Phosphate liquid crystals: novel supramolecular template for the synthesis of lamellar aluminophosphates with natural form

Abstract

The thermal properties ofn-alkylammonium dihydrogenphosphates, [C_nH_2n+1NH₃⁺ ][H₂PO₄^– ], where 6≤n≤18, have been investigated for the first time. It was discovered that for decylammonium (n=10), the material undergoes several polymorphic phase transitions before ultimately transforming to a smectic liquid crystal mesophase. The crystal to liquid crystal transformation of this phase was studied by in situ variable temperature polarizing optical microscopy and revealed intriguing micron dimension surface patterns. Similar thermal behaviour was observed when the material was dispersed in a polyethylene glycol non-aqueous solvent. The results have direct implications for the growth and form of surface patterned lamellar aluminophosphate morphologies prepared organo-thermally from aluminium oxide, phosphoric acid and n-alkylamines in polyethylene glycol-based solvents. Topological defects present in the precursor alkylammonium phosphate mesophase appear to be responsible for the emergence of surface textured lamellar aluminophosphate replica materials with biomimetic form. Phosphate liquid crystals represent a new class of supramolecular templates for the synthesis of a wide variety of mesostructured metal phosphates.

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