PHD
  1. Inorganic chemistry  1.1. Coordination chemistry  1.1.1. Ligand field theory  1.1.2. Crystal field theory  1.1.3. Molecular Orbital Theory for Coordination Compounds  1.1.4. Stability of Coordination Compounds  1.1.5. Electronic spectra of coordination compounds  1.1.6. Isomerism in Coordination Compounds  1.1.7. Kinetics and mechanism of coordination reactions  1.2. Organometallic Chemistry  1.2.1. Metal Carbonyls  1.2.2. Metal alkyl and aryl  1.2.3. Fischer and Schrock carbonaceans  1.2.4. Oxidative Addition and Reductive Elimination  1.2.5. Metal Hydrides  1.2.6. Catalysis by organometallic compounds  1.2.7. Metallocenes and Sandwich Complexes  1.2.8. CH activation  1.3. Solid state chemistry  1.3.1. Crystal structures and lattices  1.3.2. Band theory and electrical properties  1.3.3. Defects in the crystal  1.3.4. Synthesis of solid state materials  1.3.5. Magnetic and optical properties of solids  1.3.6. Superconductivity  1.3.7. Solid state ionics  1.4. Bio-inorganic chemistry  1.4.1. Metalloproteins and enzymes  1.4.2. Metal ion transport and storage  1.4.3. The role of metals in medicine  1.4.4. Bioinspired catalysis  1.4.5. Metal–DNA interactions  1.4.6. Metal Complexes in Medical Science  1.5. Lanthanides and Actinides  1.5.1. Electronic configuration and oxidation states in lanthanides and actinides  1.5.2. Spectral and Magnetic Properties in Lanthanides and Actinides  1.5.3. Separation and Extraction of Lanthanides and Actinides  1.5.4. Coordination chemistry of f-block elements  1.6. Main Group Chemistry  1.6.1. Chemistry of boron compounds  1.6.2. Chemistry of Silicon and Germanium Compounds  1.6.3. Chemistry of Phosphorus and Sulfur Compounds  1.6.4. Organosilicon chemistry  1.6.5. Noble Gas Chemistry
  2. Organic chemistry  2.1. Reaction mechanism  2.1.1. Nucleophilic substitution reactions  2.1.2. Electrophilic addition and substitution reactions  2.1.3. Elimination reactions  2.1.4. Rearrangement reactions  2.1.5. Radical reactions  2.1.6. Pericyclic Reactions  2.1.7. Photochemical reactions  2.2. Stereoscopic  2.2.1. Chirality and optical activity  2.2.2. Structural analysis  2.2.3. Stereoelectronic effects  2.2.4. Asymmetric synthesis  2.2.5. Dynamic Stereochemistry  2.3. Organometallic Chemistry in Organic Synthesis  2.3.1. Organolithium and organomagnesium reagents  2.3.2. Transition metal catalyzed coupling reactions  2.3.3. Palladium-catalyzed reactions  2.3.4. Olefin Metathesis  2.3.5. Gold and silver catalysis  2.4. Natural products chemistry  2.4.1. Alkaloids and terpenoids  2.4.2. Steroids and Flavonoids  2.4.3. Total synthesis of natural products  2.4.4. Biosynthesis of natural products  2.5. Supramolecular Chemistry  2.5.1. Host-Guest Chemistry  2.5.2. Self-assembly and molecular recognition  2.5.3. Supramolecular Catalysis  2.5.4. Molecular Machines
  3. Physical Chemistry  3.1. Thermodynamics  3.1.1. Laws of Thermodynamics  3.1.2. Chemical Potential and Equilibrium  3.1.3. Statistical thermodynamics  3.1.4. Non-equilibrium thermodynamics  3.2. Quantum Chemistry  3.2.1. Schrödinger equation and its applications  3.2.2. Molecular orbital theory  3.2.3. Density functional theory  3.2.4. Post-Hartree–Fock methods  3.3. Chemical kinetics  3.3.1. Reaction rate theory  3.3.2. Mechanism and rate laws  3.3.3. Catalysis and enzyme kinetics  3.3.4. Reaction dynamics  3.4. Spectroscopy and molecular structure  3.4.1. Infrared Spectroscopy  3.4.2. UV-visible spectroscopy  3.4.3. Nuclear Magnetic Resonance Spectroscopy  3.4.4. Mass Spectrometry  3.4.5. Raman Spectroscopy  3.5. Surface and Colloid Chemistry  3.5.1. Absorption and Catalysis  3.5.2. Surfactants and micelles  3.5.3. Colloidal Stability  3.5.4. Nanomaterials and Interfaces
  4. Analytical chemistry  4.1. Chromatography  4.1.1. Gas Chromatography  4.1.2. High Performance Liquid Chromatography  4.1.3. Thin Layer Chromatography  4.1.4. Ion Chromatography  4.2. Electroanalytical techniques  4.2.1. Voltammetry and Polarography  4.2.2. Conductometry and potentiometry  4.2.3. Colometry  4.3. Spectroscopic Methods  4.3.1. Atomic absorption spectroscopy  4.3.2. Fluorescence Spectroscopy  4.3.3. X-ray diffraction  4.3.4. Electron paramagnetic resonance spectroscopy  4.4. Chemometrics  4.4.1. Data processing and statistical methods  4.4.2. Multidisciplinary analysis  4.4.3. Machine Learning in Analytical Chemistry
  5. Theoretical and Computational Chemistry  5.1. Molecular dynamics simulation  5.2. Quantum chemistry methods  5.3. Computational drug design  5.4. Machine Learning in Chemistry  5.5. Ab initio molecular dynamics
  6. Biophysics and Medicinal Chemistry  6.1. Drug discovery and design  6.2. Enzyme kinetics and inhibition  6.3. Chemical biology approach  6.4. Protein-ligand interactions  6.5. Bioorthogonal chemistry
  7. Materials chemistry  7.1. Polymer chemistry  7.1.1. Polymerization mechanism  7.1.2. Functional Polymers  7.1.3. Biodegradable Polymer  7.1.4. Conducting and semiconducting polymers  7.2. Nano Chemistry  7.2.1. Nanoparticles and nanostructures  7.2.2. Carbon-based nanomaterials  7.2.3. Quantum dots  7.3. Energy and Environmental Chemistry  7.3.1. Battery and Fuel Cell Chemistry  7.3.2. Green chemistry and sustainable materials  7.3.3. Photocatalysis

PHD → Physical Chemistry → Surface and Colloid Chemistry ↓


Surfactants and micelles


The science of surfactants and micelles is a cornerstone of surface and colloid chemistry, a sub-discipline within physical chemistry. Surfactants and micelles are important in a variety of applications ranging from industrial formulations to biological systems. Understanding these entities provides insight into their behavior and functionality in complex environments.

What are surfactants?

Surfactants or surface-active agents are compounds that reduce the surface tension between two liquids or between a liquid and a solid. They have a unique molecular structure characterized by at least two distinct regions: a hydrophilic (water-attracting) head and a hydrophobic (water-repelling) tail. This dual nature allows surfactants to accumulate at interfaces and alter the physical properties of surfaces.

General structure: R - X

Where R represents the hydrophobic tail and X represents the hydrophilic head.

Types of surfactants

Surfactants can be classified based on the nature of their hydrophilic head group:

  • Anionic surfactants: These contain a negatively charged head group. Example: Sodium dodecyl sulfate (SDS).
  • Cationic surfactants: These have a positive charge on the head group. Example: Cetyltrimethylammonium bromide (CTAB).
  • Nonionic surfactants: These do not have any charge. Example: TWEEN 20.
  • Zwitterionic surfactants: These have both positive and negative charges but are overall neutral. Example: Phosphatidylcholine.

How surfactants work

Surfactants reduce surface tension through adsorption at the interface. The hydrophobic tails of the surfactant are embedded in the nonpolar phase, such as oil, while the hydrophilic heads remain in the aqueous phase. This arrangement stabilizes emulsions and foams, which are mixtures of two normally immiscible liquids.

Hydrophilic Head Hydrophobic tail

Micelles: formation and function

Micelles are spherical structures that form when surfactant molecules arrange themselves in a specific manner in solution. Micelles form spontaneously when the concentration of surfactant in solution exceeds a particular threshold, known as the critical micelle concentration (CMC). In these structures, the hydrophobic tails face toward the center of the sphere, away from the surrounding water, while the hydrophilic heads face the aqueous environment.

Hydrophilic Hydrophobic main

Micelles perform several functions:

  • Solubilization: They aid in the solubilization of hydrophobic compounds in aqueous solutions, making processes such as drug delivery in pharmaceutical applications possible.
  • Detergent: Micelles trap oil and greasy stains, allowing them to be washed away with water.
  • Transport: In biological systems, micelles can transport lipophilic vitamins and other molecules.

Critical micelle concentration (CMC)

CMC is an important parameter in the study of surfactants. It represents the concentration at which surfactant molecules begin to form micelles. Below the CMC, surfactant molecules exist primarily as individual units; above the CMC, micelle formation predominates. CMC values are affected by factors such as temperature, the presence of salts, and the nature of the surfactant.

CMC 0 Surfactant Concentration Surface tension

The measured surface tension decreases with increasing surfactant concentration up to the CMC. After reaching the CMC, the surface tension stabilizes because the additional surfactant molecules contribute to micelle formation rather than surface activity.

Examples and applications of surfactants and micelles

Detergents and soaps

Surfactants are essential components of detergents and soaps used in cleaning processes. Their ability to emulsify oils and retain dirt in suspension allows their efficient removal from surfaces. Soaps composed of fatty acids and strong alkalis such as sodium hydroxide are classical examples of surfactants.

C17H35COONa (Sodium Stearate)

Personal care products

In personal care products, surfactants are present as emulsifiers in lotions, creams, and shampoos. These formulations require the stable combination of aqueous and oily substances. Surfactants enable this stability by reducing the interfacial tension between the phases.

Environmental applications

Environmental engineering leverages surfactants to remove hydrocarbon and heavy metal contamination in soil and groundwater. By forming micelles, surfactants increase the solubility and mobility of otherwise insoluble contaminants, thereby increasing extraction efficiency.

Factors affecting surfactant and micelle behavior

The behavior and efficiency of surfactants and micelles are affected by a variety of factors:

pH and ionic strength

Changes in pH can affect the charge state of the surfactant head group, particularly in anionic and cationic surfactants. Increased ionic strength often lowers the CMC and increases micelle stability by shielding the head group charge and reducing repulsion.

Temperature

Temperature affects both CMC and micelle formation due to changes in kinetic energy and solubility. Generally, increasing temperature decreases the hydrophobic effect that induces micelle formation, leading to an increase in CMC.

Surfactant composition

The length and saturation level of the hydrophobic tail affects micelle size, shape, and CMC. The presence of long hydrophobic tails and double bonds decreases the CMC and promotes different micelle architectures such as rod-like or disc-like shapes.

Micelle formation beyond aqueous solution

While aqueous solutions are common for surfactant studies, micelles can form in non-aqueous systems such as organic solvents or supercritical fluids. These inverted micelles have hydrophilic cores, making them suitable for solubilizing polar compounds in a non-polar environment.

Conclusion

Surfactants and micelles are important components in chemistry, having wide applications in various fields. They add significant value due to their ability to alter surface properties and enhance solubility. By understanding the mechanisms that govern their behavior, we can better utilize their capabilities to develop new technologies and improve existing processes.


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