Practical Application of Intermolecular Forces

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Practical Application of Intermolecular Forces

• A Study of Adhesives

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Introduction

• Adhesive The name for the glue. There are many
  types of adhesives, which include
• Yellow and White Glue
• Instant Glue
• Contact Cement
• Polyurethane Glue
• Epoxy Glue
• Spray Adhesive
• Construction Glue
• Hot Glue
• Substrates The material that is being glued
  together. Plastic, wood, metal, ceramic, glass,
  rubber, etc.

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An adhesive is a substance that sticks to the
surface of an object such that two surfaces
become bonded.
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The adhesive will wet or cover the substrate,
when the Intermolecular forces between the glue
and the substrate are stronger than the
Intermolecular forces between the glue and glue.
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Good wetting occurs if the adhesive spreads out
over the substrate in a uniform film and in doing
so makes a lower degree contact angle between the
substrate and the adhesives Poor wetting occurs
when the adhesive forms droplets on the surface
making a higher degree contact angle
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For an adhesive to wet a surface, the adhesive
should have a lower surface tension, than the
solids surface energy (or critical surface
tension),
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Adhesive viscosity refers to the resistance for
the glue to flow . A low viscous adhesive will
flow into the spaces and gaps in the substrates
surface producing maximum coverage forming a
mechanical bond to the substrate.
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Adhesive Curing

• Once the adhesive is applied to the substrate, it
  will begin to cure, or form a permanent bond
• Different Adhesives have different mechanisms in
  which the curing takes place

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Drying As the liquid solvent evaporates or is
absorbed by the substrate, the solid adhesive is
left behind, causing the bond to form
These adhesives come ready to use and set to a
colorless glue line at room temperature by losing
water. Elmers glue is one example.
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Cooling The adhesive is applied hot, and when
cooled it becomes a solid, producing the bond
Mostly animal glues, these glues are applied hot
and cure by cooling
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Chemical Reaction For two part adhesives, there
is a reaction that occurs to form a crossed link
adhesive
Often called Epoxy this glue is a thermosetting
polymer formed from reaction of an epoxide
"resin" with polyamine "hardener".
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Moisture Cure Adhesive absorbs water from the
atmosphere or substrate to form a polymer layer
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UV Cure Ultraviolet light is absorbed by the
polymer to form crosslinks that cure very
quickly.
Mostly used in industrial applications, these
adhesives are used in manufacturing electronics
and create a very strong bond
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Anaerobic Adhesives When deprived of oxygen,
the adhesive hardens to form the bond
Aerobic adhesives remain liquid until isolated
from oxygen in the presence of metal ions, such
as iron or copper. For example, when an
anaerobic adhesive is sealed between a nut and a
bolt on a threaded assembly, it rapidly cures
or hardens to form a tough cross-linked plastic
with tenacious adhesion to many metals.
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So What sticks to what?
In the following lab you will investigate wetting
and curing with some commonly used household glues