Wildcards in layerDefinition

I've been working on a widget to allow a user to filter the display of a FeatureLayer by setting a layerDefinition expression in the parent ArcGISDynamicMapServiceLayer's layerDefinitions property. I'm wondering if it is possible to use wildcard expressions in the layerDefinition? I've tried using both '*' and '%' as wildcard characters. I have tried using '=' and 'LIKE' as the logical operators in the expression but none of those options seem to work?

Thanks!