The present disclosure describes an additive that may be used in the manufacture of thin-film polyamide composite membranes. Thin-film polyamide composite membranes are used in filtration processes, such as reverse osmosis and nanofiltration. The additive may be an amino-siloxane compound. The amino-siloxane compound includes repeated groups of silicon bonded to oxygen with at least one amine functional group. Optionally, the amino-siloxane compound may also include a hydrophilic group. The additive reacts with an aqueous phase and an organic phase to form a thin polyamide film on a porous substrate.