Epoxy polymers. II. Macrostructure

Cuthrell, R. E.

doi:10.1002/app.1968.070120601

Cited by 72 publications

(38 citation statements)

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“…The harder, nodular domain in the matrix has been attributed to highly crosslinked material and the soft interstitial regions to less crosslinked, low molecular mass material. 8,11,28 The high crosslink density regions have been reported to be only weakly attached to the surrounding matrix, 10,11 and their size varies with cure process and other conditions. 10 A previous AFM study also reported that the air surface of an amine-cured epoxy is homogeneous.…”

Section: Surface Interface and Bulk Microstructures Of Epoxymentioning

confidence: 98%

“…A number of studies have reported that a thermoset epoxy network is inhomogeneous, containing high crosslink density regions from 6 nm to 10 4 nm in diameter and some low crosslinked interstitial regions. [8][9][10][11][12] On the other hand, several studies contend that the epoxies have a homogeneous microstructure. [13][14][15][16] One study suggested that the nodular structures often observed in the epoxy materials by electron microscopy are artifacts resulting from the interaction of the electron beam or etching agents with the sample surface.…”

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confidence: 97%

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Microstructure and morphology of amine-cured epoxy coatings before and after outdoor exposures—An AFM study

Nguyen

Oudina

et al. 2005

J Coat. Technol. Res.

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Atomic force microscopy (AFM) has been used to study the morphology and microstructure of an amine-cured epoxy before and after outdoor exposure. Measurements were made from samples prepared in an essentially CO 2 -free, H 2 O-free glove box and from samples prepared in ambient conditions. For those prepared in a CO 2 -free glove box, AFM imaging was conducted on (1) an unexposed air/coating surface, (2) an unexposed coating bulk, (3) an unexposed coating/substrate interface, and (4) a field exposed air/coating surface. For samples prepared in ambient conditions, only the unexposed air/coating surface was investigated. The same regions of the exposed samples were scanned periodically by the AFM to monitor changes in the surface morphology of the coating as UV exposure progressed. Small angle neutron scattering and Fourier transform infrared spectroscopy (FTIR) studies were performed to verify the microstructure and to follow chemical changes during outdoor exposure, respectively. The results have shown that amine blushing, which occurs only under ambient conditions, had a significant effect on the surface morphology and microstructure of the epoxy. The surface morphology of the samples prepared under CO 2 -free, dry conditions was generally smooth and homogeneous. However, the interface and the bulk samples clearly revealed a two-phase structure consisting of bright nodular domains and dark interstitial regions, indicating an inhomogeneous microstructure. Such heterogeneous structure of the bulk was in good agreement with results obtained by small angle neutron scattering of unexposed samples and by AFM phase imaging of the degraded sample surface. The relationship between submicrometer physical changes and molecular chemical degradation is discussed.

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Section: Surface Interface and Bulk Microstructures Of Epoxymentioning

confidence: 98%

mentioning

confidence: 97%

Microstructure and morphology of amine-cured epoxy coatings before and after outdoor exposures—An AFM study

Nguyen

Oudina

et al. 2005

J Coat. Technol. Res.

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“…These entailed spontaneous development of impermeable nanogel particles during the early stages of cure, yielding densely cross-linked nodules embedded within a partially cured polymer matrix. 19,29,54 This hypothesis (and the accompanying chemical heterogeneity within epoxy networks) was rejected by Dušek and others based on bulk scattering experiments and thermal analysis, where no evidence was found to support the formation of a two-phase material. 42,55 In the present study, a direct comparison of SEM and AFM imaging was undertaken, and it is clear that whilst SEM imaging resolved some surface features (giving the appearance of isolated nodules), the more detailed profiles gathered using AFM indicate that samples are comprised of fused globular structures.…”

Section: Afm-ir Analysismentioning

confidence: 99%

Insights into Epoxy Network Nanostructural Heterogeneity Using AFM-IR

Morsch

Liu

Lyon

et al. 2015

ACS Appl. Mater. Interfaces

113

115

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The first direct observation of a chemically heterogeneous nanostructure within an epoxy resin is reported. Epoxy resins comprise the matrix component of many high performance composites, coatings and adhesives, yet the molecular network structure that underpins the performance of these industrially essential materials is not well understood. Internal nodular morphologies have repeatedly been reported for epoxy resins analysed using SEM or AFM, yet the origin of these features remains a contentious subject, and epoxies are still commonly assumed to be chemically homogeneous. Uniquely, in this contribution we use the recently developed AFM-IR technique to eliminate previous differences in interpretation, and establish that nodule features correspond to heterogeneous network connectivity within an epoxy phenolic formulation.

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“…Some cured epoxies appear to be two-phase systems consisting of floccular aggregates of different crosslink densities than the bulk of the material. 28 -30 The average size of the floccules in a given polymer was found by Cuthrell 28,29 to be controlled by the rate of heat transfer to the sample during the initial stages of the cure. Large floccules are usually found near thermally insulating surfaces, that is, silicon resin and with a low-temperature curing process.…”

Section: Rate Of Diffusionmentioning

confidence: 99%