Probabilistic Physics-integrated Neural Differentiable Modeling for Isothermal Chemical Vapor Infiltration Process

Chemical vapor infiltration (CVI) is a widely adopted manufacturing technique used in producing carbon-carbon and carbon-silicon carbide composites. These materials are especially valued in the aerospace and automotive industries for their robust strength and lightweight characteristics. The densification process during CVI critically influences the final performance, quality, and consistency of these composite materials. Experimentally optimizing the CVI processes is challenging due to long experimental time and large optimization space. To address these challenges, this work takes a modeling-centric approach. Due to the complexities and limited experimental data of the isothermal CVI densification process, we have developed a data-driven predictive model using the physics-integrated neural differentiable (PiNDiff) modeling framework. An uncertainty quantification feature has been embedded within the PiNDiff method, bolstering the model's reliability and robustness. Through comprehensive numerical experiments involving both synthetic and real-world manufacturing data, the proposed method showcases its capability in modeling densification during the CVI process. This research highlights the potential of the PiNDiff framework as an instrumental tool for advancing our understanding, simulation, and optimization of the CVI manufacturing process, particularly when faced with sparse data and an incomplete description of the underlying physics

Synthesis and Integration of Nanostructured Carbon: Carbon Nanotube-Polymer Nanocomposites and Graphene

Nanostructured carbon, in the form of tubes or sheets, exhibits exceptional thermal and electrical properties. Graphene, a single atomic sheet of hexagonal sp2 bonded carbon, posesses a thermal conductivity higher than diamond, with an extremely high electron mobility. Carbon nanotubes (CNT), which are tubes composed of one or more graphene sheets, also posess high thermal conductivity and electron mobility. One of the major problems facing the application of nanomaterials is integration into already existing material systems. A second challenge is controlled synthesis of nanomaterials. In this dissertation research novel methods were investigated for coupling carbon nanotubes to polymer matrices, as well as new approaches for controlling the synthesis of graphene and reduced graphene oxide like carbon (R-GOC) on copper (Cu) foils via chemical vapor deposition. It was determined that carboxylic functionalization of carbon nanotubes was effective in improving the coupling of CNTs to polymer matrices, affecting the thermal transport of the resulting CNT-polymer nanocomposites. From the CVD studies it was established that the cooling phase gases flowed after deposition influence the growth mechanics of graphene on Cu foil. Further CVD studies showed that methane may be decomposed directly onto quartz to form reduced graphene oxide like carbon thin films. The obtained thermal characterization results are important for development of CNTs as fillers for composite pastes with high thermal conductivity, and the results of the CVD studies are important for developing further understanding of growth mechanics of bilayer graphene and other nanostructured carbon. In addition to the fundamental study of CVD synthesis of graphene and R-GOC, this dissertation work includes engineering of graphene and R-GOC to various applications, including the development of the thinnest flexible transistor with active materials made from all-2D materials, as well as large-scale electron transparent windows, and transparent conducting thin films

Crystal Structures of 2-Bromo-1,1,1,3,3,3-Hexa­methyl-2-(Tri­methyl­sil­yl)Tris­ilane and 2-Bromo-1,1,1,3,3,3-Hexa­isopropyl-2-(Triiso­propyl­sil­yl)Tri­silane

The synthesis and crystal structures of two tris­(tri­alkyl­sil­yl)silyl bromide compounds, C9H27BrSi4 (I, HypSiBr) and C27H63BrSi4 (II, TipSiBr), are described. Compound I was prepared in 85% yield by free-radical bromination of 1,1,1,3,3,3-hexa­methyl-2-(tri­methyl­sil­yl)tris­ilane using bromo­butane and 2,2′-azobis(2-methyl­propio­nitrile) as a radical initiator at 333 K. The mol­ecule possesses threefold rotational symmetry, with the central Si atom and the Br atom being located on the threefold rotation axis. The Si—Br bond distance is 2.2990 (12) Å and the Si—Si bond lengths are 2.3477 (8) Å. The Br—Si—Si bond angles are 104.83 (3)° and the Si—Si—Si bond angles are 113.69 (2)°, reflecting the steric hindrance inherent in the three tri­methyl­silyl groups attached to the central Si atom. Compound II was prepared in 55% yield by free-radical bromination of 1,1,1,3,3,3-hexa­isopropyl-2-(triiso­propyl­sil­yl)tris­ilane using N-bromo­succinimide and 2,2′-azobis(2-methyl­propio­nitrile) as a radical initiator at 353 K. Here the Si—Br bond length is 2.3185 (7) Å and the Si—Si bond lengths range from 2.443 (1) to 2.4628 (9) Å. The Br—Si—Si bond angles range from 98.44 (3) to 103.77 (3)°, indicating steric hindrance between the three triiso­propyl­silyl groups

All Two-Dimensional, Flexible, Transparent, and Thinnest Thin Film Transistor

In this article, we report only 10 atomic layer thick, high mobility, transparent thin film transistors (TFTs) with ambipolar device characteristics fabricated on both a conventional silicon platform as well as on a flexible substrate. Monolayer graphene was used as metal electrodes, 3-4 atomic layers of h-BN were used as the gate dielectric, and finally bilayers of WSe2 were used as the semiconducting channel material for the TFTs. The field effect carrier mobility was extracted to be 45 cm(2)/(V s), which exceeds the mobility values of state of the art amorphous silicon based TFTs by similar to 100 times. The active device stack of WSe2-hBN-graphene was found to be more than 88% transparent over the entire visible spectrum and the device characteristics were unaltered for in-plane mechanical strain of up to 2%. The device demonstrated remarkable temperature stability over 77-400 K. Low contact resistance value of 1.4 k Omega-mu m, subthreshold slope of 90 mv/decade, current ON-OFF ratio of 10(7), and presence of both electron and hole conduction were observed in our all two-dimensional (2D) TFTs, which are extremely desirable but rarely reported characteristics of most of the organic and inorganic TFTs. To the best of our knowledge, this is the first report of all 2D transparent TFT fabricated on flexible substrate along with the highest mobility and current ON-OFF ratio

Effects of Functionalization on Thermal Properties of Single-Wall and Multi-Wall Carbon Nanotube-Polymer Nanocomposites

Carboxylic functionalization (-COOH groups) of carbon nanotubes is known to improve their dispersion properties and increase the electrical conductivity of carbon-nanotube - polymer nanocomposites. We have studied experimentally the effects of this type of functionalization on the thermal conductivity of the nanocomposites. It was found that while even small quantities of carbon nanotubes (~1 wt%) can increase the electrical conductivity, a larger loading fraction (~3 wt%) is required to enhance the thermal conductivity of nanocomposites. Functionalized multi-wall carbon nanotubes performed the best as filler material leading to a simultaneous improvement of the electrical and thermal properties of the composites. Functionalization of the single-wall carbon nanotubes reduced the thermal conductivity enhancement. The observed trends were explained by the fact that while surface functionalization increases the coupling between carbon nanotube and polymer matrix it also leads to formation of defects, which impede the acoustic phonon transport in the single wall carbon nanotubes. The obtained results are important for applications of carbon nanotubes and graphene flakes as fillers for improving thermal, electrical and mechanical properties of composites.Comment: 25 pages; 6 figure