Why is a membrane polar on the outside and non-polar in the inside?
Phospholipids in aqueous solution under the proper conditions organize themselves into micelles and other structures - the minimum energy state.  This allows the polar head groups to interact with water in the bulk solution, while the non-polar carbon chains are 'protected' from the polar environment.  Water is attracted to water, and the polar head groups are attracted to water, the non-polar carbon chains are excluded.
You can get inverse micelles in non-polar solvents.