Increase In D-spacing Research Articles

Synthesis and characterization of a novel chitosan/montmorillonite/hydroxyapatite nanocomposite for bone tissue engineering

Recently, biopolymer-based nanocomposites have been replacing synthetic polymer composites for various biomedical applications. This is often because of the biocompatible and biodegradable behavior of natural polymers. Several studies have been reported pertaining to the synthesis and characterization of chitosan(chi)/montmorillonite(MMT) and chitosan (chi)/hydroxyapatite (HAP) for tissue engineering applications. In the present work, a biopolymer-based novel nanocomposite chitosan/montmorillonite (MMT)/hydroxyapatite (HAP) was developed for biomedical applications. The composite was prepared from chitosan, unmodified MMT and HAP precipitate in aqueous media. The properties of the composites were investigated using x-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM) and thermogravimetric analysis (TGA). Nanomechanical properties were measured using nanoindentation. Cell culture experiments were also conducted in order to ascertain the biocompatibility of the composite. The XRD results indicate that an intercalated structure was formed with an increase in d-spacing of montmorillonite. FTIR studies provide the evidence of molecular interaction among the three different constituents of the composite. AFM images show well-distributed nanoparticles in the chitosan matrix. The composites also exhibit a significant enhancement in nanomechanical property as compared to pure chitosan as well as the chi/HAP and chi/MMT composites. The TGA results indicate that an intercalated nanocomposite was formed with improved thermal properties even compared to chi/MMT composites. The results of cell culture experiments show that the composite is biocompatible and has a better cell proliferation rate compared to chi/HAP composites. This work represents the design of a novel clay–chitosan–hydroxyapatite composite with improved mechanical properties that has potential applications in bone tissue engineering.

Characterisation of Chitosan-Coated Vesicles Encapsulating DNA Suitable for Gene Delivery

Encapsulation of DNA (varying type and molecular weight) in vesicles (dehydration-rehydration vesicles; DRV) prepared from zwitterionic phospholipids using the dehydration-rehydration method was determined to be in the range of 10-90%. Encapsulation was dependent on the amount of DNA added but not its molecular weight. Zeta potential measurements of the DRV suggested that DNA was associated with the vesicles exterior, while small angle neutron scattering (SANS) studies indicated that DNA was trapped in the interlamellar water space between lipid bilayers-as evidenced by a slight decrease in bilayer thickness and an increase in d-spacing. Circular dichroism measurements determined the conformation of the DNA in the DRV was not the usual B-form but rather a structure more reminiscent of the less hydrated, C-form, supporting the suggestion that DNA was present in the interlamellar water space. DRV were successfully coated with chitosan as evidenced by SANS studies and zeta potential measurements. The amount of chitosan coating the DRV [quantified by ultra violet (UV)/Vis spectroscopy] was dependent upon the starting concentration of chitosan and independent of the presence of DNA. Chitosan-coated DRV containing DNA exhibited an improved size stability while 'empty' uncoated vesicles were poorly stable. A coating of chitosan reduced the amount of DNA leaking from the vesicles.

Spatially resolved strain measurements in Mo-alloy micropillars by differential aperture x-ray microscopy

Spatially resolved strain distributions in the NiAl matrix and the ∼550–1000 nm Mo fibers of a NiAl–Mo eutectic were investigated by microbeam x-ray diffraction. Position sensitive d-spacings for the individual phases were obtained from spatially resolved and energy-resolved Laue patterns. For embedded Mo fibers, the measured elastic strain is consistent with the predicted thermal mismatch strain between the NiAl and Mo phases. However, when the NiAl matrix is etched back to expose Mo micropillars, the d-spacing increases to that of unconstrained Mo, indicating release of the compressive residual strain in the Mo fibers.

Preparation and crystalline morphology of biodegradable starch/clay nanocomposites

An organically modified clay (o-clay) and a pristine clay (p-clay) were used to prepare biodegradable thermoplastic starch (TPS)/clay nanocomposites by melt processing. The gelatinization behaviour of starch with glycerol/H2O was investigated and the gelatinized temperature (Tgel) was determined using a polarized optical microscopy (POM) equipped with a hot stage. The morphologies of gelatinized starch and extruded starch were revealed by scanning electron microscopy (SEM). Thermal stabilities of starch/clay nanocomposites were evaluated under N2 atmosphere using thermogravimetric analysis (TGA). Transparent films of starch/clay hybrids were fabricated by hot pressing. Intercalation of starch into clay galleries and crystalline structure of starch were investigated using X-ray diffraction (XRD). It was found that the increase in d-spacing of organically modified clay was due to starch molecular intercalation while the increase in d-spacing of pristine clay was mostly caused by glycerol intercalation because of the narrow valid d-spacing of pristine clay and special ring-like monomer of starch. The mechanism of starch intercalation in clay galleries was discussed.

The Swelling Behavior of Organoclays

Natural clay minerals are ideal nanofillers for polymer materials and have been attracted tremendous research and development interests in the past decade. The manufacture of clay nanofillers relies largely on the exfoliation of clay particle into individual clay platelets. Thus, understanding the interlayer swelling of clay minerals upon the adsorption of surfactants is important to the fabrication and design of polymer nanocomposites. This paper reports our recent experimental and theoretical studies on a variety of organoclays that show a linear relationship between the increase of d-spacing and the mass ratio between organic and clay.

Degradation and stability of polyaniline on exposure to electron beam irradiation (structure–property relationship)

Polyaniline (PAni) was prepared by electrochemical polymerization and subjected to different doses of electron beam (EB) irradiation. The effect of EB irradiation causes both chain scission and cross-linking process in PAni, which depends on irradiation dose. The degree of chain scission and cross-linking in PAni by EB irradiation is characterized through XRD, TGA, DSC, solubility, EPR and electrical properties measurement. The results reveal that with increase in EB irradiation dose from 0 to 150 kGy DC and AC conductivity and dielectric constant are found to increase mainly due to the chain scission or further doping in PAni. Due to irradiation there is change in the structure of PAni, such as decrease in the d-spacing, inter-chain separation, thermal stability and T g but increase in the percent crystallinity and solubility. With further increase in the EB irradiation dose from 150 kGy onwards the DC and AC conductivity and dielectric constant are decreased due to the cross-link formation or dedoping in PAni, which causes the decrease in percentage of crystallinity and solubility and increase in d-spacing, inter-chain separation, thermal stability and T g of PAni.

Effect of clay–water interactions on clay swelling by X-ray diffraction

Clay swelling is a very common phenomenon observed in sedimentary rocks and soils. It is one of the major causes for permeability reduction in hydrocarbon reservoirs. The aim of this work is to characterize the swelling behavior of bentonite and of two clays from Brazilian petrolific basins. X-ray diffraction (XRD) was used to quantify the swelling characteristics of these clays under contact with salt solutions, as in the reservoir. The measurement of interplanar spacing of the swollen clay was measured 24 h after the preparation of the paste. Their diffractograms displayed well-defined peaks at low angles, even for (0 0 1) d-spacing values larger than 50 Å. Two types of mechanisms for clay swelling were identified: crystalline swelling (limited d-spacing increase) and osmotic swelling (large d-spacing values). The critical salt concentration (CSC) value, i.e., the salt concentration at which clay changes from crystalline to osmotic swelling, was obtained. The method used in this work allows one to determine the compatibility between reservoir clays and foreign fluids and to avoid the osmotic swelling conditions that can cause permeability reduction in natural hydrocarbon reservoirs.

Preparation and properties of a poly(2-cyano-1,4-phenylene terephthalamide)/layered silicate nanocomposite

The in situ polymerization method was used to prepare a poly(2-cyano-1,4-phenylene terephthalamide)/layered silicate nanocomposite with organically-modified clay (Cloisite® 30B, southern clay), which was spun into well-oriented fibers and cast into film in the lyotropic and isotropic state, respectively. The degradation temperature of the nanocomposite (∼550°C) was similar to that of poly (2-cyano-1,4-phenylene terephthalamide) and its strength (and modulus) linearly increased with the amount of the layered silicate in the nanocomposite. The intercalated structure was observed using transmission electron microscopy and X-ray diffraction with an increase in d-spacing of the layered silicate from 18.7 Å (the organically modified layered silicate; cliosite 30B) to 21.1 Å (nanocomposite). The layered silicate in the nanocomposite was well oriented during fiber spinning and film casting. The normal of the surface of the layered silicate was perpendicular to the fiber axis and the surface of the cast film. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 640–645, 2006

The interlayer swelling and molecular packing in organoclays

Understanding the interlayer swelling and molecular packing in organoclays is important to the formation and design of polymer nanocomposites. This paper presents recent experimental and molecular simulation studies on a variety of organoclays that show a linear relationship between the increase of d-spacing and the mass ratio between organic and clay. A denser molecular packing is observed in organoclays containing surfactants with hydroxyl–ethyl units. Moreover, our simulation results show that the head (nitrogen) groups are essentially tethered to the clay surface while the long hydrocarbon chains tend to adopt a layering structure with disordered conformation, which contrasts with the previous assumptions of either the chains lying parallel to the clay surface or being tilted at rather precise angles.

Control of fluorescence emission color of benzo 15-crown-5 ether substituted oligo phenylene vinylene–ceramic nanocomposites

Nanocomposites of benzo 15-crown-5 ether substituted oligo phenylene vinylene (CE–OPV) were prepared by solution intercalation into a surface treated bentone clay, B34, in both the presence and absence of Eu 3+ ions, and were characterized using X-ray diffraction (XRD) and fluorescence techniques. The intercalation of B34 by CE-OPV increases the d-spacing (gallery height) of B34, the increase being more in the presence of metal ion than in its absence. The increase in d-spacing of a related material, poly[1,4,-(2,5-bis (tetra ethylene oxide substituted)) phenylene vinylene (EO-PPV)] due to intercalation into clay is greater than that by CE-OPV. Results on intercalation of small benzo-crown ether molecules themselves into B34 in the presence and absence of Eu 3+, are also presented to help elucidate the process. The fluorescence emission maxima of the nanocomposites of CE-OPV, CE-OPV-Eu 3+ and EO-PPV showed a steady blue shift as a function of B34 composition and the results are explained in terms of partial intercalation of the fluorophores into the clay.

Structure development and isothermal crystallization behaviour of compatibilized PET/expandable fluorine mica hybrid nanocomposite

The compatibilized PET/expandable fluorine mica (ME) hybrid nanocomposite (CN) prepared by in situ polymerization technique showed a partially exfoliated structure of ME in PET matrix by XRD analysis, owing to its broad crystalline peak accompanied by an increase of d-spacing as compared to PET/ME uncompatibilized composite (UC). The analysis by TEM revealed a better dispersion of ME in PET for CN as compared to aggregates of ME in case of UC. Further, the isothermal crystallization behaviour studied using DSC for the same at different crystallization temperature (T c,) revealed a significant decrease of crystallization half time and remarkable increase of crystallization rates (almost 2 times than pure PET) for CN in contrast to UC. The Avrami exponent n lowered to 2.3 for CN as compared to 3.1-3.4 for pure PET at various T c. The activation energy (E a) determined from Arrhenius equation reduced dramatically for CN. These various observations could be explained based on the nucleation efficiency by ME accompanied by different crystallization/growth process occurring in case of hybrid nanocomposite.

The effect of crystallization on the structure and morphology of polypropylene/clay nanocomposites

AbstractThe effect of crystallization on the structure and morphology of maleic anhydride grafted polypropylene (PP‐MA)/clay (montmorillonite) nanocomposites (PPCNs) is presented. Wide‐angle X‐ray diffraction (WAXD) measurements of PPCNs crystallized at different temperatures show that the extent of intercalation increases with the crystallization temperature. The enhancement of intercalation occurs with lower clay content PPCNs, and maximum intercalation takes place for 4 wt% clay content. The mechanism of intercalation has been proposed through crystallization. Excess γ‐form of the crystallite of PP‐MA appears in presence of clay, possibly because of the confinement of the polymer chain between the clay particles. WAXD data also reveals that d‐spacing increases gradually with clay content. The decrease of spherulitic size is observed with increasing clay content, which indicates that clay particles act as nucleating agents. Lamellar textures have been explored by using small angle X‐ray scattering (SAXS) and transmission electron microscopy (TEM), which exhibit that both the lamellar thickness and long period of the PPCNs are higher than those of PP‐MA.

Intercalation of alcohols in Ag sulfonates: topotactic behavior despite flexible layers.

This article presents the inaugural intercalation study of a layered metal sulfonate network. Silver triflate forms intercalation complexes with straight chain primary alcohols from ethanol (C(2)H(5)OH) to eicosanol (C(20)H(41)OH). Single-crystal data for the EtOH adduct, 1, are presented which show that the intercalation is coordinative to Ag. In contrast to many other layered hosts, no preheating of Ag triflate is required to liberate a coordination site for intercalation to take place, owing to the ability of the triflate ion to reorient. Crystal structure parameters for 1: C(4)H(6)F(6)S(2)O(7)Ag(2), a = 5.345(7) A, b = 11.310(2) A, c = 12.004(2) A, alpha = 116.87(1) degrees, beta = 90.46(1) degrees, gamma = 99.59(1) degrees, triclinic, space group P, Z = 2. Intercalate 1 presents the triflate ion in an unprecedented mu(5)-coordination mode. PXRD data on the family of complexes show that the intercalation is topotactic, as verified by the linear increase in d-spacing and calculated c-axis lengths for the intercalates, with increasing chain length. The data also show that the alcohol intercalates adopt an interdigitated rather than bilayer arrangement.

Structure and Dynamic Viscoelastic Properties of Acylated Chitosans in the Melt State.

Rheological properties of acylated chitosans with various acyl lengths were measured in the melt state. The acylated chitosans have two rheological transitions corresponding to rather abrupt decreases in viscoelastic functions and an abrupt drop in the height of plateau of the storage modulus. These transition temperatures become lower with increasing length of side chains. The time-temperature superposition principle was applied to dynamic viscoelastic functions for acylated chitosans. The time-temperature superposition fails for acylated chitosans with shorter acyl length. However, for an acylated chitosan with the longest acyl length, the viscoelastic data can be superposed into three separated master curves in different temperature ranges. Wide-angle X-ray diffraction measurements indicate that acylated chitosans have a layered structure. Temperature dependencies of d-spacing attributable to this layered structure indicate two transitions, whose temperatures reasonably correspond to those of the rheological transitions, exist. When the temperature exceeds the lower transition temperature, the d-spacing increases with increasing temperature, and the transition temperatures decrease with increasing length of side chains. The decreases of dynamic viscoelastic functions are associated with the layer spacing changes. It is suggested that the abrupt decrease of the plateau height is caused by the interchain movement of molecules or reorganization of the structure.