A facile strategy was proposed to prepare intrinsically-photoresponsive elastomer that simultaneously exhibited excellent mechanical toughness, stability and photoresponse. Some high-definition biomechanical applications were successfully demonstrated.

By means of in situ small-/wide-angle X-ray scattering (SAXS/WAXS) techniques, nucleation mechanism for Form I crystals of polybutene-1 (PB-1) has been investigated by heating the early-stage polymorphic transformation specimens (from Form II to Form I) above the nominal melting temperature of Form II crystals. Upon selective melting of Form II crystals at 124 °C, the SAXS curves of the few surviving Form I nanocrystals (volume content about 4.6%) in the melt can be fitted using a form factor for polydisperse cylinders. The geometrical size of Form I cylindrical nanocrystals was around height ≈40 ± 2 nm and radius ≈ 23 ± 1 nm when the aging time reached 12 h. Surprisingly, the height of Form I nanocrystals not only increased with lamellar thickness (d c) of initial Form II crystals but also was always larger than the d c of both initial Form II and pure Form I (i.e., complete transformation). We estimated that the Form I folded-chain nanocrystals consist of two parts, namely, the nuclei of Form I and the epitaxial growth of Form I crystals. Furthermore, our findings suggested that nucleation of Form I has a higher chance to occur at the thicker part of initial Form II crystals. This is probably because the longer parallel-chain stems give rise to a reduction of conformational entropy of the chains, allowing a smaller energy barrier for nucleation of Form I.

The melting–recrystallization characterizations of quenched β-form isotactic polypropylene (β-iPP) lamellar crystals in ultrathin films were investigated via the self-seeding method. We found lath-like shaped α-iPP crystals generated within the region occupied by the initial β-iPP lamellae and calculated their average number density (N α). Intriguingly, two slopes were derived from the semi-logarithmic plot of N α versus partial melting temperature (T s), which reflects that N α is determined by βα-recrystallization and αα-recrystallization as T s is below and above 157 °C, respectively. Furthermore, our experimental observations clearly demonstrate that two phase selection pathways, that is, ββ- and βα-recrystallization, are possible upon melting of the quenched β-iPP lamellae. In particular, we found that ββ-recrystallization emerges as the preferred route for the case of an initial β phase with sufficiently high thermal stability, which is probably thermodynamically controlled rather than kinetically controlled. Otherwise, βα-recrystallization will be the dominant process due to the growth kinetics.

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We present experimental evidence that the transformation from one solid phase to another solid phase within a faceted polymer single crystal passes through a transient mesomorphic phase. This phase exists in the boundary zone separating the two crystalline phases of isotactic polybutene-1 (PB-1), i.e., Form II and Form I of PB-1. Employing real-time atomic force microscopy in tapping mode (TM-AFM), we followed the crystal–crystal transformation in time. TM-AFM measurements performed at about 20 °C under a nitrogen atmosphere with high humidity have allowed through differences in viscoelastic properties and associated changes in thickness to distinguish the two crystalline phases as well as the boundary zone. Measurements at an elevated temperature of 90 °C (which was far below the melting temperatures of both Form II and Form I crystals) further revealed that this boundary zone shows a transient and diffuse character and a distinctly increased thickness. Using high-resolution phase imaging of TM-AFM, we observed that within this rather extended boundary zone of up to some hundred nanometers at elevated temperatures, Form I crystals with a diameter of around 30 nm were growing in a softer and featureless matrix phase. The boundary zone and so the growth front of the Form I crystal advanced at an almost constant rate, suggesting that chains in the mesomorphic phase were considerably mobile. Our observation of an extended boundary zone probably indicates that compared to a direct crystal–crystal transformation, the corresponding free energy barrier for this transformation is lower within such a zone. Hence, our here presented model study sheds light on the poorly understood and complex pathways involved in a solid–solid transformation within a polymer single crystal.