laminated composites with 15 wt% BNN-30 fillers display the optimal comprehensive properties. In-plane λ(λ//) and λ⊥ reach the maximum of 2.37 and 1.07 W·m−1·K−1, 146.9% and 132.6% higher than those of Si-GFs/epoxy laminated composites (λ// = 0.96 W·m−1·K−1 and λ⊥ = 0.46 W·m−1·K−1), respectively, and also about 10.8 and 4.9 times those of pure epoxy resin (λ// = λ⊥ 0.22 W·m−1·K−1). And the heat-resistance index (THRI), dielectric constant (e), dielectric loss (tanδ), breakdown strength (E0), surface resistivity (ρs) as well as volume resistivity (ρv) are 197.3 °C, 4.95, 0.0046, 22.3 kV·mm−1, 1.8 × 1014Ω, and 2.1 × 1014Ω·cm, respectively.

Thermally Conductive and Insulating Epoxy Composites by Synchronously Incorporating Si-sol Functionalized Glass Fibers and Boron Nitride Fillers

With the trend of device miniaturization and higher integration, polymer composites with high thermal conductivity are highly desirable for efficient removal of accumulated heat to maintain high performance of electronics. In this work, epoxy composites embedded with three-dimensional hexagonal boron nitride (BN) scaffold were fabricated. The BN-poly(vinylidene difluoride) (PVDF) scaffold was prepared by the salt template method using PVDF as the adhesive, while the corresponding epoxy composite was manufactured with vacuum-assisted impregnation. The epoxy/BN-PVDF composite exhibits high thermal conductivity with low loading of BN. The thermal conductivity of epoxy/BN-PVDF composite achieved 1.227 W/(m K) with 21 wt % BN, contributed by the constructed BN pathway held together by PVDF adhesive. In addition, PVDF could be further converted into carbon by thermal treatment, further enhancing the thermal conductivity of epoxy/BN-C composites through alleviating the phonon scattering at the interfaces, eventually obtaining thermal conductivity of 1.466 W/(m K). This type of epoxy-based composite with high thermal conductivity is promising to be used as thermal management materials in advanced electronic devices.

Salt Template Assisted BN Scaffold Fabrication toward Highly Thermally Conductive Epoxy Composites.

Understanding of the polymerization mechanism of the phthalonitrile-based resins containing benzoxazine and their thermal stability

Dielectric film with ultrahigh thermal stability based on crosslinked polyarylene ether nitrile is prepared and characterized. The film is obtained by solution-casting of polyarylene ether nitrile terminated phthalonitrile (PEN-Ph) combined with post self-crosslinking at high temperature. The film shows a 5% decomposition temperature over 520 °C and a glass transition temperature (Tg) around 386 °C. Stable dielectric constant and low dielectric loss are observed for this film in the frequency range of 100–200 kHz and in the temperature range of 25–300 °C. The temperature coefficient of dielectric constant is less than 0.001 °C−1 even at 400 °C. By cycling heating and cooling up to ten times or heating at 300 °C for 12 h, the film shows good reversibility and robustness of the dielectric properties. This crosslinked PEN film will be a potential candidate as high performance film capacitor electronic devices materials used at high temperature.

/pdf/crosslinked-polyarylene-ether-nitrile-film-as-flexible-2o0y8llin2.pdf

Crosslinked polyarylene ether nitrile film as flexible dielectric materials with ultrahigh thermal stability

For fiber reinforced composite laminates, properties of laminates can be significantly affected by interfacial properties. In this work, a kind of phthalonitrile containing aromatic ether nitrile linkage (PEN-BAPh) was applied to modify glass fibers (GFs). Cured PEN-BAPh on GFs surface were investigated by Fourier transform infrared spectroscopy (FT-IR) and Ultraviolet–visible spectroscopy (UV–Vis). Scanning electron microscope (SEM) and thermogravimetry (TGA) testing were also applied to confirm the modification. Then, modified fiber-reinforced phthalonitrile-based resin composite laminates were fabricated. As the results indicated that all of the composite laminates showed improved flexural strength, flexural modulus and glass transition temperature (Tg = 296.8–299.6 °C). Improved interfacial adhesion was also studied via interlaminar shear strength (ILSS), impact strength test and monitoring the fracture surfaces. Stable dielectric constants, relative low dielectric loss and outstanding thermal stability (T5% > 350 °C) were obtained for designed composite laminates.

Modification on glass fiber surface and their improved properties of fiber-reinforced composites via enhanced interfacial properties

Enhanced thermal conductivity of benzoxazine nanocomposites based on non-covalent functionalized hexagonal boron nitride

In this study, the dielectric properties of poly(arylene ether nitrile) (PEN) were effectively improved by the incorporation of conducting polyaniline (PANI). Sulfuric acid doped PANI was prepared and incorporated into the PEN matrix as additives by using the solution-casting method. The micro-morphologies, mechanical, thermal and dielectric properties of the obtained PANI/PEN nanocomposites were investigated in detail. SEM observation showed that the PANI phase is homogeneously dispersed in the PEN matrix. The obtained PANI/PEN nanocomposites showed good thermal stability as the glass transition temperatures and initial decomposition temperatures of them are higher than 190 and 270 °C. The dielectric constant of the composites was significantly improved after the introduction of PANI, and the dielectric constant of the composite PANI/PEN100 reaches 23.5 (250 Hz), with an increment of 650 % when 10 wt% of PANI is introduced. The temperature dependencies of dielectric constant measurement showed that the dielectric constant of the PANI/PEN composites is stable before 180 °C and these composites can be long-term used at high temperature for their good reversibility and robustness during the heating and cooling scans. These PANI/PEN composites will be a potential candidate as high performance electronic devices materials used at high temperature.

Kui Li

Papers

Understanding of the polymerization mechanism of the phthalonitrile-based resins containing benzoxazine and their thermal stability

Crosslinked polyarylene ether nitrile film as flexible dielectric materials with ultrahigh thermal stability

Modification on glass fiber surface and their improved properties of fiber-reinforced composites via enhanced interfacial properties

Enhanced thermal conductivity of benzoxazine nanocomposites based on non-covalent functionalized hexagonal boron nitride

Improving dielectric properties of polyarylene ether nitrile with conducting polyaniline