8 research outputs found
Fluorinated surfactants in solution: Diffusion coefficients of fluorinated alcohols in water
Intra-diffusion coefficients of three
fluorinated alcohols, 2,2,3,3,3-pentafluoropropan-1-ol (PFP),
2,2,3,3,4,4,4-heptafluorobutan-1-ol (HFB) and 2,2,3,3,4,4,5,5,5-nonafluoropentan-1-ol (NFP) in water
have been measured by the PFGâNMR spin-echo technique as a function of temperature and
composition, focusing on the alcohol dilute region. For comparison, intra-diffusion coefficients of 2,2,2-
trifluoroethanol (TFE) and HFB have also been measured in heavy water using the same method and
conditions. As far as we know, these are the
first experimental measurements of this property for these
binary systems. Intra-diffusion coefficients for NFP in water and for TFE and HFB in heavy water have also
been obtained by molecular dynamics simulation, complementing those for TFE, PFP and HFB reported in
a previous work. The agreement between experimental and simulated results for PFP, HFB and NFP in
water is reasonable, although presenting higher deviations than for the TFE/water system. From the
dependence of the intra-diffusion coefficients on temperature, diffusion activation energies were
estimated for all the solutes in water and heavy water
Surface crystallization of ionic liquid crystals
The evidence for surface crystallization in ionic liquids is scarce. The existing reports seem to be contradictory
as for its driving forces, since in the two compounds investigated in the literature, the
contribution of coloumbic and van der Waals forces is very different. In this work 1-dodecyl-3-
methylimidazolium tetrafluoroborate was studied and its surface crystallization characterized by surface
tension, ellipsometry and optical microscopy. The results obtained seem to reconcile previous
observations, and it was further shown, using the same techniques, that this phenomenon is prevalent in
other ionic liquids. MD simulation results illustrate the different possibilities of organization, providing
reasonable models to rationalize the experimental observations.This work was developed with the scope of the project CICECO â
Aveiro Institute of Materials, UID/CTM/50011/2019, Associate
Laboratory LSRE-LCM, UID/EQU/50020/2019, and of Instituto
de TelecomunicaçoËes/IT (UID/EEA/50008/2013) â funded by
national funds through FCT/MCTES (PIDDAC). M. A. R. M.
acknowledges financial support from NORTE-01-0145-FEDER-
000006 â funded by NORTE2020 through PT2020 and ERDF,
and P. J. C. acknowledges the FCT for the contract IF/00758/2015. A. R. Bastos from UA is acknowledged for help in the
ellipsometry measurements. M. C. C. aknowledges FAPESP
(2012/05027-1) and CNPq (310272/2017) for financial support.info:eu-repo/semantics/publishedVersio