You can create a Slide on Surface constraint to attach an nParticle object to a target surface (an nCloth surface, or a passive collision object), and allow the constrained nParticles to move or slip along the surface to which it is constrained.
You can use a Slide on Surface constraint instead of collisions, and in most cases, it works faster than collisions. For example, you can Slide on Surface constrain a liquid nParticle object to the outside of a passive object bucket, so that the particles drip down the edges of bucket.
To create an nParticle Slide on Surface constraint
 -select the target surface to which you want to constrain the nParticle object.
-select the target surface to which you want to constrain the nParticle object. 
               The target surface can be an nCloth or passive collision object that is part of the same Nucleus system as the nParticle object, or a non-Nucleus object. You cannot use other nParticle objects as target surfaces for a Point to Surface constraint.
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            The nParticle object is now constrained to the target surface, and both are connected to the nParticle object’s Maya Nucleus solver through a dynamicConstraint node.
The preset properties on the dynamicConstraint node determine the constraint’s type (in this case, a Slide on Surface constraint) and how it behaves. For example, you can create a Slide on Surface constraint with the following attribute settings:
 Except where otherwise noted, this work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License
 Except where otherwise noted, this work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License