In this thesis the self-assembly behavior of block copolymers diluted with ionic
liquids has been investigated. Initial experiments involved characterizing the selfassembly
of poly(styrene-b-methyl methacrylate) (PS–PMMA) and poly(butadiene-bethylene
oxide) (PB–PEO) copolymers at dilute concentrations (~1 wt%) in the ionic
liquids 1-butyl-3-methylimidazolium hexafluorophosphate ([BMI][PF6]) and 1-ethyl-3-
methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMI][TFSI]). Dynamic light
scattering and cryogenic transmission electron microscopy results showed that the ionic
liquids behave as selective solvents for the PMMA and PEO blocks of the copolymers,
and that the micelle morphology and self-assembly behavior of the block copolymers in
the ionic liquids was analogous to that observed in conventional solvents.
At increased solution concentrations (≥ 20 wt%) the lyotropic mesophase
behavior for PB–PEO diluted with [BMI][PF6] and [EMI][TFSI], and poly(styrene-bethylene
oxide) (PS–PEO) diluted with [EMI][TFSI] was investigated via small angle
X-ray scattering. These experiments showed a microstructure phase progression with
addition of ionic liquid that was analogous to that expected for an increase in the PEO
volume fraction of the bulk copolymers. Additionally, an increase in the lamellar
microstructure domain spacing with ionic liquid content indicated that both ionic liquids
behave as strongly selective solvents for the PEO blocks of the copolymers.
The ionic conductivity of the concentrated PS–PEO/[EMI][TFSI] solutions was
measured via impedance spectroscopy, and found to be in the range of 10−3 S/cm at elevated temperatures (~100 °C). Additionally, the ionic conductivity of the solutions
was observed to increase with both ionic liquid content and molecular weight of the
PEO blocks of the copolymer.
Finally, preliminary investigations of the microstructure orientation in thin films
of a concentrated PS–PEO/[EMI][TFSI] solution were conducted. The copolymer
microstructure was observed to align perpendicular to the film surface with short term
(≤ 2 hours) thermal annealing. Longer term thermal annealing resulted in a transition to
parallel alignment of the copolymer microstructure relative to the film surface.