Browsing by Author "Zhang, Chunyan"
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Item Carbon Additive Manufacturing with a Near-Replica “Green-to-Brown” Transformation(Advanced Materials, 2023-05-30) Zhang, Chunyan; Shi, Baohui; He, Jinlong; Zhou, Lyu; Park, Soyeon; Doshi, Sagar; Shang, Yuanyuan; Deng, Kaiyue; Giordano, Marc; Qi, Xiangjun; Cui, Shuang; Liu, Ling; Ni, Chaoying; Fu, Kun KelvinNanocomposites containing nanoscale materials offer exciting opportunities to encode nanoscale features into macroscale dimensions, which produces unprecedented impact in material design and application. However, conventional methods cannot process nanocomposites with a high particle loading, as well as nanocomposites with the ability to be tailored at multiple scales. A composite architected mesoscale process strategy that brings particle loading nanoscale materials combined with multiscale features including nanoscale manipulation, mesoscale architecture, and macroscale formation to create spatially programmed nanocomposites with high particle loading and multiscale tailorability is reported. The process features a low-shrinking (<10%) “green-to-brown” transformation, making a near-geometric replica of the 3D design to produce a “brown” part with full nanomaterials to allow further matrix infill. This demonstration includes additively manufactured carbon nanocomposites containing carbon nanotubes (CNTs) and thermoset epoxy, leading to multiscale CNTs tailorability, performance improvement, and 3D complex geometry feasibility. The process can produce nanomaterial-assembled architectures with 3D geometry and multiscale features and can incorporate a wide range of matrix materials, such as polymers, metals, and ceramics, to fabricate nanocomposites for new device structures and applications.Item Structural determinants and thermal properties of CVD diamond thin films and 3D printed MWCNT/PLA(University of Delaware, 2024) Zhang, ChunyanThermal dissipation is critical to the performance, lifespan, and reliability of electronics, electronic packaging, and many structural materials. It remains a challenging bottleneck in high-performance computing and electronic devices due to the ever-growing high-density power transport, architectural complexity, miniaturization, functionalization, and new state-of-the-art applications. It is, therefore, of great significance to develop high thermally conductive materials to address this and other related challenges. Toward this goal, this dissertation focuses on the development of carbon-based materials, specifically diamond films and multi-walled carbon nanotube (MWCNT)-reinforced polymer composites, with tailored structures for scalable thermally related multifunctional applications. These materials hold promises for advancing high performance electronic devices, electronic packaging, battery thermal management, and other fields demanding efficient heat dissipation. ☐ We investigated the correlations between the structural and thermal properties of diamond films, including the relationship between structures and thermal conductivity (k) and thermal conductance (G) of the diamond film deposited on silicon. The measured k values for 0.63-μm diamond and 2.2-μm cubic silicon carbide (3C-SiC) film were 241 W/(mK) and 297 W/(mK), respectively. The relatively low k of the polycrystalline diamond film is plausibly attributable to the effects from grain size of less than the phonon free path and grain boundaries, which increase phonon scattering rate and reduce the k value. The measured G values for diamond-film/Si (100) and 3C-SiC-film/Si (100) were 18 MW/(m2K) and 77 MW/(m2K), respectively. The low G value at the diamond-film/Si (100) interface is attributable to several factors: significant interfacial amorphous layer, large Debye temperature mismatch, lattice constant mismatch and phonon frequency mismatch between diamond and Si (100). These results suggest that the film structure and especially the interfacial microstructure significantly impact the k value of the films and G value of the interfaces. In this work, we directly measured and compared the G of the diamond-film/Si (100) and 3C-SiC-film/Si (100) interfaces and the calculation confirmed that the diamond-film/SiC would be the best material system with high interfacial thermal conductance. This research represents an important step toward obtaining highly thermally conductive material systems, essential for various next generation applications based on diamond thin films. ☐ Just like diamond, CNT is another essential carbon polymorphs with unique and exceptional physical and mechanical properties. CNT-reinforced polymer composites have garnered significant attention due to their processibility and cost-effectiveness in addition to the synergistic properties and enhancement afforded by CNT. In this work, we prepared a high-loading printable filament for 3D printing and printed MWCNT-reinforced nanocomposites with MWCNTs aligning along a specified direction. The as-printed vertically (or through-plane) aligned structure, composed of 20 wt.% MWCNT/PLA, exhibits a through-plane thermal conductivity (k_⏊) of ~0.575 W/(mK), which is around 2.64 times that of horizontally aligned structure (~0.218 W/(mK)) and around 6 times that of neat PLA at 35 °C. The k_⏊ of the vertically aligned structure, with heat flow parallel to MWCNT alignment, exhibits a significant improvement compared to the horizontally aligned structure with heat flow perpendicular to the MWCNT alignment, indicating the importance of MWCNT orientation in enhancing k. In this work, we first achieved the fabrication of 20 wt.% MWCNT/PLA composites with desired MWCNT alignment using fused deposition modeling (FDM), demonstrating high improvement in the k values of the composites and high MWCNT content simultaneously. Furthermore, 3D printed nanocomposites with high MWCNT loading show outstanding thermomechanical properties. Subjecting the printed object to a controlled heating environment results in the formation of a 3D carbon scaffold that preserves the original alignment of MWCNT. ☐ To advance the applications of polymer composites demanding superior functional and mechanical properties, a novel manufacturing method named composite architected mesoscale process (CAMP) has been explored. In the CAMP process, a 3D carbon scaffold serves as a valuable preform for incorporating desired matrix components, including thermosets, metals and ceramics. This enables the design and manufacturing of advanced structural and functional materials. MWCNT/epoxy nanocomposites produced through the CAMP process demonstrate enhanced mechanical properties. ☐ These investigations on carbon-based materials demonstrate that the diamond-films on SiC substrate with desired interface and structure are essential to pave the way for solving thermally related applications, such as coating layers for laser mirrors and cosmological mirrors in space telescopes, and the hierarchical arrangements of MWCNT through 3D printing and CAMP can be a powerful engineering strategy to create customized structures for scalable thermal- and mechanical-related applications, such as battery pack and electronic packaging materials.