THE STUDY OF MOLECULAR INTERACTIONS IN STABILIZERS AND PLASTICIZER THROUGH ULTRASONIC MEASUREMENTS

Transcription

1 27 THE STUDY OF MOLECULAR INTERACTIONS IN STABILIZERS AND PLASTICIZER THROUGH ULTRASONIC MEASUREMENTS 1 R. KAVITHA, 2 S. JAYAKUMAR, 3 R. UMA 1 Department of Chemistry, Easwari Engineering College, Chennai 89 2 Department of Physics, Vivekananda college, Mylapore, Chennai 04 3 Department of Chemistry, Pachaiyappa s College, Chetpat, Chennai 30 vijayabijeet@yahoo.co.uk, jk_5454@yahoo.co.in ABSTRACT Ultrasonic technology has wide range of applications in research, industry and medicine. Ultrasound involves low power waves which pass through materials without affecting their physical or chemical structure. However, very high intensity ultrasound can be used to cause chemical and physical changes in materials. The study of the propagation of behavior of ultrasonic waves in solids, liquids, liquid mixtures, electrolyte solutions, suspensions, polymers etc., is now rather well established as an effective means for examining certain physical properties of materials or medium [1-3]. Ultrasonic technique is a promising tool to obtain information on the nature and strength of inter-molecular interaction in dilute solutions regarding propagation, dispersion, attenuation of ultrasonic wave in a medium with the structural aspect. Keywords: Glycol, Stabilizer, Plasticizer,, excess functions and negative deviation 1. INTRODUCTION The physicochemical behaviour of various binary mixtures such as molecular interactions, association, dissociation and complex formation, which are of special interest in chemical and electrochemical processes [1, 2]. The study of molecular interaction in the solid - liquid mixtures is of considerable importance in the elucidation of the structural properties of the molecules. The results have been discussed in terms of molecular interactions. Zinc and calcium are used as stabilizer and propylene glycol is used as plasticizer. The values of ultrasonic velocity (U), density ( ) and viscosity ( ) for the pure components is given in Table 1. From the experimental values, a few acoustical parameters such as adiabatic compressibility (ß), acoustical impedance (Z), molar sound velocity (R), Wada s constant (W), molar volume (V m ), free volume (V f ), intermolecular free length (L f ), internal pressure ( ), absorption coefficient ( /f 2 ) viscous relaxation time ( ), degree of intermolecular attraction ( ), excess ultrasonic velocity (U E ), excess adiabatic compressibility (ß E ), excess acoustical impedance (Z E ), excess free length (L f E ) and excess molar volume (V m E ) were derived over the entire mole fraction range. Ultrasonic velocities have also been evaluated theoretically with the help of Impedance relation, Nomoto relation, Van Dael & Vangeel relation and Junjie relation. The suitability of these theories and equations were checked by comparing theoretical values of ultrasonic speeds with the values obtained experimentally. Literature survey showed that no measurements have been previously reported for the mixtures reported in this paper [4-6]. 2. MATERIALS AND METHODS The chemicals used were of analytical grade and obtained from E.Merck company. Thermostatically controlled well-stirred water bath whose temperature was maintained to ±0.01 K accuracy was used for all the measurements. Binary mixtures were prepared by weighing in airtight bottles, the possible uncertainty in the concentration is estimated to be less than ± Densities of pure components and their mixtures were determined by using a 1 X 10-5 m 3 double arm pycnometer. The density values from triplicate replication at the temperature of 303 K were reproducible within 2 X 10-2 kg m -3. The uncertainty in density and excess molar volume values were found to be 4 X 10-2 kg m -3 and X 10-6 m 3 mol -1 respectively. Ostwald s viscometer having capacity of about 15 ml and the capillary having a length of about 90 mm and 0.5 mm internal diameter has been used to measure the flow times of pure liquids and liquid mixtures and it was calibrated with benzene (density g cm -3 ) and doubly distilled water (density g cm -3 ) at 303 K. The flow time of pure liquids and liquid mixtures were repeated for five times. The uncertainty of viscosity was X 10 3 m Pas. Speed of sound was measured by using a variable path, single crystal interferometer. (United scientific company, India), working at 2 MHz frequency. The interferometer was calibrated using toluene. Measurement of speed of sound through medium was based on the accurate determination of the wavelength of ultrasonic waves of known frequency produced by quartz crystal in the measuring cell. The interferometer cell was filled with the test liquid, and water was circulated around the measuring cell from a thermostat. The uncertainty was estimated to be 0.1ms -1.

2 28 The adiabatic compressibility (ßs) was calculated by the equation ß = 1/ U 2 (1) Where is the density of mixture and U is the ultrasonic velocity of the mixture. The acoustical impedance (Z) was calculated by the equation, Z = U (2) Where is the density of mixture and U is the ultrasonic velocity of the mixture. The molar sound velocity (R) was calculated by the equation R = (M eff / ) U 1/3 (3) Where U is the ultrasonic velocity of the mixture. The molar compressibility or Wada s constant (W), was calculated by the equation W =(M / ) ß 1/7 (4) Where M is the relative molar mass and ß is the adiabatic compressibility. The intermolecular free length (L f ) was calculated by the equation L f =k ß ½ (5) Where K = 1.98 X 10-6, the Jacobson constant (Jacobson 1952). The Free volume was calculated by the equation V f = (M eff U/K ) 3/2 (6) Where K = 4.28 X 10 9 for all liquids which is a temperature independent constant. The internal pressure was calculated by the equation = {brt / (V 2 V f ) 1/3 } (7) b is a packing factor, R is a gas constant, V f is free volume and T is temperature. The absorption coefficient was calculated by the equation ( /f 2 ) = (8 2 /3 U 3 ) (8) is viscosity of the mixture and is the density of the mixture. The viscous relaxation time was calculated by the equation = ( 4 /3 U 2 ) (9) is viscosity of the mixture and is the density of the mixture. The degree of intermolecular attraction ( ) was calculated by the equation = (u 2 / u 2 im) 1 (10) Where u 2 im =1/ {(x 1 M 1 + x 2 M 2 )(x 1 /M 1 u x 2 /M 2 u 2 2 )} The U E, ß E, Z E, L f E, and V m E were derived over the entire mole fraction range by using the general equation A E = A (X i A 1 + (1-X i ) A 2 ) (11) Where A is the corresponding parameters (U, ß, Z, L f, and V m ) of binary mixture and A 1 and A 2 are the corresponding pure component values. The sound velocity can be correlated with the relation called Impedance relation which is represented as U IM = (X 1 Z 1 + X 2 Z 2 ) / (X X 2 2 ) (12) where X, Z, denote the mole fraction, acoustic impedance and density of the component respectively. Nomoto derived an empirical formula for the sound velocity in binary mixture. It is given by the equation 3 (X 1 R 1 + X 2 R 2 ) U NR = [R/V] 3 = (13) (X 1 V 1 + X 2 V 2 ) Where X, R, V denote the mole fraction, molar sound velocity and molar volume at temperature T of the component. The acoustical behaviour of binary mixture was studied in detail by Van Dael etal. The expression for sound velocity (U IMR ) of binary mixtures can be obtained from equation [1/(X 1 M 1 + X 2 M 2 )] 1/2 U IMR = (14) [X 1 /M 1 U X 2 /M 2 U 2 2 ] Where X, M and U are the mole fraction, molecular weight and sound velocity of component. Junjie derived an empirical formula for the sound velocity in binary mixture. It is given by the equation -1/2 (X 1 V 1 + X 2 V 2 ) X 1 V 1 X 2 V 2

3 29 U jun = (15) (X 1 M 1 + X 2 M 2 ) 1/ U1 2U2 Where X, V, M, denote the mole fraction, molar volume, molecular weight and density of the components. The percentage deviation of the experimental velocity from the theoretical value is given by the equation U Theo - U Expt Percentage deviation in velocity = X 100 (16) U Theo 3. RESULTS AND DISCUSSION The ultrasonic velocity, density and viscosity data for the pure components at 303 K are given below: Table 1 Comparison of density, ultrasonic velocity and viscosity data at 303 K U X 10 Component -1 m/s Kg/m 3 Nsm -2 Zinc Calcium Propylene glycol Table 2 gives the measured and acoustic parameters such as ultrasonic velocities (U), density ( ), viscosity ( ), adiabatic compressibility (ß), acoustical impedence (Z), molar sound velocity (R), molar compressibility (W), molar volume (V m ), free volume (V f ), Table 3 gives the thermodynamic properties like intermolecular free length (L f ), internal pressure ( ), absorption coefficient ( /f 2 ), viscous relaxation time ( ), degree of intermolecular attraction ( ), Table 4 gives the excess parameters like excess ultrasonic velocity (U E ), excess adiabatic compressibility (ß E ), excess acoustical impedance (Z E ), excess free length (L E f ), excess molar volume (V E m ), Table 5 gives the theoretical values of ultrasonic velocity calculated from Impedance, Nomoto, Van Dael & Vangeel and Junjie s relation along with the experimental ultrasonic velocity and percentage deviation for the binary mixtures zinc - propylene glycol and calcium propylene glycol over the entire composition range at 303 K. Table 2 : Measured and acoustic parameters of binary mixtures at 303 K Conc of U ms -1 / / Z / 10 6 R W V m / 10-1 V f / 10-8 Kgm -3 Nsm -2 Kg -1 ms -2 Kg m -2 s -1 m 3 mole -1 m 3 mole calcium propylene glycol Table 3 : Thermodynamic parameters of binary mixtures at 303 K

4 30 Conc of L f / m / 10 6 atm /f 2 / / 10-9 m -1 s 2 s / 10-1 m calcium propylene glycol Table 4 : Excess parameters of binary mixtures like U E, ß E, Z E,L f E and v m E at 303 K Conc of U E E / Z E / 10 5 ms -1 Kg -1 ms -2 Kg m -2 s -1 E L f / m V m E / 10-3 m 3 mole calcium propylene glycol

5 31 Table 5 Experimental velocities and theoretical velocities along with the percentage deviation of binary mixtures at 303 K Conc of Ultrasonic velocity U / ms -1 % Deviation EXPT Imp Nom VDV Junjie s Imp Nom VDV Junjie s calcium propylene glycol Fig.1 : Excess parameters of and calcium propylene glycol It can be observed from the ultrasonic velocity (U) values is found to increase with increase in concentration of s. The increase in ultrasonic velocity indicates the greater association due to the intermolecular hydrogen

6 32 bonding between the solute and the solvent molecules. This predicts that components used in this present investigation are aliphatic in nature, so the interaction between aliphatic molecules is less when compared with interaction between aliphatic aromatic molecules. The density values (ρ) increases with increase in concentration which predicts that there is greater interaction between the components [12]. The viscosity values ( ) increases with increase in concentration which gives some reliable information about molecular interaction [13]. In Zn. St PG and Ca. St PG system, large viscosity variation is observed. The adiabatic compressibility (β) decreases with increase in concentration for Zn. St PG, and Ca. St PG system. The decrease in adiabatic compressibility brings the molecules to a closer packing resulting in decrease of free length. Further, it strengthens the strong molecular association between the unlike molecules through hydrogen bonding. Increase in chain length of the component decreases adiabatic compressibility which reveals the intermolecular interactions leading to compact structural arrangement. Acoustic impedance (Z) increases linearly in Zn. St PG and Ca. St PG system, confirms the presence of molecular association between - glycol molecules through intermolecular hydrogen bonding [18]. Rao s constant (R) and Wada s constant (W) shows linear variation for the binary mixtures Zn. St PG, and Ca. St PG system predicting the absence of complex formation and only weak interaction exists in all these cases. Molar volume (V m ) decreases with increase in concentration. The variation of free volume (V f ) shows non linear variation with increase and decrease values with increase in concentration for Zn. St PG and Ca. St PG system. The intermolecular free length (L f ) also follows the same trend as that of adiabatic compressibility for Zn. St PG and Ca. St PG system, decrease in free length with increase in concentration identifies significant interaction between s and glycols due to which the structural arrangement is considerably affected [22] and also decrease with increase in the chain length of the glycols. It can be seen that the internal pressure (π) decreases with increase in concentration, confirms the existence of weak interaction for Zn. St PG and Ca. St PG system, internal pressure decrease at low concentration but as concentration increases, internal pressure increases predicting strong interaction is possible among the components in binary mixture. The absorption coefficient value (α/f 2 ) shows non linear variation with decrease and increase value with increase in concentration for Zn. St PG, and Ca. St PG. It shows the presence of molecular interaction at high concentraton. The values of relaxation time (τ) shows non linear variation in both Zn. St PG and Ca. St PG system confirms the presence of some specific interaction among the component at higher concentration. The interaction parameter (α) signifies that unlike interactions are relatively strong compared to like interactions. It is evident from the increased values of intermolecular attraction explains the interaction between unlike components whereas decreased values explains the interaction between like components [25]. α value increase for Zn. St PG and Ca. St PG system, identifies the existence of interaction among them. The excess velocity (U E ) shows positive deviations [28] predicts the weak interaction due to dispersion force. It shows non linear variation for Zn. St PG and Ca. St PG system. It states that molecular association of the component is stronger than dissociation of the molecules, which leads to the formation of cluster formation. The sign and magnitude of actual value depends upon the strength of two opposing effects, the greater negative deviation in both excess adiabatic compressibility and excess free length enhance the attractive interaction. This is confirmed by greater negative deviation in Ca. St PG and Zn. St PG system. It was reported that the positive deviation in excess impedance (Z E ) indicates the presence of strong interactions between component molecules in the binary mixture [34]. Zn. St PG and Ca. St PG system shows non linear variation identifies strong molecular interaction among them. The excess molar volume (V E m ) is negative for entire composition range. This may be due to strong unlike interactions between molecules, excess molar volume decreases with increase in concentration. The theoretically predicted ultrasonic velocities are compared with the experimentally determined velocities. The assumption for formation of the ideal mixing relation is that, the ratio of specific heats of ideal mixtures and the volumes are also equal. Therefore no such molecular interaction is taken into account. Negative deviation is observed for for Zn. St PG and Ca. St PG system, deviation follows the order U Vdv > U Jun > U Nom > U Imp Based on the above consideration, Van Dael & Vangeel and Junjie relation shows maximum negative deviation, where as Nomoto s and impedance relation are in fairly good agreement with the experimental velocity values. CONCLUSION The ultrasonic velocity data and other acoustical parameters give valuable information to understand the solute solvent interactions in the binary mixture, it may be suggested that the strength of interactions between aliphatic and aliphatic molecules is less. However, in Ca. St PG system, maximum molecular interaction is observed. It predicts the disruption of like forces in glycols and association of both components occurs partially. Comparatively in Zn. St PG system shows only weak physical attraction indicating that the mixture is

7 33 immiscible blend. In comparison among s, molecular interaction is greater with calcium than with zinc. This variation may be due to the influence of metal ion in s towards plasticizer on mixing. Ca. St PG > Zn. St PG From the computed data calculated, Nomoto and Impedance relation agrees well with experimental sound velocity values and greater negative deviation values in Van Dael and Vangeel and Junjie relation confirms the existence of strong molecular interaction between stabilizers and plasticizer. REFERENCES 1. V. Desai, M.A. Shenoy, P.R. Gogate, Chem. Eng. J. 140 (2008) A.M. Bisdow, K.H. Ebert, Macromol. Chem. 176 (1975) W. Schnable, Polymer degradation, Hanser, New York, USA, Alig I Feller K H and Sauberlich R Acta Polymerica 31 (1980) A.I. Lavrentyev, S.I. Rokhlin, Ultrasonics 39 (2001) Hourston D J and Hughes I D Polymer, 19 (1978) Singh Y P, Das S, Maiti S and Singh R P J. Pure Appl. Ultrason., 3 (1981) Mikkonen R and Savlainen A J. Appl. Polym. Sci., 39 (1990) U.D. Harkal, P.R. Gogate, A.B. Pandit, M.A. Shenoy, Ultrason. Sonochem. 13 (2006) Chandralekha Fadnis, Illiger S R, Rao K P, Demappa T Carbohydrate Polymers, 74 (2008) Seetharaman V, Kalyanasundaram S, Gopalan A Journal of Molecular Liquids 121 (2005) Erol Okan S, Salmon Ph.S, Champeney D C, Petri I Mol. Phys. 84 (1995) Barlow A J, Erginsav A Polymer 16 (1975) R Kumar, S Jayakumar and V Kannappan., Indian Journal of Pure & Applied Physics., Vol. 46. March 2008, pp Ulagendran, R Kumar, S Jayakumar and V Kannappan., Journal of Molecular liquids., 148 (2009) pp