Fill a steel pot with a thick cornstarch and water solution. Smack it HARD with a hammer. The hammer will bounce off completely dry, exactly as though it had hit cement, minus the flying chips. A slow knife thrust, on the other hand, will pass straight through it unimpeded. Sound like Dune to anyone? The "fluid" they use is made of polymers that are far longer than starch molecules, even, and instead of water, it's a more viscous oil-like fluid (except unlike oil, it's polar like solvents).

Also, replaceable composite armor packs for tanks have been using liquids, oils or gels for decades. It's one of the very few known ways to defocus the impulse delivered by shaped charges, another being to actually incorporate explosives themselves into the armor pack (not a great idea for vests!) These techniques are pretty much useless against DU projectiles, especially the "self-sharpening" ones.