Section 7.11
Section 7.11 Surfactants
7.11
Surfactants
Surfactants are molecules that lower surface tension of liquids. (The word is an abbreviation of surface active agent.) The most common surfactant molecules have one end that is water-soluble (hydrophilic) and the other end water insoluble (hydrophobic) (see Fig. 7.10). As the word implies, the hydrophilic end is strongly attracted to water while the hydrophobic has very little attraction to water but is attracted and is readily soluble in oily liquids. Many different types of surfactant molecules are found in nature or as products of laboratory synthesis.
When surfactant molecules are placed in water, they align on the surface with the hydrophobic end pushed out of the water as shown in Fig. 7.11. Such an alignment disrupts the surface structure of water, reducing the surface tension. A small concentration of surfactant molecules can typically reduce surface tension of water from 73 dyn/cm to 30 dyn/cm. In oily liquids, surfactants are aligned with the hydrophilic end squeezed out of the liquid. In this case the surface tension of the oil is reduced.
Hydrophobe
Hydrophile FIGURE 7.10 Schematic of a surfactant molecule.
FIGURE 7.11 Surface layer of surfactant molecules.
Chapter 7 Fluids (a)
(b)
(c) FIGURE 7.12 Action of detergents. (a) Oil drop on a wet spot. (b) The hydrophobic end of surfactant molecules enter the oil spot. (c) The oil spot break up into smaller section surrounded by hydrophilic ends.
The most familiar use of surfactants is as soaps and detergents to wash away oily substances. Here the hydrophobic end of the surfactants dissolves into the oil surface while the hydrophilic end remains exposed to the surrounding water as shown in Fig. 7.12. The aligned surfactant molecules reduce the surface tension of the oil. As a result, the oil breaks up into small droplets surrounded by the hydrophilic end of the surfactants. The small oil droplets are solubilized (that is suspended or dissolved) in the water and can now be washed away.
Surfactants are widely used in experimental biochemistry. In certain types of experiments, for example, proteins that are hydrophobic such as membrane proteins and lipoproteins must be dissolved in water. Here surfactants are used to solubilize the proteins in a process similar to that illustrated in Fig. 7.12.
The hydrophobic ends of the surfactant molecules dissolve into the surface of the protein. The aligned hydrophilic ends surround the protein, solubilizing it in the ambient water.
7.11
Surfactants
Surfactants are molecules that lower surface tension of liquids. (The word is an abbreviation of surface active agent.) The most common surfactant molecules have one end that is water-soluble (hydrophilic) and the other end water insoluble (hydrophobic) (see Fig. 7.10). As the word implies, the hydrophilic end is strongly attracted to water while the hydrophobic has very little attraction to water but is attracted and is readily soluble in oily liquids. Many different types of surfactant molecules are found in nature or as products of laboratory synthesis.
When surfactant molecules are placed in water, they align on the surface with the hydrophobic end pushed out of the water as shown in Fig. 7.11. Such an alignment disrupts the surface structure of water, reducing the surface tension. A small concentration of surfactant molecules can typically reduce surface tension of water from 73 dyn/cm to 30 dyn/cm. In oily liquids, surfactants are aligned with the hydrophilic end squeezed out of the liquid. In this case the surface tension of the oil is reduced.
Hydrophobe
Hydrophile FIGURE 7.10 Schematic of a surfactant molecule.
FIGURE 7.11 Surface layer of surfactant molecules.
Chapter 7 Fluids (a)
(b)
(c) FIGURE 7.12 Action of detergents. (a) Oil drop on a wet spot. (b) The hydrophobic end of surfactant molecules enter the oil spot. (c) The oil spot break up into smaller section surrounded by hydrophilic ends.
The most familiar use of surfactants is as soaps and detergents to wash away oily substances. Here the hydrophobic end of the surfactants dissolves into the oil surface while the hydrophilic end remains exposed to the surrounding water as shown in Fig. 7.12. The aligned surfactant molecules reduce the surface tension of the oil. As a result, the oil breaks up into small droplets surrounded by the hydrophilic end of the surfactants. The small oil droplets are solubilized (that is suspended or dissolved) in the water and can now be washed away.
Surfactants are widely used in experimental biochemistry. In certain types of experiments, for example, proteins that are hydrophobic such as membrane proteins and lipoproteins must be dissolved in water. Here surfactants are used to solubilize the proteins in a process similar to that illustrated in Fig. 7.12.
The hydrophobic ends of the surfactant molecules dissolve into the surface of the protein. The aligned hydrophilic ends surround the protein, solubilizing it in the ambient water.