Volumetric, acoustic and thermal properties of aqueous N,N-dimethylformamide system. Effect of temperature and composition

Journal Pre-proof Volumetric, acoustic and thermal properties of aqueous N,Ndimethylformamide system. Effect of temperature and composition

Marlena Komudzińska, Magdalena Tyczyńska, Małgorzata Jóźwiak, Andrzej Burakowski, Jacek Gliński PII:

S0167-7322(19)34959-1

DOI:

https://doi.org/10.1016/j.molliq.2019.112321

Reference:

MOLLIQ 112321

To appear in:

Journal of Molecular Liquids

Received date:

4 September 2019

Revised date:

6 December 2019

Accepted date:

13 December 2019

Please cite this article as: M. Komudzińska, M. Tyczyńska, M. Jóźwiak, et al., Volumetric, acoustic and thermal properties of aqueous N,N-dimethylformamide system. Effect of temperature and composition, Journal of Molecular Liquids(2019), https://doi.org/ 10.1016/j.molliq.2019.112321

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© 2019 Published by Elsevier.

Journal Pre-proof

Volumetric, acoustic and thermal properties of aqueous N,N-dimethylformamide system. Effect of temperature and composition Marlena Komudzińskaa, Magdalena Tyczyńskaa*, Małgorzata Jóźwiaka, Andrzej Burakowskib, Jacek Glińskib a

Department of Physical Chemistry, Faculty of Chemistry, University of Łódź, Pomorska 165, 90-236 Lodz, Poland

b

Faculty of Chemistry, University of Wrocław, F. Joliot - Curie 14, 50-383 Wrocław, Poland [email protected]

ABSTRACT , speed of sound

and isobaric specific heat capacity

pr

This paper presents the density

oo

f

*

( ) of an aqueous N,N-dimethylformamide (DMF) system. The measurements were

e-

performed over the entire composition range of (DMF + water) at four temperatures: 293.15,

of the system

Pr

298.15, 303.15 and 308.15K. The density data was used to calculate the excess molar volume , the partial molar volume of DMF (

molar expansion volume coefficient (

al

rn

Jo u

their molar counterparts (

system, excess molar functions

), as well as the

). Based on the sound velocity and heat capacity

values, it was possible to calculate the isobaric ( capacities, as well as the isentropic

) and water (

) and isochoric (

and isothermal compressibility

) molar heat coefficients and

). To study the structural changes in the examined were determined and the results

were compared with ideal systems. Changes in the obtained values of the physicochemical parameters, as functions of composition and temperature, were analyzed in terms of the molecular interactions and structural differentiation of the investigated binary mixtures. The temperature effect exhibited a regular relationship with regard to the analyzed functions. Keywords: N,N-dimethylformamide + water mixture; density; speed of sound; isobaric molar heat capacity; isochoric molar heat capacity

1

Journal Pre-proof 1. Introduction Due to their widespread use in industry and laboratory practice, liquid mixtures are of great importance. Hence, their structures and the intermolecular interactions occurring within them are of particular interest for many researchers. Careful analysis of the physicochemical parameters of multi-component liquid systems can provide a wealth of knowledge about the structure and mutual interactions between their components. A range of methods, such as densimetry, viscometry and calorimetry, can be used to determine the properties of such binary liquids [1–4]. In addition, studies can employ sound velocity measurements: they are

f

accurate and easy to perform, and provide an important insight into the behavior of liquid

oo

mixtures. As the results depend very much on the forces of molecular interactions and on the volume and shape of the molecules within the mixture components, acquired acoustic data

pr

allows an accurate evaluation to be made of changes occurring in intermolecular interactions [5–7].

e-

Thanks to their similarity to proteins, amides can be used as model substances for

Pr

basic research into protein systems.They also have a wide range of potential applications in industry, mainly as solvents and cosolvents. Of these, N,N-dimethylformamide (DMF) is a compound with high durability and thermal stability. It does not break down during

al

distillation under reduced pressure, nor does it tend to hydrolyze even at high temperatures.

rn

DMF is characterized by unlimited miscibility in water and many organic solvents, including alcohols, esters, ethers, ketones and aromatic hydrocarbons. In addition, due to the absence of

Jo u

structural effects, such as its lack of hydrogen bonds [8], DMF is a compound of particular interest as a solvent for a wide spectrum of organic and inorganic compounds. In addition, as its hydrophilic and hydrophobic properties are almost completely compensated, DMF is considered a neutral solvent from the point of view of intermolecular interactions. Aqueous–organic mixtures are an important group of solvents that are enjoying increasing interest. They play a key role in biological and medical research, as well as in various branches of industry [9]. Although amides are known to interact with water by forming hydrogen bonds, a detailed study of the hydration of small organic molecules, peptides and biological macromolecules is required to understand the specific role of the aquatic environment in determining the structure and action of proteins [10]. Amide groups could be considered as models for peptide bonds, as well as for the interactions between hydroxyl groups and amides, which have a strong influence on the solvation of amides in aqueous solutions [11]. 2

Journal Pre-proof Due to such great interest in protein behavior, and to better understand the way in which water affects the thermodynamic and kinetic aspects of the chemical activity of polypeptides, the amide – water system merits attention. Some studies have examined the effect of the composition of the system, i.e. the proportions of DMF and water (W), on the physical properties of the mixture across the entire composition range. The volumetric and the compressibility properties of aqueous DMF solutions have previously been determined [11– 18], and some theoretical studies have discussed the interactions taking place in DMF+W mixture [19,20]. However, many such investigations only examine a narrow range of concentrations and selected temperatures, and it was not possible to identify a satisfactory

oo

f

range of cp values for this system. In addition, few works have examined the nature of the heat capacity of DMF+W system [11,21]. In available data there is no combination of so many physicochemical functions under given conditions. The DMF+W mixture has previously been

pr

used to study the phenomenon of hydrophobic hydration [22–24], and still merits great

e-

attention, particularly in studies of the influence of temperature and mixture composition on its physicochemical properties.

Pr

The present paper examines the density, sound velocity and heat capacity of DMF+W system, across its entire range of compositions, at four temperatures: 293.15, 298.15, 303.15 and

volume of the system

al

308.15 K. It determines selected physicochemical quantities, including the excess molar and the partial molar volumes of DMF (

rn

also evaluates the molar expansion volume coefficient (

) and water (

) isentropic

and isothermal

Jo u

compressibility coefficient of the system and their molar counterparts ( addition, it also determines the isobaric (

) and isochoric (

); it

); in

) molar heat capacity of

the system and some of their excess molar functions It is important to note that our present findings describing the values of

. and

across

the entire composition range of DMF+W mixture at the studied temperatures have not been previously published. The work also presents precise and coherent results obtained by a range of experimental methods.

2. Experimental 2.1. Materials N,N-dimethylformamide (DMF) (Aldrich, w = 0.99) was purified and dried as described previously [25,26]. To avoid the possibility of decomposition, the tested DMF was distilled 3

Journal Pre-proof under vacuum each time before sample preparation. The purity of the received compound was 99.8%. The solutions were prepared using ultra-pure Type 1 (Millipore SigmaTM SynergyTM Ultrapure Water Purification System), boiled and degassed water. The purity and related data regarding the chemicals are given in Table 1. 2.2. Measurements 2.2.1. Density and speed of sound The density

of DMF+W mixture was measured across its the entire composition

range at four temperatures (293.15, 298.15, 303.15 and 308.15K) using an Anton Paar DMA

f

5000 analyzer. Detailed description of the density measuring device that works in the same

oo

way as in the DSA 5000 M (Anton Paar) densimeter is given elsewhere [27]. It is characterized by good repeatability of temperature (± 0.001 K) but with higher uncertainty

pr

(0.01K). According to the manufacturer’s data, density is measured with a repeatability of ±

e-

1∙10−3 kg·m−3, and an estimated uncertainty of ± 2∙10-2 kg∙m-3. Uncertainty was estimated based on the average of our own measurements and according to equations those of Fortin et

Pr

al. [28]. The expanded uncertainty was estimated according to well known equation Uc= uc·k with 0.95 level of confidence (k ≈ 2). Prior to use, the solvents were degassed in an ultrasonic

bath, and to avoid re-gassing the samples during density measurements, the temperature scan

al

was programmed from 35°C to 20°C with increments of five degrees. The solution densities

rn

are consistent with those given in our previous paper [29]. The (DMF+W) mixtures were prepared using an analytical balance (RADWAG XA

Jo u

60/220, Poland) with a precision of ± 1∙10-5 g. The speed of sound

was determined using

a computer-steered OPBOX 2.1 (Optel, Wrocław, Poland) apparatus, with an absolute accuracy better than ±0.2 m·s−1 and precision of a similar order. Measurements are based on the time taken for an acoustic signal (approximately 8 MHz) to pass through a sample of known length: in this case, 50 mm. The temperature of the sample during the measurements was stabilized by a precision Julabo F25-ME (Germany) thermostat with an accuracy of ±0.01 K; the uncertainty of the absolute temperature value was about 0.05 K, checked using a precise mercury thermometer. The density and sound velocity of (DMF+W) mixture, obtained as a molar fraction of water

at four temperatures

, are presented in Tables S1 and S2

(Supplementary material). The density and sound velocity data obtained for pure DMF and for pure water are compared with literature data in Table 2 and Table 3. Comparison of apparent molar volume and sound velocity of DMF+W mixture obtained in this work with the

4

Journal Pre-proof corresponding values available in the literature is presented in Figs. S1 and S2 in Supplementary material. 2.2.2. Heat capacity The isobaric specific heat capacity ( ) of DMF+W mixture was measured by means of a high sensitivity differential scanning calorimeter DSC III (Setaram, France). A detailed description of the measurement procedure is given by Góralski et al. [43]. Measurements were carried out in the temperature range 288.15–313.15 K with a scanning rate of 0.35 K/min. The continuous with reference method was used, with a known capacity of water as a reference substance [44]. For the measurements, a batch-type cell of about 1cm3 was applied. Assuming

oo

f

an error in absolute temperature determination of 0.05 K, the uncertainty in the isobaric specific heat capacity ( ) is approximately 0.2%. The experimental values of isobaric are presented in Table S3

pr

specific heat capacity as a function of water molar fraction

(Supplementary material). The obtained isobaric molar heat capacity of pure water and DMF,

e-

calculated on the basis of a suitable polynomial describing the dependence of specific heat capacity on temperature, is compared with literature values in Table 4. Comparison of molar

Pr

heat capacity of DMF+W mixture obtained in this work with the corresponding values

al

available in the literature is presented in Fig. S3 in Supplementary material.

3.1. Densimetry

rn

3. Results

Jo u

The addition of water to N,N-dimethylformamide was found to result in an increase in mixture density (Fig.1.) [18]. However, for all tested mixture compositions, the density was observed to decrease as the temperature increased. Based on the obtained density values, the molar volumes of DMF+W mixture can be calculated according to Eq. (1):

(1)

where:

is the density of (DMF+W) mixture, while

and

are the molar

fractions and molar masses of the mixture components, i.e. water (1) and DMF (2). To explain deviations of the system from ideality, excess properties were calculated using the following expression (Eq.(2)) [51]:

5

Journal Pre-proof (2)

where and

is excess quantity of chosen property

(

is the corresponding value of an ideal solution. Based on the obtained molar volume , the excess molar volume

of DMF+W mixture was calculated for all compositions

and temperatures according to Eq. (3):

(3)

is the volume of an ideal mixture,

f

is the molar volume of (DMF+W) mixture,

oo

where:

are the molar volumes of pure compounds, i.e. W (1), DMF (2). Based on the

pr

) using Eqs. (4) and (5).

(

)

(

)

)

(4)

(5)

rn

al

Pr

and DMF (

values, it was possible to calculate the partial molar volumes of water (

e-

calculated

Jo u

As the calculated results are in excellent agreement with those obtained previously [29], they will not be examined in the present work. The obtained values of Vm,1 and Vm,2 are presented in Fig. S4 (Supplementary material).

The volume expansion coefficient (

) was calculated from the obtained high-

accuracy density measurements using Eq. (6):

(

)

(6)

was calculated with Eq. (7) [52]

(7) 6

Journal Pre-proof

was calculated using Eq. (8) [52]:

(8)

The isobaric molar expansion coefficient (

) was calculated using Eq. (9) [53]: (9)

f

are presented in Fig. S5. These include values for all tested

oo

The obtained values of

The values of

pr

compositions and temperatures. (Supplementary material).

were all found to be positive across the entire range of tested mixed

e-

solvent composition. However, they were found to decrease almost linearly as the molar fraction of water increased. Temperature had a negligible effect on

. As noted earlier, the

Pr

addition of water to DMF strengthens the solvent structure, resulting in a reinforced structure that is less susceptible to temperature change.

rn

of Eqs. (10) and (11) [53]:

Jo u

(

where:

) were calculated on the basis

al

The excess molar volume expansion coefficients (

)

(10)

(11)

are the coefficients of volume fraction and

are the volume expansion

coefficients of pure water and DMF, respectively. The

values are given as a function of molar fraction of water at studied temperatures in

Fig. 2. The

m

values remain positive throughout the entire range of tested mixture compositions,

indicating that the mixture has a greater tendency to expand than pure solvents. In the initial range, i.e. in mixtures with a small water content ( in

m

< 0.2), only an extremely slight increase

can be observed with increasing temperature. When mixtures with greater proportions

of water are tested, the excess volume expansion visibly decreases as the temperature

7

Journal Pre-proof increases. A maximum value is described by the

function. However, although

m

its intensity decreases as temperatures increase, its position remains constant.

3.2. Sound velocity The experimental values of speed of sound, collected in Table S2 (Supplementary material), are presented in Fig. 3a and Fig. 3b. As can be seen in Fig. 3, the velocity of the sound first increases as the molar fraction of water increases; the velocity then reaches a maximum at

0.8, following which, it decreases. At lower molar volumes of water (

<

0.94), the sound velocity can be seen to decrease with increasing temperature. The sound

oo

f

velocity isotherms, as functions of the molar fraction of water, appear to intersect around ≈ 0.94; at this point, identical sound velocities can be seen for all temperatures, within

intersection at

pr

error limits. These findings are in line with those of Endo, who reports the presence of such an = 0.953 [54]. For

> 0.94, the temperature effect is reversed, that is, as the

e-

temperature increases, the speed of sound propagation increases. and molar isentropic (

The isentropic

) compressibility coefficients were

(

(12)

(13)

Jo u

al

)

rn

Pr

calculated from the obtained density and sound velocity values using Eqs. (12) and (13):

The values of

are presented in Table S4 and Fig. 4. The isothermal

isothermal compressibility coefficients (

) were calculated using Eqs. (14) and (15) based

on the obtained values of isentropic coefficients of compressibility coefficients (

and molar

, volume expansion

) and the specific heat capacities ( ) of the mixture (Table S3,

Supplementary material). (

)

(14)

(15)

8

Journal Pre-proof The shapes of the function

and

are very similar. As the

molar fraction of water in the mixtures increases from low to medium, the compressibility coefficients decrease until they reach a minimum; following this, the values increase with water content. At about

0.96, the isotherms intersect, similar to the dependence

. The courses of the functions

and

at 298.15 K are shown

in Fig. S6. (Supplementary material). Increasing the amount of water in the mixture strengthens the interactions between the water and DMF molecules, thus increasing the rigidity of the structure. As the structure of the

oo

f

mixed solvent stiffens, its compressibility is reduced. The excess molar isentropic (

) and isothermal (

pr

calculated using Eqs. (16) – (20) [53]:

) compressibility were then

id





al

Pr

e-

(16)

(17)

 S  1   S ,1   2   S ,2 

   

rn





 2V2   p ,2

Jo u

  V     2 11 p ,1 T  C p ,1  



C p ,2

2





    x1V1  x2V2  1 p ,1   2 p ,2   x1C p ,1  x2 C p ,2

  2

  (19)

)

where:

(18)

(20)

represent excess molar isentropic and isothermal compressibility, represent the molar isentropic and isothermal compressibility, and their molar values for an ideal mixture;

compressibility coefficients of pure components, and components;

the isentropic and isothermal the volume fraction of the mixture

represents the isobaric molar heat capacity of pure water (1) and DMF (2),

9

Journal Pre-proof calculated on the basis of the obtained functions

and

values (Table S3). The courses of both

are shown on Fig. 5.

3.3. Calorimetry Isobaric molar heat capacities (

) were calculated for the mixture across the whole

range of compositions at all four tested temperatures (Table S5) on the basis of the obtained isobaric specific heat capacities (Table S3). Our findings are in agreement (within the error limits) with literature data [11,21] (Fig. S3 in Supplementary material). The course of

as

were calculated using Eq. (21) [53]:

(21)

pr

oo

The values of

f

a function of molar fraction of water is presented in Fig. 6.

The molar isochoric heat capacity values are given in Table S5. Excess molar isobaric (

e-

) heat capacities were calculated using Eqs. (22) and (23). )

(22)

)

(23)

al

Pr

and isochoric (

)

are isobaric and isochoric molar heat capacities of the ideal mixture and

rn

where:

and DMF (2).

Jo u

are the isobaric and isochoric molar heat capacities of pure compounds, water (1)

is presented as a function of mixture composition in Fig. 7. The

of DMF+W mixture (Fig. 7) shows positive deviations from the ideal

mixture across the entire composition range; all the curves demonstrate parabolas, with their maxima shifted towards ranges with high water content. The dependence of density, and hence the molar volume, on temperature was determined with high precision. In addition, the pressure derivatives of the thermodynamic functions of DMF+W system and their excess values were also obtained using Eqs. (24) – (27) (Fig. 9, Table S6). (

)

(24)

10

Journal Pre-proof ( ( (

)

) )

(

(

)

(

)

(25) (

)

)

(

(26) )

(27)

The excess molar values of free Gibbs energy, enthalpy and entropy against pressure show negative deviations, while excess derivative of isobaric molar heat capacity against pressure

oo

f

shows positive deviations from ideality across the entire composition range of DMF+W. The two relationships possess minima and maxima in similar positions. This most probably indicates the presence of interactions between the N,N-dimethylformamide and water

e-

pr

molecules that have the strongest character in this composition range.

4. Discussion

Pr

The addition of water to the DMF was found to increase the density and a small minimum of density can be seen in the mixtures with high water content, i.e. for

) (Fig.1). Zaichikov et al. [55] showed that when DMF is

al

based on the function added to water, negative

0.9

values indicate that interactions between water molecules are

rn

enhanced. The minimum of the function

established that the phenomenon of weak

Jo u

hydrophobic hydration of DMF occurs slightly in solution with a predominant water content and thus indicates that DMF shows poor hydrophobic properties [56]. With increase in temperature the minimum of the function

becomes more flat. Thus, due to the

thermal movements at 303.15 K and 308.15 K we can observe only the change of the slope of the function. Owing to the porous nature of the construction of the water network, it shows the ability to create clathrates [57]. Therefore, water has the ability to incorporate various types of molecules, also hydrophobic into the intramolecular space. In mixtures with a high water content, DMF molecules may well occupy a cage of water molecules formed around the hydrophobic part of the DMF molecule. Such an arrangement causes the water structure to become more expanded, thus reducing the density in high water content in the mixture. The slightly increasing density values when going to pure DMF may be connected with changes in character of intermolecular interactions taking place in the mixture with low and medium water content. Increasing the organic component of mixture eventually results that there is not enough water molecules to form such cavities, and probably the formation of complexes 11

Journal Pre-proof between water molecules and DMF begins to predominate [14, 58]. Temperature appears to have only a small influence on the density, and this influence is weakened further in the area of

0.9. Nevertheless, across the entire tested range of compositions, density was found

to decrease as temperature increased. Those results correspond to outcomes obtained from sound velocity data (Fig. 3). Intersection ≈ 0.94 is similar to results wich have been

point on the sound velocity curve around

published for other aqueous–organic mixed solvents: those with urea, thiourea, acetamide, acetone or DMF [54], and others with dimethylurea, formamide, dimethylacetamide, diethylacetamide orhexamethylphosphospriamide [59], as well as for water with tert-butanol

oo

f

[60]. The presence of the intersection point has been associated with the creation of clathrates depending on the type of solute: the formed cage-like structures may in some cases be similar to the solid clathrate hydrates observed in some solutes. Intersection point observed on the (Fig. 4) at about

0.96 is similar to the dependence

pr

function

= 0.958, and

e-

This is in accordance with Endo [54], who reports the intersection to be at

.

proposes that the composition of the mixture at this intersection may correspond to the

Pr

stoichiometry of the formed clathrate hydrates. It is worth noticing that the compressibility value at the isothermal intersection point is ≈ 3.95∙10-10 m3∙Pa-1, which is close to the value

al

determined by Stackelberg [61] (4∙10-10 m3∙Pa-1) for regular type II clathrates. This suggests that associates with similar structures may develop in the system under investigation. Ultrasound

dependences [54,59]. At this point, the compressibility

Jo u

intersection points for

rn

velocity measurements in aqueous solutions of non-electrolytes also show the existence of

coefficients are assumed to be independent of temperature, within the studied temperature range. However, at the point of intersection of the compressibility isotherms, the molar ratio of water to solute does not always correspond to the composition of clathrate hydrates type II. The formed associates are called liquid clathrate hydrates and are characteristic of a given system. A positive deviation from ideality for molar volume expansion (Fig. 2) was observed, indicating that the mixture shows a greater tendency toward expansibility than the pure components. The greatest increase in expansibility was found at the composition at which the maximum occurs (xW ≈ 0,7). This corresponds to the position of the minimum of function (Fig.5). Invastigated system shows the greatest expansivity and the lowest compressibility at almost the same range of the mole ratio between xW ≈ 0.5–0.7. In both cases, the values of

and

were found to be negative across the entire range of 12

Journal Pre-proof compositions for DMF+W mixture. Similar findings were obtained for excess molar volume

[29]. Such negative deviations from ideality are attributed to changes in solution

structure. Following addition DMF to water, the hydrogen bonds in the water need to reorganize. This reorganization may result in the generation of interstitial accommodation of DMF within the hydrogen bonds, resulting in the observed negative contribution. This could account for the fact that the mixture becomes less compressible than pure liquids. The functions display a deep minimum at

≈ 0.55. Devyatov [62] suggests that complexes with

different stoichiometric ratios are formed in the range 0.41 <

< 0.7, while others propose

the emergence of such structures as clathrate hydrates or cluster-like structures [62,63]. As

oo

f

one could seen form the Fig. 5 through hydrogen bond formation (–C=O⋯H–O–between polar DMF and the hydrogen atom of water molecules), the structure of DMF+W mixture

The

pr

becomes less sensitive to external factors such as temperature.

values decrease almost linearly as the molar fraction of water increases (Fig. 6) and

e-

only slightly increase with increasing temperature. At high water content the interactions between water molecules become predominate. Therefore with increasing of water content the

Pr

interaction between DMF and water molecules are decreasing. This could be attributed to the clustring of water around DMF molecules. Adding DMF to water give small value of

values when going to pure DMF may be the

al

the solution. The next observed increase of

of

result of hydrogen bonding between the carbonyl group of DMF molecules and water.

rn

According to Petersen [64], hydrogen bonds between water and carbonyl oxygen are stronger

Jo u

than between water molecules. DMF molecules are structurally similar to those of formamide. However, two of the hydrogen atoms in the amine group of formamide have been replaced by methyl groups. This substitution is responsible for the differences in the volumetric and enthalpic effects observed between (DMF+W) and (water+formamide) [12]. The presence of the methyl groups in DMF is reflected in the high molar heat capacity of the mixture. Due to the fact that pure water molecules are organized into a lattice by hydrogen bonds, when the DMF is mixed with water, a slight disruption occurs in the water structure, which contributes negatively to

values (Fig 7). In addition, complexes are also formed between

the water and DMF molecules by hydrogen bonding, and these contribute positively to the values of

. As these effects predominate, positive values of

(DMF+W) system.

are observed for

increases with temperature, indicating that the hydrogen bonds in

(DMF+W) mixture have been weakened. This confirms that self-associated molecules of pure

13

Journal Pre-proof water and the non-random oriented DMF molecules caused by dipole-dipole interactions are disrupted [21,65]. Increasing the temperature also contributes to a decrease in the hydrophilic effect in aqueous mixtures containing DMF.

was found to reach a maximum at around

≈ 0.7. The largest positive deviation of the molar isobaric heat capacity relative to the ideal mixture probably indicates the existence in this range of a mixture structures in the form of complexes with different stoichiometric ratios. As a result of the formation of intermolecular hydrogen bonds in these structures, we observe the maximum. This fact is confirmed also by observed extremes on the other presented functions which appear in the , ρ, u, κS, (

) , (

) ,

(

) , (

) ). High water

f

similar molar fractions (

oo

content in the mixture give rather negative contribution to the

values due to hydrophobic

hydration appearing in this mixture content. In this region, temperature appears to have the values. The shape obtained for

is

pr

greatest influence on the obtained

e-

similar to that previously described by Checoni and Volpe [21]. For the sake of comparison, Fig. 8 presents the relationship between excess molar isobaric and isochoric thermal capacity

Pr

for DMF+W mixture as functions of mixture composition. It can be seen that the function describes a different course to that observed for

0.6 may be the result of overlap due to the

al

negative values observed in the region 0

rn

possibility of errors that may occur during calculations of 5. Conclusions

. The small

, sound velocity

Jo u

The presented work determines the density

.

, and isobaric specific heat

capacity ( ) of an aqueous N,N-dimethylformamide system across its entire composition range at four temperatures: 293.15, 298.15, 303.15 and 308.15 K. Based on these results, a range of physicochemical values were calculated: the excess molar volume of the system and the partial molar volumes of the two constituents, as well as the molar expansion volume coefficient (

), the isentropic

), the isobaric (

coefficients, and their molar values( molar

heat

capacity,

as

well

and isothermal

as

some

of

their

compressibility

) and isochoric ( excess

molar

)

functions

. These values offer an insight into the relationship between the changes in molecular interactions occurring between mixture constituents and those observed in the structure of the binary system. It appears that various types of structures are formed as a result of dipole – 14

Journal Pre-proof dipole interactions and interactions caused by hydrogen bonding; however, their nature is dependent on the composition of DMF+W mixture, and they have not been sufficiently characterized. The creation of these structures, and the consequent reorganization of mixed solvent molecules, changes the analyzed thermodynamic quantities. A number of attempts have been made to explain the behavior of DMF+W mixtures, and this diversity reflects the complexity of the intermolecular interactions taking place between the components of this mixture. It may be the case that, depending on the composition of the mixture, both clathrate hydrates and complexes with a different stoichiometry may be formed.

pr

oo

by water suggests the presence of hydrophobic hydration.

f

The changes observed in course of the analyzed functions, especially in mixtures dominated

e-

References

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Pr

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21

Journal Pre-proof Table 1 Materials. Chemical name

Molecular mass g∙mol-1

Source

Stated purity/mass fraction

Purification method

Mass fraction of water

CAS number

DMF

73.0938

Aldrich

0.998a

purification and distillation [25,26]

2∙10-4b

68-12-2

water

18.0153

7732-18-5

ultrapure

after distillation the 1NMR was the analysis method of purity.

b

determined by Karl Fisher method.

Jo u

rn

al

Pr

e-

pr

oo

f

a

22

Journal Pre-proof Table 2 Density

of pure water and DMF at pressure p = 0.1005 ± 0.005MPa.* W

DMF lit.

exp.

lit.

293.15

998.21

998.2058 [30] 998.205a

948.68

948.742 [29] 948.737 [15] 948.611 [32] 948.565 [33] 948.653 [33] 948.546 [33] 948.584 [34]

298.15

997.05

997.0474 [30] 997.047a

303.15

995.65

308.15

994.037

oo

f

exp.

al

T/K

Pr

e-

pr

943.92

939.16

939.201 [29] 939.196 [15] 939.047 [35] 939.073 [32] 939.017 [33] 939.114 [33] 943.884 [33] 939.002 [33] 939.042 [34]

934.40

934.425 [29] 934.420 [15] 934.721 [35] 934.298 [24] 934.255 [34]

Jo u

rn

995.6504 [30] 995.651a

994.0313 [30] 994.038a

943.976 [29] 943.971 [15] 944.290 [35] 943.869 [16] 943.797 [33] 943.884 [33] 939.114 [33] 943.817 [34]

a

values calculated in accordance with the recommendations of The International Association for the Properties of Water and Steam [31]. * Standard uncertainties are = 0.01K, = 0.005 MPa, and the combined expanded -2 -3 uncertainty is = 2∙10 kg∙m with 0.95 level of confidence (k ≈ 2).

23

Journal Pre-proof Table 3 of pure water and DMF at pressure p = 0.1005 ± 0.005MPa.*

Speed of sound

W

DMF

T/K lit.

exp.

293.15

1482.4

1483.42a 1482.38b

1477.3

298.15

1496.9

1498.17a 1496.73b

1458.0

1509.5

a

a

a

1519.9

1521.98 1519.85b

1457.13 [37] 1469.5 [38] 1457.69 [35] 1458.5 [39] 1457.49 [17] 1460.2 [40] 1468.0 [41]

1438.7

1438.23 [35] 1440.2 [39] 1476.2 [42]

1419.2

1421.95 [35] 1420.8 [39] 1464.6 [42]

e-

Pr

308.15

1510.98 1509.17b

lit.

al

303.15

pr

oo

f

exp.

Jo u

rn

Values calculated in accordance with the recommendations of The International Association for the Properties of Water and Steam [31]. b Calculated values using the recommended factors in Marczak's work [36]. * Standard uncertainties are = 0.01K, = 0.005 MPa, and the combined expanded uncertainty is = 0.5 m∙s-1 with 0.95 level of confidence (k ≈ 2).

24

Journal Pre-proof Table 4 Isobaric molar heat capacity (

) of pure water and N,N-dimethylformamide at chosen temperatures

at pressure p = 0.1005 ± 0.005MPa.* T/K

W

DMF lit.

in this work

lit.

293.15

75.34

75.34a 75.39b 75.34 [45]

147.5

147.16 [21] 147.3c 147.5d 147.6e

298.15

75.29

75.30a 75.32b 75.29 [45] 75.32 [18]

148.1

147.21 [48] 148.0 c 148.1b 148.15d 148.16 [49][50] 148.2 [11][39] 148.54 [46] 150.16 [21]

303.15

75.28

75.28a 75.30b 75.28 [45]

308.15

75.27

148.7

148.5 c 148.7 [50] 148.7d 148.9b 150.41 [46] 153.32 [21]

149.4

149.1 c 149.8b 152.65 [46]

al

Pr

e-

pr

oo

f

in this work

Jo u

rn

75.27a 75.28b 75.27 [45]

a

Calculated values on the basis of specific heat capacities from [30].

b

Values calculated in accordance with the recommendations of The International Association for the

Properties of Water and Steam [31]. c

Calculated values using the recommended coefficients of the quasi-polynomial equation [46]:

C p ,m R d

m T A2   Aj 3Tr j where: R – gas constant, Tr  , Tc – critical temperature. 1  Tr j 0 Tc

Calculated values using the recommended coefficients of the polynomial or cubic spline equation

[44]: e

 A1 ln 1  Tr  

j

 T    Aj 1   . R  100  j 0

C p,m

n

Calculated values on the basis of specific heat capacities from [47].

*

Standard uncertainties are = 0.01K, = 0.005 MPa, and the combined expanded –1 –1 uncertainty is = 0.002 J·g ·K with 0.95 level of confidence (k ≈ 2).

25

Journal Pre-proof

1.01

1.00

f

0.98

oo

 10-3/kgm-3

0.99

0.97 1.000

e-

pr

0.96

0.95

Pr

0.995

0.94

0.2

Fig. 1. Density

0.990 0.90 0.92 0.94 0.96 0.98 1.00

0.4

0.6

0.8

1.0

xW

Jo u

rn

0.0

al

0.93

of the DMF+W mixture at temperature: ■ 293.15 K, ● 298.15 K,

▲ 303.15 K, ▼ 308.15 K.

26

Journal Pre-proof

0.5

f

0.3

oo

0.2

pr

EEp,m·108/m3·mol-1·K-1

0.4

0.0

0.2

0.4

rn

al

0.0

Pr

e-

0.1

0.6

0.8

1.0

xW

m)

of DMF+W mixture at

Jo u

Fig. 2. Excess molar volume expansion coefficient (

temperature: ■ 293.15 K, ● 298.15 K, ▲ 303.15 K,▼ 308.15 K.

27

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1700

b

a

1700

f o

1650 1650

o r p

-1

e

u/m·s

u/m·s-1

1600

1550

l a

1500

n r u

1450

1400 0.00

r P

0.20

0.40

o J

0.60

xW

0.80

1.00

1600

1550

1500

1450 0.80

0.85

0.90

0.95

1.00

xW

Fig. 3. Experimental values of sound velocity

of DMF+W mixture a) 0

1, b) 0.8

1 at temperature: ■ 293.15 K, ● 298.15 K,

▲ 303.15 K, ▼ 308.15 K.

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5.5

a

4.6

5.0

4.4

-1

r P 10

l a

4.0

n r u

3.5

0.20

0.40

o J 0.60

0.80

1.00

4.2

of DMF+W mixture a) 0

o r p

4.0

3.8

3.6

0.90

0.92

0.94

0.96

0.98

1.00

xW

xW

Fig. 4. Isentropic compressibility

f o

e

S·10 /Pa

10

S·10 /Pa

-1

4.5

0.00

b

1, b) 0.9

1 at temperature: ■ 293.15 K, ● 298.15 K, ▲ 303.15

K, ▼ 308.15 K.

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1

-1

oo

f

-2

pr

-3

e-

-4

-5

Pr

KES ,m·1015 and KET,m·1015/m3·Pa-1·mol-1

0

0.2

0.4

Fig. 5. Excess molar compressibilities (

0.6

0.8

1.0

xW

Jo u

0.0

rn

-7

al

-6

m

(full symbol) and (

m)

(open symbol) of

DMF+W mixture at temperature: ■ 293.15 K, ● 298.15 K, ▲ 303.15 K, ▼ 308.15 K.

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140

oo

f

-1

Cp,m/J·mol ·K

-1

120

pr

100

0.2

0.4

rn

al

0.0

Pr

e-

80

0.8

1.0

xW

) of DMF+W mixture at temperature: ■ 293.15 K,

Jo u

Fig. 6. Isobaric molar heat capacity

0.6

● 298.15 K, ▲ 303.15 K, ▼ 308.15 K.

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10

-1

Cp,m/J·mol ·K

-1

8

f

E

6

pr

oo

4

0

0.2

0.4

0.6

0.8

1.0

xW

rn

al

0.0

Pr

e-

2

) of DMF+W mixture at temperature: ■

Jo u

Fig. 7. Excess molar isobaric heat capacity 293.15 K, ● 298.15 K, ▲ 303.15 K, ▼ 308.15 K.

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6

f

4

oo

CEp,m i CEV,m /J·mol-1·K-1

8

e-

pr

2

Pr

0

0.2

0.4

rn

al

0.0

Jo u

Fig. 8. Excess molar isobaric

0.6

0.8

1.0

xW

) ■ and isochoric

) ● heat capacity of DMF+W

mixture at 298.15 K.

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1.6

1.4

-1

o r p

1.0

-1 3

-1.0

l a

n r u

-2.0

0.2

0.4

o J 0.6

0.8

1.0

0.8

e

r P

E

8

-1.5

0.0

f o

1.2

-0.5

(Cp,m/p) 10 /m K mol

[(Gm/p)E, (Hm/p)E, T(Sm/p)E]106/m3 mol-1

0.0

0.6

0.4

0.2

0.0

-0.2 0.0

0.2

0.6

0.8

1.0

xW

xW

Fig. 9. Excess molar thermodynamic functions of the DMF+W mixture at 298.15K: ■ (

0.4

) , ●(

) ,▲

(

) ,▼(

) .

34

Jo u

rn

al

Pr

e-

pr

oo

f

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35

Journal Pre-proof Author statement Magdalena Tyczyńska: Writing- Original draft preparation, Writing- Reviewing and Editing, Visualization Marlena Komudzińska: Writing- Original draft preparation, Visualization, Investigation Małgorzata Jóźwiak: Supervision, Formal analysis, Conceptualization Andrzej Burakowski: Investigation

Jo u

rn

al

Pr

e-

pr

oo

f

Jacek Gliński: Supervision

36

Journal Pre-proof Declaration of interests

⊠ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Jo u

rn

al

Pr

e-

pr

oo

f

☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:

37

Journal Pre-proof Highlights

f oo pr ePr al rn

   

The density, sound velocity and heat capacity were analyzed for (DMF+W) system. The volumetric properties were discussed. The excess molar functions were calculated and interpreted. Isobaric and isochoric molar heat capacity were determined. The effect of composition and temperature was analyzed.

Jo u



38