The key difference between micelles and colloidal particles is that micelles form at a certain concentration whereas colloidal particles form as soon as the solutes are added to the solvent.
The terms micelles and colloidal particles come in analytical chemistry where colloids are discussed. Micelles are also a type of colloidal particles.
CONTENTS
1. Overview and Key Difference
2. What are Micelles
3. What are Colloidal Particles
4. Side by Side Comparison – Micelles vs Colloidal Particles in Tabular Form
5. Summary
What are Micelles?
Micelles are colloidal particles that form as aggregates of surfactant molecules. These are dispersed in a liquid medium and occurs as liquid colloids. Surfactant molecules have hydrophilic heads and hydrophobic tails. In an aqueous medium, hydrophobic single tail structures tend to repel water molecules while the hydrophilic heads tend to attract the water molecules. As a result, an aggregate forms in such a way that hydrophilic heads are in contact with the solvent, surrounding the hydrophobic tails inside the micelle.
Figure 01: Structure of a Typical Micelle
Micelles are spherical in their shape. In addition, some other shapes such as ellipsoids, cylindrical structures, and bilayers are also possible. The shape of the micelle is determined by some factors such as the molecular geometry of the surfactant molecule, surfactant concentration in the solution, temperature, pH, and the ionic strength. The process of micelle formation is called micellisation.
Moreover, micelles form when the concentration of the surfactant is greater than the critical micelle concentration of the solution. Also, the temperature of the system has to be higher than the critical micelle temperature. Usually, micelles form spontaneously because of the balance between entropy and the enthalpy of the surfactant-solvent mixture.
What are Colloidal Particles?
Colloidal particles are the particles that are dispersed in a suspension. This type of suspension is called a colloidal suspension. The suspended particles can be either soluble or insoluble particles. A colloid has two distinguishing phases of matter: liquid phase solvent and solid phase particles. The liquid phase is called the continuous phase, and the solid phase is called the dispersed phase, which is dispersed throughout the solvent. Usually, colloidal particles do not settle down or take a very long time to settle down.
Figure 02: In milk, Colloidal Particles are Butterfat Globules
Colloidal particles are easily visible through an optical microscope. Some colloids are opaque, but some are translucent. Translucent nature is due to the Tyndall effect of light scattering. There are several different types of colloids, depending on the type of liquid phase and dispersed phase. Followings are some examples.
- If the solvent is liquid and dispersed phase is gas, we call this colloid foam. The colloidal particles are gaseous aggregates. E.g. whipped cream.
- If the solvent is a solid and dispersed phase is a gas, then we call it solid foam. Here also, the colloidal particles are gaseous aggregates. E.g. aerogel.
- If the solvent phase is gas and the dispersed phase is liquid, we call it liquid aerosol. The colloidal particles are liquid aggregates. E.g. sprays.
- If the solvent phase is liquid and dispersed phase is also liquid, we call it an emulsion. E.g. milk.
- If the solvent phase is solid and the dispersed phase is liquid, we call it a gel. The colloidal particles here are liquid aggregates. E.g. agar.
- If the solvent phase is gas and the dispersed phase is solid, we call it solid aerosol. E.g. smoke.
- If the solvent phase is liquid and dispersed phase is solid, we call it as “sol”. The colloidal particles here are solid aggregates. E.g. blood.
- If the solvent phase is solid and dispersed medium is also solid, we call it solid sol. The colloidal particles here are solid aggregates. E.g. cranberry glass.
What is the Difference Between Micelles and Colloidal Particles?
Micelles are also a type of colloidal particles. The key difference between micelles and colloidal particles is that micelles form at a certain concentration whereas colloidal particles form as soon as the solutes are added to the solvent. Besides, micelles form due to the hydrophilic and hydrophobic effects while colloidal particles form due to the insolubility or saturation of the solution.
Moreover, the size of micelles can vary from 2 to 20 nanometers while the size of colloidal particles can vary from 1 to 1000 nanometers.
Below tabulation shows more comparisons related to the difference between micelles and colloidal particles.
Summary – Micelles vs Colloidal Particles
The terms micelles and colloidal particles come in analytical chemistry where colloids are discussed. Micelles are also a type of colloidal particles. The key difference between micelles and colloidal particles is that micelles form at a certain concentration whereas colloidal particles form as soon as the solutes are added to the solvent.
Reference:
1. “Micelle.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 2 Feb. 2018, Available here.
Image Courtesy:
1. “Micelle scheme-en” By SuperManu – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Glass of milk on tablecloth” By I, Chedid (CC BY-SA 3.0) via Commons Wikimedia
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