Understanding the interfacial processes of reactive nanobubbles toward agricultural applications

There is a growing interest in nanobubble (NB) technology because of its diverse applications (e.g., detergent-free cleaning, water aeration, ultra-sound imaging and intracellular drug delivery, and mineral processing). NBs have a higher efficiency of mass transfer compared to bulk scale bubbles due to the high specific surface areas. The high specific surface also facilitates physical adsorption and chemical reactions in the gas liquid interface. Furthermore, the collapse of NBs creates shock waves and the formation of hydroxyl radicals (OH). However, it remains elusive why or how NBs are stabilized in water and particularly, the states of internal pressures of NBs are difficult to measure. This thesis employs the injection of high-pressure gases through a hydrophobized ceramic membrane to produce different gaseous NBs in water. The results indicate that increasing the injection gas pressure (60–80 psi) and solution temperatures (6–40 oC) both reduce bubble sizes, which are validated by two independent models develop from the Young-Laplace equation and contact mechanics. Both models yield consistent prediction of the internal pressures of various NBs (120 psi-240 psi). The developed methods and model framework are useful to unravel properties of NBs and support engineering applications of NBs. In addition, Atomic Force Microscopy-Scanning Electrochemical Microscopy (AFM-SECM) has evolved to be a powerful tool for simultaneous topographical-electrochemical measurements at local material surfaces with high spatial resolution. Such measurements are crucial for understanding structure-activity relationships relevant to a wide range of applications in material science, life science and chemical processes. The electrochemical behavior of surface NBs on gold substrate is measured by AFM-SECM, to better understand the chemical properties of NBs. Moreover, this study investigates the effects of four types of NBs (air, oxygen, nitrogen, and carbon dioxide) on seed germination and plant growth. Nitrogen NBs exhibit considerable effects in the seed germination, whereas air and carbon dioxide NBs do not significantly promote germination. The growth of stem length and diameter, leave numbers, and leave width are promoted by NBs (except air). Furthermore, the promotion effect is primarily ascribed to the generation of exogenous reactive oxygen species (ROS) by NBs and higher efficiency of nutrient fixation or utilization

Design, Fabrication, Testing of CNT Based ISFET and Characterization of Nano/Bio Materials Using AFM

A combination of Carbon Nanotubes (CNTs) and Ion Selective Field Effect Transistor (ISFET) is designed and experimentally verified in order to develop the next generation ion concentration sensing system. Micro Electro-Mechanical System (MEMS) fabrication techniques, such as photolithography, diffusion, evaporation, lift-off, packaging, etc., are required in the fabrication of the CNT-ISFET structure on p-type silicon wafers. In addition, Atomic Force Microscopy (AFM) based surface nanomachining is investigated and used for creating nanochannels on silicon surfaces. Since AFM based nanomanipulation and nanomachining is highly controllable, nanochannels are precisely scratched in the area between the source and drain of the FET where the inversion layer is after the ISFET is activated. Thus, a bundle of CNTs are able to be aligned inside a single nanochannel by Dielectrophoresis (DEP) and the drain current is improved greatly due to CNTs` remarkable and unique electrical properties, for example, high current carrying capacity. ISFET structures with or without CNTs are fabricated and tested with different pH solutions. Besides the CNT-ISFET pH sensing system, this dissertation also presents novel AFM-based nanotechnology for learning the properties of chemical or biomedical samples in micro or nano level. Dimensional and mechanical property behaviors of Vertically Aligned Carbon Nanofibers (VACNFs) are studied after temperature and humidity treatment using AFM. Furthermore, mechanical property testing of biomedical samples, such as microbubbles and engineered soft tissues, using AFM based nanoindentation is introduced, and the methodology is of great directional value in the area

Adhesion mechanics of graphene membranes

The interaction of graphene with neighboring materials and structures plays an important role in its behavior, both scientifically and technologically. The interactions are complicated due to the interplay between surface forces and possibly nonlinear elastic behavior. Here we review recent experimental and theoretical advances in the understanding of graphene adhesion. We organize our discussion into experimental and theoretical efforts directed toward: graphene conformation to a substrate, determination of adhesion energy, and applications where graphene adhesion plays an important role. We conclude with a brief prospectus outlining open issues.Comment: Review article to appear in special issue on graphene in Solid State Communication

Structure-mechanics relationships of collagen fibrils in the Osteogenesis Imperfecta Mouse model

The collagen molecule, which is the building block of collagen fibrils, is a triple helix of two α1(I) chains and one α2(I) chain. However, in the severe mouse model of osteogenesis imperfecta (OIM), deletion of the COL1A2 gene results in the substitution of the α2(I) chain by one α1(I) chain. As this substitution severely impairs the structure and mechanics of collagen-rich tissues at the tissue and organ level, the main aim of this study was to investigate how the structure and mechanics are altered in OIM collagen fibrils. Comparing results from atomic force microscopy imaging and cantilever-based nanoindentation on collagen fibrils from OIM and wild-type (WT) animals, we found a 33% lower indentation modulus in OIM when air-dried (bound water present) and an almost fivefold higher indentation modulus in OIM collagen fibrils when fully hydrated (bound and unbound water present) in phosphate-buffered saline solution (PBS) compared with WT collagen fibrils. These mechanical changes were accompanied by an impaired swelling upon hydration within PBS. Our experimental and atomistic simulation results show how the structure and mechanics are altered at the individual collagen fibril level as a result of collagen gene mutation in OIM. We envisage that the combination of experimental and modelling approaches could allow mechanical phenotyping at the collagen fibril level of virtually any alteration of collagen structure or chemistry.United States. Dept. of Defense. Presidential Early Career Award for Scientists and EngineersNational Science Foundation (U.S.) (CAREER Award

Nanoparticle-Shelled Bubbles for Lightweight Materials

Lightweight materials that are mechanically robust are of great interest in automotive, aerospace, and construction industries. However due to the nature of materials, it is challenging to obtain materials that have high strength, stiffness and toughness, and light weight simultaneously. One approach that tries to address this limitation is the use of composite materials containing hollow microparticles, also known as syntactic foams. The incorporation of hollow microparticles decreases the density of the material at the same time that increases its specific strength. Conventional methods of fabrication of hollow particles involving bulk reactions result in high heterogeneity in geometry as well as mechanical properties, and little or no control over the shell nanostructure. This variability in the structure and properties of the hollow microparticles adversely affects the macroscopic properties of the syntactic foams and hinders the understanding of the structure-property relationship. The use of microfluidics for the generation of shelled-bubbles addresses these limitations. This microfluidic technique, in contrast to bulk methods, is based on single droplet formation, allowing for the generation of highly uniform bubbles, and enabling the assembly of nanoparticles at the interface forming stable nanoparticle-shelled bubbles. Microfluidics allow a precise control over the geometry, nanostructure and properties of the shelled-bubbles, further enabling the functionalization of the shell surface to present amphiphilicity, or the modification of the shell structure with thermal processes to enhance their mechanical behavior. These versatile nanoparticle-shelled bubbles are optimal candidates to form hierarchically assembled lightweight composites with targeted mechanical properties. In composites, the precise control over the structure and properties of the fillers allows the determination of the structure-property relationship, and enables a better understanding of the effect of the nanostructure on the macroscopic mechanical response