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The incorporation of silica nanoparticles (Si-NPs) into the polymer matrix is a growing area of interest research to produce high-performance polymer nanocomposites (NCs) across a wide range of nanotechnology applications. This improvement is due to the Si-NPs capability to self-assembly giving rise to specific well-organized structures with both short- and long-range order across a hierarchy of spatial scales, determined by both NP-NP and NP-matrix interactions, involving a careful balance among attractive driving forces, repulsive forces, and directional forces. Respect to this, the aim of the present paper is to systematically review the use of Si-NPs in polymer NCs and on the role of NPs self-assembly in determining the final material properties. Firstly, we explored the synthesis and modification of both isotropic and anisotropic Si-NPs in relation with use in NC materials, focusing on NPs dispersion and distribution, as well as on the functionalization strategies of Si-NPs. Besides Si-NPs functionalization with conventional small organic molecules, a large section is devoted to an emerging class of functionalized Si-NPs with macromolecules, namely silica hairy NPs (Si-HNPs), able to give rise a rich variety of complex assemblies and materials with new structures and functionalities. Successively, NCs materials containing Si-NPs and Si-HNPs have been explored in terms of synthetic preparation and properties. The self-organization of Si-NPs and Si-HNPs in polymer matrices has been reported and its effect on the functional materials properties have been evaluated with a critical point of view on the results, limits, and future perspectives. Our review can be considered a tutorial work, aiming at providing useful insights to researchers in the field of nanotechnology and nanoscience, taking into consideration the fundamental role of NPs self-assembly processes in determining the functional material properties.

Ladder-like polysilsesquioxanes (LPSQs) are characterized by a double-stranded siloxane backbone, whose chemical and structural properties depend on both the synthesis parameters and the nature of the organic side-chains. In the case of ladder-like (methacryloxypropyl) polysilsesquioxanes (LPMASQ), polymer matrices can be produced by exploiting the presence of photocurable methacrylate groups. Consequently, they can be used to prepare functional nanocomposites (NCs), either by blending with organic polymers such as polybutadiene or exploiting the inorganic fillers’ dispersion. Since the properties of LPMASQ-based NCs are strongly related to their structure, the structural changes of polymerized LPMASQ were investigated upon addition of low loadings of TiO2 nanoparticles (up to 3 wt%) by solid state nuclear magnetic resonance and X-ray diffraction. The filler addition leads to the reduction of the polymerization capacity of the LPMASQ organic side-chains. Moreover, a different organization of ladder chains has been highlighted, ascribable to the increase in fully condensed linear ladder units at the expenses of folded chains and defective structures. The methodological approach here adopted can be extended to other composite systems and may help to describe the properties at the filler-matrix interface, offering valuable hints for a better design of these materials. Graphical Abstract

"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 nanoparticles grown on highly porous silica with spherical and rod-like morphology were investigated by radioluminescence and photoluminescence measurements to assess the influence of intrinsic defectiveness on the optical properties. Spectroscopic analysis of ZnO/SiO2 systems unveils defect-related luminescence and a very weak excitonic emission. The samples display peculiar optical properties with unlike intensity and energy emissions, disclosing the occurrence of inequivalent defect centers in ZnO nanoparticles supported onto silica with different morphology.

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 the mechanical mixing, that could be generated by both re-absorption of ZnO emitted photons and by ionizing radiation energy deposition in the porphyrin surroundings, whose efficiency depend on the TCPP arrangement and spatial distribution. In conclusion, this work paves the way to the deeper understanding of the correlation between the synthesis and the optical interactions of ZnO scintillator coupled with organic moieties to improve their luminescence performances.

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 of the collaborative filler network, based on the hybrid double fillers, able to lend enhanced properties to rubber materials.

The localization of the rubber vulcanization reaction close to the silica filler surface was investigated in isoprene rubber composites (IR NCs): the main goal was to highlight the role of curing agents’ dispersion and filler surface features on the spatial propagation of the rubber cross-links and the resulting mechanical behavior of the material. The study was realized by tailoring the morphology of the curing activator, i.e. by vulcanizing IR NCs with Zn@SiO2 double function filler, composed of Zn(II) single sites anchored on SiO2 filler, in comparison to silica filled IR NCs vulcanized with microcrystalline ZnO. The microscopic cross-links distribution was measured by Transmission Electron Microscopy for network visualization (NVTEM) and Time Domain Nuclear Magnetic Resonance (TD-NMR). Besides the NCs mechanical behavior was characterized both at small strain and at fracture. In the presence of Zn@SiO2, higher cross-link density in proximity to SiO2 particles was evidenced, which gradually spreads from the filler surface to the bulk, induced by localization of the Zn(II) centers. IR NCs with Zn@SiO2 resulted stiffer (+45%) and with a lower fracture toughness (less than one third), compared to m-ZnO based NCs, which shows a quite homogeneous structure of the rubber cross-links network. The results highlighted the correlation between the composites structural features and their macroscopic behavior, paving the way to modulating the mechanical properties of elastomeric materials by tuning the nature of the curing agents.

The occurrence of uncontrolled electrostatic discharge (ESD) is among the major causes of damage in unprotected electronic components during industrial processes. To counteract this undesired phenomenon, ESD composites showing static-dissipative and antistatic responses are developed. In particular, static-dissipative materials are able to slow down the flow of electric charges, whereas antistatic materials directly suppress the initial charges induced by undesired charging by properly dispersing conductive fillers within an insulant matrix and thus forming a conductive filler network. In this context, the purpose of this review is to provide a useful resume of the main fundamentals of the technology necessary for facing electrostatic charging. The formation mechanisms of electrostatic charges at the material surface were described, providing a classification of ESD composites and useful characterization methods. Furthermore, we reported a deep analysis of the role of conductive fillers in the formation of filler networks to allow electric charge movements, along with an overview of the different classes of inorganic conductive fillers exploitable in ESD composites, evidencing pros/cons and criticalities of each category of inorganic fillers.

The present study reports on the synthesis of a new alkoxysilane-bearing light-responsive cinnamyl group and its application as a surface functionalization agent for the development of SiO2 nanoparticles (NPs) with photoreversible tails. In detail, cinnamic acid (CINN) was activated with N-hydroxysuccinimide (NHS) to obtain the corresponding NHS-ester (CINN-NHS). Subsequently, the amine group of 3-aminopropyltriethoxysilane (APTES) was acylated with CINN-NHS leading to the generation of a novel organosilane, CINN-APTES, which was then exploited for decorating SiO2 NPs. The covalent bond to the silica surface was confirmed by solid state NMR, whereas thermogravimetric analysis unveiled a functionalization degree much higher compared to that achieved by a conventional double-step post-grafting procedure. In light of these intriguing results, the strategy was successfully extended to naturally occurring sepiolite fibers, widely employed as fillers in technological applications. Finally, a preliminary proof of concept of the photoreversibility of the obtained SiO2@CINN-APTES system has been carried out through UV diffuse reflectance. The overall outcomes prove the consistency and the versatility of the methodological protocol adopted, which appears promising for the design of hybrid NPs to be employed as building blocks for photoresponsive materials with the ability to change their molecular structure and subsequent properties when exposed to different light stimuli.

The interaction between activators (ZnO) and co-activators (stearic acid, SA) represents a key step in the vulcanization process, to generate Zn(II) intermediate complexes that enhance the reaction kinetic and promote the shortening of sulfur bridges, leading to highly cross-linked materials. To understand the influence of the structural, morphological and surface properties of ZnO in the reactivity with SA, in this work, pure ZnO nanoparticles (NPs) and ZnO NPs anchored on SiO2 (ZnO/SiO2) were prepared through soft chemistry techniques. Tailoring of morphology and surface features was accomplished through a fine control of the synthetic parameters, as demonstrated by the careful characterization of the activators. Then, the interaction of pure ZnO and ZnO/SiO2 activators with SA in the absence of rubber was investigated by using Differential Scanning Calorimetry (DSC). The occurrence of Zn(II)-SA complexes with different thermal stability and structural properties was assessed by a comprehensive thermogravimetric and spectroscopic survey. The generation and the chemical structure of these specific vulcanization intermediates was related to the peculiar characteristics of the ZnO/SiO2 systems and, in turn, to their ability in imparting faster kinetics and higher curing efficiency to isoprene rubber nanocomposites, compared to bare ZnO. These results, besides proposing a valid benchmark for achieving further insights on the interaction of stearic acid with activators, pave the way to provide specific protocols for a better design and implementation of ZnO-based materials able to effectively enhance the rubber vulcanization process, with significant economic and environmental advantages.

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., Pirelli, Milano Bicocca University, Junta de Andalucia European Regional Development Fund -Consejeria de Conocimiento, Investigacion y Universidad, Junta de Andalucia PY20-00241 A-FQM90-UGR20, Consejo Nacional de Ciencia y Tecnologia (CONACyT) A1-S-9197

The development of hybrid nanoscintillators is hunted for the implementation of modern detection technologies, like in high energy physics, homeland security, radioactive gas sensing, and medical imaging, as well as of the established therapies in radiation oncology, such as in X-ray activated photodynamic therapy. Engineering of the physico-chemical properties of nanoparticles (NPs) enables the manufacture of hybrids in which the conjugation of inorganic/organic components leads to increased multifunctionality and performance. However, the optimization of the properties of nanoparticles in combination with the use of ionizing radiation is not trivial: a complete knowledge on the structure, composition, physico-chemical features, and scintillation property relationships in hybrid nanomaterials is pivotal for any applications exploiting X-rays. In this paper, the design of hybrid nanoscintillators based on ZnO grown onto porous SiO2 substrates (ZnO/SiO2) has been performed in the view to create nanosystems potentially suitable in X-ray activated photodynamic therapy. Indeed, cytotoxic porphyrin dyes with increasing concentrations have been anchored on ZnO/SiO2 nanoparticles through amino-silane moieties. Chemical and structural analyses correlated with photoluminescence reveal that radiative energy transfer between ZnO and porphyrins is the principal mechanism prompting the excitation of photosensitizers. The use of soft X-ray excitation results in a further sensitization of the porphyrin emission, due to augmented energy deposition promoted by ZnO in the surroundings of the chemically bound porphyrin. This finding unveils the cruciality of the design of hybrid nanoparticles in ruling the efficacy of the interaction between ionizing radiation and inorganic/organic moieties, and thus of the final nanomaterial performances towards the foreseen application.

The development of effective thermally conductive rubber nanocomposites for heat management represents a tricky point for several modern technologies, ranging from electronic devices to the tire industry. Since rubber materials generally exhibit poor thermal transfer, the addition of high loadings of different carbon-based or inorganic thermally conductive fillers is mandatory to achieve satisfactory heat dissipation performance. However, this dramatically alters the mechanical behavior of the final materials, representing a real limitation to their application. Moreover, upon fillers’ incorporation into the polymer matrix, interfacial thermal resistance arises due to differences between the phonon spectra and scattering at the hybrid interface between the phases. Thus, a suitable filler functionalization is required to avoid discontinuities in the thermal transfer. In this challenging scenario, the present review aims at summarizing the most recent efforts to improve the thermal conductivity of rubber nanocomposites by exploiting, in particular, inorganic and hybrid filler systems, focusing on those that may guarantee a viable transfer of lab-scale formulations to technological applicable solutions. The intrinsic relationship among the filler’s loading, structure, morphology, and interfacial features and the heat transfer in the rubber matrix will be explored in depth, with the ambition of providing some methodological tools for a more profitable design of thermally conductive rubber nanocomposites, especially those for the formulation of tires.

Ladder-like silsesquioxanes (SSQs) and TiO2 have been functionalized with methacryloyloxypropyl chains and embedded in a polybutadiene (PB) matrix giving rise to hybrid (organic–inorganic) nanocomposites (NCs) capable of acting as oxygen scavenging materials. The joint use of infrared spectroscopy, small-angle X-ray scattering, and permittivity measurements highlighted that the presence of TiO2, regardless of its modification, does not significantly alter the structure of the NCs, but just reduces the crosslinking degree and induces a local disorganization of the ladder-like SSQ stacks. The introduction of an optimum amount (0.5 wt%) of modified TiO2 within the polymeric matrix enhanced the oxygen uptake rate of ca. 70% with respect to the sole polymeric material. Moreover, the uptake kinetics changes from the first to second order with respect to the PB amount, clearly indicating different oxidation mechanisms. NCs containing modified TiO2 showed an oxygen uptake rate ranging from 30 to 60% higher than that achievable in the presence of bare TiO2. The superior activity of the materials containing modified TiO2 has been related to mechanistic aspects. Fluorescence and electron spin resonance spectroscopies allowed to underline the role of singlet oxygen within the polymeric matrix, although the known photochemical oxidation of PB and the TiO2 induced hydroxyl radical mediated oxidation cannot be excluded. These results open the route to highly efficient flexible oxygen scavenging materials for the protection of electronic devices such as organic based light emitting diodes, solar cells, and liquid crystal displays, which require high targets of protection from oxygen and water.

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.

Hybrid silica-based nanofillers were synthesised by grafting short chains of poly(ethylene glycol) (PEG) with different molecular weight on the surface of SiO2 porous nanoparticles. Based on this approach, homogeneous poly(ethylene oxide) (PEO)-based ceramic-in-polymer solid-state electrolytes with SiO2 loadings up to 23 wt% were obtained, thanks to the high compatibility between the two phases endowed by the grafted PEG chains. These electrolytes showed satisfying ionic conductivity and excellent resistance against dendrite piercing that enabled long operation, for more than 350 h, under continuous stripping/plating of lithium in symmetric Li/electrolyte/Li cells. Additionally, the operating life of these devices was improved by the self-healing reaction between Li dendrites and silica fillers, being able to reinstate the cycling after short circuit. Finally, a lithium metal full cell, equipped with LiFePO4 positive material and the solid-state electrolyte containing 18 wt% of SiO2, demonstrated high stability against dendrite penetration and discharge capacity at 70 °C comparable to cells based on liquid analogues.

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.

Latex compounding technique is an economic and ecosustainable alternative to melt mixing for preparing nanocomposites in which fillers are directly mixed with natural rubber in the latex aqueous dispersion. Clay minerals are excellent potential fillers to be used in masterbatches prepared exploiting this technique, but their presence is associated to the occurrence of oxidative degradation phenomena of natural rubber. In this work, by exploiting a combination of high- and low-resolution 13C and 1H Solid State Nuclear Magnetic Resonance techniques, with the support of Fourier Transform Infrared spectroscopy and thermal analyses, we characterized for the first time the oxidation phenomena occurring in sepiolite/natural rubber masterbatches obtained by the latex compounding technique. Oxidized species were identified and quantified and the dynamic properties, molecular weight and thermal stability of the rubber were characterized. Moreover, the dependence of degradation phenomena on the filler treatment and on the masterbatch work-up procedure was assessed, identifying freeze-drying as the method able to effectively protect the rubber from oxidation.

In this study, the preparation of polybutadiene/polysilsesquioxane nanocomposites (NCs) having tunable thermomechanical and dielectric properties is reported. This was achieved by using different amounts of a filler consisting of a silsesquioxane with a defined ladder-like molecular structure (LPMASQ) bearing reactive methacrylate functionalities. In detail, solid-state nuclear magnetic resonance (NMR) investigation revealed that an increasing amount of filler leads to a progressive homopolymerization of LPMASQ units resulting in the generation of domains in the composites, which induce a kind of polymer chain confinement in proximity of the hybrid interface. The evolution of the molecular organization of the inorganic nanobuilding blocks as a function of their concentration has been highlighted also by small-angle X-ray scattering (SAXS) experiments. The gradual assembly of LPMASQ units gives rise to peculiar dielectric properties along with enhanced thermal and mechanical stability of the final NCs, thus supplying suitable materials for applications in high performance dielectrics. Furthermore, these outcomes support the idea that a careful control of the molecular architecture and organization of the silsesquioxanes in a polymer matrix allows to simultaneously modulate two or more distinct functional features of polymer NCs

Organic–inorganic nanobuilding blocks (NBBs) based on silsesquioxanes (SSQs) have potential applications as nanofillers, thermal stabilizers, and rheological modifiers, which can improve thermomechanical properties of polymer hosts. The possibility to tune both siloxane structure and pendant groups can promote compatibilization and peculiar interactions with a plethora of polymers. However, the control on SSQs molecular architecture and functionalities is usually delicate and requires careful synthetic details. Moreover, investigating the influence of NBBs loading and structure on the hybrid interface and, in turn, on the polymer chains mobility and mechanical properties, may be challenging, especially for low-loaded materials. Herein, we describe the preparation and characterization of polybutadiene (PB) nanocomposites using as innovative fillers thiol-functionalized SSQs nanobuilding blocks (SH-NBBs), with both tailorable functionality and structure. Swelling experiments and, more clearly, solid-state NMR, enlightened a remarkable effect of SH-NBBs on the molecular structure and mobility of the polymeric chains, envisaging the occurrence of chemical interactions at the hybrid interface. Finally, thermal and DMTA analyses revealed that nanocomposites, even containing very low filler loadings (i.e. 1, 3 wt%), exhibited enhanced thermomechanical properties, which seem to be connected not only to the loading, but also to the peculiar cage or ladder-like architecture of SH-NBBs.

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.

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.

Sepiolite (Sep)&ndash, 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&ndash, filler and filler&ndash, 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.

The present study aims at supplying a more in-depth picture of the generation of environmentally persistent free radicals (EPFRs) from phenol (PhOH) on ZnO/SiO2 systems, by exploring the properties of ZnO nanoparticles (NPs) with different intrinsic defectivity grown on highly porous silica with a spherical (ZnO/SiO2-S) and wormlike 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 behavior of the samples in the EPFR 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 PhenOo EPFR. Instead, for ZnO/SiO2-W, intense features associated with oxygen species in proximity of VO +, VZn -, and (VZn -)2 - centers dominate the spectra, while a minor contribution of the PhenOo radical can be discovered only by signal simulation. These outcomes definitively envisage a role of the intrinsic defectivity of ZnO NPs on the final yield and stability of EPFR 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 of EPFR generation on the oxide defects chemistry.

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&ndash, rubber nanocomposites with remarkable mechanical features.

This study addresses the relationship between material morphology (size, growth parameters and interfaces) and optical emissions in ZnO through an experimental approach, including the effect of different material dimensions from bulk to nano-size, and different excitations, from optical sources to ionizing radiation. Silica supported ZnO nanoparticles and ligand capped ZnO nanoparticles are synthesized through a sol&ndash, gel process and hot injection method, respectively. Their optical properties are investigated by radioluminescence, steady-state and time-resolved photoluminescence, and compared to those of commercial micrometric powders and of a bulk single crystal. The Gaussian spectral reconstruction of all emission spectra highlights the occurrence of the same emission bands for all samples, comprising one ultraviolet excitonic peak and four visible defect-related components, whose relative intensities and time dynamics vary with the material parameters and the measurement conditions. The results demonstrate that a wide range of color outputs can be obtained by tuning synthesis conditions and size of pure ZnO nanoparticles, with favorable consequences for the engineering of optical devices based on this material.

The present study reports on a simple preparation strategy of a hybrid catalyst, TiO2/HKUST-1, containing TiO2 anatase nanoparticles (NPs) with tailored morphology and photocatalytic activity coupled with a porous metal-organic framework (MOF), namely HKUST-1, as an advanced material for the CO2 photocatalytic reduction. In detail, TiO2/HKUST-1 catalyst was prepared via an easy slow-diffusion method combined with a step-by-step self-assembly at room temperature. The growth of crystalline HKUST-1 onto titania surface was achieved by functionalizing TiO2 nanocrystals, with phosphoesanoic acid (PHA), namely TiO2-PHA, which provides an intimate contact between MOF and TiO2. The presence of a crystalline and porous shell of HKUST-1 on the TiO2 surfaces was assessed by a combination of analytical and spectroscopic techniques. TiO2/HKUST-1 nanocomposite showed a significant efficiency in reducing CO2 to CH4 under solar light irradiation, much higher than those of the single components. The role of MOF to improve the photoreduction process under visible light was evidenced and attributed either to the relevant amount of CO2 captured into the HKUST-1 porous architecture or to the hybrid structure of the material, which affords enhanced visible light absorption and allows an effective electron injection from TiO2-PHA to HKUST-1, responsible for the photochemical reduction of CO2.

The development of advanced polymer nanocomposites requires a strong filler-polymer interfacial interaction and an optimal filler nanodispersion. The incorporation of the clays into a polymer matrix frequently does not improve the composite mechanical properties, owing to both poor dispersion and macroscopic particle dimensions. In this work, pristine and organically-modified sepiolites (Sep) were structurally modified by an acid treatment, which provides nano-sized sepiolite (NS-Sep) fibers with reduced particle size and increased silanol groups on the surface layer. NS-Sep fibers were used to prepare styrene-butadiene rubber nanocomposites with enhanced mechanical properties. Dynamic-mechanical analysis of clay polymer nanocomposites demonstrated that the NS-Sep fibers provided an excellent balance between reinforcing and hysteretic behavior, compared to the large-sized pristine Sep and isotropic silica. This was related to the enhanced interfacial chemical interaction between NS-Sep and rubber, as well as to the size and self-assembly of anisotropic nanofibers to form filler network structures, as supported by transmission electron microscopy analysis. The preparation of nanocomposites, based on Sep nanofibers obtained by a simple and versatile acid treatment, can thus be considered an alternative approach for the designing of advanced clay polymer nanocomposites.

The present study provides a comprehensive investigation at the micro and nanoscale of the interface between hybrid SiO2@POSS nanofiller, where silica nanoparticles (NPs) and POSS nanocages are intimately interconnected, and Styrene Butadiene Rubber (SBR). SEM and AFM inspection and, more in depth, solid state 1H NMR revealed a remarkable fraction of rigid rubber close to the SiO2@POSS surfaces, which increases with the curing temperature. Instead, a reduced amount of immobilized rubber was detected for SBR/SiO2+POSS nanocomposites, obtained by simply mixing SBR, SiO2 and POSS. The results allowed us to propose a model for the network formation in C-SBR/SiO2@POSS. This is based on the progressive activation by dicumylperoxide (DCP) of the methacryl functionalities of POSS nanounits which, being closely connected to SiO2 NPs in SiO2@POSS, promote crosslinking in proximity of the filler surfaces, and lead to the generation of a tight network strongly bonded to the rubber chains.

Morphology-controlled titania nanocrystals (NCs) are indicated as promising building blocks for the generation of new photocatalytic materials, where precise tailoring of particle size and exposed crystal surfaces enables to fulfill specific reactivity requirements. In fact, beyond the dimensions, the presence of different TiO2 facets dramatically affects its photoactivity. This has been recently connected to the peculiar electronic band structures of specific surfaces and to their ability in promoting the concentration of different photogenerated defects. The most mature methods for the synthesis of shape-controlled TiO2 utilize organic surfactants, which commonly remain anchored to the NCs surfaces, often precluding their final use in photocatalytic applications. Although several alternatives have been provided (e.g., ligand exchange), there is still an urgent need to identify approaches for controlling morphology by also granting tunable surface functionalities, easy scalable procedures, and applicability in "friendly" materials (e.g., pellet, membranes, or flexible substrates). Bearing these challenges in mind, this chapter briefly presents the basic synthesis strategies for tuning morphology and surfaces of TiO2 NCs, focusing on those that may guarantee a transfer of the NCs intrinsic features to technological applicable photocatalytic materials. A brief state of art of the microscopic and spectroscopic techniques utilized for verify and study their morphology-dependent functionalities will be described. In this context and aiming to suggest implementation of TiO2 reactivity, a special attention will be devoted to spectroscopies (mainly ESR) allowing to monitor quasi "in situ" the photocatalytic mechanism. Finally, some perspectives for the inclusion of shape-controlled TiO2 NCs in smart materials will be proposed.