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BIBECHANA 
A Multidisciplinary Journal of Science, Technology and Mathematics 

ISSN 2091-0762 (online) 

Journal homepage: http://nepjol.info/index.php/BIBECHANA 

 
 

Investigation on solution properties of surfactants in mixed solvent 
media: Landmark towards Surface Chemistry in Eastern Nepal 

 
Ajaya Bhattarai 

Department of Chemistry, M.M.A.M.C., Tribhuvan University, Biratnagar, Nepal 
* E-mail: bkajaya@yahoo.com 

 

Accepted for publication: February 16, 2014 
 

Abstract 
Surfactants are amphiphilic molecules having a hydrophilic or water soluble moiety (head group) and a 
hydrophobic, or water insoluble moiety (tail group). Surfactants are not only related to soaps and detergents, they 
are also in heavy demand for industrial processes requiring colloid stability, metal treatments, mineral flotation, 
pesticides, oil production, pharmaceutical formulation, emulsion polymerization, particle growth and many more. 
That is why surfactants have been and continue to be a very active area of scientific research and commercial growth 
for several decades. One interesting property of surfactants is that at low concentrations, they exist solely as 
monomers. The formation of micelles, begins at a specific surfactant concentration termed the critical micelle 
concentration (cmc), where the physical properties of the solution, such as interfacial tension, electrical 
conductivity, and light scattering behaviour, often changes abruptly due to the existence of micelles. The formation 
of micelles will be able to calculate various thermodynamic parameters. These parameters make surfactants not only 
an interesting and rich area for the exploration of novel phenomena but also an area of research which can lead to 
new applications in a variety of fields. However, most of the previous studies on surfactants are limited to aqueous 
media only. Studies in mixed solvent media are very natural one as one can modulate the conformations of 
surfactants and their interactions easily by simply varying the composition of the media.  With this concept, the 
research team of Eastern Nepal has started to work the solution properties of surfactants in different mixed solvent 
media in presence and absence of salts and has also investigated cationic and anionic surfactant interaction in mixed 
solvent media. 
 
 

                        © 2014 RCOST:  All rights reserved.         
 
Keywords:  Surfactants; Mixed solvent media; Critical micelle concentration. 
 
1. Introduction 
 

Surfactants are amphiphilic materials containing both a polar long-chain hydrocarbon “tail” and polar, 
usually ionic, “head” groups. In polar solvents, for example water, this dual character of the amphiphile 
leads to self-association or micellization, the surfactant molecules arrange themselves into organized 
molecular assemblies known as micelles.  In colloidal and surface chemistry, the critical micelle 
concentration (cmc) is defined as the concentration of surfactants above which micelles form and almost 
all additional surfactants added to the system go to micelles [1]. 
 

The properties of surfactants in mixed solvent media are an interesting subject. However, very less work 
has been done for solution properties of surfactants in mixed solvent media. The following popular 
methods were used in the eastern part of Nepal for scientific investigations on the solution properties of 
surfactants in mixed solvent media: 



A. Bhattarai / BIBECHANA 11(1) (2014) 175-180: (Online Publication:  March, 2014) p.176 
 
1.1. Electrical conductivity 
 

In the case of ionic surfactants, the utilization of electrochemical measurement is much more convenient, 
especially the measurements of the electrical conductivity of their solutions with varying concentration. 
The conductometric method is based on the finding of a breaking point on the curves, which describe the 
concentration dependence of conductivity [2]. To investigate the solution properties of surfactants, the 
electrical conductivity method is very promising one as one can study the various thermodynamic 
parameters. 
 

Shah et al. [3] measured the specific conductivity of cationic surfactant (Dodecyltrimethylammonium 
Bromide) and anionic surfactant (Sodiumdodecyl Sulphate) in methanol-water mixed solvent media 
containing 0.1, 0.2 and 0.3 volume fractions of methanol at 308.15 K. The specific conductivities of 
Dodecyltrimethylammonium Bromide and Sodiumdodecyl Sulphate were increased with increment in 
concentration and decreased with increment in the volume fractions of methanol. Also, the critical micelle 
concentration (cmc) was increased with increment in volume fraction of methanol in case of both 
surfactants. The free energy of micellization (∆Gom) was calculated.  

 

Bhattarai [4] studied the solution behavior of a surfactant in methanol water mixed solvent media by 
electrical conductivity methods. Cetyltrimethylammonium bromide (CTAB) as the surfactant used in this 
investigation. The micelle behaviour of cetyltrimethylammonium bromide in methanol-water mixed 
solvent media containing 0.10 volume fractions of methanol at 308.15 K was  observed by the value of 
critical micelle concentration (cmc) obtained from conductivity and found to be 1.13 mM  which was 
higher than that of cmc of cetyltrimethylammonium bromide in water. In water, the cmc of CTAB was 
reported [5] to be 1.007 mM from conductometry. 

 

Bhattarai et al. [6] measured the specific conductivity of cetylpyridinium chloride in pure water and 
ethanol-water mixed solvent media containing 0.10, 0.20, 0.30 and 0.40 volume fraction of ethanol at 
room temperature. It was found that the conductivity of cetylpyridinium chloride decreases with the 
increase in the volume fraction of ethanol. The critical micelle concentration of cetylpyridinium chloride 
was found to be increased with the increment in the volume fraction of ethanol. 

 

Niraula et al. [7] studied the conductance of sodium dodecyl sulphate in   presence and in absence of KCl 
and NaBr in methanol-water mixed solvent media containing 0.1, 0.2, 0.3, and 0.4 volume fractions of 
methanol at 308.15 K. The results showed a sharp increase in conductivity with increase in concentration 
of sodium dodecyl sulphate. Also, the conductivity of sodium dodecyl sulphate was increased with 
addition of salts. The conductivity of sodium dodecyl sulphate was decreased with increment in amount 
of methanol. The conductance of sodium dodecyl sulphate was found more in presence of KCl than NaBr 
in methanol-water mixed solvent media containing 0.1, 0.2, 0.3, and 0.4 volume fractions of methanol. 

 

Bhattarai et al. [8] measured the specific conductivity of sodium deoxycholate in pure water and ethanol-
water mixed solvent media containing 0.10 and 0.20 volume fraction of ethanol at 303.15 K.The 
conductivity of sodium deoxycholate was found to be decreased with the increase in the volume fraction 
of ethanol. The critical micelle concentration of sodium deoxycholate was found to be increase with 
increase in the volume fraction of ethanol. 

 

Niraula et al. [9] studied conductivity of sodium dodecyl sulphate in presence and in absence of KBr and 
NaCl in methanol-water mixed solvent media containing 0.1, 0.2 and 0.4 volume fractions of methanol at 
308.15K. The results showed a sharp increase in conductivity with increase in concentration of sodium  



A. Bhattarai / BIBECHANA 11(1) (2014) 175-180: (Online Publication:  March, 2014) p.177 
 
dodecyl sulphate. Also, the conductivity of sodium dodecyl sulphate was increased with addition of salts. 
The conductivity of sodium dodecyl sulphate was found to be decreased with increment in amount of  
methanol. The conductance of sodium dodecyl sulphate was found more in presence of KBr than NaCl in 
methanol-water mixed solvent media containing 0.1, 0.2 and 0.4 volume fractions of methanol. 

 

Also, Niraula et al. [10] studied conductometric studies on the effect of NaBr   on the micellization of 
sodium dodecyl sulphate in pure water and methanol water mixed solvent media at different temperatures 
containing 0.1, 0.2, 0.3 and 0.4 volume fractions of methanol at 308.15 and 318.15 K.The conductance 
was decreased with addition of methanol. It was observed that the conductance of sodium dodecyl 
sulphate was found to be increased with increment in concentration as well as with addition of salt 
(NaBr). The result showed that critical micelle concentration increased with addition of methanol and 
with rise of temperature and decreased with addition of sodium bromide. 

 

Shah et al. [11] measured the specific conductivity of solutions of cetyltrimethylammonium bromide in 
absence and in the presence of potassium chloride in methanol-water mixed solvent media containing 
0.10, 0.20, 0.30 and 0.40 volume fractions of methanol at 308.15, 318.15 and 323.15 K. The conductance 
of cetyltrimethylammonium bromide decreased with addition of methanol. It was observed that the 
conductance of cetyltrimethylammonium bromide increased with increase in concentration as well as with 
addition of salt (KCl). The concentrations of KCl were taken 0.0001, 0.001 and 0.01 M during the 
experiments. The result showed that critical micelle concentration of cetyltrimethylammonium bromide 
increased with addition of methanol and with rise of temperature. Also, the critical micelle concentration 
of cetyltrimethylammonium bromide decreased with addition of potassium chloride.  

 

Yadav et al. [12] investigated the comparative study of conductance of sodium dodecyl sulphate in 
different percentage of ethanol water mixed solvent media at 318. 15 K and found the conductance 
decreased with increase of ethanol. 

 

Shah et al. [13] studied the effect of KCl on conductivity of dodecyltrimethylammouium bromide 
(DTAB) in presence and absence of methanol at 298.15 K and found the cmc increases with increase of 
methanol whereas decreases with the addition of KCl. 
 

The above findings were supported by other works. For example, the effect of KCl and alcohol on the 
cmc of cetylpyridinium chloride (CPC) was studied by Chung et al.[14]. They observed the decrease in 
cmc with the addition of electrolyte and vice versa. Akbas and Kartal [15] carried out an investigation on 
the effect of ethanol and ethylene glycol on the critical micelle concentration (cmc) of CTAB. They 
observed that cmc decreases upon the addition of ethanol and ethylene glycol. The value of cmc increased 
with increase in temperature, such behavior was also observed by Dubey[16].   
 

1.2. Density 
 

The density is very important parameter for the thermodynamic studies of surfactant [17]. The 
thermodynamic quantity known as the partial molar volume has proved to be very useful tool in 
elucidating the interactions occurring in solutions. Studies of partial molar volume of surfactants have 
been used to examine the behavior of surfactant solutions [18-23]. 
 

Shah et al. [24] measured the density of cetyltrimethylammonium bromide solutions in pure water and in 
methanol-water mixed solvent media containing 0.10, 0.20 and 0.30 volume fractions of methanol at 
308.15, 318.15 and 323.15 K and then calculated the partial molar volumes. The results showed almost 
constant on the partial molar volumes with increasing surfactant concentration. Also, the partial molar  



A. Bhattarai / BIBECHANA 11(1) (2014) 175-180: (Online Publication:  March, 2014) p.178 
 
volumes were found to increase with increasing temperature over the entire concentration range 
investigated in a given mixed solvent medium and these values were found to decrease with increasing 
methanol content in the solvent composition. 

 

Bhattarai et al. [25] measured the density of sodium lauryl sulfate in pure water and in methanol –water 
mixed solvent media containing (0.10, 0.20, 0.30, and 0.40) volume fractions of methanol at (298.15, 
308.15, 318.15, and 323.15) K .The results were almost constant on the partial molar volumes with 
increasing surfactant concentration. Also, the partial molar volumes were found to increase with 
increasing temperature over the entire concentration range investigated in a given mixed solvent medium 
and were found to decrease with increasing methanol content in the solvent composition. 

 

Bhattarai and Chatterjee [26] determined the densities of cetyltrimethylammonium bromide in methanol-
water mixed solvent Media at 308.15, 318.15, and 323.15 K and found the densities increase with 
increase of concentration of surfactant. Also, the densities decreased with increment of temperature and 
also decreased with solvent composition.  

 

Bhattarai et al. [27] measured the density of the binary mixtures of cetyltrimethylammonium bromide and 
sodium dodecyl sulphate in pure water and in methanol-water mixed solvent media containing (0.10, 
0.20, and 0.30) volume fractions of methanol at 308.15, 318.15, and 323.15 K. The concentrations were 
varied from (0.03 to 0.12) mol.l-1 of sodium dodecyl sulphate in the presence of ~ 5.0×10-4 mol.l-1 
cetyltrimethylammonium bromide. The results showed almost increase in the densities with increasing the 
concentration of surfactant mixture. Also, the densities were found to decrease with increasing 
temperature over the entire concentration range investigated in a given mixed solvent medium and these 
values were found to decrease with increasing methanol content in the solvent composition. The 
concentration dependence of the apparent molar volumes appeared to be negligible over the entire 
concentration range, investigated in a given mixed solvent medium and the apparent molar volumes 
increase with increasing temperature and were found to decrease with increasing methanol content in the 
solvent composition. 

 

Shah et al. [13] measured the density of dodecyltrimethylammouium bromide (DTAB) in presence and 
absence of methanol at 298.15 K and found the partial molar volume. The results showed almost constant 
on the partial molar volumes with increasing surfactant concentration and the partial molar volumes were 
found to decrease with increasing methanol content in the solvent composition.  
 

The above findings were supported by other works. For example, Iqbal and Siddiquah[28] measured the  
partial molar volume of the surfactant and found the partial molar volume increased significantly with 
temperature. With regard to the partial molar volume in a mixed solvent, Lee and Hyne[29]  have been 
determined the partial molar volumes of tetraalkylammonium chlorides in ethanol-water mixtures. They 
found the partial molar volumes decreased with increasing ethanol content in the solvent composition. 
 

1.3. Surface tension 
 

Surfactants reduce the amount of work necessary to create unit surface area i .e. surface tension of a 
solution is lowered when surfactants are present [30]. The following are a few generalizations regarding 
surface tension and surfactants, followed by a discussion of surfactants and dynamic surface tension. 



A. Bhattarai / BIBECHANA 11(1) (2014) 175-180: (Online Publication:  March, 2014) p.179 
 
Higher concentrations of surfactants lower the surface tension in comparison to the pure solvent state. The 
limiting value of surfactant concentration that produces a surface tension decrease is the critical micelle 
concentration [31]. Bhattarai [4] measured the surface tension of cetyltrimethylammonium bromide in  
methanol water mixed solvent media by Ring method. 

 

The critical micelle concentration of cetyltrimethylammonium bromide in methanol-water mixed solvent 
media containing 0.10 volume fractions of methanol at 308.15 K was obtained 1.11mM but in water, the cmc 
of CTAB was reported [5] to be 1.102 mM from tensiometry at 308.15 K which was less than the cmc of 
cetyltrimethylammonium bromide in methanol water mixed solvent media. 

 

Jha et al. [32] measured surface tension of cetyltrimethylammonium bromide in presence and in the absence of 
KCl and NaCl in aqueous media. The results showed a sharp decrease in surface tension with increase in 
concentration of cetyltrimethylammonium bromide and then almost constant value of surface tension was 
observed. Also, the surface tension was found to decrease with addition of salts.  In presence of monovalent 
salts, the critical micelle concentration of surfactant was found to decrease. 

 

Shah et al. [13] measured the surface tension of dodecyltrimethylammouium bromide (DTAB) in presence and 
absence of KCl in methanol-water mixed solvent medai at 298.15 K and found the critical micelle 
concentration increasing with solvent composition and decreasing with presence of salt.  

 

The above findings were supported by other works. For example, Bhattarai [33] measured the surface tension 
of cetyltrimethylammonium bromide and found the increase in the value of cmc with increasing methanol and 
temperature. With the addition of inorganic salts, the reduced electrostatic repulsion among the surfactant head 
groups is a key factor to influence the morphology of aggregates in ionic surfactant solutions. For conventional 
single-chain cationic surfactants, micelles may change from global to rod like or wormlike with the addition of 
inorganic salts. Hence the cmc of surfactant found to decrease with addition of inorganic salts [34, 35]. 
 

1.4. Viscosity 
Like all other surfactants, cetyltrimethylammonium bromide also shows a rapid change in viscosity when the 
physical and chemical compositions of the solution are changed. This rise in viscosity has been mainly 
attributed to the change in the structure of the cetyltrimethylammonium bromide micelles depending upon the 
ambient condition to which it has been subjected. A similar phenomenon happens on 
dodecyltrimethylammonium bromide. Viscosities of solutions increase with increase in the concentrations. The 
increase in the concentration of the surfactants, make the micelles larger. There is slightly breakage at certain 
concentration, called cmc.  
 

 It is also observed that there is increase in the viscosity with the addition of salt. By adding salt to a surfactant, 
the solution becomes thicker. The electrolyte increases the size of the micelles in the surfactants. Hence the 
addition of electrolyte to the surfactant solution induces the growth of micelle or change in morphology of 
micelle due to which viscosity is increased and hence cmc of the surfactant decreases [36]. In the presence of 
0.1 mol.l-1KBr salt, the relative viscosity of 0.01 mol.l-1 CTAB systems increases with increasing amount of 
benzyl alcohol to a value of approximate 1.9 for a benzyl alcohol content of 0.6% (v/v). If more benzyl alcohol 
is added, the viscosity is decreased. In the absence of KBr salt, the viscosity of 0.01 mol.l-1CTAB solution 
increases slightly with addition of alcohol due to the increase of volume fraction of mixed micelles [37]. 

 

The above findings of other works were supported by the work of research team of Eastern Nepal. For 
example,  Shah et al. [13] studied the effect of KCl on viscosity of Dodecyltrimethylammouium bromide 
(DTAB) in the presence and absence of methanol at 298.15 K and found the cmc increases with increase of 
methanol whereas decreases with the addition of KCl. 



A. Bhattarai / BIBECHANA 11(1) (2014) 175-180: (Online Publication:  March, 2014) p.180 
 

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