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CMC (Critical Micelle Concentration) Study of Some Detergents with or Without Electrolyte and Calculation of Thermodynamic Parameters Using Conductivity Method at Different Temperatures
Ashoke Hazra*
A.K.P.C. Mahavidyalaya, Bengai, Hooghly, West Bengal, India.
Corresponding Author E-mail: hazra.ashoke@gmail.com
Article Publishing History
Article Received on : 03 Apr 2024
Article Accepted on : 13 Jul 2024
Article Published : 25 Jul 2024
Present study determines the Critical Micelle Concentration (CMC) of some market available detergents at different temperatures in aqueous solutions. For this study we use Sunlight Surf and Safed Surf. Sodium Acetate electrolyte was used. Conductance data was taken at different temperatures (150C, 250C, 350C). From this study it was observed that with increase in temperature, cmc value decreases. Addition of electrolyte with surfactants (detergent), decrease cmc value which support our basic concept of surface chemistry. Different thermodynamic parameters like, ΔG, ΔH, ΔS were calculated and also supporting the formation of cmc.
KEYWORDS:CMC; Electrolyte; Surfactant; Temperature; Thermodynamic Parameters
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Copy the following to cite this article:Hazra A. CMC (Critical Micelle Concentration) Study of Some Detergents with or Without Electrolyte and Calculation of Thermodynamic Parameters Using Conductivity Method at Different Temperatures. Orient J Chem 2024;40(4).
Hazra A. CMC (Critical Micelle Concentration) Study of Some Detergents with or Without Electrolyte and Calculation of Thermodynamic Parameters Using Conductivity Method at Different Temperatures. Orient J Chem 2024;40(4). Available from: https://bit.ly/4daQnr6
Introduction
In surface and colloidal chemistry, CMC is defined as the concentration of surfactants above which micelles form. All surfactants show a characteristic properties i.e, CMC (Critical Micelle Concentration). Surface tension changes strongly with concentration before CMC and after reaching the CMC point, surface tension mostly constant. The value of CMC depends of different parameters like, temperature, pressure, electrolyte etc.
Many researchers studied about the CMC of surfactants many years ago [ 1-5 ] and the effect of different parameters on CMC of surfactants [ 6-9 ]. Thermodynamic parameters studied on CMC of surfactants have been done by many researchers [10-12 ].
Our aim to study on cmc of some daily usable detergents (surfactants) like, Sunlight, Safed (Market available in West Bengal) at different temperatures and effect of electrolyte for the determination of surfactants. Some thermodynamic parameters also studied. We used conductance method [ 13-17 ] for the determination of CMC (Critical Micelle Concentration).
Experimental
Materials and Apparatus
Conductivity meter for cmc measurement of different detergents (Elico 183 EC-TDS Analyser), Conductivity Electrode, Temperature Control Bath (CTT Instruments, Kolkata), Thermostat, Magnetic Stirrer etc.
Chemicals
Sodium Acetate (BDH Chemicals Ltd, England), KCl (EMerc, Mumbai), Sunlight and Safed Surf (West Bengal Market) and Deionized water.
Determination of Critical Micelle Concentration
Conductivity measurement
Conductance of detergent solution was measured by a digital conductivity meter connected with a conductivity cell. The cell constant was determined by measuring the conductance of standard KCl solution using the relation:
Specific Conductance = Observed Conductance x Cell Constant
The value of cell constant was obtained from observed conductance and specific conductance of a standard solution of 0.1 M KCl solution. CMC value of detergents was obtained from the break point of the plot of specific conductance Vs Concentration of detergent concentration.
Equivalent conductance at infinite dilution
The equivalent conductance at infinite dilution was determined from the molar conductance of the studied detergent solution at 298 K to 308 K.
Ʌ = (1000 x k)/C
Where, k= specific conductance (Scm-1), C = Normality of solution (gm. Equiv.cm-1).
Equivalent conductance at infinite dilution was measured by using Onsagar equation:
Ʌ = Ʌ0 – (AɅ0 + B) C1/2
Where A and B are constants.
Result and Discussions
Table 1 shows that the cmc (critical micelle concentration) of different detergent (surfactant) system at different temperatures from 288K to 308K. Here we have seen that for Sunlight + H2O system, cmc decrease with increase in temperature. With addition of Sodium Acetate (electrolyte) cmc also decreases with increase in temperature. This experiment was also carried out for (Safed + H2O) system. Here also cmc decreases with increase in temperature. For (Sunlight + NaOAc) system, cmc changes for all temperatures. But for (Safed + NaOAc) system cmc shows only at 308K, at lower temperatures cmc does not arises, i.e, the curve is parallel to concentration axis.
Table 1: CMC value at different temperatures of different detergents
Sl. No
System
CMC value
288K
298K
308K
1.
Sunlight + H2O
0.075
0.070
0.050
2.
Sunlight + 0.1 M NaOAc
0.150
0.120
0.100
3.
Safed + H2O
0.120
0.100
0.070
4.
Safed + 0.1 M NaOAc
0.100
–
–
Table 2 shows equivalent conductance at infinite dilution value (Ʌ0) with different temperatures. We get the Ʌ0 value from the plot of Ʌ Vs. √C of different detergent systems at different temperatures. With increase in temperature, Ʌ0 value increases for all cases. Here we see that more Ʌ0 value changes for (Safed + NaOAc) system at higher temperatures.
Table 2 : Ʌ0 value at different temperatures of different detergents.
Sl No.
System
Equivalent conductance at infinite dilution(Ʌ0)
288K
298K
308K
1.
Sunlight + H2O
475.60
496.00
525.20
2.
Sunlight + 0.1 M NaOAc
491.00
498.30
517.80
3.
Safed + H2O
484.70
485.90
495.70
4.
Safed + 0.1 M NaOAc
493.20
497.80
556.20
Table 3 shows the data of lnCMC at different temperatures of different detergent systems which helps us to calculate the thermodynamic parameters of micellization process.
Table 3: Data of lnCMC values of different detergent systems at different temperatures
Sl No.
System
lnCMC
288K
298K
308K
1.
Sunlight + H2O
-2.59
-2.65
-2.99
2.
Sunlight + 0.1 M NaOAc
-1.89
-2.12
-2.30
3.
Safed + H2O
-2.12
-2.30
-2.65
4.
Safed + 0.1 M NaOAc
-2.30
–
–
Table 4: Thermodynamic parameters of different detergent systems in different temperatures
Sl No.
System
Temperature
Thermodynamic parameters
∆H(kJ/mole)
∆G(kJ/mole)
∆S(kJ/mole)
1.
Sunlight + H2O
288K
800
-15.89
2.83
298K
-16.64
2.74
308K
-17.95
2.65
2.
Sunlight + 0.1 M NaOAc
288K
900
-14.16
3.17
298K
-15.27
3.07
308K
-16.18
2.97
3.
Safed + H2O
288K
1250
-14.76
4.39
298K
-15.65
4.24
308K
-17.22
4.11
4.
Safed + 0.1M NaOAc
–
–
–
Table 4 shows the thermodynamic data of the different detergent systems at different temperatures. The positive value of ∆H for micellization increases from Sunlight water system to Safed water system. We know that the positive value of ∆H means, the micellization process is endothermic in nature.
Negative vale of ∆G for micellization means the formation of cmc of all these detergent systems are spontaneous in nature. For these detergent systems, ∆S value for micellization is higher at lower temperature, i.e, disorder ness decreases from lower to higher temperatures which indicate the cmc value decreases from lower to higher temperatures.
Fig.1 to Fig.4 show the plot of specific conductance Vs. concentration value of different detergent systems. Break point of this curve indicates the cmc value of the system. With increase in temperature, cmc value decreases which support our basic concept of surface chemistry. This is due to the hydrophobicity and the dehydration of monomer occurs.
For the system (Safed + NaOAc) system, prominent cmc value found at 308K, but at 288K and 298K curve is parallel to concentration axis which shows that there was no break point, i.e, no cmc value.
Fig.5 to Fig.7 show the plot of lnCMC Vs. 1/T of the different detergent systems with different temperatures which helps to calculate thermodynamic parameters for micellization.
From the plo of logXcmc Vs. 1/T plot, we get the value of ∆H for different detergent systems with different temperatures.
Fig.8 to Fig.10 shows the plot of Free energy changes in micellization Vs. temperatures of different detergent systems. This plot helps us to understand the stabilization of cmc at different temperatures.
Firg.11 to Fig.13 shows the plot of Entropy change in micellization process Vs. Temperatures of different detergent systems. Change of entropy increase at lower temperature and decreases at higher temperatures i.e, cmc value decreases.
Sodium acetate can influence the solubility of detergents in water at different temperatures. At lower temperatures, the solubility of both sodium acetate and detergents may decrease. However, as temperature increases, the solubility of both compounds tends to increase. This increased solubility can affect the overall concentration of detergent molecules available for micelle formation.
Sodium acetate, being a salt, can increase the ionic strength of the solution. This increase in ionic strength can have an effect on the electrostatic interactions between detergent molecules, affecting their tendency to aggregate and form micelles. Generally, an increase in ionic strength can lead to a decrease in CMC, as higher ionic strength screens the electrostatic repulsions between charged detergent molecules, promoting micelle formation.
Sodium acetate can also affect the hydrophobic interactions between detergent molecules. As temperature increases, the thermal energy of the system increases, leading to greater molecular motion and disruption of hydrophobic interactions. This disruption may lead to a decrease in CMC at higher temperatures, as detergent molecules become more prone to forming micelles to minimize exposure of their hydrophobic tails to water.
Overall, the effects of sodium acetate on detergents and their CMC at different temperatures can be complex and depend on factors such as solubility, ionic strength, hydrophobic interactions, and pH. Experimental investigation would be necessary to fully understand the specific effects in a given detergent system.
Sodium acetate can affect the formation of critical micelle concentration (CMC) in detergents due to its influence on the solution properties, including temperature-dependent effects. Let’s explore how sodium acetate may impact the CMC of detergents over the temperature range of 15 to 35 degrees Celsius:
Sodium acetate is a salt, and salts like sodium acetate can influence the solubility of surfactants and the formation of micelles in solution. At low concentrations, sodium acetate may have a salting-out effect, which decreases the solubility of the detergent molecules.
The salting-out effect can lead to an increase in the CMC of detergents, meaning that higher concentrations of surfactants are required to form micelles in the presence of sodium acetate.
Temperature plays a crucial role in the behavior of surfactants and the formation of micelles. Generally, as temperature increases, the kinetic energy of molecules increases, promoting micelle formation.
At lower temperatures (15-25 degrees Celsius), the kinetic energy of molecules is lower, which may hinder micelle formation. In this temperature range, the presence of sodium acetate could exacerbate the salting-out effect, further increasing the CMC of detergents.
Conversely, at higher temperatures (25-35 degrees Celsius), the kinetic energy is higher, which facilitates micelle formation. In this range, the impact of sodium acetate on the CMC may be less pronounced due to the increased kinetic energy overcoming the salting-out effect to some extent.
The combined effect of sodium acetate and temperature on the CMC of detergents will depend on their relative influences.
At lower temperatures (e.g., 15°C), the influence of sodium acetate on the ionic strength may dominate, leading to a decrease in the CMC of detergents due to increased ionic strength.
At higher temperatures (e.g., 35°C), the effect of temperature on micelle formation may be more significant, potentially outweighing the influence of sodium acetate on the ionic strength. In this case, the CMC of detergents may decrease primarily due to the increase in temperature, with less pronounced effects from sodium acetate.
Conclusion
From this study it was observed that with increase in temperature, cmc value decreases. Addition of electrolyte with surfactants (detergent), decrease cmc value which support our basic concept of surface chemistry. Different thermodynamic parameters like, ΔG, ΔH, ΔS were calculated and also supporting the formation of cmc. From this study the stability of the CMC formation (Sunlight+H2O) < (Sunlight + NaOAc)< (Safed + H2O). All the thermodynamic parameters i.e, ΔH, ΔG, ΔS increased in case of (Safed + H2O) system. At lower temperatures (e.g., 15°C), the influence of sodium acetate on the ionic strength may dominate, leading to a decrease in the CMC of detergents due to increased ionic strength. At higher temperatures (e.g., 35°C), the effect of temperature on micelle formation may be more significant, potentially outweighing the influence of sodium acetate on the ionic strength. In this case, the CMC of detergents may decrease primarily due to the increase in temperature, with less pronounced effects from sodium acetate.
Acknowledgement
Author is thankful to the Department of Chemistry, A.K.P.C. Mahavidyalaya for all necessary supports and also thankful to Arnab Hazra , 1st Year Mechanical Engineering student of NIT Durgapur, West Bengal for drawing necessary plots.
References
Chen, L. J.; Lin,S. Y.; Chern, C. S.; Wu, S. C. , Physicochemical and Engineering Aspects,1997, 122(1-3),161–168.
This work is licensed under a Creative Commons Attribution 4.0 International License.
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