Tuning of the Hydrophobic and Hydrophilic Interactions in 2D Chiral Domains

The molecular arrangement in the Langmuir monolayers is determined by the interplay of the hydrophilic and hydrophobic interactions between the components. Herein, the competition between the interactions of the components of the organic dye:phospholipid HSP:DMPA mixed monolayer has been studied. The HSP:DMPA monolayer gives rise to chiral domains at the air/solution interface. Brewster angle microscopy (BAM) has been used for the recording of the micrometric structure of the chiral domains. HSP absorb radiation at the wavelength of the laser used in BAM, providing information on the organization of the polar groups. The crystalline structure of the alkyl chains of the HSP:DMPA monolayer has been described by synchrotron-based grazing incidence X-ray diffraction. The interaction between alkyl chains dominates over the aggregation of the polar headgroup in the case of a pure water subphase. By simply adding ions in the subphase, this tendency is reversed, leading to a predominance of the aggregation of the polar headgroup, and a modification of the micrometric domains. This tuning of the interplay between the different molecular regions in a monolayer might be extended to different supramolecular systems, allowing the adjustment of the molecular arrangement.