ma8b01801_si_001.pdf (618.33 kB)
Uniaxial and Mixed Orientations of Poly(ethylene oxide) in Nanoporous Alumina Studied by X‑ray Pole Figure Analysis
journal contribution
posted on 2018-11-16, 18:49 authored by Cui Su, Guangyu Shi, Xiaolu Li, Xiuqin Zhang, Alejandro J. Müller, Dujin Wang, Guoming LiuThe
orientation of polymers under confinement is a basic, yet not
fully understood phenomenon. In this work, the texture of poly(ethylene
oxide) (PEO) infiltrated in nanoporous anodic alumina oxide (AAO)
templates was investigated by X-ray pole figures. The influence of
geometry and crystallization conditions, such as pore diameter, aspect
ratio, and cooling rates, was systematically examined. All the samples
exhibited a single, volume-dependent crystallization temperature (Tc) that is much lower than that exhibited by
bulk PEO, indicating “clean” microdomains without detectable
heterogeneous nucleation. An “orientation diagram” was
established to account for the experimental observations. Under very
high cooling rates (quenching), crystallization of PEO within AAO
was nucleation-controlled, adopting a random distribution of crystallites.
Under low cooling rates, growth kinetics played a decisive role in
the crystal orientation. A relatively faster cooling rate (10 °C/min)
and/or smaller pores lead to the ⟨120⟩*||pore axis (n⃗) mode (uniaxial orientation). When
the cooling rate was lower (1 °C/min) and/or the pores were larger,
a mixed orientation, with a coexistence of ⟨120⟩*||n⃗ and ⟨010⟩*∥n⃗, was observed. The results favor
the kinetic model that the fastest growth direction tends to align
parallel to the pore axis.