Surface phase Terms Links

The organosilane stationary phase has been called a brush phase. It consists of reacting a silica surface with dimethyloctylsilyl-chlorosilane at elevated temperatures, which causes the bonding of the dimethyloctylsilyl group to the surface (Fig. 2.1). As a result, the product is a surface covered with dimethyloctylsilyl chains, like bristles of a brush. Thus, the term brush phase sometimes is used. This derivatization is monofunctional in that only one Si-O-Si link exists between the silica particle and the alkyl-bonded phase. 

We present here some aspects of the surface chemistry and some explanatory models for vrater-polymer and related Interfaces. The term "poljrmer" will be taken to mean an essentially organic material, of sufficiently high molecular weight and (or) sufficiently cross-linked that a stiff (as opposed to fluid) phase is Involved. The material Is Insoluble In water, so that the term "water-polymer" Interface refers to what Is macroscopIcally an ordinary phase boundary. Typical polymers In the present context will be polytetrafluorethylene (PTFE), and polyethylene (PE). Solutions of macromolecules are thus not considered, nor is the related topic of so-called hydrophobic bonding, although some of what Is discussed here is relevant to that subject. 

A. Surface Free Energies. Surface free energies must dominate any explanation of the adhesion between different phases which are not mechanically linked. Current levels of understanding of adhesiveness are such that actual adhesive strengths are always much less (1-0.1%) than those predicted by thermodynamic analysis, and often there is apparently little correlation between the two. Further refinement of the theory of adhesiveness will require understanding of the importance of flaws in an adhesive joint and of the relative contributions of polar and dispersive Van der Waal s interactions. The following is an analysis of adhesion in terms of surface free energies. 

---