Abstract
The filling behavior of polymers in narrow gaps or small pores is important for the dynamics of polymeric micro/nanostructure fabrication. Here, the filling behavior, the mechanical properties, and the stress versus strain relationship of 996 kD poly (methyl methacrylate) (PMMA) at a scale from micron to molecular confinement are measured. It has been found that the solid polymer exhibits elastic-plastic dominant deformation behavior at micron scale. As the scale reduces to submicron, the resistance to deformation of the polymeric solid has a pronounced reduction. A softening effect and the visco-dominant behavior which is always exhibited by melt flow is observed. In confinement conditions, an anomalous hardening effect is found. The modulus and the hardness of 996 kD PMMA have been found to increase dramatically. The stress-strain curve also exhibits an obvious hardening phenomenon which is contrary to the conventional shear thinning and deformation acceleration results. The results of this paper show that the PMMA can exhibit a change of “solid-fluid-solid” in mechanical character at micron to molecular confinement scale.
Highlights
The filling behavior of polymers in narrow gaps or small pores is important for the dynamics of polymeric micro/nanostructure fabrication
We study the influence of molecular weight on filling modes and mechanical properties of poly(methyl methacrylate) (PMMA)
Our results show the filling peaks of PMMA with large molecular weight change from single-peak to dual-peak as the gap size decreases from microns to submicrons
Summary
Filling Mode from Micron to Molecular Confinement Scale. Figure 2a shows the filling peaks of. Experiments have shown that the single-peak filling mode can be observed as the cavity width is above 700 nm This filling mode means the elastic-plastic character domains the deformation behavior of solid PMMA at this scale. This phenomenon of PS is attributed to the local entanglement depletion and shear thinning induced by high shear rate This solid-fluid-solid filling behavior of PMMA at a scale from microns to molecular confinment can be exhibited by the moduli, hardnesses and stress-strain curves. The 996 kD PMMA solid has exhibited a hardening state at the molecular confinement scale and near confinement scale under large strain deformation in narrow gaps We think this phenomenon may be caused by the ordering and bridging effects, the localized stress concentration during the large strain deformation. Decreasing the molecular weight can be helpful in increasing filling accuracy of nanostructures
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