Hydrogel membranes made from crosslinked microgel multilayers with tunable density

Membranes with precisely adjustable properties are needed to master the separation challenges in modern biochemical processes. Composite membranes are composed of a conventional membrane and an adaptive coating. Adaptive polymers like polymer brushes or hydrogels have proven to be excellent candidates for this challenge. In the present work we envision the utilization of temperature responsive microgels as colloidal building blocks, forming an adaptive separation layer on top of a porous support. Until now, microgels are mainly used as a functional gating element, influencing the retention or permeability of conventional membranes. In the present study microgel assemblies should be used as the only selective layer. To overcome the repulsive forces between the microgel particles, we utilize the interparticle crosslinking within a microgel filter cake. We could show that the crosslinking leads to stable and responsive microgel multilayers with a temperature responsive retention performance based on charge repulsion and size exclusion. The developed methodology enables the control of the filter cake compression, which can be adjusted and preserved via crosslinking enabling full control over the thickness and density of the selective layer. While the resistance of the crosslinked microgel multilayer shows the classical temperature responsiveness and collapse into a low resistance state, the retention increases simultaneously, indicating that the crosslinked microgels behave like a macroscopic hydrogel.