There has been an ever-increasing need for soft, functional materials within areas of research such as soft robotics, flexible electronics, and wearable devices. These materials must be stretchable and/or flexible, thermally and electrically conductive, and robustly adhesive to a wide variety of substrates and surfaces. Over the past several decades, soft composites consisting of functional solid particles within an elastic matrix have been developed with the aim of achieving these properties. However, solid particulate fillers in elastomeric materials have various limitations which hinders the ability to achieve the aforementioned properties simultaneously. In this work, two novel approaches to developing soft conductive adhesives are introduced in an effort to solve mechanical, thermal, electrical, and adhesive trade-offs. The composites developed herein utilize liquid metal (LM) inclusions and a combination of LM with solid silver (Ag) flakes within deformable polymer matrices to maintain mechanical compliance while also achieving thermal and electrical functionality. Furthermore, adhesive properties of LM composites are enhanced through a chemical anchoring technique, while the composition and microstructure of LM-Ag composites are designed to control functional and adhesive properties. There are several demonstrations throughout which show the ability to robustly integrate the novel soft composites with rigid materials and electronic components for the creation of resilient and functional hybrid electronic systems. / Master of Science / There has been an ever-increasing need for soft, functional materials within areas of research such as soft robotics, flexible electronics, and wearable devices. These materials must be stretchable and/or flexible, thermally and electrically conductive, and robustly adhesive to a wide variety of substrates and surfaces. Over the past several decades, soft composites consisting of functional solid particles within an elastic matrix have been developed with the aim of achieving these properties. However, solid particulate fillers in elastomeric materials have various limitations which hinders the ability to achieve the aforementioned properties simultaneously. In this work, two novel approaches to developing soft conductive adhesives are introduced in an effort to solve mechanical, thermal, electrical, and adhesive trade-offs. The composites developed herein utilize liquid metal (LM) inclusions and a combination of LM with solid silver (Ag) flakes within deformable polymer matrices to maintain mechanical compliance while also achieving thermal and electrical functionality. Furthermore, adhesive properties of LM composites are enhanced through a chemical anchoring technique, while the composition and microstructure of LM-Ag composites are designed to control functional and adhesive properties. There are several demonstrations throughout which show the ability to robustly integrate the novel soft composites with rigid materials and electronic components for the creation of resilient and functional hybrid electronic systems. Fabrication and Characterization of Multifunctional Soft Composites for Hybrid Electronic Systems Tyler A. Pozarycki (GENERAL AUDIENCE ABSTRACT) Composites are materials which are made up of two or more components with characteristics that exceed their counterparts. Steel reinforced concrete is a common example, where the steel helps to reinforce the concrete while the concrete itself gives shape to the structure. One cannot exist without the other, as the steel alone would create a meaningless skeleton and the concrete alone would not be able to withstand weights of heavier objects such as vehicles. In recent years, soft composites have become an emerging paradigm. These materials are stretchable and flexible due to their main component typically being an elastomer, while their inner component can consist of various materials that give desired functionality. For example, iron particles can grant magnetic properties and carbon can allow the material to conduct heat and/or electricity. As a result, these materials have captured the interest of scientists and researchers in various fields such as robotics, electronics, and biomedicine. However, there exists a unique challenge in developing such a material for applications in these areas. That is, the material needs to possess three critical properties simultaneously: 1) it must be compliant to various surfaces, meaning it must assume complex shapes such as those found on the human body, 2) it must be able to efficiently conduct electricity and heat, and 3) it must be able to adhere, or stick strongly to a variety of surfaces and materials for assembly. Typically, solving this problem has been attempted by fabricating soft composites with inner components consisting of metallic and ceramic particles, powders, or flakes. However, the use of these materials within elastomers, gels, and the like often create a composite which falls short of the aforementioned requirements, as the rigid inner structure and soft outer material are uncomplimentary to each other. Additionally, silicone elastomers and other similar materials typically do not adhere to a wide variety of surfaces, which further complicates the problem. In this work, two novel materials are produced in an effort to solve these long-standing issues. The first utilizes room-temperature liquid metal (LM) as the inner component to preserve overall material integrity while also using a chemical anchoring process to adhere the composites to several plastics and metals. The second consists of a flexible epoxy (naturally adhesive material) which incorporates both LM and silver flakes to create an as-prepared thermally and electrically conductive adhesive. Both soft composites are shown integrated with rigid electronic components and other materials to demonstrate the feasibility of using the composites to fabricate hybrid electronic systems.

Among the many factors that effect the atomization of a fuel spray in a com- bustion chamber, the flow characteristics of the fuel inside the injector nozzle play significant roles. The enthalpy of the entering fuel can be elevated such that it is higher than the local or downstream saturation enthalpy, which will result in the flash-boiling of the liquid. The phase change process dramatically effects the flow rate and has the potential to cause subsonic two-phase choking. The timescale over which this occurs is comparable to the flow-through time of the nozzle and hence any attempt to model this phenomenon needs to be done as a finite rate process. In the past the Homogeneous Relaxation Model (HRM) has been successfully employed to model the vaporization in one dimension. Here a full three dimensional imple- mentation of the HRM model is presented. Validations have been presented with experiments using water as working fluid. For the external spray modeling, where the fuel is said to be flash boiling, the phase change process plays a role alongside the aerodynamic breakup of the liquid and must be considered for obtaining the fuel spray characteristics. In this study the HRM model is coupled with Linearized Sheet Instability Analysis (LISA) model, for primary atomization, and with Taylor Analogy Breakup (TAB) model for secondary breakup. The aerodynamic breakup model and phase change based breakup model are designed as competing processes. The mechanism which satisfies its breakup criterion first during time integration is used to predict resulting drop sizes.

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Liquid droplet impingement on aircraft can be problematic as it leads to ice accretion. There have been many incidents of aircraft disasters involving ice accretion, such as American Eagle Flight 4184. Understanding liquid droplet impingement is critical in designing aircraft that can mitigate the damages caused by icing. However, the FAA's regulations are only specified for "Appendix C" droplets; thus, aircraft designs may not be safe when accounting for droplets such as Supercooled Large Droplets. The assumptions of many models, such as the Taylor-Analogy Breakup (TAB) model, are no longer accurate for Supercooled Large Droplets, and the physics of those models break down. Computational modeling is used to simulate droplets in the SLD regime. A Lagrangian reference frame is used in this formulation. In this reference frame, a Volume of Fluid variation of the Navier-Stokes equations is used to resolve and isolate a single droplet. Experimental data shows conflicting results for Weber Number ranges in different primary breakup mechanisms. The goal of this research is to develop a computational model of a water droplet and test it against experimental data. This work shows that the scientific consensus on Weber Number ranges for different breakup modes may not necessarily be accurate, as the computational model agrees with some sets of experimental data, but contradicts others.

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