We report that hot stretching of poly­(ethylene oxide) (PEO)-based solid polymer electrolytes (SPEs) can lead to a preferred orientation of PEO crystalline lamellae, thereby reducing the tortuosity of the ion-conduction pathway along the thickness direction of the SPE film, causing improved ionic conductivity. The hot stretching method is implemented by stretching SPE films above the melting point of PEO in an inert environment followed by crystallization at room temperature while maintaining the applied strain. The effect of hot stretching on the crystalline orientation, crystallinity, morphology, and ion transport in PEO with two types of salts, lithium bis­(trifluoromethanesulfonyl)­imide (LiTFSI) and lithium triflate (LiCF3SO3), is investigated in detail. Wide-angle X-ray scattering (WAXS) and small-angle X-ray scattering (SAXS) show that the orientation of PEO crystalline lamellae induces the formation of a short ion-conduction pathway along the through-plane direction of the SPE films, leading to 1.4- to 3.5-fold enhancement in the through-plane ionic conductivity.

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In the present study, we focused on the intermolecular H-bonding interactions of poly­[(R)-3-hydroxybutyrate] (PHB) with an inorganic material, pseudoboehmite (PB), and their effect on PHB crystallization. Noncrystallizable atactic PHB and crystallizable isotactic PHB (a-PHB and i-PHB) ultrathin films were spin-coated on a PB substrate, as well as an aluminum oxide (AO) and a gold substrate for comparison. Infrared reflection–absorption spectroscopy (IRRAS) data show an absorption peak in the carbonyl region located at 1724 cm–1 for a 2.8 nm a-PHB film deposited on PB. A peak at this frequency, often observed for thick bulk crystalline i-PHB films, was not observed for a 1.4 nm a-PHB film deposited on a gold or AO substrate, indicating that the 1724 cm–1 peak observed for a-PHB on PB is not due to a geometric confinement effect or crystallization but due to the existence of intermolecular H-bonding (H-bondinter) between −CO of a-PHB and −OH from PB. Supercooled, amorphous i-PHB was also found to exhibit the same H-bondinter with PB. It was found that a PB surface significantly modified the crystal orientation and morphologies of the films. Grazing incident wide-angle X-ray diffraction (GIWAXD) data show that the crystallites in i-PHB on PB are randomly oriented, whereas those on AO are predominantly edge-on oriented. Polarized optical microscopy (POM) images show spherulites for i-PHB on AO, whereas no spherulites were observed for i-PHB on PB. This study demonstrates a novel method of using PB to modulate the crystallization behavior of PHB thin films.

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Ultrathin films of biodegradable poly­[(R)-3-hydroxybutyrate] (PHB) and its random copolymer poly­[(R)-3-hydroxybutyrate-co-(R)-3-hydroxyhexanoate] (PHBHx) were prepared by spin-coating onto aluminum substrates with a naturally oxidized aluminum oxide (AO) surface layer or, alternatively, on gold substrates. The opposite surface of the film was in contact with ambient air. Isothermal crystallization kinetics of these films at room temperature were studied using infrared reflection absorption spectroscopy. The overall crystallization rate for all the polymers when crystallizing on AO is significantly retarded compared with the same polymer crystallizing on gold. It was found that the retardation effect was not due to a confinement effect. The crystallization retardation effect was especially enhanced for PHBHx with a higher (R)-3-hydroxyhexanoate content. Avrami analysis showed that the crystallization rate constant k (min–1) for all of the polymers on AO is approximately 3 to 4 orders of magnitude less than that found for the same polymer on gold. Grazing incident wide-angle X-ray diffraction showed that polymers on gold have both flat-on and edge-on crystallite orientations, whereas polymers on AO have a dominating edge-on crystallite orientation. Infrared studies on a quasi-monolayer film revealed no detectable H-bonding between PHB/PHBHx and the AO surface. The crystallization retardation mechanism was explained as being a sum of the dipole–dipole interactions of −CO of PHB or PHBHx and the −O–Al–O– groups of AO coupled with the rigid disordered amorphous nature of the AO surface.