posted on 2017-10-18, 15:06authored byGerardo Martínez-Rugerio, Arantxa Arbe, Juan Colmenero, Angel Alegría
The
supramolecular self-assembly of monocarboxydecyl-terminated
dimethylsiloxane oligomer is investigated and characterized by combining
different experimental methods. Thermodynamic properties were accessed
by temperature-modulated differential scanning calorimetry, and two
subambient phase transitions were identified. Fourier transform infrared
spectroscopy gave access to the main molecular entities involved in
these phase transitions. Diffraction experiments using small-angle
X-ray scattering and wide-angle X-ray scattering evidenced the development
of two distinct well-ordered sub-10 nm structures, each associated
with one of the thermal transitions, without any indication of long-range
atomic order. All the results point to the self-assembly of the oligomeric
dimers below 230 K, giving rise to supramolecular structures involving
new H-bonding interactions. A further structure is developed below
205 K by the assembly of the alkane part of the molecules in an arrangement
of hexagonally packed cylinders. Dielectric relaxation experiments
evidenced both the pronounced effect of the lowest temperature transition
on the H-bond network fluctuations and the very effective segregation
of dimethylsiloxane at lower temperatures. Moreover, we found that
the structured liquid presents a rubber-like mechanical behavior in
the temperature range 150–200 K, where dimethylsiloxane phase
remains amorphous, and at lower temperatures a glassy nanostructured
material is found.