Dynamic Surface Tension of Heterogemini Surfactants with Quaternary Ammonium Salt and Gluconamide or Sulfobetaine Headgroups

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1 Journal of Oleo Science Copyright 17 by Japan Oil Chemists Society doi : 1.56/jos.ess11 J. Oleo Sci. 66, (1) (17) Dynamic Surface Tension of Heterogemini Surfactants with Quaternary Ammonium Salt and Gluconamide or Sulfobetaine Headgroups Tomokazu Yoshimura 1* and Kanae Nyuta 1 Department of Chemistry, Faculty of Science, Nara Women s University, Kitauoyanishi-machi, Nara 6-86, JAPAN Department of Applied Chemistry, Faculty of Science, Tokyo University of Science, 1-3 Kagurazaka, Shinjuku-ku, Tokyo 16-81, JAPAN Abstract: Dynamic surface tensions of two types of heterogemini surfactants with nonidentical hydrophilic headgroups consisting of a quaternary ammonium salt (cationic) and a gluconamide (nonionic) or sulfobetaine (zwitterionic) group were measured using the maximum bubble pressure method. For these compounds, effects of alkyl chain length, structure of the hydrophilic groups, and surfactant concentration were investigated using diffusion coefficients and parameter x. The parameter x is related to the difference between the energies of adsorption and desorption of the surfactant. The values of x of heterogemini surfactants increased as the alkyl chain length increased, and they were slightly larger than that for the corresponding monomeric surfactant. This is because of an increase in hydrophobicity caused by two alkyl chains, as well as interactions between two different hydrophilic groups. Adsorption rate of the heterogemini surfactants decreased with increasing alkyl chain length, indicating slow dynamics, and inhibited adsorption to the air/water interface as the chain length increased. However, at higher concentrations, the heterogemini surfactants showed rapid and effective adsorption and increased adsorption rates at higher concentrations. Diffusion coefficients of the heterogemini surfactants decreased with increasing concentrations for all chain lengths, indicating diffusion of the solute molecules to the subsurface and adsorption of the solute from the subsurface to the surface. Key words: gemini surfactant, nonidentical hydrophilic groups, dynamic surface tension, adsorption dynamics, interface 1 INTRODUCTION Previously, in an attempt to improve the properties and suggest functionalities of gemini surfactants with two identical hydrophobic chains and two identical hydrophilic groups, novel heterogemini surfactants with nonidentical hydrophilic headgroups were designed and synthesized and their physicochemical properties and aggregation behavior in solution were investigated 1,. Heterogemini surfactants can be considered equimolar mixtures of two monomeric surfactants because they are asymmetric compounds containing different combinations of hydrophilic headgroups, such as anionic cationic, anionic nonionic, or cationic nonionic. It is well known that when two types of surfactant are mixed cationic cationic 3, anionic cationic 4 1, or ionic nonionic 11, they spontaneously form vesicles. Therefore, heterogemini surfactants can form vesicles in solution, because they possess two different hydrophilic headgroups in one molecule. We have pre- viously reported the synthesis and physicochemical properties of heterogemini surfactants with nonidentical headgroups, such as a cationic anionic one containing ammonium and carboxylate headgroups 1, 13, a cationic nonionic one containing ammonium and gluconamide headgroups 14, and a cationic zwitterionic one containing ammonium and sulfobetaine headgroups 15. These heterogemini surfactants showed low critical micelle concentrations CMCs and high efficiency in lowering the surface tension of water. It was also shown that the morphology of aggregates formed by cationic anionic- and cationic nonionic-type heterogemini surfactants in aqueous solution are significantly influenced by their alkyl chain length n 8 14 and surfactant concentration. Further, we investigated the interfacial dynamics of cationic anionic heterogemini surfactants using dynamic surface tension by the maximum bubble pressure method, and discussed diffusion of the surfactant molecules to the subsurface and adsorp- * Correspondence to: Tomokazu Yoshimura, Department of Chemistry, Faculty of Science, Nara Women s University, Kitauoyanishimachi, Nara 6-86, JAPAN yoshimura@cc.nara-wu.ac.jp Accepted May 4, 17 (received for review January 9, 17) Journal of Oleo Science ISSN print / ISSN online

2 T. Yoshimura and K. Nyuta tion of the surfactant from the subsurface to the air/water interface. However, details of the interfacial dynamics for all the varieties of heterogemini surfactants are not fully understood. Therefore, it is necessary to investigate the dynamic surface tensions of novel heterogemini surfactants with cationic nonionic- and cationic zwitterionic-type structures. Information about surfactant properties including interfacial dynamics is needed for many fields of engineering, such as in high-speed wetting of textiles, paper, and other substrates or in foaming. In this study, the dynamic surface tensions of two kinds of heterogemini surfactants consisting of a quaternary ammonium salt and a gluconamide or sulfobetaine headgroup were examined by changing the alkyl chain length and surfactant concentration, using parameters such as the diffusion coefficient and rate of fall of surface tension. EXPERIMENTAL.1 Materials Heterogemini surfactants C n AmGlu and C n AmSb used in this study consisted of two alkyl chains and nonidentical headgroups, namely, quaternary ammonium salt and a gluconamide or a sulfobetaine. Figure 1 shows the chemical structures of C n AmGlu and C n AmSb. Details of the synthetic procedures for C n AmGlu and C n AmSb have been described in our previous manuscripts 14, 15. The CMC of C n AmGlu in an aqueous solution is 1.89,.4, and.113 mmol dm 3 for n 8, 1, and 1, respectively. The CMC of C n AmSb in the presence of mmol dm 3 NaCl is 15., 1.5, and.1 mmol dm 3 for n 8, 1, and 1, respectively. The surfactant solutions for the dynamic surface tension measurements of C n AmGlu and C n AmSb were prepared using Milli-Q Plus water resistivity 18. MΩ cm.. Dynamic surface tension The dynamic surface tension was measured using a CnHn+1 N + CHCH N H3C CH3 C=O Br - HO OH Fig. 1 HO C n A mglu CnHn+1 OH OH H3C CnHn+1 N + CH3 Br(CH)3SO3 - CHCH N + C namsb CnHn+1 (CH)3 SO3 - CH3 Chemical structures of heterogemini surfactants: a quaternary ammonium salt a gluconamide type C n AmGlu n 8, 1, 1, a quaternary ammonium salt a sulfobetaine type C n AmSb n 8, 1, 1. Krüss bubble pressure tensiometer BP, by a technique that involves measuring the maximum pressure necessary to blow a bubble into a liquid from the tip of a capillary. In a bubble pressure tensiometer, gas bubbles are formed with an exactly defined rate in various liquids. They enter the liquid through a capillary made of silanized glass with a known geometry. The instrument measures the maximum pressure occurring during the bubble formation process, which is directly proportional to the surface tension. The surface tension γ for heterogemini surfactants is calculated using the Young-Laplace equation: γ P max P r 1 where γ is the surface tension at the gas-liquid interface, P max is the maximum bubble pressure, P is the hydrostatic pressure in the capillary ρ gh; ρ is the density of the liquid, g is the acceleration of gravity, and h is the immersion depth of the capillary, and r is the inner radius of the capillary. The measurements were conducted with effective surface ages of 5 ms to s at 5. In many interfacial processes, such as high-speed wetting or foaming, equilibrium conditions of adsorption at the air/water interface are not attained and dynamic processes play a major role. Therefore, dynamic surface tension measurements can gauge surfactant performance. Rosen et al. 16, 17 divided a typical plot of the change in surface tension with time into four regions: an induction region I, a rapid fall region II, a meso-equilibrium region III, and an equilibrium region IV. Eq. fits the three dynamic regions I III of this plot: γ t γ m γ γ m t 1 t x where γ t is the surface tension of the surfactant solution at time t, γ m is the meso-equilibrium surface tension where γ t shows only a small change with time, γ is the surface tension of the pure solvent, and x is a constant related to the molecular structure of the surfactant. Eq. can be converted to its logarithmic form : its logarithmic form 18 : log γ γ t γ t γ m xlogt xlogt 3 This equation provides a convenient method for evaluating the constants x and t, by plotting log γ γ t / γ t γ m versus log t. The value of t is the time required for γ t to reach a value halfway between γ and γ m, and is related to the surfactant concentration. The midpoint between γ and γ m is when the ratio equals 1 and the following can be obtained using eq. 3, t 1/ t 4 R 1/ m γ γ m t 1/ t 5 where R 1/ is the rate of fall of surface tension at t 1/. A de- 11 J. Oleo Sci. 66, (1) (17)

3 Dynamic Surface Tension of Heterogemini Surfactants crease in surface tension can be described according to the Ward and Tordai model as a diffusion-controlled adsorption process to a clean surface without convection. This process can be analyzed quantitatively using the following integral equation t 4D 1 (t)= Γ ( C t π )( + C(τ)a s t-τ ) 6 where t is time, Γ t is the surface concentration, D is the monomer diffusion coefficient, C is the bulk concentration, C t is s the concentration at the subsurface, and τ is a dummy time-delay variable. In an attempt to bypass the need for complicated numerical solutions when analyzing experimental data, asymptotic equations for both shortand long-time adsorption behavior have been derived, 1. Short-time behavior is described by considering only the first term of Eq. 6 : γ γ C RT Dt π 1 7 where γ is the surface tension of solvent. The equation for long-time behavior has been derived by Hansen and Joos, 3 : γ t γ e RTΓ C π 4Dt 1 8 where γ e is the equilibrium surface tension at infinite time and Γ is the excess surface concentration, which can be obtained from equilibrium surface tension. The long-time approximation solution of Eq. 8 should only be used to predict the adsorption mechanism. 3 RESULTS AND DISCUSSION Figures and 3 show the effect of concentration on the dynamic surface tension with log t for C n AmGlu with n 8, 1, and 1 in an aqueous solution, and C n AmSb with n 8, 1, and 1 in the presence of mmol dm 3 NaCl. The surface tensions for the surfactants decreased with increasing log t. The adsorption rates of C n AmGlu and C n AmSb were slower with increasing alkyl chain length and the surface tension of those with n 1 did not decrease at concentrations below the CMC. This indicates that dynamics of the heterogemini surfactants are very slow, and adsorption to the air/water interface becomes inhibited as the chain length increases, probably due to the steric hindrance caused by long alkyl chains connected by short spacer chains. Using Eq. 3, plots of log γ γ t / γ t γ m versus log t for C n AmGlu were obtained Fig. 4, with solid lines representing the least-squares fit. The fit parameters of t, x, and R 1/ are given by Eq. 3, 4 and Surface Surface tension tention /mn /mn m m Surface Surface tension tention /mn /mn m m Surface tension tention /mn /mn m Fig. Dynamic surface tension with the surface age for a C 8 AmGlu:,.6 mmol dm 3 ;, 1.3 mmol dm 3 ;,.58 mmol dm 3 ;, 5.16 mmol dm 3 ;, 1.3 mmol dm 3 ;,.6 mmol dm 3, b C 1 AmGlu.,.851 mmol dm 3 ;,.1 mmol dm 3 ;,.851 mmol dm 3 ;, 1. mmol dm 3 ;, 4.6 mmol dm 3 ;, 8.51 mmol dm 3 ;, 18.4 mmol dm 3, c C 1 AmGlu.,.173 mmol dm 3 ;,.867 mmol dm 3 ;,.173 mmol dm 3 ;,.433 mmol dm 3 ;,.867 mmol dm 3 ;, 1.73 mmol dm 3. J. Oleo Sci. 66, (1) (17) 1141

4 T. Yoshimura and K. Nyuta [ [ Fig. 3 Dynamic surface tension with the surface age for a C 8 AmSb:,.8 mmol dm 3 ;, 1. mmol dm 3 ;,.43 mmol dm 3 ;, 6.8 mmol dm 3 ;, 1. mmol dm 3 ;, 4.3 mmol dm 3, b C 1 AmSb.,.116 mmol dm 3 ;,.3 mmol dm 3 ;,.579 mmol dm 3 ;, 1.16 mmol dm 3 ;,.15 mmol dm 3, c C 1 AmSb.,.51 mmol dm 3 ;,.1 mmol dm 3 ;,.187 mmol dm 3 ;,.389 mmol dm 3 ;,.486 mmol dm ) ) / t - m ] γ γ γ γ L og [ - t ( L og γ - γ t ) / ( γ t - γ m ) ] Log t Log t ) L og γ - γ t ) / ( γ t - γ m ] 1-1 Fig Log t Relationship between the log γ γ t / γ t γ m and the log t for a C 8 AmGlu, b C 1 AmGlu, c C 1 AmGlu. Symbols are the same as those in Fig J. Oleo Sci. 66, (1) (17)

5 Dynamic Surface Tension of Heterogemini Surfactants 5. For C n AmGlu and C n AmSb with n 8, 1, and 1, the relationships between log C and parameters such as t, x, and R 1/ are shown in Figs. 5 and 6. For all chain lengths, the plots show a linear decrease in log t and x, and a linear increase in log R 1/ with increasing concentration. This is characteristic of a rapid and effective adsorption process, indicating as expected an increased rate of adsorption at higher concentrations 18. It is noteworthy that there was no change in the linearity of these relationships when the surfactant concentration in the bulk phase exceeded the CMC, log CMC.7, 3.65, and 4.95 for C n AmGlu with n 8, 1, and 1, respectively, and log CMC 1.8,.9, and 4.77 for C n AmSb with n 8, 1, and 1, respectively. The constant x Eq. and 3 is related to the difference between the energies of adsorption and desorption of the surfactant 18. It is known that the value of x increases with increasing hydrophobicity of the surfactant. The value of x for C n AmGlu and C n AmSb also increases as the alkyl chain length increases Figs. 5 and 6. However, large variations in x were not observed for C n AmGlu or C n AmSb. The value of x for monomeric surfactants of N-alkyl-N-benzyl-N-methylglycine with alkyl chain length 1 and 14 is reported to be 1.4 and 1.5, respectively 18. The values of x for C 1 AmGlu and C 1 AmSb at low concentrations are slightly larger than that for this monomeric surfactant with the same alkyl chain length, probably due to an increase in hydrophobicity caused by two alkyl chains, as well as interactions between two different hydrophilic groups ammonium and gluconamide or sulfate. Another way of analyzing adsorption dynamics is the diffusion controlled adsorption model. For C n AmGlu and C n AmSb with n 8, 1, and 1 at different concentrations, plots of dynamic surface tension versus t 1/ were constructed Figs. 7 and 8. These plots show a linear relationship over longer time scales low t 1/. From the gradients of the plots, values for D can be derived, and are shown in Tables 1 C n AmGlu and C n AmSb. In Figs. 7 and 8, the lines represent the fit of least squares for t 6, with the observed intercepts approximately equal to the equilibrium surface tensions obtained by the Wilhelmy method. However, for C n AmSb with n 1, this relationship was not observed. This indicates that the time taken to reach an equilibrium surface tension increases as the length of the alkyl chain increases. The diffusion coefficients of C n AmGlu and C n AmSb decreased with increasing concentration for all chain lengths, indicating that the adsorption rate at the air/water interface was reduced due to the formation of micelles in the solution. In addition, the values of the diffusion coefficients were smaller than expected. The D values of conventional monomeric surfactants were in the order of 1 1 m s 1, compared with m s 1 for C n AmGlu and C n AmSb. This indicates that for gemini surfactants, the diffusion of the solute molecules to the subsurface, adsorption of the solute from the subsurface to the surface 4, and the kinetics of adsorption at the air/water are slow due to their bulky structure. Miller has proposed a kinetic model for adsorption that takes into.5. Log t* - -4 x n Log R 1/ Fig. 5 Plots of a t, b x, c R 1/ against the logarithm of concentration, C for C n AmGlu:, n 8;, n 1;, n 1. J. Oleo Sci. 66, (1) (17) 1143

6 T. Yoshimura and K. Nyuta Log t* -4 x n R 1/ Fig. 6 Plots of a t, b x, c R 1/ against the logarithm of concentration, C for C n AmSb:, n 8;, n 1;, n 1. Surface tension tention /mn m 1 8 Surface tension tention /mn m t -1/ /s -1/ t -1/ /s -1/ 8 Surface Surface tension tention /mn /mn m m 1-1 Fig t -1/ /s -1/ Dynamic surface tension plotted against t 1/ for a C 8 AmGlu, b C 1 AmGlu, c C 1 AmGlu. Symbols are the same as those in Fig.. account the formation and dissociation of micelles 5. Further, the short-time coefficient for C n AmSb could not be obtained because the short-time scale measured was too short. The slow kinetics of adsorption observed for fluorinated gemini surfactants have also been observed previously for some hydrocarbon gemini surfactants 1, 4, J. Oleo Sci. 66, (1) (17)

7 Dynamic Surface Tension of Heterogemini Surfactants t -1/ /s -1/ t -1/ /s -1/ Fig t -1/ /s -1/ Dynamic surface tension plotted against t 1/ for a C 8 AmSb, b C 1 AmSb, c C 1 AmSb. Symbols are the same as those in Fig. 3. Table 1 Diffusion coefficient at long time of C n AmGlu calculated from dynamic surface tension. C 8 AmGlu C 1 AmGlu C 1 AmGlu Concentration Gradient D Concentration Gradient D Concentration Gradient D (mmol dm -3 ) (mn m -1 s -1/ ) ( m s -1 ) (mmol dm / ) (mn m s ) ( m s -1 ) (mmol dm -3 ) (mn m -1 s -1/ ) ( m s -1 ) CONCLUSION In this study, the dynamic surface tensions for two types of heterogemini surfactants with two different hydrophilic groups consisting of an ammonium headgroup and a sugar gluconamide headgroup cationic-nonionic type or sulfobetaine cationic-zwitterionic type Fig. 1 were investigated using the maximum bubble pressure method. The effects of alkyl chain length, surfactant concentration, and structure of the hydrophilic groups were also observed. The parameter x, which is related to the difference between the energies of adsorption and desorption of the surfactant, can be obtained from the changes in dynamic surface tension with increasing alkyl chain length from 8, to 1, to 1. For an alkyl chain length of 1, the parameter x of the heterogemini surfactants was larger than that for a zwitterionic monomeric surfactant. This indicates that as the hydrophobic interaction between the two alkyl chains increases, electrostatic interactions between two the different hydrophilic groups also increase. The diffusion coefficient of the monomer for the heterogemini surfactants was significantly lower than that for conventional monomeric surfactants, indicating slow diffusion due to a large J. Oleo Sci. 66, (1) (17) 1145

8 T. Yoshimura and K. Nyuta Table Diffusion coefficient at long time of C n AmSb calculated from dynamic surface tension. C 8 AmSb C 1 A msb C 1 AmSb Concentration Gradient D Concentration Gradient D Concentration Gradient D (mmol dm -3 ) (mn m -1 s -1/ ) ( m s -1 ) (mmol dm -3 ) (mn m -1 s -1/ ) ( m s -1 ) (mmol dm -3-1 ) (mn m s -1/ ) ( m s -1 ) molecular size. It was found that the adsorption rate decreases with increasing alkyl chain length and surfactant concentration. Large differences in the dynamic behavior of the heterogemini surfactants due to variation of the hydrophilic headgroups gluconamide and sulfobetaine were not observed. ACKNOWLEDGMENT We thank the late Prof. Kunio Esumi for his many useful suggestions in conducting this research. References 1 Alami, E.; Holmberg, K. Heterogemini surfactants. Adv. Colloid Interface Sci. 1-1, Menger, F.M.; Peresypkin, A.V. A Combinatorially-derived structural phase diagram for 4 zwitterionic geminis. J. Am. Chem. Soc. 13, Viseu, M.I.; Edwards, K.; Campos, C.S.; Costa, S.M.B. Spontaneous vesicles formed in aqueous mixtures of two cationic amphiphiles. Langmuir 16, Salkar, R.A.; Mukesh, D.; Samant, S.D.; Manohar, C. Mechanism of micelle to vesicle transition in cationic anionic surfactant mixtures. Langmuir 14, Herrington, K.L.; Kaler, E.W.; Miller, D.D.; Zasadzinski, J.A.; Chiruvolu, S. Phase behavior of aqueous mixtures of dodecyltrimethylammonium bromide DTAB and sodium dodecyl sulfate SDS. J. Phys. Chem. 97, Bergström, M.; Pedersen, J.S.; Schurtenberger, P.; Egelhaaf, S.U. Small-angle neutron scattering SANS study of vesicles and lamellar sheets formed from mixtures of an anionic and a cationic surfactant. J. Phys Chem. B 13, Kaler, E.W.; Herrington, K.L.; Murthy, A.K.; Zasadzinski, J.A.N. Phase behavior and structures of mixtures of anionic and cationic surfactants. J. Phys. Chem. 96, Marques, E.F.; Regev, O.; Khan, A.; Graca Miguel, M.Da; Lindman, B. Vesicle formation and general phase behavior in the catanionic mixture SDS DDAB water. The anionic-rich side. J. Phys. Chem. B 1, McKelvey, C.A.; Kaler, E.W.; Zasadzinski, J.A.; Coldren, B.; Jung, H.-T. Templating hollow polymeric spheres from catanionic equilibrium vesicles: Synthesis and characterization. Langmuir 16, Yuet, P.K.; Blankschtein, D. Effect of surfactant taillength asymmetry on the formation of mixed surfactant vesicles. Langmuir 1, Edwards, K.; Almgren, M. Surfactant-induced leakage and structural change of lecithin vesicles: effect of surfactant headgroup size. Langmuir 8, Yoshimura, T.; Nyuta, K.; Esumi, K. Zwitterionic heterogemini surfactants containing ammonium and carboxylate headgroups. 1. Adsorption and micellization. Langmuir 1, Nyuta, K.; Yoshimura, T.; Tsuchiya, K.; Sakai, H.; Abe, M.; Iwase, H. Zwitterionic heterogemini surfactants containing ammonium and carboxylate headgroups : Aggregation behavior studied by SANS, DLS, and cryo- TEM. J. Colloid Interface Sci. 3, Nyuta, K.; Yoshimura, T.; Tsuchiya, K.; Ohkubo, T.; Sakai, H.; Abe, M.; Esumi, K. Adsorption and aggregation properties of heterogemini surfactants containing a quaternary ammonium salt and a sugar moiety. Langmuir, Nyuta, K.; Yoshimura, T.; Esumi, K. Surface tension and micellization properties of heterogemini surfactants containing quaternary ammonium salt and sulfobetaine moiety. J. Colloid Interface Sci. 1, J. Oleo Sci. 66, (1) (17)

9 Dynamic Surface Tension of Heterogemini Surfactants 16 Rosen, M.J.; Kunjappu, J.T. Surfactants and Interfacial Phenomena. 4th ed. John Wiley and Sons, Inc., Hoboken, NJ, Hua, X.Y.; Rosen, M.J. Dynamic surface tension of aqueous surfactant solutions: I Basic parameters. J. Colloid Interface Sci. 14, Gao, T.; Rosen, M.J. Dynamic surface tension of aqueous surfactant solutions: 7. Physical significance of dynamic parameters and the induction period. J. Colloid Interface Sci. 17, Ward, A.F.H.; Tordai, L. Time dependence of boundary tensions of solutions I. The role of diffusion in time effects. J. Chem. Phys. 14, Fainerman, V.B.; Makievski, A.V.; Miller, R. The analysis of dynamic surface tension of sodium alkyl sulphate solutions, based on asymptotic equations of adsorption kinetic theory. Colloids Surfaces A 87, Eastoe, J.; Dalton, J.S. Dynamic surface tension and adsorption mechanisms of surfactants at the air water interface. Adv. Colloid Interface Sci. 85, Hansen, R.S. The Theory of diffusion controlled absorption kinetics with accpmpanying evaporation. J. Phys. Chem. 64, Rillaerts, E.; Joos, P. Rate of demicellization from the dynamic surface tensions of micellar solutions. J. Phys. Chem. 86, Kumar, A.; Alami, E.; Holmberg, K.; Seredyuk, V.; Menger, F.M. Branched zwitterionic gemini surfactants micellization and interaction with ionic surfactants. Colloids Surfaces A 8, Miller, R. Adsorption kinetics of surfactants from micellar solutions. Colloid Polym. Sci. 59, Yoshimura, T.; Ohno, A.; Esumi, K. Equilibrium and dynamic surface tension properties of partially fluorinated quaternary ammonium salt gemini surfactants. Langmuir, J. Oleo Sci. 66, (1) (17) 1147