Phase densities and lamellar morphologies of semicrystalline polyethylenesviaabsolute small-angle X-ray scattering measurements

With the crystalline volume fraction from small-angle X-ray scattering (SAXS) and the density of the crystalline phase from wide-angle X-ray diffraction, the amorphous phase density of two representative polyethylenes was calculated as a function of temperature using the absolute total SAXS scattering power or invariant. The density of the amorphous phase in semicrystalline polyethylene is crystallinity independent and is lower than melt-extrapolated values reported in the literature. Model-independent SAXS-based crystallinity values can be calculated with the aid of the densities of the crystalline and amorphous phase and the absolute SAXS invariant. Such model-independent crystallinity values can be used in SAXS curve-shape analysis procedures to obtain the average thickness of the crystalline and amorphous layers also in the case of non-ideal lamellar semicrystalline polymer morphologies for which the number-average long period cannot be retrieved from the maxima in correlation functions or interface distribution functions.

Bone nanostructure near titanium and porous tantalum implants studied by scanning small angle x-ray scattering

Bone sections including either titanium or porous tantalum implant devices used for interbody spinal fusion were investigated with position-resolved small angle X-ray scattering (sSAXS). The samples were obtained from six-month-old pigs that had undergone surgery three months prior to sacrifice. The aim of the study was to explore the possibility of using sSAXS to obtain information about thickness, orientation and shape/arrangement of the mineral crystals in bone near the implant surfaces. Detailed sSAXS scans were carried out in two different regions of bone adjacent to the implant in each of the implant samples. In the implant vicinity the mineral crystals tended to be aligned with the surface of the implants. The mean crystal thickness was between 2.1 and 3.0 nm. The mineral crystal thickness increased linearly with distance from the implant in both regions of the porous tantalum implant and in one of the regions in the titanium sample. In the second region of the titanium sample the thickest mineral crystals were found close to the implant surface. The observed differences in mineral thickness with distance from the implant surfaces might be explained by differences in mechanical load induced by the implant material and the geometrical design of the implant. The study shows that sSAXS is a powerful tool to characterize the nanostructure of bone near implant surfaces.

Nanostructure of the neurocentral growth plate: Insight from scanning small angle X-ray scattering, atomic force microscopy and scanning electron microscopy

In this study, the experimental techniques scanning electron microscopy (SEM) including energy-dispersive X-ray analysis, atomic force microscopy (AFM) and scanning small angle X-ray scattering (SAXS) have been exploited to characterize the organization of large molecules and nanocrystallites in and around the neurocentral growth plate (NGP) of a pig vertebrae L4. The techniques offer unique complementary information on the nano- to micrometer length scale and provide new insight in the changes in the matrix structure during endochondral bone formation. AFM and SEM imaging of the NGP reveal a fibrous network likely to consist of collagen type II and proteoglycans. High-resolution AFM imaging shows that the fibers have a diameter of approximately 100 nm and periodic features along the fibers with a periodicity of 50-70 nm. This is consistent with the SAXS analysis that yields a cross-sectional diameter of the fibers in the range of 90 to 112 nm and a predominant orientation in the longitudinal direction of the NGP. Furthermore, we find inhomogeneities around 7 nm in the NGP by SAXS analysis. Moving towards the bone in the direction perpendicular to the growth plate, a systematic change in apparent thickness is observed, while the large-scale structural features remain constant. In the region of bone, the apparent thickness equals the mean mineral thickness and increases from 2 nm to approximately 3.5 nm as a function distance from the NGP. The mineral particles are organized as plates in a rather compact network structure. We have demonstrated that SEM, AFM and SAXS are valuable tools for the investigation of the organization of large molecules and nanocrystallites in the NGP and adjacent trabecular bone. Our findings will be an important basis for future work into identifying the defects on nanometer length scale responsible for idiopathic scoliosis and other growth-plate-related diseases.

Preparation temperature dependence of size and polydispersity of alkylthiol monolayer protected gold clusters

The influence of preparation temperature on the size and size distribution of dodecylthiol monolayer protected gold clusters was studied. The monolayer protected clusters (MPCs) were synthesized by two different variations of the Brust-Schiffrin procedure. In all of the experiments, the stoichiometry of the reactants dodecylthiol, HAuCl(4), and sodium borohydride was kept constant, while the temperature was varied in the range of -18 to +90 degrees C. Two series were performed in which an aqueous solution of NaBH(4) was either added over 30 s or all in one portion. The size and size distribution of the MPCs were determined by small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). It has been demonstrated that in general the MPC size increases with elevated preparation temperatures.

Bulk microphase segregation of an asymmetric organometallic-inorganic diblock copolymer: a remarkable example of concentric cylinders

We report that an asymmetric diblock copolymer, poly(ferrocenyldimethylsilane-b-dimethylsiloxane) (PFS90-b-PDMS900, PDI = 1.01, volume fraction PFS = 0.20), self-assembles in the bulk state to form a hexagonal periodic structure with a remarkable morphology. Part of the major component forms the core of concentric cylinders with a mean diameter of 35.5 nm surrounded by a 7 nm thick shell of PFS. The remaining PDMS fills the interstitial spaces. The morphology was elucidated by small-angle X-ray scattering, as well as by scanning and conventional transmission electron microscopy.