Capillary infiltration kinetics in highly asymmetric porous membranes and the resulting debonding behaviors

Reliable bonding of high-performance membranes onto polymeric supporting structures is critical for capitalizing their potentials within practical filtration applications. The successful bonding typically requires infiltration of the membrane pores by a thermoplastic polymer, driven by capillary pressure and/or external pressure. In this work, we systematically examine the capillary infiltration of a polypropylene (PP) within polyethersulfone (PES) membranes with a highly asymmetric pore structure, a nominal pore size of 20 nm, and varying degrees of hydrophilicity. Most significantly, the infiltration kinetics was strongly influenced by the asymmetric pore structure in two aspects: (1) the time to achieve full infiltration from the large-pore side was approximately 4 times shorter than that from the tight-pore side; (2) When bonding from the tight-pore side, the infiltration depth, L(t) showed L (t) similar to t(1.6), instead of characteristic L (t) similar to t(0.5). The accelerated infiltration rate over time was successfully modelled with the Cai model using depth-dependent pore size that captures the asymmetric pore structure. Furthermore, chemical modification reduced the initial infiltration rate only, which is attributed to the reduction in surface porosity. No significant difference in infiltration kinetics at the later stage was observed. Mechanical integrity tests of the bonded samples display complex debonding behaviors including complete peeling, incomplete peeling, and complete membrane failure. The peel force corresponding to membrane failure appeared larger than the other two debonding modes, all of which showed insignificant dependence on the membrane chemistry or infiltration depth. Post-mortem analysis of the completely peeled sample showed PP nanofibers were pulled out of the PES membranes during debonding, emphasizing relatively weak mechanical interlocking due to the low surface porosity.

Automated summary

This study systematically examines the capillary infiltration of polypropylene within polyethersulfone membranes and identifies the significant influence of asymmetric pore structure on the infiltration kinetics. The Cai model successfully captures the accelerated infiltration rate over time. Chemical modification only affects the initial infiltration rate and has no significant impact on the later stage. Mechanical integrity tests reveal complex debonding behaviors, with the peel force corresponding to membrane failure being larger. The presence of PP nanofibers pulled out during debonding highlights the weak mechanical interlocking due to low surface porosity.