Surface modification of a microcellular porous solid: carbon foam

Abstract Microcellular solids such as carbon foams offer unique advantages over traditional solids in many applications. However, since these structures are 80–90% porous, they have a high interface/volume ratio, and surface driven properties such as atmospheric tolerance and bond formation with the matrix material are crucial for applicability. This calls for controlled surface modification techniques that can tailor surface-related properties without compromising the desirable bulk properties of the material (graphite in this case). Several types of modification, using liquid-phase and plasma-phase treatments, have been investigated by this group. One of the goals is to improve composite formation. If a composite is to be made with the foam, it needs to be infiltrated with a matrix phase (e.g. epoxy for structural composite or metal for thermal composite). Enhanced infiltration of the matrix material and optimum bond-strength is achieved by surface treatments that increase chemical affinity between the two phases. Hydrophilic coatings that increase oxygen-functional groups on the surface are seen to be very effective. The second modification goal is to enhance the foam’s durability as a stand-alone solid (such as in a lightweight sandwich structure or thermal dissipation foam). Coatings that incorporate moisture-repellent and chemically inert groups (such as fluorocarbons) achieve this. The following aspects of these coatings have been discussed: (a) chemistry of specific surface functional groups, (b) contact angle changes with water, and (c) infiltration of water (which is a predictor of infiltration of other polar compounds). The significance of these results to our understanding of composite interfaces and future fabrication issues has been discussed.