Anomalous molecular weight dependence reveals the origin of mechanical enhancement in polymer nanocomposite
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초록
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The rule of thumb in polymer processing is higher molecular weight (MW) polymers provide better physical properties but also result in an inevitable increase in viscosity. This study shows that this premise can be broken upon the incorporation of the nanoparticles in bimodal MW polymers: decreasing average MW rather mechanically reinforces the properties of polymer nanocomposites. The addition of low MW polymers into high MW PNC ironically increases the shear modulus of PNC by up to 103times. This unpredicted outcome originates from the preferred adsorption of short-chain polymers, which leads chain elongation of structural interface layer of adsorbed polymers, creating networked structures. Effective chain stretching occurs when the short chain is short enough than the long chain (Rg ratio >~2), suggesting a universal stretching factor of 2.3. Further investigations with small angle neutron scattering reveal the interfacial polymers' different chain conformation.