surfactant activity and application

The concentration of a surfactant at the interface, exceeding what would be present if the bulk concentration extended to the surface.

A dynamic equilibrium exists between surfactant molecules at the surface and in the bulk solution. This means there's a constant exchange between the surface and the bulk.

The change in surface tension (γl/v) as the bulk concentration (Cb) changes.

The aggregation of surfactant molecules in solution above a certain concentration, forming spherical structures called micelles.

The concentration at which micelles start to form in solution. Below this concentration, surfactants exist as individual monomers.

The process by which surfactants enhance the solubility of poorly soluble substances (like oils) in water.

The process by which surfactants reduce the surface tension of a liquid, leading to a decrease in interfacial energy.

The tendency of surfactant molecules to accumulate at the interface between two phases, like oil and water.

Molecules with both a water-loving (hydrophilic) and a water-hating (hydrophobic) part.

Substances that reduce the surface tension of a liquid, allowing it to spread more easily.

The tendency of a liquid to minimize its surface area due to the attractive forces between its molecules.

The process by which molecules of a substance (like a surfactant) accumulate at a surface or interface.

The ability of a substance (like a surfactant) to dissolve in a liquid, usually water.

The force of attraction between molecules of the same substance, like water molecules.

The force of attraction between molecules of different substances, like water and a hydrophobic group.

The force of attraction between molecules of the same substance, like hydrocarbon molecules.

A measure reflecting the balance between hydrophilic and lipophilic parts of a surfactant molecule, influencing its solubility and potential applications.

Surfactants with a high HLB value tend to be readily soluble in water, forming clear solutions. This property is essential for solubilizing substances that are poorly soluble in water.

Surfactants with an HLB range of 8-10 are typically soluble in water and are often used to form oil-in-water (o/w) emulsions, where tiny oil droplets are dispersed throughout a water-based medium.

Surfactants with an HLB range of 6-8 often require some agitation to dissolve in water. They are useful for wetting, which involves spreading a liquid over a solid surface, reducing surface tension.

Surfactants with an HLB range of 3-6 exhibit poor solubility in water, making them suitable for forming water-in-oil (w/o) emulsions, where tiny water droplets are dispersed in an oil-based medium.

Surfactants with a very low HLB (1-3) are generally insoluble in water. These surfactants can act as antifoaming agents, reducing the formation of foam by disrupting the stability of bubbles.

The required HLB of a substance, like an oil, refers to the specific HLB value needed to achieve desired properties, such as emulsification, in a formulation.

To create a stable emulsion, the HLB of the emulsifier (or blend of emulsifiers) should be close to (within ± 1) the required HLB of the oil phase.

The critical micelle concentration (CMC) is the concentration of a surfactant above which micelles form spontaneously in solution.

Micelles are spherical aggregates formed by surfactant molecules in solution when the concentration of the surfactant exceeds the CMC. These aggregates have a hydrophobic core and a hydrophilic outer shell.

The formation of micelles is driven by the minimization of free energy in the system. Surfactants, when concentrated enough, self-aggregate into micelles to minimize the contact between hydrophobic tails and water molecules.

Non-ionic surfactants form micelles at lower concentrations than ionic surfactants due to the absence of electrostatic repulsion between their head groups. This means they need less concentration to self-assemble.

The size and shape of micelles are influenced by factors such as the length of the hydrophobic tail and the nature of the hydrophilic head group. For instance, longer tails lead to larger micelles.

Increasing the hydrophobic tail length of a surfactant reduces the CMC (it takes less concentration to form micelles). Conversely, increasing the hydrophilic head group size increases the CMC (more concentration is needed).

Polyoxyethylated non-ionic surfactants have a greater hydrophilicity when the polyoxyethylene chain is longer. This leads to a higher CMC. Conversely, shorter chains result in lower CMCs.

The aggregation number refers to the number of surfactant molecules in a single micelle. Generally, non-ionic surfactants have higher aggregation numbers than ionic surfactants with similar hydrophobic chains.

Larger, less hydrated counterions can move into the micelle's surface, reducing the repulsion between the head groups, and making the micelle more stable.

Adding electrolytes to a solution of ionic micelles reduces the size of the micelles and their critical micelle concentration (CMC) due to a decrease in electrostatic repulsion between the head groups.

Non-ionic surfactants can form two phases when heated above their cloud point temperature. The solubility of ethoxylate surfactants decreases with increasing temperature, causing a separation of the solution into two phases. This phenomenon is reversible.

The Krafft point is the temperature at which the solubility of ionic surfactants significantly increases. Above the Krafft point, the surfactant molecules can effectively form micelles.

The critical micelle concentration (CMC) of a surfactant is the concentration at which micelles begin to form in solution. It can be determined by plotting the conductivity of the solution against surfactant concentration.

The electrical conductivity of ionic micelles is affected by the movement of ions within the solution. The viscous drag from the solvent and the counter ions around the micelle influence the conductivity.

Micelles are able to solubilize various molecules, including those that are water-soluble, polar, and non-polar. The specific solubilization site depends on the properties of the solubilizate and the surfactant.

Bound counter ions, which are responsible for the micelle's charge, can affect conductivity by slowing down the movement of the micelle. This is because they are moving in the opposite direction of the micelle.