Property enhancements and dynamic gradients in P2VP-silica nanocomopsites

A fluorescence technique is used to probe the glass transition temperature (T_g) associated with α-relaxation dynamics at different locations in poly(2-vinylprydine) (P2VP)-silica nanocomposites. The interfacial layer T_g (T_g,inter) is determined using pyrene dye molecule covalently labeled to filler surface. The average matrix T_g (T_g,matrix) is determined using evenly dispersed, free pyrene dye in the polymer matrix. For the first time, we decouple the interfacial dynamics from the the rest of polymer matrix in nanocomposites. In 2.1 kg/mol P2VP nanocomposites containing 0.5 vol% nanoparticle, T_g,inter is 21 °C higher than in neat P2VP T_g, indicating that the α-relaxation dynamics are significantly slowed down due to H-bonding between P2VP and silanol groups on the filler surface. The T_g,matrix is only 3 °C higher than neat P2VP due to the low fraction of interfacial regimes at low filler loading. Both T_g,inter and T_g,matrix increase with increasing filler loading. At same filler dispersion and filler loading, 110 kg/mol P2VP nanocomposites exhibit a much reduced T_g enhancement relative to 2.1 kg/mol P2VP nanocomposites. We hypothesize that 2.1 kg/mol P2VP chains can orderly pack and align at the filler surface, leading to higher H-bonding density and stronger T_g enhancement.