Brown's Chemistry Revision Notes -
Smart Materials and Materials Science
High performance polymers like KEVLAR
ALPHABETICAL LIST of
materials, effects etc. mentioned on these pages: Smart
Materials Science INDEX * CARBON FIBRES *
MATERIALS * ELECTROCHROMIC MATERIALS
* GORETEX * HALOCHROMIC
MATERIALS * HIGH PERFORMANCE
POLYMERS * KEVLAR * LYCRA *
MEMORY ALLOYS * MAGNETOSTRICTIVE
MATERIALS * NITINOL *
pH SENSITIVE POLYMERS *
PHOTOCHROMIC MATERIALS *
PHOTOMECHANICAL MATERIALS * PIEZO ELECTRIC EFFECT-MATERIALS *
MATERIALS * SHAPE MEMORY ALLOYS *
SHAPE MEMORY POLYMERS * SPANDEX
* TEMPERATURE-RESPONSIVE POLYMERS
* THERMOCHROMIC MATERIALS *
High performance polymers like
HIGH PERFORMANCE POLYMERS
These are polymer materials that
are extremely strong, chemically very inert and thermally very stable at higher temperatures where
other polymers might melt or degrade-decompose.
KEVLAR, ?, ?
KEVLAR is the trade name
for an aramid (aromatic amide) polymer fibre (also known as NOMEX).
Kevlar fibres are made by
spinning liquid crystal aramid oligomers (oligomers are molecules consisting
of a few monomers linked together - but much shorter than a polymer!).
Kevlar is a very strong artificial fibre
that can be
woven into materials that are very light and strong.
It is used to make flexible body armour,
i.e. it is a polymer designed for 'heavy duty' use!
is strong and tough because its molecules are held together in sheets by
strong chemical bonds and strong intermolecular forces.
The intermolecular forces
between the kevlar molecules in the sheet are hydrogen bonds, formed
by the strong directional interaction of the two permanently polar bonds
The highly polar bonds and hence
the hydrogen bonding, is due to the significant difference in
electronegativity between nitrogen and hydrogen, AND, carbon and oxygen.
The sheets of molecules are
themselves held together by strong intermolecular forces and the 'molecular
sheets' can be aligned to maximise theses forces and the combined strength
of many such sheets gives Kevlar fibres their great strength.
Along the polymer 'backbone' is
a chain of strong of -N-C-C-C-C-N- bonds continuously repeated for hundreds
or thousands of units which produces a strong rigid linear molecule.
Between adjacent aramid
molecules there are regular points where a intermolecular force can operate
(called hydrogen bonding - for A level students). This extra bonding force
holds the aramid molecules together in strong 'molecular' sheets.
The sheets are held together in
Kevlar fibres by the 'random' but 'continuous' intermolecular forces between
adjacent layers of molecules.
INDEX of SMART MATERIALS PAGES
CHROMOGENIC MATERIALS - Thermochromic, Photochromic & Electrochromic Materials
SHAPE MEMORY ALLOYS e.g. Nitinol & Magnetic Shape Memory Alloys
SHAPE MEMORY POLYMERS, pH and temperature sensitive-responsive polymers,
PART 5 High
performance polymers like KEVLAR
GORETEX, THINSULATE and TEFLON-PTFE
PIEZOELECTRIC EFFECT (PIEZOELECTRIC MATERIALS) and PHOTOMECHANICAL MATERIALS
See also INDEX
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