(315f) A General Strategy for Adhesion Enhancement in Mixed Matrix Membranes by Formation of Nano-Structured Particle Surfaces

Gas separation using polymeric membranes has emerged as a rapid growing, commercially viable alternative to traditional energy-intensive methods of gas separation. However, the performance of polymeric membranes suffers from a trade-off curve between gas permeability and selectivity. Mixed matrix membranes, comprising domains of two or more intrinsically different material types, (eg. organic polymers and inorganic zeolites), have been proposed as an evolutionary approach to surpass the trade-off curve. As demonstrated by previous researchers, the most prominent technical hurdle to the successful formation of mixed matrix membrane is to control the complex polymer-sieve interface and overcome the variety of undesirable morphologies.

Substantial efforts have been made towards modifying either the zeolite surface chemistry or the polymeric matrix in order to improve adhesion at the sieve-polymer interface. These modifications are usually limited to a specific material pair and in many cases, the adhesion improvement is not adequate to ensure a completely defect-free membrane. A more general method to engineer the particle surface without being limited to a specific material pair is highly desired. We report here such a general approach to promote the interfacial adhesion in polymer/silicate composites by creating a nano-structured morphology, which appears as a significantly roughened outer surface on the filler particles. The dramatic increase in the topological roughness (physical heterogeneity) on the sieve surfaces of type 4A zeolite is believed to provide improved interaction at the interface via thermodynamically induced adsorption and perhaps even physical interlocking of polymer chains on the surface.

Polymeric composites containing this type of modified particles exhibit defect-free interfaces. Dynamic Mechanical Analysis (DMA) tests reveal that such composites have higher moduli as compared to those containing non-treated fillers with the same loadings. Furthermore, gas permeation measurements demonstrate that these materials also show impressive enhancements in gas separation efficiency. A thermodynamic argument is proposed to qualitatively explain why such nanoscale structures may contribute to improved adhesion at the interfaces.

A great advantage of this methodology is that it need not be confined to a specific material pair, since the thermodynamic principle and potential physical interlocking mechanism are universal and applicable in every occasion where similar nanoscopic morphologies can be created on the filler surfaces. Thus it is a very promising technique to be applied in mixed matrix technology to promote the interaction between polymer and inorganic fillers.