X-ray Reflectivity Study of Langmuir Films of Amphiphilic Monodendrons

Abstract

We have used X-ray reflectivity and Π-area isotherms to study Langmuir films of a series of second- and third-generation monodendrons with hydrophobic C12H25 alkyl tails at the periphery and hydrophilic COOHCO2CH3 or crown ether groups in the core. Both the limiting molecular areas and the layer thicknesss are consistent with a model in which the chains are directed nearly perpendicularly away from the water surface.

Langmuir-Blodgett Films of Supported Polyester Dendrimers

“…The previous indicates that, when dendrimer generation increases, the molecular area doubles, because molecule size also increases, therefore taking up a greater molecular area. The found areas are close to the expected area for a chain containing phenyl rings [11] and agree perfectly with the molecular modeling calculations (Table 1). G1 has a final molecular area of A 0 = 133 Å 2 , G2, A 0 = 291 Å 2 , and G3, A 0 = 806 Å 2 ; for this series, the final molecular area varies almost linearly with the number of OH groups, as can be seen in Figure 5.…”

“…Apparently, larger surrounding polyester chains decrease the attraction to the SIO 2 molecules from the support. The explanation used by Pao et al [11], for similar results, can be employed here; thus, the hysteresis curves results indicate that the molecular area on larger generations of the studied dendrimers must be largely, but not entirely, determined by the sum of loosely packed individual alkyl chains, with the chains extending radially away from the surface. G1 polyester dendrimer has a somewhat smaller area, but not unphysically so.…”

“…Nevertheless, the general principles determining molecular conformation at the air-water interface are still under study [8–10], with unsolved questions such as the differences in the molecular shape near the interface and their relationship to the three-dimensional; the importance of the chemical functionalities of the different parts of the molecule; the shape of the formed monolayers, and so forth. So far, the knowledge of dendrimer structure in Langmuir films (at the air-water interface) comes largely from pressure-area (Π- A ) measurements, which are however open to multiple interpretations [11–16]. …”

Air–water interfacial behavior of linear-dendritic block copolymers containing PEG and azobenzene chromophores

“…Langmuir films of amphiphilic LDBCs have been obtained at the air-water interface [19][20][21][22][23][24], but thus far, Langmuir films of azobenzene-containing LDBCs have not been explored. In this work, we report the fabrication and characterization of Langmuir films based on PEG-AZOn.…”

Molecular design of branched and binary molecules at ordered interfaces

“…Similarly, no flat-on orientation of the polar crown heads was observed for monodendrons studied recently by Pao et al 134 The authors varied the number of branches All generations show a trend of the polar head and azobenzene spacer group adapting a tilted behavior beneath the water surface. For the first three compounds, the tilt angle is close to 50° from the surface normal but increases to 63° for AD12-8.…”