Fluoropolymer Membrane Surface Modification for Particle Retention

The patent applies surface modification only to the outer surface of the membrane while preserving the bulk structure. The surface is treated to create a denser layer with smaller effective pore sizes for better particle retention, while the inner bulk structure remains porous to maintain liquid permeability. This local differentiation resolves the contradiction by improving filtration at the surface without compromising overall flow through the membrane.

The membrane structure is segmented into two functional zones: a modified surface layer for particle retention and an unmodified porous bulk for liquid transport. The surface modification process (such as plasma treatment, chemical etching, or coating) creates a distinct functional layer that separates the filtration function from the permeability function, allowing each to be optimized independently.

The patent creates a surface layer with smaller effective pore sizes or tighter structure specifically at the membrane surface where particle capture occurs, while the bulk membrane maintains larger pores for efficient liquid flow. This local quality differentiation allows the membrane to achieve both tight filtration at the surface and high permeability through the bulk.

The solution transitions from uniform three-dimensional pore reduction throughout the membrane to a two-dimensional surface modification approach. By confining the pore size reduction to the surface dimension rather than throughout the entire membrane volume, the patent achieves particle retention improvement without the permeability penalty that would result from bulk pore reduction.