To save mixing my gin or vodka martinis with ice and over-diluting them I pre-mix them and put them in my freezer. When I take them out they are a sludgy mixture of randomly aligned ice sheets which melt quite quickly once in a glass. How do these sheets form? I tend to make my martinis about 8 parts vodka or gin to 1 part dry vermouth.

I make ice lollies with pure apple juice to keep the kids hydrated in the heat. But they just suck out the flavour (and sugar) and throw the ice away. This doesn't happen with commercial ice lollies. What the manufacturers' trick and can I copy it at home? 

My friend and I work in a molecular biology lab, with regular access to a -80C lab freezer.  The other researchers' and students' sample tubes/vials are kept in boxes or sealed ziplock bags in the freezer.  Occasionally, after a period of storage, a random ziplock bag will be inflated almost to bursting point.  On speculating why this could be, I suggested that the water droplets in the air that is trapped in the bag will freeze rapidly and hence expand, and the pressure increase causes the bag to inflate.  My friend disagrees, reasoning that expansion of water droplets alone can't possibly account for the huge increase in volume inside the bag.  Who is right or, if neither, what is the correct explanation?