Fast scanning calorimetry clarifies the understanding of the complex melting and crystallization behavior of polyesteramide multi-block copolymers

cited By 3Fast scanning calorimetry has been applied in order to understand the phase transitions in thermoplastic elastomers (TPEs) based on well-defined multi-block copolymers made of ‘soft’ polytetrahydrofuran and ‘hard’ terephthalate ester diamides. The intrinsically complex chemical structure of TPEs leads to complex phase transitions. By changing their thermal history over a wide range of temperature (from −100 °C to 200 °C) and cooling rates (from 10 to 4000 °C s−1), we clarify the origins of the various phases present in these materials. In particular, we study the different possibilities for the hard segments to associate depending on their mobility during the quenching phase, forming either strong and stable structures or weaker and metastable ones. Besides, we demonstrate that a minimal cooling rate of 800 °C s−1 is necessary to keep these TPEs (made of short and monodisperse hard segments) amorphous leading to a subsequent cold crystallization when heating back, at around 30 °C. Finally, we validate our interpretations by varying the copolymer composition (from 10 wt% to 20 wt% hard segments), revealing the thermal invariance of poorly organized domains. Based on these data, we also discuss the importance of chain diffusion in the crystallization process. Applying fast scanning calorimetry allows us to link fundamental understanding to industrial application. © 2018 Society of Chemical Industry. © 2018 Society of Chemical Industr

Mechanical Properties of Native and Cross-linked Type I Collagen Fibrils

Micromechanical bending experiments using atomic force microscopy were performed to study the mechanical properties of native and carbodiimide-cross-linked single collagen fibrils. Fibrils obtained from a suspension of insoluble collagen type I isolated from bovine Achilles tendon were deposited on a glass substrate containing microchannels. Force-displacement curves recorded at multiple positions along the collagen fibril were used to assess the bending modulus. By fitting the slope of the force-displacement curves recorded at ambient conditions to a model describing the bending of a rod, bending moduli ranging from 1.0 GPa to 3.9 GPa were determined. From a model for anisotropic materials, the shear modulus of the fibril is calculated to be 33 ± 2 MPa at ambient conditions. When fibrils are immersed in phosphate-buffered saline, their bending and shear modulus decrease to 0.07–0.17 GPa and 2.9 ± 0.3 MPa, respectively. The two orders of magnitude lower shear modulus compared with the Young's modulus confirms the mechanical anisotropy of the collagen single fibrils. Cross-linking the collagen fibrils with a water-soluble carbodiimide did not significantly affect the bending modulus. The shear modulus of these fibrils, however, changed to 74 ± 7 MPa at ambient conditions and to 3.4 ± 0.2 MPa in phosphate-buffered saline

Thermotropic Phase Behavior of Trialkyl Cyclohexanetriamides

The thermotropic phase behavior of symmetric cyclohexanetriamides carrying various linear and branched alkyl chains was investigated using calorimetry, microscopy, solid-state NMR, dielectric relaxation spectroscopy, and X-ray scattering techniques. Cyclohexanetriamides carrying C6 or longer linear alkyl chains formed columnar plastic phases with a pseudocentered rectangular lattice. Those with C8 or longer alkyl chain also showed a nematic liquid crystalline phase. Cyclohexanetriamides carrying branched octyl chains displayed columnar phases with rectangular lattices, except for the triamide with the highly branched tetramethylbutyl group. The occurrence of less symmetrical columnar phases is ascribed to the mode of stacking of cyclohexanetriamides which leads to noncylindrical columns. Dielectric relaxation spectra also featured highly cooperative relaxation processes related to reorientation of the macrodipolar columns in the mesophase, showing the potential of these molecules as building blocks in responsive materials