Surface tension epoxy resins

From Tables 7.7 and 7.8, it can be forecast that epoxy adhesives will wet clean aluminum or copper surfaces. However, epoxy resin will not wet a substrate having a critical surface tension significantly less than 47 dynes/cm. Epoxies will not, for example, wet either a metal surface contaminated with silicone oil or a clean polyethylene substrate. 

TPX shows an excellent peelability from a wide variety of materials. Therefore, TPX is used in applications in that separating properties are important. For this reason, it can be used as a release material in the process of curing thermosetting resins. In Table 4.4, the separating force expressed as surface tension of various materials against an epoxy resin are shown. 

DEAPA was used in several early commercial epoxy adhesive formulations. Schonhom and Sharpe9 have shown that this amine is surprisingly effective in reducing the surface tension of epoxy resins (Table 5.4). It is speculated that the utility of DEAPA adhesives is in part due to better wetting than other epoxy formulations. 

TABLE 5.4 Surface Tension of Several Epoxy Resin Formulations... 

Fluoroepoxies have gained interest because of the unique adhesion properties that can be provided by the fluorine groups. There have been several attempts to marry the properties of epoxy resins with those of fluorocarbon resins. In general these have focused on adhesive systems that (1) have a lower surface tension than unmodified epoxy or (2) have significant hydrophobicity to resist exposures in moist environments. 

As observable from the SFM topography measurements, the surface of the epoxy inside the holes of the copper film exhibits a slight convex curvature, probably due to the surface tension of the epoxy formulation. Hence, the epoxy surface nearby the Cu/epoxy interface was not in contact with the mica substrate when curing the mixture of epoxy resin and curing agent, and any interference on the curing reaction from the presence of the mica can be ruled out. On the other hand, the local slope of the curved epoxy surface is... 

In a somewhat similar fashion, Ishii et alP- have demonstrated inkjet fabrication of polymeric microlenses for optical chip packaging. UV curable epoxy resin is deposited onto optical devices by inkjet printing. When the droplets hit the surface, they form into partial spheres due to their surface tension, and are UV-cured to form the microlens with diameters from 20 to 40 tm with /-numbers of 1.0 to 11.0. Their uniformity in a microlens array was measured to be within 1% in diameter and 3 tm in pitch (total count of 36 lenses). They have also demonstrated hybrid integration of inkjetted microlenses with a wire-bonded vertical-cavity-surface-emitting laser (VCSEL) with coupling efficiencies of 4 dB higher than without the microlens. 

Finally, it is highly desirable to improve the ability to calculate the properties of surfaces and interfaces involving polymers by means of fully atomistic simulations. Such simulations can, potentially, account for much finer details of the chemical structure of a surface than can be expected from simulations on a coarser scale. It is, currently, difficult to obtain quantitatively accurate surface tensions and interfacial tensions for polymers (perhaps with the exception of flexible, saturated hydrocarbon polymers) from atomistic simulations, because of the limitations on the accessible time and length scales [49-51]. It is already possible, however, to obtain very useful qualitative insights as well as predictions of relative trends for problems as complex as the strength and the molecular mechanisms of adhesion of crosslinked epoxy resins [52], Gradual improvements towards quantitative accuracy can also be anticipated in the future. 

Several very interesting classes of materials may also result from proper fluorination of conventional monomeric or polymeric diepoxides. The conventional diepoxides or epoxies" are extremely useful adhesive materials. The epoxy resin which we have examined in this study has a surface tension of 47.2 dynes per cm. Appropriate fluorination of this... 

Completion of the reaction and the degree of conversion of the epoxy groups were determined by IR spectroscopy. To determine the equUi-brium value of the surface tension, a quantity of PEPA was added such that the extent of epoxy group conversion would not exceed 30—35%. In this case the resin remained in the liquid state. 

These findings are confirmed by study of the thermodynamic parameters of mixing of the cured epoxy resin with OP-20. At 6-7% content of surfactant, corresponding to the maximum surface tension of the polymer, a kink and an area of decrease of the Flory-Huggins parameter are observed in the dependence of X2,s on the surfactant concentration. This anomalous dependence can be explained in terms of the rearrangement of the intermolecular bonds in the polymer-surfactant system. With ED-20 initial resin, there are no extrema on the curve. Alteration of the macromolecular conformation affects the supermolecular structure of the polymer. Adding surfactant to ED-20 resin changes the form and causes a noticeable decrease of the size of the polymeric supermolecular formations. 

THE STATIC SURFACE TENSION OF EPOXY RESIN AND ITS ACETONE SOLUTIONS. 

THE STATIC SURFACE TENSION OF EPOXY RESIN AND ITS ACETONE SOLUTIONS. //ENGLISH TRANSLATION OF DOKLADY AKAD. NAUK SSSR 167 /6/ 1325-6,1966.//... 

Figure 20.27 SEM micrograph of the fracture surface of a carbon fiber epoxy resin laminate after a fiber buckling mode failure due to a longitudinal compression stress viewed under high magnification showing both tension and compressive fracture in a single fiber. Source Reprinted with permission from Ewins PD, Potter RT, Phil Trans R Soc London, A294, 507-517,1980. Copyright 1980, The Royal Society of Chemistry.

---