3-dimensional Network Structure Research Articles

Pore structure analysis of swollen dextran-methacrylate hydrogels by SEM and mercury intrusion porosimetry.

The objectives of this study were to visually examine the surface and interior morphology of a new class of biodegradable hydrogels based on dextran-methacrylate and to quantify the porous structure of these hydrogels in swollen state. Two techniques (scanning electron microscopy and mercury intrusion porosimetry) were used to analyze pore structure of dextran-methacrylate hydrogels as a function of the degree of methacrylate substitution. SEM was used to observe 3-dimensional network structure of cryofixed and fractured swollen dextran-methacrylate hydrogels. Image analysis of the SEM data revealed different pore shapes and sizes, depending on the degree of substitution and the location within the hydrogel. A higher methacrylate-substituted dextran hydrogel showed a compact and rigid pore structure, while a lower substituted hydrogel showed a delicate and fragile pore structure. Mercury intrusion porosimetry analysis of the pore structure of dextran-methacrylate hydrogels provided useful and more reliable quantitative data of pore characteristics, such as total pore area, average pore diameter, their distribution, and bulk density. The total pore area and average pore diameter of swollen dextran-methacrylate hydrogels decreased with an increase in degree of methacrylate substitution, while bulk density increased with an increase in degree of substitution.

Pore structure analysis of swollen dextran-methacrylate hydrogels by SEM and mercury intrusion porosimetry

The objectives of this study were to visually examine the surface and interior morphology of a new class of biodegradable hydrogels based on dextran-methacrylate and to quantify the porous structure of these hydrogels in swollen state. Two techniques (scanning electron microscopy and mercury intrusion porosimetry) were used to analyze pore structure of dextran-methacrylate hydrogels as a function of the degree of methacrylate substitution. SEM was used to observe 3-dimensional network structure of cryofixed and fractured swollen dextran-methacrylate hydrogels. Image analysis of the SEM data revealed different pore shapes and sizes, depending on the degree of substitution and the location within the hydrogel. A higher methacrylate-substituted dextran hydrogel showed a compact and rigid pore structure, while a lower substituted hydrogel showed a delicate and fragile pore structure. Mercury intrusion porosimetry analysis of the pore structure of dextran-methacrylate hydrogels provided useful and more reliable quantitative data of pore characteristics, such as total pore area, average pore diameter, their distribution, and bulk density. The total pore area and average pore diameter of swollen dextran-methacrylate hydrogels decreased with an increase in degree of methacrylate substitution, while bulk density increased with an increase in degree of substitution. © 2000 John Wiley & Sons, Inc. J Biomed Mater Res (Appl Biomater) 53: 258–266, 2000

The Effect of Ar+ Ion Bombardment on SiO2 Aerogel Film

Ar+ ion bombardment on SiO2 aerogel films was introduced to investigate the physical collision effect of oxygen plasma treatment on the films. The changes of internal surface adsorbing species and microstructure in the films were analyzed through the treatments. Through chemically inert Ar+ ion bombarding treatment, internal surface organic groups were partially removed. A slight increase in surface particle size was observed, which results from the condensation of SiO2 particles due to the elimination of internal surface adsorbing organics. According to the increase in the accelerating voltage of Ar+ ion, the reduction of film thickness became larger than that observed with oxygen plasma treatment. The film thickness is maintained uniform with varying the treatment time and this confirms that there is no measurable etching happened within our treatment conditions. From these it is confirmed that a collapse of 3-dimensional network structure of SiO2 aerogel film was happened though Ar+ ion bombarding treatment.

Solid-state humidity sensors

Two types, EMF and impedance, of solid-state humidity sensors based on various oxide hydrates/hydroxides with 2-dimensional (2D) layered and 3-dimensional (3D) network structures are reviewed. Selected humidity sensors based on proton-conducting NASICON (HZr 2P 3O 12) as well as sensors based on β-Ca(PO 3) 2 are discussed in detail.

Quantitative analysis on swelling behavior of ionic gels in the mixed solvents

Phase transition was observed in HSMA/PVA IPN gels having ionizable groups with 3-dimensional network structure in the mixed solvents such as water-methanol. water-acetone or water-ethanol. In order to analyze this phenomena quantitatively, two adjustable parameters related to gel properties were determined from the model based on Tanaka theory. One was the number of dissociated counterions per effective chain (f). the other was the interaction parameters (xjj) between gel and water. As increasing the composition of water, swelling of the gels occurs in the mixed solvent; the gel was shrunk instead when the water content was decreased, which was reversible regardless of the path of swelling and shrinking. A degree of swelling or shrinking of the gel was dependent upon theseX ijand f of the gel. With smallerX n and larger f. more rapid phase transition was observed. Additionally, swelling and shrinking behavior of the gel in system of two solvents and one polymer was influenced not only byx ij between gel and solvents but also by xij between two solvents.

Characterization of Dispersions

Abstract The methods of pigment dispersion analysis have been reviewed in regard to their application to rubber, plastics, and other vehicle systems. The characteristics of dispersions have been divided into three categories: (1) agglomeration (2) microdispersion (networking) and (3) polymer-phase distribution. Stylus roughness measurements on cut surfaces offer the combination of simplicity and speed of operation with high accuracy and precision for measuring pigment agglomeration in elastomer systems of known composition. This method may also be applied to the surface of thin plastic extrudates. However, optical analyses of thin cryosections are preferred for most plastics or unknown rubber compounds containing high loadings of carbon black. X-radiography is generally preferable for the analysis of inorganic agglomeration in most polymeric vehicle systems. The scanning electron microscope is also applicable for this type of analysis and has the added capability of identifying unknown agglomerates by energy dispersive x-ray analysis. Automated image-analysis techniques may also be utilized in conjunction with microscopical methods for quantifying the agglomeration of most types of pigments. For carbon blacks, the most suitable materials for on-line image analyses with transmitted light are plastics, paints, and inks which contain low black loadings. Higher carbon-black loadings in rubber can be analyzed by incident light using metallographic polishing of sulfur-hardened specimens. The microdispersion of carbon blacks at the primary aggregate level can be measured by means of electrical conductivity. This method is not applicable to inorganic pigments, large-particle-size carbon blacks, or blacks at very high or low loadings. Pigment microdispersion in different vehicle systems may also be assessed by means of scanning electron microscopy of thick cross sections (plasma etched to enhance contrast) or by transmission electron microscopy of thin cryosections. The tendency for the finer pigments to form 3-dimensional network structures in elastomers may also be measured as a function of the augmentation of dynamic modulus from high to low strain amplitudes. Pigment phase distribution in elastomer blends may be studied by scanning electron microscopy or transmission electron microscopy of thin cryosections, in conjunction with a staining or etching procedure to produce contrast between the separate polymer components. Selective staining is applicable to blends of polymers which differ significantly in their relative levels of unsaturation (e.g., NR/CIIR). Pyrolytic etching (under vacuum) may be used to produce interzone contrast in blends of polymers which differ significantly in their resistance to thermal degradation (e.g., NR/BR, NR/SBR). Pyrolysis GC may be utilized to determine the amount of carbon black in the separate phases of certain elastomer blends. This method is based on the relative intensity of the primary GC peaks for the individual polymers. The chromatographs are obtained from the bound rubber (carbon-polymer gel) that is developed during the mixing of the compound.

Radiation induced grafting of mixed monomers onto polyester and polypropylene fibers

Grafting of the mixture of acrylamide and acrylic acid onto polyester and polypropylene fibers and mixture of acrylic acid and methacrylic acid onto polypropylene by the radiation method are reported. It is observed that when pure acrylamide was used for grafting, the grafting extent was small, whereas when the mixture was used, the amount of acrylamide content in the copolymer was found to be more than the feed ratios. The results are explained on the basis of chain transfer mechanism. With methacrylic acid and acrylic acid mixtures, the rate of grafting decreased with the increase in the concentration of acrylic acid in the feed ratio, and this has been explained on the basis of the formation of either a 3-dimensional network structure or a highly branched structure involving backbone polymer molecules with acrylic acid, which prevents the diffusion of the monomer from the solution phase to the swollen phase.