Interrogation of nanostructured soft materials & interfaces from fundamental to emergent properties

• Main Author: Alsharif, Nourin
• Other Authors: Brown, Keith A.
• Language: en_US
• Published: 2020
• Subjects: Mechanical engineering
• Online Access: https://hdl.handle.net/2144/41476

The emergence of nanotechnology and nanoscience was largely due to the development of instruments that enabled sensing and manipulating materials at the nanoscale. Characterization at this scale is necessitated because nanostructured objects can exhibit drastically different properties than their bulk counterparts due to quantum effects and the increased importance of surface effects relative to bulk effects. The continuing trends of miniaturization spanning electronics, biology, and mechanics thus require that the state-of-the-art in nanomaterial characterization continues to advance in order to address the rapidly growing classes of nanomaterials and devices. In this dissertation, we present new approaches for characterizing soft materials and interfaces to address critical barriers facing their utilization, including throughput and performance. In our first study, we investigate the changes in mechanical properties of polymer nanoparticles that undergo a glass transition. Through a combination of mechanical (atomic force microscopy – AFM) and thermoanalytical (differential scanning calorimetry) methods, we observe the changes in glass transition temperature that derive from changes in particle size, absorbed water, and polymer molecular weight. We find that these polymer nanoparticles, chosen due to their ubiquitous use for drug delivery, can exhibit 50 fold lower elastic moduli under physiological conditions than they do in dry, ambient conditions as is commonly studied. This work concludes with a roadmap to allow experimentalists exploring nanoparticle mechanics to determine when direct nanoparticle indentation experiments are necessary. While the prior nanoindentation work was performed using commercial probes, these are limited in their bandwidth and ability to interrogate soft samples. To address the shortcomings of conventional indentation tools, in our next study, we explore the opportunities enabled by direct laser writing (DLW) to realize novel classes of AFM probes. Besides the capacity to image and interact with surfaces in a manner similar to conventional probes, DLW-written probes confer several useful advantages as result of their material composition and structural design flexibility, such as high-speed imaging and independent tuning of vibrational resonance modes. These results highlight the utility of tuning the structure of AFM probes in 3D and the ability to tailor individual probes using DLW without conventional wafer-scale batch processing. Lastly, to investigate surfaces with macroscale properties that emerge from the organization of matter on nanoscopic length scales, we develop a high-throughput platform for studying multifunctional surfaces capable of enzymatic activity and tunable wetting behavior. By patterning discrete domains that are uniformly functionalized, we demonstrate the co-optimization of functionalities that would otherwise be mutually exclusive. Variations in surface patterns enable optimization of the multifunctional surface by leveraging the different length scales that determine each functionality. The results presented here not only provide valuable insights regarding the co-optimization of enzymatic activity and hydrophobicity, but also show how high-throughput surface chemistry can impact our understanding and utilization of multifunctional surfaces more generally. === 2021-09-28T00:00:00Z