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Multiscale Fabrication of Fibers With Self-Crimping and Surface Wrinkling Behavior Based on Bi-layer Mechanical Instability.

紀錄類型:	書目-語言資料,手稿 : Monograph/item
正題名/作者:	Multiscale Fabrication of Fibers With Self-Crimping and Surface Wrinkling Behavior Based on Bi-layer Mechanical Instability./
作者:	Khadse, Ninad V.
面頁冊數:	1 online resource (197 pages)
附註:	Source: Dissertations Abstracts International, Volume: 85-08, Section: B.
Contained By:	Dissertations Abstracts International85-08B.
標題:	Nanoscience. -
電子資源:	click for full text (PQDT)
ISBN:	9798381448078

Multiscale Fabrication of Fibers With Self-Crimping and Surface Wrinkling Behavior Based on Bi-layer Mechanical Instability.
Khadse, Ninad V.

Multiscale Fabrication of Fibers With Self-Crimping and Surface Wrinkling Behavior Based on Bi-layer Mechanical Instability. - 1 online resource (197 pages)

Source: Dissertations Abstracts International, Volume: 85-08, Section: B.

Thesis (Ph.D.)--University of Massachusetts Lowell, 2024.

Includes bibliographical references

Instabilities in multi-material systems are prevalent in nature where they are used to generate undulating surfaces such as in a shrunken fruit or differential edge growth in flowers. These instabilities can be mimicked in polymers by fabricating bilayer structures made of polymers with a mismatch in modulus values. Research on spontaneous patterning by exploiting bilayer instability is predominantly pursued for planar geometries at various scales involving thin stiff films deposition on thick elastomeric substrates. The aim of this thesis is to investigate this phenomenon in the form of side-by-side fibers to induce extension-driven instabilities to generate buckling and wrinkling for a system consisting of polybutylene terephthalate (PBT) and a PBT based thermoplastic elastomer.In this first study, melt spinning was utilized to fabricate side-by-side microfibers at various draw rates which influenced the buckling of the fibers which increased the curvature from 0.8 mm-1 to 2.95 mm-1 for fibers with diameters from 46 μm to 30 μm respectively. Accordingly, the Young's modulus values also increased from 1.168 to 2.165 GPa due to strain-induced orientation of the molecular chains during drawing. Owing to the bilayer structure, the fibers exhibit change in curvature when subjected to heat which was quantified and shown to generate a volume expansion of 12.8% when made into battings. Using an axial stretch-release method, the stiff PBT phase was subjected to plastic deformation while the elastomer is subjected to elastic deformation. The increased surface area of the stiff phase gets compressed as the elastomer relaxes and was shown to generate nanowrinkles on the surface with pitch in the range of 260 nm to 430 nm.To generate higher extension force, electrospinning was undertaken to fabricate nanofibers. Additional polymers like thermoplastic polyurethane and Pebax® were used to investigate the influence of elastomeric phase on the generated instability. It was found that a thin skin layer is generated on the electrospun fibers due to rapid solvent evaporation. Increasing the elastomer concentration lead to a pronounced delamination effect of the skin layer due to increased compressive force generated in the fiber. These novel wrinkling structures are generated when the fibers are constrained and cannot fully relax in a helical coiled state. Analysis of helices showed a strong dependence of fiber diameter on helix curvature where curvatures were observed In the range of 0.2 μm-1 to 1.8 μm-1 for fibers with diameters from 2400 nm to 400 nm. Nanowrinkling on the surface showed a weak dependence on fiber diameter such that the pitch increased from 50 nm to 510 nm for fiber diameters in the range of 600 nm to 2400 nm. Nanofiber mats were evaluated for their thermo-mechanical response which exhibited very weak change in dimension due to the constraining of the fibers which restricts large deformations in the individual fibers. The unique wrinkling observed on these fibers can be tuned based on the materials used and the rate of extension that the charged jet experiences during the electrospinning process.To adapt and investigate the buckling phenomenon on a larger scale, designing of a three-plate die is described for the fabrication of 3D printing filament which would be used to modulate the extension by varying the printing speed which could result in preferential bending of the printed shape to attain the programmed final shape. The designed die is used for simulation studies based on proposed process parameters for extruding the filament. Based on the two design simulation studies, it was observed that a shorter die land length would be beneficial to reduce the melt mixing at the interface while still maintaining a 2 mm interdiffusion layer which will aid in adhesion during printing. The velocity profiles exhibited viscous encapsulation of the PBT phase which has a higher viscosity by the lower viscosity Hytrel melt with exit velocity of 8 mm/s.

Electronic reproduction.
Ann Arbor, Mich. :
ProQuest,
2024

Mode of access: World Wide Web

ISBN: 9798381448078Subjects--Topical Terms:

632473
Nanoscience.
Subjects--Index Terms:

BicomponentIndex Terms--Genre/Form:

554714
Electronic books.

Multiscale Fabrication of Fibers With Self-Crimping and Surface Wrinkling Behavior Based on Bi-layer Mechanical Instability.
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520 $a Instabilities in multi-material systems are prevalent in nature where they are used to generate undulating surfaces such as in a shrunken fruit or differential edge growth in flowers. These instabilities can be mimicked in polymers by fabricating bilayer structures made of polymers with a mismatch in modulus values. Research on spontaneous patterning by exploiting bilayer instability is predominantly pursued for planar geometries at various scales involving thin stiff films deposition on thick elastomeric substrates. The aim of this thesis is to investigate this phenomenon in the form of side-by-side fibers to induce extension-driven instabilities to generate buckling and wrinkling for a system consisting of polybutylene terephthalate (PBT) and a PBT based thermoplastic elastomer.In this first study, melt spinning was utilized to fabricate side-by-side microfibers at various draw rates which influenced the buckling of the fibers which increased the curvature from 0.8 mm-1 to 2.95 mm-1 for fibers with diameters from 46 μm to 30 μm respectively. Accordingly, the Young's modulus values also increased from 1.168 to 2.165 GPa due to strain-induced orientation of the molecular chains during drawing. Owing to the bilayer structure, the fibers exhibit change in curvature when subjected to heat which was quantified and shown to generate a volume expansion of 12.8% when made into battings. Using an axial stretch-release method, the stiff PBT phase was subjected to plastic deformation while the elastomer is subjected to elastic deformation. The increased surface area of the stiff phase gets compressed as the elastomer relaxes and was shown to generate nanowrinkles on the surface with pitch in the range of 260 nm to 430 nm.To generate higher extension force, electrospinning was undertaken to fabricate nanofibers. Additional polymers like thermoplastic polyurethane and Pebax® were used to investigate the influence of elastomeric phase on the generated instability. It was found that a thin skin layer is generated on the electrospun fibers due to rapid solvent evaporation. Increasing the elastomer concentration lead to a pronounced delamination effect of the skin layer due to increased compressive force generated in the fiber. These novel wrinkling structures are generated when the fibers are constrained and cannot fully relax in a helical coiled state. Analysis of helices showed a strong dependence of fiber diameter on helix curvature where curvatures were observed In the range of 0.2 μm-1 to 1.8 μm-1 for fibers with diameters from 2400 nm to 400 nm. Nanowrinkling on the surface showed a weak dependence on fiber diameter such that the pitch increased from 50 nm to 510 nm for fiber diameters in the range of 600 nm to 2400 nm. Nanofiber mats were evaluated for their thermo-mechanical response which exhibited very weak change in dimension due to the constraining of the fibers which restricts large deformations in the individual fibers. The unique wrinkling observed on these fibers can be tuned based on the materials used and the rate of extension that the charged jet experiences during the electrospinning process.To adapt and investigate the buckling phenomenon on a larger scale, designing of a three-plate die is described for the fabrication of 3D printing filament which would be used to modulate the extension by varying the printing speed which could result in preferential bending of the printed shape to attain the programmed final shape. The designed die is used for simulation studies based on proposed process parameters for extruding the filament. Based on the two design simulation studies, it was observed that a shorter die land length would be beneficial to reduce the melt mixing at the interface while still maintaining a 2 mm interdiffusion layer which will aid in adhesion during printing. The velocity profiles exhibited viscous encapsulation of the PBT phase which has a higher viscosity by the lower viscosity Hytrel melt with exit velocity of 8 mm/s.
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