Polymer nanocomposites diffusivity

A systematic study was realized on Poly(e-caprolactone) (PCL) nanocomposites the influence of different percentages of montmorillonite (MMT), of MMT intercalation degree and of different organic modifiers of MMT on the diffusion coefficient of water and dichloromethane were analyzed.  

In the case of water vapour transport, the micro-composites as well as the intercalated nanocomposites show diffusion parameters very near to PCL, while the exfoliated nanocomposites strongly deviate showing much lower values, even at low montmorillonite content (Fig. 11.4). This is an indication that in the former cases the water molecules on specific sites are not immobilized but can jump fi om one site to another. Only in the case of the exfoliated samples, the inorganic platelets, dispersed in a disordered distribution, can constitute a barrier to the path of the hydrophilic molecules. 

For the organic solvent (dichloromethane) also the intercalated samples show lower values of the diffusion parameters confirming that it is not the content of clay alone but the t) e and size of dispersion of the inorganic component in the polymer phase that is important for improving the barrier properties of the samples (Fig. 11.5). 

Particularly interesting are the results on the MMT dispersion degree in the polymeric matrix. In the case of dichloromethane, for samples with 3 wt% of MMT it was shown that the diffusion parameter decreases going from microcomposites (values very similar to pure PCL) to exfoliated nanocomposites intermediate values of diffusion were measured for die intercalated nanocomposites. In the case of water, both micro-composites and intercalated nano- 

4 log Do (Do in cm /s) to water vapour, as function of clay content for the microcomposite (M), the exfoliated nanocomposites (E) and the 3wt.% intercalated nanocomposites (I) (reprinted from ref. [38], Copyright 2003, with permission of Elsevier Science Ltd). 

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Surface immobilization by nonspecific mechanism Nonspecific bindings (eg, hydrophobic, electrostatic, van der Waals) based on the composition of the bioactive molecule as well as the carrier system (eg, polymer, protein, sugar, lipid) and the presence of functional groups Also depends on swelling ratio and density of the polymer nanocomposite ++ Diffusion... 

Since the possibility of direct melt intercalation was first demonstrated [11], melt intercalation has become a method of preparation of the intercalated polymer/ layered silicate nanocomposites (PLSNCs). This process involves annealing, statically or under shear, a mixture of the polymer and organically modified layered fillers (OMLFs) above the softening point of the polymer. During annealing, the polymer chains diffused from the bulk polymer melt into the nano-galleries between the layered fillers. 

Clay-polymer nanocomposites have proven to be interesting candidates as gas barrier materials preventing permeation of volatile gases by creating a long path for diffusion and as flame-retardant materials. Previous work mainly involves the utihzation of cationic clays, although LDH materials... 

It is generally accepted that thermal stability of polymer nanocomposites is higher than that of pristine polymers, and that this gain is explained by the presence of anisotropic clay layers hindering diffusion of volatile products through the nanocomposite material. It is important to note that the exfoliated nanocomposites, prepared and investigated in this work, had much lower gas permeability in comparison with that of pristine unfilled PE [12], Thus, the study of purely thermal degradation process of PE nanocomposite seemed to be of interest in terms of estimation of the nanoclay barrier effects on thermal stability of polyolefin/clay nanocomposites. 

Nanocomposites of MMT polymer can be obtained by direct polymer melt intercalation where the polymer chains diffuse into the space between the clay galleries. This process can be carried out through a conventional meltcompounding process [6, 4]. 

The mechanism of the improvement of thermal stability in polymer nanocomposites is not fully understood. It is often stated [126-129] that enhanced thermal stabihty is due to improved barrier properties and the torturous path for volatile decomposition products, which hinders their diffusion to the surface material where they are combusted. Other mechanisms have been proposed, for example, Zhu et al. [130] recently proposed that for polypropylene-clay nanocomposites, it was the structural iron in the dispersed clay that improved thermal stability by acting as a trap for radicals at high temperatures. 

Keywords Solar cells, organic photovoltaics (OPVs), quantum confinement effect (QCE), conjugated polymers, nanocomposites, blends, quantum dots (QDs), nanocrystals, nanorods, carbon nanotubes (CNTs), graphene, nanoparticles, alternating copolymers, block copolymers, exdton diffusion length, short-circuit current, open-circuit voltage, fill factor, photoconversion efficiency, in-situ polymerization... 

The use of nanoclays in conventional polymer nanocomposites is well known and diffuse. The advantages of the addition of nanoclays to a polymeric matrix are the improvement of mechanical properties, the enhancement of barrier effect, and the increase of chemical and thermal stability. 

Polymer nanocomposites find their first application in car hoods, which are easily attacked by NO pollutants since they are exposed to the exterior environment. NO at standard atmosphere and pressure is 29.5% NO and 70.5% N O. Polyamide-6 is highly sensitive to such pollutants. The infusion of nano-clay platelets in the polyamide matrix in general decreases the diffusivity and permeability of the nanocomposites to atmospheric oxygen... 

The mechanical properties of polymer nanocomposites are also influenced by the chemical treatment of nanoparticles due to the different neighborhood in the material. The free volume that characterizes the density of material is modified and, consequently, the penetration of fluids (solvents, oxygen) is rather favorable to degradation. The diffusion of xylene in ethylene-propylene diene terpolymer is unlike, if material presents different consistency (Fig. 14, [191]). The competitive radiochemical processes, crosslinking of polymer and degradation of covering layer are the most important reasons responsible for the different shapes of swelling curves. 

This is a three-part book with the first part devoted to polymer blends, the second to copolymers and glass transition tanperatme and to reversible polymerization. Separate chapters are devoted to blends Chapter 1, Introduction to Polymer Blends Chapter 2, Equations of State Theories for polymers Chapter 3, Binary Interaction Model Chapter 4, Keesome Forces and Group Solubility Parameter Approach Chapter 5, Phase Behavior Chapter 6, Partially Miscible Blends. The second group of chapters discusses copolymers Chapter 7, Polymer Nanocomposites Chapter 8, Polymer Alloys Chapter 9, Binary Diffusion in Polymer Blends Chapter 10, Copolymer Composition Chapter 11, Sequence Distribution of Copolymers Chapter 12, Reversible Polymerization. 

Wood is extremely resistant to mild chemicals and as such it provides a significant advantage over many alternative construction materials. The various alternative construction materials, like concrete and steel are prone to corrosion. WPG can effectively substitute these materials as it is resistant to acidic salt solutions, mild acids, and corrosive agents. The chemical resistance properties enhance further in case of wood polymer nanocomposites (Deka et al. 2012). The nanoparticles offer a tortuous path for diffusion of chemicals throughout the composites thereby improving its chemical resistance. 

The results reported on the thermal and thermooxidative decomposition of layered silicate nanocomposites are rather contradictory and do not lead to unambiguous or consistent conclusions. The results vary from enhanced decomposition, to no significant influence, to a strong improvement depending on the source and system discussed. The influence on thermal decomposition differs strongly from nanocomposite to nanocomposite. What is more, often the product release is changed rather than the primary decomposition reactions. The diffusion of the products is hindered by the decreased permeability for nanocomposites 5 wt% layered silicate-polymer nanocomposites show a reduction in gas permeability of around 40 to 60%, even for small gas molecules such as nitrogen and... 

FIGURE 6 Idealized morphology for diffusion through polymer nanocomposite containing dispersed clay platelets (David and Gupta, 2007). 

Figure 23.35 Polymer tracer diffusion in SWCNT/PS nanocomposites measured using ERD. (a) 140kd-PS distribution in 1.60vol.% SWCNT/480k PS nanocomposites as prepared and after annealing at 150°C for different times. The solid lines are fits of the diffusion equation to obtain the diffusion coefficients. Tracer diffusion in these nanocomposites is independent of annealing time (b) d-PS tracer diffusion coefficients in SWCNT/480k PS nanocomposites as a function of SWCNT...

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