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[Display omitted] • Permeation channel was constructed via amphiphilic copolymer nanoparticles packing. • The copolymer nanoparticles were prepared by soap-free emulsion polymerization. • The membrane showed the high selectivity towards amino acids and biopeptides. • This method simplified preparation of NF membrane via nanoparticles packing route. Nanofiltration (NF) as a promising candidate is widely used in charge-based separation of ampholytic biomolecules. Construction of strongly charged permeation channel of NF membrane is one of the key factors for this process. In this work, random amphiphilic copolymer (RACP) nanoparticles were first packed to prepare nanoscale permeation channel. The RACP emulsion was firstly prepared by soap-free emulsion polymerization between [2-(methacryloyloxy) ethyl] trimethyl ammonium chloride (DMC) and methyl methacrylate (MMA), and then directly depositing onto porous substrate to form nanochannel selective layer of NF membrane. The optimal NF membrane shows a relatively large pore structure (i.e., cut-off pore size is 1.43 nm) and high pure water permeance (PWP) of 13.3 L·m−2·h−1·bar−1. Moreover, it shows a desirable rejection of basic amino acids and biopeptides (i.e., ∼95%) and allows neutral or acidic ones with similar molecule weight to permeate through. This work provides an innovative and facile method directly from RACP emulsion to construct NF membrane via nanoparticle packing, which greatly simplifies the preparation procedure for NF membrane. In addition, this novel NF membrane also demonstrates great potential in charge-based separation of biomolecules. [ABSTRACT FROM AUTHOR]

Positively-charged nanofiltration (NF) membranes have attracted more attention compared with traditional negative NF membranes. In this work, one-step self-assembly strategy was designed to prepare positively-charged NF separation layer by the close packing of poly(styrene- r -quaternized 2-(dimethylamino)ethyl methacrylate) (P(St- r -QDMA)) nanoparticles (NPs) with intramolecular crosslinking structure. Meanwhile, the pore size of NF membrane was tailored by regulating the aggregation of the NPs using different ions and annealing conditions. Herein, water was used as a dispersant to obtain P(St- r -QDMA) NPs dispersion, which is non-toxic and green. The pore size cut-off (PSCO) of the separation layer is well controlled in the range of 0.98–4.04 nm. The optimal membrane showed molecular weight cut-off (MWCO) of 380 Da (i.e., PSCO, 0.98 nm) with the isoelectric point of 9.4, which effectively improved the separation performance for divalent cations (97.2 % for MgCl 2 and 96.0 % for CaCl 2) and neutral small molecules (97.7 % for VB 12 and 92.5 % for PEG400). This work gives a novel and convenient method to construct positively-charged NF membrane with controlled pore sizes, which will be a promising candidate for water softening and molecular separation. [Display omitted] • Positively-charged nanofiltration membrane was prepared by nanoparticles assembly. • The pore size of membrane was tailored by ion concentration and annealing temperature. • It is a novel and convenient preparation method. • The membrane is promising in water softening and molecular separation. [ABSTRACT FROM AUTHOR]