Gas transport phenomena in hydroxypropyl cellulose solid film retaining cholesteric liquid crystalline order

Two kinds of hydroxypropyl cellulose (HPC) films were prepared: one retained cholesteric liquid crystalline order (HPC-A), and another was amorphous (HPC-B). Gas transport phenomena in the HPC-A films were determined at 20°C, which is below the T_g of HPC, compared with those in the HPC-B films, by using mainly oxygen and nitrogen gases; herium and carbon dioxide gases were also used. The permeability coefficient P for the HPC-A films was smaller than that for the HPC-B films by approximately 10 times. The gas permselectivity, defined as the ratio of P for each gas, was affected by the liquid crystalline order, as follows: The permselectivity for the HPC-A films was greater than that of the HPC-B films. The trends of gas permeability and permselectivity for the liquid crystal-forming HPC films were the same as those reported for other liquid crystal-forming cellulosic films. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 1465–1470, 1998     

The barrier properties of polyethylene terephthalate to mixtures of oxygen, carbon dioxide and nitrogen

The diffusion and solubility of oxygen, nitrogen and carbon dioxide have been studied in amorphous and biaxially oriented films of polyethylene terephthalate (PET). To measure the sorption and desorption of each gas simultaneously in cases where mixtures of gases were studied, a mass spectrometer was used as a detector. It was found that the solubility and diffusion of nitrogen in PET were markedly affected by the presence of the other gases, oxygen and carbon dioxide with differences in detail between results for the amorphous and biaxially oriented films. It is of particular interest that the presence of oxygen reduces the solubility and increases the diffusivity of nitrogen.     

Synthesis and characterization of optically active liquid crystalline polyacrylates containing mesogenic phenylbenzoate groups

A series of novel side chain liquid crystalline polyacrylates with pendant chiral groups were synthesized. It was found that monomers with electron releasing -OC₄H₉ terminal groups seem beneficial for the formation of liquid crystalline phases. Copolymerization of the monomers was carried out and the physical properties of the copolymers were investigated. All synthesized polymers revealed liquid crystalline phases and appeared highly thermally stable with decomposition temperatures (T_d) at 10% weight loss greater than 384 °C and about 50% weight loss occurred beyond 442 °C under nitrogen atmosphere. Two miscible chiral compounds were also synthesized and used as chiral dopants to induce cholesteric liquid crystalline phases of polymers. Liquid crystalline phases of the polymers were investigated using DSC and XRD, and confirmed with POM technique. The optical properties of the induced cholesteric liquid crystalline polymers were investigated using UV-vis spectrometer. The appearance and the color variation of the polymer films before and after UV irradiation were also investigated. Typical helical morphology of the cholesteric liquid crystalline film was analyzed by SEM technique.     

Electron-beam irradiation-induced grafting of acrylonitrile onto polyethylene

Low- and high-density polyethylene (PE) films were grafted with acrylonitrile (AN) by electron beam prior to irradiation. The distribution of graft chains over the cross section of the sample film was analyzed in terms of the distribution of nitrogen atoms contained in the AN by means of an electron probe microanalyzer (EPMA), and graft sites were studied in relation to the effect of grafting temperature on the percent graft and the oxygen permeability of the sample films. It was found that diffusion of AN into the film was the rate-limiting step in the grafting process, thus restricting the grafting to the surface of the film in the initial grafting stages. However, the grafting shifted to the center of film as the graft process proceeded, until a uniform distribution of graft chains was observed across the entire film thickness. High-density polyethylene (HDPE) was found to display a higher percent graft than did low-density polyethylene (LDPE), and percent graft tended to increase with increasing grafting temperature. On the other hand, film oxygen permeability decreased with increasing percent graft, but this decreasing trend decreased with increasing percent graft. These findings suggest that the grafting is initiated by radicals trapped in the amorphous phase near the crystalline regions and at the surface of crystallites and that graft chains grow toward the amorphous regions. As for the radicals contributing to graft polymerization, it appears that AN permeates deeper near the crystalline surface and that graft chains grow from these sites.     

Reactive sputter-deposition of oxygenated amorphous carbon thin films in Ar/O2

Oxygenated amorphous carbon thin films were deposited by DC magnetron sputtering using various argon and oxygen process gas mixtures. The X-ray diffraction data indicated that the predominantly amorphous films had more defined peaks with a higher partial pressure of oxygen. Results indicated that use of oxygen in the working gas enhanced the crystalline nature of the films. Scanning electron and atomic force microscopy revealed that the surface roughness and film topography differed with the oxygen process gas variations. X-ray photoelectron spectroscopy revealed increased surface oxygen content with higher oxygen concentration in the working gas. Raman spectroscopy results suggested that the increased oxygen in the films may have led to a higher percentage of sp³-bonded carbon atoms. The growth rate (deposition rate) of the films decreased as the amount of oxygen increased. This decreased deposition rate was associated with an oxygen etching of the film.     

Effect of glucose fouling on the dissolved gases permeation through maximum‐crystallized poly(lactic acid) films

In this study, we investigated the effect of fouling on the dissolved oxygen and carbon dioxide permeation in water through maximum‐crystallized poly(lactic acid) (PLA) films by using proton nuclear magnetic resonance, attenuated total reflection‐Fourier transform infrared spectroscopy, wide‐angle X‐ray diffraction, and ultraviolet–visible spectroscopy, contact angle, water content ratio, and dissolved gas permeation. Fouling means the adhesion of contents on a container's internal surface, where content adhesion can directly influence the barrier property of the container. Glucose, a beverage ingredient, was used as a foulant. The permeation of dissolved gases in amorphous PLA film, maximum‐crystallized PLA film, and fouled maximum‐crystallized PLA film was determined. The decreased interstices in the polymer chains during crystallization resulted in the inhibition of the diffusion and decrease in the permeability coefficient of the gases. Moreover, the slope of the permeability coefficient for carbon dioxide in the Arrhenius plot was found smaller than that of oxygen's. This result indicated that the gas barrier property of dissolved carbon dioxide was considerably influenced by solubility and readily decreases during glucose fouling. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46604.     

Crosslinked hydroxypropyl cellulose films retaining cholesteric liquid crystalline order. I. Effects of cast conditions and heat treatment on the textures and order of films

To eliminate the shear-induced band texture and wrinkled texture observed on the free surface of cellulosic solid cast films retaining cholesteric liquid crystalline order, we proposed a storing process of the cast solutions: the solution is stored in the same solvent vapor atmosphere as the solution. The effect of cast conditions (the storing time) on those textures and the cholesteric liquid crystalline order was determined using the lyotropic liquid crystalline solution of hydroxypropyl cellulose in methanol with crosslinker. Furthermore, the effect of heat treatment on the liquid crystalline order in the cast films was determined. The resultant crosslinked films were observed with a polarized microscope and a scanning electron microscope, and were investigated with circular dichroism. Our findings showed that the proposed storing process is needed before starting the cast process. During the process the textures vanished, due to the relaxation of the residual stress in the solution, the cholesteric liquid crystalline order became stable, and the cholesteric pitch decreased with increasing storing time. The heat treatment also affected the liquid crystalline order of the films; the peak in the circular dichroism spectrum sharpened and shifted with heat treatment, and the shift in peak seemed to depend on the crosslinker concentration. Furthermore, the crosslinking proceeded with heat treatment. © 1995 John Wiley & Sons, Inc.     

Barrier properties of blends based on liquid crystalline polymers and polyethylene

Blends of an extrusion‐grade polyethylene and two different liquid crystalline polymers of Vectra type were prepared by melt mixing using poly(ethylene‐comethacrylic acid) as compatibilizer. Oxygen and water vapor permeability, transparency and welding strength of compression molded and film blown specimens were studied. The compression molded blends showed gas permeabilities conforming to the Maxwell equation assuming low permeability liquid crystalline polymer spheres in a high permeability polyethylene matrix. One of the liquid crystalline polymers with suitable rheological properties formed a more continuous phase in the film blown blends and a substantial decrease in oxygen and water vapor permeability was observed in these blends. The compression molded blends with 50% liquid crystalline polymer and some of blow molded blends showed very high gas permeabilities. It is believed that voids forming continuous paths through the structure were present in these samples. The blends showed significantly higher opacity than pure polyethylene.     

Swelling behavior of crosslinked hydroxypropylcellulose films retaining cholesteric liquid crystalline order,II. Effects of temperature,solvent, and pH

Crosslinked hydroxypropylcellulose (HPC) films were cast from the cholesteric liquid crystalline HPC solution in methanol. The films retained the cholesteric liquid crystalline order. The dependences of swelling behavior of our films in water and propanol on temperature and on pH of the solvent were determined. The response of our films to the changes in water, temperature and in pH was discussed. In water, the equilibrium swelling ratio (B_e) decreased with temperature whereas B_e increased with temperature in propanol. For a given composition of water and propanol, B_e was independent of temperature. B_e in the acidic solvents was higher than in the alkaline solvents. The response data to the stepwise change in temperature revealed that the deswelling behavior was more rapid than the swelling behavior in water, and the swelling-deswelling behavior was reversible. The response to the stepwise change in pH was almost the same as that of the change in temperature, but the surface of the film was attacked by the acid and became fluffy with increasing soaking time.     

Effect of film thickness on auto-oxidation in cobalt-catalyzed 1,4-polybutadiene films

Oxygen mass uptake was measured in 1,4-polybutadiene (PB) films undergoing cobalt-catalyzed oxidation in air. Films thicker than approximately 50 μm showed an increase in oxygen uptake per unit polymer mass as film thickness increased, while oxygen uptake per unit film area remained independent of thickness, suggesting that oxidation was heterogeneous and proceeded essentially as an oxidized front penetrating into the film from the surfaces exposed to oxygen. In contrast, oxidation in films thinner than about 28 μm proceeds homogeneously, with oxygen uptake per unit mass being essentially independent of thickness. In oxidized samples, oxygen and nitrogen permeability decreased by more than two orders of magnitude relative to permeability values in unoxidized samples. In thicker films, a two-phase model, based upon high levels of oxidation in a thin skin at the surface of PB and relatively low levels of oxidation in the core of the films, was used to describe gas permeability data and estimate the oxygen and nitrogen permeability in fully oxidized PB.     

The diffusion coefficients of helium,hydrogen, oxygen and nitrogen in water determined from the permeability of a stagnant liquid layer in the quasi-s

At temperatures between 10 and 60°C the diffusion coefficients of helium, hydrogen, oxygen and nitrogen in water have been determined from the permeability of a stagnant liquid layer in the quasi-steady state (SLL method). With this method we actually measure the difference in diffusive flow between two gases through a horizontal stagnant liquid layer between gas-permeable membranes. If oxygen is one of the gases, we are able to determine the diffusion coefficient of oxygen with a maximum experimental error of 3.5% and that of the other gases within 5%. Results are given and compared with experimental values stated in the literature.     

Effect of annealing on the permeation characteristics of gases of coextruded LLDPE films

The temperature dependence of both the permeability and diffusion coefficients of carbon dioxide, oxygen and nitrogen in annealed LLDPE films are studied. It is found that the values of the permeability coefficient through the annealed membranes are nearly four times larger than those through the non-annealed ones. The fact that annealing slightly diminishes the values of the diffusion coefficient leads to the conclusion that the rise in permeability detected in the films by effect of annealing should be attributed to an increase in solubility. The permeability characteristics of the films are interpreted in terms of the free volume theory.     

Rod-rod and rod-coil self-assembly and phase behavior of polypeptide diblock copolymers

Poly(γ-benzyl l-glutamate) (PBLG) forms a rigid helical rod in organic solvents. Cholesteric liquid crystalline ordering of these rods has been observed in PBLG solutions and cast films. In this research, peptidic block copolymers were created using PBLG in order to determine the effect of an added block on the classic cholesteric ordering. Peptide blocks with varied lengths and inherent secondary structures, random coil or rigid rod, were attached to PBLG molecules. The self assembly/liquid crystalline ordering of these molecules in films cast from various organic solvents was probed with transmission electron microscopy (TEM), atomic force microscopy (AFM), and X-ray diffraction (XRD). In pure PBLG and PBLG diblock copolymers with relatively small additional blocks, cholesteric liquid crystalline ordering was observed in bulk films. However, depending on the kinetics of film formation and the amount of non-PBLG block, significant changes in the nanostructure and microstructure were observed. These purely peptidic block molecules provide the opportunity to pattern materials with peptidic functionalities by taking advantage of block copolymer phase behavior and liquid crystal ordering.     

Gas permeation resistance of a perfluoroalkoxy‐tetrafluoroethylene copolymer

The permeation resistance of perfluoroalkoxy (PFA), a polytetrafluoroethylene (PTFE) copolymer, to various gases was explored. The diffusion and permeability coefficients for hydrogen, oxygen, nitrogen, and air were measured with extruded films using standard manometric techniques. For thicker films, transport properties were independent of film thickness. For the thinnest films, the diffusivity and permeability coefficients were slightly higher because of reduced crystallinity. The solubility of these apolar permeants in PFA was quite low and behaved ideally. Therefore, the permeation characteristics of air could be calculated from those of nitrogen and oxygen. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2122–2125, 2006     

Fine structure in cholesteric fingerprint texture observed by scanning electron microscopy

Summary The fine structure in some cholesteric fingerprint textures of cyanoethyl chitosan (CNCS)/acrylic acid solution and photo-solidified CNCS/polyacrylic acid composite film was studied using scanning electron microscopy (SEM), small angle light scattering (SALS) and polarizing optical microscopy (POM). Permanganic etching was developed to reveal the cholesteric liquid crystalline textures in the composite films. A schematic model was presented to explain this kind of fine structure. The directors within each cholesteric molecular layer did not orient in nematic-like order, but varied their orientation by an ill-defined period. Received: 4 October 1999/Revised version: 13 December 1999/Accepted: 24 December 1999     

Gas transport and thermal characterization of mono‐ and di‐polyethylene films used for food packaging

The permeability of carbon dioxide, oxygen, nitrogen, and air through commercial monolayer and multilayer films, based on polyethylene (PE), biaxially oriented polypropylene (BOPP), and polyamide (PA), used for food packaging is reported. The influence of temperature (from 10 to 60°C) on permeability and DSC characteristics changes was also analyzed. Literature data for gas permeability of the mentioned monofilms are quite variable due to differences in additives, thermal history, and crystallinity. In this work, the highest gas permeability is obtained for PE film at the higher temperature (50–60°C). Laminates exhibit different gas permeation behavior from that of monofilms. Generally, gas solubility coefficient increases at higher temperature (with an exception of PA/PE and BOPPcoex.met/PE), being higher for monofilms in comparison with laminates, while diffusion coefficients are lower for monofilms in comparison with laminates. The temperature dependence of the permeability, diffusivity, and solubility of gases shows two different regions in PE, BOPPcoex/PE (10–40°C and 40–60°C), PA/PE, and BOPPcoex.met (10–30°C and 40–60°C) films. Correlation between activation energies for permeation and diffusion as well as heat of sorption and 17 gas properties is performed. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1590–1599, 2006     

Electrocatalytic activity of amorphous RuO2 electrode for oxygen evolution in an aqueous solution

The electrocatalytic activity of amorphous and crystalline RuO₂ thin films for oxygen evolution in an aqueous solution was investigated. The RuO₂ films were prepared on FTO substrates by electrodeposition or RF magnetron sputtering technique. The obtained films were annealed at various temperatures. In both cases, the as-prepared films or the 200 °C annealed film had an amorphous structure, whereas the films annealed at 300 °C and over were crystallized to rutile structure. The analysis of the Tafel slope indicated that the rate-determining step in the oxygen evolution reaction on the amorphous RuO₂ was the combination of the adjacent Ru–OH groups, whereas that on crystalline RuO₂ was the dissociation of O–H bond in Ru–OH group. The onset potentials of the amorphous RuO₂ films for oxygen evolution were shifted toward the negative side by 0.06–0.03 V from those for the rutile crystalline samples. The shift of the onset potential is probably attributed to the structural flexibility which is characteristic of the amorphous surface. This result suggested that the electrocatalytic activity of amorphous RuO₂ for oxygen evolution was higher than that of rutile crystalline RuO₂.     

Preparation,characterization, and permeation property of a liquid crystal/PDMS membrane material

By introducing the ordered and flowing liquid crystalline groups into polymeric membranes, a novel liquid crystal/polydimethylsiloxane (LC/PDMS) membrane material is synthesized with PDMS containing vinyl group, polymethylhydrosiloxane and cholesteric LC as matrix materials. The chemical structure, LC behaviors and mechanical performance of the LC/PDMS crosslinked membranes are characterized by using FTIR, differential scanning calorimetry (DSC), and polarized light microscopy with a hot stage. Some factors on permeability and permselectivity for carbon dioxide and nitrogen gas are also examined. These results suggest that the membrane‐forming property and permeation properties of the crosslinked membranes are obviously enhanced due to the introduction of the LC groups into PDMS and crosslinking reaction in the preparation process. At pressure difference of 0.1 MPa and testing temperature of 40°C, the permeability coefficient for carbon dioxide and ideal separation factor for carbon dioxide and nitrogen are up to 4667 Barrer and 24.0, respectively. In addition, the incorporation of LC containing unsaturated linkage has the potential for further modification reactions such as grafting and crosslinking. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Amorphous hydrogenated carbon films as barrier for gas permeation through polymer films

The influence of amorphous hydrogenated carbon (a-C:H) coatings on the gas permeation through polymer films was investigated. a-C:H films were deposited from a 13.56-MHz RF glow discharge in methane or acetylene atmosphere. Thin poly(ethylene terephthalate) and polyimide foils were used as substrates. The permeation of the gases H₂, N₂, O₂ and CO₂ was measured and the reduction of the permeability coefficient was correlated to composition and density of the a-C:H films. The stoichiometry of the layers was analyzed using ion-beam techniques on films deposited onto silicon samples. The a-C:H/PET surfaces were analyzed using optical microscopy and atomic force microscopy (AFM). Multilayer structures comprising different types of a-C:H films were also investigated. A reduction of the permeability coefficient by 80% for hard, dense and 94% for soft, polymer-like layers was found. Surprisingly, the barrier efficacy of the coating decreases with increasing a-C:H film density. This unexpected result is attributed to the appearance of a network of deep cracks spread out over the whole coating.     

Single and mixed gas diffusion through polyethylene films

In this paper, the results of using a mass spectrometer technique to measure mixed-gas diffusion through polymer films are presented. Mixtures of oxygen, carbon dioxide and nitrogen are diffused through films of polyethylene with different degrees and type of chain branching. It is shown that in the case of pure gases Henry's law applies; the gas concentration is proportional to the partial pressure of gas. It is also demonstrated that there is a reasonable correlation between gas solubilities and the Lennard-Jones force constants, although detailed departures from this behaviour are observed for the different materials.The results show that, in general, the presence of one gas can affect the diffusion and solubility of another, although the solubility and diffusion of carbon dioxide were found to be independent of other gases. In particular, an apparent competition is observed between nitrogen and oxygen in terms of solubility. Moreover, the nature of the interaction between gases depends on the degree of branching and the state of annealing of the polyethylene. Contrary to expectation, it is shown that annealing, whilst increasing the crystallinity, increases the permeability of all gases for the only two samples studied in this regard.