Investigations into Crystallization and Fundamental Thermal Properties of Semicrystalline Polymers by Conventional and Fast Scanning Calorimetry
Abstract: This thesis presents new insights into the crystallization and
fundamental thermal properties of semicrystalline polymers investigated by a combination of
conventional thermal and structural analysis techniques and the recently developed chip
based fast scanning calorimeters. The experiments performed and the results obtained fall
into two categories. The first are investigations into ... read morethe crystallization and fundamental
thermal properties of the synthetic, semicrystalline polymer, polyvinyl alcohol (PVA) in
bulk, in thin films, and in nanofibers. The second category includes the development and
application of a new experimental technique for the preparation of electrospun fibers
suitable for fast scanning calorimetry (FSC) chip based sensors. PVA is hydrophilic,
biocompatible, biodegradable, renewable, and possesses excellent mechanical and chemical
resistance properties. It has been continuously studied since it was first synthesized
nearly 100 years ago. Despite its frequent study, complete measurements of several
fundamental thermal properties have been elusive due to thermal degradation which occurs
within its melting range. Making use of both conventional DSC and FSC techniques it was
possible to make the first, degradation free measurements of the following fundamental
properties: 1. liquid phase specific heat capacity of PVA, cpLiquid(T); 2. Specific heat
capacity increment at the glass transition for 100% amorphous material Δcpamor(Tg); 3. the
critical cooling rate, |βc|, required to quench the material and create an amorphous glass;
and 4. the rigid amorphous fraction (RAF) of PVA. Electrospun nanofibers are of interest
for both applied and fundamental research. These fibers are light, "fluffy", and delicate
and must be handled with care. This poses a unique challenge for experimenters utilizing
chip based calorimeters. Copper transmission electron microscope (TEM) grids provide a
substrate both thermally conductive and mechanically durable. Directly electrospinning
fibers onto TEM grids allowed the fibers to be transferred to chip sensors and the presence
of the grid ensured excellent sample to sensor contact. This technique was tested on the
synthetic polymer, polyethylene terephthalate (PET). Cold crystallization experiments were
performed on the fibers which were observed to break up into droplets following melting.
These experiments yielded a new, and unexpected result in that the droplet confined PET
showed a depression in the RAF.
Thesis (Ph.D.)--Tufts University, 2017.
Submitted to the Dept. of Physics.
Advisor: Peggy Cebe.
Committee: Peggy Cebe, Cristian Staii, Christoph Schick, Austin Napier, and Hugo Beauchemin.
Keyword: Condensed matter physics.read less
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