Direct identification of three crystalline phases in PEO-b-PCL-b-PLLA triblock terpolymer by In situ hot-stage atomic force microscopy

Abstract

In this work, we provide a detailed description of the tri-lamellar nanoscale morphology of a triple crystalline PEO-b-PCL-b-PLLA triblock terpolymer obtained by Hot-Stage Atomic Force microscopy (AFM) imaging and Wide Angle X-ray scattering (WAXS) analysis for the first time. The precursor PCL-b-PLLA diblock copolymer has also been included in the study for comparison purposes. A two-step crystallization protocol has been applied to create a distinct lamellar morphology. Both WAXS and AFM revealed the double crystalline nature of the diblock copolymer. However, the identification of multiple crystalline phases in the triblock terpolymer by AFM and WAXS at room temperature is not straightforward. The advantages of hot-stage AFM allowed following the evolution of the lamellar morphology and the successive melting of the tricrystalline PEO-b-PCL-b-PLLA sample during heating. Taking into account the melting temperature of each crystalline block, the existing lamellar populations were clearly identified. At 45 °C, the thinnest lamellae disappeared, due to the melting of PEO crystals. The medium size lamellae disappeared at 60 °C when PCL crystals melt. At that temperature, the only remaining crystals are those of the PLLA block. AFM mechanical modulus images provide further evidence of the lamellar self-assembly of the triblock terpolymer. The nanoscale arrangement includes lamellae of PCL, PEO, or both in between the PLLA lamellae. Hot-Stage AFM is a valuable technique to elucidate the morphological features of complex multi-crystalline systems.

Electroactive 3D printable poly(3,4-ethylenedioxythiophene)-graft-poly(ε-caprolactone) copolymers as scaffolds for muscle cell alignment

“…A similar behaviour has also been observed for PCL-co-PLA diblock copolymers. 33 These results allow us to conclude that the main structure and morphology of the PEDOT-g-PCL copolymers is not substantially affected by the heating process over the melting point (as they are able to reform as expected), which makes them ideal candidates to be manufactured by DIW in the melt state.…”

Single crystals and two‐dimensional crystalline assemblies of block copolymers

“…It is worth noting that, as shown in Figure 4B, the pre-formed single crystals provide a template for the subsequent crystallization, resulting in a certain angle between two neighbor single crystal layers, which is presumed to be due to epitaxial growth of crystals and lattice matching. In Palacios's works, [76][77][78][79][80] the sequential crystallization of each block in PEO-b-PCL-b-PLLA thin film was studied in detail, including the proper crystallization temperature and the thickness of each layer. The layered structures with much more layers compared to the above were determined by atomic force microscopy (AFM).…”

Crystallization and Morphology of Triple Crystalline Polyethylene-b-poly(ethylene oxide)-b-poly(ε-caprolactone) PE-b-PEO-b-PCL Triblock Terpolymers

“…In addition, many other factors such as composition, molecular weight, crystallization protocol, segregation strength, and block miscibility affect the crystallization behavior. As different morphologies can be developed, the final performance of the materials can be tuned by varying these factors [ 2 , 4 , 7 , 9 , 11 , 15 , 16 , 17 , 18 ].…”

“…The addition of a third potentially crystallizable block to diblock copolymers results in a more complex analysis of the crystallization behavior. Few studies have been published about tricrystalline triblock terpolymers, such as ABC-type triblock terpolymers and ABCBA pentablock terpolymers, including the apolar PE block, and the polar PEO, PCL, and PLLA blocks [ 17 , 24 , 37 , 42 , 82 , 83 , 84 , 85 , 86 , 87 , 88 , 89 , 90 , 91 , 92 , 93 , 94 , 95 , 96 ].…”

“…Very few reports have been published about the crystalline morphology in AB diblock copolymers and ABC triblock terpolymers from the melt by in situ AFM, and only two blocks crystallized in those samples [ 99 , 100 ]. Palacios et al [ 17 ] analyzed by in situ hot-stage AFM the evolution of the trilamellar morphology upon melting of the PEO- b -PCL- b -PLLA triblock terpolymer. Three different lamellar populations were detected at different temperatures; the melting of each of the populations gives information about the corresponding block: the thinnest lamellae corresponded to the PEO block (the first block to melt at 45 °C), the medium size lamellae to the PCL block (melted at 60 °C), and the thickest lamellae to the highest melting temperature block, i.e., PLLA.…”