Ultrasonic studies of aqueous solutions of poly diallyl dimethyl ammonium chloride

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1 Indian Journal of Pure & Applied Physics Vol. 42, October 2004, pp Ultrasonic studies of aqueous solutions of poly diallyl dimethyl ammonium chloride V Seetharaman, S Kalyanasundaram & A Gopalan* Department of Physics, Department of Industrial Chemistry*, Alagappa University, Karaikudi , Tamil Nadu Received 16 March 2004; accepted 14 June 2004 Poly diallyl dimethyl ammonium chloride (DADMAC) was synthesized by solution polymerization technique using potassium peroxomono sulphate. The ultrasonic velocity and density for solutions of the synthesized poly(dadmac) in the different concentration ranges are measured at three different temperatures, and K. Parameters like apparent molal compressibility, apparent molal volume and molar solvated volume in terms of molar hydration number are computed on the basis of Padova model. The variation of apparent molal compressibility and molar solvation number indicates interaction between the polymer and the solvent. [Keywords: Ultrasonic velocity, Solvation number, Adiabatic compressibility, Polymer-solvent interaction] IPC Code: B01J 19/10 1 Introduction Poly diallyl dimethyl ammonium chloride (DADMAC) and its co-polymers have various applications in the area of medical, biological and food industries. Though much work on the ultrasonic study on the solutions of polymers like PEO, PEG, PVA, PMMA, etc. has been reported 1-6, no researcher has so far considered poly(dadmac) for ultrasonic studies. Poly(DADMAC) a water soluble polymer is synthesized from quaternary ammonium salt like DADMAC and prepared through free radical initiation method. Solution or suspension or emulsion polymerization technique is used for producing the polymer. When a polymer is added to a solvent, the adiabatic compressibility of the solution is found to be less than that of the pure solvent. This is due to solvation. In solvation, the highly polar forces result in a strongly localized electric field and the solvating molecules form an incompressible region. Assuming that the compressibility of the solution is mainly due to the free solvent part, the expressions for the hydration number S, apparent molal compressibility φ k, apparent molal volume φ v and molar solvated volume φ s have been derived recently for PEG solutions 6 on the basis of Padova model 7,8. This paper describes the extension of this theory to the aqueous solutions of the newly prepared poly(dadmac) which has not been considered so far. Using the experimentally derived ultrasonic data, the theory is verified at three temperatures, and K. However, the plots required are drawn only at K as a sample. 2 Experimental Details Aqueous solutions of poly(dadmac) have been prepared by dissolving weighted quantities of polymer in the different concentration ranges. The ultrasonic velocity of the solution has been obtained using ultrasonic interferometer with a crystal of frequency 2MHz using the standard procedure with accuracy of order ±0.05%. The density of the solutions was measured using the specific gravity bottle with an accuracy of ±2 parts in All the above measurements have been carried out at three different temperatures, and K using a thermostatically controlled water bath, whose temperature can be maintained to an accuracy of ± C. 3 Results and Discussion The values of velocity and density presented in Table 1 increase with the increase of concentration at all three temperatures, and K. This observation confirms the existence of polymer-solvent interactions as observed by many researchers 9,10. In case of polymer solutions, the variation of ultrasonic parameters with concentration is due to the local mode motion (segmental confirmation changes) of macromolecules.

2 736 INDIAN J PURE & APPL PHYS, VOL. 42, OCTOBER 2004 Temp K Table 1Values of n 2, ρ, C, β, S and φ k of poly(dadmac) in water at, and K n 2 M ρ 10 3 kgm 3 C m/sec β N 1 m 2 S φ κ m 5 N 1 M 1 From eqn. Trad. eqn. (4) (5) Using the measured values of velocity C and density ρ, the adiabatic compressibility of the solution β is arrived through the equation : β = (C 2 ρ) 1 (1) and the values are given in Table 1. The increase of velocity and the decrease of adiabatic compressibility with concentration indicate that the molecules are forming a more tightly bound system 11. The hydration number (S) is computed through the Eq. (2) S = [1/n 2 ] [n 1 (Nβ/β o )] (2) where β o is the adiabatic compressibility of water. n 1 and N represent the number of moles of water present in the solution and water respectively. The obtained values are included in Table 1. The S value is found to be negative at concentrations studied and at all temperatures and decreases with concentration. The observed negative values of solvation number can also be explained on the basis of Samoilov s theory of solvation 12. The molecules of nearer solvation sphere are in dynamic equilibrium with the other water molecules. The polymer solvation may be considered not as a process leading to a combination of a certain quantity of water but rather as the effect the polymer on the translational motion of the closest water molecules. If the latter interact with the polymer more intensively than with each other, the positive solvation takes place. In this case, the exchange between the adjacent water molecules is less frequent than in pure water. On the other hand, if the water molecules approximate to the polymer molecules exchange more frequently than if there were no polymer molecules at all, the solvation becomes negative, i.e. in the solvation sphere, the polymer-water interaction is weaker than the water-water interaction 13. At each concentration, S decreases with increasing temperature. This indicates that the solute-solvent interaction becomes weak as the temperature increases. The result is in accordance with Jannelli et al 14. The hydration number at infinite dilution can throw more light on the interactions as it gives the strength of solute-solvent interactions. Hence a plot of S versus n 2 is drawn in Fig. 1 satisfying the linear relation: S = S o + S n n 2 (3) From this plot the hydration number at infinite dilution S o and the slope S n are obtained by least square fitting technique. These values are presented in Table 2.

3 SEETHARAMAN et al.: ULTRASONIC STUDIES OF AMMONIUM CHLORIDE 737 When studying the solute-solvent interactions, and in particular, hydration, it is convenient to deal not only with the total compressibility of a solution but also with the apparent molar compressibility φ k of the solute 15. Thus φ k measures solute-solvent interactions as well. The values of apparent molar compressibility in molar scale are estimated from the values of hydration number S, using the Eq. (4). φ k = -V 1 β o S (4) The values obtained are given in Table 1. φ k has positive values in all concentrations studied. Since S is negative, φ k is positive. The φ k values are also obtained using traditional equation involving compressibility and density of solution and solvent using Eq. (5) φ k = (1000/n 2 ρ o ) (ρ o β β o ρ) + (M 2 β o /ρ o ) (5) and are included in Table 1. Table 1 shows that there is a good agreement between the values obtained through the developed method and the traditional equation. This indicates that the methodology developed is on the correct lines. The variation of φ k with n 2 indicated by the Eq. (6): φ k = φ ko + S k n 2 (6) is shown in the Fig. (2). The variation of φ k with n 2 is opposite to that of S versus n 2. The values of φ k increase with concentration at all temperatures. Using Eqs [(3), (4) and (6)] one gets two equations: φ ko = -V 1 β o S o (7) S k = -V 1 β o S n (8) The intercept φ ko and slope S k values obtained from the plot (Fig. 2) as well as from the Eqs (7) and (8) are given in Table 2. The values of φ ko and S k obtained through these two routes are found to be agreeing, indicating the correctness of the theory. The limiting value φ ko, which is the apparent molal compressibility at infinite dilution is the measure of solute-solvent interaction and S k indicates solute-solute interactions. The greater value of φ ko over S k indicates that solute-solvent interaction is appreciable over the solute-solute interaction in the concentration range studied. The value of φ ko increases with temperature whereas the slope S k goes on decreasing with rise in temperatures thereby showing the dependence of φ ko with temperature (Table 2). The modulus of φ ko of the polymer considered at all temperatures follow in the same trend as S o. The apparent molal volume of a solute has been effectively used to calculate the molecular interactions Fig. 1 Variation of S with n 2 for poly(dadmac) Fig. 2 Variation of φ κ with n 2 for poly(dadmac) Table 2Values of S o, S n, φ ko, S k, φ vo, S v, φ so and S s of poly (DADMAC) in water at, and K Temp. S o S n φ κo S κ φ νo 10 6 S ν 10 6 φ so 10 6 m 3 M 1 S s 10 6 m 3 M 2 K m 5 N 1 M 1 m 5 N 1 M 2 m 3 M 1 m 3 M 2 From From From From From plot From Eq. (7) From plot From Eq. (8) plot Eq. (15) plot Eq. (16)

4 738 INDIAN J PURE & APPL PHYS, VOL. 42, OCTOBER 2004 Table 3Values of n 2, φ v and φ s of poly(dadmac) in water at, and K Temp K n 2 M From eqn. (9) φ ν 10 6 m 3 M 1 Trad. eqn. (10) From eqn. (13) φ s 10 6 m 3 M 1 Trad. eqn. (12) involved in solutions containing solute and solvent. The values of φ v at all concentrations and temperatures are estimated on the basis of Padova model in molar scale using Eq. (9) φ v = [ (Δβ/β o ) (N/n 2 ) S] V 1 (9) φ v is obtained from the values of compressibility lowering Δβ and hydration number S. The obtained values are given in Table 3. These values are found to agree well with those values obtained from the traditional method by using the density values of solution and solvent through Eq. (10). φ v = (1000/n 2 ρ o ) (ρ o -ρ) + (n 2 /ρ o ) (10) This indicates the soundness of methodology developed. The plot of φ v versus n 2 is constructed (Fig. 3) satisfying the relation φ v = φ vo + S v n 2 (11) The intercept φ vo and slope S v values are found using least square fitting technique and are given in Table 3. φ vo, the apparent molal volume at infinite dilution known as the limiting apparent molal volume, is the measure of solute-solvent interaction. The slope S v measures solutesolute interaction. φ vo increases with temperature. Fig. 3 Variation of φ v with n 2 for poly(dadmac) Padova 7,8 while studying electrolyte solutions introduced a volume known as molar solvated volume containing the solvated ion. On similar lines a new molar solvated volume φ s has been defined by the equation: φ s = [V-(n 1 -n 2 S)V 1 ]/n 2 (12) and its value has been estimated. This molar solvated volume measures the volume of the solvated part of the solute present in the solution. The molar solvated volume φ s is calculated using Eq. (13) φ s = [(V/n 2 ) (Δβ/β o )] (13) using the compressibility lowering Δβ values. These values of φ s obtained through Eqs [(12) and (13)] are

5 SEETHARAMAN et al.: ULTRASONIC STUDIES OF AMMONIUM CHLORIDE 739 Fig. 4 Variation of φ s with n 2 for poly(dadmac) given in Table 2. It is found that φ s values obtained through the Eqs [(12) and (13)] are equal. This proves the correctness of the theory developed. This volume φ s is found to vary linearly with n 2 (Fig. 4) satisfying the equation φ s = φ so + S s n 2 (14) The slope S s and intercept φ so values are computed using least square fitting technique and are presented in Table 2. The theoretical values of φ so and S s are also obtained by using Eqs [(15) and (16)] respectively represented as: φ so = φ vo + S o V 1 (15) S s = S v + S n v 1 (16) and are included in Table 2. The perusal of the Table 2 shows the agreement between these values. It is observed that the molar solvated volume at infinite dilution φ so decreases with the increase of temperature like S. This may be ascribed due to the fact that as temperature increases, solute-solvent interaction decreases thereby reducing the volume of the hydration shell. In the study of electrolytes Padova 7,8 has used the equation: φ s = V int + SV H (17) for obtaining molar volume of the solvent V H and intrinsic volume of the electrolyte V int. Extending this to the polymer solutions one gets the value of the intrinsic volume of the manomer unit of the polymer. These values of V int and V H are obtained by constructing a plot of Ф s and S (Fig. 5). Fig. 5 Variation of φ s with S for poly(dadmac) Table 4Values of V H and V int of poly (DADMAC) in water at, and K Temp K V H 10 6 m 3 M V int 10 6 m 3 M As demanded by Eq. (17), the plot Ф s versus S is found to be linear as in the case of electrolyte solutions. The slope V H and intercept V int are computed using the least square fitting technique. These values are presented in Table 4. V int gives the intrinsic volume of the polymer repeat unit since the molecular weight and the number of moles corresponding to the repeat unit is used for the calculation. 4 Conclusion On the basis of Padova s model, expressions for the hydration number S, φ k, φ v and φ s have been arrived. Similar to the case of electrolytes one can determine the value of molar solvated volume φ s of the polymer which varies linearly with n 2 like the molar hydration number S and φ v. The results indicate that one can adopt Padavo s model in the study of polymer-solvent interaction. The approach suggested by Padova for finding intrinsic volume is also found to hold good for polymer solutions. References 1 Bass H E & Tan J, J Acoust Soc Am, 93 (1993) Singh D P & Singh A P, J Acoust Soc Am, 93 (1993) Varadarajulu A & Mabu Sab P, Bull Mater Sci, 18 (1995) Donato I D, Magazu S, Maisano G, Majolino D & Pullicino A, Mol Phys, 87 (1996) Kalyanasundaram S, Natarajan B, Manuel Stephen A & Gopalan A, Acustica-Acta-Acustica, 83 (1997) 74.

6 740 INDIAN J PURE & APPL PHYS, VOL. 42, OCTOBER Kalyanasundaram S, Sundaresan B & Hemalatha J, J Polym Mater, 17 (2000) Padova J, J Chem Phys, 39 (1963) Padova J, J Chem Phys, 40 (1963) 491, 40 (1964) Narasimham A V & Mainkiam B, Indian J Phys, 68B (6) (1994) Pethrick R A, J Macromol Sci Rev Macromol Chem, 9(1) (1973) Spickler P, Ibrahim F, Fastr S, Tannenbaum D, Yun S & Stumpf F B, J Acoust Soc Am, 83(4) (1988) Zaikov G E, Jordanskji A L & Markin V S, Diffusion of electrolytes in polymer, VSP, The Netherlands, 1988, First Eng Edn, p Kalyanasundaram S, Sundaresan B & Hemalatha J, J Polym Mater, 17 (2000) Jannelli M P, Magazu S, Maisano G, Majolino D & Migliardo P, Phys Sci, 50 (1994) Chalikian T V, Saravazyan A P & Breslauer K J, Biophysical Chemistry, 51 (1994) 89.

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