Montmorillonite dispersion

Some experiments have been carried out with a sodium montmorillonite dispersion on an Sn02 electrode.77 The layer of clay adhered well to the surface and [Ru(bipy)3]2+ was successfully exchanged on to the clay. The film was electroactive but cracked readily. The addition of powdered platinum gave a more coherent layer. Other species exchanged on to the clay included [Fe(bipy)3]2+ and a trimethylammonium derivatized ferrocene. 

Whether the isolated layer model or the Donnan-like model is more appropriate depends on whether the clay particles are considered to be mainly isolated layers or mainly floes. A montmorillonite dispersion, for example, tends to be formed by isolated layers at high pH and low electrolyte concentrations, especially when the electrolyte cation is Li+ or Na+, but it is usually aggregated at low pH and high electrolyte concentrations. Therefore, in a simple titration experiment between pH 3 and 10 at low electrolyte concentration, the aggregation state can change from Hoc to isolated layer, complicating the choice of model. However, although they are conceptually different, both models should perform similarly with appropriate parameters, and the final model choice is mainly a matter of taste or mathematical convenience. 

AKNOj/j was added dropwise to a montmorillonite dispersion, then the pH was adjusted to 7 with 0.5 M NaOH. The dispersion was mixed for 2 h, washed, and freeze-dried. 

Figure 8.5 TEM micrograph of unmodified montmorillonite dispersed in water.

Magdassi S, Rodel BZ (1996) Hocculatimi of montmorillonite dispersions based on surfactant-polymer interactions. Colloids Surf A 119 51... 

Solar, L Nohales, A., Munoz-Espi, R., Lopez, D., and Gomez, C.M. (2008) Viscoelastic behavior of epoxy prepolymer/ organophihc montmorillonite dispersions. /. Polym. Sci., Part B Polym. Phys., 46 (17), 1837-1844. 

The difficulty in preparing aligned and exfoliated montmorillonite composites in epoxy was again apparent. This complication was further compromised with the preferred association at the epoxy-elastomer interface of the intercalated organomontmorillonite bundles. The result was a greater randomization of the montmorillonite dispersed phase in the epoxy. 

Intercalation, improved montmorillonite dispersion, and alignment of the montmorillonite in the direction of stress during testing were all positive factors in the significant improvement of mechanical properties. Greater hydrophobicity at the montmorillonite surface through the utilization of a long hydrocarbon chained carboxylic acid with the quat did not overcome the barrier to full exfoliation in the block copolymer. 

The viscosity of the polymer continuous phase will compromise the successful exfoliation and alignment of montmorillonite in the composite. Clever utilization of techniques that take advantage of the unique character of montmorillonite (for example, magnetic properties) will resolve the difficulties associated with high viscosities. When all else fails, casting of the polymer and montmorillonite dispersions from solution results in the successful preparation of polymer-montmorillonite nanocomposites. 

The WAXS and TEM of the 2% montmorillonite containing PP composite indicated an improved montmorillonite dispersion when compared to the above work. Apparent errors are found in the abstract of this work. The WAXS of the M A modified organomontmorillonite indicates a (001)results presented. The test samples were compression molded. The TEM indicates a random orientation of the montmorillonite. This is unfortunate and compromises the mechanical results presented based on the models presented in Chapter 5 that predict the mechanical behavior of polymer-montmorillonite nanocomposites. 

WAXS and TEM indicate that, with all of the composites, side feeding produces superior montmorillonite dispersions. The PP-g-MA compa-tibilizer with the lower MA content and higher molecular weight (PB 3150 and PB 3200) provided the best dispersion. 

The results of the above study with PBS 150 and octadecylamine-exchanged montmorillonite indicated a tensile modulus improvement of 1S8.6% with the hopper feed and 145.4% improvement with the side-feed protocol. Further work with Cloisite 20A and the side-feed protocol of the above work at the lower PBS 150 content in this study could produce further improvements of montmorillonite dispersion and subsequent improvements in the mechanical performance of PP. 

An additional feature of this work was the evaluation of the significance of silane modification of the organomontmorillonite (S-aminopro-pyltrimethoxysilane, S(2-aminoethyl)aminopropyltrimethoxysilane, and S(6-aminohexyl)aminopropyltrimethoxysilane) with regard to improved montmorillonite dispersion and the mechanical properties of PP-mont-morillonite polymer composites. 

WAXS and TEM indicated that the cycling produced significant improvements in montmorillonite dispersion and intercalation of the PP into the montmorillonite galleries. The formulation with the PP-g-MA compatibilizer demonstrated the best dispersion. The composite prepared without the compatibilizer and the organomontmorillonite was remarkably good. 

PVC and chlorinated PVC composites demonstrate a decrease in percent elongation to failure as a function of increasing Cloisite 30B content. A plateau in percent elongation to failure occurs between 3 and 5% Cloisite 30B content for PVC and chlorinated PVC. Additional work is necessary with a twin-screw extruder to prepare improved montmorillonite dispersions and injection molding of the test samples to align the particles in the direction of applied stress in order to investigate the... 

Mechanical evaluations of rubber-montmorillonite composites provide a common theme. Full exfoliation of montmorillonite in rubber is difficult. Enhancement of mechanical properties is greater than with thermoplastic polymers, because the difference in the modulus of the continuous rubber phase in relation to the montmorillonite dispersed phase is greater. Percent elongation to failure increases, modulus increases, and tensile strength increases as the concentration of montmorillonite increases in the rubber. 

The dispersed-phase stability of the organomontmorillonite [62] was not compromised. The weight percent of quat on the montmorillonite was evaluated at 0.1, 0.15, 0.2, and 0.3%. This quat will participate with the cure chemistry during vulcanization. The aqueous SBR latex (22.4% solids supplied by Jilin Petrochemical Co. Ltd.) was blended with the organomontmorillonite aqueous dispersion. The polymer-functional montmorillonite dispersion was flocculated with 2% sulfuric acid, washed with water, and dried in an oven at 50 °C for 20h. The rubber crumb was formulated at 10 phr montmorillonite content. The rubber was compounded with a two-roll mill and cured at 150°C. The compound ingredients appear to be standard with standard concentrations. 

The advent of polyurethane-montmorillonite nanocomposites presents the unique opportunity to integrate two phases (soft continuous phase with a harder dispersed phase) with a montmorillonite-dispersed nanoparticle. The opportunity to provide functionality that will cure with the urethane on the surface of the montmorillonite results in a unique composite with mechanical properties that is not duplicated by other polymer-montmorillonite nanocomposites. 

In a review of the properties and structure of the polymer electrolyte membranes for direct methanol PCs, Deluca and Elabd mentioned that some of the proposed replacements of Nafion as PEM for DMFC have higher methanol selectivities and comparable proton conductivities to Nafion [174]. Montmorillonite dispersed in Nafion , described by Song et al. [175] in 2003, and blend of PVA with the copolymer of PS-sulfonic and maleic acids, described by Kang et al. [176], seem to be the most promising ones. However, longitudinal proton conductivities of the respective membranes cited in these references may by different fi om horizontal conductivities of these membranes. 

Lagaly G., Ziesmer S., Colloid chemistry of clay minerals the coagulation of montmorillonite dispersions , Advances in Colloid and Interface Science, 2003 100-102 105-128. 

Using a homomixer, 300 g of montmorillonite were uniformly dispersed in 9 liters of deionized water at 80"C. 154 g of 12-aminododecanoic acid and 72 g of concentrated hydrochloric acid were dissolved in 2 liters of deionized water at 80 C. This solution was mixed with the montmorillonite dispersion and stirred for five minutes. The mixture was filtered to obtain aggregates, which were washed twice with water at 80°C and freeze-dried. In this way, organophilic clay was obtained in the form of a fine white powder, called 12-Mt . 

We prepaed Pd° particles in situ in the interlamellar space of montmorillonite dispersed in an aqueous medium. The support suspended in a polymer solution of adequate concentration (0.41 wt%) was stirred at 60°C for 24 h, and a Pd chloride solution containing ethanol was next added to the dispersion. The palladium chloride solution was freshly prepared (2 mM, adjusted to pH 4 with hydrochloride acid). Macromolecules were adsorbed on the clay minerals from an aqeuous solution, followed by adsorption and reduction of Pd ions. Composites of nonionic PVP/montmorillonite and cationic PDDA/montmorillonite (0.02-0.12 g polymer/1 g clay) were prepared in systems containing various concentrations of adsorbed PVP and PDDA from aqueous solution. The added metal content was 2 g/100 g clay and the metal content of the products was in the range 1.34-2.01% as determined by inductively coupled plasma atomic emission spectrosocpy (ICP-AES) analysis. The composition of the resulting systems and their monomer/Pd ratios are listed in Table 2. 

The synthesis of palladium nanoparticles on montmorillonite layer silicates was studied. The Pd particles were prepared in situ in the interlamellar space of montmorillonite dispersed in an aqueous medium. Macromolecules were adsorbed on the support from an aqueous solution, followed by adsorption and reduction of Pd ions. The Pd° nanoparticles appear and grow in the internal, interlamellar space as well as on the external surfaces of the lamellae. Well-crystallized kaolinite clay can be disaggregated by the intercalation of DMSO to individual lamellae, which may serve as excellent supports for metal nanoparticles. After the adsorption of palladium precursor, metal nanocrystals were reduced by hydrazine or sodium borohydride between the kaolinite lamellae, i.e., in the interfacial layer acting as a nanoreactor. The incorporation of nanoparticles between the lamellae was shown hy XRD measinements. This procedure makes possible the steric control and restriction of nanoparticle growth. The stability of nanoparticles can be further enhanced hy the addition of polymers (PVP) and surfactants (alkyl-ammonium salts) that are also adsorbed between the kaolinite lamellae. The presence of the particles was also verified and their sizes were quantified by TEM measurements. 

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