Imbibition, crystallization, and dynamics of polymers and water under nanometer confinement
Date issued
Authors
Editors
Journal Title
Journal ISSN
Volume Title
Publisher
License
Abstract
The way polymers penetrate into thin pores is of fundamental interest and importance for many applications in nanotechnology. In this Thesis we first investigate how polymer melts penetrate into self-ordered nanoporous alumina (AAO). The results for the imbibition height deviate from the theoretical Lucas-Washburn equation. The deviation is explained by a competition between the adsorption of polymer chains on the pore walls and the reptation of free chains under a pressure gradient. In addition, motivated by the different imbibition speeds between shorter and longer chains, we study the imbibition of homogeneous polymer blends and find an enrichment of shorter chains inside nanopores. In a second area we investigate the effect of chain topology on the imbibition, crystallization, and dynamics of polymers under confinement. Poly(ethylene oxide) (PEO) based polymers are employed including star PEOs, hyperbranched (hb) PEOs, and diblock copolymers of poly(isoprene-b-ethylene oxide) (PI-b-PEO). Despite the non-linear structure, these polymers (hbPEOs) can be infiltrated into AAO, albeit with a slower filling speed than theoretically predicted. Surprisingly, PI-b-PEO can be successfully infiltrated from an ordered state. Subsequently, we investigate polymer crystallization under confinement. Mainly homogeneous nucleation is observed. The homogeneous nucleation temperature of the non-linear topologies is identical to that of linear PEO, provided that the arm, branched, or the block molecular weight is used instead of the total molecular weight. In addition, the segmental dynamics speed-up reflecting a reduction in glass temperature. Lastly, motivated by earlier studies in our lab, we investigate the crystallization and dynamics of water under confinement. We use two confining media; one with a moderate confinement (hollow silica spheres) and one where confinement is severe (mesoporous silica). We establish the phase diagram (T vs. 1/d) of confined water over a broad area of pore sizes. The dependence of the heterogeneous and the homogeneous nucleation temperatures on pore diameter is obtained. The two lines coincide at a pore diameter of ~ 2.6 nm below which crystallization is not possible. By employing both dielectric spectroscopy and solid state nuclear magnetic resonance techniques we investigate the dynamics of ice and water within mesoporous silica. Both techniques identify -for the first time – two different states of liquid water under confinement and their dynamics is explored.