Aromatic kyun? Ek benzene ring backbone ke saath us tarah rotate ya bend nahi kar sakti jaise ek –CH₂–CH₂– chain kar sakti hai. Isliye aramid chains stiff "rods" hoti hain. Isse kya milta hai? Rods logs ki tarah pack hoti hain aur stretching resist karti hain. Glue kaise lagta hai? Ek chain ka N–H apne neighbour ke C=O se H-bond banata hai, sheets form karta hai.
Recall Feynman: ek 12-saal ke bacche ko explain karo
Socho raw spaghetti. Ek seedha strand kheenchne mein mushkil hai par side se modna ya push karna asaan. Kevlar ki chains millions of seedhe, stiff spaghetti strands jaisi hain, side-to-side tiny hooks (hydrogen bonds) se glued — isliye yeh ek amazingly tough sheet banate hain jo bullets rok le, lekin wajan almost kuch nahi. Nomex wahi spaghetti use karta hai par zig-zags mein mod kar, isliye yeh itna pack nahi ho sakta ki super strong ho, lekin yeh heat love karta hai — yeh melt ya burn nahi hoga, isliye firefighters ise pehnte hain. Aeroplanes ke liye hum carbon spaghetti bichha dete hain aur upar se ek hardening glue (epoxy) daal dete hain; glue set hokar pathar banta hai aur har strand ko jagah par rakhta hai. Light + strong = sasta flying.
Kevlar para-linked hai → seedhi rod-jaisi chains parallel pack hoti hain aur H-bond karke sheets banati hain; Nomex meta-linked hai → kinked chains loosely pack hoti hain.
Nomex fire kyun resist karta hai?
High aromatic content thermal stability deta hai; yeh melt nahi hota aur combustion support nahi karta. Firefighter suits mein use hota hai.
PBO Kevlar se zyada strong kya cheez banati hai?
Rigid fused benzoxazole heterocyclic rings poore backbone ko ek ladder-jaisi rod banate hain jisme almost koi rotatable bond nahi hota.
Polyimide kya hai aur heat-stable kyun?
Cyclic imide groups wala polymer (dianhydride + diamine se, heating par cyclise hota hai); aromatic+imide rings 300–400 °C tak scission resist karte hain.
Epoxy resin cure karne wala reaction kya hai?
Amine hardener strained epoxide (oxirane) ring ko open karta hai → cross-linked 3-D thermoset network banta hai.
FRP kya stand karta hai aur uske do parts kya hain?
Fibre-Reinforced Polymer: stiff fibres tension uthate hain, polymer matrix unhe bind karta hai aur compression/shear resist karta hai.
CFRP vs GFRP?
CFRP carbon fibres use karta hai (stiffer, lighter, costlier); GFRP glass fibres use karta hai (sasta, kam stiff).
Aerospace materials ka figure of merit kya hai?
Specific strength = tensile strength / density (σ/ρ) — strength per unit mass.
Kevlar banane wala polymerisation ka type?
Condensation (step-growth) polymerisation, HCl release karta hai.
Epoxide ring-opening itna favourable kyun hai?
3-membered ring strained hoti hai (~60° angle); opening ring strain release karta hai.
