F. Davis

Resorcinol calixarenes (resorcarenes): Langmuir-Blodgett films and optical properties

Specially synthesized amphiphilic resorcinol calixarene (resorcarene 2) molecules have been deposited as Langmuir-Blodgett (LB) films on a variety of substrates including hydrophobically treated glass slides, silicon and gold-coated glass slides. A value of 1.9 nm(2) is obtained for the area per molecule from measurements of pressure/area isotherms of the floating layer. Optical absorption studies within the ultraviolet-visible frequency region have been performed on these molecules in both LB films and in solution of resorcarene 2 in chloroform, containing 10% ethanol. Molecular aggregation in the form of dimerization is believed to take place during film formation. Further analysis has been carried out for Langmuir-Blodgett films of resorcarene 2 by using Fourier transform infra-red spectroscopy, low-angle X-ray diffraction and surface plasmon resonance (SPR) techniques. The monolayer thickness of 1.6 nm found from SPR measurements is consistent with that from other experimental observations

Size-quantization in extremely small CdS clusters formed in calixarene LB films

CdS nanoparticles have been formed within Y-type Langmuir-Blodgett (LB) films of cadmium salts of calix(8)- and calix(4)-arene by reaction with H2S. UV-vis absorption spectra of the LB films, measured at room temperature, show well-resolved transitions between size-quantization levels in CdS clusters. The size of the CdS particles, obtained by Gaussian fitting of the experimental spectra, is 1.5 +/- 0.3 nm, which is much less than those reported for fatty acid LB films. The particle size does net depend either on the type of calixarene or the number of LB layers. LB films were also characterised by X-ray diffraction and ellipsometry which show the film thickness do not change substantially after treatment with H2S. The mechanism of CdS nanoparticles formation is discussed

Complexation of metal ions with Langmuir-Blodgett films of novel calixarene azo-derivative

Abstract The complexation properties of Langmuir–Blodgett (LB) films of an amphiphilic calix(4)resorcinarene substituted by four arylazo groups with some heavy metal ions were studied using UV-vis spectral measurements. It was shown that soaking samples in metal salt solutions leads to irreversible decrease of absorbance at 460 nm. Efficiency of complexation is found to depend on both metal cations and anions. Effects of film thickness, solution concentration and time of exposure have also been studied. It was also shown that the addition of a small amount of aromatic compounds such as aniline, leads to a further decrease in the absorbance of the films. The presence of metal salts in the film was directly confirmed by XPS. The mechanism of ion complexation is discussed.

The temporal and thermal stability of pyroelectric calix[8]arene Langmuir–Blodgett films

Abstract Pyroelectric Langmuir–Blodgett (LB) films of calix[8]arene have been prepared using the alternate-layer technique. The technique allows the co-deposition of carboxyl and amino-substituted calix[8]arenes, and results in the alternating acid/amine/acid… layer structure. A pyroelectric coefficient of up to 15 μC m−2 K−1 has been obtained from a 13 alternate layer t-butyl calix[8]arene LB film. The pyroelectric response of this system has been shown to remain constant over ∼5000 continuous heating and cooling cycles. The introduction of metal ions into the LB matrix dramatically increases the temperature range over which the pyroelectric activity can be measured.

The effect of pendant chain structure on the pyroelectric behaviour of calix(8)arene Langmuir-Blodgett films

Abstract The variation of the pyroelectric response (temperature-dependent electric polarisation) of alternate-layer acid/amine films of calix(8)arenes differs according to the structure of their pendant hydrophobic chains. t-Butyl calix(8)arenes exhibit larger pyroelectric coefficients than the t-octyl analogues. A coefficient of 15 μC m −2 K −1 has been obtained for a 13-alternate-layer sample of acid- and amine-substituted t-butyl calix(8)arene.

Morphology and binding of spontaneously assembled multilayers of calix-4-resorcinarenes

Abstract Calix-4-resorcinarenes form multilayers (7–40 layers) by self-assembly from hydrophobic solvents such as hexane on various substrates. Hydrophilic solvents such as ethanol reverse this process. Infrared and X-ray photoelectron spectroscopy, together with X-ray and neutron reflectometry measurements are described. Comparison is made with similar measurements on Langmuir-Blodgett films of these materials. The aim of this work was to study the structure and morphology of the multilayers in the context of a model which has been proposed for their bilayer structure and which is based on the X-ray crystal structure of calix-4-resorcinarene 1. These multilayers have been found to bind glutaric acid selectively.

Temperature-independent conductivity of Langmuir-Blodgett films of a helical polymer and its salt complex

A helical polyether-lithium perfluorophenate complex bearing alkyl side-chains has been shown to form well-organised Langmuir-Blodgett (LB) assemblies. Y-type deposited LB films of the preformed complex (1:1) exhibit a conductivity (normal to the plane) -2 orders of magnitude higher than that of the bulk at 20°C and -9 orders of magnitude greater than the pure uncomplexed polymer LB film. Infrared spectroscopy has confirmed the presence of the salt in these deposited films. These results demonstrate that this preformed polymer complex does not lose its salt component to the aqueous subphase as a Langmuir film. The ionic conductivity of the polymer complex LB film is temperature independent over the region 20-90°C, above which partial disruption to the film occurs with a lowering of the conductivity.

Langmuir–Blodgett multilayers of imidazoles

Abstract Langmuir–Blodgett (LB) multilayers have been formed from a wide variety of compounds but the basic studies from which others have developed have involved a long hydrocarbon chain terminated at one end by a hydrophilic group. The quaternary ammonium ion has a greater attraction for water than do the other groups which have been used and is so hydrophilic as to preclude the formation of LB layers of straight chain molecules terminated by this group. Certainly all such molecules up to and including octadecyl trimethyl ammonium bromide form micelles in preference to monolayers at the air/water interface though metastable monolayers of this compound have been reported. Quaternized imidazoles have, like quaternary ammonium ions, a positive charge but seem more likely to form LB films. We have thus explored the properties of several of these compounds with a view to producing one which has the desired properties. In order to combat the highly hydrophilic nature of the imidazole group it is necessary to employ a highly hydrophobic ‘tail group’. Thus our most successful compound contains two octadecyl alkyl chains. We have studied the behaviour of this compound at the air/water interface and have found that the nature of the subphase has a very marked influence on the shape of the isotherms. With nitric acid added to the subphase to bring about a pH of 3.5 it is possible to obtain good Y deposition with deposition ratios equal to one in both the upward and downward directions. However we have not been able to achieve LB deposition using any other acid. On heating, the compound in question it changes from a crystalline structure to a smectic structure at 55°C.

Structures and binding of LB films of calix-8-arenes

Abstract A series of three calix-8-arenes have been successfully deposited as Langmuir-Blodgett films up to 100 layers thick and studied by means of a quartz crystal microbalance, X-ray diffraction and infra-red spectroscopy. These layers have been shown to gain weight when exposed to dilute aqueous solutions of caesium bromide over periods of up to several hours. From our results we deduce that the ions are adsorbed vertically through the film rather than in a transverse manner. The kinetics of adsorption are similar to those found for other LB systems.

The preparation and conductivity of LB films of a novel polymer electrolyte and its complexes with sodium triflate and eicosylamine

Surface pressure-repeat unit area isotherms of a novel helical polyether bearing -C 16 H 33 side chains (C16O5), its two-component complex with NaCF 3 SO 3 and its three-component complex with C 20 H 41 NH 2 are described. The areas per molecular repeat unit following addition of salt by uptake from the aqueous phase and by addition in a pre-prepared three-component mixture follow the sequence C16O5 < C16O5: NaCF 3 SO 3 (subphase) < C16O5:NaCF 3 SO 3 (premixed) < C16O5:NaCF 3 SO 3 :C 20 H 41 NH 2 , where the amine was added by the alternate layer LB technique. Grazing incidence IR confirms the presence of salt in the LB films (20 layers: 10 C16O5:NaCF 3 SO 3 /10 C 20 H 41 NH 2 ) and the formation of a single-phase three-component complex is supported by DSC of bulk materials. Ionic conductivities of the three-component systems, measured normal to the LB layers, show that the pre-prepared sample has the highest conductivity and demonstrates temperature independent conductivity (10 -7 S/cm) over the range ambient to approx. 80°C.