Colloids & amphiphiles – In aqueous solution, how are micelles of fatty acids oriented with respect to water exposure and core packing?

Introduction / Context:
Micelles are supramolecular aggregates formed by amphiphiles, such as fatty acids, when dispersed in water above a critical micelle concentration. Understanding how hydrophilic and hydrophobic moieties orient relative to the aqueous environment is fundamental in biochemistry, membrane science, and drug delivery.

Given Data / Assumptions:

• Fatty acids possess a polar, ionizable carboxylate head and a nonpolar hydrocarbon tail.
• Water is a polar solvent that favors interactions with charged/polar groups.
• Micelles minimize the free energy associated with exposing hydrophobic surfaces to water.

Concept / Approach:
To reduce the hydrophobic effect penalty, amphiphiles orient so that polar head groups remain solvated at the micelle surface, while hydrophobic tails are sequestered in an apolar core. Fatty acid carboxylate groups (hydrophilic heads) hydrogen-bond/ionically interact with water; the alkyl chains cluster internally, driving micelle formation.

Step-by-Step Solution:

Verification / Alternative check:
Scattering and spectroscopic studies show micellar radii with hydrated surfaces and hydrophobic cores; detergents demonstrate similar orientations, enabling solubilization of membrane proteins.

Why Other Options Are Wrong:

• Hydrocarbon chains facing solvent contradicts the hydrophobic effect.
• Equal exposure has no basis; micelles have distinct core–shell architecture.

Common Pitfalls:
Confusing micelles (spherical, tails in) with bilayers (two leaflets) or reverse micelles (nonpolar solvent, reversed orientation).

Final Answer:
Both (a) and (b) describe the same correct orientation