Why is tape and velcro sticky? What is happening on the molecular scale of ‘stickiness’?
In: Physics
All surfaces are inherently rough at a molecular level. Any adhesive is just a substance that is flexible enough to get into the nooks and crannies of such a surface and get “wedged” inside it.
Similarly velcro is mafe up of many hook shaped plastic tines which hook on to fibers on the surface and create a bond. That’s why velcro works best with cloth like wool but won’t stick on fine silk or nylon which have fewer stray fibers.
PS: This is only valid for weak adhesives like tape not for strong adhesives like cyno acyrelic glues which work more on a chemical reaction level
velcro is actually little hooks and loops which lock together but are easily able to pull apart!! i recommend googling “velcro close up” for some cool photos of how this works.
Velcro has 2 sides, the first is soft and made of tiny loops. The second rough side is made of hooks. The hooks catch on the loops until you pull them apart.
Like people have said, velcro uses physical action between tiny hooks and loops. Nature also does this with different plant seeds that hook into animal fur to get carried around. Nothing is ever really smooth, Even at the smallest scales it’s always full of little cracks and crevices.
Most glues use this method to bind by mechanical action. That’s also why most glue instructions say to rough up the surface first. To give it more little nooks and crannies to get into and hold fast.
On the molecular scale is when things start getting weird. At this level stickiness becomes more about electric charges. For example on the pads of their feet geckos have tiny tiny little hairs that branch out into even tinier little hairs.
Using something called Van der Waal’s forces these little hairs essentially create tiny magnets with the molecules and atoms of what they’re climbing on. Even though each individual hair has a very weak magnetic attraction there are so many of them they allow something big like the gecko to stick to walls and ceilings.
Things like super glue use this level of stickiness they get into the same nooks and crannies like mechanical glue but then they make use of certain chemical reactions to cause the electrically charged level of stickiness. And that’s why things like superglue are so strong.
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