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Fig. 12. At room temperature, a stable phase (Ph-Ia) made of
ꢀ
triclinic microcrystals in P1 space group prevails whereas at
temperatures above 80–100 ꢀC (depending on n) a semi-
crystalline layered phase with the alkyl tails in the molten state
but aligned and extensively interdigitated is formed (Ph-II). The
semicrystalline Ph-II phase becomes fully melted above ꢄ160 ꢀC
with formation of a smectic-A mesophase (Ph-III); in this phase
both choline iodide and alkyl tails are in a disordered state but
the layered arrangement is still preserved with a higher degree
of interpenetration of the alkanoyl chains. The structural
changes taking place by heating effect are reversible. Never-
theless a metastable elusive phase (Ph-Ib) appears when Ph-III
is cooled to room temperature; the structure of Ph-Ib is not
well characterized but presumably it is similar to Ph-II but with
a degree of side chain interpenetration comparable to Ph-III.
Fig. 12 Raw scheme of crystalline, semicrystalline and liquid-crystal
phases observed for nACh$I.
selection of the pictures taken from 16ACh$I is shown in Fig. 11
and a complete assortment of images illustrating the texture
changes occurring in the other members is afforded in the ESI†
le. Samples for observation were prepared by casting from chlo-
roform at room temperature so they were initially in Ph-Ia phase.
The high crystallinity of Ph-Ia previously evidenced by both DSC
and WAXS is reected in the crystal-mosaic texture present in the
rst pictures taken at low temperatures; this well-dened
geometrical morphology was lost aer heating above 100 ꢀC and
not recovered any more. The texture seen at 125 ꢀC corresponds to
Ph-II which was observed to evolve with expansion of the material
indicating that the Ph-Ia to Ph-II conversion takes place with a
decrease in density inagreement with theincrease in the interlayer
spacing revealed by SAXS. A close inspection of this picture
revealed the presence of the features characteristic of a smectic
mesophase, which is in full agreement with SAXS results. Further
Acknowledgements
This work received nancial support from MCINN of Spain with
Grants MAT2009-14053-C02-01 and MAT2012-38044-C03-03
and from AGAUR with grant 2009SGR1469. Thanks also given
to Dr Campos from UPC for her guidance in the single crystal
preparation method. Portions of this research were carried out
at the A2 beamline of light source DORIS III at DESY (Hamburg,
Ge); authors are indebted to Dr S. Funari for his invaluable
assistance. Thanks also to the Basque Government for the Ph.D.
grant awarded to Ainhoa Tolentino.
ꢀ
heating at temperatures above ꢄ165 C led to Ph-III which dis-
played a texture not very different from that of Ph-II. In fact,
according to WAXS/SAXS data, Ph-II and Ph-III phases will share
the same stratied patternwith alkanoyl chains inthe moltenstate
intercalated between the layers where the choline iodide counter-
parts are located. Differences between the two phases concern the
order degree of the ionic layer, which is crystallized in Phase II but
disordered in Phase III, and the interdigitation degree, which is
greater in Phase III. Aer cooling down to room temperature a
strongly birefringent material devoid of any distinctive texture was
generated; according to DSC and diffraction data it must corre-
spond to Ph-Ib, Ph-Ia of even a mixture of both.
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