Two immiscible uids converging at microchannel cross-junction results in the for- mation of periodic, dispersed microslugs. This microslug formation phenomenon has been proposed as the basis for a fuel injection system in a novel, discrete mono- propellant microthruster design for use in next-generation nanosatellites. Previous experimental work has demonstrated the ability to repeatably generate fuel slugs with characteristics commensurate with the intended application. In this work, numerical modeling and simulation are used to further study this problem, and identify the sensitivity of the slug characteristics to key material properties including surface ten- sion, contact angle and fuel viscosity. These concerns are of practical concern for this application due to the potential for thermal variations and/or uid contamination during typical operation. For each of these properties, regions exist where the slug characteristics are essentially insensitive to property variations. Future microthruster system designs should target and incorporate these stable ow regions in their baseline operating conditions to maximize robustness of operation.