Surfactants Essay

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groups by a spacer group of varying nature: hydrophilic or hydrophobic, rigid or flexible. These surfactants represent a new class of surfactants that is finding its way into surfactant-based formulations. Dimeric surfactants represent a new class of surfactants. They are made up of two amphiphilic moieties connected at the level of the head groups or very close to the head groups by a spacer group.
4-octylphenol polyethoxylate (Triton X
(n = 9-10)
Hexadecyltrimethylammonium bromide (C
Hydrophobic group
Figure 2.1: Hydrophilic and hydrophobic groups of some surfactant molecules.
X-100, C8H17-C6H4-(OC2H4)nOH,C14H22O(C ammonium C16TAB, C19H42BrN)
Hydrophilic group
In a phenomenon termed the “hydrophobic effect”, 4 surfactants act the way they do in aqueous systems due to their nature/structure and the nature/structure of water. Once a surfactant monomer is added to water, water forms a “cage” around the hydrophobic carbon chain. This enclosure is driven by the strength of the hydrogen bonds between the water molecules, leading to loss of entropy of the water molecules. It is this entropy loss rather than bond energy that leads to an unfavorable free energy change for the process. Once added to a system, before equilibrium is reached between the surfactant monomers at the interface and those in the bulk, surfactants concentrate at the interfaces, where they gradually decrease the overall free energy or surface tension of the system. Their orientation at the interface varies, depending on the components of the system. At a water/ air interface, the head group is buried in the solution while the tail group extends out of the solution. At oil/air interface, the tail group is buried i...

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...chanism of ionic surfactants differs from that of nonionic surfactants.
The schematic of a typical surfactant adsorption isotherm frequently seen for the adsorption of ionic surfactants on oppositely charged surfaces is commonly divided into four regions,9, 10 the shape of a typical adsorption isotherm of a nonionic surfactant follows Langmuir equation.
Unlike ionic surfactants, the adsorption isotherms of nonionic surfactants do not have clear transition points. At very low concentration, nonionic surfactant monomers adsorb via
Admicelle Hemimicelle Micelle (formed in solution)
Inverse Micelle
hydrogen bonding between the substrate and the hydrophilic groups. The amount of adsorbed surfactant increases slowly with increasing equilibrium concentration in the bulk phase. After the
CHC or CAC, the slope of the isotherm increases until the CMC and then flattens out.8
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