Do phototriac optoisolators (e.g. MOC3021) require pulse trains?
Once you put the minimum current through the LED (10mA or whatever the datasheet tells you for the grade of product you have) the triac turns on. If the current through the triac exceeds the holding current during the time the LED is on, the triac will stay on until the current drops below the holding current. Otherwise it will not stay on. The holding current varies with temperature and unit-to-unit considerably. Presumably you intend to inhibit charging of the cap to ensure the current drops far enough. 

In the case of mains switching a (possibly somewhat) inductive load it is sometimes useful to feed a pulse train to the optocoupler to save power, but that's not your proposed situation. Also, optocouplers used in a phase control application will have a pulse train at double the mains frequency because they have to trigger on for each half cycle- again not your situation. 

Note: It is "triac" not "TRIAC" as triac is not an acronym.