Inducing uniform single-crystal like orientation in natural rubber with constrained uniaxial stretch

Abstract

The effect of flow on crystallization is commonly attributed to entropic reduction, which is caused by stretch and orientation of polymer chains but overlooks the role of flow on final-state free energy. With the aid of in situ synchrotron radiation wide-angle X-ray diffraction (WAXD) and a homemade constrained uniaxial tensile testing machine, polycrystals possessing single-crystal-like orientation rather than uniaxial orientation are found during the constrained stretch of natural rubber, whereas the c-axis and a-axis align in the stretch direction (SD) and constrained direction (CD), respectively. Molecular dynamics simulation shows that aligning the a-axis of crystal nuclei in CD leads to the lowest free energy increase and favors crystal nucleation. This indicates that the nomenclature of strain-induced crystallization may not fully account for the nature of flow-induced crystallization (FIC) as strain mainly emphasizes the entropic reduction of initial melt, whereas stress rather than strain plays the dominant role in crystal deformation. The current work not only contributes to a comprehensive understanding of the mechanism of flow-induced crystallization but also demonstrates the potential application of constrained uniaxial tensile stretch for the creation of functional materials containing polycrystals that possess single-crystal-like orientation.

Towards a Supertough Thermoplastic Polyisoprene Elastomer Based on a Biomimic Strategy

“…Although the CI of R‐4A‐PIP at the maximal strain is slightly higher than that of B‐4A‐PIP, the CI curve of B‐4A‐PIP is above R‐4A‐PIP throughout the stretching process, meaning that the SIC evolution of B‐4A‐PIP is always one step ahead of R‐4A‐PIP. Noteworthily, the onset strain of crystallization of B‐4A‐PIP is 4, which is smaller than that of R‐4A‐PIP and approaches the onset strain of vulcanized NR with chemical cross‐linking network . The excellent crystallization characteristics of B‐4A‐PIP could be attributed to the stronger confinement effect introduced by the terminal oligopeptides.…”

Performance on absolute scattering intensity calibration and protein molecular weight determination at BL16B1, a dedicated SAXS beamline at SSRF

“…More devices such as a GISAXS heating chamber and relative humidity controlling chamber are also being produced. Besides the foreseen sample surroundings, the beamline also reserves the ability to install the users' own specialized sample devices, as has happened in a series of works (Zhou et al, 2015;Liu et al, 2014;Huang et al, 2014). Supporting laboratories with ultrapure water system, magnetic stirrer, electronic balance, ultrasonic apparatus, centrifuge, electric oven, vacuum drying apparatus, polarizing microscope and atomic force microscope are also provided for users.…”

Towards a Supertough Thermoplastic Polyisoprene Elastomer Based on a Biomimic Strategy

“…Proton nuclear magnetic resonance ( 1 HNMR) spectra reveal that all the copolymers possess high 1,4 contents above 96 %(Supporting Information, Figure S1), which is essential for SIC.H omopolymerization of Al-IP was carried out to analyze the microstructures of the obtained copolymers. [26] Theexcellent crystallization characteristics of B-4A-PIP could be attributed to the stronger confinement effect introduced by the terminal oligopeptides.A ccording to Toki et al, [4] vulcanized NR has anaturally occurring network and this naturally occurring network can act as constraints to assist the induction of SIC,l eading to higher crystallinity and modulus than vulcanized IR. When the ratio of [Al-IP]/[IP]/[Nd] is 20:2500:1, Thet erminal block segments consist of about 40 polar units and another 107 polar units are randomly distributed in the left polymer chain.…”

“…The crystallinity index (CI) as afunction of strain (a)for samples during stretching is shown in Figure 2a.I ti sn oted that the ultimate strains of B-4A-PIP and R-4A-PIP in WAXD experimental condition are higher than those in Figure 1a. [26] Theexcellent crystallization characteristics of B-4A-PIP could be attributed to the stronger confinement effect introduced by the terminal oligopeptides.A ccording to Toki et al, [4] vulcanized NR has anaturally occurring network and this naturally occurring network can act as constraints to assist the induction of SIC,l eading to higher crystallinity and modulus than vulcanized IR. [24,25] At the slower strain rate during the WAXD experiments,m ore hydrogen bonds were relaxed and crosslinking density was reduced, leading to the increase of ultimate strains.Especially for R-4A-PIP,its hydrogen bonds are weaker and the trend is more obvious.T he typical synchrotron wide-angle X-ray diffraction patterns of samples at strain ratio of 11 are shown in Figure 2b.C ompared with B-OH-PIP and R-OH-PIP,t he crystallization characteristics of B-4A-PIP and R-4A-PIP are remarkably improved.…”

“…Although the CI of R-4A-PIP at the maximal strain is slightly higher than that of B-4A-PIP,the CI curve of B-4A-PIP is above R-4A-PIP throughout the stretching process,m eaning that the SIC evolution of B-4A-PIP is always one step ahead of R-4A-PIP.Noteworthily,the onset strain of crystallization of B-4A-PIP is 4, which is smaller than that of R-4A-PIP and approaches the onset strain of vulcanized NR with chemical cross-linking network. [26] Theexcellent crystallization characteristics of B-4A-PIP could be attributed to the stronger confinement effect introduced by the terminal oligopeptides.A ccording to Toki et al, [4] vulcanized NR has anaturally occurring network and this naturally occurring network can act as constraints to assist the induction of SIC,l eading to higher crystallinity and modulus than vulcanized IR. Here,w ep ropose that the introduced physical cross-linked network in B-4A-PIP have the same role as the natural network in NR.…”