INTRODUCTION
Surfactants play a very crucial role in our daily used products and in research fields1. The last decade has seen the extension of cationic surfactant application to high technology areas such as electronic printing, magnetic recording, biotechnology and microelectronics2,3. The solution properties of nonionic surfactants and polymers alone and mixture has been extensively studied4,5.
The study of binary and ternary liquid systems comprising surfactants and polymers has garnered significant interest due to their diverse industrial applications, ranging from pharmaceuticals to enhanced oil recovery.
The physicochemical studies of polymer-surfactant solution have created much interest regarding their industrial importance6,7.
Triton-X-100, a widely-used nonionic surfactant, exhibits complex behavior when mixed with water-soluble polymers like polyacrylic acid (PAA). Understanding the interactions within such systems is crucial for optimizing their performance in various applications. In this article, we studied the interactions properties of aqueous solutions containing Triton-X-100, a commonly used nonionic surfactant, in conjunction with polyacrylic acid (PAA), a water-soluble polymer. By employing experimental techniques to measure density, viscosity, and ultrasonic velocity across varying concentrations and temperatures, we aim to unravel the intricate interplay between Triton-X-100 and PAA molecules.
MATERIALS AND METHODS:
Materials:
Nonionic surfactant Triton-X-100 was purchased from Loba Chemie, India. The Additive used is water soluble polymer Polyacrylic acid (PAA) (Mol. Wt. 50,000) was purchase from Otto Chemica India. Doubly distilled water was used for preparation of all solutions. Triton-X-100 solutions were prepared in 30% ethanol.
Surfactant-Triton-X-100-
Additive-PAA-
Methods:
Ultrasonic Velocity Measurement:
The ultrasonic velocity measurement is useful in understanding interaction between surfactant-polymer systems and provides the information of micelle in solution8. The interferometer cell was filled with the solution under test and connected to output terminals of the high frequency generator through the shielded cable. Water was circulated around the measuring cell from a thermostat to maintain require temperature. When the solution in cell attains the temperature of bath, the micrometer screw was slowly moved till the anode current meter showed at maximum. The frequency ‘f’ of the crystal is accurately known. Here the frequency of the crystal is 2 MHz, the ultrasound velocity (U) was calculated by using formula: U= λ x f
The various physical parameters calculated from the measured values of density (ρ), viscosity (η) and ultrasound velocity (U) using the standard formula9,10.
Adiabatic Compressibility (βad) = 1/ρU2
Intermolecular free length (Lf) = K (βad) ½
Molar
Sound Velocity (Rm) = (
/ρ)
U 1/3
Specific Acoustic Impedance (Z) = (ρU)
Molar
Volume (Vm) =
/ρ)
Surface Tension (γ) = (U 3/2) (6.3 x 10-4) ρ
Where
U is the ultrasonic velocity, ρ is the density; K is the Jacobson’s
temperature depended constant [(84.875+0.375T) x 10-8], is the
effective molecular weight and can be calculated using relation.
= X1M1+
X2M2
Where M1 and M2 are molecular weights and X1 and X2 are the mole fractions of component-1 additive and component-2 surfactant solution as solvent.
RESULT AND DISCUSSION:
Density Measurement:
The densities of Triton-X-100 (0.0155%) were assessed at various temperatures (Table 1). It was noted that within a specific concentration of solution, density decreases with rising temperature, because on increasing temperature, kinetic energy of particles, thermal agitation, and volume of solution increases11.
The densities of Triton-X-100 (0.0155%) exhibit an upward trend with the increase in concentration of PAA and decreases with increasing temperature (Table 2 a and b). Such density increments signify enhanced solvent-solvent and solute-solvent interactions, potentially stemming from volume contraction induced by the presence of solute molecules. The fluctuations in densities can be elucidated through the co-sphere overlap model. Here, the overlapping of hydration co-spheres between hydrophobic-hydrophobic and ion-hydrophobic groups leads to a net reduction in volume. Conversely, interactions involving ion-hydrophilic and hydrophilic-hydrophilic groups contribute to volume expansion12-16.
Viscosity Measurement:
It was noted that as temperatures increases, the viscosity of Triton-X-100 (0.0155% w/v) decreases. Furthermore, viscosity measurements were conducted on Triton-X-100 (0.0155%) in the presence of polymer PAA across diverse concentrations and temperatures. Remarkably, the viscosity of Triton-X-100 increases with increasing PAA concentration but declines with increasing temperatures (Table 3). The increase in viscosity with increase in concentration of PAA indicates the increase in cohesiveness present in the solute-solvent molecules17. The rise in viscosity attributed to stronger hydrophilic-hydrophobic interactions in aqueous media. The hydrophobic segments of surfactant congregate forming hydrophobic domain. These domains serve as intermolecular cross links which boosting viscosity.
Ultrasonic Velocity of Triton-X-100 (0.0155% w/v):
The data indicates that, according to Table 1, for the Triton-X-100 system, as temperature increases, density, adiabatic compressibility, and intermolecular free length decreases, consequently leading to increases in ultrasonic velocities, acoustic impedance, molar volumes, molar sound velocities, and surface tension. The rise in ultrasonic velocities with increasing temperature is attributed to structural reorganization resulting from hydration18,19.
Ultrasonic Velocity of Triton-X-100 and PAA Mixed System:
This study investigates the ultrasonic velocity measurement of Triton-X-100 and polyacrylic acid (PAA) mixed systems, with the concentration of Triton-X-100 maintained at its critical micelle concentration (CMC) while varying the concentration of PAA additive and temperature of mixed system (Table 2 a and b). Measurements were conducted at temperatures of 298.15 K, 303.15 K, 308.15 K, and 313.15 K to explore the effects of temperature on the physical interactions within the system. On experimental analysis it was noted that, density (ρ), adiabatic compressibility (βad) and intermolecular free length (Lf) decreased with increasing temperatures, while ultrasonic velocities (U), specific acoustic impedance (Z), molar volumes (Vm), and molar sound velocities (Rm) demonstrated an upward trend. Additionally, at particular temperature, the ultrasonic velocities displayed a non-linear relationship with PAA concentration, reaching a peak at 0.03% PAA concentration. This indicates complete dissolution of Triton-X-100 and making the medium more and clearer. The ultrasonic velocity then decreases with increase in concentration of PAA, the hydrophobic potion of surfactant may associate to form micelle rods. Formation of such rods may interfere with ultrasonic velocity. Hence ultrasonic velocity decreases with increase in concentration of PAA. These findings contribute to a deeper understanding of the thermodynamic and acoustic behavior of Triton-X-100/PAA mixed systems, providing insights into their physical interactions under varying conditions.
In the data provided in Table 2(a) and Table 2(b), concerning the nonionic surfactant-PAA mixed system, it is observed that the ultrasonic velocity exhibits an upward trend with increasing temperature. But at a fixed temperature, there is a rise in ultrasonic velocities, followed by a subsequent decline with increasing concentrations of PAA. Notably, at a PAA concentration of 0.03%, the ultrasonic velocities reach their maximum value due to structural rearrangement induced by hydration20,21. Additionally, this phenomenon may be attributed to alterations in overall free energy and changes in micelle shape from spherical to cylindrical/rod-like structures and that interfere the propagation of ultrasonic waves. The peak ultrasonic velocity corresponds to the aggregation of monomers into micelles. The subsequent decrease in velocity could be linked to a transition in micelle shape from cylindrical/rod-like to spherical configurations. This intriguing observation is closely associated with the well-established interpolymeric association reactions occurring between polyethylene oxide and polycarboxylic acids.
The variation of sound velocity with concentration of surfactant is given by the relation.
dU/dc = - (U/2) [(1/ρ) (dρ/dc) + (1/ βad) (dβad / dc)]
According to the Eyring and Kincaid model of sound wave propagation, the intermolecular free length decreases as the ultrasonic velocity value increases22,223. This concept is reinforced by the anticipated decrease in βad with higher concentrations of surfactant, indicating potential interactions between the solute and solvent. As ultrasonic velocity increases, the intermolecular free length (Lf) and adiabatic compressibility (βad) decrease, and vice versa. This inverse relationship aligns with the Eyring and Kincaid model. The decrease in Lf and βad values with increase in ultrasonic velocity suggests substantial interaction between PAA and the surfactant, influencing the structural arrangement within the solution mixture, indicative of strong solute-solvent interactions and less closely packed molecules. The variation of βad reveals insights: minimal compressibility enhances bond strength, while maximal compressibility signifies weaker bond strength between molecules. The increase in βad values, attributed to the removal of solvent molecules around ions, supports weak interactions. Furthermore, βad values decrease with increasing concentrations of PAA, further emphasizing the intricate interplay between the components in the solution mixture. The increase in specific acoustic impedance (Z) with increase in concentration and temperature are an indicative of the increase in intermolecular forces with the addition of PAA with surfactant because of aggregation of solvent molecules around solute, which induces strong solute-solvent interaction24. Further, the higher value of specific acoustic impedance (Z) confirms the stronger interaction between the PAA and surfactant.