Dengxun Ren

Bio: Dengxun Ren is an academic researcher from University of Electronic Science and Technology of China. The author has contributed to research in topics: Curing (chemistry) & Phthalonitrile. The author has an hindex of 9, co-authored 25 publications receiving 197 citations.

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

Abstract: 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.

Design of h-BN-Filled Cyanate/Epoxy Thermal Conductive Composite with Stable Dielectric Properties

Abstract: The thermal conductive cyanate ester/epoxy (CE/AG80) composites with hexagonal boron nitride (h-BN) reinforced were manufactured and investigated. The low and stable dielectric constant/loss of the composites with respect to both frequency (500 Hz-100 kHz) and temperature (50-350 °C) were discussed as functions of the content of h-BN. It was found that the low and stable dielectric constant/ loss of the composites can be maintained in the whole frequency range at room temperature, and the mutations of constant/loss at the frequency of 1 kHz occurred above 280 °C for all of the samples. Moreover, a remarkable enhancement of the thermal conductivity (0.54 W/mK a 1.8-fold enhancement) was achieved with the introduction of h-BN and significantly outperformed traditional thermal conductive fillers. The significant improvements of the thermal conductivity of the composites were analyzed by the Agari’s model and the parameters of C1 and C2 were also calculated.

Thermal Stability of Allyl-Functional Phthalonitriles-Containing Benzoxazine/Bismaleimide Copolymers and Their Improved Mechanical Properties.

Abstract: Copolymerization is the typical method to obtain the high-performance resin composites, due to its universality and regulation performance. It can be employed among various resin matrices with active groups to obtain the desired structures, and subsequently, the outstanding properties. In this work, the copolymerization between the allyl-functional phthalonitrile-containing benzoxazine resin (DABA-Ph) and 4,4′-bis(Maleimidodiphenyl)methane (BMI) were monitored. The interactions among the active groups including allyl moieties, maleimide, benzoxazine rings and nitrile groups were investigated. Differential scanning calorimetry (DSC) and dynamic rheological analysis (DRA) were used to study the curing behaviors and the processing properties. The possible curing processes were proposed and confirmed by Fourier transform infrared spectroscopy (FTIR). Then, glass fiber-reinforced DABA-Ph/BMI composites were designed, and their thermal-mechanical properties were studied. Results indicated that all the composites exhibited outstanding flexural strength, flexural modulus, and high glass-transition temperatures (Tg > 450 °C). The thermal stability of the composites was studied by thermogravimetry (TGA) and evaluated by the integral program decomposition temperature (IPDT). it is believed that the excellent thermal mechanical properties and outstanding Tg as well as good thermal stability would enable the reinforced copolymer-based laminates to be applied in wider fields.

Graphene related materials for thermal management

Abstract: Almost 15 years have gone ever since the discovery of graphene as a single atom layer. Numerous papers have been published to demonstrate its high electron mobility, excellent thermal and mechanical as well as optical properties. We have recently seen more and more applications towards using graphene in commercial products. This paper is an attempt to review and summarize the current status of the research of the thermal properties of graphene and other 2D based materials including the manufacturing and characterization techniques and their applications, especially in electronics and power modules. It is obvious from the review that graphene has penetrated the market and gets more and more applications in commercial electronics thermal management context. In the paper, we also made a critical analysis of how mature the manufacturing processes are; what are the accuracies and challenges with the various characterization techniques and what are the remaining questions and issues left before we see further more applications in this exciting and fascinating field.

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

Abstract: 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.

Understanding the Application Life Cycle

Abstract: Every time you create an iOS project, it will likely include at least two .swift files: ViewController.swift and AppDelegate.swift. A ViewController.swift file connects to a scene in a storyboard and lets you write code that manages the user interface. Each time you add another view controller scene to the storyboard, you’ll likely need another ViewController.swift file (under a different name) to manage any user interface objects such as buttons, text fields, or switches.