Do you have that annoying problem where every time you touch something you shoot electric sparks from your fingertips? Or your newly transplanted hair stands on end. Welcome to the phenomenon of static electricity!
Static electricity is caused by an imbalance in the positive and negative charges between touching objects. Usually the objects involved are not good electrical conductors, which allows electrical charges to accumulate within the object or on their surface. This in fact is what ‘static’ refers to. It’s the ‘inert accumulation’ of electrical charges on or within an object as opposed to the ‘flowing’ electrical current that powers our homes.
WHAT IS AN ELECTRICAL CONDUCTOR?
An electrical conductor is a material through which electrical charges move freely. Insulating materials are the opposite – electrical charges don’t move through them very well. Therefore, when a material that isn’t a good conductor (insulating) collects additional electrical charges, they tend to accumulate on the surface of the material instead of moving through it as they would in a good conducting material. Glass, plastics, and wood are good insulating materials. Most metals, particularly copper, are good conducting materials.
WHAT ARE ELECTRICAL CHARGES?
Electrical charges originate right down in the tiniest particles in nature – the subatomic protons and electrons in atoms. Protons, or positive charges, are located in the nucleus of an atom along with neutral neutrons. Electrons, or negative charges, orbit in pairs around the nucleus in layers called energy shells. They’re held in orbit like this because, being negatively charged, they’re attracted to the positive charge of the nucleus. The strength of this bonding though varies between substances and atoms. Some materials have atoms with very weak bonds between nucleus and electrons whilst others have atoms with very strong bonds.
Atoms are also electrically neutral – they have an equal number of protons and electrons, which balances their negative and positive energy. In most cases (but not all, which is significant for static electricity as we explain in the next paragraph!), atoms are also stable. This means they have a full outer shell of electrons, or are paired up with other atoms in order to share electrons in their outer shells, thus giving them both/all a full outer shell.
We mentioned unstable atoms, and atoms with weak bonds, above. Atoms with weakly bonded electrons can easily lose them. Their electrons will readily ‘jump ship’ and join up with other atoms, notably unstable atoms ie atoms with space in their outer shells for more electrons. In the case of static electricity, this ‘ship jumping’ can happen when two different (usually non-conductive) materials come into contact, particularly if one of the materials has a stronger ‘attraction’ for electrons than the other. The ‘stronger attraction’ is usually those unstable atoms referred to above.
TRIBOELECTRICITY, THE TRIBOELECTRIC EFFECT, AND TRIBOELECTRIC SCALE
Materials with the ability to gain or lose electrons like this are referred to as triboelectric materials. The way in which electrical charges are transferred via these materials is the triboelectric effect, and the charge generated by the process is triboelectricity. Note – the triboelectric effect isn’t the only way to generate static electricity but it is the commonest way to do it.
When triboelectric materials touch, weakly bound electrons on one material are attracted to atoms with incomplete outer shells on the other material, and move across. When these materials or surfaces are subsequently separated, the electrons remain behind. This is the triboelectric effect. Scientists have graded triboelectric materials on a scale (the Triboelectric Scale) according to their propensity for either giving away, or attracting, electrons. The higher the material is on the scale, the more likely it is to give away electrons to those materials below it. In addition, the further away from each other on the scale 2 materials are, the greater the static charge they will generate if they come into contact.
THE TRIBOELECTRIC SCALE
Note – there are many slightly different versions of this ranking as some materials have very similar or almost identical triboelectric properties and usually won’t produce much if any triboelectric effect when they come into contact amongst themselves.
++++++++ POSITIVE ++++++++
+ Polyurethane, foam
+ Polyurethane, solid
+ Rabbit Fur
+ Human hair
+ Machine Oil
− Hard rubber
− Saran (“cling film”)
− Polyvinylchloride (PVC)
− Silicone rubber
− Ebonite (very hard vulcanized rubber)
CREATING TRIBOELECTRICAL STATIC CHARGE
When an electrically neutral atom loses electrons, this creates an imbalance between the number of electrons and protons it has ie between its negative and positive charges. It ends up with more protons than it has electrons, which gives it a positive electrical charge. For the atoms in the material gaining these electrons, it’s the reverse process. They end up with more electrons than protons, or more negative than positive charges, so become negatively charged. Atoms that have lost their electrical neutrality and become either positively or negatively charged like this are called ions. A positively charged ion is a cation. A negatively charged ion is an anion.
Until recently, it was thought that this simple principle – the build up of either negative or positive charges on a surface, is the cause of static build up. Recent discoveries however have found this to be an overly simplistic view and that there are actually a number of processes involved. It seems that static charge is in reality a “medley” of negative and positive charges on a surface that add up to either a negative or positive charge overall.
THOSE AWFUL STATIC SHOCKS!
If you look at the Triboelectric Scale, you’ll notice that atoms in human skin are amongst the highest known ‘donators’ of electrons! We lose them easily when we touch another non-conductive material below us on the Triboelectric Series, which goes a long way towards explaining why we’re so easily afflicted with static electricity. We also gain electrons from dry air and touching Polyurethane objects.
When we lose or gain electrons like this, our skin become positively or negatively charged respectively. Non-conductive triboelectric materials like skin have no way of naturally dispersing these charges so they accumulate. Then, when we touch something with a different electrical charge, and so long as the electrical imbalance between our now charged skin and that object is great enough, electrons will ‘jump’ from the negatively charged object to the positively charged object. It’s this process that creates the classic static electricity spark. If we’re the positively charged object the electrons will jump from the negatively charged object to us, and vice versa.
STATIC ELECTRICITY AND BAD HAIR DAYS
Of course no discussion about static or triboelectricity is complete with discussing another fascinating principle of science, one that forms the basis of all those science experiments you probably did in high school with sticking balloons, magnets et al. The principle is that objects with negative and positive charges naturally gravitate towards each other. Those with similar charges repel. This is why 2 magnets will push each other away and why a piece of plastic, or an article of clothing that’s built up static charge, will cling annoyingly to your person.
It works like this – as we’ve mentioned, your skin loses electrons when it comes into contact with another non-conductive triboelectric material like plastic, nylon or silk, which are all below it on the Triboelectric Scale. This means your skin becomes positively charged whilst the material you’re touching becomes negatively charged when it gains those additional electrons. As negative charges attract positive charges, the objects stick to you. This is static cling at work.
The opposite of static cling happens when something with individual strands like your hair becomes charged. It may pick up electrons from the air or from contact with one of the materials above it on the Triboelectric Scale, and become negatively charged. Alternatively, it may lose electrons and become positively charged when you wear a woollen, fur or silk scarf or hat. Because like charges repel, your strands of hair try to move away from each other and voila – you have a bad hair day happening!
Wearing moisturiser helps reduce static cling as moisture is a good electrical conductor and will help disperse static charge. Likewise spraying your hair with a light misting of water will also curb its fly away behaviour.