Gels from a semifluorinated n-alkane in fluorinated solvents as a probe for intermolecular interactions (original) (raw)
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Gelation of Perfluorinated Liquids by N-Alkyl Perfluoroalkanamides
Langmuir, 2005
Gels comprised of low-molecular-mass organic gelators (LMOGs), N-alkyl perfluoroalkanamides [F(CF2)mCONH(CH2)nH; FmNHn], and several perfluorinated liquids are described. The gelation ability of the amides has been compared to that of two analogous alkyl perfluoroalkanoates. The properties of these gels have been correlated with the N-alkyl and (to a lesser extent) perfluoroalkyl chain lengths in the FmNHn by X-ray diffraction, polarizing optical microscopy, infrared spectroscopy, and small-angle neutron scattering. The gels are thermally reversible and require generally very low concentrations (<2 wt %) of LMOG. Several of the gels have been stable at room temperature for >1 year, thus far. The incompatibility of the fluorocarbon and hydrocarbon segments causes the LMOGs to aggregate into lamellae within the fibrils that constitute the basic unit of the gel networks. IR spectroscopic studies of these gels indicate that additional ordering within the aggregate units is enforced by intermolecular H-bonding among amide groups.
Thermodynamic study of (perfluoroalkane+alkane) mixtures: Excess and solvation enthalpies
The Journal of Chemical Thermodynamics, 2007
A newly designed calorimetric technique and calculation procedure have been used to obtain partial molar enthalpies, H i , and excess enthalpies, H E , for binary mixture of hexane + perfluoro-n-alkanes (C5-C8) and perfluorohexane + n-alkanes (C5-C8), + cyclohexane, and + 2-methylheptane. All mixtures are endothermic, and the heat effects increase with the size of the second component. The H E and H i values found are the largest ever observed for mixtures of non-polar compounds. An estimate of the excess heat capacity for (perfluorohexane + 2-methylheptane) has been obtained from H i at two different temperatures. From H i at infinite dilution and from the known enthalpies of vaporization, the enthalpies of solvation, D solv H , have been evaluated either for alkanes and perfluoroalkanes in both hexane and perfluorohexane solvent. Solute-solvent interactions have been examined by describing the D solv H with an additive scheme of surface interactions and by applying the Scaled Particle Theory. The effects of chain lengthening, branching, and cyclization have been discussed. Perfluoroalkanes proved to be inert molecules that interact weakly with themselves as well as with alkanes.
N-Alkyl Perfluoroalkanamides as Low Molecular-Mass Organogelators
Journal of the American Chemical Society, 2003
A new class of low molecular-mass organogelators (LMOGs), N-alkyl perfluoroalkanamides, F(CF2)nCONH(CH2)mH, is described. The molecules are designed to exploit the incompatibilities of their three molecular parts, and the results demonstrate that this strategy can be used to tune molecular aggregation and gel stability. The gelating properties of these LMOGs have been examined in a wide variety of organic liquids (including alkanes, alcohols, toluene, n-perfluorooctane, CCl4, and DMSO) as a function of the N-alkyl and perfluoroalkyl chain lengths by X-ray diffraction, polarizing optical microscopy, infrared spectroscopy, differential scanning calorimetry, and small-angle neutron scattering (SANS). The gels are thermally reversible and require generally very low concentrations (<2 wt %) of LMOG. Several of the gels are stable for very long periods at room temperature. The incompatibility of the fluorocarbon and hydrocarbon segments causes the LMOGs to aggregate, probably into lamellae within the fibrils that constitute the basic unit of the gel networks. The SANS studies show that the cross-sections of fibers in the gel networks of LMOGs with shorter perfluoroalkyl chains are much larger than those with longer ones. Comparisons with the gelating properties of some analogous esters (F(CF 2)nCO2(CH2)mH) and diblock perfluoroalkylalkanes (F(CF2)n(CH2)mH) indicate that additional ordering within the aggregate units is enforced by the intermolecular H bonding among amide groups that is evidenced by IR spectroscopy. Analyses of these results and structure/solvent correlations are provided.
Aggregation of semifluorinated alkanes in cyclic organic solvents: A SAXS study
Colloid and Interface Science Communications, 2019
Semifluorinated alkanes (SFA) are diblock molecules able to self-assemble in various organic media due to their fluorophilic/fluorophobic interactions. Such mixtures accordingly represent a model system for the further elaboration of soft-templated inorganic materials in totally anhydrous media. The aggregation behavior of four SFA species has been studied in two different organic and cyclic solvents in function of temperature by small angle X-ray scattering (SAXS). As long as the SFA-solvent mixtures remain in the liquid state, SAXS patterns reveal an aggregation behavior dependent on temperature and concentration, and on the internal structure of the SFA. We identify the relevant parameters governing the aggregation of these molecules based on the simulation of SAXS data versus temperature.
Journal of Chemical & Engineering Data, 2020
The SAFT-γ Mie group-contribution approach is extended to describe the fluid-phase behavior and excess properties of mixtures of linear alkanes and perfluoroalkanes, as well as the properties of their "chemical molecular mixtures", perfluoroalkylalkanes. Two sets of transferable binary group parameters are proposed for the interactions between the CH 3 , CH 2 and CF 3 , CF 2 functional groups, by adjusting both the unlike interaction energy (ε kl) and repulsive Mie exponent (λ kl r), in order to describe simultaneously the vapor−liquid equilibria (VLE), the upper critical solution temperature (UCST) of the corresponding liquid−liquid equilibria (LLE), and the excess properties of the n-hexane + nperfluorohexane mixture. These parameters are then transferred to describe the properties of other binary mixtures. The theoretical predictions are found to be in excellent agreement with the available experimental data. The same parameters are further used to predict the fluid phase behavior of several perfluoroalkylalkanes with different relative lengths of the hydrogenated and fluorinated segments. In this case an additional CH 2 CF 2 group is defined to account for the "extra" attractive interaction imparted to these compounds by the presence of a significant dipole moment at the alkyl-perfluoroalkyl junction.
A comparative study of thermodynamic properties of binary mixtures containing perfluoroalkanes
Journal of Thermal Analysis and Calorimetry, 2008
Literature data on molar excess enthalpies and molar excess Gibbs energies, liquid-liquid equilibria, activity coefficients at infinite dilution and partial molar enthalpies at infinite dilution of binary mixtures of n-perfluoroalkanes (C 5 -C 8 )+n-alkanes (C 5 -C 8 ) and of n-perfluorohexane+linear monoethers of general formula, CH 3 (CH 2 ) m -O-(CH 2 ) n -CH 3 (m,n=1-4), are treated in the framework of DISQUAC, an extended quasichemical group contribution theory. The systems are characterized by two or three types of contact surfaces: aliphatic (CH 3 , CH 2 , CH and C groups), fluorine (F group) and oxygen (O group). Using a limited number of adjusted contact interchange energies parameters, structure dependent, the model provides a fairly consistent description of the thermodynamic properties as a function of concentration. The model may serve to predict missing data.
VLE and LLE of perfluoroalkane + alkane mixtures
Fluid Phase Equilibria, 2002
Vapour-liquid equilibria (VLE) of binary mixtures of n-perfluorohexane plus a n-alkane (C 5 -C 8 ) and of n-hexane plus a n-perfluoroalkane (C 5 -C 8 ) were determined using a head-space gas-chromatographic technique. Excess molar Gibbs energies, G E , for the systems investigated have been obtained by a least-square treatment of equilibrium data. Liquid-liquid equilibria (LLE) were determined by turbidimetry for n-perfluorohexane + n-C n H 2n+2 (n = 6-8) mixtures and the observed T-x curves compared with those predicted by the temperature dependence of activity coefficients. All mixtures show strong positive deviations from ideality, which increase with the size of the second component. Solute-solvent and solute-solute interactions have been examined by calculating and discussing solvation Gibbs energies and Kirkwood-Buff integrals. Perfluoroalkanes proved to be inert molecules that interact weakly with themselves as well as with alkanes.
Molecular Physics, 2021
The solubility of water in liquid n-perfluorohexane and in an equimolar mixture of n-hexane + nperfluorohexane is experimentally determined as a function of temperature. The solubility of water in the equimolar mixture is significantly higher than the average of the solubilities in the pure solvents suggesting, for the first time, that mixing hydrogenated and perfluorinated chains enhances the solubility of water. The solubility in the equimolar mixture of n-hexane + n-perfluorohexane is also determined theoretically with the SAFT-γ Mie group-contribution approach, allowing a direct quantitative estimate of how much the large deviations from ideality contribute to the solubility of water in the mixture. In addition, the SAFT-γ Mie approach is used to represent the solubility of water in a number of n-perfluoroalkylalkanes, covering a range of relative lengths of the hydrogenated and perfluorinated chains. The theory can be used to predict the relative extent of the solubility of water in the different solvents, in good agreement with the experimental data. This is accomplished by using a single parameter to describe the strong attractive interaction between water and the CH 2 CF 2 group at the junction between the hydrogenated and perfluorinated segments, which is known to be responsible for the increased solubility of water in these substances.
Perfluorocarbon-Hydrocarbon Discrete Intermolecular Aggregates: An Exceptionally Short N⋯I Contact
Supramolecular Chemistry, 2002
1-Iodoperfluoroheptane (1a) and tetramethylethylenediamine (2, TMEDA) form the 2:1 ratio stable aggregate 3a and a similar behaviour is shown by 1-iodoperfluoroalkanes 1b-e and iodopentafluorobenzene 1f. These aggregates have been characterised in solution by 1 H/ 19 F-NMR spectroscopy and in the solid state through IR and single crystal X-ray diffraction. The determined structure of 3a (triclinic, a 5 6.2283(10), b 5 9.250(2), c 5 15.098(3) Å , a 5 81.369(5), b 5 81.397(5), g 5 86.010(5), V 5 849.3(3) A 23 , T 5 175(3) K, space group P-1 (No. 2), Z 5 1; d(calc) 5 2.167 g cm 23 ; 4121 independent reflections, 3665 with I o > 2(I o); final refinement gave R1 5 0.0400, wR2 5 0.0901) showed the second shortest N• • •I interaction found in the crystallographic literature [2.762(3) Å ] and the interdigitation of perfluorocarbon and hydrocarbon modules due to cooperative -C-H• • •F-C-interactions. Calculations to quantify these latter interactions have been also performed.