DYNAMICS OF HIGH-TEMPERATURE MEMBRANE MODELS COMPOSED OF 5-ALKOXYISOPHTHALIC ACIDS AS INVESTIGATED BY H-2-NMR SPECTROSCOPY

High-temperature stable lamellar structures composed of 5-(octadecylox y)isophthalic acid (C(18)ISA) and 5-(dodecyloxy)isophthalic acid (C(12 )ISA), specifically deuterated in the alkyl chain (C(18)ISA-d(37)), ar omatic head group (C(12)ISA-d(3)), or acid moieties (C(18)ISA-COOD), w ere studied with solid-state H-2-NMR spectroscopy. Combined with resul ts from earlier work, it is concluded that apolar interactions between the long alkyl chains in C(18)ISA stabilize the solid on heating unti l 433 K and the liquid-crystalline phase on cooling, even when contrib utions from the hydrogen bonds are weak. The apolar interactions betwe en the shorter alkyl chains in C(12)ISA are weaker, and the liquid-cry stalline phase present on cooling is destabilized. The C(n)ISA systems thus provide promising high-temperature model membrane structures, du e to the possibility of balancing the apolar interactions (alkyl chain length) and polar interactions (H-bonding of the head group).