Paper Menu >>
Journal Menu >>
Advances in Ma terials Physics and Che mist ry, 2012, 2, 177-180 doi:10.4236/ampc.2012.24B046 Published Online December 2012 (htt p://www.SciRP.org/journal/ampc) Copyright © 2012 SciRes. AMPC Investigation of the Surface Properties of Vinyl Ethers – Sodi um 2-Acrylamido-2-Methylpropanesulfonate Copolymers S. Kh. Khussa i n, E. M. Shaikhutdinov, N . Zh. Seit kaliyeva, A. Zh. Zhenisova Department of app l ied ch emis try, Kazakh National Technical University named after Kanysh Satpaev, Almaty, Kazakhstan Email: sarah_khussain@mail.ru Received 2012 ABSTRACT The surface properties of water soluble copolymers vinyl ethers of monoethanolamine and ethylene glycol with sodium 2-acryla mid o-2-methyl-propanesulfonate were investigated by studying adsorption at the aqueous solution – air interface. It is found that copolymers have considerably higher surface activity in comparison with poly- sodium 2-acryla mid o-2-methyl-propanesulfonate. Keywords: Surface Active Copo lymers; Adsorption; Interface; Standard Free Energy of Adsorption 1. Introduction Investigat io n of th e behavio r of macromolecu les at th e interface is one of the biggest challenges because surface phenomena in pol ymers and po lymeric material s play an i mportant role in the whole complex of their properties, especially in their structural and mechan ical propert ies. The combination of the polar hydrophilic groups and non- polar hydrophobic parts of chain in macromolecules gives to the functional areas of polymers the surface-active properties and the possibility to use them as flocculants, flotation reagents, antistatic agents, stabilizers of disperse systems, etc., used in the oil, pharmaceutical and textile industry, metallurgy, agri- culture and for other purposes. We have synthesized new multifunctional copolymers of vinyl ethers of monoethanolamine and ethylene glycol with sodium 2-acrylamido-2-methyl-propanesulfonate by free- radi- cal copolymerization in aqueous medium [1,2]. This report is devoted to the determination of surface-active properties of these copolymers by studying the adsorption at the aqueous solution-air interface. 2. Experimental The Na-AMPS monomer was prepared from 2-acrylamido-2- methylpropanesulfonic acid (H-AMPS) (the content of the main product was no less than 99 wt %) purchased from Avocado Research Chemicals Ltd. (Switzerl and). Ethylene glycol vinyl ether (EGVE) and monoethanolamine vinyl ether (MEAVE) were purified by vacuum distillation (Tb=72C/30 kP a, nD20= 1.4356 and Tb=45–46C/1.333 kPa, nD20= 1.4357 respectively). The free-radical copolymerization of Na-AMS and MEAVE was performed in an inert medium at 60°C at various molar ratios of the starting monomers in aqueous solution. The reac- tion was carried out in the presence of an equimolar mixture of sodium bisulfite and potassium persulfate as a redox initiator. The weight of the initiator was 0.1% with respect to the total weight of comonomers. The composition of the copolymer was determined by IR- spectroscopy and potentiometric titration on an EV-74 ionome- ter with t he use of glass and silver chloride elect r odes. Adsorption of copolymers at the air-water solution interface was studied by measuring surface tension. Surface tension (σ) of polymer sodium 2-acrylamido-2-methyl-propanesulfonate (Na-AMPS) aqueous solution, copolymer of ethylene glycol vinyl ether- sodium 2-acrylamido-2-methyl- propanesulfonate (EGVE-Na-AMPS), and copolymer of monoethanolamine vinyl ether - sodium 2-acrylamido-2-methyl- propanesulfonate (MEAVE-Na-AMPS) was measured at 298 K by the Wilhelmy [3]. The σ value of solutions was calculated according to the equati o n [4 ] : () 2( ) m mg ld рa σ − = + (1) where mp and ma - the mass of the plate in the solution and air, respectively; g – gravitational acceleration; l and d - the width and thickness of the submerged part of the plate, respectively. Retraction force of the plate to the solution was measured usin g a t orsion balance to an accur acy of ±10-6 kg. To determine the equilibrium value of surface tension, the measure ment for each solu tion ther mostat icall y-controlled to an accurac y of ± 0.5 0C was perfor med after 2 4 hou rs. The avera ge value σ was found then from several measurements. The accu- racy of surface tensio n measu rement did not exceed ±0 ,3 mN / m. 3. Results and Discussion Figures 1 and 2 show kinetics of surface tension reduction of the copolymer aqueous solution depending on adsorption time. S. Kh. KHUSSAIN ET AL. Copyright © 2012 SciRes. AMPC 178 It is evident that, for aqueous solutions of the copolymer, the equilibrium value of surface tension (σ) is reached during sev- eral hours, which is typical for high molecular surface active compounds. The adsorption of macromolecules at interface has its own peculiarities, among which the most important - the slowness of the process [5]. It manifests itself, particularly, in reducing the surface tension of aqueous solutions of macromolecular sub- stances in the range of long t ime. The process can be divided in two stages: 1) the diffusion of macromolecu les at th e interface 2) the restructuring of certain segments of the macromole- cules o n polarity at the in terface und er the action of the su rface force field. In order to obtain information on the duration of the copoly- mer adsorption the relaxation times of adsorbed layers were calculat ed on kin etic dat e according t o equati on [6]: lg (στ - σ∞) = lg (σ0 - σ∞) – τ / 2,3 ϑ, (2) where στ - surface tension value of solution at time τ, mN/m; σ0 – the initial of surface tension at τ = 0, mN/m; σ∞ – the equilibrium value of surface tension (after 24 h.),mN/m; ϑ - relaxation time of the adsorption layer, min. m1 = 24.7 mol. MEAVE % in the polymer co mpos ition Figure 1. Kinetics of the surface tension reduction of polymer MEAVE - Na-AMPS at different concentrations of aqueous solu- tions (wt %) in solution: 0.02 (1), 0.04 (2), 0.09 (3), 0.12 (4), 0.5 (5). m1 = 30 mol.% VEEG in the polymer composition Figure 2. Kinetics of the surface tension reduction of polymer VEEG - Na-AMPS at differe nt concentrations of aqueous solutions (wt %): 0.02 (1), 0.04 (2), 0.06 (3), 0.08 (4), 0.12 (5) The relaxation times of polymer adsorption layers VEMEA - Na-AMPS and VEEG-Na-AMPS at the interface solution - air are shown in Table 1. Analysis of the data (Table 1) shows that in the case of the copolymer VEMEA-Na-AMPS relaxation time is directly pro- portional to the concentration of the copolymer, whereas for the copo lymer VEEG-Na-AMPS, this dependence passes through a maximum. Obviously, this is due to the conformation of the molecules of copolymers. At low concentrations of the solution of the copol ymer macro molecules are i n a more expand ed con- formation and reorientation of the branched structure of the copolymer VEEG-Na-AMPS takes more time. Subsequent increase of copolymer solution concentration raises quantity of simultaneously adsorbing macromolecules which leads to de- crease of vacant place on surface. As a result the reorientation of macromolecular segments on polarity at the air- solution interface becomes difficult and, hence, relaxation time of ad- sorp tion layer decreas e [6] . The isotherm of surface tension of copolymer solution VEEG - Na-AMPS and MEAVE - Na-AMPS based on equilibrium value of σ was constructed (Figure 3, curve 2,3), together with Ta ble 1. The relaxation time of adsorption layers of copolymers MEAVE - Na-AMPS and VEEG - Na-AMPS at different concentrations of solution. Copolymer Concentration of copolymer, wt. % Relaxation time ϑ, min. MEAVE – Na-AMPS 0,02 145 0,04 147 0,09 150 0,12 152 0,50 172 VEEG-Na-AMPS 0,02 190 0,04 423 0,06 500 0,08 126 0,12 87 S. Kh. KHUSSAIN ET AL. Copyright © 2012 SciRes. AMPC 179 Figure 3. Isotherms of surface tension of aqueous solutions poly- NaAMPC (1) and copolymer MEAVE - Na-AMPS (3), copolymer VEEG - Na-AMPS (2). the isotherm of surface tension water solution poly- Na-AMPS (Figure 3 , curve 1). As can be seen from the Fig ure 3, the curve σ = f (c) of co- polymer MEAVE - Na-AMPS is below the curve VEEG - Na- AMPS, which indicates that surface activity of monoethanola- mine vinyl ether copolymer is higher compared to VEEG - Na-AMPS. The higher surface activity polymer VEMEA-Na- AMPS explained by the formation of intramolecular salt bond between a mino- and sulfonic acid groups, resulting in increased hydrophobicity of the copolymer and is its compactness: C CH O SO 3 NH C CH 2 CH 3 CH 3 n CH 2 CH CH 2 m O RNa - where R — (CH2)2 — OH, and — ( CH2)2 — NH2 Based on isotherms the surface activity on Rebinder (GRe) for poly- Na-AMPS and copolymers was determined according to equat ion [7] (Table 2): Re 0 lim() c d Gdc σ → = − (3) Table 2 demonstrates that surface activity of copolymer ex- ceeds ones of homopolymer approximately more than 3 times. Table 2. Physical - chemical properties of surface layers of polymers. The system GRe⋅10-3, (mN m-1) / (kmole m-3) ∆ ads G0298 , kJ / mole Poly-Na-AMPS 1,5 1 8,0 Copolymer MEAVE - Na-AMPS 9,1 22,6 Copolymer VEEG - Na-AMPS 5,2 21,2 The values of polymer’s standard free energy of adsorption (∆adsG0298) were calculated in order to identify the causes and mechanism of change in surface activity and adsorption. In addition, it is important characteristic of a spontaneous accu- mulation of substance at the interface and is a measure of the surface active macromolecu le’s desire to adsorb. Standard free energy of adsorption was calculated according to the equation [8]: ∆adsG0298 = -RT ln GRe, (4) where T- the absolute temperature, R- the universal gas con- stant. As seen from the values shown in Table 2, the gain in stan- dard free energy adsorption in transition from homopolymer to copolymer VEEG- Na-AMPS is about 3 kJ/base-mole, and to copolymer MEAVE - Na-AMPS is 4,6 kJ/base-mole. Thus, the results of this study lead us to conclude that in aqueous solutions the MEAVE - Na-AMPS and VEEG-Na- AMPS copolymer have higher surface activity and adsorption at the interface solution-air proceeds easier than poly-Na- AMPS, i.e. vinyl ether u nits in the polymer chain increases the surface activity of macr omolecules . REFERENCES [1] K. Zh. Abdiyev, S. Kh. Khussain, N. Zh. Seitkaliyeva, “New macromolecular surface active substant based on monoethano- lamine vinyl ether,” Vestn. Kazakh. Nats. Univ., No.2, vol. 31, pp. 321-323, 2003. [2] E. M. Shaikhutdinov, S. Kh. Khussain, K. Zh. Abdiyev, A. Zh. Zhenisova, N. Zh. Seitkaliyeva, “New copolymers of 2-acrylamido-2-methyl-propanesulfonic acid, and vinyl ethers,” Proc. XVIII Mendeleev Congress on General and Applied Che- mistry. -Moscow, vol. 2, p. 608, 2007. [3] V. A. Kabanov, I. M. Papisov, “Complex formation between complementary synthetic polymers and oligomers in dilute solu- tions,” Visokomolec. soiyed., No. 2, vol. 21A, pp. 243 – 261, 1979. [4] A. Adamson, “Physical Chemistry of Surfaces,” Moscow, 1979, pp. 10 9 - 118. [5] D. J. Adams, M. T. A. Evans, J. R. Mit ch ell, M . C. Ph illips , P. M. Rees, “Adsorption of Lysozime and some Acetyl derivatives at the Air-Water Interface,” J. Polym. Sci., Part C, No 34, pp. 167 – 169, 1971. [6] A. A. Trapeznikov, V. G. Vince, T. Yu. Shirokova, “The kinetics of the reduction of surface tension in solutions of pro- teins,” Colloid. Zh. , No 2, vol. 43, pp. 322 – 329, 1981. S. Kh. KHUSSAIN ET AL. Copyright © 2012 SciRes. AMPC 180 [7] K. F. Zhigach, P. A. Rebinder, “Surface activity of hydrophilic colloid“, Zh. Phyz. Khim., vol. 13, pp. 94 – 105, 1939. [8] V. G. Babak, M. A. Anchipolovsky, G. A. Vikhoreva, I. G. Lukina, “The mechanism of the synergistic action of bromide and tetradetciltrimetilammonium and karboximetilhitin forming surface active substance-polyelectrolyte complexes on the surface tension of mixed aqueous solutions,” Colloid. Zh., No 2, vol. 58, pp. 155-162, 1996. |