A micro-Raman study of Cu-particulate-filled epoxy matrix composites

Abstract

Epoxy resins are used in structural applications ranging from high-performance composites for aerospace applications to encapsulants for the microelectronics industry because of their high thermal resistance, high tensile strength and modulus, and good chemical resistance. It is well known that the most important factors that influence their performance are the molecular architecture, the ratio between the epoxide and the hardener, and the cure conditions, frequently at a high temperature, which determine the final properties of the material. The influence of the filler particles on the curing is still a subject of study and clearly depends on the nature of the particles [1][2][3][4][5]. Epoxy matrix composites find new applications every day in several areas of engineering and technology. For example, copper-filled composites have a high possibility of being used in microelectronics because the high thermal conductivity of copper allows the composite to be a good heat dissipator, which serves as protection to electronic devices [6,7]. The matrix-particle interphases also play an important role. The physical properties of the polymeric composites can be significantly influenced by their thermal history; in fact, internal stresses are developed during the fabrication process and further thermal treatments. Abstract. A micro-Raman study is carried out to investigate the influence of the filler on the curing process of bisphenol A diglycidyl ether (DGEBA)-based epoxy matrix composites. The composites are cured (14 h at 393 K) with an anhydride (methyl tetrahydro phthalic anhydride, MTHPA, 100:90 pbw), catalyzed with a tertiary amine (0.7 pbw) and filled with a 30% volume of Cu particles of approximately 75 !m in diameter. The experimental results are compared with those obtained for the same epoxy resin unfilled and for the same composite with Cu filler but not catalyzed. The micro-Raman experimental technique is used to search for information on the curing process in different regions of the matrix, near to and far from the copper filler, taking into account the results of differential-scanning-calorimetry measurements performed on the same composites. The results provide information on the influence of the copper filler on the curing process of the epoxy matrix. Differences were observed in the peaks associated with the epoxy ring and the ester group as a function of the distance to the nearest copper particle, but no differences were observed between the different composites.

Matrix–particle interactions in catalyzed and uncatalyzed copper‐filled epoxy matrix composites

“…Cu(II) complexes are also formed in both composites but in a greater amount in the uncatalyzed sample, as can be concluded from the increase in the peaks at 934.2 eV and 934.7 eV. In our previous work, Raman confocal measurements performed on the samples studied in this work show peaks corresponding to Cu 2 O in the region near the particles, but it could not be discerned if CuO was also present.…”

“…Although it is known that the system diglycidyl ether of bisphenol A resin (DGEBA)–anhydride can react with copper substrates, scarce information is available on the effects of copper inclusions on this system. No differences in the chemical structure of an epoxy matrix between catalyzed and uncatalyzed copper‐filled composites were observed by confocal Raman measurements . However, it would be expected that different kinds or amounts of copper complexes are formed depending on the kinetics of curing.…”

Raman imaging of residual stress distribution in epoxy resin and metal interface

“…The molecular vibration energy changes due to the displacement of the atoms in the molecule during deformation by mechanical stress, thus shifting the corresponding Raman peak. Therefore, the measurement of the peak shift makes it possible to determine the stress in the substance . By using a lens focused laser as the incident light to obtain the Raman spectrum only from a micrometer‐sized region, it is possible to measure the stress in a microregion of the interface and stress anisotropy .…”

“…Most of the stress measurements using Raman spectroscopy have mainly been performed on semiconductors, oxide, ceramics, graphene, and composite materials . As examples of applications to resin samples, the tensile stress in the axial direction of highly oriented fibers such as aramid, polyethylene, natural and synthetic polyamides, polyester/PET, and poly(paraphenylene benzobisoxazole) have been reported.…”

“…In previous reports aimed at measuring the stress distribution of bulk samples, a PbO thin film as a Raman active material was coated on an epoxy resin, or an alumina particle as a tracer for detecting the stress was mixed with the epoxy resin, and the peak shift derived from the alumina tracer was measured . However, this method may be problematic in that the physical properties of the resin may be changed by mixing in an inorganic filler with a different hardness . Therefore, it is desirable to measure stress distribution using the peak shift of the bulk resin itself without an added tracer.…”