Langmuir Monolayer Properties of Perfluorinated Double Long-Chain Salts with Divalent Counterions of Separate Electric Charge at the Air−Water Interface

Abstract

The novel perfluorinated double long-chain salts with divalent counterions of separate electric charge, 1,1-(1,omega-alkanediyl)-bispyridinium perfluorotetradecane- carboxylate [CnBP(FC14)2 : n = 2, 6, 10, 14], were newly synthesized and their interfacial behavior was investigated by Langmuir monolayer methods. Surface properties [surface pressure (pi)-, surface potential (DeltaV)-, dipole moment (micro perpendicular)-area (A) isotherms] and morphological images of CnBP(FC14)2 monolayers on a subphase of water and on various NaCl concentrations were measured by employing the Wilhelmy method, the ionizing electrode method, fluorescence microscopy (FM), and Brewster angle microscopy (BAM). CnBP(FC14)2 formed a stable monolayer on water at 298.2 K, where these pi-A isotherms shifted to a larger molecular area with increasing charge separation and had no transition point from a disordered phase to an ordered one. On the contrary, the pi-A isotherms on NaCl solutions moved to the smaller areas, showed the transition and higher collapse pressures compared to the pi-A isotherms on water. These results suggested that a sodium chloride subphase induced the condensation of CnBP(FC14)2 molecules upon compression. In addition, it is quite noticeable that a dissociation of CnBP counterion from CnBP(FC14)2 occurs on NaCl solutions, depending on the extent of charge separation. This phenomenon was supported by the changes of the limiting area, transition pressure, collapse pressure, repeated compression-expansion cycle curve, and DeltaV behavior of perfluorotetradecanoic acid (FC14). Furthermore, temperature dependence of these monolayers was investigated, and an apparent molar quantity change on the phase transition was evaluated on 0.15 M NaCl. The morphological behavior of CnBP(FC14)2 and FC14 monolayers was also confirmed by FM and BAM images.

Collapsed States of Langmuir Monolayers

“…It is well known that intermolecular interactions in the monolayers are strongly related to the alkyl chain length 46 and the critical packing parameter S, which is expressed by the ratio between the volume of the hydrophobic lipid tail t and the product of the cross-sectional lipid head area A and the critical lipid chain length l , t/ Al 47 49 . The long alkyl chains make strong hydrophobic interactions; therefore, increasing the rigidity of monolayer 46,50 , while the value of S defines the spontaneous curvature formed during collapse formation. If S 1, the transformation will spontaneously lead to a positive-curvature, while S 1, a negative-curvature tends to form.…”

Two-Component Langmuir Monolayers and LB Films of DPPC with Partially Fluorinated Alcohol (F8H9OH)

“…The use of a 20 mW He-Ne laser emitting p-polarized light of 632.8 nm wavelength and a 10 objective lens allowed a lateral resolution of 2 μm. The angle of the incident beam to the interface was fixed to the Brewster angle 53.1 at 298.2 K. The reflected beam was recorded with a high grade charge-coupled device CCD camera EHDkamPro02, EHD Imaging GmbH, Germany , and the BAM images were digitally saved on the computer hard disk 11,12,26 .…”

“…As mentioned above, the solidification of DPPC monolayers induced by the F8H9OH addition results from the decrease in π eq against X F8H9OH . Therefore, the slope of ∂π eq /∂X can be considered to express the degree of the solidification negative or fluidization positive 8,26 . The inclination for the DPPC/F8H9OH system 0 The experimental π c values also vary against X F8H9OH .…”

Interfacial Properties of Binary Systems Composed of DPPC and Perfluorinated Double Long-Chain Salts with Divalent Counterions of Separate Electric Charge

“…Furthermore, increasing the salt spacer length leads to a loose-packed monolayer. However, the spacers in salts with spacers longer than C8 orientate toward the air, which results in folding and a wicket-like conformation 25,26 . The interfacial behavior of fluorinated salts CnBP FC14 2 , n 2, 6, or 10 at the air-water interface has been studied previously 26 .…”

“…However, the spacers in salts with spacers longer than C8 orientate toward the air, which results in folding and a wicket-like conformation 25,26 . The interfacial behavior of fluorinated salts CnBP FC14 2 , n 2, 6, or 10 at the air-water interface has been studied previously 26 . The spacer moieties of C2BP FC14 2 and C6BP FC14 2 dissociate to the bulk just after spreading, whereas the C10BP FC14 2 headgroups remain bonded to the hydrophobic chains when spread on a 0.15 M NaCl solution.…”