The effect of the chemical modification
of poly(propylene glycol)
(PPG) end groups on the molecular dynamics under 2D confinement and
the polymer/matrix interactions (including interfacial energies) was
investigated by a combination of differential scanning calorimetry
(DSC), broadband dielectric spectroscopy (BDS), surface tension and
contact angle measurements. The replacement of −OH groups in
native PPG allowed to modify the interactions with the hydroxyl groups
attached to the pore walls of nanoporous aluminum oxide (AAO) membranes
of various pore diameter. It was found that the observed reduction
in the glass transition temperature (T
g) of the core polymers correlates well with a general trend (the
higher the solid–liquid interfacial tension, γSL, the lower T
g,confined) reported earlier.
Moreover, we demonstrated that although the interfacial solid–liquid
energy seems to be almost the same for each studied herein material,
a clear change in the crossover temperature (T
c), related to the vitrification of the polymers adsorbed to
the pore walls, is noted. Interestingly, the shift in T
c with respect to the glass transition temperature of
the bulk polymer scales well according to the decreasing ability in
the formation of H bonds in the order PPG–OH → PPG–NH2 → PPG–OCH3 for the constant γSL. One can add that no such effect is found for the glass
transition of the core polymers, where a similar shift of the T
g was recorded. This finding has been discussed
in the context of various sensitivity of the studied materials to
the density fluctuations, equilibration phenomena occurring below T
c, etc. We believe that our finding will help
in a better understanding of an interplay between interfacial and
core molecules and contribute significantly to the discussion on the
impact of interfacial interactions on the molecular dynamics of polymers
under 2D confinement.
Examining the relationship between the glass transition temperature, conductivity and molecular weight of tailored imidazolium-based PILs synthesized via RAFT.
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