Cross-Linking Effect on Segmental Dynamics of Well-Defined Epoxy Resins

Shundo, Atsuomi; Aoki, Mizuho; Yamamoto, Satoru; Tanaka, Keiji

doi:10.1021/acs.macromol.1c00513

Cited by 61 publications

(60 citation statements)

References 56 publications

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“…However, such an effect is not as clear as compared with the effect of the increased conversion degree as presented in Figure . We may also expect impacts of the HNS architecture on other important macroscopic properties of epoxy networks, such as fragility, thermal transition and degradation, moisture absorption, and solvent crack resistance, ,,− which is the subject of our current research.…”

Section: Resultsmentioning

confidence: 99%

Local Mechanical Properties of Heterogeneous Nanostructures Developed in a Cured Epoxy Network: Implications for Innovative Adhesion Technology

Nguyen

Aoki

Liang

et al. 2021

ACS Appl. Nano Mater.

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The physical performance of an epoxy-based material is largely influenced by the formation of heterogeneous nanostructures (HNSs) in the glassy three-dimensional epoxy network. Thus, understanding the connectivity and local mechanical properties of HNSs formed in cured epoxy networks is of critical importance in the development of advanced epoxy-based materials for innovative adhesion technology. Here, we use bimodal atomic force microscopy (AFM) to map the local mechanical responses of HNSs evolved in an epoxy−amine system during curing. Both modulus and dissipated energy quantities describing the elastic and adhesive responses, respectively, were simultaneously obtained at different harmonic vibrations in each bimodal AFM measurement. HNSs exhibiting different elastic and adhesive responses were clearly visualized for all epoxy networks at different levels of curing. The architecture and local mechanical responses of HNSs were visibly altered with increasing degree of conversion. Soft domains representing network regions with relatively lower elastic moduli and weaker adhesive interactions were dominant and continuously connected at initial stages of curing up to conversion degrees of ∼91%. However, hard domains became increasingly connected upon approaching the fully cured stage. In combination with previously reported results obtained using the particle tracking technique to study the network heterogeneity at lower conversion degrees of the same epoxy system, we were able to provide a full picture describing the generation and development of mechanical heterogeneities in the network during curing in which the length scale of the heterogeneities decreased from several hundred nanometers at the pregelation stage to ∼10 nm at the fully cured stage.

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Section: Resultsmentioning

confidence: 99%

Local Mechanical Properties of Heterogeneous Nanostructures Developed in a Cured Epoxy Network: Implications for Innovative Adhesion Technology

Nguyen

Aoki

Liang

et al. 2021

ACS Appl. Nano Mater.

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“…Epoxy resins, which are based on formation of networks between epoxy and amine compounds via curing reactions, are an important class of thermoset resins. Since epoxy resins are generally in a glassy state under ambient conditions, 1,2 epoxy resins are usually brittle, which is a critical drawback in resins used as structural materials. 3,4 One common approach to overcoming this issue is to disperse soft particles into the epoxy matrix as a filler.…”

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confidence: 99%

In situ transmission electron microscopy observation of the deformation and fracture processes of an epoxy/silica nanocomposite

Wang

Maeda²,

Aoki

et al. 2022

Soft Matter

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“…DGEBA and n -alkyl diamines were well mixed at a molar ratio of 2:1, which was equivalent in the stoichiometry of epoxy and amino groups to initiate the curing reaction. The mixture, which was heated up to 353 K, was placed on a Teflon substrate with a silicon mold and then pre-cured at 353 K for 12 h. All samples were further post-cured at 453 K for 12 h, resulting in an apparent completion of the reactions, which was confirmed by Fourier transform infrared (FT-IR) spectroscopy . Pre- and post-curing processes were conducted under a nitrogen atmosphere.…”

Section: Methodsmentioning

confidence: 99%

“…We recently studied the segmental dynamics of epoxy resins in which the three-dimensional network was well defined and systematically varied in terms of the cross-linking density . It was found that as the cross-linking density increased, the glass transition temperature ( T g ) increased with an associated reduction in the spatial size scale of the cooperative rearranging region (CRR).…”

Section: Introductionmentioning

confidence: 99%

Effect of Cross-Linking Density on Horizontal and Vertical Shift Factors in Linear Viscoelastic Functions of Epoxy Resins

et al. 2021

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Epoxy resins are an important class of thermosetting resins, and their network structure, obtained by the curing reaction of epoxy and amine compounds, plays an important role in the material properties. We here revisited a time−temperature superposition (TTS) principle applied to the dynamic viscoelastic functions of epoxy resins, in which the network was well defined and systematically varied on the basis of the length of nalkyl diamine. The superimposition of isothermal curves in the frequency domain required not only a horizontal shift but also a vertical shift, regardless of the length of n-alkyl diamine. The temperature dependence of the horizontal shift factor, a T , could be well expressed by the Williams−Landel−Ferry equation. The fitting parameter, called C 2 , increased with decreasing alkyl chain length of the diamine, meaning that the thermal expansion of the free volume was suppressed due to greater cross-linking density. This was qualitatively confirmed by a full-atomistic molecular dynamics (MD) simulation. Meanwhile, the vertical shift factor, b T , increased with increasing temperature, and the extent was smaller with increasing crosslinking density. This can be explained in terms of the entropic contribution to the modulus in the temperature region above the glass transition temperature. The entropy change estimated using the isobaric molar heat capacity from the MD simulation strongly supported this hypothesis. The knowledge here obtained should be useful for a better design of thermosetting polymers as well as for the prediction of long-term durability.

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Cross-Linking Effect on Segmental Dynamics of Well-Defined Epoxy Resins

Cited by 61 publications

References 56 publications

Local Mechanical Properties of Heterogeneous Nanostructures Developed in a Cured Epoxy Network: Implications for Innovative Adhesion Technology

Local Mechanical Properties of Heterogeneous Nanostructures Developed in a Cured Epoxy Network: Implications for Innovative Adhesion Technology

In situ transmission electron microscopy observation of the deformation and fracture processes of an epoxy/silica nanocomposite

Effect of Cross-Linking Density on Horizontal and Vertical Shift Factors in Linear Viscoelastic Functions of Epoxy Resins

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