Natural rubber–SiO 2 nanohybrids: interface structures and dynamics

Gangadharan²,

Patnaik

2019

ACS Omega

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The preparation of natural rubber (NR)–silica (SiO 2 ) elastomeric composites with excellent mechanical properties along with better self-healing ability remains a key challenge. Inspired by the energy dissipation and repairability of sacrificial bonds in biomaterials, a strategy for combining covalent and noncovalent sacrificial networks is engineered to construct a dual hybrid network. Here, the approach used to fabricate the composites was self-assembly of NR, bearing proteins and phospholipids on its outer bioshell, with SiO 2 via metal-ion-mediated heteroaggregation effected by reversible electrostatic and H-bonds. Further, covalent cross-links were incorporated by a silane coupling agent, bis [3-(triethoxysilyl) propyl] tetrasulfide. The intrinsic self-healing ability of the composite at the molecular level was studied by broadband dielectric spectroscopy that unraveled the mechanism of the healing process. The synergistic effect between the molecular interdiffusion of the cross-linked NR chains and the electrostatic and H-bonding interactions imparted an exceptional self-healing characteristic to the liquid–liquid-mixing-prepared NR–SiO 2 composites with improved mechanical performance. Specifically, the segmental relaxation dynamics of the healed composite was largely restricted due to increased number of ion–dipole interactions and S–S cross-links at the junction of the cut surface. We envisage that this extraordinary healing property, unreported yet, would be of great importance toward the design of novel NR–SiO 2 elastomeric hybrids with superior mechanical properties.

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Design of Dual Hybrid Network Natural Rubber–SiO₂ Elastomers with Tailored Mechanical and Self-Healing Properties

Gangadharan²,

Patnaik

2019

ACS Omega

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“…In such systems, the structural configuration of the H‐ bond donor (D) and acceptor (A) guides the overall stability of the resultant complex system [100–101] . Using molecular mechanics simulations, Sattar et al., 2019 [102–103] elucidated that secondary electrostatic and ion‐dipole interactions alongside H‐bonding between SiO 2 NP and natural rubber (NR) (end‐functionalized with nucleic acid and phospholipid) can contribute additional stabilization leading to their self‐assembly.…”

Section: Polymer‐filler Interfacial Interactions In Pncs: What Are the Parameters?mentioning

confidence: 99%

Interface Structure and Dynamics in Polymer‐Nanoparticle Hybrids: A Review on Molecular Mechanisms Underlying the Improved Interfaces

2021

ChemistrySelect

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In a nano‐assembly of soft polymer chains and hard filler nanoparticles (NPs), the intermolecular interactions at the polymer‐filler interface lead to variations in viscoelastic properties in the vicinity of the NP surface. However, unravelling the molecular parameters controlling the entropic and enthalpic interactions, including polymer chain conformation, dynamics, dispersion mechanisms and confinement effects across the interfacial region, has been remote and challenging. Even though the polymer‘s molecular structure and the NPs surface chemistry contribute to these interfacial interactions, the underlying mechanism behind the enhanced dynamic‐mechanical performance is still a hot topic of debate. By controlling the chemistry of NPs and polymer matrix in model nanocomposites, many efforts have been made in elucidating the physical origin of the structure and dynamics of the interfacial polymer layer with estimates varying from 1 to 10 nm around the spherical NPs. Therefore, understanding the interface structure and dynamics influenced by polymer‐NP interaction is of great technological importance. In this article, the latest polymer‐particle interface literature developments are reviewed where computational simulations, calorimetry, and dielectric spectroscopy studies have been used to examine the constraints levied by the interface structure on segmental relaxation dynamics of polymer chains in the vicinity of NP surface.

“…[107][108][109] Recently, by adopting calorimetric, broadband dielectric measurements, and molecular mechanics based on the MM + force field, we studied the self-healing properties of SiO 2 NP (silica) reinforced natural rubber (NR) PNCs, directly correlating their self-healing ability at the micro/macroscopic to molecular level utilizing ionic and covalent cross-linkers. [110][111][112] Specific intermolecular interactions, such as ion-dipole and H-bonding interactions, proved to be the driving forces for the structured assembly leading to the NR-SiO 2 hetero-aggregate. As a unique structural model, MM + simulation of the aqueous canonical ensemble of the hybrid showed the stable molecular conformation to reveal the SiO 2 NP spherical core encapsulated by a hydrophobically interconnected NR polymer layer as the outer shell.…”

Section: Energetic Requirements For Spontaneous Self-healingmentioning

confidence: 99%

Design Principles of Interfacial Dynamic Bonds in Self‐Healing Materials: What are the Parameters?

Chemistry An Asian Journal

Patnaik

2020

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Polymers and polymer nanocomposites (PNCs) are extensively used in daily life. However, the growing requirement of advanced PNCs laid persistent environmental issues due to deformation‐induced damage that once formed, does not vanish at future stages. Therefore, self‐healing materials with significantly enhanced long life and safety have been designed to epitomize the forefront of recent advances in materials chemistry and engineering. Self‐healing PNC (SH‐PNCs) materials are a class of smart composites in which nanoparticles induce interfacial reconstruction via multiple covalent and non‐covalent interactions culminating in improved mechanical strength and self‐healing capability. However, since the filler nanoparticles are independent of the reversible supramolecular network, the filler incorporation destroys the self‐healing ability but could enhance the mechanical strength. Hence, the molecular parameters controlling the alliance of robust mechanical strength with virtuous self‐healing ability is a crucial challenge. Herein, we review the latest developments that have been made in self‐healing materials and puts advancing insights into the fabrication of SH‐PNCs in which the combination of covalent bonds and non‐covalent interactions provides an optimal balance between their mechanical performance and self‐healing capability. We highlight the importance of specific entropic, enthalpic changes, polymer chain conformations and flexibility that enable the reconstruction of damaged surface and physical reshuffling of dynamic bonds at the interface of cut surfaces.