Shock value
Question: Could someone please tell me why and how fabric conditioners reduce
the amount of static electricity in clothes?
Answer: Static electricity is an imbalance of electric charge: a lack or
overabundance of electrons on the surface of the material. This typically occurs
by 鈥渢ribocharging鈥濃�攚hen two materials are brought into contact then
separated, electrons are exchanged by the materials, leaving one with a positive
charge and the other with a negative charge. Friction between the two materials
can enhance this charge-separation process.
Under normal atmospheric conditions, fibres such as cotton and wool have a
relatively high moisture content, which makes them slightly conductive. This
prevents the charge separation from occurring by allowing static electricity to
be conducted away. However, synthetic materials have a high surface electrical
resistance鈥攑articularly when humidity is low鈥攁nd this prevents the
charge dissipating. A layer of fabric conditioner simply reduces the electrical
resistance of the surface of fabrics.
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Paul Thompson
Twickenham, Middlesex
Answer: Static build-up in clothing is caused by fibre-to-fibre,
fibre-to-person and even fibre-to-air friction, and depends on the type of fibre
from which the garment is made. The amount of static build-up is also highly
dependent on the relative humidity鈥攖he higher the humidity the lower the
charge. Fibres such as rayon, silk, wool, cotton and linen have high moisture
鈥渞egain鈥濃�攖heir fibres absorb a great deal of moisture at a given humidity
from a bone dry condition鈥攁nd are low in static. Fibres such as polyester,
acrylic and polypropylene, having low moisture regain, are high in static.
Anti-static finishes or sprays come in two types. The first are made of
molecules that contain polar groups, in which charge is unevenly distributed,
and these act as conductors to dissipate static charge. The second type are
humectants, or water-absorbing materials, that also permit the textile to
dissipate static electricity. The increased moisture present on the surface or
within the fibre itself increases electrical conductance, helping to drain away
the charge.
Textile technologists can design fibres and fabrics to minimise static
electricity. In carpets, a small percentage of fibres (up to 3 per cent) can
have either a carbon core or a carbon strip to drain away static charge. Carpets
and upholstery fabrics may also be made with carbon lampblack mixed into the
latex or hot-melt backing material for the same purpose.
If the carpet is made of yarn spun from staple fibres, a small percentage of
stainless steel fibres or fibres coated with aluminium or silver vapour may be
incorporated into the blend to reduce static electricity. However, less than 5
per cent of this type of fibre can be used because otherwise the fabric takes on
a grey tinge.
Bob Wagner
Plymouth Meeting, Pennsylvania
Answer: Fabric conditioners contain a type of compound called a surface
active agent or surfactant. It鈥檚 a cationic surfactant, meaning it鈥檚 a long
molecule (rather like an oil or a fat) with a positive charge at one end. Often
the surfactant used is an ammonium compound in which the nitrogen atom is
surrounded by four organic groups.
During the washing process the negative charge that forms on the surface of
the fabric draws the positive end of the surfactant molecules to itself. These
long oily molecules then lubricate the fibres to prevent the friction that
causes static cling. It makes ironing easier, and allows the weave to relax and
supply that soft, fluffy feel.
Richard Phillips
Fayetteville, Arizona
Skull splitter
Question: Why do we have headaches? What are they?
Answer: It depends on the kind of headache.
Sinus headaches are probably caused by fluid pressure changes in the central
nervous system, or differential pressures across tissue systems, which stretch
small nerves in the sinuses. Recent medical research has found the sinuses to be
the main outlets for excess cerebrospinal fluid. Tight membrane patterns can
also squeeze minor blood vessels, creating the conditions known to produce
migraine.
The second type are headaches that are caused by simple chemical changes
within the cerebrospinal fluid. The CSF is the lymphatic system of the central
nervous system, and it needs to be replaced on a regular basis. In order to do
this it needs water, and many headaches are caused simply because there is not
enough water available to overcome osmotic pressure.
If the salinity of the CSF increases slightly its pressure goes up, and this
creates a fuzzy pressure headache which is relieved a few minutes after we
rehydrate by drinking water. The cause of the ache may be slight changes in
neurochemistry, or simply the increased pressure irritating nerve roots.
Elevated blood pressure can also raise the pressure of the CSF, as can more
serious things such as tumours.
Then there are headaches that are caused by tension patterns in the dura, the
outermost membrane surrounding the brain and spinal cord. These elastic
structures respond to tension changes as small as 20 grams in the spine, thorax
or abdomen. Because the membranes could potentially touch the surface of the
brain, and have both cranial and peripheral nerves running through them, the
potential for causing headaches is high. The source of these headaches may be
any relatively minor tension change in the body, hence the increase in headaches
we experience when we are under stress. This is a very probable cause of
migraines.
Headaches can also be caused by nerve damage. And finally, there are
headaches caused by infection of the outer membranes of the central nervous
system. When this becomes serious, it is known as meningitis.
Andrew Cook
Norwich
This week鈥檚 questions
Does my bum . . . ? I recently remarked to a female friend of mine that a lot
of the girls in Swindon wear black trousers and denim jackets. She told me it
was because black trousers 鈥渕ake your bum look smaller鈥�. Is this true? Can it be
scientifically proven?
Neil Taylor
Swindon, Wiltshire
Skin creep: My three-year-old son stumped me this morning. He was wiping
something from the window with his bare hands and wanted to know why his skin
squeaked on the glass. I didn鈥檛 know. Does anybody else?
Dawn Hanna
North Vancouver, Canada