Change collision properties through time I've recently started working with blender. For a project i'm working on i would like to visualize evapotranspiration of a park. 

My animation starts with nighttime where dew is created (picture 1) where the trees and grass collect particles with a collision. 

Picture 1:



Then during day the trees, grass and water should evaporate particles. But because there is a collision on the trees, the particles will stick to the bottom of the trees... (see red circle picture 2).

Picture 2:



Question: is there a way to change the properties of the collision after a certain frame?
Like many of the values in blender the collision properties can be animated. You can't enable/disable collision entirely but you can change properties such as friction and stickiness so that it is effectively disabled.

Either with the cursor over the value press I or  RMB and select Insert Keyframe, then go to another frame, adjust the value and insert another keyframe.

When changing values in an on/off manner it is common to add keyframes on two neighbouring frames. In the graph editor, you will want to change the interpolation type by selecting the keyframes, pressing T and choosing either vector or constant to prevent value variations between frames.