Immobilized Polymer Fraction in Hyperbranched Polymer/Silica Nanocomposite Suspensions

Influence of Eco-Friendly Processing Aids on Silica-Based Rubber Composites

As eco-friendly “green tires” are being developed in the tire industry, conventionally used carbon black is being replaced with silica in rubber compounds. Generally, as a lubricant and dispersing agent, processing aids containing zinc ions have been employed as additives. However, as zinc is a heavy metal, alternative eco-friendly processing aids are required to satisfy worldwide environmental concerns. Furthermore, non-toxic, degradable, and renewable processing aids are required to improve the mechanical properties of the rubber composites. In this study, we evaluated the effects of diverse silica-based processing aids containing hydrocarbon, benzene, and hydroxyl functional groups on the mechanical properties of rubber composites. Among them, rubber composites that used amphiphilic terpene phenol resin (TPR) with hydrophilic silica showed compatibility with the hydrophobic rubber matrix and were revealed to improve the mechanical and fatigue properties. Furthermore, owing to the enhanced dispersion of silica in the rubber matrix, the TPR/styrene butadiene rubber composites exhibited enhanced wet grip and rolling resistance. These results indicated that TPR had multifunctional effects at low levels and has the potential for use as a processing aid in silica-based rubber composites in tire engineering applications.

Rapid and high-concentration exfoliation of montmorillonite into high-quality and mono-layered nanosheets

After montmorillonite (MTM) was first exfoliated into nanosheets as a reinforcing filler in the 1980s, layered clay became a hotspot of interest. However, to date, the exfoliation of the resource-rich and inexpensive layered MTM into high-quality nanosheets still remains a significant challenge. Herein, a simple and effective strategy to exfoliate layered MTM into mono-layered sheets via the aggregation of polyethyl-phosphate glycol ester (Exolit OP 550) is proposed. A significant decrease in exfoliation time from 120 min to 3 min was observed at room temperature only via a gentle stirring process. Moreover, various factors that reduce the viscosity of the mixture could be utilized to boost the exfoliated concentration to a record high value of 100 wt%, which is an increase of 460-2400% compared with that in other works. A tentative model was also proposed to illustrate the exfoliation mechanism based on the detection of segmental confined movement, structural evolution, and polymer-clay interaction. Particularly, the as-observed critical concentration of 200 wt% MTM indicated a saturation effect for the surface-adsorbed polymer. The critical concentration for the onset of exfoliation was 150 wt%. In addition, the structure of the exfoliated nanosheets in Exolit OP 550 underwent a temperature-sensitive and irreversible transformation. Thus, our study may provide new insight for the exfoliation of clay.

Rivet-Inspired Modification of Aramid Fiber by Decorating with Silica Particles to Enhance the Interfacial Interaction and Mechanical Properties of Rubber Composites

A rivet-inspired method of decorating aramid fiber (AF) with silica particles (SiO2) is proposed to produce SiO2@AF hybrid materials that have largely enhanced interfacial interaction with the rubber matrix. AF was firstly surface-modified with polyacrylic acid (PAA) to obtain PAA-AF, and SiO2 was silanized with 3-aminopropyltriethoxysilane to obtain APES-SiO2. Then, SiO2@AF was prepared by chemically bonding APES-SiO2 onto the surface of PAA-AF in the presence of dicyclohexylcarbodiimide (DCC) and 4-dimethylaminopyridine (DMAP). With the incorporation of SiO2@AF into the rubber matrix, SiO2@AF hybrid materials with high surface roughness can play a role as 'rivets' to immobilize large numbers of rubber chains on the surface. The tear strength and tensile strength of rubber composite that filling 4 phr SiO2@AF are dramatically increased by 97.8% and 89.3% compared to pure rubber, respectively. Furthermore, SiO2@AF has superiority in enhancing the cutting resistance of rubber composites, in contrast with unmodified AF and SiO2. SiO2@AF is suitable to be applied as a novel reinforcing filler in rubber composites for high performance.

Natural rubber-SiO2 nanohybrids: interface structures and dynamics

Homogeneous dispersion of silica nanoparticles (SiO₂ NPs) in natural rubber (NR) is a key challenge for engineering high-performance nanocomposites and elucidation of their structure on a molecular basis. Towards this, the present work devised a novel route for obtaining 3D self-assembled SiO₂ NP-NR nanocomposites under aqueous conditions and in the presence of Mg²⁺, by establishing a molecular bridge that clamped the negatively charged NR and SiO₂ colloidal particles with a favoured NR-SiO₂ NP hetero-aggregation. The characteristic NR-SiO₂ NP hetero-aggregates displayed a decreased heat capacity with increase in the SiO₂ mass-fraction, implying a restricted NR chain mobility. Such changes in the interfacial layers were tapped by ²⁹Si NMR, DFT calculations and molecular dynamics simulations towards a mechanistic understanding of the structure and dynamics of the NR/SiO₂ NP hybrid. Simple models were used to illustrate basic ideas; specific electrostatic interactions such as ion-dipole and H-bonding interactions proved to be the driving forces for the organized assembly leading to the NR-SiO₂ hetero-aggregate over the NR-NR or SiO₂ NP-SiO₂ NP homo-aggregate. Molecular dynamics simulation of the aqueous canonical ensemble of the hybrid showed the stable molecular conformation to reveal a SiO₂ NP spherical core encapsulated by a hydrophobically interconnected NR polymer layer as the outer shell, as a unique structural model. Specifically, the lipid end of the NR was involved electrostatically while the lysine end (the protein part of NR) H-bonded to the core silica cluster thereby restricting random aggregation. The calculated negative free energy changes for the hetero-aggregate composites via their vibrational and rotational spectra proved the spontaneity of composite formation.

Role of Dynamical Heterogeneities on the Mechanical Response of Confined Polymer

Confinement induces various modifications in the dynamics of polymers as compared to bulk. We focus here on the role of dynamical heterogeneities on the mechanics of confined polymers. Using a simple model that allows computation of the mechanical response over 10 decades in frequency, we show that the local mechanical coupling controlling the macroscopic response in the bulk disappears in a confined geometry. The slowest domains significantly contribute to the mechanical response for increasing confinement. As a consequence, the apparent glass transition is broadened and shifted towards lower frequencies as confinement increases. We compare our numerical predictions with experiments performed on poly(ethylacrylate) chains in model filled elastomers. We suggest that the change of elastic coupling between domains induced by confinement should contribute significantly to the polymer mobility shift observed on filled systems.

Revealing the three-dimensional filler structure in a rubber matrix based on fluorescein modified layered double hydroxides

A facile fluorescent labeling method was developed to track the filler structural evolution in a rubber matrix, which could be helpful in understanding the Payne effect in the filled compounds.

Characterizing the nanoclay induced constrained amorphous region in model segmented polyurethane–urea/clay nanocomposites and its implications on gas barrier properties

AFM images of the segmented PU/clay nanocomposite with labeling of various phases.

Direct Evidence for Percolation of Immobilized Polymer Layer around Nanoparticles Accounting for Sol-Gel Transition in Fumed Silica Dispersions

Immobilized polymer fractions have been claimed to be of vital importance for sol-gel transitions generally observed in nanoparticle dispersions but remain a matter of debate regarding mechanism and difficulty for prediction. Here we investigate the immobilized layer structures of trifunctionality polyether polyol (PPG) near the surfaces of hydrophilic and hydrophobic fumed silica (FS) nanoparticles to reveal the role of surface chemistry on the molecular dynamics and sol-gel transitions of the dispersions. Using modulated differential scanning calorimetry, we measure the specific heat capacity during glass transition and the enthalpy during cold-crystallization. Comparing with hydrophobic FS that forms a fully immobilized (glassy) layer, we find that hydrophilic FS immobilizes more PPG, forming a partially immobilized outer layer being unable to crystallize next to the inner glassy layer. By correlating the thickness of the glassy layer with half of the minimum spacing between nanoparticles, we directly evidence the percolation of this layer along the nearest neighbor nanoparticles responsible for the sol-gel transition. Using effective volume fraction including the glassy layer, we successfully construct master curves of relative viscosity of both hydrophilic and hydrophobic FS dispersions, pointing to a common sol-gel transition mechanism mediated by the surface chemistry.

Graphene nanosheets decorated with ZnO nanoparticles: facile synthesis and promising application for enhancing the mechanical and gas barrier properties of rubber nanocomposites

In this study, graphene nanosheets decorated with ZnO nanoparticles (NZG) were prepared from graphene oxide by a facile solvothermal method.

Biocompatible SiO2in the Fabrication of Stimuli-Responsive Hybrid Composites and Their Application Potential

Organic/inorganic hybrid composite materials have been extensively studied as they combine the properties of inorganic material and organic polymer. Among the inorganic material biocompatible silica (SiO2) is an interesting candidate for application in biotechnology because such material is wide spread in nature as well as in medicine. During the last few decades, stimuli-responsive polymers are drawing much attention from the researchers for application versatility such as target-specific delivery of drug and corrosion inhibitors. Considering the biocompatibility and many such important properties as high cargo loading capacity, long blood circulation lifetime, enhanced permeability and retention, mechanical strength, and easy processability, combination of SiO2particles with stimuli-responsive polymers is gaining attention over the last decade. This review article will report the progress made towards the development and application of stimuli-responsive hybrid composites based on SiO2.

Hyperbranched polymers: advances from synthesis to applications

This review summarizes the advances in hyperbranched polymers from the viewpoint of structure, click synthesis and functionalization towards their applications in the last decade.

Synthesis and characterization of thermally stable, hydrophobic hyperbranched polyimides derived from a novel triamine

A novel aromatic triamide 1,3,5-tri[4-(4-aminophenoxy)phenyl] benzene (TAPOPB) with prolonged chain segments and ether bonds was successfully prepared through a three-step reaction. Then a series of hyperbranched polyimides (HBPIs) were synthesized using A2 + B3 polycondensation from various commercial aromatic dianhydrides and TAPOPB. The HBPIs showed good solubility, thermal stability with glass transition temperatures ( Tg) between 218°C and 320°C, and temperature at 10% weight loss of 502.1–561.7°C in nitrogen atmosphere. Meanwhile, they had decent mechanical properties whose tensile strength and modulus were higher than 72.37 MPa and 1.039 GPa, respectively. Water uptake of less than 0.96% was obtained. The truncation wavelengths of the films were all greater than 400 nm with a good application prospect in UV protective coating. Most contact angles were more than 90°, promising to be used as hydrophobic material.

Nanocomposites Based on Hyperbranched Polymers and Montmorillonite

Nanocomposites based on hyperbranched polymers and sodium montmorillonite were prepared over the full range of compositions. The XRD analysis showed the full exfoliation of silicate layers at lower silicate content (up to 9.1 wt%). With the further increase of silicate loading, an intercalated structure was developed with a constant d-spacing due to the unique structure of hyperbranched polymers. The heat capacity jump at the glass transition of the nanocomposites was found to deviate from the two-phase model prediction, indicating the formation of a rigid amorphous fraction. The glass transition temperature and heat capacity jump behaviors suggested that the molecular mobility of hyperbranched polymers were restricted by the introduction of silicate layers. The mechanical properties of the nanocomposites were also investigated.