Surface Modification Of Microporous Polypropylene Membrane Based On Facial Amphiphilicity Of Cholic Acid

Bile acids are natural compounds that exist in most animals. Bile acids possess special facial amphiphilic structure with unusual distribution of hydrophobic and hydrophilic regions. Up to now, the properties of bile acids, such as facial amphiphilicity, chirality, self-assembly, biocompatibility, and chemicalstability of the steroid nucleus, make them have a wide range of potential applications in chemistry, material, biomedical, and supermolecules. However, researchers have not paid enough attention to the modification work of bile acids on materials surfaces. In this work, inspired by the facial amphiphilicity and self-assembly properties of bile acids, cholic acid (CA) was chosen to modification the surface of Polypropylene Microporous Membrane (MPPM). Our work is based on physical modification method and chemical modification method respectively. Besides, the properties of modified membranes was studied in detail, and their potential applications were also discussed. Our specific studies are concentrated on the following aspects:Chemical modification method is carried by immobilizing poly(2-hydroxyethyl methacrylate) brushes (poly(HEMA)) on membrane via UV-initiated graft polymerization. CA was then chemically bound to the polymer brushes with condensing agent DCC/DMAP. Physical modification method is carried by soaking MPPM in the CA solution. CA can self-assemble on the surface of MPPM directly. The structure changes of the CA modified membranes were characterized by ATR/FT-IR and XPS, which indicates that CA was successfully bounded to the polymer brushes. The grafting degree of poly(HEMA) and reactive degrees of CA were measured by the Gravimetric method. The influence of HEMA concentration on poly(HEMA)-grafting degree were investigated, as well as the influence of CA concentration and absorbing time on CA absorbing amount.The properties of CA modified MPPM were characterized by water contact angle measurement, fluorescence spectrometry, fluorescence microscopy, FESEM, pure water flux measurement. The results indicates that the surface of CA-containing polymer brushes modified MPPM is solvent-responsive. Meanwhile, it was found that multilayer of CA self-assembled on the surface of MPPM in the way of layer-by-layer. The CA self-assembled MPPM showed improved permeation property. The results suggest that bile acids self-assembly could also be developed to an easy and effective strategy for the surface modification of membranes.This work innovatively introduces CA to the surface of MPPM, which riches the researching work of CA. Chemical and physical methods were utilized to modify MPPM with CA respectively. Solvent-responsive and CA self-assembled MPPM were obtained. This work expands the application fields of CA.