Interdiffusion of Cadmium Arachidate in Langmuir-Blodgett Films

Abstract

The interdiffusion of Cadmium Arachidate (CdA) in Langmuir-Blodgett films has been studied by neutron reflection at the Intense Pulsed Neutron Source of Argonne National Laboratory. One of the samples consisted of a few layers of perhydro H-CdA deposited on a silicon support, overlayered with a few layers of deuterated D-CdA, for a total thickness of ∼300 Angstroms. In a second sample the layers of perhydro-and deuterated- CdA were separated by two monolayers of Hn-octadecene/co-maleic acid copolymer. When heated for 15 minutes at 70°C, well below the disorder temperature [1], approximately 25% of the D-CdA molecules were replaced by H-CdA molecules, although the overall Langmuir-Blodgett film structure is known to remain unchanged [1]. The presence of copolymer layers limited the interdiffusion process to about 5%.

Stability of Cadmium Arachidate Langmuir−Blodgett Multilayers as Determined by Neutron and X-ray Reflectivity

“…It is not possible to identify any degree of interdiffusion within the tolerance of our model parameter determination. Stroeve et al in contrast observed substantial changes in their multilayer supported on a hydrophilic substrate. Additional data were collected after annealing at 70 °C for total times of 30 min (not shown) and 150 min.…”

“…Peak splitting characteristic of the presence of both d- and p-chains in the same layer was observed in multilayers deposited on hydrophilic substrates after annealing at 85 °C for 1 h. The magnitude of the effect was interpreted as indicating that 25% of the perdeuterated chains had moved into layers originally deposited with p-CdA. Neutron reflectivity (NR) spectra from similar samples measured in an earlier study displayed marked changes after annealing for 15 min at 70 °C, while NR spectra from comparable multilayers of all p-CdA or all d-CdA showed no change after the same annealing. Further FTIR measurements 39 with samples containing a polymeric bilayer sandwiched between the several layers of p-CdA and several layers of d-CdA indicated that this exchange could be slowed by the polymeric barrier.…”

“…This difference allowed for the investigation of interdiffusion using all three samples 6p6d, 6p4d, and 2xppdd. The sample 6p6d was considered first and annealed at 70 °C for 15 min in order to reproduce the heating schedule used by Stroeve et al 40 Figure 7 presents the NR data for 6p6d in the unannealed and annealed states. Only slight changes are seen in Figure 7a for the 15 min anneal, including subtle increases in intensity at values of k near 0.015 Å -1 and for the two Bragg maxima near 0.065 and 0.102 Å -1 .…”

Structure and Stability of Two-Component Langmuir−Blodgett Multilayers Containing Cadmium Arachidate and Polyglutamate Determined by Reflectivity

“…Critical to the exploitation of thin film Langmuir−Blodgett (LB) multilayers as devices is an understanding of the multilayer's interfacial microstructure and its stability. The interdiffusion of cadmium arachidate (CdA) molecules in multilayers containing only protonated CdA (p-CdA) and deuterated CdA (d-CdA) has been considered in a few studies. − Two-component multilayers are an important special case which has been considered very little. , Furuno et al. considered two-component multilayers containing poly(1-benzyl- l -histidine) and stearic acid, in which the two components were intentionally mixed within individual layers.…”

Temporal Stability of a Bilayer in a Langmuir−Blodgett Multilayer and Its Dependence on Multilayer Structure

“…Rearrangement, or molecular movement, in multilayers has been observed by using AFM, 3 IR, 4 FTIR, 5 Raman, 6,7 optical microscopy, 8 and electron diffraction 2b as well as by fluorescence 9 and neutron reflectometry, 1,5,[10][11][12] Many of these studies have focused on the sample behavior at temperatures above ambient, but some work on mobility at room temperature has been done. Schwartz et al 3 have directly imaged the restacking of molecules of a single monolayer and three-layer multilayers to form thicker multilayer regions using AFM.…”