Microcomposites diffusivity

The diffusion of some aromatic solvents (benzene, toluene, and p-xylene) through microcomposites of NR/carboxylated styrene-butadiene rubber (XSBR) latex blend membranes (70/30) was investigated by Stephen et al. Results indicated that the blend membrane exhibited unexpected diffusion behaviour, and this was attributed to the immiscibility of the two blend... 

The barrier properties of the PCL-based composites were investigated. The transport properties, sorption and diffusion, were measured by a microgravimetric method . The studied model permeants were methylene chloride and water vapour for which the zero concentration diffusion coefficient Dq was determined. The presence of clay (hydrophilic platelets) in the composite gives rise to specific sites on which water molecules can be entrapped and immobilized, thus the water sorption increases on increasing the clay content, particularly for microcomposites containing Cloisite Na It was found out that the microcomposites as well as the intercalated nanocomposites have diffusion parameters for water vapour very near to those of pure PCL. 

In case of CH2CI2 organic vapour, the sorption at low vapour pressure is mainly dominated by the amorphous fraction present in PCL. At high vapour content, the sorption curves show an exponential increase of sorption due to the plasticization of the matrix by methylene chloride. The diffusion parameters of the microcomposites are very close to imfilled PCL while the intercalated samples show lower diffusion parameters confirming that it is... 

Figure 6. Dependence of water vapour diffusion log Do (Do = zero concentration diffusion coefficient) on the clay content of microcomposites, intercalated nanocomposites, and exfoliated nanocomposites.

In a departure from historical approaches to introducing fillers in UHMWPE, researchers from Colorado State University have developed a novel UHMWPE-hyaluronan microcomposite [50, 51]. This microcomposite is detailed in Chapter 18. Hyaluronan is a natural lubricant in articular cartilage. By incorporating this biomolecule into UHMWPE, researchers theorized that wear could be reduced. Because hyaluronan is hydrophilic and UHMWPE is hydrophobic, fabrication of an UHMWPE-hyaluronan microcomposite is by no means a straightforward proposition and is accomplished via a complex and elegant multistep procedure. The process, which is described in greater detail in Chapter 18, begins with the production of a porous UHMWPE substrate, which constitutes the matrix of the microcomposite. The hyaluronan is complexed with quaternary ammonium cations (CTA-I-) and silylated [52]. A solution of silyl hyaluronan-CTA is then diffused into the open celled porous UHMWPE matrix, chemically crosslinked in situ, and then hydrolyzed... 

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-... 

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