Tailoring the structure-property of segmented ionenes through analysis of thermomechanical and electrical properties
Date
2022-12
Authors
Taghavimehr, Mehrnoosh
Major Professor
Advisor
Montazami, Reza RM
Ommen, Danica
Hashemi, Nicole
Xiang, Chunhui
Pint, Cary
Committee Member
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Abstract
Ionenes are ion-containing polymers with ions located on the polymer backbone. This
characteristic of ionenes can be used to tailor the structure of polymers for a variety of
applications.
In this dissertation, we have investigated the effects of ionene microstructure on the
properties of elastomeric samples. Placement of charge density in segmented ionenes can be
controlled through the selection of soft/hard segments, changing the ratio of soft/hard segments,
the molecular weight alteration of the soft segment, and microphase separation. The influences
of these parameters were investigated through the synthesis of ionenes with various properties,
while the structure-property relationships were scrutinized.
In the first study, the results from molecular dynamics (MD) simulations of the ionene
structure were compared with the experimental tests to evaluate the effect of microphase
separation and ionic aggregation of ionene on their properties. The results of this study are
discussed in detail in Chapter 3.
The second study focused on using poly(ethylene glycol) (PEG) as the soft segment
component of segmented block ionenes with two types of aliphatic hard segments (linear
aliphatic and DABCO). All PEG samples created crystallized structures, and the highest melting
temperature was obtained for PEG50/DD-ionene in both hard segment types, which confirms the
effect of phase mixing on limiting the crystallinity in PEG75/DD-ionenes. The results of this
study are discussed in detail in Chapter 4.
The third study was based on the previous investigated to compare the effect of soft
segment type on final properties using PTMO monomer as the soft segment. In this set of
samples, the aromatic configuration of the hard segment created a more phase segregated
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structure, particularly in DABCO-based PTMO25/DD-ionenes. This sample showed a broad
rubbery plateau which is related to a high fraction of ionic aggregates and the formation of a
stable network. The results of this study are discussed in detail in Chapter 5.
In Chapter 6, two molecular weight of PEG soft segment (1000 and 4000 g/mol) were selected to
study the effect of spacer length. From XRD results, it was evident that PEG1k/DD-ionenes
formed an amorphous morphology and the crystalline structure occurred by increasing the
molecular weight of PEG to 4000 g/mol. This significant change in crystalline structure resulted
in an obvious difference in mechanical properties.
Due to the versatility of the ionene design, a variety of potential applications for well-defined
ionenes can be suggested. In Chapter 7, we focused on designing the composite components to
change the electrical properties as a function of soft to hard segment ratios of aliphatic ionenes.
We integrated carbon nanofibers (CNFs) and modified CNFs to create electrically conductive
networks. The sensitivity of ionene composites under strain and recovery of the structure after
unloading were selected as effective measures to identify the optimum components of the
composite for sensing applications.
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Type
dissertation