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Recently, the significant improvements in polymer composites properties have been mainly attributed to the ability of filler nanoparticles (NPs) to self-assemble into highly anisotropic self-assembled structures. In this work, we investigate the self-assembly of core-shell NPs composed of a silica core grafted with polybutadiene (PB) chains, generating the so-called “hairy” NPs (HNPs), immersed in tetrahydrofuran solvent. While uncoated silica beads aggregate forming uniform compact structures, the presence of a PB shell affects the silica NPs organization to the point that by increasing the polymer density at the corona, they tend to self-assemble into linear chain-like structures. To reproduce the experimental observations, we propose a theoretical model for the two-body that considers the van der Waals attractive energy together with the polymer-induced repulsive steric contribution and includes an additional three-body interaction term. This term arises due to the anisotropic distribution of PB, which increases their concentration near the NPs contact region. The resulting steric repulsion experienced by a third NP approaching the dimer prevents its binding close to the dimer bond and favors the growth of chain-like structures. We find good agreement between the simulated and experimental self-assembled superstructures, confirming that this three-body steric repulsion plays a key role in determining the cluster morphology of these core-shell NPs. The model also shows that further increasing the grafting density leads to low-density gel-like open structures.

The coupling of ZnO-based nanomaterials with organic photosensitizers (PS) is potentially interesting for cancer treatment under X-ray. In these conditions, ZnO nanoparticles (NPs) convert the X-ray into UV-Vis emission, promoting the PS excitation and producing reactive oxygen species (ROS). Main advantages for in vivo applications are ZnO photostability and biocompatibility, even if its efficient coupling with different PS (typically porphyrin) is still a controversial issue, as both a high ZnO luminescence yield and a good overlapping of ZnO emission-PS absorption spectra are necessary, along with a suitable energy transfer between ZnO and PS. In this perspective, the aim is the investigation of the optical properties of an ad-hoc system composed of porphyrin functionalized ZnO NPs anchored on SiO2 NPs (ZnO/SiO2). The goal is the understanding of the optimal conditions for a good energy transfer efficiency of ZnO-porphyrin structures, including the role of ZnO-PS proximity, to promote their application in anti-cancer therapies and imaging with ionizing radiations. First, amorphous ZnO NPs of 5-6 nm were anchored onto SiO2 NPs (~80 nm); then, ZnO/SiO2 was functionalized with different porphyrin contents (tetrakis(4-carboxyphenyl)porphyrin, TCPP, 0.3 – 3.0 wt%) by exploiting a silane grafting agent (3-aminopropyl)triethoxysilane. The structural characterization demonstrated that increasing TCPP amounts were bonded to SiO2 depending on the TCPP loading. The optical properties were preliminary tested in dimethylformamide, used as solvent reaction for TCPP anchoring on SiO2. The Photoluminescence Analysis (PL) revealed a high luminescence of ZnO NPs and the occurrence of a radiative energy transfer between ZnO and TCPP, that was not visible in a mechanical mixing of ZnO and TCCP, highlighting their optical interaction upon functionalization. Besides, TCPP emission was hugely enhanced under X-ray in the Radioluminescence (RL), whereas no enhancement was detectable in t

Composite materials based on hybrid filler systems can be a promising approach to produce advanced rubber nanocomposites (NCs). Recently, the positive effect of the combined use of silica and sepiolite on NCs mechanical properties has been reported, compared to those of compounds reinforced with the same amount of the only silica filler. In this context, the present work aims at studying the possible synergistic self-assembly of nanosilica and sepiolite in the generation of a cooperative hybrid filler network in rubber-based NCs, in connection with material performance for tires application. In detail, the influence of the introduction of a secondary anisotropic filler in conjunction with isotropic nanosilica on their dispersion and interaction with the rubber matrix has been comprehensively investigated, in order to define the best formulation ensuring low rolling resistance and significant fuel saving. NCs, containing simultaneously silica and sepiolite, either pristine (Sep) or chemically modified (mSep) by an acid treatment, were prepared by combining latex compounding technique (LCT) and melt blending. Rheological and dynamic-mechanical analyses highlighted that the use of a double white filler, constituted by particles with different aspect ratio, affords a good balance between efficient reinforcement and low Payne effect. Tansmission electron microscope (TEM) analysis evidenced the formation, within the rubber matrix, of cooperative superstructures due to the self-assembly of sepiolite and silica nanoparticles containing occluded rubber, when the secondary filler is mSep. The peculiar characteristics of mSep, characterized by fibers shorter than Sep and higher surface silanol bonding sites, bring about significant interactions between mSep and silica, which promote self-assembly of the two fillers in a collaborative hybrid network, improving dynamic-mechanical performances. These results, even if related to sepiolite/silica NCs, demonstrate the effective role

The efficiency of sulfur vulcanization reaction in rubber industry is generally improved thanks to the combined use of accelerators (as sulphenamides), activators (inorganic oxides), and co-activators (fatty acids). The interaction among these species is responsible for the formation of intermediate metal complexes, which are able to increase the reactivity of sulfur towards the polymer and to promote the chemical cross-links between the rubber chains. The high number of species and reactions that are involved contemporarily in the process hinders the complete understanding of its mechanism despite the long history of vulcanization. In this process, ZnO is considered to be the most efficient and major employed activator and zinc-based complexes that formed during the first steps of the reaction are recognized to play a main role in determining both the kinetic and the nature of the cross-linked products. However, the low affinity of ZnO towards the rubber entails its high consumption (3–5 parts per hundred, phr) to achieve a good distribution in the matrix, leading to a possible zinc leaching in the environment during the life cycle of rubber products (i.e., tires). Thanks to the recent recognition of ZnO ecotoxicity, especially towards the aquatic environment, these aspects gain a critical importance in view of the urgent need to reduce or possibly substitute the ZnO employed in rubber vulcanization. In this review, the reactivity of ZnO as curing activator and its role in the vulcanization mechanism are highlighted and deeply discussed. A complete overview of the recent strategies that have been proposed in the literature to improve the vulcanization efficiency by reducing the amount of zinc that is used in the process is also reported.

"Hairy" nanoparticles (HNPs), i.e. inorganic NPs functionalized with polymer chains, are promising building blocks for the synthesis of advanced nanocomposite (NC) materials having several technological applications. Recent evidence shows that HNPs self-organize in a variety of anisotropic structures, resulting in an improvement of the functional properties of the materials, in which are embedded. In this paper, we propose a three-step colloidal synthesis of spherical SiO2-HNPs, with controlled particle morphology and surface chemistry. In detail, the SiO2 core, synthesized by a modified Stöber method, was first functionalized with a short-chain amino-silane, which acts as an anchor, and then covered by maleated polybutadiene (PB), a rubbery polymer having low glass transition temperature, rarely considered until now. An extensive investigation by a multi-technique analysis demonstrates that the synthesis of SiO2-HNPs is simple, scalable, and potentially applicable to different kind of NPs and polymers. Morphological analysis shows the overall distribution of SiO2-HNPs with a certain degree of spatial organization, suggesting that the polymer coating induces a modification of NP-NP interactions. The role of the surface PB brushes in influencing the special arrangement of SiO2-HNPs was observed also in cis-1,4-polybutadiene (cis-PB), since the resulting NC exhibited the particle packing in "string-like" superstructures. This confirms the tendency of SiO2-HNPs to self-assemble and create alternative structures in polymer NCs, which may impart them peculiar functional properties.

ZnO is a worldwide used activator for a rubber vulcanization process, which promotes fast curing kinetics and high cross-linking densities of rubber nanocomposites (NCs). However, its extended use together with leaching phenomena occurring during the production and life cycle of rubber products, especially tires, entails potential environmental risks, as ecotoxicity toward aquatic organisms. Pushed by this issue, a novel activator was developed, which introduces highly dispersed and active zinc species in the vulcanization process, reducing the amount of employed ZnO and keeping high the curing efficiency. The activator is constituted by Zn(II) single sites, anchored on the surface of SiO2 nanoparticles (NPs) through the coordination with functionalizing amino silane groups. It behaves as a double-function material, acting at the same time as a rubber reinforcing filler and a curing activator. The higher availability and reactivity of the single-site Zn(II) centers toward curative agents impart faster kinetics and higher efficiency to the vulcanization process of silica/isoprene NCs, compared to conventionally used ZnO activators. Moreover, the NCs show a high cross-linking degree and improved dynamic mechanical properties, despite the remarkably lower amount of zinc employed than that normally used for rubber composites in tires. Finally, the structural stability of Zn(II) single sites during the curing reactions and in the final materials may represent a turning point toward the elimination of zinc leaching phenomena.

The present study explores the exploitation of ladder-like polysilsesquioxanes (PSQs) bearing reactive functional groups in conjunction with SiO2 nanoparticles (NPs) to produce UV-curable nanocomposite coatings with increased hydrophobicity and good thermal resistance. In detail, a medium degree regular ladder-like structured poly (methacryloxypropyl) silsesquioxane (LPMASQ) and silica NPs, either naked or functionalized with a methacrylsilane (SiO2@TMMS), were blended and then irradiated in the form of a film. Material characterization evidenced significant modifications of the structural organization of the LPMASQ backbone and, in particular, a rearrangement of the silsesquioxane chains at the interface upon introduction of the functionalized silica NPs. This leads to remarkable thermal resistance and enhanced hydrophobic features in the final nanocomposite. The results suggest that the adopted strategy, in comparison with mostly difficult and expensive surface modification and structuring protocols, may provide tailored functional properties without modifying the surface roughness or the functionalities of silsesquioxanes, but simply tuning their interactions at the hybrid interface with silica fillers.

Biocomposites based on sepiolite (Sep) clays and natural rubber latex (NRL) are novel green synthetic materials with significant mechanical performance obtained by an eco-friendly and sustainable mixing procedure, without the use of surfactants. In this work, experiments and theory are combined to investigate the stability of colloidal dispersions formed by a mixture of both negatively charged Sep fibers and non-adsorbing NRL particles. Experiments were performed by adding Sep fibers to NRL dispersions with different Sep/NRL volume fractions to evaluate the effect of Sep dispersion and NRL loading on the flocculation process. In order to theoretically understand the experimental results on colloidal stability, a density functional approach was applied to calculate the depletion interaction between two Sep fibers induced by the presence of naturally charged NRL, and an effective one-component mean-field free energy was developed to predict the phase behavior of the Sep/NRL mixture. The existence of a depletion attraction, enhanced by the electrostatic repulsion between Sep and NRL, is shown to be strong enough to induce the flocculation of the mixture at determined Sep and NRL volume fractions. The theoretical predicted phase diagram is in excellent qualitative and quantitative agreement with the experimental results, indicating that this electrostatically-enhanced depletion effect plays a key role in the colloidal stability of this system. To the best of our knowledge, this study represents the first attempt to tackle how depletion effects can be exploited to produce and control Sep/NR biocomposites.

ZnO nanoparticles (NPs) anchored on SiO2 (ZnO/SiO2) demonstrated to be an activator of higher efficiency in the sulfur crosslinking of isoprene rubber (IR) in comparison with conventional microcrystalline ZnO. The better performance of this innovative catalytic filler has been associated with: (i) the faster Zn reaction with stearic acid and curatives, to form the sulfurating complexes at the beginning of the curing process; (ii) the faster formation of large amounts of mono- and di- sulfide cross-linking short chains through a breaking-down mechanism of longer poly-sulfide chains, which account for the higher cross-linking density of the final cured material. In the first step of the curing reaction activated by ZnO/SiO2, the formation of a stearate bridged dimeric zinc complex has been suggested as potential highly reactive intermediate responsible for accelerating the cross-linking reaction

Novel activators are proposed aimed at introducing more disperse and active zinc species in the vulcanization process, reducing the amount of employed ZnO and keeping high curing efficiency. The activators ZnO@SiO2 and Zn@SiO2 are constituted by ZnO nanoparticles (NPs) (4-6 nm) or Zn centers supported on silica NPs, the common reinforcing filler in rubber composites for tyres. They behave as double function fillers, at the same time acting as rubber reinforcing filler and as activator of vulcanization and demonstrate high efficiency in the vulcanization process of Silica/Isoprene nanocomposites., Novel activators are proposed aimed at introducing more disperse and active zinc species in the vulcanization process, reducing the amount of employed ZnO and keeping high curing efficiency. The activators ZnO@SiO2 and Zn@SiO2 are constituted by ZnO nanoparticles (NPs) (4-6 nm) or Zn centers supported on silica NPs, the common reinforcing filler in rubber composites for tyres. They behave as double function fillers, at the same time acting as rubber reinforcing filler and as activator of vulcanization and demonstrate high efficiency in the vulcanization process of Silica/Isoprene nanocomposites.

A new family of silica fillers, featuring unique particle shape and tailored surface chemistry, was developed in order to improve the balance between hysteresis and reinforcement of rubber nanocomposites (NC) materials. On the basis of this, new elastomeric tyre compositions were developed, giving rise to the SmartNET ™ Silica industrial technology. This technology allows to create a strong, long-lasting tyre with high rolling efficiency, thanks to its natural anisotropic orientation, which reduces heating while increasing elasticity, to help minimize energy dissipation, A new family of silica fillers, featuring unique particle shape and tailored surface chemistry, was developed in order to improve the balance between hysteresis and reinforcement of rubber nanocomposites (NC) materials. On the basis of this, new elastomeric tyre compositions were developed, giving rise to the SmartNET ™ Silica industrial technology. This technology allows to create a strong, long-lasting tyre with high rolling efficiency, thanks to its natural anisotropic orientation, which reduces heating while increasing elasticity, to help minimize energy dissipation

The present study aims at supplying a more in-depth picture of the Environmentally Persistent Free Radicals (EPFRs) generation from phenol (PhOH) on ZnO/SiO2 systems, by exploring the properties of ZnO nanoparticles with different intrinsic defectivity grown on highly porous silica with spherical (ZnO/SiO2_S) and worm-like morphology (ZnO/SiO2_W). In detail, besides an extensive structural, morphological, and surface investigation, the occurrence of inequivalent defect centers in the samples was tracked by photoluminescence (PL) experiments, which unveiled, for ZnO/SiO2_W, intense blue emissions possibly involving radiative recombination from Zni excited levels to the valence band or to VZn levels. Electron Spin Resonance (ESR) spectra, corroborated these results and revealed a remarkably different behaviour of the samples in the EPFRs formation model reaction. In fact, upon PhOH contact, the ESR spectrum of ZnO/SiO2_S showed the exclusive presence of a weak isotropic signal ascribable to a PhenO• EPFR. Instead, for ZnO/SiO2_W, intense features associated to oxygen species in proximity of VO+, VZn‒ and (VZn‒)2‒ centers dominate the spectra, while a minor contribution of PhenO• radical can be discovered only by signals simulation. These outcomes definitively envisage a role of the intrinsic defectivity of ZnO NPs on the final yield and stability of EPFRs generation, with VO+ and VZn‒ defects possibly involved in dissociative adsorption or oxidation processes at the oxide surface. Although this work focuses on ZnO, it is expected to foster a critical re-examination and integration of important results on other metal oxide/silica systems already reported in the literature, offering the chance to better evaluate the dependence EPFRs generation on the oxide defects chemistry.

Sepiolite (Sep)-styrene butadiene rubber (SBR) nanocomposites were prepared by using nano-sized sepiolite (NS-SepS9) fibers, obtained by applying a controlled surface acid treatment, also in the presence of a silane coupling agent (NS-SilSepS9). Sep/SBR nanocomposites were used as a model to study the influence of the modified sepiolite filler on the formation of immobilized rubber at the clay-rubber interface and the role of a self-assembled nanostructure in tuning the mechanical properties. A detailed investigation at the macro and nanoscale of such self-assembled structures was performed in terms of the organization and networking of Sep fibers in the rubber matrix, the nature of both the filler-filler and filler-rubber interactions, and the impact of these features on the reduced dissipative phenomena. An integrated multi-technique approach, based on dynamic measurements, nuclear magnetic resonance analysis, and morphological investigation, assessed that the macroscopic mechanical properties of clay nanocomposites can be remarkably enhanced by self-assembled filler structures, whose formation can be favored by manipulating the chemistry at the hybrid interfaces between the clay particles and the polymers.

Global industry is showing a great interest in the field of sustainability owing to the increased attention for ecological safety and utilization of renewable materials. For the scientific community, the challenge lies in the identification of greener synthetic approaches for reducing the environmental impact. In this context, we propose the preparation of novel biocomposites consisting of natural rubber latex (NRL) and sepiolite (Sep) fibers through the latex compounding technique (LCT), an ecofriendly approach where the filler is directly mixed with a stable elastomer colloid. This strategy favors a homogeneous dispersion of hydrophilic Sep fibers in the rubber matrix, allowing the production of high-loaded sepiolite/natural rubber (Sep/NR) without the use of surfactants. The main physicochemical parameters which control Sep aggregation processes in the aqueous medium were comprehensively investigated and a flocculation mechanism was proposed. The uniform Sep distribution in the rubber matrix, characteristic of the proposed LCT, and the percolative filler network improved the mechanical performances of Sep/NR biocomposites in comparison to those of analogous materials prepared by conventional melt-mixing. These outcomes indicate the suitability of the adopted sustainable procedure for the production of high-loaded clay–rubber nanocomposites with remarkable mechanical features.

The crosslink density and distribution inside the polymer matrix affect the mechanical properties of rubber nanocomposites (NCs). Since the catalytic activity of zinc has a central role in the formation of crosslinks, this study focuses on the effect that the structure of the catalytic sites and their localization inside the polymer matrix have on the mechanical behavior of rubber materials. To do this, a new highly efficient activator, Zn@SiO2 based on zinc single sites anchored onto the silica surface, is used as double function filler, acting as both activator and reinforcing filler. The mechanical properties of rubber NCs prepared with Zn@SiO2 are compared to NCs conventionally cured with ZnO particles. The results suggest that localizing the catalytic sites at different distance from the filler particles dispersed in the rubber matrix is a promising tool to control the crosslinking density and distribution, which means tuning the mechanical properties of rubber NCs.