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.
10
X-100, C8H17-C6H4-(OC2H4)nOH,C14H22O(C ammonium C16TAB, C19H42BrN)
Hydrophilic group
O(C2H4O)n)
11
2.2 MICELLE FORMATION BY SURFACTANTS
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...
... middle of paper ...
...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
14
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
Rodriquez, R., & Martin, R. (1999). Exogenous surfactant in newborns. Respiratory Care Clinics of North America 5. (4), 595-616
...this system is increased or decreased, then the time taken to reach equilibrium will not be effected after it was in equilibrium stage.
Osmosis and Diffusion Investigation Aim: To examine the process of osmosis and diffusion. Part A: Step 1: Q1.[IMAGE] Q2. The jiggling motion is visible because the fat globules are constantly being bombarded by smaller particles. [IMAGE] Q3.
This increase in potential energy increases the amount of kinetic energy that can be released in the system therefore causes the system to be ...
a) With the rise in ADH concentration, the permeability of the collecting tubules to water
Water has a great number of roles in living organisms, this is largely to do with the structure and covalent bonding in a single water molecule, and between water molecules. Around 75% of the earth is covered in water, and it is reffered to as the most important Biochemical. Its chemical symbol is: H2O In a water molecule there are two bonding pairs and two non-bonding pairs of electrons. These four pairs of electrons repel one another, forming a tetrahedral pattern.
It is based on physics, and the 2nd law of thermodynamics. A liquid is vaporized through compression, which requires kinetic energy. This draws the energy needed from the direct area; causing a loss in energy and then it
There are three main variables that determine whether a liquid will posses capillary action. (Davis, 1995)
The lipid bilayer is made up of two layers of amphophilic molecules and their main purpose is to act as a barrier for the cell against water molecules. The two layers are composed of a hydrophilic head and hydrophobic tail and they can form spontaneously. The hydrophilic heads are polar an...
The polarity of the water makes it cling to itself. This is also known as cohesion which permits water or H2O to tolerate ecstasy at the time it is being positioned under pressure. For example, oil is not polar and it does not dissolve in water, but it does form droplets. The property of cohesion is also being observed when water arranges in a dome-like shape. Hydrogen bonds are the type of bonds that hold water molecules together and assist them in attraction to on another. Cohesion also aids in the expansion of surface tension. Surface tension is the effect on the surface of a liquid that makes it behave as a stretched elastic membrane; it is caused by unbalanced intermolecular forces. For example, if a small piece of paper was placed on water dewdrops, the paper would float on top the water dewdrops denying the fact that the paper is much denser than the water itself. The weak hydrogen bonds that hold water molecules together is attributed to cohesion and surface tension. Hydrogen bonds can break and reorganize with prodigious occurrence. Surface te...
This is an example of a soap molecule. The hydrocarbon end is non polar and hydrophilic (water hating) and the carboxylate end is polar and hydrophilic (water loving). This the property which allows it to clean, it acts as an emulsifying agent. The soap disperses in water to form miscelles where a negatively charged surface is formed and hydrocarbon chains are in the centre. These miscelles surround droplets of dirt or grease suspending them in the water so they can be washed away.
Most of the water in the beaker travels up through the xylem, and most evaporates through the stomata, into the air.
Aim: To investigate the pattern in the amount by which a hanging piece of elastic stretches when a load force is applied and the amount by which the stretch is reduced when the load is removed.
Each water molecule consists of one oxygen atom and two hydrogen atoms. The oxygen atom (or the apex of the water molecule) bears a slight electronegative charge while hydrogen possesses a more positive one. Because opposite charges attract, the water molecules are drawn together. When an oxygen atom is linked to a neighboring molecule's hydrogen atom, a bond called a hydrogen bond is formed. In an ice crystal the hydrogen bonds to give the shape of the crystal so that the grid of molecules surrounds relatively to large spaces. In a liquid form, water has no such spaces; so ice is less dense and will float on liquid water. If not for this, great bodies of water would freeze from the bottom up without the insulation of a top layer of ice and all life in the water would die.
Laundry detergents have had a great impact on the society since it helps our life in keeping ourselves clean, lessens our job or the use of our energy in cleaning our appliances. Laundry detergents have come a long way since the very first bar soaps, made from animal fat and lye, were offered for sale in the 1700s. In the 1950s, homemakers had more options of fabric care since the introduction of synthetic detergents were placed on the market. However; during the 1970s, the most significant innovation in advanced cleaning was made available to clean specific types of stains. Every detergent manufacturer has secret ingredients and mixtures to produce their specific brands of laundry detergent. Many of these ingredients are extracted from plants,