Probing The Surface And Interface Of Epoxv Resin By No Linear Optical Technique

Epoxy resin, a species of thermosetting polymer material with favorable adhesion,insulation, corrosion resistance and high strength performance, has become animportant and indispensable foundation in most of the industrial fields such aselectronics, electrical, mechanical manufacturing, chemical corrosion, aerospace,shipbuilding, transportation, chemical building materials, water conservancy,hydropower, and so on. Many attentions are focused on it due to such a n importantrole. However, due to the limited characterization techniques, the bulk structure andcuring process could only studied by infrared or differential scanning calorimeter,resulting no direct reflects on epoxy surface and interface structure.With the development of science and technology, a unique interface sensitivityand selectivity spectroscopy techniques, Sum frequency generation (SFG), has beenrapidly developed in the last twenty years, becoming one of the most powerful meansof experimental research on material surface and interface structure. Therefore, in ourstudy, SFG is employed to commence a systematic research on the epoxy resin incombination with other characterization methods, estimating the impact of theexternal environment on the surface structure, the curing kinetics of the surface orresin bulk, as well as the relationship between epoxy resin adhesive performance andits surface or interface structure. The main conclusions are summarized as follows:(1) SFG and contact angle measurement were used to monitor the surfacestructure of epoxy resin in different environment. The surface structure of glyceroldiglycidyl ether and resorcinol diglycidyl ether were almost not affected by moistureinduction, while they changed after thermal anneal treatment instead, causing themethylene group segregated to the surface and the hydrophilic epoxy groups to thebulk of epoxy resin.The surface structure of polybutadiene-modified epoxy resin (B008-8) was notinfluenced by the environmental change at the same condition. The reason is that thepeak of2995cm-1in ssp polarization combination should be attributed to the end of the vinyl CH2instead of the epoxy peak and the orientation of the end of the vinylCH2is combined by the tilt angle and twist angle, forming a special order side tilt andtorsion structure on the surface, thereby engendering a strong SFG signal.(2) DCPD was used to investigate the curing kinetic process of the epoxy surfaceand bulk. The result shows that the curing process of surface and bulk is notsynchronous. The curing process of bulk is fast and complete while the surface isslow and can not achieve completely cured even though extending the curing time.Surface energy of dicyclopentadiene-modified epoxy resin (DCPD) andbisphenol A can be obtained by testing the static contact angle of water anddiiodomethane. It is found that bisphenol A has high surface energy, the surface ismainly occupied by DCPD while the content of bisphenol A is small, as a result, thesurface of DCPD can not be completely cured. This conclusion can be confirmed bychanging the curing temperature. Since the content of curing agent is small on thesurface, the surface curing process can not influenced by varying curing temperatureor the curing time, while the curing reaction process is accelerated by elevating thecuring temperature in the bulk.(3) The adhesive property of biphenyl-type epoxy resin (BPE) and DCPD isinvestigated. The result shows that both of them have poor adhesive property to Cu.the addition of B008-8, which has flexible chain, significantly increases the bondproperty of DCPD and BPE, and the adhesion strength increased with the increasingcontent of B008-8. At the simulation of ageing experiment, the system still haveexcellent bond property after B008-8is added to the system. From the experimentalanalysis it is found that the surface energy of B008-8is the lowest among the threekinds of epoxy resins. The interfacial energy of B008-8is also lowest between thethree kinds of epoxy resins and Cu substrate. That is to say, B008-8contact with Cusubstrate directly. It is confirmed by SFG measurement.Comparing to DCPD or BPE, B008-8is preferentially contact with the Cusubstrate, so it has a well bond property. B008-8can react with DCPD or BPE easily,forming a dense network structure with excellent adhesive capacity, which preferablyprevents epoxy chain configuration from destroying.