Strong headgroup interactions drive highly directional growth and unusual phase co-existence in self-assembled phenolic films

Self-assembled materials as surface coatings are used to confer functional properties to substrates but such properties are highly dependent on the molecular organization that can be controlled through tailoring the non-covalent interactions. For monomolecular films, it is well-known that strong, dipolar interactions can oppose line tension generating non-circular domain growth. While many surfactant films exhibit liquid crystalline arrangement of the alkyl chains, there are relatively few reports of crystalline headgroups. Here we report the self-assembly of phenolic surfactants where the combination of hydrogen bonding and pi-stacking leads to a herringbone arrangement of the headgroups, generating a molecular super-lattice that can be observed using grazing incidence X-ray diffraction; such an arrangement has been previously proposed for related phenolic systems but never experimentally observed. We also investigated using pH to modulate the intermolecular interactions and the response of the system in...