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HLB Scale, Solubilization, Detergency and Adsorption at Solid Interface

HLB is an acronym for hydrophilic-lipophilic balance. It is based on the idea that some molecules of surfactants may have hydrophilic groups.

HLB scale

HLB is an acronym for hydrophilic-lipophilic balance. It is based on the idea that some molecules of surfactants may have hydrophilic groups; however, other molecules may have lipophilic groups; and some molecules may have both hydrophilic and lipophilic groups. The hydrophilic and lipophilic components dissolve in both aqueous and oily phases. Correlating and evaluating these characteristics of surfactants is essential for their application to various fields, such as lotions and emulsions, which have their dispersed systems. To express the amphiphilic nature of the molecule as a balance between hydrophilic and lipophilic portions, it is common to use the HLB system.

Based on the balance between the weight percentages of the groups in a surfactant molecule or a mixture of surfactants, we can predict the molecular behavior of the surfactant molecular structure. HLB was developed into a semi-empirical model by Griffin in 1949 and its development in 1954. It is a number on a scale of 1-40 (see Figure 1). Based on the HLB value, the surfactant is classified as water-soluble or oil-soluble according to its relative solubility. A low number of hydrophilic groups results in fewer hydrophilic groups than lipophilic groups for the emulsifier. As an example, spans have a very low HLB number; they are also oil-soluble. A span, for example, has no high-level buoyancy; they are also oil-soluble.

Figure 1

Hydrophilicity is determined by the number of hydrophilic groups present on the molecule and therefore a higher HLB number indicates a more hydrophilic emulsifier. In addition to having higher HLB numbers, tweens are water-soluble. Due to their water-soluble nature, Tweens result in an o/w emulsion as the water phase predominates. According to Table.1 at the bottom, the standard HLB range ranges from 1 to 20, with one exception. Sodium lauryl sulfate is a surfactant that dissolves in water well and is commonly added to almost all heterogeneous systems as well as almost any common detergent. The HLB value of a surfactant is additive, so the surfactant can be blended with known values to obtain the desired one. The appropriate HLB value can be determined in several ways.



Solubilization

A thermodynamically stable isotropic solution is prepared by adding a component to a substance that is normally insoluble in a liquid or by devising methods to make it soluble by adding a component or by other means suitable for the particular application.

Solubility - Solutes dissolve in a given amount of solvent up to a certain amount

Factors that affect solubilization

Nature of solvent and solute - Depending on the kind of solute, the amount that dissolves will vary. The amount of lead (II) chloride that can be dissolved in 100 grams of water at room temperature is only one gram; however, the amount of zinc chloride that can be dissolved in 200 grams. Thus, lead II chloride can dissolve a greater amount of zinc chloride in the same amount of water

1. Temperature - It is generally observed that solubility increases as temperature rises and decreases as the temperature falls, but this is not always true. We must, however, follow two recommendations: Endothermic processes increase solubility as they get hotter and vice versa.

Example - Increasing the temperature increases potassium nitrate solubility.

As temperatures increase or decrease, the solubilization of endothermic reactions changes.

Example - As the temperature increases, calcium oxide becomes less soluble.

An exothermic process, however, causes a decrease in solubility as a result of increased temperatures.

Example - As the temperature increases, calcium oxide becomes less soluble, Cold solvents are more solubilizing than hot liquids.

2. Pressure - It is generally believed that changes in pressure do not affect the solubility of liquid or solid solutes. In the case of gaseous solutes, increases in pressure increase solubility, and decreases in pressure decrease solubility

3. Particle size - The increase in solubility is due to the increase in surface energy with decreasing solute particle size. Particles that are very small typically less than a micrometer can cause this effect, but generally, it is not major

Detergency

A surface-active agent's detergency is one of its most important properties. The term detergent refers to surface-active agents. Typically, the Detergency term is used when removing or cleaning grease, oil, or dirt from a solid surface. Detergency depends on the formation of micelles. A large part of the process revolves around the action of surfactant molecules.
  1. The surfactant needs to have good wetting properties to effectively contact the solid surface.
  2. In addition, it can remove dirt from the bulk liquid.
For this property to occur, the surface tension of the medium in which the surfactant is dissolved must be lowered. It lowers the interfacial tension between a media (e.g. air and water, water and stain, stain and fabric) and so contributes to the removal of dirt. Dirt and grease have an easier time coming off dirty dishes, clothes, and other surfaces due to the water's lower surface tension, which helps keep them in the dirty water. When the head of the washer is in the water, it attracts any stains towards the water, rather than pulling them away from the fabric.

By surrounding the stain particles and breaking them up, surfactant molecules force the stain particles away from the fabric surface. Once detached, they are suspended in the wash water and removed. Surfactants are beneficial for oily contaminants since they can emulsify and solubilize them.

Adsorption at a solid interface

When molecules are attracted to a surface (a layer of molecules on the surface), they form an adsorption reaction. An adsorbate is a material that is being adsorbate. Adsorbent: material that acts as an adsorbent. Ion exchange resin and activated carbon are examples.

The adsorption process called physical adsorption or physisorption is characterized by weak interactions between molecules that bind the adsorbate to the surface. Real gas behaves differently than ideal gases due to this as well. Chemical adsorption refers to the adsorption of gas molecules and atoms on a solid, primarily by chemical bonds. As an example, hydrogen chemisorption on nickel would be one.

The adsorption of gases by solids

  • Nature of gas
  • Reversible character
  • Adsorption and surface area
  • The thickness of adsorbed layer of gas
  • Heats of adsorption
  • Effect of pressure
  • Effect of temperature

The influence of adsorption on solids through gas adsorption

  1. The proportion of adsorption dependent upon the surface area. Adsorption is primarily a surface phenomenon. The increased surface area of the adsorbent will increase the amount of gas that is absorbed.
  2. Natural gas - Solid is adsorbing gas of a particular nature depending on the type of gas. Adsorption is more readily achieved when gas is more easily liquefiable.
  3. The heat of adsorption - A solid surface that is adsorbing one gm mole of gas emits heat as a result of adsorption. Adsorption is the process of air molecules settling on solid surfaces. Adsorption is thus analogous to the condensation of gases into liquids. Therefore, adsorption is exothermic like condensation.
  4. Reversible character - There is reversibility in physical adsorption. It is possible to remove the gas adsorbing on a solid at conditions of reverse temperature and pressure.
  5. Effect of temperature - Low temperature causes physical adsorption to occur rapidly, while high temperatures cause it to decrease. As most chemical reactions increase in temperature, so does chemisorption. In other words, temperature increases can often result in chemisorption instead of physical adsorption.
  6. Effect of pressure - When pressure increases, adsorption occurs, and when pressure decreases, desorption occurs.
  7. The thickness of physically adsorbed layer of gases - A layer of one molecular thickness forms. A thick multimolecular layer forms, though, when the pressure is exceeded.
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Ankur Choudhary is India's first professional pharmaceutical blogger, author and founder of Pharmaceutical Guidelines, a widely-read pharmaceutical blog since 2008. Sign-up for the free email updates for your daily dose of pharmaceutical tips.
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