Interlayer organic molecules

Suzuki et al. [20] used polyvinyl alcohol (PVA) in the exchange reactions with aluminum hydroxy cations. They showed that neutral PVA molecules were intercalated into the interlayer spaces of montmorilIonite and that even in the presence of PVA in the interlayer spaces, all of the interlayer cations were completely exchanged with aluminum hydroxy cations. The calcined sample showed very sharp pore size distribution at 25 A. The above two examples suggest that in combination with suitable organic molecules or cations it would be possible to obtain different pore structures even from the same kind of metal-hydroxy cations and sols. 

The peculiar layer structure of these clays gives them cation exchange and intercalation properties that can be very useful. Molecules, such as water, and polar organic molecules, such as glycol, can easily intercalate between the layers and cause the clay to swell. Water enters the interlayer region as integral numbers of complete layers. Calcium montmorillonite usually has two layers of water molecules but the sodium form can have one, two, or three water layers this causes the interlayer spacing to increase stepwise from about 960 pm in the dehydrated clay to 1250, 1550, and 1900 pm as each successive layer of water forms. 

The expanded or expandable 2 1 clay minerals vary widely in chemical composition and in layer charge. These minerals are characterized by the presence of loosely bound cations and layers of water or polar organic molecules between the silica sheets. The interlayer width is reversibly variable. The interlayer water can be driven off at temperatures between 120° and 200°C. Sodium, calcium, hydrogen, magnesium, iron, and aluminum are the most common naturally occurring interlayer cations. 

All the non-expanded 2 1 and 2 1 1 layer silicates can have their interlayer cations removed. Water and organic molecules can then penetrate between these layers to form expanded layer minerals. 

Assuming large clusters may approximate the band structure of the crystal, what energy is required to excite electrons into the Fe(4s) conduction band in Fe2 bearing clays Can such electrons reduce organic molecules adsorbed in the surface or trapped in the interlayer ... 

The experimental studies of interactions of organic molecules adsorbed or intercalated in the interlayer space of clay minerals are very extensive. These experimental investigations were reviewed in several monographs [15-17]. In this part, we will review only experimental studies concerning systems of kaolinitic minerals (specifically dickite and kaolinite) with formamide (FA), N-methylformamide (MFA) and dimethylsulfoxide (DMSO) since theoretical studies of interactions of small organic molecules with clay minerals are devoted to intercalates and adsorbates of kaolinitic minerals with these organic molecules. This will allow to compare theoretical results with available experimental data. 

Many experimental investigations of intercalates dickite-FA (D-FA), dickite-MFA (D-MFA) and kaolinite-DMSO (K-DMSO) applied IR and Raman spectroscopy, NMR technique and X-ray diffraction. These works are mostly devoted to the study of the position of the organic molecule in the interlayer space of kaolinite, interactions between the organic molecule and the layers of dickite and kaolinite, and the influence of mineral structure to the intercalation capability. 

It has also been reported that the interlayer spacing in hydrotalcite particles can be increased by intercalation with organic molecules, such as citric acid.88 Results were given for linear burning rates from a UL-94 horizontal bum test comparing nano- and micro-hydrotalcite modified epoxy resin. At 5 wt % addition level the microcomposite gave a reduction in bum rate of unmodified epoxy resin from around 22 to 18mm/min. With the apparent nanocomposite variant, also at 5 wt %, the burn rate was less than 5mm/min. 

Metal ions and organic molecules adsorbed in the interlayer space and on the edges of clay minerals can transform to other chemical species via many different processes. The sorbed metal ions can undergo redox and hydrolytic reactions,... 

Costa cl al. (C58) showed that superplasticizers increase the fluidity of C,S pastes much as they do that of cement pastes. Studies on individual anhydrous and hydrated compounds in aqueous and non-aqueous media indicate that calcium lignosulphonate and superplasticizers are adsorbed by C -S-H, AFm phases or CH but not by C,S, C,A or C,AH (R54, R55,R56,C58,M 105), though they appear to be taken up by unhydrated P-CiS (C59). The admixtures also enter interlayer sites of C4AF1. and perhaps also of C -S--H (R55). Intercalation of organic molecules in C4AH, is a well-established effect (Section 6.1.1),... 

Fig. 5 shows XRD patterns of Cu-intercalated samples after calcination at elevated temperatures. The products after calcination at 350 °C in N2 exhibited no diffraction peaks, but the SEM observation suggested that the fibrous crystalline shape was almost retained without deposits on the surface. Thus, the sample probably consisted of CuOx-stuffed layered composites with unequal interlayer distances. The formation of anatase-type TiOz and Cu from the noncrystalline layered composite was observed after heating at >400 °C in N2. When the precursor was heated in air (Cu-450-air), however, these phases were scarcely observed. This means that residual organic molecules in the interlayer would play... 

---