What you, guys, think that is a biggest challenge - improvement in explosives possible? I think it's not new - stronger HE. I think that it's about finding liquid propellent, liquid heavy canon gunpowder - excuse me - gunliquid. I know that there were some experiments with water solution or suspension of metylene dinitramine MEDINA - I do not have solubility data for that, but it dissapeared from all literature, which I can reach, after one article published, and that was that some country succesfully fired one shell. I know that MEDINA is nasty explosive, simile to HMX, so poor barell of that canon had to take enormous shock.
I know that purpose of this forum is not to help members to become rich, but if one solves the problem, he'll become rich as A.Nobel...;)

Primary explosives that are only sensitive to heating and not to friction/shock.

I highly doubt there will ever be a substance sensitive to heat but not friction as, if I'm not correct, friction causes the substance to heat and because of that the substance ignites.

I think it would be an amazing discovery if we could find a way to cool down matter as fast as we can heat it up. The so called "cold bomb" The problem would be to find a reaction that is so strongly endothermic that it could cool surrounding matter quickly. Cryogens like LN2 don't count becouse of the production and storage issues associated with them, but we really do not have anything that is as strongly endothermic as common exothermic reactions are exothermic. At least to my knowlege...