Question

Which of the following gel/hydrogel is formed by a physical gelation mechanism?

• A. ( \text{Polyester gel} ) \
• B. ( \text{Gelatin} ) \
• C. ( \text{CMC-g-acrylic acid} ) \
• D. ( \text{Polydimethyl siloxane} ) \

Hint:

Remember the key difference between physical and chemical gelation: physical gels are formed by reversible non-covalent bonds (e.g., hydrogen bonds, hydrophobic interactions) and are often temperature-sensitive, while chemical gels involve irreversible covalent bonds. Gelatin's thermoreversible property is a strong indicator of its physical gelation mechanism.

Answer 1

The Correct Option is B

Gelation mechanisms can be broadly categorized into physical and chemical gelation.
Physical gelation involves non-covalent interactions such as hydrogen bonding, hydrophobic interactions, van der Waals forces, and ionic interactions, leading to reversible gel formation.
Chemical gelation involves the formation of covalent bonds, resulting in irreversible gel formation.
Gelatin is a classic example of a hydrogel that forms via a physical gelation mechanism.
It is derived from collagen and forms a thermoreversible gel.Upon cooling, its polypeptide chains form triple helices, which then aggregate to form a 3D network stabilized by hydrogen bonds and hydrophobic interactions.
This process is reversible upon heating.Polyester gels and CMC-g-acrylic acid often involve chemical crosslinking for gel formation.
For instance, CMC-g-acrylic acid implies grafting of acrylic acid onto carboxymethyl cellulose, which can then be chemically crosslinked.
Polydimethyl siloxane (PDMS) can form gels through chemical crosslinking (e.
g., hydrosilylation reaction).Therefore, Gelatin is the correct answer as it forms a gel through physical, reversible interactions.