2011-04-22, 09:19 AM
It's most likely related to how the two materials interact (and in this case, react). Each of them alone (noting them A and B) has weaker intermolecular interactions A-A and B-B than the interaction A-B.
That way when they are mixed the overall specific volume of the solution is lower than that of A or B.
Since this is an epoxy glue, the base is a linear or branched polymer (not reticulated) with certain chemical functions along its chain, the hardener is a small molecule at least bi-functional with a chemical group that reacts with those of the polymer. When these two are mixed the smaller molecules bridge different polymer chains making a 3D spider web that renders the polymer no longer fluid. This process also reduces the specific volume of the polymer since the molecules are closer together because of the bridges made by the hardener.
Moreover, often times there is a solvent in the base so it's less viscuous and so easier to apply/mix. That solvent also evaporates, contributing to the loss of volume on the final product.
That way when they are mixed the overall specific volume of the solution is lower than that of A or B.
Since this is an epoxy glue, the base is a linear or branched polymer (not reticulated) with certain chemical functions along its chain, the hardener is a small molecule at least bi-functional with a chemical group that reacts with those of the polymer. When these two are mixed the smaller molecules bridge different polymer chains making a 3D spider web that renders the polymer no longer fluid. This process also reduces the specific volume of the polymer since the molecules are closer together because of the bridges made by the hardener.
Moreover, often times there is a solvent in the base so it's less viscuous and so easier to apply/mix. That solvent also evaporates, contributing to the loss of volume on the final product.