Heterostructured clays with regularly alternating interlayers of organic and inorganic exchange cations

Few investigations have been reported on mixed organic and inorganic exchanged forms of smectite clays. Such mixed ion clay systems may have interesting materials properties since they can potentially combine hydrophilic- and hydrophobic-clay interlayers into a single phase material. This work contains the first examples of the synthesis of mixed ion heterostructured fluorohectorite clays that have regularly alternating organic and inorganic exchanged interlayers. The potential of such an interlayer arrangement becomes apparent when (hydrophobic) organic modified clay galleries need to be dispersed in water.; Three complementary strategies to the synthesis of mixed ion heterostructured clays are described. Pathway I involves the partial replacement of hydrated metal exchange ions by the direct addition of onium ions to a clay suspension. Route II embodies the reverse approach where a homoionic organic exchanged clay is treated with a concentrated NaCl solution to produce an organic and inorganic mixed ion heterostructured clay product. Equal molar quantities of the two homoionic end member clays are reacted in water to produce a mixed ion heterostructured clay in approach III.; The mixed ion heterostructure formation process was probed with two series of onium ions in an attempt to elucidate this spontaneous segregation behavior of the intercalates. The onium ions used were of the type C_nH _(2n+1)N(C_mH_(2m+1))₃+ in the series (n = 4–22 & m = 4) and (n = 16 & m = 1–5). The onium ion alkyl tail length determines the extent of metal ion replacement in a partial ion exchange reaction. Quantitative onium ion loading is obtained when the onium ion alkyl tail exceeds 10 carbon units. Segregation of cationic species into distinct alternating galleries is directed by the onium ion head group.; Large onium ion head groups (propyl- or larger, m $\ge$ 3) move the center of onium charge away from the silicate layers and preclude commingling of cationic species within one interlayer. This forces the smaller hydrated metal ions to take positions on the other side of the organic exchanged interlayers and results in heterostructure formation. The smaller methyl- and ethyl-onium ion head groups, m = 1 or 2, effectively neutralize the clay layer charge and do not produce heterostructured clays. Instead, they initiate the formation of phase segregated homoionic parent end member clays.; However, heterostructure formation is not limited to mixed ion clay systems with half a cation exchange equivalent of onium ions. Complete heterostructure conversion also occurs for mixed ion clays that have an overall onium ion fraction between 0.35 and 0.50. Also, intercalation experiments established the relationship between clay layer charge location and 1:1 C₁₆H ₃₃NBu₃+ and Na+ mixed ion heterostructure formation.; Finally, a model is proposed that describes the processes and requirements needed when mixed ion heterostructured clays are synthesized.