Why might it be very difficult to visualize the separation of cis - and trans-2-butene by tlc?

An isomers cis 2 butene have a very closely similar physical properties and chemical properties to trans 2 butene. The isomers also behave similarly for many analytical test. The separation makes difficult on TLC for these isomers. Depending on the outside forces like temperature and radiations imparting on it the isomers changes into each-other.