Large-Scale Fabrication of Boron Nitride Nanosheets and Their Utilization in Polymeric Composites with Improved Thermal and Mechanical Properties

We calculate the double resonant (DR) Raman spectrum of graphene, and determine the lines associated to both phonon-defect processes, and two-phonons ones. Phonon and electronic dispersions reproduce calculations based on density functional theory corrected with GW. Electron-light, -phonon, and -defect scattering matrix elements and the electronic linewidth are explicitly calculated. Defect-induced processes are simulated by considering different kind of idealized defects. For an excitation energy of $\epsilon_L=2.4$ eV, the agreement with measurements is very good and calculations reproduce: the relative intensities among phonon-defect or among two-phonon lines; the measured small widths of the D, $D'$, 2D and $2D'$ lines; the line shapes; the presence of small intensity lines in the 1800, 2000 cm$^{-1}$ range. We determine how the spectra depend on the excitation energy, on the light polarization, on the electronic linewidth, on the kind of defects and on their concentration. According to the present findings, the intensity ratio between the $2D'$ and 2D lines can be used to determine experimentally the electronic linewidth. The intensity ratio between the $D$ and $D'$ lines depends on the kind of model defect, suggesting that this ratio could possibly be used to identify the kind of defects present in actual samples. Charged impurities outside the graphene plane provide an almost undetectable contribution to the Raman signal.

/pdf/theory-of-double-resonant-raman-spectra-in-graphene-55hadiikn1.pdf

Theory of double-resonant Raman spectra in graphene: intensity and line shape of defect-induced and two-phonon bands

Factors affecting thermal conductivities of the polymers and polymer composites: A review

Both aminopropylisobutyl polyhedral oligomeric silsesquioxane (NH2-POSS) and hydrazine monohydrate were utilized to functionalize graphene oxide (GO), and to obtain chemically modified graphene (CMG), which was then used for preparing thermally conductive CMG/polyimide (CMG/PI) nanocomposites via a sequential in situ polymerization and electrospinning-hot press technology NH2-POSS molecules were grafted on the GO surface, and CMG was obtained by the reaction between NH2-POSS and GO The thermal conductivity coefficient (λ), glass transition temperature (Tg) and heat resistance index (THRI) of the prepared CMG/PI nanocomposites were all increased with increasing the CMG loading The λ value of the CMG/PI nanocomposites with 5 wt% CMG was significantly improved to 105 W m−1 K−1, about 4 times higher than that of the pristine PI matrix (028 W m−1 K−1) The corresponding Tg and THRI values were also increased to 2130 and 2823 °C, respectively Moreover, an improved thermal conductivity model was proposed and predicted the λ values of the nanocomposites more precisely than those obtained from the typical Maxwell, Russell and Bruggemen classical models

Significantly enhanced and precisely modeled thermal conductivity in polyimide nanocomposites with chemically modified graphene via in situ polymerization and electrospinning-hot press technology

Fluorine-containing polyimide (PI) with low dielectric constant (e) value was firstly synthesized by a polycondensation reaction of 4, 4-(hexafluoroisopropyl) diphthalic anhydride (6FDA), 1, 3, 4-triphenyldiether diamine (APB) and 1, 3-bis(3-aminopropyl) tetramethyldisiloxane (GAPD). γ-glycidoxypropyltrimethoxysilane (KH-560) and aminopropylisobutyl polyhedral oligomeric silsesquioxane (NH2-POSS) were synchronously performed to functionalize the surface of boron nitride (f-BN) fillers, which were then utilized as thermally conductive fillers to fabricate the corresponding f-BN/PI composites. NH2-POSS was successfully grafted on the surface of BN fillers. All the f-BN/PI composites presented better thermal conductivities, dielectric and thermal properties than those of BN/PI composites at the same addition of BN fillers. The obtained thermal conductivity coefficient (λ) of the f-BN/PI composites with 30 wt% f-BN was 0.71 W/mK, higher than that of BN/PI composites with 30 wt% BN (λ of 0.69 W/mK). Modified Hashin-Shtrikman model demonstrated that f-BN possessed relatively lower thermal resistance with PI matrix. Meantime, the corresponding e and dielectric loss tangent (tanδ) value of the f-BN/PI composites was decreased to 3.32 and 0.004, respectively, lower than that of BN/PI composites with 30 wt% BN (e of 3.77 and tanδ of 0.007). Moreover, the corresponding heat resistance index (THRI) and glass transition temperature (Tg) of the f-BN/PI composites was further enhanced to 280.2 °C and 251.7 °C, respectively.

Enhanced thermal conductivities and decreased thermal resistances of functionalized boron nitride/polyimide composites

An anisotropic thermally conductive film with tailorable microstructures and macroproperties is fabricated using a layer-by-layer (LbL) assembly of graphene oxide (GO) and nanofibrillated cellulose (NFC) on a flexible NFC substrate driven by hydrogen bonding interactions, followed by chemical reduction process. The resulting NFC/reduced graphene oxide (RGO) hybrid film reveals an orderly hierarchical structure in which the RGO nanosheets exhibit a high degree of orientation along the in-plane direction. The assembly cycles dramatically increase the in-plane thermal conductivity (λX) of the hybrid film to 12.6 W·m–1·K–1, while the cross-plane thermal conductivity (λZ) shows a lower value of 0.042 W·m–1·K–1 in the hybrid film with 40 assembly cycles. The thermal conductivity anisotropy reaches up to λX/λZ = 279, which is substantially larger than that of similar polymeric nanocomposites, indicating that the LbL assembly on a flexible NFC substrate is an efficient technique for the preparation of polymeric n...

Highly Anisotropic Thermal Conductivity of Layer-by-Layer Assembled Nanofibrillated Cellulose/Graphene Nanosheets Hybrid Films for Thermal Management

Highly thermal conductive polymer composites with minimized content of fillers are desirable for handling the issue in thermal management in modern electronics. However, the difficulty of filler dispersion restricts the heat dissipation performance of thermoplastic composites and the intermolecular interaction is another crucial factor in this problem. In the present study, the hydrogen bond was used to regulate the formation of the three-dimensional boron nitride (3D BN) interconnected network to act as a high thermal conductive network in thermoplastic polyamide-imide (PAI) materials. The prepared electrical insulated PAI/3D–BN composites have a thermal conductivity (TC) of 1.17 W·m–1·K–1 at a low BN loading of 4 wt %/2 vol % and exhibit a thermal conductivity enhancement of 409%. We attribute the increased TC to the construction of 3D BN interconnected network and the hydrogen bond regulated between hydroxylated BN and polyvinyl alcohol, in which an effective thermal conductive network is constructed. ...

Hydrogen Bond-Regulated Boron Nitride Network Structures for Improved Thermal Conductive Property of Polyamide-imide Composites

The anisotropic thermally conductive flexible films with nanofibrillated cellulose (NFC) and in situ reduced graphene oxide (RGO) nanosheets are prepared via a vacuum-assisted self-assembly technique. The hybrid films exhibit superior in-plane thermal conductivities, and a value of 6.168 W m−1 K−1 is achieved with 30 wt% GO loading. Noteworthily, the through-plane thermal conductivities are extremely low (≤0.072 W m−1 K−1). The high anisotropy of the thermal conductivity is systematically investigated and correlated to the alignment of RGO nanosheets. Moreover, hybrid films exhibit excellent flexibility as well as high tensile strength. The aligned RGO nanosheets significantly delayed the thermal degradation of the hybrid films. The strongly anisotropic thermally conductive properties of these films can be useful for their application in thermal management.

Anisotropic thermally conductive flexible films based on nanofibrillated cellulose and aligned graphene nanosheets

It is urgent to fabricate a class of green plastics to substitute synthetic plastics with increasing awareness of sustainable development of an ecological environment and economy. In this work, a novel green plastic constructed from cellulose and functionalized graphene has been explored. The mechanical properties and thermal stability of the resultant cellulose/functionalized graphene composite plastics (CGPs) equal or even exceed those of synthetic plastics. Moreover, the in-plane thermal conductivity of CGPs can reach 9.0 W·m–1·K–1 with only 6 wt % functionalized graphene loading. These superior properties are attributed to the strong hydrogen-bonding interaction between cellulose and functionalized graphene, the uniform dispersion of functionalized graphene, and the alignment structure of CGPs. Given the promising synergistic performances and ecofriendly features of CGPs, we envisage that CGPs as novel green plastics could play important roles in thermal management devices.

A Green Plastic Constructed from Cellulose and Functionalized Graphene with High Thermal Conductivity

With the development of polymer-based composite materials technologies and the continuous expansion of its application scale, the research focus has shifted from performance and quality to multifun...

Control of a Dual-Cross-Linked Boron Nitride Frameworkand the Optimized Design of the Thermal Conductive Network for ItsThermoresponsive Polymeric Composites

Siqi Cui

Papers

Highly Anisotropic Thermal Conductivity of Layer-by-Layer Assembled Nanofibrillated Cellulose/Graphene Nanosheets Hybrid Films for Thermal Management

Hydrogen Bond-Regulated Boron Nitride Network Structures for Improved Thermal Conductive Property of Polyamide-imide Composites

Anisotropic thermally conductive flexible films based on nanofibrillated cellulose and aligned graphene nanosheets

A Green Plastic Constructed from Cellulose and Functionalized Graphene with High Thermal Conductivity

Control of a Dual-Cross-Linked Boron Nitride Frameworkand the Optimized Design of the Thermal Conductive Network for ItsThermoresponsive Polymeric Composites