Amine　monomers　of　different　chemical　structures　and　multiple　reactive　functional　groups,　namely　tris(2-aminoethyl)amine　(TAEA),　triethylenetetramine　(TETA),　and　1,3-diaminopropane　(DAP)　was　reacted　with　acyl　chloride　monomers　such　as　1,3,5-benzenetricarbonyl　chloride　(TMC)　and　suberoyl　chloride　(SC)　to　synthesize　polyamide　thin　film　composite　membranes　through　interfacial　polymerization.　The　effect　of　membrane　formation　mechanisms　on　nanofiltration　was　investigated,　A　variable　monoenergy　slow　positron　beam　was　used　to　explore　the　differences　in　the　free　volume　diameters　of　polyamide　layers　composed　of　different　chemical　structure.　The　results　revealed　that　the　polymerization　degree,　free　volume　diameter,　and　selective　layer　thickness　of　the　polyamide　layers　were　strongly　correlated　with　each　other.　Specifically,　a　high　polymerization　degree　induced　a　small　free　volume　diameter　and　a　thin　selective　layer.　The　cross-linked　TAEA-TMC　polyamide　layer　exhibited　a　free　volume　diameter　of　3.9　A　and　was　the　thinnest　(168　nm)　among　the　synthesized　membranes,　whereas　the　linear　DAP-SC　polyamide　layer　was　the　thickest　(873　nm)　with　a　free　volume　diameter　of　4.7　A.　Finally,　a　stability　test　on　the　TAEA-TMC/PAN　showed　a　slight　fluctuation　during　the　36　h　filtration,　salt　rejection　maintained　stability　at　around　97%　and　water　flux　of　22.3　L　m(-2)　h(-1).　(C)　2017　Elsevier　B.V.　All　rights　reserved.