THE SCIENCE OF STICKING

Hold on,
let go.

Sticking is two pulls working together.

Adhesion is a substance clinging to something else; cohesion is a substance holding on to itself. Every glue, tape and sticky note balances the two, and a gecko's foot shows how to do it with no glue at all.

STICK then let go

Compare the grips

A small green gecko clinging upside down to a pane of glass, its splayed toes pressed flat against the surface — AI-generated image, not a photograph of a real person or place.

Cling to the surface
Hold yourself together
Know how to let go
Two pulls, one bond

THE SHORT ANSWER

Two kinds
of stickiness.

A bond can fail at the surface or in the middle.
Good sticking needs both pulls to hold.

ADHESION

Clinging to something else

The US Geological Survey describes adhesion as water being attracted to other substances, like a droplet hanging from the end of a pine needle.

Compare the grips

LOW TACK

A glue made to let go

In 1968 a chemist made an adhesive of tiny acrylic spheres that touched surfaces only at points: strong enough to hold paper, weak enough to peel off.

Read the story

GECKOS

Sticking with no glue

Gecko toes carry about two million microscopic hairs. Berkeley researchers found they cling by weak attractions between molecules.

See the numbers

A QUICK GRIP CHECK

How does it
hold on?

Pick something sticky to see how it holds and how it lets go. The bar shows how permanent the hold is meant to be.

Grip check

Choose a sticky thingA raindrop on a needleA sticky noteA gecko's toeMany everyday gluesSuperglue

A raindrop on a needleAdhesion

The drop holds itself together by cohesion and clings to the needle by adhesion, the USGS explains.

A sticky notePeels clean

Its adhesive is made of tiny spheres that touch only at points, so it holds paper yet comes away without tearing and can be stuck again.

A gecko's toePeels at 30°

Millions of hairs grip by van der Waals forces. When a hair is levered up to a 30-degree angle, its tiny tips come away easily.

Many everyday gluesSets as it dries

Many glues bond as their solvent evaporates, after seeping into small cracks and pores and then hardening.

SuperglueSets with moisture

Cyanoacrylates react with water; even water vapour in the air starts the reaction. They form a strong polymer that is hard to tear apart.

Sources: USGS Water Science School; Compound Interest, The chemistry of superglue; Lemelson-MIT; UC Berkeley news releases (2000, 2002).

Based on the US Geological Survey, Compound Interest, Lemelson-MIT and UC Berkeley research news.

TWO NUMBERS WORTH KNOWING

Small contacts,
big hold.

One figure from a gecko's foot,
one from the life of a weak glue.

≈ 2million

Microscopic hairs on a gecko's toes

Each hair ends in hundreds to thousands of tiny pads. Researchers reported in Nature in 2000 that the combined force of all the hairs is about 10 times what is needed to pull a gecko off a wall.

GECKO FEET · UC BERKELEY

12years

From weak adhesive to the shelf

The low-tack adhesive was made in 1968. A colleague later saw it could anchor paper bookmarks, and the notes launched nationwide in the US in 1980.

LOW-TACK GLUE · LEMELSON-MIT

A 2002 UC Berkeley study ruled out a film of water as the gecko's secret and concluded the grip comes from the shape of the hairs, not their chemistry.

FOUR THINGS TO NOTICE

Sticky science
at the kitchen table.

These ideas show up in everyday jobs, from mending a mug to marking a page.

Watch a raindrop
Cohesion holds the drop together; adhesion keeps it clinging to whatever it lands on, like a pine needle.
Give glue somewhere to go
Glue grips partly by seeping into small cracks and pores and then hardening, as well as by attraction between molecules.
Peel, do not pull
Geckos let go by peeling their toes. Peeling a note or tape from one edge works on the same idea.
Keep superglue off skin
Skin holds moisture, which can start superglue setting. Packets warn to keep it away from eyes and mouth.

Two pieces of broken pottery being pressed together over a workbench, a thin line of clear glue along the join — AI-generated image, not a photograph of a real person or place.

A hand peeling a yellow sticky note from the page of an open book, leaving the paper unmarked — AI-generated image, not a photograph of a real person or place.

THE WEAK GLUE

A failure that
found its job.

In 1968 a chemist made a low-tack adhesive from tiny acrylic spheres. He hoped it might become a spray or a noticeboard surface, but for five years no one found a use for it.

Then a colleague, annoyed that paper bookmarks kept slipping from his hymn book in choir, saw that the weak glue could hold them in place. After about five more years of work, the reusable notes launched in 1980.

Questions

Questions people ask

What is the difference between adhesion and cohesion?

Cohesion is a substance sticking to itself, like water molecules holding a drop together. Adhesion is a substance sticking to something else, like a drop clinging to a pine needle.

How does glue actually stick?

Several things help. Weak attractions between molecules, such as van der Waals forces, hold glue to a surface, and glue also seeps into tiny cracks and pores before it hardens. The details for particular glues are still not fully understood.

Why does superglue set so fast?

Cyanoacrylates react with water, and even the water vapour in the air is enough to start the reaction. The molecules link into a long, strong polymer chain.

How do geckos stick to walls?

Their toes carry about two million microscopic hairs, each ending in many tiny pads. UC Berkeley researchers found the hairs cling by van der Waals forces, weak attractions between molecules.

Why can a sticky note be restuck?

Its adhesive is made of tiny acrylic spheres that touch a surface only at points, so the bond holds paper but comes apart without tearing and can be used again.

Hold on,
let go.