Polymers under Extreme Nanoconfinement*

Polymers under nanoconfinement can show significantly deviated properties from bulk. Capillary Rise Infiltration (CaRI) can produce extreme polymer confinement by infiltrating the polymer into densely-packed nanoparticle (NP) films. Here, we use CaRI films to study physical and chemical properties of polymers under extreme nanoconfinement, including glass transition temperature (T_g), fragility, and thermal degradation. Polystyrene(PS)/SiO₂ and Poly(2-vinylpyridine)(P2VP)/SiO2 CaRI films were used as the model systems with weak and strong interfacial interactions. The degree of confinement was tuned by using polymers with different molecular weights and NPs with different sizes (forming pores with 3-30 nm average size). We show that T_g can increase by ~57 K for PS and ~100 K for P2VP confined in 3 nm pores. Furthermore, P2VP in CaRI films shows broader glass transition width but slightly lower fragility than bulk, indicating the gradient of dynamics in the pores. The thermal stability of both polymers are significantly enhanced in CaRI films with less char formation. The details of the process shows that the activation energy of PS degradation can increase by ~50 kJ/mol under nanoconfinement.