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DOI: 10.1039/B9PY00330D (Paper) Polym. Chem., 2010, 1, 698-701

Acoustical parameters of polyacrylamide with sodium (meta) silicate and potassium silicate solution at 303 K

S. Ravichandran *a and K. Ramanathan b
aDepartment of Physics, Sathyabama University, Chennai, 600 119, Tamilnadu, India. E-mail: rs_ravichandran@yahoo.com
bDepartment of Physics, Thiagarajar College of Engg, Madurai, 15, Tamilnadu, India

Received 31st October 2009 , Accepted 7th January 2010

First published on 15th February 2010

Abstract

The ultrasonic velocity (U) and density (ρ) have been measured in mixtures of polyacrylamide solution in sodium meta silicate and potassium silicate solutions in different concentrations at 303 K. Based on the data obtained, the adiabatic compressibility (βad), intermolecular free length (Lf), acoustic impedance (Z) and relative association have been calculated. Variations of the acoustical parameters in polyacrylamide are studied with silicate solutions. The results have been discussed in terms of various interactions present in these mixtures and relative associations in the components.

1. Introduction

Ultrasound has been extensively used to determine the ion-solvent interactions in aqueous solutions containing electrolytes.1,2 Acoustical parameters have been determined to study the ion-solvent interactions in alkali and alkaline earth metal ions.

Das and Jha employed the ultrasonic velocity and viscosity measurements to determine the co-ordination of Co2+ ions in aqueous solutions containing different anions.3 They found that the number of water molecules present in the co-ordination sphere varies with the anion. Acoustical parameters have been determined to study the ion-solvent interactions in alkali and alkaline earth metal ions.4 In spite of having industrial and biological importance, so far no systematic studies have been done on the acoustical properties of solutions containing transition of metal ions. This paper deals with the calculation of acoustical parameters such as adiabatic compressibility, free length, acoustic impedance and relative association from the measured ultrasonic velocity and density.

2. Experimental

The ultrasonic velocities were measured in aqueous solutions of polyacrylamide (PAA) (MERCK-MW-5000000) with sodium meta silicate and potassium silicate solutions by ultrasonic interferometer (Mittel Enterprises, New Delhi) operating at 2 MHz. Doubly distilled water was used in all cases. Polyacrylamide solution was prepared at a concentration of 0.1%. The densities were measured by specific gravity bottle and are accurate to three decimal places. All the experiments were carried out at 303 K.

Sodium meta silicate powder (GR grade, MW = 284.20 g mol−1) and potassium silicate solution were employed. From the standard solution, 1%, 0.25 N and 0.5 N solutions were prepared. The polyacrylamide solution and sodium meta silicate solution were mixed at different volume ratios and ultrasonic studies were reported.

3. Results

Ultrasonic velocities and densities are measured for the mixture of polyacrylamide with sodium meta silicate and potassium silicate solutions at different volume ratios and the data are shown in Tables 1–3. The other acoustical parameters are calculated by using as usual formulae.5,6
Table 1 The density (ρ), ultrasonic velocity (U), mole fraction (Cm), adiabatic compressibility (β), intermolecular free length (Lf), acoustic impedance (Z) and relative association (RA) data for polyacrylamide with sodium meta silicate solutions
Volume ratio of PAA[thin space (1/6-em)]:[thin space (1/6-em)]Na meta Si/ml ρ/kg m−3 U/m s−1 Cm of Na Si β × 10−10/kg m−2 S−1 L f × 10−12/m Z/kg m−2 S−1 RA
0.5% of PAA vs. 1% of Na meta silicate
50[thin space (1/6-em)]:[thin space (1/6-em)]00 1000 1513 0.00000 4.3684 1.324 1513000 1.000
40[thin space (1/6-em)]:[thin space (1/6-em)]10 1008 1528 0.99980 4.2497 1.305 1540010 1.005
30[thin space (1/6-em)]:[thin space (1/6-em)]20 1004 1521 0.99995 4.3044 1.314 1527434 1.003
20[thin space (1/6-em)]:[thin space (1/6-em)]30 1006 1517 0.99998 4.3209 1.316 1525500 1.005
10[thin space (1/6-em)]:[thin space (1/6-em)]40 1006 1514 0.99999 4.3352 1.319 1523467 1.006
50[thin space (1/6-em)]:[thin space (1/6-em)]50 1006 1520 0.99997 4.3005 1.313 1529534 1.005
20[thin space (1/6-em)]:[thin space (1/6-em)]80 1008 1521 0.99999 4.2854 1.311 1533866 1.007
00[thin space (1/6-em)]:[thin space (1/6-em)]50 1012 1526 1.00000 4.2449 1.305 1543957 1.009
0.5% of PAA vs. 0.25 N of Na meta silicate
50[thin space (1/6-em)]:[thin space (1/6-em)]00 1000 1513 0.000000 4.3684 1.324 1513000 1.000
90[thin space (1/6-em)]:[thin space (1/6-em)]10 1005 1523 0.999981 4.2899 1.312 1530590 1.003
80[thin space (1/6-em)]:[thin space (1/6-em)]20 1010 1530 0.999985 4.2298 1.302 1545311 1.006
70[thin space (1/6-em)]:[thin space (1/6-em)]30 1014 1533 0.999991 4.1943 1.297 1554822 1.009
60[thin space (1/6-em)]:[thin space (1/6-em)]40 1021 1537 0.999994 4.1460 1.290 1569339 1.012
50[thin space (1/6-em)]:[thin space (1/6-em)]50 1022 1542 0.999996 4.1183 1.285 1574727 1.015
40[thin space (1/6-em)]:[thin space (1/6-em)]60 1025 1546 0.999997 4.0802 1.279 1585289 1.018
30[thin space (1/6-em)]:[thin space (1/6-em)]70 1028 1551 0.999999 4.0424 1.273 1594680 1.020
20[thin space (1/6-em)]:[thin space (1/6-em)]80 1032 1557 0.999999 3.9985 1.266 1606655 1.022
10[thin space (1/6-em)]:[thin space (1/6-em)]90 1033 1563 1.000000 3.9624 1.261 1614473 1.022
00[thin space (1/6-em)]:[thin space (1/6-em)]50 1038 1567 1.000000 3.9259 1.255 1626016 1.026

Table 2 The density (ρ), ultrasonic velocity (U), mole fraction (Cm), adiabatic compressibility (β), intermolecular free length (Lf), acoustic impedance (Z) and relative association (RA) data for polyacrylamide with sodium meta silicate solutions
Volume ratio of PAA[thin space (1/6-em)]:[thin space (1/6-em)]Na meta Si/ml ρ/kg m−3 U/m s−1 Cm of Na M Si β × 10−10/kg m−2 S−1 kg m−2 S−1 m Z/kg m−2 S−1 RA
0.5% of PAA vs. 0.5 N of Na meta silicate
50[thin space (1/6-em)]:[thin space (1/6-em)]00 1000 1513 0.00000 4.3684 1.324 1513000 1.000
40[thin space (1/6-em)]:[thin space (1/6-em)]10 1014 1536 0.999992 4.1828 1.295 1556672 1.008
30[thin space (1/6-em)]:[thin space (1/6-em)]20 1024 1550 0.999997 4.0656 1.277 1586994 1.016
20[thin space (1/6-em)]:[thin space (1/6-em)]30 1038 1567 0.999998 3.9239 1.254 1626127 1.026
10[thin space (1/6-em)]:[thin space (1/6-em)]40 1048 1579 0.999999 3.8282 1.239 1654768 1.033
00[thin space (1/6-em)]:[thin space (1/6-em)]50 1062 1600 1.000000 3.6784 1.215 1699340 1.042
0.5% of PAA vs. 1 N of Na meta silicate
50[thin space (1/6-em)]:[thin space (1/6-em)]00 1000 1513 0.000000 4.3684 1.324 1513000 1.000
40[thin space (1/6-em)]:[thin space (1/6-em)]10 1028 1549 0.999996 4.0582 1.276 1591332 1.020
30[thin space (1/6-em)]:[thin space (1/6-em)]20 1049 1578 0.999998 3.8189 1.238 1655417 1.034
20[thin space (1/6-em)]:[thin space (1/6-em)]30 1071 1610 0.999999 3.6021 1.202 1724326 1.049
10[thin space (1/6-em)]:[thin space (1/6-em)]40 1090 1629 0.999999 3.4587 1.178 1775088 1.063
00[thin space (1/6-em)]:[thin space (1/6-em)]50 1116 1667 1.000000 3.2254 1.137 1860331 1.081

Table 3 The density (ρ), ultrasonic velocity (U), coefficient of viscosity (η), adiabatic compressibility (βad), intermolecular free length (Lf), acoustic impedance (Z) and relative association (RA) data for polyacrylamide with potassium silicate solutions
Volume ratio of PAA[thin space (1/6-em)]:[thin space (1/6-em)]potassium Si/ml ρ/kg m−3 U/m s−1 Cm of K Si β × 10−10/kg m−2S−1 Lf × 10−12/m Z/kg m−2 S−1 RA
0.1% of PAA vs. 0.5% of potassium meta silicate
50[thin space (1/6-em)]:[thin space (1/6-em)]00 1002 1513 0.000000 4.3596 1.322 1516026 1.000
40[thin space (1/6-em)]:[thin space (1/6-em)]10 1046 1525 0.999992 4.1112 1.284 1595025 1.043
30[thin space (1/6-em)]:[thin space (1/6-em)]20 1089 1547 0.999997 3.8395 1.241 1684139 1.081
20[thin space (1/6-em)]:[thin space (1/6-em)]30 1126 1560 0.999998 3.6508 1.209 1756200 1.115
10[thin space (1/6-em)]:[thin space (1/6-em)]40 1164 1579 0.999999 3.4475 1.176 1837502 1.148
00[thin space (1/6-em)]:[thin space (1/6-em)]50 1205 1595 1.000000 3.2621 1.144 1921975 1.184
0.25% of PAA vs. 0.5% of potassium meta silicate
50[thin space (1/6-em)]:[thin space (1/6-em)]00 1004 1507 0.000000 4.3857 1.326 1513028 1.000
40[thin space (1/6-em)]:[thin space (1/6-em)]10 1045 1526 0.999996 4.1105 1.284 1594451 1.041
30[thin space (1/6-em)]:[thin space (1/6-em)]20 1084 1542 0.999998 3.8823 1.248 1670986 1.077
20[thin space (1/6-em)]:[thin space (1/6-em)]30 1124 1562 0.999999 3.6486 1.209 1755182 1.108
10[thin space (1/6-em)]:[thin space (1/6-em)]40 1159 1577 0.999999 3.4703 1.179 1827511 1.139
00[thin space (1/6-em)]:[thin space (1/6-em)]50 1207 1603 1.000000 3.2250 1.137 1934604 1.179

The density of polyacrylamide with sodium meta silicate and potassium silicate solution is measured and given in Tables 1–3. It is observed that the density of a solution varies linearly with the addition of salt solution. The rate of variation of density is observed with increasing the concentration of a solution. But, in the case of 1% dilute solution of sodium meta silicate, non-linear variations are observed. It indicates the ion-solvent interactions in a mixed solution of polyacrylamide and sodium meta silicate or potassium silicate solution.6

The velocity of mixed solution of polyacrylamide with sodium meta silicate (Fig. 1) and potassium meta silicate solutions are measured at low concentrations. The velocity is increased with increasing the concentration of sodium meta silicate and potassium silicate solution (Fig. 2). However, the rate of variation of velocity increases as the concentration of salt solution increases. This again supports the close packing of molecules at higher concentration. This indicates good solubility of solvent and ion-solvent interaction increases with concentration,7 while in the case of polyacrylamide with 1% of sodium meta silicate solution, the velocity increases non-linearly with concentration. The velocity decreases to minimum value and again it increases with the increased concentration. These observations indicate that there are weaker ion-solvent interactions in the mixed solutions of polyacrylamide with 1% of sodium meta silicate solution.8 This non-linear variation of velocity indicates the presence of dipole-ion interaction in the system.


A graph of the ultrasonic velocity and volume of sodium meta silicate in polyacrylamide mixed solutions.
Fig. 1 A graph of the ultrasonic velocity and volume of sodium meta silicate in polyacrylamide mixed solutions.

A graph of the ultrasonic velocity and volume of potassium silicate in polyacrylamide mixed solutions.
Fig. 2 A graph of the ultrasonic velocity and volume of potassium silicate in polyacrylamide mixed solutions.

The computed values of adiabatic compressibility of mixed solution of polyacrylamide with sodium meta silicate solution and potassium silicate solution are shown in Fig. 3 and 4. The adiabatic compressibility decreases with increasing concentration of the solution. But in the case of PAA with 1% of sodium meta silicate solution non-linear variations are obtained. The decrease in the values of compressibility in the present study indicates significant interaction between polyacrylamide and molecules of sodium meta silicate/potassium silicate solution.7,9


A graph of the adiabatic compressibility and volume of sodium meta silicate in polyacrylamide mixed solutions.
Fig. 3 A graph of the adiabatic compressibility and volume of sodium meta silicate in polyacrylamide mixed solutions.

A graph of the adiabatic compressibility and volume of potassium silicate in polyacrylamide mixed solutions.
Fig. 4 A graph of the adiabatic compressibility and volume of potassium silicate in polyacrylamide mixed solutions.

The computed values of free length of the solutions are presented in Tables 1–3. The free length is a thermodynamic property measured by the ultrasonic velocity and it is the distance between the surfaces of the neighboring molecules. Even a small decrease in free length on addition of salt solution explains the fact that the molecules of polyacrylamide and the molecules of sodium meta silicate or potassium silicate become closer. The variations of intermolecular free length of a mixed solution are shown in Fig. 3 and 6. The closer packing of the molecules indicates that there are dipole–dipole interactions between the polyacrylamide and sodium meta silicate and potassium silicate solution.10 But the increase in free length after the addition of 1% of sodium meta silicate solution is due to weak interactions and it indicates complex formation between unlike molecules.6


A graph of the intermolecular free length and volume of sodium meta silicate in polyacrylamide mixed solution.
Fig. 5 A graph of the intermolecular free length and volume of sodium meta silicate in polyacrylamide mixed solution.

A graph of the intermolecular free length and volume of potassium silicate in polyacrylamide mixed solution.
Fig. 6 A graph of the intermolecular free length and volume of potassium silicate in polyacrylamide mixed solution.

The derived acoustic parameters and acoustic impedance of sodium meta silicate and potassium silicate salt solution in polyacrylamide are given in Tables 1–3. Acoustic impedance is the ratio of the sound pressure to the vibrational velocity of the particles of the medium. In all of the solutions of polyacrylamide with sodium meta silicate and potassium silicate, acoustic impedance increases with concentration, whereas the non-linear variations are observed in the 1% of sodium meta silicate solution. The acoustic impedance is minimal for the pure sodium meta silicate solution as well as for the volume ratio 40[thin space (1/6-em)]:[thin space (1/6-em)]10. The acoustic impedance being the function of velocity and density, increases with the increase in concentration for a good interaction and in the former case, the interaction is poor.

4. Discussion

The ultrasonic velocity of the mixed solutions of polyacrylamide with sodium meta silicate solutions in low concentrations was measured and results are presented in Table 1. Non-linear variations are observed. It increases in the beginning followed by a decrease and then it increases again. This observation suggests that sodium meta silicate is not thoroughly miscible with polyacrylamide in all proportions. There must be densification at the volume ratio of 40[thin space (1/6-em)]:[thin space (1/6-em)]10, but it is lost at 30[thin space (1/6-em)]:[thin space (1/6-em)]20 and above. At 50[thin space (1/6-em)]:[thin space (1/6-em)]50 and above the ultrasonic velocity starts increasing. The increasing portions are therefore attributed to through mixing of both the components. When the fresh sodium meta silicate is mixed with polyacrylamide the ultrasonic velocity decreases. Hence there may be more and more interaction between polyacrylamide and sodium meta silicate leading to densification.

At 50[thin space (1/6-em)]:[thin space (1/6-em)]00, there may well be dispersion of polyacrylamide. At 40[thin space (1/6-em)]:[thin space (1/6-em)]10, the added sodium meta silicate may enhance the dispersion of polyacrylamide, i.e. it makes the medium less dense. But at 30[thin space (1/6-em)]:[thin space (1/6-em)]20, there may be a strong association leading to more densification of the medium. It is similar at volume ratios of 20[thin space (1/6-em)]:[thin space (1/6-em)]30 and 10[thin space (1/6-em)]:[thin space (1/6-em)]40.

Table 2 illustrates the gradual increase in velocity with increasing the ratio of sodium meta silicate to polyacrylamide. Hence, there may be more and more segregation of polyacrylamide chains with the increasing concentration of silicate. The sodium silicate with its associated water can go between the polymer chains and disperse them. This only happens when there is a strong interaction between the polyacrylamide and sodium meta silicate. The decrease in intermolecular length with increase in amount of sodium meta silicate clearly supports this view.

Table 3 illustrates the increase in velocity with increase in potassium silicate. Hence potassium silicate may aid suppression of inter chain interactions in polyacrylamide. The increase in density and decrease in free length clearly supports the suppression of inter chain interaction in the polyacrylamide solutions.

Acknowledgements

The authors are grateful to Dr Arumugam, Scientist, Central Leather Research Institute, Chennai, Tamilnadu and Dr V. Rajendran, Director, Centre for Nano Technology, K.S.R College of Engineering & Technology, Namakkal District, for encouragement. The authors are also grateful to Dr P Palanichamy, Professor, Department of Chemistry, Anna University, Chennai, Tamil Nadu for support in this research work.

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