Surface and foaming properties of an anionic CO2-switchable tail surfactant

Robin R. Benedix; Hailey Poole; Diana Zauser; Natalie Preisig; Philip G. Jessop; Cosima Stubenrauch

doi:10.1515/tsd-2023-2524

Publicly Available Published by De Gruyter June 6, 2023

Surface and foaming properties of an anionic CO₂-switchable tail surfactant

Robin R. Benedix
Robin R. Benedix studied Chemistry at Stuttgart University and completed his Master Thesis in 2022. He has been a PhD student in Physical Chemistry at Stuttgart University, Germany, since June 2023.
, Hailey Poole
Hailey Poole received her dual master’s degree in chemistry from Queen’s University and Stuttgart University in 2021. She worked as an organic chemist and operations manager at OzoneBio, Canada, from April to November 2022. She has been an environmental scientist at livestock water recycling, Canada, since November 2022.
, Diana Zauser
Diana Zauser was trained as a chemical laboratory technician at the Kerschensteiner School, Stuttgart, Germany. She successfully completed her training in 1990 and since then has been working at the Institute of Physical Chemistry at Stuttgart University, Germany.
, Natalie Preisig
Dr. Natalie Preisig studied Physics and received her Diploma in Physics at Omsk State University, Russia, in 1992. She worked as scientific officer at the Institute of Catalysis, Omsk, Russia from 1992 to 2002. She received her PhD in Physical Chemistry at Cologne University, Germany, in 2007. In 2008 she was a postdoctoral research fellow at University College Dublin, Ireland. Since 2009 she has been working as a senior researcher at Stuttgart University, Germany.
, Philip G. Jessop
Philip G. Jessop earned a PhD in Inorganic Chemistry at the University of British Columbia, Canada, in 1991. After that he was a postdoctoral fellow at the University of Toronto and then later worked as a contract researcher for Prof. Ryoji Noyori in Japan from 1993 to 1996. He then served as a faculty member at the University of California, Davis. Since 2003 he has been working at Queen’s University in Canada, helping to create two spin-off companies and GreenCentre Canada, a non-profit center for the commercialization of green chemistry technologies.
and Cosima Stubenrauch
Prof. Dr. Cosima Stubenrauch studied Chemistry and received her PhD in Physical Chemistry at the TU Berlin, Germany in 1997. After a one-year postdoctoral fellowship at the Université Paris Sud, she worked at Cologne University from 1999 to 2004, where she finished her Habilitation. From 2005 to 2009 she worked as a senior lecturer at University College Dublin, Ireland. Since 2009 she has been full professor at Stuttgart University, Germany. Furthermore, since 2014 she has been Dean of the Chemistry Faculty at Stuttgart University and since 2010 she has been docent at the KTH Royal Institute of Technology, Stockholm (Sweden).

From the journal Tenside Surfactants Detergents

https://doi.org/10.1515/tsd-2023-2524

Abstract

CO₂-switchable materials in general and CO₂-switchable surfactants in particular are of great interest in environmental research. There is a great potential to make processes more environmentally friendly by enhancing reusability and circularity and thus reducing material costs and energy consumption by replacing common non-switchable surfactants with their switchable counterparts. Inspired by this, the present work deals with the surface and foaming properties of aqueous solutions of the novel anionic CO₂-switchable tail surfactant sodium 4-(methyl(octyl)amino)butane-1-sulfonate. In the presence of N₂, the unprotonated surfactant is able to stabilize foams. By switching, i.e. by protonating the CO₂-responsive trialkyl amine group in the surfactants hydrocarbon chain, the amphiphilic nature of the surfactant is reduced which is indicated by an increase of the plateau surface tension and a higher CMC compared to the non-protonated surfactant. Furthermore, the ability of the protonated surfactant to stabilize foams is reduced.

Keywords: CO2-switchable materials; CO2-switchable tail surfactant; foam properties; surface tension; sustainability

1 Introduction

Switchable or stimuli-responsive materials have the ability to switch back and forth between two states, which reduces the consumption of energy and materials. For example, a switchable surfactant can be switched between a state in which it is an effective surfactant, stabilizing suspensions, emulsions and foams, and a state in which it is an ineffective surfactant, incapable of stabilizing such dispersions. In contrast, conventional surfactants continue to stabilize dispersions even when the dispersion is no longer wanted. For example, foam flotation, a method for separating desirable minerals from undesirable minerals in a crushed ore, requires a stable foam for the separation step but in the following step the foam is no longer wanted [1]. Unfortunately, the surfactants and other agents continue to stabilize the foam, so that additional chemicals such as defoamers and additional energy must be used to destroy the foam. If switchable surfactants are used, then switching the surfactant to its ineffective state should be sufficient to eliminate the foam, without any need for the addition of demulsifiers.

Literature examples of switchable surfactants can be categorized by the type of trigger that is used to induce the transition of the surfactant between the effective and ineffective forms [2, 3]. Light-responsive surfactants are known but unlikely to be suitable for most foam applications because it requires the foam to be transparent. Voltage-responsive surfactants require the foam to be electrically conductive, which may or may not be feasible. Acids, bases, oxidants, and reductants can be used as triggers but they accumulate in the solution, leading to contaminated aqueous waste streams and to steadily increasing contamination if the aqueous phase is to be reused for multiple cycles. Carbon dioxide as a trigger does not (i) accumulate in the system, (ii) contaminate the aqueous waste stream, (iii) require transparency or conductivity. CO₂ is also an abundant waste material, and its use as a trigger therefore is an example of waste recycling. CO₂-switchable surfactants are known in the literature [4]. We expect that the use of CO₂-switchable surfactants in foam flotation and other processes involving foams will reduce the energetic and materials consumption of the processes relative to the use of conventional surfactants.

We showed in our previous study that traditional defoamers can be replaced by CO₂-switchable additives [5]. Adding the CO₂-switchable additive N,N,N,N-tetramethyl-1,4-butanediamine (TMBDA) to a solution of the commercially available tetradecyl trimethyl ammonium bromide (C₁₄TAB), one can influence surface and foam properties by switching the additive. A more appealing way, however, to achieve control over foam stability is by avoiding defoamers and additives and by replacing non-switchable surfactants with CO₂-switchable surfactants. CO₂-switchable surfactants which allow switching foam stability have already been reported [2, 3, 6], [7], [8], [9], [10], [11]. However, the surfactants studied are nearly exclusive head-switchable compounds, i.e. they contain a nitrogen in the head group. Protonating this nitrogen, one generates a cationic surfactant. An overlooked kind of surfactant are CO₂-switchable tail surfactants which have a CO₂-responsive functional group in their hydrocarbon chain and were first reported by Xu et al. [12]. In that study switchable emulsion stability was investigated with the anionic surfactant 11-dimethylamino-undecyl sulfate sodium salt (DUSNa). In its unprotonated form, DUSNa is able to stabilize an emulsion. When CO₂ is added to the emulsion, even at only 1 bar, the CO₂-switchable tail surfactant is reversibly converted to its corresponding bicarbonate salt (Figure 1 [top]), which results in an oil/water phase separation [12]. Similar results were obtained using CO₂-switchable additives to influence non-switchable surfactants [13], [14], [15], [16]. There is also a report of cationic surfactants that are pH-switchable in the tail and might quite possibly be CO₂-switchable as well (e.g. 3-(dodecyl(methyl)amino)-N,N,N-trimethylpropan-1-aminium chloride, or [CH₃(CH₂)₁₁N(Me)CH₂CH₂CH₂NMe₃]Cl) [17].

Figure 1:

Molecular structure and switching scheme of (top) 11-dimethylamino-undecyl sulfate sodium salt (DUSNa) and (bottom) sodium 4-(methyl(octyl)amino)butane-1-sulfonate (C₈N(Me)C₄SO₃Na). By sparging CO₂ through an aqueous solution of the surfactant, the CO₂-responsive trialkyl amine group gets protonated and the unprotonated surfactant is converted into its bicarbonate salt.

Here we present a tail switchable surfactant with the switchable group not being at the end of the hydrophobic chain but in the middle. With surface tension and foam measurements, this study investigates for the first time the surface and foaming properties of surfactant solutions containing the novel CO₂-switchable tail surfactant sodium 4-(methyl(octyl)amino)butane-1-sulfonate (C₈N(Me)C₄SO₃Na) (Figure 1 [bottom]).

2 Experimental procedure

2.1 Synthesis of the CO₂-switchable tail surfactant

Under N₂, a solution of N-methyloctylamine (6.5 g, 0.045 mol, from BLDpharm, purity 97 %) in 20 mL ethyl acetate was added dropwise to a solution of 1,4-butane sultone (5 g, 0.041 mol, from BLDpharm, purity 98 %) in 15 mL ethyl acetate under stirring and at room temperature [18]. The reaction mixture was heated up to 90 °C and stirred for 44 h. After cooling down to room temperature, the reaction mixture was filtered and washed with diethyl ether. The solvent of the filtrate was evaporated under reduced pressure. A yellowish oil (3 g, yield 26 %) was obtained. NaOH (0.429 g, 0.011 mol) was added to a solution of the yellowish oil in methanol. The mixture was stirred overnight at room temperature and the methanol was evaporated under reduced pressure. The white solid was dried under vacuum to yield sodium 4-(methyl(octyl)amino)butane-1-sulfonate (2.88 g, yield 87 %).

¹H NMR (500 MHz, DMSO-d₆): 0.86 (t, 3H, CH₃), 1.25 (s, 10H, CH₂), 1.43–1.55 (m, 6H, CH₂), 2.14 (s, 3H, N–CH₃), 2.29 (t, 4H, N–CH₂), 2.42 (t, 2H, S–CH₂).

2.2 Surface tension measurements

The surface tension of the aqueous solutions was measured as a function of the surfactant concentration under either air or CO₂. For measurements under air, the Du Noüy ring method was used. The measurements were done with the Dynamic Contact Angle measuring device and force Tensiometer (DCAT) from DataPhysics. The surfactant solutions were pre-sparged with N₂ (Np: N₂ pre-sparged) for 20 min using a P2 frit (⌀_pore = 41–100 μm) before a measurement was started. This was done to remove dissolved CO₂ so that the TMBDA was as unprotonated as possible. The sample vessel was rinsed three times with double-distilled water and cleaned with 5 mL of the surfactant solution. After this, 15 mL of the surfactant solution was placed in the sample vessel. Before every measurement the Du Noüy ring was rinsed with double-distilled water and annealed three times. The measurement was stopped either if the stop condition was reached (standard deviation < 0.02 mN m⁻¹ with n = 30, i.e. the last 30 measurement points) or after 15 min at the latest.

For measurements under CO₂ the Profile Analysis Tensiometer (PAT-1) from SINTERFACE Technologies was used. The solutions were pre-sparged with CO₂ (Cp: CO₂ pre-sparged) for 20 min using a P2 frit (⌀_pore = 41–100 μm) before a measurement was started. This was done to lower the pH so that the TMBDA was as protonated as possible. Before the first measurement was started, the gas tubes of the PAT-1 were purged with CO₂ for 20 min. The cuvette was rinsed three times with double-distilled water and cleaned with 5 mL of the surfactant solution. After this, 15 mL of the surfactant solution was placed in the cuvette and the remaining air space above the solution was sparged with CO₂. The capillary was rinsed with double-distilled water and dried before being placed into the surfactant solution. CO₂ was then pushed through the steel capillary (⌀ = 2 mm) to create a buoyant bubble [19]. The bubble size was kept constant within one measurement and for each subsequent dilution. The measurements were stopped after the surface tension reached a plateau or after 15 min at the latest. All solutions were measured at (23 ± 1) °C.

2.3 Foam measurements

The foam measurements were carried out with the commercially available FoamScan from Teclis. With image analyses, the FoamScan was used to monitor foamability, foam stability, and foam bubble sizes. The foaming solutions contained 130 mM C₈N(Me)C₄SO₃Na in order to account for depletion and were pre-sparged with either N₂ (Np) or CO₂ (Cp) before the experiments were carried out [20]. The pre-sparged solution (60 mL) was inserted into the FoamScan and foamed through a porous disc (P2, ⌀_pore = 41–100 μm) with N₂ or CO₂ with a flow rate of Q = 84 mL min⁻¹ until a foam volume of V_foam = 120 mL was generated. The foam generation and the foam decay were monitored by a CCD camera. Every experiment was carried out three times. A two-dimensional image of the foam bubbles was projected through a glass prism and was recorded by another CCD camera at a height of 110 mm. The bubble pictures were first modified with the image editing program ImageJ to yield skeletonized images of the bubbles [21, 22]. The modified images then were evaluated with the cell size analysis (CSA) software in order to obtain information about the arithmetic mean radius 〈r〉 and the polydispersity index (or normalized standard deviation)

(1) P I = 〈 r 2 〉 − 〈 r 〉 2 〈 r 〉 ,

of the foam bubbles, where 〈r²〉 is the arithmetic mean of the squares of the bubble radii [21].

The liquid fraction of the foam was determined by conductivity measurements at a height of 85 mm.

3 Results and discussion

3.1 Surface properties

The surface properties of aqueous solutions of sodium 4-(methyl(octyl)amino)butane-1-sulfonate (C₈N(Me)C₄SO₃Na) were investigated to clarify how the switching of the surfactant affects the critical micelle concentration CMC, the plateau surface tension σ_CMC the maximum surface concentration Γ_max and the minimum head group area A_min. For this purpose, the surface tension was measured as a function of the surfactant concentration at (23 ± 1) °C under either air or CO₂. The surfactant solution was either pre-sparged with N₂ (Np: N₂ pre-sparged) or CO₂ (Cp: CO₂ pre-sparged), respectively. The σ(c)-curve of the Np solution under air and of the Cp solution under CO₂ can be seen in Figure 2. The CMC of the Np solution is 23 mM and was determined at the minimum of the σ(c)-curve. The maximum surface concentration was determined by fitting the σ-ln(c)-curve with a 2nd order polynomial and by applying the Gibbs adsorption isotherm for ionic surfactants [23]. It holds

(2) Γ = − 1 2 R T ( ∂ σ ∂ ln c ) p , T ,

where Γ is the surface concentration (Γ_max for c = c_CMC), R = 8.314 J mol⁻¹ K⁻¹ is the universal gas constant, T is the temperature, and (∂σ/∂ ln c)_p,T is the slope of the σ(ln c)-curve [23]. The maximum surface concentration was determined at the CMC (23 mM) and is 2.5 × 10⁻⁶ mol m⁻². For the minimum head group area, we obtained 67 Å² with

(3) A min = 1 Γ max · N A ,

where N_A = 6.022 × 10²³ mol⁻¹ is the Avogadro constant.

Figure 2:

Surface tension as a function of the surfactant concentration at (23 ± 1) °C of an aqueous C₈N(Me)C₄SONa solution. The solution was measured under air and CO₂ and was pre-sparged with N₂ (Np, green) and CO₂ (Cp, red), respectively. The σ(ln c)-curves below the CMC were fitted using 2nd order polynomials.

Comparing the σ(ln c)-curve of the Np solution with the σ(c)-curve of the Cp solution, one sees that the curve of the Np solution has a minimum while that of the Cp solution does not. That is believed to be a result of the fact that, regardless of the pH, the surfactant is always a mixture of the neutral and protonated forms. Based upon a pK_a of 10.7, typical for a protonated trialkyl amine, the % protonation of the surfactant amine group can be calculated using previously published equations [24]. The Np solution consists primarily of unprotonated surfactant but at the concentration at the minimum surface tension, 14 % of the surfactant molecules are protonated, causing the dip in the σ(c)-curve well-known for surfactant mixtures (see Figure 2 in Ref. [25]). On the other hand, the surfactant in the Cp solution is well over 99.9 % protonated, so even though a small amount of unprotonated surfactant is present, its concentration is insufficient to affect the shape of the surface tension curve. Note that one can calculate the CMC of the fully unprotonated surfactant if one knows the CMC of the fully protonated spezies, the CMC of the mixture and the composition of the mixture (see equation (13) in Ref. [25]). The calculated CMC is listed in Table 1.

Table 1:

The critical micelle concentration CMC, the plateau surface tension σ_CMC, the maximum surface concentration Γ_max and minimum head group area A_min of an aqueous C₈N(Me)C₄SO₃Na solution. The surface tensions were measured under air and CO₂, respectively. The solutions were pre-sparged with N₂ and CO₂, respectively. The values in the last column are calculated/estimated according to Clint et al. [25].

System	CMC (mM)	σ_CMC (mN m⁻¹)	Γ_max (10⁻⁶ mol m⁻²)	A_min (Å²)
C₈N(Me)C₄SO₃Na (Np under air), 86 % unprotonated	23	40	2.5	67
C₈N(Me)C₄SO₃Na (Cp under CO₂), fully protonated	62	43	1.9	88
C₈N(Me)C₄SO₃Na fully unprotonated	21	<35	n.a.	n.a.

By switching the surfactant, i.e. protonating the CO₂-responsive trialkyl amine group in the hydrocarbon chain, the CMC increases by 39 mM up to 62 mM (Table 1). The plateau surface tension also increases by 3 mN m⁻¹ up to 43 mN m⁻¹. Thus, the protonated surfactant is more hydrophilic and less surface active, i.e. the protonation reduces the amphiphilic nature of the surfactant. The protonation of the CO₂-responsive trialkyl amine group also leads to a decrease of the maximum surface concentration by 0.6 × 10⁻⁶ mol m⁻² down to 1.9 × 10⁻⁶ mol m⁻² and consequently to an increase of the minimum head group area by 21 Å² up to 88 Å², which is the result of an increasing electrostatic repulsion between the surfactant molecules.

3.2 Foam properties

The time evolution of the foam volume V_foam, the arithmetic mean radius 〈r〉, and the polydispersity index (or normalized standard deviation) PI of the foam bubbles were investigated for foams generated either with N₂ or CO₂. In Figure 3, the time evolution of the foam volume of foams generated with aqueous 130 mM C₈N(Me)C₄SO₃Na solutions is shown for (top) foaming with N₂ and (bottom) foaming with CO₂. Before foaming, the solutions were pre-sparged with either N₂ (Np) or CO₂ (Cp). We will first discuss foams generated with N₂ (Figure 2 [top]). Looking at the data one sees that it takes 75 s to generate 120 mL of foam with the Np solution, which is 20 s faster than with the Cp solution (Table 2) The liquid fraction directly after foam generation is similar for both foaming solutions (ε_Np = 11.8 % vs. ε_Cp = 12.8 %). More distinct, however, is the difference in the foam stabilities. The half-life t_1/2, i.e. the time during which the foam collapses to half of its volume, of foams generated with the Np solution is 1000 s which is more than three times longer than t_1/2 of foams generated with the Cp solution (t_{1/2, Cp} = 310 s). The difference in foam stability is explained by the reduced amphiphilic nature of the protonated surfactant, which is less capable of stabilizing foams.

Figure 3:

Time evolution of the foam volume V_foam for foams stabilized with an aqueous 130 mM C₈N(Me)C₄SO₃Na solution. The solution was either pre-sparged with N₂ (Np, green) or pre-sparged with CO₂ (Cp, red); (top) foamed with N₂ (Q = 84 mL min⁻¹); (bottom) foamed with CO₂ (Q = 84 mL min⁻¹).

Table 2:

Time evolution of the arithmetic mean radius 〈r〉 and polydispersity index PI (extracted from Figure 4) of the foam bubbles after generation as well as t₁₂₀ and the half-life t_1/2 of foams stabilized with an aqueous 130 mM C₈N(Me)C₄SO₃Na solution. The solutions were either pre-sparged with N₂ (Np, green) or CO₂ (Cp, red) before foaming with N₂.

System		t/s			t₁₂₀/s	t_1/2/s
System		0	100	200	t₁₂₀/s	t_1/2/s
C₈N(Me)C₄SO₃Na, Np, N₂	〈r〉 (mm)	0.28	0.27	0.28	75	1000
	PI	0.16	0.24	0.38
C₈N(Me)C₄SO₃Na, Cp, CO₂	〈r〉 (mm)	0.34	0.32	–	95	310
	PI	0.42	0.49	–

In Figure 3 (bottom) the time evolution of the foam volume of foams generated with CO₂ can be seen. Regardless of pre-sparging, no foam is generated over a period of 1200 s. This gives a glimpse into the kinetics of switching. Foaming the Np solution with CO₂, one rapidly converts the surfactant from its unprotonated form into its bicarbonate salt. Therefore, and because foams generated with CO₂ are in general less stable than foams generated with N₂ [8], there is no foam formation for either the Np or the Cp solution. However, the same rapid conversion happens also in the other direction because it is possible to generate foam with the Cp solution and N₂ in a time not much longer than for the Np solution (Figure 3 [top]). Due to the lack of foaming, no liquid fraction ε and no cell size pictures of the foam bubbles were recorded for the measurements with CO₂ as the foaming gas.

Let us conclude by looking at the mean bubble sizes and the PI of the bubbles of foams generated with N₂. The cell size analysis pictures of the foam bubbles generated with the Np solution is shown in Figure 4 together with the bubble size distributions at 0 s, 100 s, and 200 s after foam generation. The initial mean bubble size is 0.28 mm and does not change over a period of 200 s (Table 2). However, the PI increases from 0.16 to 0.38, indicating that coalescence is the main mechanism of decay in the first 200 s.

Figure 4:

Cell size analysis pictures and bubble size distributions n/n_total plotted versus the bubble radius r for foams stabilized with an aqueous 130 mM C₈N(Me)C₄SO₃Na solution foamed with N₂. Photos were taken 0 s, 100 s, and 200 s after foam generation stopped. (Top) the surfactant solution was pre-sparged with N₂ (Np, green). (Bottom) the surfactant solution was pre-sparged with CO₂ (Cp, red).

Due to the higher instability of the foam generated with the CO₂ pre-sparged (Cp) solution, the foam already starts to decompose at the camera height after 100 s and after 200 s only a few remnants of the foam are left to be seen (Figure 4 [bottom]). At 0 s the average bubble size of this foam is 0.34 mm. However, the PI is rather large with 0.42. Looking at the bubble size distribution n/n_total at 0 s (Figure 4 [bottom left]), one sees that nearly 90 % of the foam bubbles have a radius between 0.25 mm and 0.35 mm. Thus, the large PI is mainly due to the presence of three large bubbles.

4 Conclusions and outlook

The new anionic surfactant sodium 4-(methyl(octyl)amino)butane-1-sulfonate (C₈N(Me)C₄SO₃Na) is CO₂-switchable due to an amine group embedded in the hydrophobic tail. If an aqueous solution of this surfactant is saturated with CO₂, then the amine group becomes protonated and the CMC and plateau surface tension are significantly increased relative to those of the same surfactant in the absence of CO₂. The bicarbonate salt of the protonated surfactant contains a hydrophilic charged group in the middle of the hydrophobic tail and therefore has reduced amphiphilic character. The ability of this surfactant to stabilize a foam is greater if CO₂ is absent. If a solution of the surfactant has been pre-sparged with N₂ gas (Np: N₂ pre-sparged) and then foamed with N₂, the resulting foam has a half-life of 1000 s. In contrast, if a solution of the surfactant has been pre-sparged with CO₂ gas (Cp: CO₂ pre-sparged) and then foamed with N₂, a foam can still be generated but it is much less stable, because a substantial fraction of the surfactant is still protonated, thus having reduced amphiphilicity and being ineffective at stabilizing a foam. If the gas used to create the foam is CO₂, then a foam cannot be generated over a period of 1200 s regardless of the pre-sparging of the solution. Even if the solution was N₂ pre-sparged, a foam could not be generated with CO₂. That shows that the switching process is rapid; introduction of the CO₂ foaming gas protonates enough of the neutral surfactant in the first few seconds to reduce the neutral surfactant concentration below that necessary to stabilize a foam.

Future avenues of research suggested by this study are the development of other surfactants with CO₂-switchable tails, including surfactants containing cationic or nonionic head groups, or with the amine group placed at different positions along the length of the hydrophobic tail. In addition, use of these tail-switchable surfactants to applications that require temporary foams will be explored, with the hope that their reversible switchability will reduce energy and materials consumption and thereby reduce the economic and environmental costs of such processes.

Corresponding author: Cosima Stubenrauch, Institute of Physical Chemistry, University of Stuttgart, Stuttgart, Germany, E-mail: cosima.stubenrauch@ipc.uni-stuttgart.de

About the authors

Robin R. Benedix

Robin R. Benedix studied Chemistry at Stuttgart University and completed his Master Thesis in 2022. He has been a PhD student in Physical Chemistry at Stuttgart University, Germany, since June 2023.

Hailey Poole

Hailey Poole received her dual master’s degree in chemistry from Queen’s University and Stuttgart University in 2021. She worked as an organic chemist and operations manager at OzoneBio, Canada, from April to November 2022. She has been an environmental scientist at livestock water recycling, Canada, since November 2022.

Diana Zauser

Diana Zauser was trained as a chemical laboratory technician at the Kerschensteiner School, Stuttgart, Germany. She successfully completed her training in 1990 and since then has been working at the Institute of Physical Chemistry at Stuttgart University, Germany.

Natalie Preisig

Dr. Natalie Preisig studied Physics and received her Diploma in Physics at Omsk State University, Russia, in 1992. She worked as scientific officer at the Institute of Catalysis, Omsk, Russia from 1992 to 2002. She received her PhD in Physical Chemistry at Cologne University, Germany, in 2007. In 2008 she was a postdoctoral research fellow at University College Dublin, Ireland. Since 2009 she has been working as a senior researcher at Stuttgart University, Germany.

Philip G. Jessop

Philip G. Jessop earned a PhD in Inorganic Chemistry at the University of British Columbia, Canada, in 1991. After that he was a postdoctoral fellow at the University of Toronto and then later worked as a contract researcher for Prof. Ryoji Noyori in Japan from 1993 to 1996. He then served as a faculty member at the University of California, Davis. Since 2003 he has been working at Queen’s University in Canada, helping to create two spin-off companies and GreenCentre Canada, a non-profit center for the commercialization of green chemistry technologies.

Cosima Stubenrauch

Prof. Dr. Cosima Stubenrauch studied Chemistry and received her PhD in Physical Chemistry at the TU Berlin, Germany in 1997. After a one-year postdoctoral fellowship at the Université Paris Sud, she worked at Cologne University from 1999 to 2004, where she finished her Habilitation. From 2005 to 2009 she worked as a senior lecturer at University College Dublin, Ireland. Since 2009 she has been full professor at Stuttgart University, Germany. Furthermore, since 2014 she has been Dean of the Chemistry Faculty at Stuttgart University and since 2010 she has been docent at the KTH Royal Institute of Technology, Stockholm (Sweden).

Author contributions: Robin R. Benedix conceptualized the study, carried out all experiments, analyzed all data, and wrote the first draft of the manuscript. Hailey Poole conceptualized the study. Diana Zauser synthesized and purified the CO₂-switchable tail surfactant. Natalie Preisig reviewed and edited the manuscript. Philip G. Jessop conceptualized the study, reviewed, and edited the manuscript. Cosima Stubenrauch conceptualized the study, supervised the study, reviewed, and edited the manuscript. All authors contributed to and approved the final draft of the manuscript.
Research funding: This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
Conflict of interest statement: There are no conflicts to declare.

References

1. Cantat, I., Cohen-Addad, S., Elias, F., Graner, F., Höhler, R., Pitois, O., Rouyer, F., Saint-Jalmes, A. Foams: Structure and Dynamics; Oxford University Press, Incorporated: New York, 2013.Search in Google Scholar

2. Brown, P., Butts, C. P., Eastoe, J. Stimuli-responsive surfactants. Soft Matter 2013, 9, 2365–2374; https://doi.org/10.1039/C3SM27716J.Search in Google Scholar

3. Fameau, A. L., Fujii, S. Stimuli-responsive liquid foams: from design to applications. Curr. Opin. Colloid Interface Sci. 2020, 50, 101380; https://doi.org/10.1016/j.cocis.2020.08.005.Search in Google Scholar

4. Jessop, P. G., Cunningham, M. F. CO2-switchable Materials: Solvents, Surfactants, Solutes and Solids; Royal Society of Chemistry: Croydon, 2021.Search in Google Scholar

5. Benedix, R. R., Botsch, S., Preisig, N., Kovalchuk, V., Jessop, P. G., Stubenrauch, C. Influence of a CO2-switchable additive on the surface and foaming properties of a cationic non-switchable surfactant. Soft Matter 2023, 19, 2941–2948; https://doi.org/10.1039/D3SM00273J.Search in Google Scholar

6. Xu, W., Gu, H., Zhu, X., Zhong, Y., Jiang, L., Xu, M., Song, A., Hao, J. CO2-controllable foaming and emulsification properties of the stearic acid soap systems. Langmuir 2015, 31, 5758–5766; https://doi.org/10.1021/acs.langmuir.5b01295.Search in Google Scholar PubMed

7. Wang, Z., Ren, G., Yang, J., Xu, Z., Sun, D. CO2-responsive aqueous foams stabilized by pseudogemini surfactants. J. Colloid Interface Sci. 2019, 536, 381–388; https://doi.org/10.1016/j.jcis.2018.10.040.Search in Google Scholar PubMed

8. Poole, H., Jessop, P. G., Stubenrauch, C. Foaming and defoaming properties of CO2‐switchable surfactants. J. Surfactants Deterg. 2022, 25, 467–475; https://doi.org/10.1002/jsde.12597.Search in Google Scholar

9. Li, D., Ren, B., Zhang, L., Ezekiel, J., Ren, S., Feng, Y. CO2-sensitive foams for mobility control and channeling blocking in enhanced WAG process. Chem. Eng. Res. Des. 2015, 102, 234–243; https://doi.org/10.1016/j.cherd.2015.06.026.Search in Google Scholar

10. Jiang, J., Ma, Y., Cui, Z. Smart foams based on dual stimuli-responsive surfactant. Colloids Surf. A Physicochem. Eng. Asp. 2017, 513, 287–291; https://doi.org/10.1016/j.colsurfa.2016.10.056.Search in Google Scholar

11. Halios, C. H., Landeg-Cox, C., Lowther, S. D., Middleton, A., Marczylo, T., Dimitroulopoulou, S. Chemicals in European residences – Part I: a review of emissions, concentrations and health effects of volatile organic compounds (VOCs). Sci. Total Environ. 2022, 839, 156201; https://doi.org/10.1016/j.scitotenv.2022.156201.Search in Google Scholar PubMed

12. Xu, Y., Zhang, Y., Liu, X., Chen, H., Fang, Y. Retrieving oil and recycling surfactant in surfactant-enhanced soil washing. ACS Sustainable Chem. Eng. 2018, 6, 4981–4986; https://doi.org/10.1021/acssuschemeng.7b04614.Search in Google Scholar

13. Su, X., Robert, T., Mercer, S. M., Humphries, C., Cunningham, M. F., Jessop, P. G. A conventional surfactant becomes CO2-responsive in the presence of switchable water additives. Chem. Eur. J. 2013, 19, 5595–5601; https://doi.org/10.1002/chem.201203419.Search in Google Scholar PubMed

14. Lu, H., Guan, X., Wang, B., Huang, Z. CO2-switchable oil/water emulsion for pipeline transport of heavy oil. J. Surfactants Deterg. 2015, 18, 773–782; https://doi.org/10.1007/s11743-015-1712-8.Search in Google Scholar

15. Lu, H., Liu, D., Wang, B., Qing, D., Huang, Z. CO2-switchable nanoemulsion based on N,N-dimethyl oleoaminde-propylamine (DOAPA) and sodium dodecyl sulphate (SDS). J. Dispersion Sci. Technol. 2016, 37, 1819–1825; https://doi.org/10.1080/01932691.2016.1141361.Search in Google Scholar

16. Fan, Y., Zhang, Y., Liu, X., Zhong, K., Ge, Z. Recovery and recycling of CO2/N2-switchable anionic surfactants in emulsions. J. Surfactants Deterg. 2017, 20, 1301–1309; https://doi.org/10.1007/s11743-017-2022-0.Search in Google Scholar

17. Oh, H., Wos, J. A., Gardner, R. R., Bates, T. Cleaning compositions comprising pH-switchable amine surfactants. U. S. Patent 8,877,696 B2, 2014.Search in Google Scholar

18. Ward, R. S., Davies, J., Hodges, G., Roberts, D. W. Synthesis of quaternary alkylammonium sulfobetaines. Synthesis 2002, 16, 2431–2439; https://doi.org/10.1055/s-2002-35215.Search in Google Scholar

19. Javadi, A., Mucic, N., Karbaschi, M., Won, J. Y., Fainerman, V. B., Sharipova, A., Aksenenko, E. V., Kovalchuk, V. I., Kovalchuk, N. M., Makievski, A. V., Krägel, J., Miller, R. Interfacial dynamics methods. In Encyclopedia of Colloid and Interface Science: With 81 Tables; Tadros, T. F., Ed.; Springer reference: Springer: Berlin, Heidelberg, 2013; pp. 637–676.10.1007/978-3-642-20665-8_171Search in Google Scholar

20. Boos, J., Drenckhan, W., Stubenrauch, C. On how surfactant depletion during foam generation influences foam properties. Langmuir 2012, 28, 9303–9310; https://doi.org/10.1021/la301140z.Search in Google Scholar PubMed

21. Boos, J., Drenckhan, W., Stubenrauch, C. Protocol for studying aqueous foams stabilized by surfactant mixtures. J. Surfactants Deterg. 2013, 16, 1–12; https://doi.org/10.1007/s11743-012-1416-2.Search in Google Scholar

22. Schneider, C. A., Rasband, W. S., Eliceiri, K. W. NIH Image to ImageJ: 25 years of image analysis. Nat. Methods 2012, 9, 671–675; https://doi.org/10.1038/nmeth.2089.Search in Google Scholar PubMed PubMed Central

23. Martínez-Balbuena, L., Arteaga-Jiménez, A., Hernández-Zapata, E., Márquez-Beltrán, C. Applicability of the Gibbs adsorption isotherm to the analysis of experimental surface-tension data for ionic and nonionic surfactants. Adv. Colloid Interface Sci. 2017, 247, 178–184; https://doi.org/10.1016/j.cis.2017.07.018.Search in Google Scholar PubMed

24. Alshamrani, A. K., Vanderveen, J., Jessop, P. G. A guide to the selection of switchable functional groups for CO2-switchable compounds. Phys. Chem. Chem. Phys. 2016, 16, 19276–19288; https://doi.org/10.1039/C6CP03302D.Search in Google Scholar

25. Clint, J. H. Micellization of mixed nonionic surface active agents. J. Chem. Soc., Faraday Trans. 1 1975, 71, 1327; https://doi.org/10.1039/f19757101327.Search in Google Scholar

Received: 2023-04-25

Accepted: 2023-05-04

Published Online: 2023-06-06

Published in Print: 2023-07-26

Surface and foaming properties of an anionic CO₂-switchable tail surfactant

Abstract

1 Introduction

2 Experimental procedure