ABSTRACT
This thesis investigates the standard free energy of micellization of sodium dodecyl sulfate (SDS) in aqueous solutions, with and without the presence of monovalent (Na2SO4) and divalent (NiSO4.6H2O) salts, using conductometric analysis at laboratory temperature. The study reveals that the specific conductivity of SDS solutions increases with surfactant concentration, exhibiting two distinct linear regions with varying slopes. The intersection of these lines indicates the Critical Micelle Concentration (CMC) of SDS. The CMC of SDS without adding salts was found to be 0.0079M (7.90mM), while the CMC of SDS in presence of 0.001 M Na2SO4 was 0.00688M (6.88mM) 0.005M Na2SO4 0.00545M(5.45mM) and in presence of 0.001M NiSO4.6H2O was 0.0059M(5.90mM),0.01M NISO4.6H2O was 0.00441M (4.41mM). In the presence of salts, the critical micelle concentration values decreases which are explained on the basic of the nature and ion size of the added ion. The addition of salts results in a notable decrease in the CMC of SDS, with NiSO4 causing a more significant reduction compared to NazSO.Higher salt concentrations lead to a more pronounced decrease in CMC. Additionally, the Gibbs free energy of micellization decreases with higher CMC but increases with increasing salt concentrations. These findings suggest that salts, particularly divalen tones, significantly influence micelle formation by reducing the CMC and altering thethermodynamic parameters of micellization. The results have implications for the optimization of surfactant systems in various industrial and chemical applications.
CHAVTER 1
1. INTRODUCTION
LiGeneral Snzoduetion
Sudium dodecyl suifte (SDS) isa comnonly and gbaly used aninie vurfatant know for is ability o fonn stable vesicles and moelles. t consists of a 12aton slighatie shain witha sulfate group, which makes it effective in various fieds like biotecenology biochemistry, and polymer tecbnology (Zhang, CE Lin, 196) Ir's ceicad formula is CihsNaso, and structural fornula is HCACH)h0-50N The structural fomula represents the molecular structure of Sodiurm Dodecyl Sulfate (SDS) h shows that the lhydrocarbon tail (4CACH)u-) is atached to a sllonate goup (-
Figure 1; Structural formula of SDS
SONat) dhrough an ether linkage (0) Sodium dodecyl sulfate (SDS) is found to exhibit diversified structural characteristics depending on its environment and interactions. In Aqueous micellar solutions, SDS foms spherical micelles with a dÃameter of 6.0 nm at a concentration of 0.91 M, showing s polyınorphous transition phenomenon (Yuri A Mirgorod,Alexander Chekadanov, Tatiana A . Dolenko, 2019)
The molecular weight of sodium dodecyl sulfate (SDS) is approximately 288.38 g/mol. (Hiroyuki Matsumoto, 2019), The CMC of SDS is found to be 8.2mM (P. Mukerjee, Citical Micelle Concentration of Aqueous Surfactant Systems, 1971).
I is considered to be of bigh significance and used in verities of fields like detergents, personal care products, industrial process (Feng, 2023).
This surfactant is estimated to have a market value of S950 million by 2030, after growing at a CAGR of 5.3% during 2024-2030. P'eople these days are inclined towards eco- friendly personal care products, this growing trend highly favors the use of SDS as it is derived from coconut oil, palm kernel oil, or milk. Here, we determine several parameters like pre-micellar, and post-micellar slopes, critical micelle concentration CMC), degree of micellar dissociation (a), standard free energy of micellization (AGO m), the free energy of surfactant tail transfer (AG,trans) of SDS in the presence and absence of salts.
1.2.Surfactants
Surfactants, known as surface active agents, are essential compounds with a significant impact on various industries and everyday consumer products. They exhibit a wide range of capabilities, including the reduction of surface tension in liquids and the improvement of their wetting, spreading, emulsifying, and foaming characteristics. In the realm of textile dyeing, surfactants are utilized to ensure uniform dye penetration into fabrics, as well as to facilitate the blending of insoluble dyes and fragrances in aqueous solutions. Moreover, these compounds find applications in industrial settings such as oil recovery, where they are employed to effectively separate oil from water. Comprising hydrophobic (lipophilic) and hydrophilic (hydrophilic) regions within their molecular structure, surfactants are categorized as amphiphilic molecules, enabling them to interact adeptly with both water-based and oil-based substances. The hydrophilic segment of a surfactant molecule exhibits an affinity for water and is typically characterized by polar or charged groups, whereas the hydrophobic portion repels water and consists of nonpolar or hydrocarbon chains. Typically featuring a lengthy hydrophobic tail and a compact hydrophilic head group, surfactant molecules, when introduced into a water environment, tend to align themselves at the water-air or water-oil interface to diminish surface tension. Consequently, the hydrophilic section interacts with water molecules, while the hydrophobic segment positions itself away from the aqueous environment, leading to the formation of structures like micelles or monolayers. These assemblies play a crucial role in the solubilization or dispersion of hydrophobic substances, such as oil or grease in water (Smriti Mukherjee, 2023).
1.2.1. Classification of Surfactants
Surfactants are categorized based on the charge of the polar head group into four main groups: anionic, cationic, zwitterionic, and nonionic surfactants Anionic surfactants are characterized by a negatively charged hydrophilic head group, with carboxylates, sulfates, and sulfonates being common types. These surfactants are extensively utilized in various cleaning products like detergents, soaps, and shampoos. Examples of anionic surfactants include sodium dodecyl sulfates (SDS) and sodium lauryl ether sulfates (SLES).
Cationic surfactants, on the other hand, feature a positively charged hydrophilic head group, often derived from quaternary ammonium compounds with alkyl or benzyl groups. They find widespread use as disinfectants, fabric softeners, and in hair conditioning products, with cetyltrimethylammonium chloride (CTAC) being a common example.
Nonionic surfactants lack an electrical charge in their hydrophilic head group, making them versatile and suitable for applications requiring low toxicity and effective detergency. These surfactants are present in numerous personal care items, laundry detergents, and industrial cleaners, exemplified by ethoxylated alcohols and polyethylene glycol ethers.
Zwitterionic surfactants, also known as amphoteric surfactants, possess both positively and negatively charged groups in their structure, enabling them to function as either anionic or cationic surfactants depending on the solution's nature. They are commonly found in gentle personal care products like baby shampoos, body washes, and facial cleansers, with Cocamidopropyl betaine being a notable example. (Dahal, 2023)
1.3.Micelle and Critical Micelle Concentration (introduction)
Amphiphiles form molecular aggregation in the solution above a narrow concentration range this aggregation is called a micelle. The narrow concentration range above which micelle are formed is called CMC (Moroi, 2013).
In simple understanding, surfactants are the molecules present at the surface that undergo adsorption at an interface, consequently causing a modification in surface tension. The aqueous solution containing such substances exhibits colloidal properties. When there is increase in concentration, these molecules tend to form aggregates, which are referred to as association colloids or micelles. The concentration threshold at which these micelles come into existence is identified as the critical micelle concentration (CMC).
Typically, the number of surfactant molecules present in these aggregates falls within the range of 50-100, although in certain cases, it could extend up to 1000. Micelles have found extensive application owing to their ability to dissolve highly hydrophobic analytes or influence the selectivity of chromatographic systems. A crucial parameter when dealing concentration beyond which micelles initiate formation Several factors, such as the introduction of electrolytes (Corrin, 1946)buffer pH (CE Lin 1995), temperature (Paridel, 2000), incorporation of organic modifiers (Carey, 1960),presence of additives (CF. Lin, 2001) among others, contribute to variations in this valuecompared to that obtained in pure water. The behavior of micelle formation within aqueous solutions containing surfactants is of notable theoretical interest. Consequently, mumerous researchers have conducted both experimental and theoretical investigations in this domain.
Nevertheless, these examinations have primarily focused on individual surfactants, with only a limited number of studies delving into micelle formation involving surfactant blends Several theoretical models concerning the formation of mixed micelles composed of two types of monovalent soaps have been documented. These models have indicated a reasonable agreement between the calculated CMC values of surfactant mixtures and the corresponding experimental data.
However, when applying these equations to mixed micelles consisting of monovalent and bivalent surfactants, the comparison between theoretical predictions and experimental results becomes challenging due to the complexity of calculating the surface potential. This study aims to theoretically elucidate the formation of mixed micelles between monovalent and bivalent surfactants by refining the equation to incorporate the electrical potential at the charged micelle surface and the hydrophobic interactions between the surfactant's alkyl chain (Ojha, 2022).
1.4.Micelle and CMC (formation)
When micelles form, the properties of a surfactant solution change significantly due to the lower mobility of the aggregated ions or molecules compared to individual ones. Below the Critical Micelle Concentration (CMC), the solution consists of monomers acting as a strong electrolyte, while above CMC, it behaves as a partially ionized system. The conductivity sharply increases in the low concentration region and remains constant after reaching CMC, which can be easily determined as the intersection point of two linear trends. The study of conductivity in ionic surfactants is widely practiced, expecially in relation to the formation of aggregates below the CMC and the extrapolation of micelle properties at varying concentrations (Ojha, 2022).
Surfactants are known for their ability to reduce surface tension in water when added in small quantities. The critical micelle concentration (CMC) can be determined by observing discontinuities in surface tension plots or through conductivity measurements, which depict characteristic patterns. Below the CMC, surfactant molecules are loosely integrated into the water structure, whereas above the CMC, they start forming their structures like aggregates with hydrophobic and hydrophilic sections. The phase behaviour of surfactants can be further diversified with the inclusion of additives or co- surfactants, as seen in a study on SDS aggregation at room temperature with and without Na2SO4 and NiSO4.6H2O using the conductivity method in aqueous medium (Ojha, 2022).
Figure 2: Micelle formation and CMC representation
1.7.Application of SDS
1.7.1. Cleaning
The utilization of cleaning and hygiene SDS is prominent in the realm of detergents utilized for laundry, encompassing a wide array of cleaning applications (Eduard Smulders, 2007). This particular compound serves as a remarkably efficient surfactant, crucial for tasks involving the elimination of oily stains and residues.
Noteworthy is its prevalence in industrial products like engine degreasers, floor cleaners, and car exterior cleaners, where it is present in higher concentrations.
Moreover, it plays a key role in various personal care products such as hand soap, toothpastes, shampoos, shaving creams, and bubble bath formulations due to its foam-producing (lather) and surfactant properties.
1.7.2. Food Additives
Within the domain of Food additives, Sodium dodecyl sulfate, also recognized as sodium lauryl sulfate (SLS), is acknowledged as a generally recognized as safe (GRAS) component for food applications as per the USFDA (21 CFR 172.822). Its functions extend to serving as an emulsifying agent and whipping aid (Igoe, 1983).
For instance, while employed as an emulsifier in conjunction with egg whites, strict regulations outlined in the United States Code of Federal Regulations dictate its maximum permissible concentrations. Additionally, in the preparation of marshmallows as a whipping agent, prescribed limitations on its usage are specified to ensure the proper attributes of the end product, including its effect on sweetness perception (Adams, 1985)
1.7.3. Laboratory applications
SDS finds extensive application in Laboratory procedures ("Sodium Lauryl Sulfate-National Library of Medicine HSDB Database", 2017)particularly in the context of lysing cells during RNA or DNA extraction, and in denaturing proteins as a precursor to electrophoresis in the sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) technique. Its mechanism involves disrupting non-covalent bonds within proteins, thereby inducing denaturation, which alters the conformation and shapes of protein molecules. The binding affinity of proteins to SDS is such that one molecule binds to every 2 amino acid residues, resulting in a uniform net negative charge across all proteins, facilitating consistent charge-to-mass ratios (Janson LW,2 012) Consequently, the differential mobility of polypeptide chains within the gel primarily reflects their length rather than their native charge or shape, simplifying the analysis of protein molecules by size-based separation post-denaturation with SDS(Ninfa A, 2009)
1.7.4. Pharma applications
In pharmaceutical realms, Sodium lauryl sulfate serves as an ionic solubilizer and emulsifier, lending itself to a wide array of applications encompassing liquid dispersions, solutions, emulsions, tablets, foams, and semi-solids such as creams, lotions, and gels (pharmaceutical.basf.com., 2021).Furthermore, SLS is harnessed for lubrication purposes during the manufacturing process. Notable brand names associated with pharmaceutical-grade SLS include Kolliphor SLS and Kolliphor SLS Fine (SLS, 2021).
1.7.5. Niche Uses
Sodium lauryl sulfate has niche applications as an efficacious topical microbicide, particularly for intravaginal administration, aimed at inhibiting and potentially averting infections caused by a variety of enveloped and non-enveloped viruses like the herpes simplex viruses, HIV, and the Semliki Forest virus (Piret J., 2002). When SDS is dispersed in water, it can create liquid membranes that function as effective particle separators (Birgitt Boschitsch Stogin, 2018). This mechanism operates akin to a reverse filter, permitting the passage of large particles while entrapping the smaller ones.
1.8.Rationale
The critical micelle concentration [CMC] is a fundamental property of surfactants that holds significant importance. In a laboratory setting, the CMC of sodium dodecyl sulfate [SDS] in an aqueous solution was determined, along with the impact of Na2S04, NiS04, and A12S04 on the CMC of SDS, employing a conductivity meter. Among various methodologies, conductivity measurement is highlighted as the most direct approach to determining the CMC, mainly due to its simple implementation in a laboratory setting. To determine the critical micelle concentration of SDS accurately, it is essential to observe variations in concentration alongside conductance. Consequently, solutions containing 0.05M SDS in pure water, and 0.001M and 0.005M of Na2S04 and NiS04.6H2O respectively were prepared. The data collected from the conductivity meter experiment will be graphed against concentration using suitable plotting software, and the critical micelle concentration will be determined by solving a set of equations. The point of intersection on the graph signifies the critical micelle concentration (CMC) of the system. A comparison between the CMC of SDS with and without the addition of Na Sos and NiSo4.6H₂O salts was conducted within the laboratory setting
1.9.Objectives
1.9.1. General Objectives
i.To determine the critical micelle concentration of sodium dodecyl sulfate sulfate [SDS] in an aqueous solution
ii. To conductometrically determine the CMC of SDS in the presence of Na2SO4, and NISO4.6H2O
iii. To conduct a comparative analysis of the impact on the CMC values of SDS in the absence and presence of Na and Ni salts (sulfate salts) conductometrically.
1.9.2. Specific Aims
i. To investigate the Gibbs free energy change of the given surfactant in presence and absence of salts.
ii. To compare and contrast differences in free energy with concentration of salts.
1.9.3. Limitations
i.Scope of Salts Tested: The study primarily focuses on the effects of specific salts, namely Na2SO4 and NiSO4.6H2O on the critical micelle concentration (CMC) of SDS. This limited selection may not fully represent the diverse range of ionic interactions that could occur with other salts or surfactants, potentially affecting the generalizability of the findings.
ii. Conductivity Measurement Limitations: While conductivity measurement is highlighted as a direct method for determining CMC, it may not capture all nuances of micellization behavior, especially in complex systems. Factors such as temperature fluctuations, impurities in the solution, or variations in ionic strength could influence conductivity readings and, consequently, the accuracy of CMC determination.
iii. Laboratory Conditions: The experiments were conducted under controlled laboratory conditions, which may not accurately reflect real-world scenarios. Variations in environmental factors such as temperature, pressure, and concentration gradients in practical applications could lead to different micellization behaviors than those observed in the study.
iv. Electrostatic Interactions: The study mentions that surfactant counterions can impact micelle formation through electrostatic interactions. However, the investigation may not have fully explored the complexities of these interactions, particularly in systems with varying ionic strengths or in the presence of multiple surfactants.
v. Focus on Free Energy: The primary aim of the study is to compare free energy differences with salt concentration. While this is a valuable aspect, it may overlook other important thermodynamic parameters that could provide a more comprehensive understanding of micellization processes.
CHAPTER 2
2. LITERATURE REVIEW
2.1. Background
Micelle formation plays a pivotal role in aqueous surfactant systems, as emphasized in various experimental and theoretical studies conducted by multiple researchers. Yet, the main concentration of these studies has predominantly been on individual surfactants,with only a limited number of researchers looking into micelle formation in surfactant mixtures. (P. Mukerjee, Critical Micelle Concentration of Aqueous Surfactant Systems,1971) (Shinozuka, 1979), a comprehensive review of electrochemical methods for determining the critical micelle concentration (CMC) is yet to be published. Previous studies have compiled CMC values of surfactants in critical tables (P. Mukerjee, Critical Micelle Concentration of Aqueous Surfactant Systems, 1971), (Rosen, 1989) (van Os, 1993) Recent studies conducted by Dubin propose that the presence of surfactant counterions could potentially impact the formation of micelles through electrostatic interactions, leading to an elevated quantity of micelles per chain at higher levels of ionic strength. A recent review (Patist, 2002) on CMC determination highlighted various methods(about 13) but only one method, namely conductivity measurement belongs to the electrochemical nature.
2.2. Description of process
The determination of the critical micelle concentration (CMC) of sodium dodecyl sulfate (SDS) in aqueous solutions, along with the influence of Na2S04 and NiS04 on this CMC, was conducted using a conductometric method. Initially, the conductivity of a 0.05M SDS solution in distilled water was measured at 25°C. Subsequently, the experiment involved the incremental addition of 2 mL of distilled water to the SDS solution, with the corresponding decrease in conductivity recorded to observe the dilution effect.
Following this, the conductance measurements were repeated with the addition of 2 mL of 0.001 M Na2S04,0.005 M Na2S04 and similar readings were taken, totalling around 35 measurements at the same temperature. The procedure was then replicated using 0.001M NiS04,0.005 NiSo4 allowing for the assessment of how these salts affected the conductance of the SDS solution through the conductivity meter.
2.3. Various Methods of Finding CMC
tensiometry), electrochemical (e.g., conductimetry), optical (dynamic light scattering), or spectroscopic (e.g., fluorescence or ultrasonic spectroscopy) techniques (Dominguez,
Fernandez, Gonzalez, Iglesias, & Montenegro, 1997). Most of the physicochemical property changes can be used for the determination of the CMC, provided the measurements of particular properties can be carried out accurately. The selection of a method to determine the CMC of a surfactant depends on the structure and properties of the surfactant and the equipment availability in the experimenter's laboratory. The use of different methods may permit to obtain the complementary and comparative results. This paper presents the determination of the CMC of SDS in aqueous solution and the presence
of Na2S04 and NiS04 conductometrically. The methods for CMC determination are based
on employing one of both characteristic micelle-forming compound properties: changing
of properties of interfaces, or formation of micelles. There are a large number of methods
that have been applied for the CMC determination. These methods can be generally
divided into two classes:
i. Direct measurements, when a change of some property of the solution of micelle-
forming compound with its increasing concentration is observed. Change of slope
or discontinuity of property-concentration dependence gives the CMC value. The methods of direct CMC measurements are, e.g., surface tension, electrical conductivity, osmotic pressure, refractive index, and viscosity.
ii. Indirect measurements, when a change of some property of another substance (the
probe), present in the solution of micelle-forming compound, with increasing concentration of the compound is observed. The voltammetric and spectrometric methods are the typical methods used for indirect CMC determination.
CHAPTER 3
3. MATERIALS AND METHODS
3.1.Materials
The determination of the conductance of sodium dodecyl sulfate (SDS) in the presence and absence of salts such as NazSos and NiSo .6H10 in an aqueous medium was conducted through a process of conductometry in the laboratory. The essential components for determining the Critical Micelle Concentration (CMC) are a conductivity meter, cotton, beaker, pipette, measuring cylinder, sodium dodecyl sulfate, sodium sulphate, nickel sulphate, potassium chloride and distilled water. The measurement ofconductance was performed using a Digital conductivity meter model ME-976 at a frequency of 2000 Hz with a cell constant of 1.0cm. The calibration of the cell was performed by the technique developed by Lind and his associates, employing a potassium chloride solution. Multiple distinct solutions were prepared and analyzed to verify the reproducibility of the obtained results. The sodium dodecyl sulfate (SDS) was acquired from Merck Life Science Private Limited in Mumbai, India, while Nickel sulphate was obtained from Galaxo8mithKline Pharmaceuticals, Mumbai, India. Sodium sulphate was purchased from Thermo Fisher Scientific India Pvt. Ltd. in Mumbai, India. The water used in the experiments was doubly distilled. The solution was prepared at room
temperature.
3.2.Methods
The CMC of sodium dodecyl sulfate in aqueous solution and the effect of Na:SO, and NiSO4.6H2O was determined conductometrically. It started with the sodium dodecyl sulfate of 0.05M which was prepared by dissolving 1.442gm of SDS in 100mL of water. The sample was incubated overnight. Approximately, 30mL of SDS was placed in one beaker, while around 100mL of distilled water was placed in another. The calibration of the conductivity meter was conducted at a temperature of 25°C, followed by the measurement of the conductance of SDS. Successively, 2mL of SDS was extracted and2mL of distilled water was introduced, with the conductivity being recorded in both SDS
and the aqueous solution. Subsequently, solutions of 0.001M and 0.005M Na2SO4 along with 0.05M SDS were prepared in 100 mL of distilled water. 2mL of the resulting mixture was withdrawn, and 2mL of Na2SO4 was added to the beaker, with the conductance being measured after each addition. Likewise, a solution of 0.001 M and 0.005M Nickel sulphate heptahydrate and 0.05M SDS was prepared. 30mL of the blend was utilized for conductivity measurement; 2mL of the mixture was extracted, and 2mL of NiSO4.6H₂O was added incrementally, with the conductance being monitored. A total of 35 readings were recorded and finally, specific conductance was found. The CMC was calculated
using a curve plot. This value of CMC, Post Micellar value and Pre Micellar value helped
in calculating of dissociation constant(a),XCMC while they are used in calculating
standard free energy.
1.3. Electrochemical methods for the CMC determination
The determination of CMC is generally based on the localization of the position of a breaking point in the concentration dependencies of selected physical or chemical properties of surfactant solutions. Because of the surface activity of these substances, measurements of the surface tension of surfactant solutions represent the principal method of CMC determination. However, it is a rather tedious and time-consuming
procedure.
In the case of ionic surfactants, the utilization of electrochemical measurements is much more convenient, especially the measurements of the electrical conductivity of their solutions with varying. The conductometric method is based on the finding of a breaking point on the curves, which describes the concentration dependence of conductivity. It is well-known, that the conductivity of any solution is directly proportional to the concentration of its ions.
CHAPTER 4
RESULTS AND DISCUSSIONS
When the conductivity of solutions is assessed with increasing surfactant concentration, the plots of specific conductivity against surfactant concentration exhibit two distinct straight lines characterized by varying slopes. The commencement of micelle formation at higher surfactant concentrations leads to a change in slope as the conductivity escalates in a divergent fashion. The point of intersection between these two straight lines is identified as the Critical Micelle Concentration (CMC) of the surfactant. The relationship between the conductivity of a solution and the concentration of its ions is linear. The initiation of micelle formation is pinpointed on the concentration-dependent specific conductivity (k) curve as a pivotal breaking point. This breaking point signifies the CMC of the surfactant. The determination of CMC involves the generation of graphs through auser-friendly plotting program, with the CMC values derived from the solution of two
equations.
Figure 11 shows specific conductance vs concentration plots of SDS in the presence of
0.001 M Na2SO4. The CMC was found to be 6.876mM. Here, Gibbs Free Energy was
-39.492KJ/Mole.
0.005 M Na2SO4. The CMC was found to be 5.45mM. Here, Gibbs Free Energy was
calculated as -37.14650KJ/Mole.
Figure 13 shows specific conductance vs concentration plots of SDS in the presence of
0.001 M NISO4.6H2O.The CMC was found to be 5.9 mM. Here, Gibbs Free Energy was
calculated as -42.412KJ/Mole.
Figure 14 shows specific conductance vs concentration plots of SDS in the presence of
01 Ni506H2O. The CMC was found to be 4.4088mM. Here, Gibbs Free Energy was
iculated as -38.058 KJ/Mole..
Figure 15 shows the comparison of CMC of SDS in presence and absence of NiSO4
6H2O at different concentration.
CHAPTER 5
5. CONCLUSIONS AND RESULTS
5.1.Conclusion
The determination of the critical micelle concentration (CMC) of sodium dodecyl sulfate(SDS) in an aqueous solution and the impact of Na,SO, and NiSO, 60 on the CMC of SDS were conducted through a conductometric method in the laboratory Findings revealed a reduction in the CMC of sodium dodecyl sulfate upon the addition of salte The decrease in CMC after the addition of salt (specifically Na SO, and NiSO, 61.0) is linked to the presence of counter ions among surfactant molecules or ions. An observable discontinuity in the conductivity-concentration curve was noted. When NiSO. 610 is present, the decrease in the CMC of sodium dodecyl sulfate is more pronounced
compared to the effect of Na2SO4. Likewise, the fall of CMC is more in the case of high
concentration than that of low concentration salts. On the other hand, the Gibbs free
energy falls with the rise of CMC. Thus, high-concentration salts have descending CMC
but ascending Gibbs free energy.
5.2.Suggestions for future work
The results provide good information about the CMC of a surfactant in an aqueous solution and the effect of CMC on the addition of Na2SO4 and NiSO4.6H.O salts used in this method can also be replaced by other salts like ZnSO4, MgSO, etc. The CMC of trivalent salts can also be determined by this method.REFERENCES
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