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Publication
Nanocomposites: dispersion quality and percolation threshold
Book Contribution - Book Chapter Conference Contribution
Introduction
The last two decades a lot of research was spent on nanocomposite. The key factor in attaining the superior properties of these novel hybrid materials is the achievement of high levels of nanofiller dispersion of the incorporated low amounts of nanosized filler particles, resulting in a vast amount of polymer/filler interphase. [1]
Materials and Methods
The nanocomposites used in this work were prepared by melt mixing techniques, using Poly(?-caprolactone) (PCL) or Poly(propylene) (PP) as polymer matrix. As nanofiller particles we used silicates based on natural montmorillonite (exchanged with quaternary alkyl ammonium ions), multi walled carbon nanotubes (MWNTs) and cellulose nanocrystals.
The nanocomposites of this work were prepared by melt mixing
Morphological information was obtained from atomic force microscopy (AFM), Transmission electron microscopy (TEM) and Wide-angle X-ray scattering (WAXS). Small angle oscillatory shear rheometry ('dynamic rheometry') experiments were carried out using a cone-and-plate geometry. Thermal characterization was performed using Modulated Temperature Differential Scanning Calorimetry (MTDSC). The mechanical properties of the various materials were assessed by determining their secant modulus (3-point bending mode).
A simulation program called Macropac (Version 6.1) (Intelligensys Ltd) was used to model the packing of objects into a simulation container.
Results and discussion
A comprehensive overview of available methods for assessing nanofiller dispersion is presented for a wide range of layered silicate-based nanocomposites, carbon nanotube-based nanocomposites and nanocomposites containing cellulose nanocrystals. [2]
Focusing on their respective strengths and weaknesses, rheological, mechanical and thermal characterization approaches are evaluated in direct relation to morphological information. [3] An advanced thermal analysis methodology (using MTDSC) is employed for the characterization of the PCL and PP nanocomposites. During quasi-isothermal crystallization, the presence of high aspect ratio nanofillers strongly affects the amount of crystalline-amorphous interface, thus increasing the recorded excess heat capacity (Cpexcess). This increase is in direct relation to the nanofiller dispersion quality. [4]
In a second part of the work, the minimum loading of nanofiller particles needed to obtain a physical network (percolation network) was studied using a simulation program called Macropac (Intelligensys Ltd) (see Figure 1). [5]
Figure 1: 3-D visualization of a packing of plate-like structures, mimicking silicate platelets, obtained using Macropac simulation software.
Conclusions
It is observed that the degree of filler dispersion is strongly influenced by the specific matrix/filler interactions and the processing conditions.
It is concluded that each techniques used to study the nanofiller dispersion in nanocomposites provides information on a different level of the quality of the dispersion. In other words, a combination of different techniques is needed to make a qualitative assessment of the nanofiller dispersion.
References
[1] M. Alexandre, P. Dubois, Materials Science and Engineering. (2000), 28, 1-63.
[2] Y. Habibi, A.-L. Goffin, et al. Journal of Materials Chemistry (2008), 18, 5002-5010.
[3]H.E. Miltner, N. Watzeels, et al., European Polymer Journal (2010), 46, 984-996.
[4] H.E. Miltner, N. Watzeels, et al., Journal of Materials Chemistry (2010), 20, 9531-9542.
[5] Shiho Akagawa, Takashi Odagaki, Physical Review E (2007), 76, 051402(5).
The last two decades a lot of research was spent on nanocomposite. The key factor in attaining the superior properties of these novel hybrid materials is the achievement of high levels of nanofiller dispersion of the incorporated low amounts of nanosized filler particles, resulting in a vast amount of polymer/filler interphase. [1]
Materials and Methods
The nanocomposites used in this work were prepared by melt mixing techniques, using Poly(?-caprolactone) (PCL) or Poly(propylene) (PP) as polymer matrix. As nanofiller particles we used silicates based on natural montmorillonite (exchanged with quaternary alkyl ammonium ions), multi walled carbon nanotubes (MWNTs) and cellulose nanocrystals.
The nanocomposites of this work were prepared by melt mixing
Morphological information was obtained from atomic force microscopy (AFM), Transmission electron microscopy (TEM) and Wide-angle X-ray scattering (WAXS). Small angle oscillatory shear rheometry ('dynamic rheometry') experiments were carried out using a cone-and-plate geometry. Thermal characterization was performed using Modulated Temperature Differential Scanning Calorimetry (MTDSC). The mechanical properties of the various materials were assessed by determining their secant modulus (3-point bending mode).
A simulation program called Macropac (Version 6.1) (Intelligensys Ltd) was used to model the packing of objects into a simulation container.
Results and discussion
A comprehensive overview of available methods for assessing nanofiller dispersion is presented for a wide range of layered silicate-based nanocomposites, carbon nanotube-based nanocomposites and nanocomposites containing cellulose nanocrystals. [2]
Focusing on their respective strengths and weaknesses, rheological, mechanical and thermal characterization approaches are evaluated in direct relation to morphological information. [3] An advanced thermal analysis methodology (using MTDSC) is employed for the characterization of the PCL and PP nanocomposites. During quasi-isothermal crystallization, the presence of high aspect ratio nanofillers strongly affects the amount of crystalline-amorphous interface, thus increasing the recorded excess heat capacity (Cpexcess). This increase is in direct relation to the nanofiller dispersion quality. [4]
In a second part of the work, the minimum loading of nanofiller particles needed to obtain a physical network (percolation network) was studied using a simulation program called Macropac (Intelligensys Ltd) (see Figure 1). [5]
Figure 1: 3-D visualization of a packing of plate-like structures, mimicking silicate platelets, obtained using Macropac simulation software.
Conclusions
It is observed that the degree of filler dispersion is strongly influenced by the specific matrix/filler interactions and the processing conditions.
It is concluded that each techniques used to study the nanofiller dispersion in nanocomposites provides information on a different level of the quality of the dispersion. In other words, a combination of different techniques is needed to make a qualitative assessment of the nanofiller dispersion.
References
[1] M. Alexandre, P. Dubois, Materials Science and Engineering. (2000), 28, 1-63.
[2] Y. Habibi, A.-L. Goffin, et al. Journal of Materials Chemistry (2008), 18, 5002-5010.
[3]H.E. Miltner, N. Watzeels, et al., European Polymer Journal (2010), 46, 984-996.
[4] H.E. Miltner, N. Watzeels, et al., Journal of Materials Chemistry (2010), 20, 9531-9542.
[5] Shiho Akagawa, Takashi Odagaki, Physical Review E (2007), 76, 051402(5).
Book: EUROPEAN POLYMER CONGRESS EPF2011
Publication year:2011
Keywords:nanocomposites, Advanced thermal analysis, Dispersion, Percolation threshold