Experimental modeling of solvent-casting thin polymer films

An apparatus was designed and assembled to study the solvent removal from solution-cast thin polymer films. The computer interfacing of a thermogravimetric analyzer, spectrophotometer, electronic flowmeters, and control valves for the apparatus enabled the preprogramming of the carrier gas velocity, carrier gas solvent content, and temperature profiles to simulate the environment experienced in large parallel flow industrial driers. The apparatus has also been designed and operated to enable the visual observation of the drying film with an optical microscope. Initial experimental studies conducted with the apparatus involved the effect of temperature on solvent removal. The results indicate that high dryer gas temperatures can apparently cause skinning of the film surface resulting in slower solvent removal rates. The skin formation can be suppressed by higher solvent concentration in the carrier gas. The visual observations revealed the formation of standing waves in the film surface during drying at high gas velocities (>2OO cm/min). The wave formation at least partially overcomes the effect of skinning by increasing the surface area of the film, and may be the manifestation of flow instabilities involving circulation within the film.     

Diffusion coefficient in polymer solutions

Molecular diffusivity of a solute in a solvent may be determined by measuring the extent of dispersion of solute in solvent flowing in a straight circular tube under the conditions of laminar flow. This simple and rapid method for determination of molecular diffusivity in aquous polymer solutions is discussed. Experimental results show a substantial reduction in the solute diffusivity with increase in polymer concentration.     

A novel piezoelectric ceramic with high Curie temperature and high piezoelectric coefficient

0.02Pb(Sb_1/2Nb_1/2)O₃-0.98Pb_1-xBa_x(Zr_0.53Ti_0.47)O₃ (PSN-PB_xZT) ceramics with high Curie temperature and high piezoelectric properties were prepared by traditional solid state reaction measurement to meet the requirements for high temperature applications, and the crystal structure, dielectric, piezoelectric and ferroelectric properties were investigated. All the samples show a tetragonal crystal structure at room temperature and there was no noticeable change with the increasing of Ba²⁺ content. Doping of Ba²⁺ markedly improved piezoelectric properties of PSN-PZT, the maximum d₃₃~560 pC/N, T_c ~317 °C at x = 0.05. Their outstanding piezoelectric properties will drive the development of high temperature industrial applications.     

Transformation of waterborne hybrid polymer particles into films: Morphology development and modeling

Films cast from multiphase polymer particles have the potential to combine the properties of their components synergistically. The properties of the film depend on the hybrid polymer architecture and the film morphology. However, how the polymer microstructure and particle morphology are transformed during film formation to determine the film morphology is not well understood. Here, using waterborne alkyd-acrylic nanocomposite particles in a case study, it was found that phase migration leading to the formation of aggregates occurred during film formation. A coarse-grained Monte Carlo model was developed to account for the effects of polymer microstructure and particle morphology on the morphology of the film. The model was validated by comparing its predictions with the observed effects, and then used to explore combinations of polymer microstructure and particle morphology not attainable with the system used as a case study. Significantly, the compatibility of the phases was found to have a greater influence than the morphology of the particles in determining the film structure.     

High voltage coefficient piezoelectric materials and their applications

The piezoelectric d_ij coefficient is often regarded in materials science as the most important figure of merit of piezoelectric performance. For many applications, the piezoelectric g_ij coefficient which correlates to voltage output and sensitivity of a piezoelectric material can be considered of equal or increased importance, however is often an overlooked parameter in materials science literature. The aim of this review is to highlight the importance of this parameter and to provide insight into the mechanisms that drive a high piezoelectric voltage coefficient in single crystal, polycrystalline, and composite form. For bulk ceramics, special attention is given to tetragonal systems due to the availability of electrical and crystallographic data allowing for a clear structure-property relation. Orthorhombic and rhombohedral systems are mentioned and specific cases highlighted, however investigating structure-property relations is difficult due to the lack of crystallographic datasets. Composite materials have been the forefront of high g_ij piezoelectric materials over the decades and are therefore also considered in both ceramic-matrix and polymer-matrix form. An overview of applications in medical, energy, fishing and defence industries where a high g_ij is desirable are considered and the scientific and commercial considerations that must be made for the transition from laboratory to industry are discussed from the perspective of integrating new piezoelectric materials into sonar devices.     

Simultaneously enhanced piezoelectric response and piezoelectric voltage coefficient in textured KNN‐based ceramics

<001> ‐textured 0.99(K_0.49Na_0.49Li_0.02)(Nb_0.97‐xSb_0.03Ta_x)O₃‐0.01CaZrO₃ [abbreviated as 0.99KNLN_0.97‐xST_x‐0.01CZ, x = 0.03, 0.07, 0.10, 0.15, 0.20, 0.25] ceramics were prepared by templated grain growth (TGG) method and a two‐step sintering process. Giant longitudinal piezoelectric coefficient d₃₃ (391 pC/N) and piezoelectric strain coefficient d₃₃* (630 pm/V under an AC E‐field of 20 kV/cm) can be obtained in the textured ceramics with x = 0.25. All textured ceramics display superior k_p (>54%) and g₃₃ (>23 × 10^?3 Vm/N) which are in an order of magnitude with PZT ceramics. The maximum value of k_p (~63.3%) obtained in textured ceramics with x = 0.15 is higher than that of famous textured LF4 ceramics. Excellent comprehensive properties suggest that <001> ‐textured 0.99KNLN_0.97‐xST_x‐0.01CZ ceramics are promising candidates in the field of lead‐free piezoelectric materials.     

Matrix influence on the piezoelectric properties of piezoelectric ceramic/polymer composite exhibiting particle alignment

This study was addressed to the influence of an electric field strength applied at fabrication process and matrix properties, such as the dielectric constant and the Young's modulus, on “pseudo‐1‐3 piezoelectric ceramic/polymer composite” in order to further enhance the piezoelectricity of that. The pseudo‐1‐3 piezoelectric ceramic/polymer composite consists of linearly ordered piezoelectric ceramic particles in polymer material. Silicone gel, silicone rubber, urethane rubber, and poly‐methyl‐methacrylate, which exhibit different dielectric constants and Young's modulus, were used as matrices to evaluate the matrix influence. The piezoelectricity of the pseudo‐1‐3 piezoelectric ceramic/polymer composite was evaluated using the piezoelectric strain constant d₃₃. The d₃₃ is one of the indices of the piezoelectric properties for piezoelectric materials. As a result, it was confirmed that d₃₃ of the pseudo‐1‐3 piezoelectric ceramic/polymer composite increased with the increase of the electric filed strength applied at fabrication process, though, it reached a constant value at a certain strength value. Further it was confirmed that dielectric constant of the matrix had a small influence on d₃₃ of the pseudo‐1‐3 piezoelectric ceramic/polymer composite, however, in case of matrix of lower Young's modulus, d₃₃ was increase. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41817.     

Electrochemical and electrogravimetric behaviors of conducting polymer. Theoretical aspects and application to co-polymer films based on juglone

Redox mechanisms of conducting polymers are not yet fully understood. Attractive analytical tools and pertinent models are necessary to achieve this goal. In this paper, numerical simulations based on a theory dealing with ions transfer through electroactive film/electrolyte interface was developed to predict the behavior of a conducting polymer called poly(JUG-co-JUGA). The main advantage of this approach is that it can be applied for any polymer assuming a mixed conducting material and a thin enough film neglecting the transport effect. It is the first time where the same model allows both classical cyclic electrogravimetry (current and mass over a potential scan) and ac-electrogravimetry (electrochemical impedance and mass/potential transfer functions) to be estimated theoretically. Moreover and to our knowledge the electrochemical behavior of poly(JUG-co-JUGA) was examined through these techniques for the first time. It is shown herein that the cation transfer is preponderant but the free solvent motion must be taken into account. This effect is not detected by classical electrochemical measurements but only by combining electrochemical characterization to gravimetric measurements.     

Interdependence of piezoelectric coefficient and film thickness in LiTaO3 cantilevers

Electromechanical energy demands on homogenous thick films of piezoceramics with sufficiently large piezoelectric constant and reproducible performance. Single-phase LiTaO₃ films deposited by sol-gel processing have been fabricated as cantilevers to investigate the interdependence of dielectric and piezoelectric properties as a function of film thickness. Phase pure LiTaO₃ films with varying thickness in the range of 2.07-4.37 µm on stainless steel substrates were obtained after calcination of samples at 650°C. The relative permittivity of optimized spin-coated films peaked at 479.73 (1 kHz), whereas the piezoelectric coefficient (d₃₃ mode) determined by piezoresponse force microscopy was in the range of 21-24 pm/V. The effect of poling was studied through the butterfly and phase curves. A figure of merit (FOM) up to 3.29 (10⁻¹⁸ m²/V²) was determined for cantilever devices, which were able to generate a peak-to-peak voltage of 0.046-0.15 V using a 1 MΩ resistor as an impedance load at a fixed acceleration of 1.5 m/s². While the power density was in the range of ~4-20 × 10⁻⁹ W/m³, which increased with the increasing film thickness. The leakage current density decreased in the range of 4 × 10⁻⁵-6 × 10⁻⁷ A/m² in the same direction. As both ferroelectric and piezoelectric properties of LiTaO₃ films are dependent on film thickness, an optimal energy conversion efficiency was obtained for a thickness of ~3 µm. Furthermore, these devices were tested up to a temperature of 150°C for voltage generation. Given the need for lead-free piezoelectric materials for environmental applications, these LiTaO₃ cantilevers are very promising for vibrational energy harvester (VEH) applications especially due to their cost effectiveness, small size, stability at higher temperatures, and repeatable properties, which makes them suitable for MEMS devices for industrial applications.     

Measurement of diffusion coefficient and partition coefficient of sodium in nonionic polymer membranes

The difficulties involved in the measurement of the partition coefficient and diffusion coefficient of NaCl in hydrophilic polymer membranes are examined by the initial rate and late-time analysis of desorption data for three nonionic polymer systems. The late-time analysis, based on the plot of the logarithmic relative desorption versus time, was found to be useful when the diffusion is Fickian and the magnitude of D₂/l² is small. Depending on the magnitude of D₂/l², an accurate measurement of k₂ and determination of D₂ cannot be achieved without correction for the effect of surface salt solution, impossible with late-time analysis. The initial rate measurement was found more versatile for general non-Fickian diffusion and it gave a means of correction of the errors involved in estimating the partition coefficient. In general, the diffusion of NaCl in hydrophilic polymers is not ideal Fickian and the discrepancy between the two analyses is appreciable.     

Effect of hexagonal boron nitride on the coefficient of frictions of organic-inorganic hybrid polymer thin films for metal surface coatings

Abstract

Organic-inorganic hybrid coatings were developed via a sol-gel method using hexagonal boron nitride (h-BN) as a ceramic filler material incorporated into a polymeric matrix. To investigate the effects of h-BN on the properties of polymer-based coatings, parameters such as hardness, coefficient of friction, and hydrophobicity were investigated. Colloidal silica (CS), methyltrimethoxysilane (MTMS), water, and acid catalyst containing coatings were prepared by varying the content of h-BN from 10% to 25%. All the coatings were prepared with the same experimental procedure and coated on 1050 aluminum alloy plates. The compensating contents of MTMS and colloidal silica with a fixed molar ratio of MTMS and CS were set to be 1:1.2, and a specific amount of the catalyst was utilized. Coatings were examined by Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), and energy-dispersive X-ray spectroscopy (EDS). The most promising physical properties were determined to be the pencil hardness of 8B, adhesion strength of 5B, coefficient of friction of 0.332?N, and water contact angle of 114.75°. Therefore, it can be concluded that the h-BN improves the physical properties of polymeric coatings. In addition, this study demonstrates the effect of h-BN on the adherence of polymer matrix-based hybrid coatings.     

A new monomeric FRET-acceptor for polymer interdiffusion experiments on polymer dispersions

The properties of the non-fluorescent dye [1-(4-nitrophenyl)-2-pyrrolidinmethyl]-acrylate (NPP-A) have been evaluated with respect to its use in Fluorescence resonant energy transfer (FRET) experiments in polymers. NPP-A is attractive as a FRET-acceptor because its absorption spectrum has good spectral overlap with the emission spectrum of phenanthrene, where the latter is a widely used donor. Importantly, NPP does not fluoresce and therefore does not interfere with time-resolved measurements of the donor fluorescence. The label is well compatible with free radical polymerization. For two polymers, namely (butyl acrylate)-co-(methyl-methacrylate) (50/50) and (butyl methacrylate), the Förster radii were determined from the dependence of the FRET efficiency on the concentration of the acceptor. The results agree within the error. The Förster radius of the phenanthrene–NPP donor–acceptor pair was determined as R₀ = 2.47 ± 0.03 nm.     

Effect of the host polymer on the nanomechanical and morphological properties of templated polymer films

Atomic force microscopy and nanoindentation have been applied to the study of thin molecularly templated polymer films. The template was chosen to be the readily hydrogen‐bonded cotinine molecule and three different polymer hosts, Elvamide® nylon, Nylon‐6, and poly(4‐vinylphenol) were compared. The host polymer was shown to affect the nature of the template‐host interaction resulting in varying surface morphologies and differences in the nanohardness. These observations were shown to reflect differences in the underlying interaction chemistry, specifically, whether or not the polymer may be imprinted in the film production process. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 877‐883, 2013     

Permeability studies on heterogeneous polymer films

Oxygen permeability data on heterogeneous films prepared from mixtures of different polymer latices were compared with predictions of a permeability theory of Higuchi based on an idealized barrier model. The theory attempts to evaluate the effect of perturbations of the diffusion process associated with the presence of a discontinuous internal-phase component. An approximate form of the theoretical permeability expression was found to render reliable predictions of the effective permeability of heterogeneous barrier systems. When the partition of the permeant between different phases of the barrier is sufficiently rapid, the theory becomes applicable to the early, nonsteadystate, stage of permeation. Implications of the general applicability of the Higuchi theory to heterogeneous systems are discussed with respect to the interaction between the constitutents and the associated departures from the ideal behavior assumed for the model.     

Excluded volume effect on polymer films

Using Monte Carlo methods we have investigated the excluded volume effect on polymer melts in two dimensions. Investigating chain lengths of up to N = 59 at concentration $\text{c =}\text{5}\text{6}$, our results strongly support predictions made recently by de Gennes: (1) end-to-end distance and gyration radius exhibit Gaussian behaviour ∝ √N; (2) but their prefactors differ significantly from their random flight values; (3) in contrast to three-dimensional melts the chains are strongly segregated.     

Ion, solvent and polymer dynamics in polyaniline conducting polymer films

We describe the application of a new model for the visualization of mobile species (ion and solvent) transfers accompanying redox switching of electroactive films. The system studied was polyaniline, for which the mobile species population changes were determined from redox-driven film mass changes using a thickness shear mode acoustic wave resonator. Acoustic admittance data were used to establish conditions under which the resonator frequency response could be interpreted gravimetrically. Charge and frequency changes accompanying the first redox transition of polyaniline films exposed to aqueous perchloric acid were then used to determine the film's ion and solvent populations. The data are best described by a mechanism in which the early stages of film oxidation are associated with proton transfer (exit) and the latter stages with perchlorate transfer (entry) to satisfy electroneutrality; solvent enters throughout film oxidation and exits throughout film reduction. The alternative of a single ion satisfying electroneutrality throughout would require the rather less likely situation of a non-monotonic solvent flux. Application of the model's diagnostic criteria indicates that the film solvent population is in equilibrium on the timescale of slow scan voltammetry, but shows thermodynamic non-idealities. Hysteresis in the film ion population signals failure of the redox state to maintain equilibrium with the applied potential.     

Studies on polymer latex films: II. Effect of surfactants on the water vapour permeability of polymer latex films

Poly(butyl methacrylate) films have been prepared from surfactant-free latices which had post-added commonly used latex stabilisers. Water vapour transmission rates were used to study film permeability in relation to morphology, which was also studied by freeze fracture replication transmission electron microscopy. The extent of latex coalescence depended upon the chemical nature of the stabiliser employed and at monolayer coverage was not necessarily deleterious to the barrier properties of the films.     

油田含聚污水聚合物降解技术室内实验研究

三次采油技术是油田开发后期稳油增产的主要措施,但随着三次采油技术大规模推广应用,原油脱出污水含聚合物增加,含聚污水处理量也大幅度增加。聚合物的存在造成污水黏度增加、油水分离速度减慢,是造成油田污水处理难度增加的主要原因。因此选择技术经济可行的聚合物降解技术是油田含聚污水处理的关键,通过对几种聚合物降解技术室内模拟实验评价对比,为油田含聚污水处理技术优选提供依据。