The communication also covered the need to address potential risks for health and environment. In the European Commission published a first regulatory review of EU legislation with respect to nanomaterials. In the European Parliament responded to the European Commission Communication in a resolution[ 30 ] and did the following:.
Notification requirements for all nanomaterials placed on the market on their own, in preparations or in articles. While first nanospecific provisions were integrated in the Regulation EC no. Indeed, the European Commission started projects to investigate the needs for additional provisions.
These reports depict the Commission's main conclusions regarding nanomaterials: According to the European Commission, the REACH registration and proof of safe use for nanomaterials should be based on a case by case approach, and each type of nanomaterial should be clearly described.
Since only very limited information about nanomaterials was provided in the first registration period by December , the Commission proposes to improve the situation in future by adaption of the REACH Regulation. The Commission initiated a public consultation on how the annexes of REACH could be amended to ensure that nanomaterials are registered more clearly under REACH and that the safe use of nanomaterials is adequately demonstrated within the registration dossiers, as part of an impact assessment in May [ 32 ].
The consultation comprised five potential policy options which were measured against a baseline that assumes no new policy actions. The consultation asked how respondents consider the potential impact of the options on cost, safety and overall efficiency of the regulatory process based on 37 main questions and subquestions. The consultation closed mid of September The initial results of the consultation were presented at the Member State experts' meeting in October In total, responses to the questionnaire were submitted.
The results were split into two opposites. The final results of the impact assessment are now expected for early [ 33 ]. However, the Commission plans to revise the annexes only and not the main text of the regulation. The Commission justifies this approach by being able to use the faster and lighter comitology procedure and by avoiding to re-open the general REACH discussion. This approach was supported by a majority of Member States, at least as a first step. In our view one reason for the Commission to choose the comitology procedure is that the Commission has a stronger position than during the ordinary legislative procedure.
Similar discussions on regulatory frameworks take place in other countries and in academia[ 34 — 36 ]. However, this publication focuses on the ongoing discussion in Europe.
In our opinion, the planned amendments and, in particular, the refusal regarding the adaptation of the main text of REACH are not sufficient in order to receive adequate, meaningful and relatable information on nanomaterials. In the interest of legal clarity and certainty, we propose that the definition for nanomaterials should be integrated in Article 3.
Furthermore, additional amendments of the REACH regulation should be conducted which will be presented in the following chapters. There is a high variety of existing nanomaterials which differ in chemical composition, size, shape, crystallinity and surface modification.
Figure 1 shows exemplarily a small excerpt of the variety of possible nanomaterials. Taking into account this plurality of physico-chemical characteristics and resulting changes in the hazard profile, an approach must be found to adequately cover nanomaterials under REACH. There are two approaches conceivable to cover nanomaterials under REACH- treating them as substances on its own or as specific forms of a substance.
Schematic illustration of different forms of a substance. The bulk form and nanoforms of the same chemical composition could be treated as different substances within the meaning of REACH. To be more precise, such an approach could use the change of different parameters e.
REACH and in particular the classification, labelling, packaging CLP Regulation[ 37 ] base in general on the assumption that a substance has an intrinsic hazard profile independent from the manufacturing process. However, this approach has limitations already for bulk materials. For example, bulk materials of the same substance can differ in their hazard profiles based on impurities or macroscopic particle size, leading to different classifications under the CLP Regulation.
As already mentioned above, different nanomaterials of the same chemical composition often have very different properties and, subsequently, can differ in their hazard profile. This condition for instance can be utilised to define nanomaterials as substances on their own. However, the paper does not provide criteria for this decision. In the context of this approach, there is a need for clear criteria to avoid a split-up in many substances with small tonnages below the REACH triggers for registration requirements due to the variability of nanomaterials.
Some stakeholders are in favour of considering nanomaterials as substances on their own. If even the different nanoforms of a substance were treated as different substances, such an approach would need very low tonnage triggers for the registration and data obligations in REACH.
A proposal from KemI gives an impression of some of the necessary changes[ 40 ]. However, the KemI proposal does not include an approach how to differentiate between different nanomaterials of the same chemical composition.
In summary, for the legal implementation of such an approach, clear criteria to decide if two nanomaterials of the same chemical composition are different substances in the meaning of REACH are necessary. It must be carefully considered what the consequences of the aforementioned change of the substance definition are for other pieces of legislation that address substances as such.
Furthermore, such an approach would need a comprehensive review of the diverse instruments of the REACH regulation in order to ensure the workability of the instruments like data sharing, substance evaluation, information requirements and chemical safety assessment. Basically the same requirements for nanomaterials can be implemented with a different approach which is more in line with the substance definition and structure of the REACH regulation.
The bulk form and nanoforms of the same chemical composition could be treated as the same substance in the context of REACH. This includes a differentiated consideration of the bulk form and nanoform and the different nanoforms of the same substance respectively. Separate risk assessments shall be performed for the different nanoforms. An adequate handling of surface-treated nanomaterials has to be defined. Tonnage bands and information requirements need to be adjusted, and even the role of the downstream user has to be reconsidered.
For all these requirements, the burden of proof has to be on the side of the registrant. In the following sections, we will present some corner stones of the proposal published by the German federal authorities responsible for REACH[ 41 ]. One important aspect is the substance identity. Generally, for a well-defined substance under REACH, the substance identity is defined solely by the molecular structure and chemical composition.
Bulk and nanomaterial with the same molecular structure are chemically identical. This means that the bulk form and nanoform of a substance generally have to be registered in the same dossier. Therefore, the concept follows the characteriser approach. Nevertheless, special characteristics concerning eco- toxicology, toxico-kinetics and environmental fate, together with the existing uncertainties and special features with regard to mode of action, necessitate requirements which go beyond those laid down in REACH to date.
Nanomaterials have a low bulk density. This comes along with a typically high technical effectiveness caused by a high specific surface area and changes of reactivity, respectively. These characteristics together allow a wide dispersive use by a low mass application of the substance.
Therefore and because of the uncertainties regarding eco- toxicology, environmental fate and exposure information requirements should already apply at lower tonnage bands. This nanospecific annex covers information requirements for the different tonnage levels.
With respect to environment, these nanospecific information requirements subject chronic tests instead of acute tests at lower tonnage levels. Regarding the presumable partitioning of nanomaterials within the environment, appropriate target organisms have to be taken into account. That means information requirements must cover toxicity to sediment and soil organisms at lower tonnages. Furthermore, low water solubility as the exclusive waiving criterion for aquatic testing is not appropriate for nanomaterials, since also insoluble nanomaterials can show effects in the environment.
Future adjustments regarding assessment concepts and test guidelines have to be taken into account. Information requirements should first of all include a comprehensive characterisation of the nanoforms. This means that for each nanoform within a substance registration in addition to the identification of the chemical composition for substance identity, a characterisation of morphological parameters e.
However, it has to be noted that the further development and standardisation of reference methods for characterisation are still ongoing. The registrant can use the information on the nanoforms' characteristics to ascertain if different nanoforms of a substance can be considered jointly or separately for the fulfilment of information requirements. This decision should be based on the aforementioned physical and chemical parameters and whether these differ or equal in a relevant way.
A difference should be considered as relevant if it is likely that it leads to a change of the hazard profile. If nanoforms of a substance differ in a relevant way, information requirements have to be fulfilled separately for the individual forms.
In a further step, an endpoint-specific waiving and read across between different nanoforms of the same substance should be possible on a scientific basis. The process of examination whether different nanoforms can be considered jointly or separately for information requirements is illustrated in Figure 2.
Examining different nanoforms to be joined or separated for the fulfilment of information requirements. For nanomaterials, the surface to volume ratio dramatically increases with decreasing size and thus the surface plays a major role in the interaction with its surroundings.
However, excessive nano-Al 2 O 3 results in the appearance of agglomerates that increase the porosity of the materials and eventually lead to the decline in their mechanical properties. The variation in the microstructure with the amount of nano-alumina is shown in Figure 7. Scanning electron micrographs of the fractured surface of nano-micro composite self-lubricating ceramic tool material with different content of Al 2 O 3 [ 11 ] a 0 vol.
Owing to the size effect of nanomaterials, the grain boundaries of nanomaterials have a higher volume fraction than microscale and traditional materials [ 46 ]. In composites, good bonding between the filler and the matrix is critical to improving their mechanical properties [ 47 , 48 , 49 ]. Therefore, grain boundaries are one of the important factors affecting the mechanical properties of nanomaterials, especially nanocomposites. In general, the denseness, chemical bonding properties, and structural properties of the grain boundaries affect the mechanical properties of nano-materials.
Accordingly, the factors that can affect grain boundary structure also indirectly affect the mechanical properties of nanomaterials. Researchers can modify the matrixes by adding nanoparticles to improve their mechanical properties [ 50 ].
The principle of this method is to improve the interfacial structure of the matrix by adding nanoparticles and to use the size effect of the nanoparticles to fill the pores in the interface of the matrix to make it denser, thereby indirectly improving its stress transmission and elasticity. The interface performance caused by deformation improves the mechanical properties. Zhu et al. The coating facilitates stress transfer and prevents crack propagation, thereby increasing the toughness of the composite.
Many other methods, such as high-temperature sintering and thermal cycle loading, are used to improve the mechanical properties of nanomaterials. Zucchelli et al. The combination of the two phases promotes the mechanical properties and improves the interface hardness and elastic modulus of the enamel—steel interface. Zhang et al. Lin et al. In situ micrographs of studied enamel during heating at different temperatures [ 52 ].
In addition to the aforementioned methods for modifying the interfacial properties of nanomaterials, many other modification methods can achieve the same purpose. Their principles are undeniably similar and can be roughly divided into two types. The first type is to improve the interfacial properties and increase the interfacial bonding of nanomaterials by adding nanoparticles to the matrix to fill the pores of the interface structure of the matrix.
The second type is to improve the interface of nanomaterials by processing nanomaterials, enhancing the component diffusion process between two-phase or multi-phase materials, or controlling the growth process of crystal grains.
Mechanical properties of nanomaterials refer to the mechanical characteristics of nanomaterials under different environments and various external loads. A large amount of literature has studied the mechanical properties of nanomaterials. However, these studies mainly focus on improving the mechanical properties of nanomaterials by adding nanoparticles to the matrix which is generally not a nanomaterial. Few researches on the mechanical properties of pure nanomaterials are studied.
More details of mechanical properties of metal nanomaterials obtained including Vickers hardness, fracture toughness, fracture strength, ultimate tensile strength, as well as impact strength are provided in Table 3. Mechanical properties of metal nanomaterials [ 56 , 57 ]. It can be seen that nanomaterials with metal nanoparticles have higher fracture toughness and fracture strength than monolithic Al 2 O 3.
This phenomenon should be attributed to the addition of nanoparticles. The pinning effect of metal particles inhibits the grain growth of Al 2 O 3 matrix, making the grain size of the nanocomposite smaller than that of monolithic Al 2 O 3 , resulting in grain refinement, and leading to the improvement of mechanical properties of the nanocomposite [ 56 ].
Interestingly, the hardness of nanocomposites with nano-Cu is lower than that of monolithic Al 2 O 3 , while the hardness of nanocomposites with nano-Ni-Co is higher than that of monolithic Al 2 O 3 ,which is probably due to the reason that the hardness of Cu is lower than that of Al 2 O 3 , and the addition of nano-Cu weakens the hardness of nanocomposites to some extent.
Similarly, the hardness of nano-Ni-Co is higher than that of Al 2 O 3. The addition of nano-Ni-Co increases the hardness of nanocomposites to a certain extent. In addition, the last three sets of data in Table 3 show that the hybrid composites have higher Vickers hardness, impact strength and ultimate tensile strength compared to the single reinforced composites due to the combined effect of SiC and B 4 C. Table 4 shows the mechanical properties of non-metallic nanomaterials.
It is obviously that the addition of multi-walled carbon nanotubes to skutterudites will lead to a decrease in the mechanical properties of the nanocomposite. This is due to the formation of carbon nanotubes agglomerates inside the skutterudites. The plane like agglomerates act as slip planes and planes in which cracks can easily propagate, thereby leading to sample fracture already at low mechanical loads [ 58 ].
It is undeniable that most organic nanomaterials do not have mechanical properties like hardness and compressive strength, because most nanomaterials are flexible materials. Mechanical properties of non-metallic nanomaterials [ 51 , 58 , 59 ]. The last five groups of data in Table 4 show that the tensile strength gradually decreases with the increase of nano-HA which may be related to the fragile interface between nano-HA and nano-PLLA.
The flexural strength of the nanocomposites first increased and then decreased with the increase of nano-HA. In recent years, nanomaterials have received widespread attention due to their unique properties and their importance in technical applications. Many researchers have begun research work on nanomaterials [ 60 ]. These researches mainly focus on three aspects: theoretical research, simulation analysis and experimental study.
In theoretical research, Tseng et al. Zahedmanesh et al. As for simulation analysis, Wu [ 63 ] studied the mechanical behavior of Cu nanowires by molecular dynamics method, and obtained the stress-strain relationship of nanowires through numerical simulation Figure Simulation model of Cu nanowire [ 63 ].
The three-dimensional schematic diagram of the simulated nano-twinned Cu with spherical Ag inclusions [ 64 ] a Simulation model b The same structure without Cu atoms. In addition, the green and red atoms are respectively the atoms which are in local fcc and hcp lattices. The blue atoms represent the silver atoms. In terms of experimental study, researchers are focusing on modifying nanomaterials, that is, improving the mechanical properties of nanomaterials [ 65 ].
At present, a common method is to add nanoparticles to the matrix to improve the mechanical properties of the nanomaterials. For example, the strength of functionally graded materials can be enhanced by adding carbon nanotubes [ 66 ]. The mechanical and tribological properties of bone cement can be improved by adding nano-HA [ 67 ]. The mechanical properties of the matrix can be improved by adding electrospun polymer nanofibers to the matrix [ 68 , 69 ].
In addition, some researchers are also investigating the process parameters to promote nanomaterial performance or microstructure. They are attempting to identify the mechanisms that improve the performance of nanomaterials by determining the optimal process parameters or methods to construct nanomaterials [ 71 , 72 ]. Daudin et al. Metal nanoparticles are the first artificially prepared nanoparticles.
Compared with other nanomaterials, nanometal materials have the longest development time, and thus, they have been extensively researched.
Nanometals, such as gold, silver, and zinc, have been widely used to improve the physical, chemical, and mechanical properties of various materials, including paper, archaeological stone, paint, wood, and medical equipment. A functionalized polymer containing nano-Ag can be used not only as an effective fungicide but also as a reinforcement of historical and cultural relics [ 74 ].
The addition of nano-Zn can improve the leaching and corrosion resistance of Nanhuang pine [ 75 ]. Nano-Ag and nano-Cu can improve the antibacterial properties of commercial particleboard and increase its lifespan [ 76 ]. In addition, some nano metal compounds have also been used in catalysts, antibacterial and antiseptic research [ 77 , 78 , 79 ]. With regard to inorganic non-metallic nanomaterials, researchers are focusing on nano-cement and nano-concrete.
Their mechanical properties are improved by adding nanoparticles to cement-based materials or concrete and promoting the dispersion of nanoparticles in the matrix [ 80 , 81 ].
Nano-Si has excellent properties, such as high melting point, high hardness, and high chemical stability. It is a promising candidate for improving the performance of cement-based materials [ 82 , 83 , 84 ].
The addition of the nano-Si could produce an increase in the compressive and flexural strengths of the cement mortar [ 85 ].
Aside from nanometal materials and inorganic non-metal nanomaterials, scientists have made progress in organic nanomaterial research [ 86 , 87 , 88 ]. They have attempted to incorporate graphene oxide into polyvinyl alcohol nanofibers to obtain nanocomposites with bettermechanical properties [ 89 , 90 ].
Kashyap et al. Graphene oxide-doped polyvinyl alcohol nanofibers can be used as a hard template to assist the growth of TiO 2. This article mainly introduced the influence of four different factors on the mechanical properties of nanomaterials, namely, nanoparticle selection, production process, grain size, and grain boundary structure.
These factors do not affect the mechanical properties of nanomaterials individually but interact and depend on each other. In the course of this, he noted, scaling issues would arise from the changing magnitude of various physical phenomena: gravity would become less important whereas surface effects would become increasingly more significant.
The field of nanoscience and nanotechnology is now growing very rapidly. According to the UK Royal Society, nanoscience is defined as the study of phenomena and manipulation of materials at atomic, molecular, and macromolecular scales, where properties differ significantly from those at a larger scale. Nanotechnologies are the design, characterization, production, and application of structures, devices, and systems by controlling shape and size at the nanoscale.
Nanomaterials cross the boundary between nanoscience and nanotechnologies and link these both areas together. Generally, nanomaterials deal with sizes of nanometers or smaller in at least one dimension.
The material properties of nanostructures are different from the bulk due to the high surface area over volume ratio and possible appearance of quantum effects at the nanoscale. The study of size and shape effects on material properties has attracted enormous attention due to their scientific and industrial importance. It is therefore a great pleasure to edit this special issue. In this rapidly progressing area of nanoscience and nanotechnology, it is always important to highlight the most recent and active areas that are being pursued and highlight them to the scientific community.
Thus, this special issue brings to fore several such closely related yet diverse areas that encompass this field and are actively being investigated. The papers that appear in this special issue have been grouped according to their themes: size effect on mechanical properties, size effect on catalytic properties, and so forth.
Zeng and H. Yu; they found that the structural distortions on the quantum dots depend both on the kind of dopant and on the size of the dots. Delogu and M. Moscia describes molecular dynamics simulation results concerning the structural phase transition of the Ag—Cu nanoalloy. Zhang et al. Wong and V. Vijayaraghavan showcases the nanomechanics of single- and double-walled carbon nanotubes using molecular dynamics simulations.
Also investigating elastic properties, D.
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