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Physicochemical Insights on Alkylcarbonate – Alkanol Solutions Rafael Alcalde, Mert Atilhan, Jose Luis Trenzado, and Santiago Aparicio J. Phys. Chem. B, Just Accepted Manuscript • DOI: 10.1021/acs.jpcb.6b02961 • Publication Date (Web): 12 May 2016 Downloaded from http://pubs.acs.org on May 24, 2016

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The Journal of Physical Chemistry

Physicochemical Insights on Alkylcarbonate – Alkanol Solutions Rafael Alcalde,a Mert Atilhan,b José Luis Trenzado,*c and Santiago Aparicio*a a b c

Department of Chemistry, University of Burgos, 09001 Burgos, Spain

Department of Chemical Engineering, Qatar University, P.O. Box 2713, Doha, Qatar

Departamento de Física, Universidad de Las Palmas de Gran Canaria, 35017 Las Palmas G.C., Spain

*Corresponding authors: [email protected], +34 947 258 062 (S.A.) and [email protected], +34 928 452 730 (J.L.T.)

ABSTRACT: Macroscopic properties and structuring at the molecular level of dialkylcarbonate + 1-alkanol mixed fluids have been studied as a function of alkyl chain lengths in 1-alkanol and dialkylcarbonate, mixtures composition and temperature. A combined experimental and computational approach was considered for studying the relationships between the nanoscopic structure of the mixed fluids, nature, extension and organization of hydrogen bonding, and physicochemical properties. Thermodynamics characterization, using excess and mixing properties, are related with the strength and characteristics of intermolecular forces. Classic molecular dynamics simulations and quantum chemistry calculations provide a detailed picture of mixed fluids’ structuring and dynamic behavior.

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INTRODUCTION The study of properties for complex liquid mixtures is of great relevance because of the intimate relationship between intermolecular forces and fluids’ macroscopic physicochemical properties.1 The development of predictive models for thermophysical properties in multicomponent liquid mixtures2,3 stands on a deep knowledge of the mechanism of homo and hetero-association between involved molecules,4 which is related with the type of functional groups present in the molecules and with the size and shape of these molecules. Therefore, studying complex liquid mixtures both from macroscopic and microscopic viewpoints is of remarkable interest for scientific and applied engineering purposes. Considering the complexity of factors controlling the properties of multicomponent liquid mixtures, the most suitable option for analysing their macroscopic behaviour and their structure at the molecular level is to carry out studies in which a reduced number of functional groups and/or molecular characteristics are considered at the same time, for isolating their main features.5 For this purpose, our group has studied these last years the properties and structuring of several types of liquid mixtures considering different types of molecules, such as amides,6 alkyl lactates7 and glymes.8 Among these types of studied molecules, those based in dialkylcarbonates showed significant properties.9 The presence of the carbonate polar functional group together with apolar alkyl chains, for which the length can be tuned that leads to increase in the steric and hydrophobic effects, will determine the properties of mixtures upon mixing with other organic solvents. Likewise, being eco-fiendly materials10 dialkylcarbonates have several relevant technological applications such as fuel additives11 or as solvents in lithium batteries,12 which combined with the ability of developing sustainable synthesis procedures,13 justify their use as alternative to many traditional solvents. Likewise, dialkylcarbonates, especially dimethylcarbonate (DMC), are considered as green solvent14,15 due to their suitable environmental, biodegradable and toxicological properties.16,17,18,19,20,21 Therefore, the properties of dialkylcarbonate containing liquid mixtures need to be considered in detail upon mixing with relevant types of cosolvents. In a previous work,9 the characteristics of dialkylcarbonate + n-alkane binary solvents were studied using a combined experimental and theoretical approach. Therefore, in order to increase the complexity of the intermolecular forces for systems containing dialkylcarbonates, the properties of dialkylcarbonates + 1-alkanol binary mixtures are 2


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studied in this work. The presence in the mixtures of carbonate and hydroxyl functional groups should lead to remarkable homo and hetero-association by hydrogen bonding, which would lead to large deviations from ideality from the thermodynamic viewpoint. These hydrogen bonds will determine fluids’ structuring at nanoscopic level, which would be linked with their thermodynamic macroscopic behaviour. Previous studies have showed the prevalence of cis-cis isomer (∼ 99 % at close to ambient temperature) for pure liquid DMC,22 which is maintained upon mixing with nalkanes.9 The cis-cis isomer has 1.0 D dipole moment, in contrast with 4.5 D for the cis – trans one, which, in spite of being in very marginal concentration in pure DMC, tends to selfaggregate.22 Therefore, it is necessary to analyse the geometric properties of dialkylcarbonates upon

mixing with 1-alkanols, considering the effect of developing

heteroassociations by hydrogen bonding. The characterization of dialkylcarbonate + 1-alkanol mixtures, Figure 1, was carried out in this work using a combined experimental and computational approach, which will provide the micro and macroscopic information and their relationships. A thermophysical experimental study was carried out in a first stage, in which two relevant properties (density and dynamic viscosity) were measured as a function of mixture compositions, length of alkyl chains in dialkylcarbonate (dimethyl and diethylcarbonate) and in 1-alkanol (1-butanol, 1hexanol, 1-heptanol and 1-nonanol), and temperature. Density and viscosity were selected for the study because of its relevance for practical purposes and also because their intimate connection with the intermolecular forces and steric effects at the molecular level. In a second stage of the study, a theoretical approach using both quantum chemistry calculations, based on the Density Functional Theory (DFT), and classical molecular dynamics simulation was developed. These theoretical results provided information on the strength, geometry and topology of intermolecular forces, the dynamics of interacting molecules and many other nanoscopic characteristics that are not obtained via experiments easily and yet they can provide a detailed vision of the fluids’ properties at the molecular level. Therefore, the main objective of this work is to provide for the very first time a detailed microscopic and macroscopic characterization of dialkylcarbonate + 1-alkanol solvents, considering the characteristics of intermolecular forces from a bottom - up approach.

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METHODS Materials. Origins and stated purities of chemicals used in this study are reported in Table S1 (Supporting Information). Before being used, all reagents were kept over freshly activated molecular sieves of type 4 nm (Union Carbide) and degassed by ultrasound. All chemicals were used without further purification. Comparison of measured physical properties of pure components with the literature values are given in Table S2 (Supporting Information), showing good agreement for the studied temperature range. All the binary mixtures were prepared by mass using an electronic balance (Mettler AE240) with a precision of ±0.01 mg. The error in the mixtures mole fraction is estimated to be less than ±0.00004. Thermophysical Properties. Densities (ρ) of pure liquids and their binary mixtures were obtained by using an Anton-Paar (DMA-60/602) vibrating-tube densimeter. Water (Panreac Hiperpur-plus) and n-heptane (Fluka > 99.5%) were used as calibrating fluids.23,24 The temperature of the densimeter measurement cell was determined with a CKT-100 thermometer from Anton-Paar. The average uncertainties of the density and the excess molar volume were estimated to be less than ±0.00002 g⋅cm–3 and ± 0.003 cm3⋅mol–1, respectively. The kinematic viscosities (v) of pure liquids and their binary mixtures were measured with several Ubbelohde viscometers for a Schott-Gerätte automatic measuring unit (model AVS 350) provided with a transparent thermostat bath CT 1450/2, which allows temperature stabilization with a tolerance of 0.01 K. The kinematic viscosity was computed using the equation ν = Κ (t–ϑ) where ϑ is the Hagenbach correction, t is the flow time and K is the capillary constant. Viscometer calibration was provided by the instrument manufacturer, and thus, the uncertainty of kinematic viscosity measurements was estimated to be less than 0.4 %. Molecular Modelling. Density Functional Theory (DFT) studies were carried out using the Gaussian 09 (Revision D.01) package,25 all of them for B3LYP26,27,28 functional with 631+G(d,p) basis set. Interaction energy, ΔE, was calculated as the difference of the energy for the molecular pair and the sum of the energies for the corresponding monomers, all of them at the same theoretical level. Basis set superposition error (BSSE) was corrected for ΔE using the counterpoise procedure.29 Atoms in a Molecule (AIM),30 using the AIM2000 program,31 and Natural Bond Orbital (NBO)32 calculations were carried out to infer more 4


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details on the topology and characteristics of intermolecular interactions for the studied molecular pairs. Molecular dynamics simulations were carried out using the MDynaMix v.5.2 molecular modelling package.33 The forcefield parameterization for the studied dialkylcarbonates and 1-alkanols are reported in Table S3 (Supporting Information). The systems under MD study are reported in Table S4 (Supporting Information) together with the number of molecules considered for the simulation boxes, temperatures and pressures. Cubic boxes were used for all the MD simulations, which were initially build at low density (∼ 0.2 g cm-3) using the Packmol program.34 Periodic boundary conditions were applied. These initial boxes were subjected to several heating (up to 500 K) and quenching steps to the corresponding simulation temperature to assure equilibration, which was analysed through the constancy of total potential energy. After these equilibration steps, 10 ns production runs in the NPT ensemble were carried out for each system reported in Table S4 (Supporting Information). Pressure and temperature was controlled using the Nose–Hoover method. Coulombic interactions were handled according to the Ewald summation method35 (15 Å for cut-off radius). Equations of motion were solved using the Tuckerman–Berne double time step algorithm36 (1 and 0.1 fs for long and short time steps). Lorentz-Berthelot mixing rules were used for handling Lennard-Jones terms.

RESULTS AND DISCUSSION The properties of pure dialkylcarbonates (DMC and DEC) were studied by our group in a previous work9 showing the prevalence of cis-cis isomers in liquid phase (roughly 99 %), with very minor changes with temperature increase, in agreement with previous literature studies.22,37,38 These results also showed the development of preferential interactions between neighbour DMC or DEC molecules between O2 atoms and alkyl chains. Therefore, the changes in molecular arrangements and physicochemical properties for DMC and DEC upon mixing with 1-alkanols will be analysed in the following sections. The measured density and dynamic viscosity for dialkylcarbonate + 1-alkanol systems as a function of alkyl chain length in dialkylcarbonate (DMC and DEC) and 1-alkanol (BUT, HEX, HEP and NON), of mixtures composition and of temperature are reported in Tables S5 to S20 (Supporting Information). These experimental properties allowed calculating excess molar volume, VE, and mixing viscosity, Δη, using well-known thermodynamic 5



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relationships,39 which are reported in Tables S5 to S20 (Supporting Information) and plotted in Figure S1 to S16 (Supporting Information). The large amount of thermophysical data included in the Supporting Information may be summarized with results reported in Figure 2. All the studied mixtures are characterized by expansion upon mixing, positive VE, and negative Δη, Figures 2a and 2c. These properties point to a disruptive effect by alkylcarbonates on the hydrogen bonding networks of 1-alkanols upon mixture formation, which leads to volume expansion and a decrease in viscosity in comparison with linear combinations of the properties. Excess molar volume show maxima at equimolar composition for all the studied mixtures, whereas the minima for mixing viscosity appears for 2:1 1-alkanol:dyalkylcarbonate molar ratios, which points to the development of strong intermolecular interactions between both types of molecules, especially for 1-alkanol rich solutions. The excess molar volume and mixing viscosity, in absolute value, increase with increasing 1-alkanol alkyl chain length both for DMC and DEC, with maxima and minima of these properties evolving with an almost linear trend with the size of the 1-alkanol, Figures 2b and 2d. This shows a larger disruptive effect of dialkylcarbonates for longer 1-alkanols. Regarding the effect of dialkylcarbonate size, mixing viscosity does not change on going from DMC to DEC for a fixed 1-alkanol, whereas lower expansions are inferred for DEC. The comparison of results reported in this work for dialkylcarbonate + 1-alkanol systems with those previously reported for dialkylcarbonate + n-alkane9 shows that the introduction of the hydroxyl group leads to a decrease in excess molar volume and an increase, in absolute value, of mixing viscosity. For example, the comparison of results for DMC + n-nonane with those for DMC + 1-nonanol show a 36.5 % in the maxima of excess molar volume at 303 K, and analogously a 41.6 % decrease is obtained for DEC + n-nonane compared with DEC + 1nonanol. Likewise, mixing viscosity minima evolves from -0.07 mPa s for n-nonane systems9 to -2.69 mPa s for 1-nonanol systems. Therefore, the role of alkanol alkyl chains on mixture properties stands on their trend to expand the liquids upon mixing with alkylcarbonates, although this expansive effect is partially balanced by the trend of developing heteroassociations between the 1-alkanol and the dialkylcarbonate, which is clearly a contractive effect. Nevertheless, the large negative mixing viscosities obtained for all the studied systems show the disruptive effect of DMC and DEC on 1-alkanol hydrogen bonding networks. This disruptive effect increases with increasing 1-alkanol alkyl chain, larger mixing 6


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viscosities, showing that alcohol – carbonate interactions are more effectively developed for short chain 1-alkanols. The 1-alkanols studied in this work (BUT to NON) are amphiphilic molecules, which determines the formation of hydrogen bonding aggregates in neat fluids. In spite of the middle size of alkyl chains for the studied 1-alkanols, available studies have reported conflicting models on the size and type of aggregates, e.g. for neat 1-octanol chainlike or micellar – type aggregates have been proposed, although linear oligomers seem to prevail in liquid state with a large variation of size and shape.40,41 The trend to develop linear aggregates in 1-alkanols have been confirmed by several experimental and theoretical studies, these results showed that roughly 80 – 90 % of the 1-alkanol hydroxyl groups develop two hydrogen bonds with a very minor degree of branching.41,42,43 In this way, the average cluster numbers reported in the literature are 2.89 for BUT44 or 5 for 1-octanol.40 Molecular dynamics calculations reported in this work for BUT allowed the calculation of percentage of hydroxyl groups developing 0 (monomers), 1 (dimers or terminal hydroxyl groups), 2 (linear trimers), 3 (branching) or 4 hydrogen bonds, leading to 2.2, 13.3, 76.7, 7.6 and 0.2 % at 303 K. These results for neat BUT show the development of extensive hydrogen bonding leading to linear chains with 2.70 average aggregation number in excellent agreement with previous results.41-44 Mixing of 1-alkanols with DMC or DEC leads to a disruption of alkanol-alkanol hydrogen bonding partially balanced by new alkanol – DMC / DEC hydrogen bonding, as confirmed by excess and mixing properties. Therefore, in a first stage of this research we analysed the characteristics of dialkylcarbonate – dialkylcarbonate interactions and 1-alkanol – dialkylcarbonate hydrogen bonding using DFT approach. DFT studies provide information about short range interactions, which are relevant for inferring the main characteristics of 1alkanol – dialkylcarbonate structuring, middle and long range effects having also a relevant role on liquid state properties are analysed using MD simulations. In the DFT study, DMC – DMC and DEC – DEC interactions are analysed by exploring the full potential energy surface considering eight initial configurations, which were reduced to the three ones reported in Figure 3. The main characteristics of DMC monomers have been studied in detail in the literature,45 and thus, only DMC – DMC or DEC - DEC dimers will be considered in this work. Results in Figure 3 show the development of cyclic dimers, which according to AIM approach are characterized by two bond critical points (BCPs) and a ring critical point (RCP). The 7



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characteristics of these dimers are very similar both for DMC and DEC, the values for electron density and the laplacian of electron density are in the low limit for being considered as hydrogen bonds,46 and although some controversy has been raised on the too stringent character of AIM criteria for defining weak hydrogen bonds47 the interaction between the carbonyl oxygen and hydrogens in alkyl groups show moderate strength as also inferred from the values of binding energies. The NBO analysis of DMC – DMC and DEC – DEC interactions is reported in Table 1, in which the interactions are characterized by the by the hyperconjugation-induced charge transfer between the corresponding oxygen lone pairs (keto in Figures 3a to 3d, and also ether in Figures 3e and 3d) and the anti-bonding orbitals of –CH3 (DMC) or –CH2- (DEC) groups. It is well-known that the larger the second-order perturbation energy, E(2), the stronger the interaction. The values of E(2) reported in Table 1 are low for most of the studied dimers, especially for those reports in Figures 3c and 3d. The efficiency of donor-acceptor interactions according to NBO is analysed considering that it can be improved by decreasing energy difference (lower ΔE values) and increasing symmetry (larger Fij). The results reported in Table 1 shows that the main factor controlling donor – acceptor interaction is Fij, which are too low for all the studied dimers, especially for those in Figures 3c and 3d, and thus, in spite of the suitable ΔE values the poor symmetry between the donor and the acceptor leads to moderate charge transfer. Regarding DFT characterization of 1-alkanol – dialkylcarbonate 1:1 interactions, although several initial configurations were initially considered exploring different alkanol – dialkylcarbonate interaction sites, all of them led after energy minimization to the two ones reported in Figure 4. Two possibilities are inferred for BUT – DMC / DEC interactions: i) hydroxyl – carbonyl oxygen or ii) hydroxyl – ether oxygen, with the first one being remarkably stronger both for DMC and DEC. These interactions are characterized by a BCP in the case of DMC and by two BCPs and a RCP for DEC, although the second BCP (BCP_2) and the RCP are remarkably weaker than the first one as inferred from electron density and laplacian of electron density, Figure 4. The main BCP (BCP_1) shows values for electron density and laplacian of electron density in the middle of the range for defining a hydrogen bond according to AIM criteria, which justify the values of binding energies reported in Figure 4. Nevertheless, the values of binding energies reported in Figure 4 point to a preference

of

developing

hydrogen

bonding through the

carbonyl

oxygen in

dialkylcarbonates. The NBO analysis reported in Table 2 show that larger change transfer 8


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from oxygen lone pairs in carbonyl than in ether groups to antibonding orbitals in BUT hydroxyl group, which would also justify the stronger interaction through the first group. Likewise, the interaction is characterized by a high degree of symmetry between the donor and the acceptor for each hydrogen bond, which would justify the E(2) and binding energy values. The dialkylcarbonate – dialkylcarbonate interactions and the hydrogen bonding between 1-alkanols and dialkylcarbonates described in the previous paragraphs should lead to remarkable changes in the corresponding vibrational spectra, which was calculated using DFT for the optimized dimers reported in Figures 3 and 4. The shifting of carbonyl and hydroxyl stretching frequencies is reported in Table 3. Regarding diakylcarbonate – dialkylcarbonate interactions, they are characterized by redshifting for all carbonyl groups involved in the dimer interactions, whereas free carbonyl groups (Figures 3e and 3e) suffer blue shifting. In the case of BUT – DMC / DEC interactions carbonyl involved in hydrogen bonding with the alcohol also suffer redshifting, whereas non-interacting carbonyl groups are blueshifted. BUT hydroxyl groups show very large redshifting upon interacting both with DMC and DEC. The reported DFT results lead to a picture of short-range interactions in the studied systems, but additional characteristics for longer range interactions and esteric effects, which develop a pivotal role for liquid state properties need to be analyzed according to MD simulations. The forcefield parameterization used in this work for dialkylcarbonates was tested in a previous work showing good agreement with experimental properties for neat dialkylcarbonates.9 Nevertheless, in this work several relevant physicochemical properties for BUT + DMC mixtures have been predicted from MD and compared with experimental results for analysing the performance of the applied parameterization that was used for describing the physicochemical properties of these mixed fluids. Therefore, density, dielectric constant (from the fluctuations of the total molecular dipolar momenta),48 selfdiffusion coefficients (from mean square displacements and Eintein’s equation) and dynamic viscosity (from Green-Kubo equation) were calculated together with the corresponding excess and mixing properties and compared with experimental data when available, Figure 5. Results in Figure 5a show reasonable agreement between experimental and MD predicted density in the, with largest deviations being obtained for BUT rich mixtures. Nevertheless, a reasonable agreement for excess molar volume is obtained both in sign, position of the 9



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maximum and expansion upon mixing, confirming the suitability of the used parameterization for describing volumetric properties of the studied mixtures. The predictions of dielectric constants using MD simulations it is not a simple task considering that this property correlations of short and long range interactions,49,50 and thus being very sensitive to minor forcefield details. In the case of alcohols, values reported in the literature obtained from MD are up to 50 % lower than experimental ones,51 which may be justified considering the diversity of hydrogen bonded aggregates in liquid 1-alkanols,40 which is remarkably difficult to be accurately captured using MD. The values for dielectric constant in neat DMC and BUT at 303 K are 1.59 and 9.29, respectively, being almost the half of 3.2 and 17.43 (both at 298.15 K) experimental data, respectively.52,53 but in good agreement with previous simulations using non-polarizable forcefields.54 The evolution of dielectric constant with mixture composition for BUT + DMC system reported in Figure 5b shows a clear nonlinear trend leading to negative mixing property with minima at roughly 2:1 BUT:DMC mole ratios. The addition of DMC to BUT disrupts the BUT hydrogen bonding network leading to less polar mixtures by the formation of DMC-BUT aggregates. The ability of the MD model for predicting the dynamics of the studied mixtures was analysed using self-diffusion coefficients and dynamic viscosity, Figures 5c and 5d. MD leads to larger viscosities in comparison with experimental data but the changes with mixture composition, and thus the mixing viscosity, are in excellent agreement with experimental results, Figure 5d. Regarding molecular diffusion, results in Figure 5c, which could not be compared with experimental data, show larger diffusion rates for DMC than for BUT, in agreement with the lower viscosity of DMC, but the curves showing the changes with composition are almost the same for both components, Figure 5c. Likewise, self-diffusion curves evolves through maxima with mixture composition, with these maxima appearing for 2:1 BUT:DMC mole ratios, in agreement with mixing dielectric constant and viscosity reported in Figures 5b and 5b, showing the weakening of BUT-BUT hydrogen bonding upon mixing with DMC partially balanced by BUT-DMC interactions. The results reported in Figure 5 shows the suitable performance the used MD forcefield parameterization, and thus, a deeper characterization of the structuring of these mixed fluids at the nanoscopic level can be inferred using MD results. In a first stage, arrangements at the molecular level were analysed using radial distribution functions, RDFs. RDFs for the corresponding centers-of-mass are reported in Figure 6. BUT-BUT interactions 10


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are characterized by a first intense and narrow peak at 4.55 Å (in the whole composition range), followed by a second (shifting to lower distances with increasing DMC concentration) and even a third band, Figure 6a. These BUT-BUT RDFs are in agreement with BUT-BUT hydrogen bonding decreasing with increasing DMC amounts, the coordination numbers reported in Figure 7 obtained from RDFs show a non-linear decrease of BUT molecules around a central BUT one, with larger number of BUT molecules in the 2nd shell and lower in the 1st shell in comparison with linear trends. This may be justified considering that although the addition of DMC molecules weakens BUT-BUT interactions, the development of BUTDMC ones with 2:1 stoichiometry leads to a certain enrichment of BUT molecules in the second shell around BUT. The DMC-DMC interactions are characterized by two peaks, Figure 6b, the first and less intense one would correspond to dimers interacting through ether oxygen, as for the dimer in Figure 3e, whereas the most intense second one would correspond to interactions through the carbonyl site, Figures 3a and 3c. Not remarkable features are obtained for larger distances in RDFs for DMC-DMC interactions, which confirms the trend for developing dimers. Likewise, the variation of coordination numbers for DMCDMC with increasing DMC concentration follows a linear trend, Figure 7. Regarding BUTDMC interaction, the two peaks in RDFs at 4.5 and 6.3 Å confirm the development of hydrogen bonding, which is maintained in the full composition range, Figure 7. The specific atomic sites for developing intermolecular interactions were analysed in Figures 3 and 4 using DFT but should be confirmed in bulk liquid phases using site-site RDFs reported in Figure 8. The two peaks in RDFs for Hb-O3 interactions reported in Figure 8a confirm that in spite of the disruptive effect of DMC on BUT-BUT self-association, BUT-BUT hydrogen bonding is maintained in full composition range. The first maxima appear at 1.90 Å (in agreement with distances reported in Figure 4 from DFT), which would correspond to a BUT molecule directly hydrogen bonded to DMC, and a second maxima at 3.5 Å corresponding to another BUT molecule hydrogen bonded with the first BUT one but not with DMC. This arrangement would lead to 2 BUT : 1 DMC complexes for BUT – rich mixtures (the second peak in RDFs vanishes for DMC-rich mixtures), in agreement with the behaviour of physicochemical properties reported in Figures 5b to 5d. Results in Figures 8b and 8c show that the weak DMC-DMC interactions can be developed both through the O1 and O2 sites, in agreement with the similar strength of interactions reported in Figure 3. For the preferential atomic sites for DMC-BUT interactions, results in Figures 8d and 8e clearly show that the 11



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hydrogen bonding is developed through the O2 carbonyl site whereas very minor hydrogen bonding is developed through the O1 ether site. The results for Spatial distribution functions (SDFs) reported in Figure 9 show that BUT molecules are placed on top of carbonyl group in DMC (in agreement with the arrangement reported in Figure 4a) with DMC molecules being placed mainly around the DMC methyl groups and with minor spots above and below the DMC molecular plane. This arrangement is maintained in the whole composition range, and thus BUT and DMC molecules occupy different regions around a central DMC molecule, without interfering between them and allowing efficient BUT-DMC and DMC-DMC interactions with the same molecule. For the spatial arrangement around BUT molecules, a central BUT molecule may develop two hydrogen bonds with other BUT molecules, which correspond to the spots above and below the hydroxyl group reported in Figure 9, and at the same time one of these spots is shared for developing hydrogen bonds with DMC molecules. This scheme of interaction is maintained in the whole composition range. The strong trend for developing BUT-BUT and BUT-DMC hydrogen bonding showed in Figures 8 and 9 is quantified in Figure 10 in which the percentage of BUT molecules developing i BUT-BUT hydrogen bonds, fi, and the percentage of DMC molecules developing i BUT-DMC hydrogen bonds, gi, is reported. Regarding BUT self-association, results in Figure 10a show that for low DMC concentration (x < 0.2) most of BUT molecules develop two hydrogen bonds, which would lead to BUT-BUT trimers as the prevailing aggregate in a similar way as in neat BUT. For x > 0.2 the number of BUT molecules developing just one hydrogen bond, which would correspond to BUT-BUT dimers increases, evolving through a maximum, and so does the population of BUT monomers. The degree of branching in BUTBUT aggregates is very small even for BUT rich mixtures (low f3 and almost null f4), showing the trend to develop linear aggregates in the full composition range. This behaviour of BUTBUT aggregates is justified by the trend to develop BUT-DMC heteroassociations reported in Figure 10b. For low DMC concentration (x < 0.2) roughly all the DMC molecules develop one or two hydrogen bonds with surrounding BUT molecules, and this trend for BUT-DMC hydrogen bonding is maintained in the full composition range. The results in Figure 10 shows a remarkable non-linear evolution of aggregation with mixture composition, this is quantified in Figure 11 in which the average number of BUT-BUT and BUT-DMC hydrogen bonds per BUT or DMC molecule, respectively, is reported. The evolution of the average number of BUT-BUT hydrogen bonds deviates from the linear behaviour showing less 12


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interactions than the ones expected by the decreasing of BUT concentration whereas the opposite behaviour is obtained for BUT-DMC molecules. These results confirms the prevailing trend for developing BUT-DMC hydrogen bonds which decreases the number of BUT-BUT interactions, and thus leading to the deviations of thermodynamic ideality reported in Figure 2. Previous studies have showed the prevalence of cis-cis isomer for neat DMC,22 which was maintained upon mixing with n-alkanes.9 The distribution of DMC isomers in DMC + BUT mixtures was calculated in the full composition range from the probability distribution of the corresponding torsional angles, Figure S17 (Supporting Information), showing that the cis-cis isomer is the prevailing arrangement in the whole composition range, and although for highly diluted DMC solutions the percentage of cis-trans isomer is slightly larger than in neat DMC, the trend for developing BUT-DMC hydrogen bonds does not change the prevailing molecular orientation of DMC molecules. The results in Figure 2a showed expansion upon mixing for DMC + BUT mixtures, which should be related with the hydrogen bonding reported in previous sections but also with orientational effects derived from molecular rearrangements for developing BUT-DMC interactions. For this purpose, the distribution of cavity sizes in DMC + BUT mixtures is reported in Figure 12. Cavities distribution was calculated using a method in which a network of randomly distributed point was placed in the simulation boxes and the distance between each gridpoint and the edge of the closest atom, defined by its van der Waals spherical radius, was calculated. These results show that neat BUT has smaller cavities than neat DMC, i.e. the development of BUT-BUT hydrogen bonded aggregates leads to more efficient packings in BUT than the weaker DMC-DMC ones. For BUT + DMC mixtures, the results in Figure 12 show the first peak in cavities distribution, corresponding to the most probable cavity sizes (smaller ones) shifting towards larger sizes with increasing DMC mole fraction, and at the same time other features corresponding to larger cavities (e.g around 0.5 and 0.75-1.00 Å) are also shifted toward larger sizes. Therefore the addition of DMC molecules to BUT increases the size of available cavities in the mixed fluid in comparison with neat BUT, which would justify from the molecular viewpoint the positive excess molar volume reported in Figure 2a. The hydrogen bonding in the studied liquid mixtures should have a strong effect on the dynamics of molecules in the corresponding solvation spheres reported in Figure 6, this 13



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effect was quantified through the residence times around each molecule reported in Figure 13. For a central DMC molecule, interacting neighbour DMC molecules stay shorter times than BUT molecules in the first solvation shell whereas the opposite behaviour is obtained in the second shell, which can be justified with the weaker DMC-DMC interactions in comparison with BUT-DMC ones, Figures 3 and 4. Nevertheless, these results show that once a molecule leaves the first solvation shell around another DMC it stays in the second shell because it may interact with the BUT molecule developing hydrogen bonding with the first one. The residence time of BUT molecules around a central BUT is large especially for BUTrich mixtures but it decreases remarkably on going to DMC-rich solution, in agreement with results in Figure 10 showing the decrease in BUT-BUT aggregates sizes which would allow a larger BUT mobility. The strengths of intermolecular interactions for BUT-DMC mixtures in liquid phases are reported in Figure 14a. These results confirm the prevalence of BUT-DMC interactions in the whole composition range, and they decrease in an almost linear way with increasing DMC mole fraction. The discussion of results in previous paragraphs have been centered in the behaviour of BUT – DMC mixtures, but this study has also analysed the effects of alkyl chains in 1alkanol and dialkylcarbonate. Likewise, the temperature effect on the properties and nanostructuring has also been studied. From the experimental viewpoint, the alkyls chain and temperature effects are summarized in Figure 15. Regarding excess molar volume, increasing 1-alkanol chains increases expansion and going from DMC to DEC decreases expansion, but for all of them increasing with increasing temperature. In the case of mixing viscosity, the dialkylcarbonate has no effect and increasing alkanol chain leads to larger, in absolute value, property, with all of them evolving in a non-linear way with increasing temperature, especially for longer alkanols. From the nanoscopic viewpoint, the molecular arrangements does not suffer remarkable changes in the studied temperature range, hydrogen bonding is mostly maintained and the structure of the shell suffers very minor changes as the radial distribution functions shows in Figure S18 (Supporting Information). The effects of alkyl chain lengths in radial distribution function are reported in Figure 16 where it is shown that all the maxima remains in the same positions for all the studied alkanols and both for DMC and DEC, showing minor structural differences in the solvation shells and hydrogen bonding. These temperature and alkyl chain effects are quantified more in detail through the solvation numbers reported in Figure 17, showing minor decreases for 14


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all the interacting pairs with increasing temperature and with increasing alky chain length in alkanol and alkylcarbonate. The temperature effect, Figure 17a, may be justified considering the strength of intermolecular interactions reported in Figure 14c, which shows weakening upon heating but with minor changes; e.g. BUT-DMC interactions are weakened a 11 % on going from 293 to 353 K. Results in Figure 14b show that DEC-DEC interactions are stronger than DMC – DMC ones because the larger alkyl chain would increase the number of LennardJones contacts, and thus the lower solvation numbers reported in Figure 17b for DEC are justified by steric effects. The effect of 1-alkanol alkyl chain length on intermolecular interaction energies is complex, Figure 14b, showing that increasing alkanol size weakens DMC-DMC and DEC-DEC interactions but increases alkanol – alkanol ones. This effect is justified also through an increase of Lennard-Jones contacts between alkanol molecules with increasing number of –CH2- groups, and thus the decreasing solvation numbers in Figure 17b rise also from steric effects because of the larger molecular sizes. The average number of hydrogen bonds per molecule slightly decreases with increasing temperature and remains almost constant with increasing 1-alkanol length, whereas those mixtures involving DEC molecules lead to lower number of alkanol – dialkylcarbonate hydrogen bonds than those with DMC whereas for the opposite behaviour is obtained for alkanol – alkanol interactions, Figure 18. Likewise, increasing of cavities size upon heating is inferred, Figure 19a, in agreement with the increasing excess molar volume reported in 15b. The effect of 1-alkanols size on cavities distribution is reported in Figure 19b showing a widening of distribution peaks with increasing size leading to more free space available. Regarding the effect of dialkylcarbonate size, the effect is very minor in cavities distribution but also widening of curves is inferred, and thus increase of free space. Temperature effect on nanoscopic dynamics is reported in Figure 20a for residence times showing increasing molecular mobility, changing in a non-linear way, for all the considered solvation spheres and evolving in a parallel way. Increasing alkanol sizes decreases mobility in solvation spheres as also does increasing dialkylcarbonate chain length, Figure 20b. The self-diffusion coefficients reported in Figure 21a follows a non-Arrhenius behaviour in the studied temperature range. Moreover, the mobility of dialkylcarbonate molecules is larger than for any of the studied 1alkanols, and molecules in DEC mixtures diffuse slower than in DMC ones, especially for short alkanols although the effect of dialkylcarbonate size almost vanishes for long alkanols (HEX, HEP and NON), Figure 21b. In spite of these minor changes upon heating or increasing 15



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alkyl chain lengths, subtle orientational changes are produced as the changes in dielectric constant reported in Figure S19 (Supporting Information) show. These orientational changes leads to less polar mixtures upon heating (increasing random arrangement of dipoles by heating) and with increasing alkyl chain lengths both in 1-alkanols and dialkylcarbonates.

CONCLUSIONS The structure and properties of 1-alkanol + dialkylcarbonate liquid mixtures were studied using a combined computational and experimental approach as a function of mixtures composition, temperature and types of alkanol and dialkylcarbonate. These mixed fluids show highly non-ideal behaviour which is justified from the molecular viewpoint by the development of strong alkanol – dialkylcarbonate hydrogen bonding which disrupts the alkanol – alkanol aggregates even for low dialkylcarbonate concentrations. This trend for developing heteroassociation by hydrogen bonding leads to fluids rearrangement upon addition of dialkylcarbonates to 1-alkanols, which leads to larger available free space. The hydrogen bonding is only slightly weakened by heating and shows almost null changes with increasing molecular sizes.

ACKNOWLEDGEMENT This work was funded by Ministerio de Economía y Competitividad (Spain, project CTQ2013-40476-R) and Junta de Castilla y León (Spain, project BU324U14). We also acknowledge The Foundation of Supercomputing Center of Castile and León (FCSCL, Spain) for providing supercomputing facilities. The statements made herein are solely the responsibility of the authors.

ASSOCIATED CONTENT Supporting Information Table S1 (chemicals used for experiments); Table S2 (comparison of thermophysical properties with literature data); Table S3 (forcefield parameterization); Table S4 (systems used for molecular dynamics simulations); Tables S5-S20 (thermophysical properties and Redlich-Kister fittings); Figures S1–S16 (plots of excess molar volume and mixing viscosity for the studied systems); Figure S17 (percentage of DMC cis-cis isomers); Figure S18

16


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(temperature effect on radial distribution functions); Figure S19 (temperature effect of calculated dielectric constant).

17



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Table 1. NBO Analysis of the studied dialkylcarbonate – dialkylcarbonate complexes computed in gas phase at B3LYP/6-31+G(d,p) theoretical Level. All values obtained for optimized structures reported in Figure 3. Second-order perturbation energy, E(2), energy difference among the donor and the acceptor, ΔE, and Fock matrix element between the donor and the acceptor, Fij. Interactions are those remarked with blue arrows in Figure 3 in the same ordering. All the interactions are established from the corresponding oxygen lonely pairs (pair 1 or 2) to the corresponding antibonding C-H orbitals. oxygen complex

interaction

donor pair

Figure 3.a

top

1 2 1 2 1 2 1 2 1 2 1 2

bottom Figure 3.c

top bottom

Figure 3.e

top bottom

Figure 3.b

top bottom

Figure 3.d

top bottom

Figure 3.f

top middle bottom

1 2 1 2 1 2 1 2 1 2 1 2 1 2

E(2) / kJ mol-1 DMC-DMC 7.91 2.05 7.95 2.01 0.38 0.25 0.42 0.25 7.24 1.80 6.11 – DEC-DEC 7.95 2.38 7.95 2.38 0.29 0.21 0.25 0.21 4.94 3.18 1.51 0.84 0.38 –

ΔE / au

Fij / au

1.19 0.74 1.19 0.74 1.16 0.72 1.16 0.72 1.20 0.75 1.04 –

0.042 0.018 0.043 0.018 0.009 0.006 0.010 0.006 0.041 0.017 0.035 –

1.19 0.74 1.18 0.74 1.16 0.71 1.15 0.71 1.20 0.75 1.03 0.77 1.31 –

0.043 0.019 0.042 0.019 0.008 0.006 0.007 0.006 0.034 0.022 0.017 0.012 0.010 –

18


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Table 2. NBO Analysis of the studied dialkylcarbonate – BUT complexes computed in gas phase at B3LYP/631+G(d,p) theoretical Level. All values obtained for optimized structures reported in Figure 4. Second-order perturbation energy, E(2), energy difference among the donor and the acceptor, ΔE, and Fock matrix element between the donor and the acceptor, Fij. Interactions are those remarked with blue arrows in Figure 4 in the same ordering. The interactions are established from the oxygen lonely pairs in alkylcarbonate (pair 1 or 2, C=O) to the corresponding antibonding O-H orbital in BUT (interactions for complexes in Figures 4a, 4c, 4b, top interaction, and 4d, top interaction), or from oxygen lonely pairs in BUT (pair 1 or 2) to antibonding C-H orbitals in DEC (complexes in Figures 4b and 4d, top interactions). oxygen complex

interaction

donor pair

Figure 4.a

top

Figure 4.c

top

1 2 1 2

Figure 4.b

top bottom

Figure 4.d

top bottom

1 2 1 2 1 2 1 2

E(2) / kJ mol-1 DMC-BUT 28.83 10.88 24.48 0.38 DEC-BUT 27.41 20.63 0.59 0.50 19.83 2.18 1.00 –

ΔE / au

Fij / au

1.26 0.82 0.11 1.86

0.083 0.043 0.073 0.008

1.25 0.81 0.99 0.71 1.11 0.85 1.02 –

0.081 0.058 0.008 0.008 0.065 0.020 0.014 –

19



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Table 3. Results of vibrational spectra for alkylcarbonate – alkylcarbonate and alkylcarbonate – BUT complexes reported in Figures 3 and 4. All values calculated at B3LYP/6-31+G(d,p) theoretical Level. Δν(C=O) and Δν(O-H) stand for the shifting of C=O (DMC or DEC) or O-H (BUT) stretching frequencies, respectively, in comparison with values calculated for isolated DMC or DEC or BUT at the same theoretical level. Δν < 0 indicates redshifting in comparison with isolated alkylcarbonates or BUT molecules. -1

-1

complex Δν(C=O) / cm complex DMC-DMC Figure 3.a -9.6 Figure 4.a Figure 3.c -5.5 Figure 4.c Figure 3.e -11.2 a b 2.3 DEC-DEC Figure 3.b -9.6 Figure 4.b Figure 3.d -6.7 Figure 4.d Figure 3.f -8.8 a 3.0 b a b For C=O interacting; for C=O non-interacting.

Δν(C=O) / cm DMC-BUT -5.9 12.0

-1

Δν (O=H) / cm

DEC-BUT -26.4 12.7

20


-97.8 -59.2

-126.2 -63.3

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Figure Captions.

Figure 1. Atom and molecular labelling for molecules studied in this work.

Figure 2. Experimental excess molar volume, VE, and mixing viscosity, Δη, for x (DMC or DEC) + (1-x) 1-alkanols at 303 K and 0.1 MPa. Panels b and d show the effect of 1-alkanol number of carbon atoms, n, on the maximum E

E

value of V (V

max)

and on the minimum value of Δη (Δηmin).

Figure 3. AIM analysis for dialkylcarbonate - dialkylcarbonate complexes computed in the gas phase at the B3LYP/6-31+G(d,p) theoretical level. Symbols: small red dots represent bond critical points, BCP; small yellow dots represent ring critical points, RCP; large dots represent atoms (black, carbon; red, oxygen; and gray, hydrogen) and pink lines represent bond paths. Ring paths are omitted for the sake of simplicity. ΔE stands for counterpoise-corrected binding energy in gas phase. Values at the top left corner of each panel show parenthesized electron density and laplacian of electron density for the selected intermolecular critical points.

Figure 4. AIM analysis for dialkylcarbonate – 1-alkanol complexes computed in the gas phase at the B3LYP/631+G(d,p) theoretical level. Symbols: small red dots represent bond critical points, BCP; small yellow dots represent ring critical points, RCP; large dots represent atoms (black, carbon; red, oxygen; and gray, hydrogen) and pink lines represent bond paths. Ring paths are omitted for the sake of simplicity. ΔE stands for counterpoise-corrected binding energy in gas phase. Values at the top left corner of each panel show parenthesized electron density and laplacian of electron density for the selected intermolecular critical points.

Figure 5. Experimental, exp, and molecular dynamics, MD, properties for x DMC + (1-x) BUT at 303 K and 0.1 MPa. ρ, stands for density; VE for excess molar volume; ε for dielectric constant; Δε for mixing dielectric constant; DDMC and DBUT for self-diffusion coefficients of DMC and BUT, respectively; η for dynamic viscosity; Δη for mixing viscosity.

Figure 6. Center-of-mass radial distribution functions, g(r), for x DMC + (1 − x) BUT at 303 K. All values from molecular dynamics simulations.

Figure 7. Coordination numbers, N, for the corresponding molecular pairs in x DMC + (1-x) BUT at 303 K obtained from the radial distribution functions reported in Figure 3. The radii R of the solvation spheres for the calculation of N were 4.75 and 7.65 Å for DMC around DMC (first and second solvation sphere, respectively), 6.70 and 10.70 Å for BUT around BUT (first and second solvation sphere, respectively), 5.30 and 7.60 Å for BUT around DMC (first and second solvation sphere, respectively). All values from molecular dynamics simulations.

21



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Figure 8. Site-site radial distribution functions, g(r), for x DMC + (1 − x) BUT at 303 K. Atom labelling as in Figure 1. All values from molecular dynamics simulations. Figure 9. Spatial distribution functions around DMC (top row) and BUT (bottom row) for x DMC + (1 − x) BUT at 303 K. All values from molecular dynamics simulations.

Figure 10. Percentage of BUT molecules developing 0, 1, 2, 3 or 4 BUT – BUT hydrogen bonds, fi, and of DMC molecules developing 0, 1 or 2 BUT – DMC hydrogen bonds, gi, in x DMC + (1 − x) BUT at 303 K. The criteria for o

defining hydrogen bonds were 3.0 Å and 60.0 for donor-acceptor distances and angles.

Figure 11. Average number of hydrogen bonds, NH-bonds, between the reported sites for x DMC + (1 − x) BUT at 303 K. Atom labelling as in Figure 1. The criteria for defining hydrogen bonds were 3.0 Å and 60.0o for donoracceptor distances and angles. NH-bonds are calculated per BUT molecule, for Hb-O3, and per DMC molecules, for Hb-O2. All values from molecular dynamics simulations.

Figure 12. Distribution of cavity sizes in x DMC + (1 − x) BUT at 303 K. Gray arrows indicate evolution with increasing DMC mole fraction of the three main features in the Figure. All values from molecular dynamics simulations.

Figure 13. Residence time, tres, of the center-of-mass of one type of molecule around another molecule for x DMC + (1 − x) BUT at 303 K from molecular dynamics simulations. tres was calculated from the exponential decay of conditional probability P(t) for the center of mass of a molecule to remain within a sphere of radius R+δr around a given center of mass of another molecule, entering the sphere of radius R-δr at time t=0. The radii R of the solvation spheres for the calculation of tres were 4.75 and 7.65 Å for DMC around DMC (first and second solvation sphere, respectively), 6.70 and 10.70 Å for BUT around BUT (first and second solvation sphere, respectively), 5.30 and 7.60 Å for BUT around DMC (first and second solvation sphere, respectively). Values of R were obtained from RDFs reported in Figure 6. All values from molecular dynamics simulations.

Figure 14. Intermolecular interaction energy, Einter, as the sum of Lennard-Jones and coulombic contributions for x dilakylcarbonate + (1-x) 1-alkanol from molecular dynamics. Results in panel a show composition effect for x DMC + (1-x) BUT at 303 K; in panel b, length of alkyl chain effects for x DMC + (1-x) 1-alkanol or x DEC + (1-x) BUT (x = 0.5) at 303 K, with n being the number of carbon atoms in 1-alkanol; in panel c, temperature effects for x DMC + (1-x) BUT (x = 0.5). All values from molecular dynamics simulations.

E

E

Figure 15. Experimental temperature effect on the maximum value of V (V Δη (Δηmin), for x (DMC or DEC) + (1-x) 1-alkanols at 303 K and 0.1 MPa.

22


max)

and on the minimum value of

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Figure 16. (a) Center-of-mass and (b,c) site – site radial distribution functions, g(r), for alkylcarbonate (DMC or DEC)+ 1-alkanol (BUT, HEX, HEP or NON) for equimolar mixtures at 303 K. All values from molecular dynamics simulations.

Figure 17. (a) Temperature and (b) alkyl chains effect on coordination numbers in the first solvation shells, N, for the corresponding molecular pairs in (a) DMC + BUT (x = 0.5) or (b) DMC + 1-alkanol and DEC + 1-alkanol (x = 0.5), at 303 K. Values calculated from the radial distribution functions reported in Figure S17 (Supporting Information) and Figure 14. Radii for first solvation shells as in Figure 5. All values from molecular dynamics simulations. In panel b, n stands for the number of carbon atoms in 1-alkanol.

Figure 18. (a) Temperature and (b) alkyl chains effect on the number of hydrogen bonds, NH-bonds, between the reported sites for (a) DMC + BUT (x = 0.5) or (b) DMC + 1-alkanol and DEC + 1-alkanol (x = 0.5), at 303 K. Atom o

labelling as in Figure 1. The criteria for defining hydrogen bonds were 3.0 Å and 60.0 for donor-acceptor distances and angles. NH-bonds are calculated per 1-alkanol molecule, for Hb-O3, and per DMC or DEC molecules, for Hb-O2. All values from molecular dynamics simulations. In panel b, n stands for the number of carbon atoms in 1-alkanol.

Figure 19. (a) Temperature and (b) alkyl chains effect on the distribution of cavity sizes in (a) DMC + BUT (x = 0.5) or (b) DMC + 1-alkanol and DEC + 1-alkanol (x = 0.5), at 303 K. All values from molecular dynamics simulations.

Figure 20. (a) Temperature and (b) alkyl chains effect on residence time, tres, of the center-of-mass of one type of molecule around another molecule for (a) DMC + BUT (x = 0.5) or (b) DMC + 1-alkanol and DEC + 1-alkanol (x = 0.5), at 303 K. Values calculated as in Figure 10. All values from molecular dynamics simulations. In panel b, n stands for the number of carbon atoms in 1-alkanol.

Figure 21. (a) Temperature and (b) alkyl chains effect on self-diffusion coefficients, D, of DMC or DEC or 1alkanol, for (a) DMC + BUT (x = 0.5) or (b) DMC + 1-alkanol and DEC + 1-alkanol (x = 0.5), at 303 K. All values from molecular dynamics simulations. In panel b, n stands for the number of carbon atoms in 1-alkanol.

23



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O2

O2

O

O

H1,C2

H3C

C2,H1

O C1 O O1 O1

CH3

H1,C3

H3C

HO

R

C2,H1

O C1 O O1

DMC

C3,H2

Page 24 of 47

C2,H1 C3,H1

CH3

O1 DEC

R = – (CH2)n – CH3 C4,H2

Hb,O3

n = 2 (1-butanol) n = 4 (1-hexanol) n = 5 (1-heptanol) n = 7 (1-nonanol)

Figure 1.

24


BUT HEX HEP NON

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Figure 2.

25



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 3.

26


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Figure 4.

27



0

(b)

0.9 0.2 0.8

ρ (exp) ρ (MD) VE (exp) VE (MD)

0.7 0

0.25

0.5 x

VE / cm3 mol-1 ε

0.4

0 1

(d)

DBUT (MD)

1

-0.4

6 -0.8 4

3

0

η (exp) η (MD) ∆η (exp) ∆η (MD)

-0.2

0.9 0.8

2

-0.4

1

-0.6

0.7

-1.2

2

0.75

4

DDMC (MD)

(c)

8

1

1.1

ε (MD) ∆ε (MD)

0.6

0

-1.6 0

0.25

0.5 x

0.75

0

0.5

1

0

0.25

0.5 x

Figure 5.

28


0.75

1

-0.8 0

0.25

0.5 x

0.75

1

∆η / mPa s

10

η / mPa s

0.6

(a)

∆ε 109 D / m2 s-1

1.1

ρ / g cm-3

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 47

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x DMC + (1-x) BUT (a) BUT-BUT

2.5

g(r)

2 1.5 1 0.5 0 2.5

(b) DMC-DMC

g(r)

2 1.5 1 0.5 0 2.5

(c) BUT-DMC 2 g(r)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1.5 1 0.5 0 0

5

10 r/Å

15

20

Figure 6.

29


x=1.0 x=0.9 x=0.8 x=0.7 x=0.6 x=0.5 x=0.4 x=0.3 x=0.2 x=0.1 x=0.0


x DMC + (1-x) BUT (a) 2nd shell

25 20

DMC around DMC BUT around DMC BUT around BUT

N

15 10 5 0 8

(b) 1st shell

6 N

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 30 of 47

4 2 0 0

0.25

0.5 x

0.75

Figure 7.

30


1

Page 31 of 47

x DMC + (1-x) BUT

12

(a) BUT-BUT (Hb-O3)

g(r)

8

4

0 2

(b) DMC-DMC (H1-O1)

g(r)

1.5 1 0.5 0 2

x=1.0 x=0.9 x=0.8 x=0.7 x=0.6 x=0.5 x=0.4 x=0.3 x=0.2 x=0.1 x=0.0

(c) DMC-DMC (H1-O2) g(r)

1.5 1 0.5 0 2

(d) BUT-DMC (Hb-O1)

g(r)

1.5 1 0.5 0 12

(e) BUT-DMC (Hb-O2)

8 g(r)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


4

0 0

5

10 r/Å

15

20

Figure 8.

31



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Figure 9.

32


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Page 33 of 47

100

f0

(a)

f1

fi

75

f2 f3

50

f4

25 0 100

g0

(b)

g1

75 gi

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


g2

50 25 0 0

0.25

0.5 x

0.75

Figure 10.

33


1


0.8 BUT - DMC (Hb - O2) BUT - BUT (Hb - O3)

0.6 NH-bonds

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 34 of 47

0.4

0.2

0 0

0.25

0.5 x

0.75

Figure 11.

34


1

Page 35 of 47

0.025

x=1.0 x=0.9 x=0.8 x=0.7 x=0.6 x=0.5 x=0.4 x=0.3 x=0.2 x=0.1 x=0.0

0.02

P(R)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


0.015 0.01 0.005 0 0

0.25

0.5 0.75 R/Å

1

Figure 12.

35


1.25

Page 36 of 47

33

x DMC + (1-x) BUT DMC around DMC (a) 2nd shell

31

BUT around DMC BUT around BUT

29 27 25 23

21

(b) 1st shell tres / ps

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

tres / ps


17

13

9 0

0.25

0.5 x

0.75

Figure 13.

36


1

Page 37 of 47

x DMC + (1-x) 1-alkanol x = 0.5 x DEC + (1-x) 1-alkanol x = 0.5

x DMC + (1-x) BUT 0

-10

-20

-20

x DMC + (1-x) BUT x = 0.5 -14

-40 -60 -80

-18 Einter / kJ mol-1

Einter / kJ mol-1

-16

Einter / kJ mol-1

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


-30 -40

(a) 0

(b)

-60 0.25

0.5 x

0.75

1

-22 -45

-50

-50

-100

DMC-DMC DMC-alkanol alkanol - alkanol (in DMC) DEC-DEC DEC-alkanol alkanol - alkanol (in DEC)

-20

4

5

-55 6

7

8

9

(c) 293

n

313

333 T/K

Figure 14.

37


353


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 15.

38


Page 38 of 47

Page 39 of 47

6

(a)

alkylcarbonate – alkanol (com – com)

DEC

g(r)

4

NON HEP DMC HEX BUT

2

0 20

(b) alkanol – alkanol (Hb – O3)

g(r)

15

DEC

10 5

DMC

0 30

(c) alkanol – alkylcarbonate (Hb – O2) DEC

20 g(r)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


10 DMC

0 0

5 r/Å

Figure 16.

39


10


4

x DMC + (1-x) BUT x = 0.5

x DMC + (1-x) 1-alkanol x = 0.5 x DEC + (1-x) 1-alkanol x = 0.5 4

3

3

2

2

N

DMC around DMC ALKANOL around DMC ALKANOL around ALKANOL (in DMC) DEC around DEC ALKANOL around DEC ALKANOL around ALKANOL (in DEC)

N

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1

1

0

Page 40 of 47

(a) 280

(b)

0 300

320 340 T/K

360

4

Figure 17.

40


5

6

7 n

8

9

Page 41 of 47

x DMC + (1-x) 1-alkanol x = 0.5 x DEC + (1-x) 1-alkanol x = 0.5

x DMC + (1-x) BUT x = 0.5 0.50

0.50

ALKANOL - ALKANOL (Hb - O3, in DMC) BUT(Hb- DMC ALKANOL - DMC - O2) (Hb - O2) ALKANOL - ALKANOL (Hb -(Hb O3, in- O3) DEC) BUT - BUT ALKANOL - DEC (Hb - O2)

0.45

0.45 0.40 NH-bonds

0.40 NH-bonds

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


0.20

0.35 0.25

0.20

(a)

(b)

0.15

0.15 280

300

320 T/K

340

360

4

5

6

7 n

Figure 18.

41


8

9


x DMC + (1-x) 1-alkanol x = 0.5 x DEC + (1-x) 1-alkanol x = 0.5 0.04 NON (b)

x DMC + (1-x) BUT x = 0.5

0.025

293 K 303 K 313 K 323 K 333 K 343 K 353 K

(a)

0.02

DEC

0.03

HEP HEX BUT

P(R)

0.015 P(r)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 42 of 47

0.02 DMC

0.01 0.01

0.005

0

0 0

0.25 0.5 0.75 R/Å

1

1.25

0 0.25 0.5 0.75 1 1.25 R/Å

Figure 19.

42


Page 43 of 47

21

x DMC + (1-x) 1-alkanol x = 0.5 x DEC + (1-x) 1-alkanol x = 0.5 55 DMC around DMC

x DMC + (1-x) BUT x = 0.5

tres / ps

13

9

5

ALKANOL around DMC ALKANOL around ALKANOL (in DMC) DEC around DEC ALKANOL around DEC ALKANOL around ALKANOL (in DEC)

45

17 tres / ps

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


35 25 15

(a) 280

(b)

5 300

320 T/K

340

360

4

5

6

7 n

Figure 20.

43


8

9


x DMC + (1-x) 1-alkanol x = 0.5 x DEC + (1-x) 1-alkanol x = 0.5 1.2

x DMC + (1-x) BUT x = 0.5

3

DDMC

2

109 D / m2 s-1

109 D / m2 s-1

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 44 of 47

1

1

DALKANOL (in DMC) DDEC

0.8

DALKANOL (in DEC)

0.6 0.4 0.2

0

(a)

280

(b)

0

300

320 340 T/K

360

4

5

6

7 n

Figure 21.

44


8

9

Page 45 of 47

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Graphic Table of Contents

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Physicochemical Insights on Alkylcarbonate ... - ACS Publications

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