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Porosity Characterization of Electrospun Polycaprolactone via Laser Metrology

Liu, Yi-xiao
http://orcid.org/0000-0001-6436-7766
http://rave.ohiolink.edu/etdc/view?acc_num=osu164131738936522

Abstract Details

2022, Doctor of Philosophy, Ohio State University, Materials Science and Engineering.
Electrospinning is an electrohydrodynamic process generating polymeric micro or nanofibers having immense technological benefits in biomedical, energy, and filtration applications. However, the microstructural heterogeneity inherent to electrospun materials has led to unreliable performance, fundamentally limiting the potential of this technology. While this heterogeneity is readily revealed by point-to-point comparisons (e.g., electron microscopy), full quantification remains challenging due to the extremely limited field-of-view associated with these techniques. To address this, we developed a novel technique that can characterize internal porosity gradients in thin films that reflect the large-scale microstructural heterogeneity of electrospun deposits. Accurate measurements of both as-spun depositions and the same depositions post-densification, are obtained via contact-free laser metrology. A formula was developed to enable ‘mapping’ of the spatial porosity distribution by comparing both dimensions and quantifying the vertical shrinkage. The automated prototype developed generates porosity ‘maps’ – each consisting of ~14,000 datapoints at a spatial resolution of ~1 mm – within a few hours, an achievement > 1,000 times faster than traditional methods such as porosimetry. Our technique also enables in situ characterization thus minimizing the risk of sample distortion or other artifacts. In addition, the technique is believed to be compatible with any other open-porous materials that can be densified. Utilizing this innovation, an extensive investigation was conducted to understand the porosity gradients found within tubular electrospun polycaprolactone (PCL), a frequently studied polymer thanks to its specific combination of biocompatibility and biodegradability. Variations in porosity values are found in many examples of electrospun PCL and can range from ~0 to 88% within the same deposition in extreme cases. These variations also exhibit significant sensitivity to a variety of process parameters such as applied bias, collector rotation, solvent composition, and relative humidity, highlighting the importance of stringent control over fabrication conditions for consistent electrospun products. Some aspects of dual-needle deposition were also examined. During the course of this study, two novel phenomena were observed in electrospun PCL. The predominate fiber orientation was found to be aligned to the axial direction of the rod collector, orthogonal (surprisingly) to the direction of rotation. PCL fibers were also found to self-assemble into a distinct, vertically stacked configuration across the deposition, creating extensive roughness visible even to the naked eye. We have established electrodynamic models in which these phenomena are attributed to, respectively, specific electric field associated with cylindrical collector geometry, and the dynamic interaction between fiber deposition and charge dissipation. Qualitative agreement with experimental results is achieved in numerical simulations. To summarize, electrospinning is a promising technique to produce micro or nanofibers for various applications. To understand the inherent microstructural heterogeneity of electrospun materials, we have developed a novel technique that ‘maps’ the porosity gradients present in thin deposits using laser-based dimensional measurements. We also investigated these porosity trends in response to specific process conditions. This dissertation could serve as the first step toward understanding and ultimately controlling the heterogeneity of electrospun microstructures.
John Lannutti (Advisor)
Jinghua Li (Committee Member)
Heather Powell (Committee Member)
Pelagia-Iren Gouma (Committee Member)
220 p.
Engineering; Materials Science; Mechanical Engineering; Mechanics; Nanoscience; Nanotechnology; Polymers
Electrospinning; Porosity; Nanofiber; Characterization; Metrology; Heterogeneity; Polycaprolactone; Bending Instability; Sintering; Self-assembly; Alignment; Multi-needle Electrospinning;

Recommended Citations

Citations

  • Liu, Y.-X. (2022). Porosity Characterization of Electrospun Polycaprolactone via Laser Metrology [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu164131738936522

    APA Style (7th edition)

  • Liu, Yi-xiao. Porosity Characterization of Electrospun Polycaprolactone via Laser Metrology. 2022. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu164131738936522.

    MLA Style (8th edition)

  • Liu, Yi-xiao. "Porosity Characterization of Electrospun Polycaprolactone via Laser Metrology." Doctoral dissertation, Ohio State University, 2022. http://rave.ohiolink.edu/etdc/view?acc_num=osu164131738936522

    Chicago Manual of Style (17th edition)

osu164131738936522
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