Brown's Chemistry Revision Notes -
Smart Materials and Materials Science
®, THINSULATE and TEFLON-PTFE
ALPHABETICAL LIST of
materials, effects etc. mentioned on these pages: Smart
Materials Science INDEX * CARBON FIBRES * CHROMOGENIC
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 *
THINSULATE and TEFLON-PTFE
Note that Gore-Tex/Goretex is a registered
trade mark ®
Nylon is a synthetic polymer used to make fabrics
for the clothing industry, but on its own it is not very waterproof.
If the nylon is coated with polyurethane it becomes
a much tougher durable waterproofed material for outdoor clothing.
Unfortunately the polyurethane coating doesn't allow
water vapour through so you get too hot, sweaty and uncomfortable, because the
sweat can't evaporate to keep you cool.
Gore-Tex is the registered trade name often applied to a
particular design of (usually outdoor) clothing fabric that is designed to keep you dry in the rain without
- Strictly speaking it is the patented name a
porous form of the polymer PTFE made by stretching the polymer fibres in a
controlled way to create fine pores.
- So the GoreTex itself is actually one
layer in the fabric design for a particular clothing application e.g. anorak
- GORE-TEX ®
is an excellent breathable, waterproof textile fabric used in
high-performance clothes such as walking boots, hiking boots and mountain
coats. Unlike ordinary synthetic textiles like nylon, GORE-TEX stops rain
from getting in but lets perspiration (sweat condensation) out. So it keeps
you dry on the outside and dry on the inside at the same time.
BUT how does a Gore-Tex membrane work?
- GoreTex fabric is made up of a layer of a plastic based on
expanded PTFE and this is laminated onto a layer of another fabric. Gore-Tex
is a laminate containing layers of the polymers nylon, PTFE (Teflon) and
- The PTFE layer contains millions of tiny holes
(called pores) per square millimetre. The pores are 20,000 times smaller
than a water droplet, BUT, individual water molecules are 700 x smaller than
pore, so water molecules can pass through the pores, but NOT water droplets
e.g. of rain!
- Each pore is big enough to allow individual water
molecules to pass through, BUT, not big enough for water droplets to pass
through. The intermolecular bonding forces between water molecules are quite
strong and water droplets like to stay intact due to these attractive forces
rather than adhere to the hydrophobic PTFE layer.
- It is the tiny holes in the PTFE layer that
let individual water vapour molecules through, i.e. it is breathable, so
sweat escapes through the micro pores but rain water (liquid droplets) can't
- The outer fabric
surface repels water - hydrophobic in nature, combined with the tiny size of
the PTFE pores ensures the water-proof properties of Gore-Tex fabrics.
Each pore is too small for water droplets to pass through, but big
enough to let water vapour molecules from sweat to go through (transpiration
- This illustrated in the diagram above,
the fabric material is multi-layered (a sort of 'sandwich' composite).
- So, if you sweat in this 'breathable'
material, the water vapour can escape keeping you cooler, and you don't get
the discomfort from sweat condensate,
- AND, because water droplets can't pass
through the outer tough protective layer, you should keep dry in wet
- Also note, that without the outer tough protective
layer e.g. nylon or polyester, the GoreTex membrane would be easily damaged
and it wouldn't be waterproof and windproof.
- Gore-Tex products have all the useful
properties of nylon-polyurethane fabrics but breathable materials!
Therefore you have a 'breathable' fabric
which can be combined with insulation materials such as
Thinsulate to make
outdoor clothing that keeps you both dry (waterproof) and warm (insulating).
THINSULATE is the
trademark of a specially designed commercial synthetic fibre material that
can be used for insulation in clothing e.g. gloves or winter jackets.
Thinsulate fibres are much
thinner than most other artificial fibres like nylon an polyester used in
Human hair is 0.1 mm (100 μm),
thinsulate fibs 0.010 - 0.015 mm, 10-15x thinner!
molecule same as Lycra?
They are produced as a dense
tangled web of fibres that trap lots of air between the thin fibres and
reflect heat too.
Polyesters like polyethylene
terephthalate (PET), poly(propene) and poly(ethene) are used to make
This considerably reduces heat
loss, i.e. from your body and so clothes containing layers of this material
keep you very warm.
They are supposed to be at least
as good as duck down for insulation, but less water-absorbent and resistant
to crushing than duck down.
The good thermal insulation
effect is due to the high density of fibres produced by utilising very fine
fibres which increases the efficiency of the air gaps to reduce heat flow.
Thinsulate is supposed to allow
moisture to escape e.g. from sweat, which is supposed to evaporate, so
Thinsulate is credited in being a 'breathable' material like
Gore-Tex. described above.
A further advantage is that
thinsulate fibres absorb very little water, so they retain their insulating
properties and still keep you warm even if your clothes get wet.
TEFLON - poly(tetrafluoroethene)
TEFLON need ref in oil-polymer pages
The formation of the polymer of
poly(tetrafluoroethene) by the polymerization of the monomer
tetrafluoroethene (n is a very large number and can be several thousand!)
TEFLON is the trade name the polymer called poly(tetrafluoroethene)
or polytetrafluoroethene, known by its acronym of PTFE.
PTFE is noted for its marked
chemical inertness and high thermal stability - very heat resistant, only
softens at 320oC.
The excellent chemical
resistance is characteristic of all highly fluorinated polymers.
It is also an excellent
electrical insulator and so is used in hard wearing insulating material
It is unusually slippery for a
polymer and is used in kitchen equipment e.g. to make non-stick coatings for pans - food adhesion is
reduced by the particular molecular properties of PTFE.
It is used in the clothing
industry to make clothes fabrics that dirt finds difficult to stick to.
Because PTFE is strong and chemically unreactive
can be used to make pipes to carry potentially corroding fluid and containers
for storing and transporting chemicals.
Its properties also make it useful as
a component in the production of Gore-Tex.
PTFE (Teflon) is hydrophobic, meaning it
easily repels and shreds water AND it is also oleophobic and shreds oil in
the same way it repels water. Both types of these liquids has difficulty in
adhering to a PTFE surface.
Because surfaces coated with Teflon are
both oleophobic and hydrophobic, they are not readily wetted by either
liquids allow them to be used in a variety of applications where a clean
surface is particularly desirable e.g.
Cleaning surfaces is easier and more
thorough AND a surface can be made self-cleaning.
PTFE coating materials bond with many
different surfaces at the nano-scale to create easy-clean, water and oil
resistant, anti-smudge coatings.
This type of coating is being used for
eyeglasses and other surfaces such as flat panel displays, and stainless
Part 6d. Hydrophobic coatings and
super hydrophobic coatings
As already mentioned above, specialised
PTFE coatings create a water-repellent (hydrophobic) and oil-repellent
(oleophobic) surface to repel water, dust, oil, and dirt on surfaces
allowing for easy-clean glass and easy-clean metal.
There are many other materials such as
silicone polymers that give materials good water repellent (hydrophobic)
properties but water repellence varies from material to material - not all
are super repellent!
- Ultrahydrophobic (or superhydrophobic) surfaces are
highly hydrophobic, i.e., extremely difficult to wet. A droplet of
water impacting on these kind of surfaces can fully rebound like an elastic
- How do superhydrophobic surfaces work? e.g. coating a
with a super hydrophobic spray or dipping the object into a
super hydrophobic liquid.
- A superhydrophobic coating is a nanoscopic
surface layer that has extremely effective water repellent properties.
- The intermolecular bonding forces between water
and the nanoscale super -hydrophobic coating are extremely weak, hence
the water forms into droplets and cannot wet the surface. This explanation
applies to all hydrophobic water repellent surfaces, but superhydrophobic
materials have an outstanding water repellence.
- Superhydrophobic coatings rely on a delicate micro or
nano structure for their repellent properties.
- Unfortunately, this delicate structure is easily
damaged by abrasion or cleaning so these coatings are usually applied to
surfaces not prone to wear e.g. electronic components.
- Super hydrophobic coatings reduce friction in fluids
e.g. a boat hull moving through water, but here, the constant friction would
require constant re-application of such a coating to maintain a high degree
- Apparently silica-based super hydrophobic nanoscale
coatings are the most cost effective to use?
- Super hydrophobic materials can also be made from
e.g. titanium dioxide (TiO2) nanotubes, carbon nanotubes, metal
- I assume that many of the applications of PTFE
described above, can also be done with the newer superhydrophobic coatings,
and even better i.e. from hydrophobic to superhydrophobic?
- Note that most applications mentioned are to do with
an exterior surface coating, but Gore-Tex is a multilayered fabric material,
but I assume its hydrophobic nature is not as good as a super-hydrophobic?
- Nature note: As ever, 'mother nature' through
evolution, was there first! There are many super hydrophobic surfaces in
nature, including lotus leaves, butterfly wings and duck feathers etc. where
a water repellent surface is desirable!
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
Nanomaterials including carbon nanotubes, carbon fibres and silver nanoparticles
are on a separate page
More on chemistry applications:
Uses of 220+ chemical elements, compounds, mixtures &
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