Epoxy interphases

Adhesion - Current Research and Application. WulfF Possart 

Copyright 2005 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim ISBN 3-527-31263-3 

In principle, this ratio can also affect the IP concentration profile in a quahta-tive sense. When considering a homogeneous epoxy-amine mixture just brought into contact with the surface of an adherend or a fiUer particle, preferential adsorption of the amine molecules will result in local variations of the amine/epoxy concentration ratio r (to be defined below). Assuming a comparably fast diffusion of the amine molecules, their quick enrichment at the interface will result in a near-interface zone of increased r values and an adjacent zone of amine depletion, i.e., with reduced r values. Similar concentration variations are dealt with in the field of surface-driven phase separation in polymer solutions and mixtures [8]. While the wetting layer is in local equihbrium with the depletion layer, the diffusion from the bulk down the concentration gradient into the latter feeds the growth of the former. 

The IP concentration gradients once established will translate into spatial variations of the final network of crosslinks as well as of the related mechanical properties. In a simplified approach, this kind of IP can be thought of as a series of slabs each of which is characterized by a different but constant concentration ratio r. 

One of the key parameters defining the mechanical properties of the cured epoxy is the crosslink density. In a diepoxy fully cured with a diamine, if additional effects such as side reactions are neglected, each primary amine group is expected to react with two epoxide groups. Branched crosslinks result from this situation. With the chemical functionalities /a = 4 and /e = 2 of the diamine and the diepoxy molecules, respectively, the amine/epoxy mixing ratio, r, is given by Eq. (1), where and Ng denote the respective numbers of moles [10]. 

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Garton, A. and Daly, J.H. (1985). Characterization of the aramid-epoxy and carbon-epoxy interphases. Polym. Composites 6, 195-200. 

Fig. 9. A transmitted electron micrograph of an ultramicrotomed section of an aluminum-epoxy interphase. The highly ordered structure in the center is a 3.3 micron thick aluminum oxide layer present on the base metal. The featureless area is the epoxy matrix. The light areas within the oxide are fractures caused by the microtoming. The epoxy has however penetrated to the bottom of all of the 50 nm pores in the oxide...

FIG. 6—Fracture surface produced under ASTM D 2559 to show the high orientation parallel to the wood orientation even thou fracture is mainly in the epoxy interphase region. 

The results show that the crosslinking state and the degradation processes in the epoxy network depend not only on the type of curing agent and the aging regime. The properties of the stainless steel also change these properties within the epoxy interphase at the contact. 

Figure 11.1 Applied gross compression stress (as a percentage of the ultimate notched [O/eoigs compression strength) versus the cycles (log of n), for the 810-A and O materials under / = 10 fatigue. , epoxy interphase , PVP interphase...

The finite element analyses showed that the properties of the CNT/polymer interphase play an essential role for MWCNTs as reinforcements and the exploitation of the load-bearing character of the inner walls. Hence, concerning the preparation method one will need to take this into account to provide a sufficient bond/shear modulus at/of the CNT/epoxy interphase, possibly through the relevant functionalisation of MWCNTs. 

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