INTRODUCTION There are great varieties of surfactants available in the market. So due to widespread uses of surfactants and industrial applications the surfactants are used in almost every chemical industry 1-3 of which the following may be worth mentioning; detergents, paints, cosmetics, pharmaceutical, fibers and plastics. Water-soluble surfactants are used together in many formulations and industrial processes to determine the properties of the surfactant by the addition of polymer 4-14 . Moreover, surface active agents play vital role in the oil industry. They are also used for environmental protection e.g. in oil slick dispersants a fundamental understanding of physical chemistry of surfactants is vital for the preparation of emulsion and suspension in foams. In micro emulsion, in wetting and adhesion, etc., the amphiphiles are of great importance in arriving at the right composition and control of the system involved. The basic characteristic of surfactants in a solution is that the concentration of the surfactants always remains high at the surface than in the bulk of liquid. The most common forms of surfactants are constituted of two portions that is non- polar or hydrophobic portion and a polar or hydrophilic portion 15,16 . Investigating the Association Behaviour of Cetyltrimethylammonium Bromide as Affected by the Content of Non-steroidal Antiinflammatory Drug and Temperature ABDUR RAUF 1,* , WAJID REHMAN 2 , MALIK AMANULLAH 1 , ABDULLAH KHAN 3 and MOHAMMAD AKRAM 4 1 Department of Chemistry, Gomal University, Dera Ismail Khan, Pakistan 2 Department of Chemistry, Hazara University, Mansehra, Pakistan 3 Department of Environmental Sciences, Hazara University, Haripur Campus, Haripur, Pakistan 4 Institute of Chemical Sciences University of Peshawar, Peshawar-25120, Pakistan *Corresponding author: E-mail: rauf_afnan@yahoo.com (Received: 15 February 2012; Accepted: 7 August 2012) AJC-11925 Critical micelle concentration of N-cetyl N,N,N-trimethyl ammonium bromide and its mixture with drug naproxen sodium were determined at different temperature by using surface tension technique. Naproxen sodium has been found to exhibit typical amphiphilic behaviour in aqueous solution in that they accumulate at interface, depressing the surface tension and form aggregate in solution at sufficiently high concentration. So critical micelle concentration of cetyltrimethylammonium bromide decreased as the concentration of drug increases and same is the case with temperature. Thermodynamic parameters like ΔGmic, ΔHmic and ΔSmic of micellization of cetyltrimethylammonium bromide were also determined in the presence of naproxen sodium salt at different temperature, which shows that free energy of micellization, is favoured in the presence of drug and become more favourable with the temperature. Key Words: Surfactant, Cetyltrimethylammonium bromide, Naproxen sodium, Effect of temperature, CMC determination. Head Group Linear or poravahed hydrocarbon The polar portion of the molecule is usually termed the head group and interacts strongly with surface active agents. Since the major applications of surfactants is detergency in G10 to G16 range. Therefore, the consideration for commercial point of view is the availability of hydrophilic groups of required length and the cost should be low. The hydrophilic group based on the hydrocarbon is basically available from the sources such as petrochemicals, natural vegetable and natural animal fats. Surfactants are a group of material that have involved with growing and ever changing need of society. Substances conta- ining in the same group, which are strongly hydrophobic (water repellent) and hydrophilic (water loving) orient themselves in different ways when dissolved or dispersed in water or non- aqueous solvents such orientation, which could also be in the form of aggregates of oriented molecules, termed micelles, is known as activity and materials exhibiting this are known as surface active agents often abbreviated as surfactants. Fig. (a, b) indicates orientation of surfactants in polar and non-polar system. Asian Journal of Chemistry; Vol. 25, No. 1 (2013), 559-562