abstract
Recently, some works claim that hydrophobic deep eutectic solvents could be prepared based on menthol and monocarboxylic acids. Despite of some promising potential applications, these systems were poorly understood, and this work addresses this issue. Here, the characterization of eutectic solvents composed of the terpenes thymol or L(-)-menthol and monocarboxylic acids is studied aiming the design of these solvents. Their solid-liquid phase diagrams were measured by differential scanning calorimetry in the whole composition range, showing that a broader composition range, and not only fixed stoichiometric proportions, can be used as solvents at low temperatures. Additionally, solvent densities and viscosities close to the eutectic compositions were measured, showing low viscosity and lower density than water. The solvatochromic parameters at the eutectic composition were also investigated aiming at better understanding their polarity. The high acidity is mainly provided by the presence of thymol in the mixture, while L(-)-menthol plays the major role on the hydrogen-bond basicity. The measured mutual solubilities with water attest to the hydrophobic character of the mixtures investigated. The experimental solid-liquid phase diagrams were described using the PC-SAFT equation of state that is shown to accurately describe the experimental data and quantify the small deviations from ideality.
keywords
DIRECTIONAL ATTRACTIVE FORCES; EQUATION-OF-STATE; PERTURBED-CHAIN SAFT; CARBOXYLIC-ACIDS; ASSOCIATING FLUIDS; IONIC LIQUIDS; TRANSDERMAL DELIVERY; PHASE-EQUILIBRIA; SKIN PERMEATION; DEEP
subject category
Chemistry; Science & Technology - Other Topics; Engineering
authors
Martins, MAR; Crespo, EA; Pontes, PVA; Silva, LP; Bulow, M; Maximo, GJ; Batista, EAC; Held, C; Pinho, SP; Coutinho, JAP
our authors
Emanuel de Almeida Crespo
Collaborator
Liliana Patrocínio da Silva
Collaborator
acknowledgements
This work was developed in the scope of the project CICECO - Aveiro Institute of Materials, POCI-01-0145-FEDER-007679 (ref. FCT UID/CTM/50011/2013) and Associate Laboratory LSRE-LCM, POCI-01-0145-FEDER-006984 (ref. FCT UID/EQU/50020/2013), both financed by national funds through the FCT/MEC and when appropriate cofinanced by FEDER under the PT2020 Partnership Agreement. This work is also a result of project "AlProcMat@N2020 - Advanced Industrial Processes and Materials for a Sustainable Northern Region of Portugal 2020", with the reference NORTE-01-0145-FEDER-000006, supported by Norte Portugal Regional Operational Programme (NORTE 2020), under the Portugal 2020 Partnership Agreement, through the European Regional Development Fund (ERDF). M.A.R.M acknowledges FCT for her Ph.D. grant (SFRH/BD/87084/2012). FCT is also acknowledged for funding the project DeepBiorefinery (PTDC/AGRTEC/1191/2014). P.V.A.P. and G.J.M. thank the national funding agencies CNPq (National Council for Scientific and Technological Development) (305870/2014-9, 309780/2014-4, 140702/2017-2, 406918/2016-3, 406963/2016-9), FAPESP (Research Support Foundation of the State of Sao Paulo) (2014/21252-0, 2016/08566-1), FAEPEX/UNICAMP (Fund for Research, Teaching, and Extension) (0125/16), and CAPES (Coordination of Improvement of Higher Level Personnel) for financial support and scholarships. E.A.C thanks FCT for the Ph.D. grant SFRH/BD/130870/2017. C.H. acknowledges financial support from Max Buchner Research Foundation and from German Science Foundation (DFG) HE 7165/7-1.