Because aggregates on optical films can cause light to scatter, the goal is to make the films as smooth and uniform as possible. David N. Donovan. Convection is actually caused both by heating and the Earth's gravity. Any aggregates in space-produced films can only reach the quartz through the slower process of diffusion . Because microgravity reduces convection, films made in space have fewer polymer aggregates than those made on Earth.
Convection causes other problems for the production of optical films.
Convection can affect the distribution of molecules in a fluid, so films created on Earth can have regions that are rich or poor in certain molecules rather than evenly dispersed throughout. Because there is little convection in a microgravity environment, scientists can produce smoother and more uniform films in space. These films were developed by the 3M Corporation using physical vapor transport. That will show us how to do things differently on the ground. The ultimate goal is to be able to produce uniform thin-films here on Earth.