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Aggregate of nanoparticles: rheological and mechanical properties.

Wang Y, Wu X, Yang W, Zhai Y, Xie B, Yang M - Nanoscale Res Lett (2011)

Bottom Line: By this modified elastic model, the size of the network mesh can be estimated by the elastic modulus of the network which can be easily obtained by rheology.The stress to destroy the aggregates, i.e., the yield stress (σy), and the elastic modulus (G') of the network are found to be depended on the concentration of nano-silica (ϕ, wt.%) with the power of 4.02 and 3.83, respectively.Via this concentration dependent behavior, we can extrapolate two important mechanical parameters for the agglomerates in a dense packing state (ϕ = 1): the shear modulus and the yield stress.

View Article: PubMed Central - HTML - PubMed

Affiliation: College of Polymer Science and Engineering, State Key Laboratory of Polymer Materials Engineering, Sichuan University, Chengdu, 610065, China. ysjsanjin@163.com.

ABSTRACT
The understanding of the rheological and mechanical properties of nanoparticle aggregates is important for the application of nanofillers in nanocompoistes. In this work, we report a rheological study on the rheological and mechanical properties of nano-silica agglomerates in the form of gel network mainly constructed by hydrogen bonds. The elastic model for rubber is modified to analyze the elastic behavior of the agglomerates. By this modified elastic model, the size of the network mesh can be estimated by the elastic modulus of the network which can be easily obtained by rheology. The stress to destroy the aggregates, i.e., the yield stress (σy), and the elastic modulus (G') of the network are found to be depended on the concentration of nano-silica (ϕ, wt.%) with the power of 4.02 and 3.83, respectively. Via this concentration dependent behavior, we can extrapolate two important mechanical parameters for the agglomerates in a dense packing state (ϕ = 1): the shear modulus and the yield stress. Under large deformation (continuous shear flow), the network structure of the aggregates will experience destruction and reconstruction, which gives rise to fluctuations in the viscosity and a shear-thinning behavior.

No MeSH data available.


Related in: MedlinePlus

Dynamic elastic modulus of the nano-silica agglomerate prepared by compression molding at 5 MPa.
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Figure 3: Dynamic elastic modulus of the nano-silica agglomerate prepared by compression molding at 5 MPa.

Mentions: According to the percolation theory [20,22], the relationship between the storage modulus and the concentration ϕ (wt.%) can be express by G' = Gsϕα (ϕ ≥ ϕc, ϕc, the critical concentration for the forming of gel network). The power α was found to be 3.83 in our study as shown in Figure 3b. It is noted that Gs should have a physical meaning and, here, we propose it as the shear modulus of the agglomerates at the dense packing state (DPS), i.e., the state of ϕ = 1, and call it the stack shear modulus. We believe that Gs is a fundamental parameter relating to mechanical properties of agglomerate and is different from that of the bulk. It may be affected by the size, the surface characteristics, and the bulk properties of the nanoparticles. Actually, the agglomerates of nanoparticles can be viewed as a state of quasi-DPS and they are prevalent in nanocomposites. Therefore, this parameter is very important for the nanocomposites when the mechanical properties are of interest. However, as far as we know, the modulus of the bulk, not the aggregates, is usually used to evaluate the contribution of the nanoparticles to the mechanical properties of the nanocomposite [23]. At the same time, the mechanical properties of the agglomerates have been seldom reported [10,24]. For nano-silica employed in this study, we obtain Gs ≈ 107.92 Pa which is obviously lower than the bulk (ca. 1011 Pa) [1], but larger than the experimental result 2.2 × 106 Pa (Figure 3), which is likely to be caused by the difficulty in compressing the nanoparticles into a disk of DPS on the whole and should be further investigated in the future.


Aggregate of nanoparticles: rheological and mechanical properties.

Wang Y, Wu X, Yang W, Zhai Y, Xie B, Yang M - Nanoscale Res Lett (2011)

Dynamic elastic modulus of the nano-silica agglomerate prepared by compression molding at 5 MPa.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211159&req=5

Figure 3: Dynamic elastic modulus of the nano-silica agglomerate prepared by compression molding at 5 MPa.
Mentions: According to the percolation theory [20,22], the relationship between the storage modulus and the concentration ϕ (wt.%) can be express by G' = Gsϕα (ϕ ≥ ϕc, ϕc, the critical concentration for the forming of gel network). The power α was found to be 3.83 in our study as shown in Figure 3b. It is noted that Gs should have a physical meaning and, here, we propose it as the shear modulus of the agglomerates at the dense packing state (DPS), i.e., the state of ϕ = 1, and call it the stack shear modulus. We believe that Gs is a fundamental parameter relating to mechanical properties of agglomerate and is different from that of the bulk. It may be affected by the size, the surface characteristics, and the bulk properties of the nanoparticles. Actually, the agglomerates of nanoparticles can be viewed as a state of quasi-DPS and they are prevalent in nanocomposites. Therefore, this parameter is very important for the nanocomposites when the mechanical properties are of interest. However, as far as we know, the modulus of the bulk, not the aggregates, is usually used to evaluate the contribution of the nanoparticles to the mechanical properties of the nanocomposite [23]. At the same time, the mechanical properties of the agglomerates have been seldom reported [10,24]. For nano-silica employed in this study, we obtain Gs ≈ 107.92 Pa which is obviously lower than the bulk (ca. 1011 Pa) [1], but larger than the experimental result 2.2 × 106 Pa (Figure 3), which is likely to be caused by the difficulty in compressing the nanoparticles into a disk of DPS on the whole and should be further investigated in the future.

Bottom Line: By this modified elastic model, the size of the network mesh can be estimated by the elastic modulus of the network which can be easily obtained by rheology.The stress to destroy the aggregates, i.e., the yield stress (σy), and the elastic modulus (G') of the network are found to be depended on the concentration of nano-silica (ϕ, wt.%) with the power of 4.02 and 3.83, respectively.Via this concentration dependent behavior, we can extrapolate two important mechanical parameters for the agglomerates in a dense packing state (ϕ = 1): the shear modulus and the yield stress.

View Article: PubMed Central - HTML - PubMed

Affiliation: College of Polymer Science and Engineering, State Key Laboratory of Polymer Materials Engineering, Sichuan University, Chengdu, 610065, China. ysjsanjin@163.com.

ABSTRACT
The understanding of the rheological and mechanical properties of nanoparticle aggregates is important for the application of nanofillers in nanocompoistes. In this work, we report a rheological study on the rheological and mechanical properties of nano-silica agglomerates in the form of gel network mainly constructed by hydrogen bonds. The elastic model for rubber is modified to analyze the elastic behavior of the agglomerates. By this modified elastic model, the size of the network mesh can be estimated by the elastic modulus of the network which can be easily obtained by rheology. The stress to destroy the aggregates, i.e., the yield stress (σy), and the elastic modulus (G') of the network are found to be depended on the concentration of nano-silica (ϕ, wt.%) with the power of 4.02 and 3.83, respectively. Via this concentration dependent behavior, we can extrapolate two important mechanical parameters for the agglomerates in a dense packing state (ϕ = 1): the shear modulus and the yield stress. Under large deformation (continuous shear flow), the network structure of the aggregates will experience destruction and reconstruction, which gives rise to fluctuations in the viscosity and a shear-thinning behavior.

No MeSH data available.


Related in: MedlinePlus