Clay-polymer interface

Studies involving the use of organically modified clay particles in heterophase polymerization are rather scarce. Indeed, we are aware of only two reports that combine the emulsion or suspension polymerization approaches and ion-ex-change reaction. In one of these reports, AI BA is immobiHzed in the clay interlayer region to yield exfoliation of MMT in the PMMA matrix through suspension polymerization [135]. In another relevant study, it was demonstrated that exfoliated structures could be obtained by post-addition of an aqueous dispersion of layered silicates (either MMT or laponite) into a polymethyl methacrylate latex suspension produced in the presence of suitable cationic compounds (cationic initiator, monomer or surfactant) [136]. Since the latex particles were cationic and the clay platelets anionic, strong electrostatic forces were developed at the polymer/clay interface. 

In ternary nanocomposites, compatibilizers have been mostly used to improve the adhesion at the polymer/filler interface rather than to modify the polymer/elastomer interface. Mishra et al. [80] compounded PP/EPDM/organoclay (75/25/5 wt%) and added PP-g-MA (1 wt% MA) as a compatibilizer with a clay/PP- -MA ratio of 1/3. They characterized the interlayer spacing of the clay platelets by XRD and observed that it increased from 3.4 to 4.3 nm for systems without and with compatibilizer. This was attributed to a better diffusion of the PP-g-MA chains inside the interlayer spacing thanks to their functional groups. Numerous other authors prepared and characterized ternary composites with a compatibilizer. Examples include Lim et al. [81] and Lee et al. [5] on PP/PP- -MA/POE/ organoclay systems, Mehta et al. [23] on PP/PP-g-MA/EPR/organoclay systems, and Liu and Kontopoulou [24,45] on PP/PP-g-MA/ethylene-octene copolymer/silica composites. It should be noted that the compatibilizer itself may affect the properties of the matrix... 

G. Defontaine, A. Barichard, S. Letaief, C. Feng, T. Matsuura, C. Detellier, Nanoporous polymer - clay hybrid membranes for gas separation. Journal of Colloid and Interface Science 343 (2010) 622-627. 

In this contribution, we intend to introduce recent work dedicated to polymer-clay nanocomposites based on sepiolite and palygorskite fibrous silicates. We will consider as a priority the role of the interface between the mineral surface and the polymer matrix. In fact, this type of clay is markedly hydrophilic because their surface is covered by hydroxyl groups, mainly silanol groups (=Si-OH) [17, 22], and therefore they are compatible with many polar polymers. However, chemical modification of the silicate surface could be necessary for adjusting their... 

The increase of stress at break in thermoplastic-based nanocomposites is usually related to the nature of the interactions between the matrix and the filler. Table 5.1 shows the tensile stress values for different matrix day nanocomposites. Nanocomposites such as exfoliated nylon 6-based nanocomposites [78] or intercalated PMMA-based nanocomposites [80] exhibit an increase in the stress at break. This increase is usually due to the polar (PMMA) and even ionic interactions (nylon 6 grafted onto the layers) between the polymer and silicate layers. In polypropylene (PP) and PS nanocomposites, the interactions between polymer matrix and clay interface are weak, so no enhancements in tensile stress were observed. 

Stmctural data from XRD were combined with the ESR results in order to assess the extent and intensity of polymer-clay interactions at the interface. XRD measurements revealed that the silicate layers were exfoliated in the PMA matrix as the clay content was less than 15wt.%. ESR speara clearly indicated that the mobility of PMA chains in the nanocomposites is constrained due to the attractive interactions in the interface region, even though the DSC measurement showed little difference between the PMA homopolymer and PMA-clay nanocomposites. The restricted molecular motion is caused primarily by attachment of TMC moieties on the silicate platelet surface, and additionally by the polar interaction between the ester groups and the siloxane oxygen on the basal surfaces of the silicates, as seen in Figure 22(a). 

Surface Behavior. Most extraction processes deal with several phases. At the boundaries between these phases, an interface exists which can be populated with or depopulated of polymer. Situations in which the polymer should accumulate at the surface of one phase are 1. the flocculation of clays and fines or 2. the formation of foams, while situations in which the polymer should depopulate the surface of the phase boundary are 3 minimizing adsorption in mineral acid leaching or 4. minimizing surface tension with surfactants in oil recovery by miscible flooding.,... 

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