Abstract
In the present investigation, experimental values of density, viscosity, and ultrasonic velocity of polyvinylchloride in dimethylformamide are measured at different concentrations and temperatures at 1 MHz frequency. Using these data, different acoustical parameters have been calculated to understand molecular interactions between solute and solvent. This study is helpful in understanding the polymer and solvent interaction. The effect of concentration and temperature on various parameters has been discussed.
1. Introduction
Acoustical studies in polymer solution and in solid polymers have been the subject of research in recent years [1–5]. A review of literature on acoustical studies on polymer solution reveals that ultrasonic velocity measurement studies are helpful in understanding the nature of molecular interactions in solute and solvent [6–9]. Polyvinylchloride (PVC) is a well-known versatile thermoplastic commodity, whose production and consumption are second as worldwide compared to other plastics. Polyvinylchloride is generally used and known to have the advantages of low ingredient cost, wide processing versatility, and high decorative potential and is used to manufacture various types of products ranging from highly rapid to very flexible. Many researchers [10, 11] have carried out pioneering work on polymer/polymer compatibility using ultrasonic techniques. As polyvinylchloride is an industrially important polymer, therefore it is decided to study the molecular interactions of polyvinylchloride in dimethylformamide.
Takeda and Endo [12] observed the viscosity of dilute polyvinylchloride solution. B. Thapa et al. studied the ultrasonic studies of polyvinylchloride in cyclohexanone and 1, 4-dioxane. Xiang et al. [13] explored effective means of characterizing structural changes of PVC particles during gelation and fusion of PVC plastisol’s with small angle light scattering. Thakore et al. [14] studied the compatibility of the blend system of PVC and starch acetate in 1, 4 dioxane from viscometric, ultrasonic, and density measurements. In order to observe the influence of heat and concentration, an experiment was carried out at different concentrations and temperatures. Very limited literature is available on polyvinylchloride, so it is interesting to study molecular interaction in polyvinylchloride. In the present investigation, various acoustical parameters at different temperatures and concentrations of polyvinylchloride in dimethylformamide have been calculated and the results are discussed in terms of molecular interaction of the solute and the solvent. Acoustical parameters are useful in understanding the physiochemical behavior of PVC and dimethylformamide, production, and their applications in different fields.
2. Experimental Details
In the present investigation, polyvinylchloride (molecular weight ≈ 134.5 Da) in the liquid form is used with dimethylformamide. The solutions were prepared by adding the known volume of polyvinylchloride to a fixed volume of dimethylformamide and stirring under reflex until a clear solution was obtained. The concentration range studied in solution is 1%, 0.8%, 0.6%, 0.5%,0.4%, and 0.3% in the temperature range of 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, and 65°C at 1 MHz frequency. Ultrasonic velocity is measured by using the variable path ultrasonic interferometer (Mittal Enterprises, New Delhi, Model No. F-81), with a reproducibility of ±4 m/s at 30°C. The temperature of the solution has been kept constant by circulating water from the electronically operated digital constant temperature bath (Mittal Enterprises, New Delhi) with an accuracy of ±0.1°C) through the outer jacket of the double-walled measuring cell containing experimental liquid. The densities at different temperatures were measured using 10 ml specific gravity bottle and single pan microbalance. The uncertainty in density measurements was found to be 0.5 kg/m3. The viscosity of the mixtures was determined by using Ostwald’s viscometer, which was kept inside a double-walled jacket, in which water from the thermostat water bath was circulated. The inner cylinder of this double-walled glass jacket was filled with water of the desired temperature so as to establish and maintain the thermal equilibrium. In each measurement, the uncertainty was measured to be 0.01 MPa.s. The acoustical parameters are calculated by using the standard formulae given as follows [15–17]:where is the density of the medium, is the ultrasonic velocity in the medium, is the viscosity of the medium, is the frequency, is the wavelength, is the absorption coefficient, and is the Jacobson coefficient.
3. Results and Discussion
In the present investigation, the solution property parameters, namely, density, viscosity, ultrasonic velocity, adiabatic compressibility, acoustic impedance, intermolecular free length, relaxation time, and ultrasonic absorption for polyvinylchloride with dimethylformamide in a temperature range of 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, and 65°C and a concentration range of 1%, 0.8%, 0.6%, 0.5%,0.4%, and 0.3%, have been presented in Tables 1–8, respectively.
Density, viscosity, and ultrasonic velocity are presented in Tables 1–3, and their variation with temperature and concentration is presented in Figures 1–6, respectively. Table 1 and Figures 1 and 2 show the variation of density with temperature and concentration, respectively. It is reported that density decreases with the increase in temperature and increases with the increase in concentration of polyvinylchloride in the solution. Increase in the density is due to the fact that the number of polymer chains added to solution increases with the increase in concentration of the PVC. As compared to solvents, polymers have large molecular weight that also contributes in the increase in density. The results reported in the present investigation are in good agreement with the results reported by earlier researchers [18, 19]. Viscosity is an important property, and it depends on the molecular size, shape, and intermolecular attraction. The measurement of viscosity provides useful information about solute-solvent and solute-solute interaction. Table 2 and Figures 3 and 4 report the variation of viscosity with temperature and concentration, respectively. It is observed that viscosity decreases with the increase in temperature and increases with the increase in concentration of polyvinylchloride in the solution. The solution becomes more and more viscous as the solute is added; less fluidity thus leads to the increase in viscosity. With the increase in the concentration, the fractional resistance between the layers of the medium increases and that increases viscosity. A similar behavior was made by previous authors [20]. Ultrasonic velocity decreases with the increase in temperature due to weakening of the intermolecular force and increases with the increase in concentration of polyvinylchloride as presented in Table 3 and Figures 5 and 6, respectively. This may be due to the increase in mobility of the molecules which may further increase the cohesion between molecules and thus filling all the available free spaces between it. These trends in the ultrasonic velocity may be due to structural changes taking place in the mixture because of increasing intermolecular forces. A similar trend is observed by earlier authors [21]. Narasimham et al. have concluded the similar results for polyvinylchloride solutions [22]. Table 4 and Figure 7 show that intermolecular free length increases with the increase in temperature and decreases with the increase in concentration of polyvinylchloride as presented in Table 4 and Figure 8. The variation of ultrasonic velocity in solution depends on intermolecular free length. According to the model proposed by Erything and Kincaid [23], ultrasonic velocity is inversely proportional to intermolecular free length and ultrasonic velocity should decrease if the intermolecular free length increases and vice versa. The results reported in present study are in agreement with the proposed model. Variations of adiabatic compressibility with temperature and concentration are shown in Table 5 and Figures 9 and 10, respectively. It is reported that adiabatic compressibility increases with the increase in temperature and decreases with the increase in concentration of polyvinylchloride in solution. This decrease in the value suggests the weakening of molecular interactions in the liquid mixtures. This may be explained in terms of the electrostatic effects of the polymer on the surrounding solvent molecules. The results also indicate that the medium becomes more compressible. The adiabatic compressibility is inversely proportional to the square of velocity; therefore, the trend in the adiabatic compressibility is reverse of the trend of ultrasonic velocity with temperature and concentration. As the velocity increases with concentration and the density does so, the compressibility must decrease with the increase in concentration of PVC. Some earlier workers have also reported similar behavior of adiabatic compressibility [24]. Acoustic impedance is an important property as it is related to elastic properties of the medium. Therefore, its variation with temperature and concentration is studied. Table 6 and Figures 11 and 12 show the variation of acoustic impedance with temperature and concentration. It is found that acoustic impedance decreases with the increase in temperature and increases with the increase in concentration of polyvinylchloride in solution. This is the opposition of the medium to the longitudinal wave motion. Due to the greater interaction among the molecules, there is more opposition that results in the increase in the value. This may be also due to the increase in density and viscosity in solution and also because of the increase in elasticity of the medium. Table 7 and Figures 13 and 14 represent the variation of relaxation time with temperature and concentration, respectively. It is observed from Table 7 and Figure 13 that relaxation time decreases with the increase in temperature and increase with the increase in concentration of polyvinylchloride in the solution (Table 7 and Figure 14). The relaxation time occurs due to the structural relaxation process, and it is presumed that the molecules get rearranged because of the cooperative process. The variation of ultrasonic absorption with temperature and concentration is presented in Table 8 and Figures 15 and 16, respectively. It is clear that ultrasonic absorption decreases with the increase in temperature and increases with the increase in the concentration of polyvinylchloride in the solution. The increase of relaxation time and ultrasonic absorption with concentration can be explained in terms of the motion of macromolecular interchain forces which are influenced by density, viscosity, and ultrasonic velocity.
4. Conclusion
Density, viscosity, and ultrasonic velocity have been measured for polyvinylchloride in dimethylformamide at different concentrations and temperatures. Using these values, different acoustical parameters such as adiabatic compressibility, acoustic impedance, intermolecular free length, relaxation time, and ultrasonic absorption have been calculated. Effects of temperature and concentration have been studied on these parameters that can lead to structural investigation of the medium. The results indicate that there is strong interaction between the polymer and the solvent at a higher concentration. This study is helpful in understanding the behavior of polymer, their production, and uses.
Data Availability
The data used to support finding are included within the article.
Disclosure
This study was performed in the Ultrasonic and Dielectric Laboratory.
Conflicts of Interest
The authors declare that they have no conflicts of interest.