ABSTRACT
Surfactant means surface active agent which tends to accumulate at the surface and change its properties. They are active at interfaces between liquid/liquid, solid/liquid or liquid/gas. Surfactants play a significant role in many practical applications like detergents, fabric softeners, motoroils, paints, adhesives, inks, deinking of recycled papers, froth flotation process, enzymatic process, emulsions and laxatives, etc. The capacity of various surfactants can be detrimentally reduced at high temperature and high saline conditions. Also, the use of surfactants is generally limited by the loss due to surfactant adsorption that takes place during processes. For example, surfactant gets absorbed on the reservoir rock during its use in oil recovery. Therefore, a new category of surfactants called nano-surfactants or nanoparticle-based surfactants were formulated to overcome these shortcomings.
The word nano-surfactant is a combination of nanoparticle and surfactant. Nanoparticle is a particle having a particle size less than 100 nm and a surfactant is an amphiphilic molecule which consists of both hydrophilic and hydrophobic parts. Therefore, nano-surfactants are molecules which have a small size as well as are amphiphilic in nature. Sometimes these are also termed as amphiphilic nanoparticles. Nano-surfactants show synergetic behavior of both nanoparticle and surfactant. Nano-surfactants overcome various shortcomings of conventional surfactants by remaining stable at higher temperatures and higher salt concentrations.
This chapter discusses nano-surfactants based on their origin that can be natural or man-made. Naturally occurring nano-surfactants include materials like graphite, fullerene, etc. Man-made nano-surfactants can be synthesized by using both organic and inorganic nanoparticles. Organic nanoparticles include carbon-based nanoparticles such as carbon nanotubes (CNTs), carbon nanohorns, nano diamond, etc. and inorganic nanoparticles can be based on Si, Fe, Cu, Ni, etc. There are two methods to synthesize nano-surfactants. First method includes the suspension of nanoparticles in surfactant solution via electrostatic forces and the second one includes the introduction of amphiphilic groups on the nanoparticles surface by electrostatic interaction or covalent bond followed by their suspension in carrier fluid/basefluid.
Properties of nano-surfactants have been discussed. Factors like type, size and shape of nanoparticle, type of surfactant/amphiphilic group attached to the surface of nanoparticles, synthetic procedure adopted for nano-surfactant preparation, colloidal stability of nanoparticles which affects the functioning of nano-surfactants have been explained. Characterization methods used to characterize nano-surfactants such as scanning electron microscopy-energy dispersive X-ray (SEM-EDX), transmission electron microscopy (TEM), Zeta potential and dynamic light scattering (DLS) have been summarized.
