What Makes Glue Sticky? (Blog)

What makes things sticky?

Here at FineCal, we’re no strangers to adhesives. We supply the manufacturing and engineering industry with an assortment of adhesives, whether that’s glue, sealants or tape - all of which have varying strengths and are used on a range of materials and for different purposes.

But the magic of ‘glue’ can easily be overlooked in a landscape of more obviously clever technology. From PVA to superglue, the power of adhesives is present in our daily lives without us really taking much notice. Laptops, desks, windowsills and our mobile phones are all kept together with the stuff… but have you ever stopped to wonder what makes things sticky?

Never really thought about it? Don’t worry, you’re not alone. We thought we’d prepare a basic, no frills, pub friendly way of explaining just how Glue works.

What Makes Things Sticky: A Brief History of Glue

Okay, so glue’s not new. As a species, we’ve been harnessing the power of adhesives long before we even understood why it made things stick to each other. In the past, we exploited the more natural adhesives available to us, as opposed to the artificial ones we’re more likely to employ today.

The earliest types of adhesives include sugar and water, boiled animal fats and tree sap, all of which have been observed  in  historical Egyptian Tombs, ancient pottery and burial sites - but what makes these solutions act as adhesives: why are they sticky?

Forces At Work: Adhesion & Cohesion

Before any glue comes into the equation, there are much larger, less sticky, and less visible powers at work; forces.  Adhesion and Cohesion, to be exact. For those of you who have only a hazy memory of their science O-level/GCSE, these are the two of the forces that work together to help things stick together.

Adhesion is the force that brings two separate materials together – much like when a water droplet sticks to a shower curtain or a windowpane. Water is highly adhesive, so sticks to the window or plastic curtain.

Cohesion is the force that ‘sticks together particles of the same substance’ – which is the force behind water droplets forming together to create a bigger droplet. Eventually, they become so large and heavy that gravity gets the better of them, and they fall to the ground, causing the adhesion stop them from sticking. The Cohesion has prevented the Adhesion from working.

 

All properties have an element of Adhesion and cohesion, but the more adhesive and the less cohesive a property is; the more likely it is to stick to another property.

An alternative example of adhesion and cohesion at work is to replace the water droplets with tomato ketchup. It has adhesive properties, so, like the water, it sticks to the shower curtain. However its cohesive forces aren’t as strong as water, meaning the ketchup isn’t trying as hard to conjoin with other ketchup on the curtain. This means it’s more likely to stay put on the shower curtain, because gravity can’t drag it down.

Sandwich the tomato ketchup between two shower curtains, and the adhesive nature of the sauce will cause them to stick together, causing the tomato ketchup to act as an adhesive.

The Reactions

But it’s not just these forces that help things stick together. After all, it would be quite alarming to find yourself on a plane that was stuck together entirely by the force of ketchup, let alone bringing gravity into that equation. No, when it comes to industrial glues, we need to get serious.

Further Forces & Chemicals

Modern adhesives serve very specific purposes, with some created to use solely on plastics, others with metals, and others with wood.

It’s this variety of surfaces that makes it difficult to define how all glues work, as the success of the adhesion is often based on what is being stuck together. But they generally fall into one of two categories:

  • Adsorption

As well as the force of adhesion, weak electrostatic forces (a negative and positive attraction between a substance) cause a strong bond between the adhesive and the object it’s applied to. This added electrostatic force causes the connection the two to be much stronger than adhesion alone, even though there’s actually no chemical bond between the two substances.

  • Chemisorption

In some cases, glue and the surface it’s applied to can actually create a new chemical bond, merging together to create a new chemical compound at the joint. This essentially creates a new substance that links the adhesive to the object it’s been applied to. These glues are some of the strongest in the world and are used in a variety of engineering industries.

Stick That In Your Knowledge Bank!

And that’s that, a very simplistic explanation of what makes adhesives work – enough, at least, to explain over a pint at the pub. But this is a topic that you can get really get lost in; researchers are still investigating what makes new compounds of glue so strong, meaning there is mystery still in the topic. You can read about our Epoxy adhesives in more detail on the FineCal website, or explore the range of adhesives we have online. 

Our glues range can be found here, which features a recently added range from Bondloc. https://finecal.co.uk/index.php?route=product/category&path=582