Running behavior of glucose, galactose and mannose in TLC

I have separated the sugars glucose, galactose and mannose by thin-layer-chromatography. My question is why these sugar have different running behaviors and a separation is possible.  

Glucose have the lowest Rf-value, then galactose and mannose have the highest Rf-value in my experiments.  

I thought it might be something to do with the position of the $\ce{-OH}$ groups (axial, equatorial) but I have no firm explanation at the moment.


Thanks for every explanation concerning the topic.


