Sodium-montmorillonite platelets

Four types of silicate clays were obtained from Southern Clay Products (Austin, TX). Laponite-RD (LRD) is a synthetic hectorite-type clay with each platelet having a diameter of 25-30nm and a thickness of Inm (aspect ratio 25-30). Cloisite Na+ (Na-MMT) is naturally occurring sodium montmorillonite with aspect ratio of 75-100 (diameter of 75-lOOmn and thickness of Imn). Cloisite lOA (ClOA) and Cloisite 30B... 

Use of the RAFT technique has evolved from the use of a free RAFT agent i.e. the RAFT agent is not attached to the clay layers) to the use of RAFT agents anchored on the clay platelets. Moad and co-workers used RAFT-mediated polar polymers that are miscible with polypropylene (PP) and then melt blended both polymers i.e. polymers and PP) in the presence of sodium montmorillonite to yield PP-CNs. Salem and Shipp showed that the use of free RAFT agents to the prepare polystyrene-, poly(methyl methacrylate)- and poly(butyl acrylate)-clay nanocomposites by in situ intercalative polymerization in bulk led to products with well-controlled molecular weights and narrow... 

Cationic polyacrylamide (tradename Superfloe C-491) was provided by CYTEC (West Paterson NJ). This is a copolymer containing 5 mol % of positively-charged repeat units. Southern Clay Products, Inc. (Gonzales, TX) supplied natural sodium montmorillonite (MMT) (tradename Cloisite NA ). This clay is negatively-charged in deionized water. MMT platelets have a density 2.86 g/cm diameter of 2 13ttm, and thickness of Inm. Poly(ethylene terephthalate) (PET) film, with a thickness of 179ttm, was purchased from Tekra (New Berlin, WI) and used as the substrate for LbL deposition. 

Smectite - The smectites are water swellable cl s having a sheet or platelet structure. Smectite is the mineralogical term for this class of clays, which includes montmorillonite, hectorite, and saponite. Montmorillonite clays derive their name from the Montmorillon section of France where this material was first observed and later classified. Most smectites are more commonly known under the geological term bentonite. By convention, a bentonite is understood to be an ore or product with a substantial smectite content. The name bentonite derives from Fort Benton, Wyoming, the site of an important deposit. Lattice substitutions within the smectite clays creates a charge imbalance which is compensated by exchangeable alkali and alkaline earth cations. This contributes to the ability of these clay to swell and impart considerable plasticity in ceramic formulations. When the exchangeable cations are predominately sodium, the individual platelets can separate to produce a colloidal structure in water. 

---