Surface characterization of 1-butyl-1-ethylpiperidinium bromide by inverse gas chromatography

Article abstract of DOI:10.1016/j.molliq.2019.110945

This work addresses the surface characterization of an organic salt based on a piperidinium cation and a halide anion, similar to a first generation ionic liquid, using the Inverse Gas Chromatography (IGC)technique. IGC was employed in order to assess the dispersive surface energy and the acid/base character of 1-butyl-1-ethylpiperidinium bromide, [C₂C₄PIP]Br at a temperature range (313.15–343.15 K)well below its melting point, where the retention mechanism is governed by the surface adsorption of the probes. This type of characterization was possible due to the high melting point of [C₂C₄PIP]Br, namely 413.15 K. The dispersive component of the surface energy was estimated with the aid of the Schultz method and the Dorris-Gray method. Results obtained using the first method were higher than the ones obtained by the latter. The discrepancy between the two methods was found to increase with the increase of temperature. The acid/base characterization was implemented by using the Flour and Papirer approach as well as the Brookman and Sawyer method. The acidity and basicity constants of the surface of [C₂C₄PIP]Br revealed that it is amphoteric with a predominantly basic character.

Full text of DOI:10.1016/j.molliq.2019.110945

Accepted Manuscript
Surface characterization of 1-butyl-1-ethylpiperidinium bromide
by inverse gas chromatography
Stella K. Papadopoulou, Nicolas Papaiconomou, Stéphane Baup,
Cristina Iojoiu, Lenka Svecova, Pierre-Xavier Thivel
PII:
DOI:
Article Number:
Reference:
S0167-7322(18)36601-7
https://doi.org/10.1016/j.molliq.2019.110945
110945
MOLLIQ 110945
To appear in:
Journal of Molecular Liquids
Received date:
Revised date:
Accepted date:
18 December 2018
1 May 2019
7 May 2019
Please cite this article as: S.K. Papadopoulou, N. Papaiconomou, S. Baup, et al., Surface
characterization of 1-butyl-1-ethylpiperidinium bromide by inverse gas chromatography,
Journal of Molecular Liquids, https://doi.org/10.1016/j.molliq.2019.110945
This is a PDF file of an unedited manuscript that has been accepted for publication. As
a service to our customers we are providing this early version of the manuscript. The
manuscript will undergo copyediting, typesetting, and review of the resulting proof before
it is published in its final form. Please note that during the production process errors may
be discovered which could affect the content, and all legal disclaimers that apply to the
journal pertain.

ACCEPTED MANUSCRIPT
Surface characterization of 1-butyl-1-ethylpiperidinium bromide
by inverse gas chromatography
Stella K. Papadopouloua,*, Nicolas Papaiconomoua,b, Stéphane Baupc,
Cristina Iojoiua, Lenka Svecovaa, Pierre-Xavier Thivela
a Université Grenoble Alpes, Université Savoie Mont Blanc, CNRS, Grenoble INP, LEPMI,
38000 Grenoble, France
b Institut de Chimie de Nice, Université Côte d’Azur, UMR CNRS 7272, Parc Valrose, F-
06108 Nice Cedex 2, France
c Université Grenoble Alpes, CNRS, Grenoble INP, LRP, 38000 Grenoble, France
*
Corresponding author e-mail address: papadopoulou.styliani@gmail.com (S.K
Papadopoulou)
1

ACCEPTED MANUSCRIPT
Abstract
This work addresses the surface characterization of an organic salt based on a piperidinium
cation and a halide anion, similar to a first generation ionic liquid, using the Inverse Gas
Chromatography (IGC) technique. IGC was employed in order to assess the dispersive surface
energy and the acid/base character of 1-butyl-1-ethylpiperidinium bromide, [C2C4PIP]Br at a
temperature range (313.15-343.15 K) well below its melting point, where the retention
mechanism is governed by the surface adsorption of the probes. This type of characterization
was possible due to the high melting point of [C2C4PIP]Br, namely 413.15 K. The dispersive
component of the surface energy was estimated with the aid of the Schultz method and the
Dorris-Gray method. Results obtained using the first method were higher than the ones obtained
by the latter. The discrepancy between the two methods was found to increase with the increase
of temperature. The acid/base characterization was implemented by using the Flour and Papirer
approach as well as the Brookman and Sawyer method. The acidity and basicity constants of
the surface of [C2C4PIP]Br revealed that it is amphoteric with a predominantly basic character.
Keywords: Ionic liquids; Inverse gas chromatography; 1-butyl-1-ethylpiperidinium bromide;
Surface energy; Acid-base interactions
2

ACCEPTED MANUSCRIPT
1
Introduction
Ionic liquids (ILs) are salts exhibiting low melting points, typically below 100°C, composed of
anions and large organic cations, such as imidazolium, pyridinium, pyrrolidinium and less
commonly piperidinium [1-6]. ILs have a number of interesting properties such as non-
volatility, non-flammability, high thermal and ionic conductivity and an enhanced solvation
ability for a wide range of materials [1, 4, 5, 7]. On these grounds, ILs have been widely
explored as ‘green’ media in chemical and catalytic reactions, distillations, liquid-liquid
extractions and solvent-aided crystallizations [1, 4, 5]. Other studies report the utilization of
ILs as lubricants, in gas separation processes and as gas storage media [7]. ILs were also
employed as electrolytes in batteries, electrochemical capacitors [3] and as catalysts [8].
Piperidinium based ILs are of special interest for electrochemical applications due to their water
immiscibility, high conductivities and wide electrochemical windows [9, 10]. As piperidinium
based ionic liquids contain only saturated carbons, Shukla demonstrated that for a given anion,
these ILs exhibit higher melting points and are thermally more stable than the respective
imidazolium ILs having the same alkyl chains appended on the cation [9, 10]. In particular,
piperidinium bromide salts exhibit very high melting points (in the vicinity of 200°C) whereas
their homologous imidazolium bromide salts are either liquids or present low melting points [9,
10]. When ionic liquids are involved in applications such as extraction and catalysis, the
presence of a second phase (liquid of gas) other than the ionic liquid is required. Reactions,
interactions and chemical exchanges that take place at the interface of the two-phase systems
strongly depend on the surface properties of each fluid [11]. Therefore, the understanding of
surface related properties of ionic liquids, such as their surface energy and acid-base character
is necessary for the elucidation of the mechanisms that govern these reactions [7, 12-15].
Although there is a plethora of experimental studies investigating the surface tension of ionic
liquids with various techniques [16], only a restricted number of publications address the
estimation of the dispersive surface energy of ionic liquids with the use of inverse gas
chromatography (IGC). Over the past years, inverse gas chromatography has proved to be a
valuable tool towards the characterization of the surface and thermodynamic properties of
various inorganic and organic materials such as polymers, fillers and pharmaceuticals [17]. It
should be outlined that the choice of the measurement temperature range is crucial in IGC as it
determines the state (melt or solid) of the material under study, governing thus the retention
mechanism of the probes (surface adsorption in the case of solids or mixing with bulk of the
melt) [17].
3

ACCEPTED MANUSCRIPT
Although during the last decade IGC appears to be very popular for the thermodynamic
characterization of ionic liquids [8, 18-26], it has rarely been utilized for their surface
characterization. This is due to the fact that such characterization should be conducted at a
temperature range below the melting point of the IL in order to ensure that the interaction
mechanism between the probes and IL is surface adsorption [17]. On these grounds, as ILs
exhibit low melting points, IGC is rather appropriate for the surface analysis of high melting
point salts or for the thermodynamic characterization of ionic liquids.
The group of Wang has published a series of papers on the surface [27-29] and thermodynamic
characterization [8, 18, 30-33] of methyl imidazolium ILs by means of IGC. To our knowledge,
these are the only IGC studies addressing the surface characterization of ionic liquids [27-29].
It has to be stressed that the authors conducted both the surface and the thermodynamic
characterizations at the same experimental temperature range, which is well above the melting
point of the studied ILs [34]. Given the fact that the studied substances were in all cases in the
liquid state and thus the probes’ interaction mechanism was bulk absorption, the measurement
temperatures used in these three studies were not appropriate for the surface characterization of
the methyl imidazolium ILs.
In the current contribution, we present the results of the IGC surface characterization of 1-butyl-
1-ethylpiperidinium bromide [C2C4PIP]Br. Piperidinium based ILs is a family of ionic liquids
much less studied than those based on imidazolium or pyridinium cations for example [35].
Concerning their IGC characterizations, only a limited number of studies have reported the
estimation of the thermodynamic properties of piperidinium-based ILs bearing anions other
than the bromide anion, or with different alkyl chain appended onto the cation, as those present
in [C2C4PIP]Br [36-38]. 1-butyl-1-ethylpiperidinium bromide is an organic salt being by all
aspects similar to halide-based ionic liquid, with the exception that its melting point is above
373 K. Hence, IGC measurements were performed at 313.15-343.15 K, a temperature range
which is below the melting point of [C2C4PIP]Br. The energy, enthalpy and entropy of
adsorption of polar probes on the surface of the salt, the dispersive component of the surface
energy and the Lewis acidity and basicity constants of [C2C4PIP]Br were determined. The
dispersive interactions were investigated with the aid of well-known methods proposed by
Dorris and Gray and by Schultz, whereas the specific interactions of the polar probes were
calculated using the Brookman and Sawyer approach and the Flour and Papirer method.
In this article, after the theoretical background section and a section dedicated to detailing the
procedure used for carrying out the IGC analysis, results will be presented and discussed.
4

ACCEPTED MANUSCRIPT
2
Theoretical background
Contrary to the conventional gas chromatography, in IGC, the material under study is packed
into the column where injections of carefully selected probes with known physicochemical
properties are made [17, 39, 40]. The probes can be injected onto the column either at infinite
dilution or at finite concentration. In the case of infinite dilution, the injection of minor amounts
of the tested solvent makes sure that the retention is governed by the stationary phase-probe
interactions and the probe-probe interactions are avoided [17].
The key measurement in IGC experiments is the net retention volume of the probes, 푉푁. It is
expressed as the volume of the carrier gas necessary to elute the solute from the column and is
calculated by the following equation [41]:
푇
푉푁 = 푗퐹푀(푡푅 − 푡푀) 푇 (1 − 푝
)
(1)
푊
0
푝
퐹
where 푡푅, 푡푀 are the probe’s and marker’s retention times, respectively, 퐹푀 is the carrier gas
flow rate measured at the column outlet at ambient pressure, 푝0 and at room temperature, 푇퐹 .
Also, 푇 is the column temperature, 푝푊 is the vapor pressure of water at 푇퐹 and 푗 is the James
and Martin factor used to correct the gas carrier compressibility, defined as [41]:
2
푝
푝
푖
(
(
⁄
) −1
3
푗 = [
2
푝
0
]
(2)
3
푖
⁄
) −1
푝
0
where 푝푖 and 푝0 are the column inlet and outlet pressures, respectively.
2.1
Dispersive interactions
The dispersive component of the surface energy of a solid, 훾푠푑, can be determined, using the
Dorris-Gray method [36], as described by the following equation:
2
퐶퐻
2
1
훾푠푑 = (4훾 ) (−Δ퐺
)
퐶퐻
2
(3)
푁훼
퐶퐻
2
where Δ퐺퐶퐻 is the adsorption free energy of one methylene group, 푁 is the Avogadro’s
2
number, 훼퐶퐻 is the cross-sectional area of an adsorbed methylene group (6 Å2) and 훾퐶퐻2is the
2
surface free energy of a solid material constituted by methylene groups only, such as linear
polyethylene [훾퐶퐻 = 35.6 − 0.058푡, with t being the working temperature, in °C)]. The
2
adsorption free energy of one methylene group is calculated by the following equation:
Δ퐺퐶퐻 = −푅푇 ln (푉
)
(4)
푁(푛+1)
2
푉
푁(푛)
5

ACCEPTED MANUSCRIPT
where 푉푁(푛+1) and 푉푁(푛) are the retention volumes of n-alkanes with n + 1 and n carbon atoms,
respectively, 푇 is the column temperature and 푅 is the ideal gas constant. The slope of the
straight line obtained by a plot of the surface free energy of adsorption
of
n-alkanes 푅푇 ln 푉푁 versus the number of their carbon atoms is equal to the free energy of
adsorption of a methylene group, Δ퐺퐶퐻
.
2
Another method used for the calculation of the dispersive component of the surface free energy,
is the one proposed by Schultz et al. [42] and is based on the following equation:
푑
푑
√
−Δ퐺푎 = 푅푇 ln 푉푁 = 2푁훼 훾푠 훾푙 + 퐶
(5)
where 훼 is the surface area of the probe molecules, 훾푠푑 and 훾푙푑 are the dispersive components of
the surface energy of the solid and the liquid probe, respectively and 퐶 is a constant. 훾푠푑 can be
extracted from the slope of the linear plot of the 푅푇 ln 푉푁 values of n-alkanes versus the term
푑
√
훼 훾푙 .
2.2
Specific interactions
The non-dispersive character of the stationary phase is studied by the employment of probes
that can also interact through specific intermolecular forces with the stationary phase. When a
polar probe is injected in the column, it interacts with the material under study by both
dispersive and specific interactions. The term specific includes all types of interactions, i.e.
polar, hydrogen bonding, metallic or magnetic, apart from the dispersive ones (London forces)
[17]. Hence, the contribution of specific interactions to the free energy of adsorption, Δ퐺푠푝,
can be considered as the difference between the total free energy of adsorption, Δ퐺푎푑푠, and the
dispersive contribution to the free energy of adsorption Δ퐺푑. Several methods have been
proposed for the determination of the Δ퐺푠푝 [17]. In the present study, Δ퐺푠푝 was calculated
through the use of the Flour and Papirer approach [43] and the Brookman and Sawyer method
[44]. The estimation of Δ퐺푠푝 is based on a plot of Δ퐺 or simply 푅푇 ln 푉 values of both polar
푛
and apolar probes versus their boiling temperatures (푡푏, in °C) according to the Brookman and
Sawyer method, or the log 푝0, logarithm of their saturated vapor pressure, according to the Flour
and Papirer method. The n-alkane series leads to a linear plot, which constitutes a reference
straight line for the dispersive interactions. The contribution of specific interactions to the free
energy of adsorption, Δ퐺푠푝, corresponds to the vertical distance between the −Δ퐺푎푑푠 value and
the reference line according to the equation:
푠푝
푎푑푠
푟푒푓
(
)
(
)
(
)
⁄
−Δ퐺
= −Δ퐺
− −Δ퐺
= 푅푇 ln(푉푁 푉푁,푟푒푓
)
(6)
6

ACCEPTED MANUSCRIPT
where 푉푁 is the net retention volume of the polar probe and 푉푁,푟푒푓 the net retention volume of
a hypothetical alkane with the same boiling point or saturated vapor pressure as that of the polar
probe.
The specific enthalpy, Δ퐻푠푝, can be determined after the calculation of the specific component
of the free energy of adsorption at various temperatures. When plotting the Δ퐺푠푝 values as a
function of the reciprocal temperature, 푇−1, Δ퐻푠푝 is calculated from the slope of the straight
line corresponding to the following relation:
푠푝
푠푝
Δ퐺푠푝 푇 = Δ퐻 ∙ 1 푇 − Δ푆
(7)
⁄
⁄
The enthalpies of specific interactions between the examined surface and the polar probe can
be used for the estimation of the 퐾퐴 and 퐾퐵 indices reflecting the acidity (electron acceptor)
and basicity (electron donor) of a solid surface, respectively [17, 45-47] and are related to the
acidic or basic character through the equation:
∗
∗
−Δ퐻푠푝 퐴푁 = 퐾퐴 ∙ 퐷푁 퐴푁 + 퐾퐵
(8)
⁄
⁄
where 퐷푁 [45] and퐴푁∗ [47] are Gutmann’s donor and modified acceptor numbers of the polar
probes, respectively. Hence, 퐾퐴 and 퐾퐵 can be determined by the slope and intercept,
∗
∗
respectively, of the straight line obtained when plotting Δ퐻푠푝 퐴푁 versus 퐷푁 퐴푁 . The
⁄
⁄
⁄
퐾퐵 퐾퐴 ratio provides an empirical basis for the classification of a surface with respect to
⁄
⁄
acidity-basicity. At 퐾퐵 퐾퐴 > 1 the surface is considered to be basic, while for 퐾퐵 퐾퐴 < 1
the surface is considered to be acidic [17].
3
Experimental
Materials
3.1
For the synthesis of the ionic liquid, 1-bromobutane (99%), 1-ethylpiperidine (99%) and
acetonitrile were used and were purchased from Sigma Aldrich.
For the IGC analysis, the following solvents were used as probes: n-octane, n-nonane, n-decane,
n-undecane, n-dodecane, acetonitrile, n-butanol, pyridine and chloroform. The characteristics
of the solvents used for the IGC analysis are presented in Table 1. All solvents were of the
highest available purity and were purchased from Sigma Aldrich. Chromosorb W HP (100/120)
mesh was used as the solid support (Antelia, France). All the gases used were purchased from
Air Liquide and were of high purity.
7

ACCEPTED MANUSCRIPT
Table 1. Physical and chemical properties of the probes used for the IGC analysis [27, 47-52]
훼
퐷푁
(kJ mol-1) (kJ mol-1)
퐴푁∗
훾푙푑
(mJ/m2)
Probe
Boiling Saturated
Character
(10-19 m2)
point
(°C)
vapor
pressure
(kPa)
n-Octane
n-Nonane
n-Decane
125.7
150.8
174.2
n/a
n/a
n/a
n/a
n/a
0
n/a
n/a
Neutral
Neutral
Neutral
Neutral
Neutral
Acidic
1.871
0.580
0.181
0.056
6.29
6.89
7.5
21.3
22.7
23.4
24.6
n/a
n-Undecane 195.9
n-Dodecane 216.3
8.1
n/a
n/a
0.018
0.930
8.7
25.4
n-Butanol
Pyridine
117.7
115.3
61.2
-
-
-
-
-
-
-
-
38.1
0.6
2.772
138.6
0
Basic
Chloroform
Acetonitrile
26.165
12.147
22.6
19.7
Acidic
81.6
59
Amphoteric
3.2
Synthesis and characterization of 1-butyl-1-ethyl piperidinium bromide
1-butyl-1-ethylpiperidinium bromide (Figure 1) was synthesized as previously reported [53].
Briefly, 1-bromobutane was mixed with 1-ethylpiperidine in 100 mL acetonitrile at reflux for
2 days. The solvent was then evaporated using a rotary evaporator. The resulting product
appearing as a white solid was washed several times with ethyl acetate. After filtering, the
product was initially dried on a rotary evaporator to remove the remaining solvent and then
dried under vacuum (~0.1 mbar) for 24 hours. The final product was obtained as a white solid.
1
Purity was checked by Nuclear Magnetic Resonance Spectroscopy (1H NMR). The H NMR
spectrum was collected on a Bruker WM 400 MHz spectrometer in Dimethysulfoxide (DMSO-
d6) as solvent. The spectrum is given in the Supplementary Material section (Figure S1). The
chemical shift of different protons from [C2C4PIP]Br are at: 3.36-3.30, (6H, m, (CH2)3-N+,
3,6), 3.25-3.21, (2H, t, CH2-N+, 4), 1.77 (4H, m, 2 CH2, 2), 1.58-1.53 (4H, m, CH2, 1,7), 1.37-
1.28 (2H, m, CH2, 8), 1.19-1.15 (3H, t, CH3, 5), 0.95-0.92 (3H, t, CH3, 9).
8

ACCEPTED MANUSCRIPT
Figure 1. Structure of [C2C4PIP]Br. The protons observed in the NMR spectrum were
identified.
The melting point of [C2C4PIP]Br was assessed by Differential Scanning Calorimetry using a
TA Instruments DSC 2920 modulated DSC device. The sample was heated from 25°C to 250°C
at a heating rate of 5K/min. The DSC thermogram is presented in the Supplementary Material
section (Figure S2). The melting point of the [C2C4PIP]Br was found to be 140 °C.
3.3
Column preparation and IGC setup
The IGC experiments were performed using a Perkin Elmer Clarus 480 gas chromatograph,
equipped with a flame ionization detector (FID). The data acquisition was made with the AZUR
software. The retention times of the probes were determined after the calculation of the first-
order moment of the concentration distribution. This was necessary due to the slight “tailing”
observed at the elution profile of the probes [41]. High purity helium was used as the carrier
gas and methane was used as a marker. The flow rate of helium was measured with a soap
bubble flowmeter connected to the end of the column, at room temperature. The experiments
were performed at infinite dilution, by injecting manually 0.1 μL of each probe with a 1 μL
Hamilton syringe. At least three injections of each probe were made and the retention time was
taken as the average of the three measurements. The standard deviation was less than 2% in all
cases.
The IGC experimental conditions and the column characteristics are presented in Table 2. A
stainless steel column was used for the measurements and was washed with acetone prior to
use. The stationary phase of the column was prepared via the coating method proposed by Al-
Saigh and Munk in order to better control the amount of the salt coated on the solid support
[54]. [C2C4PIP]Br was coated onto Chromosorb W HP at a loading of 20.7% w/w. The column
was preconditioned overnight to the working conditions (temperature and helium flow rate) in
9

ACCEPTED MANUSCRIPT
order to remove any possible contaminants that could be eluted during measurements. The
protocol regarding the preparation of the column was described in detail elsewhere [50, 55, 56].
Table 2. Chromatographic conditions and column specifications
1-butyl-1-ethylpiperidinium bromide
Injector temperature (K)
Detector temperature (K)
Column temperatures (K)
Column type of material
Column length (cm)
473.15
473.15
313.15, 323.15, 333.15, 343.15
SS 316 ASTM A-269
70
Column O.D (inch)
1/8
20.7
10
[C2C4PIP]Br loading (%)
Flow rate (mL/min)
4
Results
Dispersive component of the surface energy
4.1
The dispersive component of the surface energy of 1-butyl-1-ethylpiperidinium bromide was
calculated at the temperature range 313.15-343.15 K, using the Dorris-Gray method and the
approach proposed by Schultz.
4.1.1 Dorris-Gray method
The slope of the line obtained when plotting the 푅푇 ln 푉푁 values of n-alkanes versus their
number of carbon atoms yields the free energy of adsorption of a methylene group, Δ퐺퐶퐻 as
2
indicated by Eq. (4). The corresponding plot is illustrated in Figure 2. The dispersive component
of the surface energy of [C2C4PIP]Br was calculated via Eq. (3) according to the Dorris-Gray
method. The values of 훾푠푑 together with their maximum errors are presented in Table 3.
10

ACCEPTED MANUSCRIPT
313.15 K
12
323.15 K
333.15 K
343.15 K
10
8
6
4
2
0
-2
8
9
10
11
12
Number of carbon atoms
Figure 2. Surface free energy of adsorption of n-alkanes 푅푇 ln 푉푁 on [C2C4PIP]Br versus their
number of carbon atoms, measured at the temperature range 313.15-343.15 K.
4.1.2 Schultz method
Figure 3 illustrates the surface free energy of adsorption of n-alkanes 푅푇 ln 푉푁 , on [C2C4PIP]Br
푑
√
as a function of the term 푎 훾푙 , measured between 313.15 and 343.15 K , according to the
Schultz method. The values of the surface area of n-alkanes and the values of their dispersive
surface energies listed in Table 1 in combination with Eq. (5) were used for this purpose. Results
are listed in Table 3.
11

ACCEPTED MANUSCRIPT
313.15 K
12
323.15 K
333.15 K
343.15 K
10
8
6
4
2
0
-2
3.00E-018
3.50E-018
4.00E-018
4.50E-018
(ld)0.5 [m2(mJ/m2)0.5]
Figure 3. Surface free energy of adsorption of n-alkanes 푅푇 ln 푉푁 , on [C2C4PIP]Br versus
푑
√
푎 훾푙 measured at the temperature range 313.15-343.15 K.
Table 3. Dispersive component of the surface energy of [C2C4PIP]Br at the temperature range
313.15-343.15 K, obtained by the Dorris-Gray and the Schultz methods
T (K)
Dorris-Gray method
Schultz method
훾푠푑 (mJ/m2)
푅2
훾푠푑 (mJ/m2)
푅2
313.15
323.15
333.15
343.15
37.5 ± 1.7
35.2 ± 0.8
33.9 ± 1.3
30.6 ± 0.7
0.998
0.999
0.999
0.999
34.0 ± 1.7
31.3 ± 1.2
29.7 ± 1.4
26.3 ± 1.0
0.998
0.999
0.998
0.999
12

ACCEPTED MANUSCRIPT
40
Dorris-Gray
γds= -0.23T+109.5
R2= 0.98
Schultz
38
36
34
32
30
28
26
24
γds= -0.25T+112.9
R2= 0.98
310
315
320
325
330
335
340
345
T (K)
Figure 4. Variation of the dispersive component of the surface energy of [C2C4PIP]Br with
temperature, at the temperature range 313.15-343.15 K, obtained by the Dorris-Gray and the
Schultz methods
Focusing on Figure 2 and Figure 3 we notice that good linearity was achieved for the
dependence of the free energy of adsorption with the increasing number of aliphatic carbons
푑
√
(Dorris-Gray method) or with the 푎 훾푙 term (Schultz method). The dispersive component of
the surface energy of [C2C4PIP]Br obtained by the Dorris-Gray and the Schultz methods was
plotted as a function of temperature (Figure 4) and the values are given in Table 3. For all
studied temperatures, high correlation coefficients R² values were found. It appears that the
dispersive component of the surface energy of [C2C4PIP]Br presents a decreasing trend with
the increase of temperature [57]. Moreover, based on Figure 4 we notice that the dependence
of 훾푠푑 with temperature is almost linear, and when comparing the slopes corresponding at the
descending trend obtained by both methods, we observe that they are similar.
In addition, we notice that the 훾푠푑 values calculated with the aid of the Dorris-Gray method are
higher with respect to those obtained with the Schultz method. The discrepancy between the
results calculated by these methods increases with temperature. This trend is in line with the
results presented in pertinent literature [58-66].
13

ACCEPTED MANUSCRIPT
As it was mentioned in the introduction, there is no study in literature addressing the estimation
of the dispersive surface energy of piperidinium or bromide based ILs. However, the surface
tension of piperidinium ILs has been assessed by techniques other than IGC (see Table 4).
Table 4. Surface tension values of piperidinium based ILs taken from literature and dispersive
component of the surface energy results of [C2C4PIP]Br of the present study
훾 (mJ/m2)
훾푠푑 (mJ/m2)
T (K)
[C3C1PIP][NTf2]
[C4C1PIP][NTf2] [68]
[C2C4PIP]Br
(this work)
-
298
35.2 [69] / 35.3 [68]
34.5 [67] / 35.1 [68]
34.5 [68]
34.2
34.0
33.5
33.0
32.5
32.1
303.2
313.2
323.2
333.2
343.2
-
34.0 - 37.5
31.3 - 35.2
29.7 - 34.0
26.3 - 30.6
34.0 [68]
33.5 [68]
33.0 [68]
Osada et al. [67] reported the surface energy of 1-methyl-1-propylpiperidinium
bis(trifluoromethanesulfonyl)imide ([C3C1PIP][NTf2]) measured with the Dynamic Light
Scattering (DLS) technique. Bhattacharjee et al. [68] assessed the surface energy of
[C3C1PIP][NTf2] and [C4C1PIP][NTf2] (1-Butyl-1-methylpiperidinium bis (trifluoromethyl
sulfonyl)imide) by using the contact angle method. The comparison between our results (last
column in Table 4) with literature data is not straightforward for several reasons; firstly, the
latter concern surface energy values contrary to the former which concern values of dispersive
surface energy. Furthermore, as it has been shown, the measuring techniques of the surface
energy as well as the sample purity have an impact on the values of 훾 [16, 68]. Moreover, the
anion [NTf2]- ((bistrifluoromethanesulfonyl)imide) reported in the literature is a polyatomic,
bulky and very weakly coordinating anion. It is thus very different from the small and
coordinating bromide ion studied here. On these grounds, only a rough comparison between
literature data and the results of this study can be made. As a first remark, the same temperature
dependence of 훾 and is 훾푠푑 observed for all ILs, all values decrease with increasing temperature.
It is well known that the surface tension depends on the contribution of the groups which are
exposed at the surface [16, 68]. In the case of ionic liquids, when the cation bears long alkyl
14

ACCEPTED MANUSCRIPT
side chains and is thus bulkier than the anion, the surface tension is affected primarily by the
nature of the cation [16, 68].
4.2
Acid-base interactions
The ability of the ionic liquid to intermolecular specific interactions with other substances is
strongly dependent on the presence of acidic and basic sites on its surface.
The assessment of the acid-base interactions of a surface includes the calculation of the specific
component of the free energy of adsorption of a probe, Δ퐺푠푝, the specific component of the free
푠푝
⁄
enthalpy of adsorption of a probe, Δ퐻 and the ratio 퐾퐵 퐾퐴 of the examined surface [17]. As
it has been mentioned in Section 2.2, several methods have been developed for the acid-base
characterisation of a material through the use of the IGC technique. The Schultz method allows
푑
the estimation of Δ퐺푠푝 through the use of the term 훾푙 , whereas the Papirer method and the
√
Brookman and Sawyer method are based on the saturated vapor pressures and the boiling points
of the probes, respectively. The latter two properties are readily available in literature, contrary
to the molecular area and the dispersive component of the surface tension of polar probes. The
discrepancy between the values of 훾푠푑 and 푎 of polar probes appearing in literature [65, 70] is
due to the presence of one or more functional groups [59]. For the above reasons, although in
the present study the Schultz method was employed for the dispersive surface energy
calculation of [C2C4PIP]Br, the acid-base interactions were studied with the aid of the Flour
and Papirer method and the Brookman and Sawyer method.
4.2.1 Flour and Papirer method
Figure 5 presents the results of the energies of adsorption of n-alkanes and polar probes on the
surface of [C2C4PIP]Br versus the logarithm of their saturated vapour pressure, according to
the Flour and Papirer method. The straight reference line defines the London dispersive
interactions, while the energies of adsorption polar probes lie above this line.
15

ACCEPTED MANUSCRIPT
10
8
6
4
2
0
Gsp
-2
-4
-6
-8
-10
n-alkanes
n-butanol
pyridine
chloroform
acetonitrile
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
log (po)
Figure 5. Energy of adsorption of n-alkanes and polar probes on the surface of [C2C4PIP]Br
versus the logarithm of their saturated vapour pressure, at 343.15 K.
The values of the specific component of the free energy of adsorption Δ퐺푠푝 of the polar probes
used in this study are high. The fact that the Δ퐺푠푝 values of the Lewis acidic, basic, and
amphoteric probes lie above the reference line of n-alkanes suggests that all types of active sites
are present on the surface of [C2C4PIP]Br [71]. The highest Δ퐺푠푝 values, correspond to
acetonitrile, which has an amphoteric character.
4.2.2 Brookman and Sawyer method
The contribution of specific interactions to the free energy of adsorption Δ퐺푠푝 of polar probes,
was calculated by the aid of the Brookman and Sawyer method, as shown in Figure 6.
16

ACCEPTED MANUSCRIPT
10
n-alkanes
n-butanol
pyridine
chloroform
acetonitrile
8
6
4
2
0
Gsp
-2
-4
-6
-8
40
60
80
100 120 140 160 180 200 220 240
Tb (oC)
Figure 6. Energy of adsorption of n-alkanes and polar probes on the surface of [C2C4PIP]Br
versus their boiling temperatures, at 343.15 K.
The Δ퐺푠푝 values obtained by both methods exhibit the same trend. Similarly to the conclusion
extracted by the Flour and Papirer analysis, results show that both acidic and basic sites exist
on the surface of [C2C4PIP]Br. However, the dominant character of the surface is determined
⁄
by means of the 퐾퐵 퐾퐴 ratio.
For such an estimation, the values of the enthalpy and entropy of adsorption of polar probes on
the surface of [C2C4PIP]Br were calculated by the aid of Eq. (7) and via a plot of Δ퐺푠푝 values
versus the reciprocal temperature, 푇−1. The results obtained by both methods employed are
reported in Table 5.
Table 5. Specific components of the enthalpy and entropy of adsorption of polar probes on the
surface of [C2C4PIP]Br at the temperature range 313.15-343.15 K
Flour and Papirer method
Brookman and Sawyer method
Probe
-Δ푆푠푝
-Δ푆푠푝
−Δ퐻푠푝
−Δ퐻푠푝
(kJ/mol)
(J/mol K)
(kJ/mol)
(kJ/mol K)
n-Butanol
Pyridine
5.59
7.74
6.48
6.51
11.31
9.30
15.56
8.99
Chloroform
Acetonitrile
24.07
0.63
59.58
-18.48
28.73
3.55
66.41
-13.84
17

ACCEPTED MANUSCRIPT
The enthalpies and entropies of adsorption of polar probes on the surface of [C2C4PIP]Br
estimated with the Flour and the Brookman methods are comparable, with the exception of n-
butanol. The enthalpy of adsorption of all probes was found to be exothermic in all cases.
Acetonitrile which is an amphoteric probe presents the highest enthalpy of adsorption whereas
chloroform which is acidic has the lowest Δ퐻푠푝 implying that [C2C4PIP]Br is amphoteric with
a basic character. The values of the specific components of the entropy of adsorption of polar
probes on the surface of [C2C4PIP]Br follow the same trend as discussed above. Acetonitrile
has the highest Δ푆푠푝 values, indicating that the surface is amphoteric. Moreover, we notice that
all Δ푆푠푝 values are negative, with the exception of acetonitrile. The adsorption of a probe from
a surface is usually accompanied by an entropy loss as the probe passes from the less ordered
vapor phase to the more ordered adsorbed phase. In the case of acetonitrile, the entropy increase
implies an increase in the degrees of freedom which could be attributed to the rearrangement
of the surface [72].
4.2.3
Acidity and basicity constants
The values for the specific enthalpies of polar probes were employed in order to evaluate the
acidity and basicity constants of [C2C4PIP]Br. According to Eq. (8) the 퐾퐴 and 퐾퐵 constants
∗
can be assessed by the slope and the intercept, respectively, of a plot of Δ퐻푠푝 퐴푁 versus
⁄
∗
⁄
퐷푁 퐴푁 . Based on the values of the Gutmann’s donor and modified acceptor numbers of the
polar probes presented in Table 1 as well as the values of Δ퐻푠푝 obtained by the two methods
used, 퐾퐴 and 퐾퐵 constants were evaluated (Figures 7 and 8). Examining the two plots we can
∗
∗
deduce that, in both cases, linear dependencies of Δ퐻푠푝 퐴푁 versus 퐷푁 퐴푁 were achieved,
based on the high values of the regression coefficients. Similar plots for the estimation of the
퐾퐴 and 퐾퐵 constants appear in literature [27, 51, 62, 68]. The results of the acidity and basicity
constants of the surface of [C2C4PIP]Br are reported in Table 6.
⁄
⁄
18

ACCEPTED MANUSCRIPT
14
12
10
8
Y= 0.054X+0.36
pyridine
R2=0.993
6
4
2
chloroform
n-butanol
0
acetonitrile
0
50
100
150
200
250
DN/AN*
Figure 7. Determination of the 퐾퐴 and 퐾퐵 values of the of [C2C4PIP]Br based on the Flour and
Papirer approach.
Y= 0.065X+0.52
R2=0.995
16
14
12
10
8
pyridine
6
4
chloroform
2
n-butanol
0
acetonitrile
-2
0
50
100
150
200
250
DN/AN*
Figure 8. Determination of the 퐾퐴 and 퐾퐵 values of the of [C2C4PIP]Br based on the Brookman
and Sawyer method.
19

ACCEPTED MANUSCRIPT
Table 6. Acidity and basicity constants of the surface of [C2C4PIP]Br
⁄
Method
퐾퐴
퐾퐵
퐾퐵 퐾퐴
Flour and Papirer
Brookman and Sawyer
0.054
0.065
0.36
0.52
6.67
8.00
⁄
The 퐾퐵 퐾퐴 ratios calculated by the Flour and Papirer method and the Brookman and Sawyer
method suggest that the surface of 1-butyl-1-ethylpiperidinium bromide has a predominantly
Lewis basic character. This conclusion is in line with the findings of the analysis based on the
values of the energy and enthalpy of polar probes, presented in paragraphs 4.2.1 and 4.2.2.
⁄
Despite the fact that the 퐾퐵 퐾퐴 ratios are not similar, we can safely conclude that [C2C4PIP]Br
⁄
is a Lewis base, since in both cases the 퐾퐵 퐾퐴 ratio is greater than 1.
Bearing in mind the structure of 1-butyl-1-ethylpiperidinium bromide, we notice that both
acidic and basic moieties are present in the molecule. As no comparable work has been carried
out previously for solid organic salts or ionic liquids below their melting point, neither the
comparison with literature nor the interpretation of our results are straightforward.
Nevertheless, a tentative explanation can be given as following. Since in our case, the ions of
the salt are relatively small and bound together, the overall basicity of [C2C4PIP]Br is due to an
average of all of its parts, i.e. the alkyl groups, the positive charge on the nitrogen atom and the
Br- anion. As reported previously in IGC studies dealing with polymers, CH2 and CH3 groups
are known to be weak Lewis acidic sites [50, 72, 73]. On the other hand, Br-, as F- or Cl- anions,
is a dense, monoatomic and relatively electronegative anion, and is known to be basic [50, 74].
The positive charge on the nitrogen is acidic, but is expected to be hidden and to be sterically
hindered by the alkyl groups bound to it. Therefore, we can surmise that the general basic
character of [C2C4PIP]Br is due to the relatively dense and monoatomic bromide anion.
Conclusions
This contribution reports for the first time on the surface characterization of a piperidinium
based organic salt, 1-butyl-1-ethylpiperidinium bromide, by means of IGC. Measurements were
conducted at a temperature range (313.15-343.15 K), well below the melting point of
[C2C4PIP]Br (413.15 K) to ensure that the dominant retention mechanism of the probes is
adsorption onto the surface. The Schultz and the Dorris-Gray methods were used for the
calculation of the dispersive component of the surface energy. Results showed that 훾푠푑 decreases
with temperature. Moreover, the comparison of the dispersive component of the surface energy
20

ACCEPTED MANUSCRIPT
of [C2C4PIP]Br with that of two piperidinium based ILs revealed that the results of this study
are comparable with literature values. The anion does therefore not appear to play a crucial role
in the surface energy of the piperidnium-based organic salts studied here and in the literature.
The acid/base characterization based on the Flour and Papirer approach and the Brookman and
Sawyer method showed that the surface of [C2C4PIP]Br is amphoteric with a predominantely
basic character, a conclusion which is further supported by taking into account the molecular
structure of [C2C4PIP]Br bearing, both, weak Lewis acidic and basic sites.
Acknowledgments
The authors acknowledge Grenoble INP for post-doctoral fellowship for S.P. and financial
support for this project.
References
[1] S. Genand-Pinaz, N. Papaiconomou, J.-M. Leveque, Removal of platinum from water by
precipitation or liquid-liquid extraction and separation from gold using ionic liquids,
Green Chem. 15 (2013) 2493-2501.
[2] T.M. Koller, C. Steininger, M.H. Rausch, A.P. Fröba, A Simple Prediction Method for
the Surface Tension of Ionic Liquids as a Function of Temperature, Int. J.Thermophys.
38 (2017) 167.
[3] T. Mandai, K. Yoshida, K. Ueno, K. Dokko, M. Watanabe, Criteria for solvate ionic
liquids, Phys. Chem. Chem. Phys. 16 (2014) 8761-8772.
[4] V. Mazan, I. Billard, N. Papaiconomou, Experimental connections between aqueous-
aqueous and aqueous-ionic liquid biphasic systems, RSC Adv. 4 (2014) 13371-13384.
[5] P. Pollet, E.A. Davey, E.E. Urena-Benavides, C.A. Eckert, C.L. Liotta, Solvents for
sustainable chemical processes, Green Chem. 16 (2014) 1034-1055.
[6] F. Pena-Pereira, A. Kloskowski, J. Namiesnik, Perspectives on the replacement of
harmful organic solvents in analytical methodologies: a framework toward the
implementation of a generation of eco-friendly alternatives, Green Chem. 17 (2015)
3687-3705.
[7] H.F. Almeida, A.R.R. Teles, J.A. Lopes-da-Silva, M.G. Freire, J.A. Coutinho, Influence
of the anion on the surface tension of 1-ethyl-3-methylimidazolium-based ionic liquids,
J. Chem. Thermodyn. 54 (2012) 49-54.
21

ACCEPTED MANUSCRIPT
[8] L. Deng, Q. Wang, Y. Chen, Z. Zhang, J. Tang, Determination of the solubility parameter
of ionic liquid 1-octyl-3-methylimidazolium hexafluorophosphate by inverse gas
chromatography, J. Mol. Liq. 187 (2013) 246-251.
[9] M. Shukla, S. Saha, A Comparative Study of Piperidinium and Imidazolium Based Ionic
Liquids: Thermal, Spectroscopic and Theoretical Studies, in: Ionic Liquids-New Aspects
for the Future INTECH Open Access Publisher, 2013.
[10] M. Shukla, H. Noothalapati, S. Shigeto, S. Saha, Importance of weak interactions and
conformational equilibrium in N-butyl-N-methylpiperidinium bis (trifluro-
methanesulfonyl) imide room temperature ionic liquids: Vibrational and theoretical
studies, Vib. Spectrosc. 75 (2014) 107-117.
[11] G. Járvás, J. Kontos, G. Babics, A. Dallos, A novel method for the surface tension
estimation of ionic liquids based on COSMO-RS theory, Fluid Phase Equilib. 468 (2018)
9-17.
[12] T.M. Koller, M.H. Rausch, K. Pohako-Esko, P. Wasserscheid, A.P. Frꢀba, Surface
tension of tricyanomethanide-and tetracyanoborate-based imidazolium ionic liquids by
using the pendant drop method, J. Chem. Eng. Data 60 (2015) 2665-2673.
[13] G. Law, P.R. Watson, Surface tension measurements of N-alkylimidazolium ionic
liquids, Langmuir, 17 (2001) 6138-6141.
[14] S.A. Mirkhani, F. Gharagheizi, N. Farahani, K. Tumba, Prediction of surface tension of
ionic liquids by molecular approach, J. Mol. Liq. 179 (2013) 78-87.
[15] J. Restolho, J.L. Mata, B. Saramago, On the interfacial behavior of ionic liquids: Surface
tensions and contact angles, J. Colloid Interf. Sci. 340 (2009) 82-86.
[16] M. Tariq, M.G. Freire, B. Saramago, J.A. Coutinho, J.N.C. Lopes, L.P.N. Rebelo, Surface
tension of ionic liquids and ionic liquid solutions, Chem. Soc. Rev. 41 (2012) 829-868.
[17] A. Voelkel, B. Strzemiecka, K. Adamska, K. Milczewska, Inverse gas chromatography
as a source of physiochemical data, J. Chromatogr. A 1216 (2009) 1551-1566.
[18] Y. Chen, Q. Wang, Z. Zhang, J. Tang, Determination of the Solubility Parameter of Ionic
Liquid 1-Hexyl-3-methylimidazolium Hexafluorophosphate by Inverse Gas
Chromatography, Ind. Eng. Chem. Res. 51 (2012) 15293-15298.
[19] U. Domańska, A. Marciniak, Measurements of activity coefficients at infinite dilution of
aromatic and aliphatic hydrocarbons, alcohols, and water in the new ionic liquid
[EMIM][SCN] using GLC, J. Chem. Thermodyn. 40 (2008) 860-866.
[20] K. Heydar, M. Nazifi, A. Sharifi, M. Mirzaei, H. Gharavi, S. Ahmadi, Determination of
Activity Coefficients at Infinite Dilution of Solutes in New Dicationic Ionic Liquids
22

ACCEPTED MANUSCRIPT
Based on Morpholine Using Gas–Liquid Chromatography, Chromatographia, 76 (2013)
165-175.
[21] M. Królikowski, M. Królikowska, The study of activity coefficients at infinite dilution
for organic solutes and water in 1-butyl-4-methylpyridinium dicyanamide,
[B4MPy][DCA] using GLC, J. Chem. Thermodyn. 68 (2014) 138-144.
[22] A. Marciniak, M. Wlazło, Activity Coefficients at Infinite Dilution Measurements for
Organic Solutes and Water in the Ionic Liquid 1-(3-Hydroxypropyl)pyridinium
Trifluorotris(perfluoroethyl)phosphate, J. Phys. Chem. B 114 (2010) 6990-6994.
[23] A. Marciniak, M. Wlazło, Activity coefficients at infinite dilution and physicochemical
properties for organic solutes and water in the ionic liquid 1-(2-methoxyethyl)-1-
methylpiperidinium bis(trifluoromethylsulfonyl)-amide, J. Chem. Thermodyn. 49 (2012)
137-145.
[24] F. Mutelet, J.-N. Jaubert, Accurate measurements of thermodynamic properties of solutes
in ionic liquids using inverse gas chromatography, J. Chromatogr. A 1102 (2006) 256-
267.
[25] F. Mutelet, J.-N. Jaubert, Measurement of activity coefficients at infinite dilution in 1-
hexadecyl-3-methylimidazolium tetrafluoroborate ionic liquid, J. Chem. Thermodyn. 39
(2007) 1144-1150.
[26] Q. Wang, Y. Chen, L. Deng, J. Tang, Z. Zhang, Determination of the solubility parameter
of ionic liquid 1-allyl-3-methylimidazolium chloride by inverse gas chromatography, J.
Mol. Liq. 180 (2013) 135-138.
[27] Q. Wang, Y. Chen, Z. Zhang, J. Tang, Determination of Surface Characteristics of Ionic
Liquid [1-Hexyl-3-methylimidazolium Hexafluorophosphate] by Inverse Gas
Chromatography, J. Chem. Eng. Data 58 (2013) 2142-2146.
[28] Y. Chen, Q. Wang, L. Deng, Z. Zhang, J. Tang, Characterization of surface properties of
1-allyl-3-methylimidazolium chloride ionic liquid by inverse gas chromatography, Chin.
J. Chromatogr. 31 (2013) 147-150.
[29] T. Ban, X.-P. Li, C.-L. Li, Q. Wang, Surface Characterization of a Series of 1-Alkyl-3-
methylimidazolium-Based Ionic Liquids by Inverse Gas Chromatography, Ind. Eng.
Chem. Res. 57 (2018) 12249-12253.
[30] X. Li, Q. Wang, L. Li, Y. Ding, Determination of the thermodynamic parameters of ionic
liquid 1- hexyl- 3⁃ methylimidazolium tetrafluoroborate by inverse gas chromatography,
Chin. J. Chromatogr. 33 (2015) 58-64.
23

ACCEPTED MANUSCRIPT
[31] X. Li, Q. Wang, L. Li, L. Deng, Z. Zhang, L. Tian, Determination of the thermodynamic
parameters of ionic liquid 1-hexyl-3-methylimidazolium chloride by inverse gas
chromatography, J. Mol. Liq. 200 (2014) 139-144.
[32] L. Deng, Q. Wang, Z. Zhang, J. Tang, Determination of thermodynamic parameters for
ionic liquid 1-hexyl-3-methylimidazolium trifluoromethansulfonate by inverse gas
chromatography, Chin. J. Chromatogr. 32 (2014) 169-173.
[33] L. Tian, Y. Chen, Q. Wang, Chin. J. Appl. Chem. 34 (2017) 824-832.
[34] S. Zhang, X. Lu, Q. Zhou, X. Li, X. Zhang, S. Li, Ionic Liquids: Physicochemical
Properties, Elsevier, Amsterdam, 2009.
[35] U. Domańska, M. Królikowska, K. Paduszyński, Physico-chemical properties and phase
behaviour of piperidinium-based ionic liquids, Fluid Phase Equilib. 303 (2011) 1-9.
[36] U. Domańska, K. Paduszyński, Measurements of activity coefficients at infinite dilution
of organic solutes and water in 1-propyl-1-methylpiperidinium bis {(trifluoromethyl)
sulfonyl}imide ionic liquid using g.l.c, J. Chem. Thermodyn. 42 (2010) 1361-1366.
[37] A. Marciniak, M. Wlazło, Activity coefficients at infinite dilution and physicochemical
properties for organic solutes and water in the ionic liquid 1-(2-methoxyethyl)-1-
methylpiperidinium trifluorotris(perfluoroethyl)phosphate, J. Chem. Thermodyn. 57
(2013) 197-202.
[38] K. Paduszyński, U. Domańska, Limiting Activity Coefficients and Gas–Liquid Partition
Coefficients of Various Solutes in Piperidinium Ionic Liquids: Measurements and LSER
Calculations, J. Phys. Chem. B 115 (2011) 8207-8215.
[39] M.N. Belgacem, G. Czeremuszkin, S. Sapieha, A. Gandini, Surface characterization of
cellulose fibres by XPS and inverse gas chromatography, Cellulose, 2 (1995) 145-157.
[40] J. Kolodziejek, A. Voelkel, K. Heberger, Characterization of hybrid materials by means
of inverse gas chromatography and chemometrics, J. Pharm. Sci. 102 (2013) 1524-1531.
[41] J.R. Conder, C.L. Young, Physicochemical Measurement by Gas Chromatography,
Wiley, New York, 1979.
[42] J. Schultz, L. Lavielle, C. Martin, The role of the interface in carbon fibre-epoxy
composites, J. Adhesion, 23 (1987) 45-60.
[43] C. Saint Flour, E. Papirer, Gas-solid chromatography: a quick method of estimating
surface free energy variations induced by the treatment of short glass fibers, J. Colloid
Interf. Sci. 91 (1983) 69-75.
[44] D.J. Brookman, D.T. Sawyer, Specific Interactions Affecting Gas Chromatographic
Retention for Modified Alumina Columns, Αnal. Chem. 40 (1968) 106-110.
24

ACCEPTED MANUSCRIPT
[45] V. Gutmann, The Donor-Acceptor Approach to Molecular Interactions, Plenum Press,
New York, 1978.
[46] D.P. Kamdem, S.K. Bose, P. Luner, Inverse Gas-Chromatography Characterization of
Birch Wood Meal, Langmuir, 9 (1993) 3039-3044.
[47] F.L. Riddle, F.M. Fowkes, Spectral Shifts in Acid-Base Chemistry .1. Vanderwaals
Contributions to Acceptor Numbers, J. Am. Chem. Soc. 112 (1990) 3259-3264.
[48] D. Cava, R. Gavara, J. Lagaron, A. Voelkel, Surface characterization of poly (lactic acid)
and polycaprolactone by inverse gas chromatography, J. Chromatogr. A 1148 (2007) 86-
91.
[49] T.E. Daubert, R.P. Danner, Physical and Thermodynamic Properties of Pure Chemicals:
Data Compilation, Hemisphere, New York, 2001.
[50] S.K. Papadopoulou, G. Dritsas, I. Karapanagiotis, I. Zuburtikudis, C. Panayiotou, Surface
characterization of poly (2, 2, 3, 3, 3-pentafluoropropyl methacrylate) by inverse gas
chromatography and contact angle measurements, Eur. Polym. J. 46 (2010) 202-208.
[51] J.M.R.C.A. Santos, J.T. Guthrie, Lewis acid/base character and crystallisation properties
of poly(butylene terephthalate), J. Chromatogr. A 1379 (2015) 92-99.
[52] K. Vasanth Kumar, F. Rocha, On the effect of a non-ionic surfactant on the surface of
sucrose crystals and on the crystal growth process by inverse gas chromatography, J.
Chromatogr. A 1216 (2009) 8528-8534.
[53] N. Papaiconomou, J. Estager, Y. Traore, P. Bauduin, C. Bas, S. Legeai, S. Viboud, M.
Draye, Synthesis, Physicochemical Properties, and Toxicity Data of New Hydrophobic
Ionic Liquids Containing Dimethylpyridinium and Trimethylpyridinium Cations†, J.
Chem. Eng. Data 55 (2010) 1971-1979.
[54] Z.Y. Al-Saigh, P. Munk, Study of polymer-polymer interaction coefficients in polymer
blends using inverse gas chromatography, Macromolecules, 17 (1984) 803-809.
[55] S.K. Papadopoulou, C. Panayiotou, Assessment of the thermodynamic properties of
poly(2,2,2-trifluoroethyl methacrylate) by inverse gas chromatography, J. Chromatogr. A
1324 (2014) 207-214.
[56] S.K. Papadopoulou, I. Karapanagiotis, I. Zuburtikudis, C. Panayiotou, Thermodynamic
characterization of poly(2,2,3,3,3-pentafluoropropyl methacrylate), J. Polym. Sci. Pol.
Phys. 48 (2010) 1826-1833.
[57] S. Ramanaiah, V. Karde, P. Venkateswarlu, C. Ghoroi, Effect of temperature on the
surface free energy and acid–base properties of Gabapentin and Pregabalin drugs − a
comparative study, RSC Adv. 5 (2015) 48712-48719.
25

ACCEPTED MANUSCRIPT
[58] A. Voelkel, K. Batko, K. Adamska, B. Strzemiecka, Determination of Hansen solubility
parameters by means of gas-solid inverse gas chromatography, Adsorpt. Sci. Technol. 26
(2008) 93-102.
[59] A. van Asten, N. van Veenendaal, S. Koster, Surface characterization of industrial fibers
with inverse gas chromatography, J. Chromatogr. A 888 (2000) 175-196.
[60] B. Shi, Y. Wang, L. Jia, Comparison of Dorris–Gray and Schultz methods for the
calculation of surface dispersive free energy by inverse gas chromatography, J.
Chromatogr. A 1218 (2011) 860-862.
[61] L.H.G.J. Segeren, M.E.L. Wouters, M. Bos, J.W.A. van den Berg, G.J. Vancso, Surface
energy characteristics of toner particles by automated inverse gas chromatography, J.
Chromatogr. A 969 (2002) 215-227.
[62] H. Ocak, S. Mutlu-Yanic, F. Cakar, B. Bilgin-Eran, D. Guzeller, F. Karaman, O.
Cankurtaran, A study of the thermodynamical interactions with solvents and surface
characterisation
of
liquid
crystalline
5-((S)-3,7-dimethyloctyloxy)-2-[[[4-
(dodecyloxy)phenyl]imino]-methyl]phenol by inverse gas chromatography, J. Mol. Liq.
223 (2016) 861-867.
[63] M.A. Mohammad, Chromatographic adhesion law to simplify surface energy calculation,
J. Chromatogr. A 1318 (2013) 270-275.
[64] L. Lapčík, M. Otyepka, E. Otyepková, B. Lapčíková, R. Gabriel, A. Gavenda, B.
Prudilová, Surface heterogeneity: Information from inverse gas chromatography and
application to model pharmaceutical substances, Curr. Opin. Colloid In. 24 (2016) 64-71.
[65] J.A.F. Gamelas, E. Ferraz, F. Rocha, An insight into the surface properties of calcined
kaolinitic clays: The grinding effect, Colloid. Surface. A 455 (2014) 49-57.
[66] C. Bilgiç, F. Tümsek, Determination of the acid/base properties of MgY and NH4Y
molecular sieves by inverse gas chromatography, J. Chromatogr. A 1162 (2007) 83-89.
[67] R. Osada, T. Hoshino, K. Okada, Y. Ohmasa, M. Yao, Surface tension of room
temperature ionic liquids measured by dynamic light scattering, J. Chem. Phys. 130
(2009) 184705.
[68] A. Bhattacharjee, P.J. Carvalho, J.A. Coutinho, The effect of the cation aromaticity upon
the thermophysical properties of piperidinium-and pyridinium-based ionic liquids, Fluid
Phase Equilib. 375 (2014) 80-88.
[69] M. Oliveira, M. Dominguez-Perez, O. Cabeza, J. Lopes-da-Silva, M. Freire, J. Coutinho,
Surface tensions of binary mixtures of ionic liquids with bis (trifluoromethylsulfonyl)
imide as the common anion, J. Chem. Thermodyn. 64 (2013) 22-27.
26

ACCEPTED MANUSCRIPT
[70] M.N. Belgacem, A. Gandini, in: E. Pefferkorn (Ed.), Interfacial Phenomena
in Chromatography, Marcel Dekker Inc., New York, 1999.
[71] A.B. Nastasović, A.E. Onjia, S.K. Milonjić, S.M. Jovanović, Surface characterization of
macroporous glycidyl methacrylate based copolymers by inverse gas chromatography,
Eur. Polym. J. 41 (2005) 1234-1242.
[72] J. Santos, K. Fagelman, J. Guthrie, Characterisation of the surface Lewis acid–base
properties of the components of pigmented, impact-modified, bisphenol A
polycarbonate–poly (butylene terephthalate) blends by inverse gas chromatography–
phase separation and phase preferences, J. Chromatogr. A 969 (2002) 119-132.
[73] J.M.R.C.A. Santos, J.T. Guthrie, Study of a core-shell type impact modifier by inverse gas
chromatography, J. Chromatogr. A 1070 (2005) 147-154.
[74] M.-L. Abel, M.M. Chehimi, F. Fricker, M. Delamar, A.M. Brown, J.F. Watts, Adsorption
of poly(methyl methacrylate) and poly(vinyl chloride) blends onto polypyrrole: Study by
X-ray photoelectron spectroscopy, time-of-flight static secondary ion mass spectroscopy,
and inverse gas chromatography, J. Chromatogr. A 969 (2002) 273-285.
27

ACCEPTED MANUSCRIPT
Highlights


1-butyl-1-ethyl piperidinium bromide, [C2C4PIP]Br is solid at room temperature
Surface characterization of [C2C4PIP]Br was performed with the IGC technique below its
melting point

The dispersive component of the surface energy calculated with the Schultz and the Dorris-Gray
methods


results of [C2C4PIP]Br are comparable with similar piperidinium based ionic liquids
The surface of [C2C4PIP]Br is amphoteric with a basic character bearing both weak Lewis acidic
and basic sites
28