Effect of Niobium Modifications to PZT (53/47) Thin Films Made by a Sol-Gel Route

Niobium-modified lead zirconate titanate thin films (PNZT) with nominal compositions, Pb_(1–0.5x) (Zr_0.53 Ti_0.47)_1–x Nb _x O₃:x = 0.02–0.07, have been prepared using a diol based sol-gel route. Single-layer (0.5 m) films were fabricated on platinised silicon substrates by spin-coating. The effect of niobium additions with regard to phase development, microstructure, and ferroelectric and dielectric properties were investigated for different annealing temperatures. For comparison, unmodified PZT films were also prepared. Niobium substitution increased the crystallisation temperatures for perovskite PNZT phase formation. The values of remanent polarisation P _r and dielectric constant _r were found to decrease with the introduction of Nb. For example, in films heated at 700°C for 15 min, the P _r value of an unmodified PZT film was 31 C cm^–2, compared to 17 C cm^–2 for an x = 0.05 PNZT film, whilst respective relative permittivity values fell from 1190 to 600. The highest Nb concentration film, x = 0.07, did not display any switchable polarisation characteristics, which is consistent with high levels of intermediate pyrochlore phase.     

Time-dependent mixing and demixing processes in binary lipid monolayers studied by mixed and separate spreading using film pressure and film potential measurements

Using both spreading techniques — mixed spreading and separate spreading- and, simultaneously, film pressure and film potential measurements, the mixing behavior of the following five binary systems was investigated and compared: 1) system 1,2-dilauroyl-phosphatidylethanolamine/cholesterol; 2) system 1,2-dimyristoyl-phosphatidylethanolamine/cholesterol; 3) system 1,2-dipalmitoyl-phosphatidylethanolamine/cholesterol; 4) system Na-eicosyl sulphate/hexadecanol; 5) system phosphatidic acid/1,2-dimyristoyl-phosphatidylethanolamine.Analyzing the time and concentration dependence of the /a isotherms and v/a isotherms (^s = film pressure, v ^s potential,a=average area per molecule in mixed films in the monolayers) of the binary monolayers it can be concluded that the components of the binary systems 1–4 are complete miscible in the monolayers. On the other hand the components of the system 5 are probably partially miscible only.     

The application of dielectric analysis to drying latex films

Measurements of real and imaginary capacitance (C andC) have been made during the drying of a film-forming latex. In one experiment dielectric measurements at frequencies between 1 Hz and 100 kHz were made simultaneously with gravimetric measurements on a microbalance. It was found that both the rate of water evaporation and the a.c. conductance decrease sharply at high polymer volume fraction. These results are discussed qualitatively in terms of a model for the film-forming process. In another experimentC andC were recorded at 10 Hz along with automatic measurements of the build-up of the scratch resistance of the film. It was found that the mechanical response to film-formation appears significantly earlier than the dielectric response. This is also discussed qualitatively in terms of the model.The authors would like to thank Dr. I. Abrahams, Dr. S. Bell, and Dr. M. Reading for useful discussions regarding this work and M. Bahra for his help with the TFA measurements.     

Performance characteristics of suspended particulate reagent-iminodiacetate as a binding agent for diffusive gradients in thin films

The performance characteristics of an alternative binding agent, suspended particulate reagent-iminodiacetate (SPR-IDA), for use with DGT methodology were investigated. The parameters investigated during this study included gel hydration, blank levels, elution factor (f_e), capacity, the effects of pH on the binding of trace metals by DGT. The novel application of this resin for use as a quantitative standard for laser ablation ICP-MS was also evaluated. To further constrain the results for the SPR-IDA binding agent, parallel experiments were performed using resin gel containing Chelex 100, which has been widely reported in the literature. Hydration results showed that the SPR-IDA resin gel reached a stable dimension and weight within ∼30 min and was dimensionally stable for ≤6 months. The measured DGT blanks for the SPR-IDA resin were 0.0023, 0.15, 0.21, 0.0033 and 0.011 ng disc⁻¹ for Co, Ni, Cu, Cd and Pb, respectively. The elution factor differed for the two resin types with the Chelex 100 recoveries slightly lower than previous reports and the SPR-IDA resin showing on average ∼5-9% better recoveries than DGT containing Chelex 100. The measured capacity of DGT discs containing the SPR-IDA binding agent was 0.26 mg Cd, similar to the calculated value of 0.29 mg Cd, indicating the entire resin layer was available for metal uptake.Both resin types performed equally well when deployed in 1 mM NaNO₃ solutions with DGT measurements of ∼100% of direct solution measurements for Co, Ni and Cd. However, DGT measurements of Cu and Pb systematically decreased with increasing solution pH down to ∼50% of solution values at pH 8.0, due to artifacts resulting from colloid formation during the addition of the metals. This was remedied by adding the metals as dilute salt standards and addition of Mg(NO₃)₂ to eliminate adsorption to the container walls. In the latter experiments, DGT measured concentrations of Co, Ni, Cu, Cd and Pb were in agreement with solution concentrations. Deployment of DGT in solutions with increasing concentrations of trace metals yielded linear results, suggesting that quantitative analysis using simplified laser ablation techniques should be possible using this newly characterized SPR-IDA resin gel.     

Surface properties of the binary mixed systems of alkylpyridinium halides and sodium alkylsulfonates

Surface properties of the binary mixed systems of decyl- and dodecylpyridinium chloride or bromide and sodium pentyl- and heptylsulfonate have been investigated. The surface tension of solutions of equimolar mixtures of surfactants and individual surfactants was measured, and the composition of mixed monolayers and surface interaction parameter β were calculated with the regular solution theory. Our results indicate that the properties of mixed films depend on both ionic strength and the kind of added inorganic electrolyte. With the increase of inorganic electrolyte concentration, the content of more surface active ions in the adsorption films enhances and is the highest in the presence of NaI and the smallest when solutions contain NaCl. Mutual interactions in mixed adsorbed films were found to be attractive. However, the strength of interaction weakens with the increase of ionic strength and depends on the kind of inorganic ions in the order: Cl⁻>Br⁻>I⁻.     

Surfactant in the gaseous phase II. Influence on stability of foams and thin liquid films

The influence of the vapors ofn-amyl orn-decyl alcohol on the stability of single thin liquid films, single bubbles, and foam columns was determined. It was found that the presence of surfactant vapors lowered the stability of foams and single foam films. The mechanism of the destabilizing action of the surfactant vapors on wet, dynamic foams under dynamic conditions is discussed. It is shown that the destabilizing action of the surfactant vapors is a further indication that surface elasticity forces are the main factor determining stability of wet, dynamic foams.     

Surface forces in wetting films

A short review of various components of surface forces acting in a non-symmetrical system such as wetting films is presented here. Experimental results are compared with modified DLVO theory, which includes, besides dispersion and electrostatic, structural (solvation) forces caused by a change in liquid structure in conditions of confined geometry. The peculiarities of disjoining pressure isotherms and conditions of the film stability of non-polar and polar simple liquids, as well as of aqueous solutions of electrolytes and surfactants, are systematically considered from a historical perspective.     

Electrochemically formed fullerene-based polymeric films

The recent results of investigations involving the electrochemical formation of polymers containing fullerenes and studies of their properties and applications are critically reviewed. From a structural point of view, these polymers can be divided into four main categories including (1) polymers with fullerenes physically incorporated into the foreign polymeric network without forming covalent bonds, (2) fullerene homopolymers formed via [2+2] cycloaddition, (3) “pearl necklace” polymers with fullerenes mutually linked covalently to form polymer chains, and (4) “charm bracelet” polymers containing pendant fullerene substituents. The methods of electrochemical polymerization of these systems are described and assessed. The structural features and properties of the electrochemically prepared polymers and their chemically synthesized analogs are compared. Polymer films containing fullerenes are electroactive in the negative potential range due to electroreduction of the fullerene moieties. Related films made with fullerenes derivatized with electron-donating moieties as building blocks are electroactive in both the negative and positive potential range. These can be regarded as “double cables” as they exhibit both p- and n-doping properties. Fullerene-based polymers may find numerous applications. For instance, they can be used as charge-storage and energy-converting materials for batteries and photoactive units of photovoltaic cell devices, respectively. They can be also used as substrates for electrochemical sensors and biosensors. Films of the C₆₀/Pt and C₆₀/Pd polymers containing metallic nano-particles of platinum and palladium, respectively, effectively catalyze the hydrogenation of olefins and acetylenes. Laser ablation of electrochemically formed C₆₀/M and C₇₀/M polymer films (M=Pt or Ir) results in fragmentation of the fullerenes leading to the formation of hetero-fullerenes, such as [C₅₉M]⁺ and [C₆₉M]⁺.Dedicated to Professor Dr. Alan M. Bond on the occasion of his 60th birthday.     

The influence of preparation method of OC1OC6-PPV films on the photo-oxidation process

Poly(p-phenylene vinylene) (PPV) derivatives are well known for their applications in polymer light emitting diodes (PLEDs). PPV derivatives are highly susceptible to photo-oxidation though, which is mainly caused by the scission of the vinyl double bond on the polymer backbone. In this work, we show that Langmuir-Blodgett (LB) films are less degraded than cast films of a PPV derivative (OC₁OC₆-PPV). Both films had similar thickness (∼50 nm) to allow for a more realistic comparison. Degradation was monitored with UV-vis and FTIR spectroscopies. The results indicated that cast films were completely degraded in ca. 400 min, while LB took longer time, i.e. about four times the values for the cast films. The differences can be attributed to the more compact morphology in the LB than in the cast films. With a compact morphology the diffusion of oxygen in the LB film is hampered and this causes a delay in the degradation process.     

Smart Biopolymer-Based Nanocomposite Materials Containing pH-Sensing Colorimetric Indicators for Food Freshness Monitoring

Nanocomposite biopolymer materials containing colorimetric pH-responsive indicators were prepared from gelatin and chitosan nanofibers. Plant-based extracts from barberry and saffron, which both contained anthocyanins, were used as pH indicators. Incorporation of the anthocyanins into the biopolymer films increased their mechanical, water-barrier, and light-screening properties. Infrared spectroscopy and scanning electron microscopy analysis indicated that a uniform biopolymer matrix was formed, with the anthocyanins distributed evenly throughout them. The anthocyanins in the composite films changed color in response to alterations in pH or ammonia gas levels, which was used to monitor changes in the freshness of packaged fish during storage. The anthocyanins also exhibited antioxidant and antimicrobial activity, which meant that they could also be used to slow down the degradation of the fish. Thus, natural anthocyanins could be used as both freshness indicators and preservatives in biopolymer-based nanocomposite packaging materials. These novel materials may therefore be useful alternatives to synthetic plastics for some food packaging applications, thereby improving the environmental friendliness and sustainability of the food supply.