Effect of free volume hole-size on fluid ingress of glassy epoxy networks

Water diffusion and swelling stresses in highly crosslinked epoxy matrices

“…Some authors have suggested that a smaller crosslinking density, e.g. witnessed by a lower T g , is generally associated to smaller free volume (due to the collapsing of the flexible network chains), probably determined by an increased mobility of the chains of the physical network [18,19]. This would explain why DGEBF is absorbing less water than DGEBA, and with a lower diffusion rate (Fig.…”

“…Such higher density determines an intrinsically smaller chain mobility, which is by some authors usually associated to a less compact system, and hence to a higher free volume [5,11,12,19]. With temperature increase, the more flexible DGEBF network is probably more sensitive to the increased kinetics of water absorption, and this can provide an explanation for the reduction of the gap with DGEBA in absorbed water.…”

“…The kinetic of swelling stress development follows that of water diffusion, so DGEBF is slower in diffusing water and in reaching the maximum swelling stresses. The more severe decrease of glass transition temperature exhibited by DGEBF with aging is related with a reduction of cross-link density that could foster a further compacting of the free volume [19]. If this rationale is true, than the ingress of water in the kernel of the sample becomes more difficult with aging time, and this can be one reason for the persistence of high swelling stresses and their slower relaxation gradient.…”

Mapping water uptake in an epoxy-phenolic coating

“…A number of studies have concluded that resins containing a greater proportion of free volume absorb more water when polarity is controlled. [36][37] [38][39] [40] Equilibrium water uptake is, however, primarily determined by the hydrogen bonding capability of the network (polarity). [41][42] [43] [44] In such studies, the polarity and/or free volume of resins is commonly controlled using the cross-linker to epoxy ratio [33] [45] or else the chemical structure of the cross-linker.…”

“…[41][42] [43] [44] In such studies, the polarity and/or free volume of resins is commonly controlled using the cross-linker to epoxy ratio [33] [45] or else the chemical structure of the cross-linker. [36][46] [47] When considering localised water uptake however, a major source of heterogeneity lies in the distribution of cross-linking density, which is typically large for epoxy resins (characterised by high molecular weight distributions prior to gelation, yielding broad Tg transitions by DSC analysis [48][49]).…”