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Understanding the dynamic behavior of hydrogel formation induced by a temperature ramp is essential for the design of gel-based injectable formulation as drug-delivery vehicles. In this study, the dynamic behavior of the hydrogel formation of Pluronic F108 aqueous solutions within different heating rates was explored in both macroscopic and microscopic views. It was discovered that when the heating rate is increased, the gelation temperature window (hard gel region) shrinks and the mechanical strength of the hydrogel decreases. A given system at different heating rates would lead to different crystalline structural evolutions. The time-resolved small-angle X-ray scattering (SAXS) experiments at a heating rate of 10 °C/min disclose that the crystalline structure of micelle packing in the hydrogel exhibits a series of transitions: hexagonal close-packed (HCP) to face-centered cubic (FCC) and body-centered cubic (BCC) structures coexisting and then to the BCC structure along with the increasing temperature. For the system at equilibrium, the BCC structure exclusively dominates the system. Furthermore, the addition of a hydrophobic model drug (ibuprofen) to the F108 aqueous solution promotes hard gel formation at even lower temperatures and concentrations of F108. The SAXS results for the system with ibuprofen at a heating rate of 10 °C/min demonstrate a mixture of FCC and BCC structures coexisting over the whole gelation window compared to the BCC structure that exclusively dominates the system at equilibrium. The addition of ibuprofen would alter the structural evolution to change the delivery path of the encapsulated drug, which is significantly related to the performance of drug release.

In this study, small-angle X-ray scattering (SAXS) is successfully employed to investigate the structure of the DPPC/diC7PC disc-shaped bicelles incorporated with different amounts of C16-PEG2000-Ceramide lipids. The incorporation of the C16-PEG2000-Ceramide lipids could provide an antifouling capability to the bicelle for biomedical applications. However, traditionally it is believed that most of the incorporated PEGlylated lipids should lie in the rim of the disc-shaped bicelle. In this study, high sensitivity SAXS reveals the distribution of the added C16-PEG2000-Ceramide lipids in both the planar region and in the rim of the bicelle. The PEG brushes of C16-PEG2000-Ceramide lipids form a second shell outside the lipid headgroup shell of the bicelle. A double shell disc bicelle model is used in analyzing the SAXS data. The lipid density of C16-PEG2000-Ceramide in the rim is found to be about 1.7 times the C16-PEG2000-Ceramide lipid density in the planar region for all three C16-PEG2000-Ceramide concentrations, 1, 2, and 3 mM. Moreover, the bicelle core radius can be predicted well using the actual molecular ratio of lipids in the planar region to the lipids in the rim of the bicelles in the model calculation.

The diblock copolymer polystyrene-block-poly(N-methyl 4-vinylpyridine iodide) (PS-b-P4VPQ) with the molecular weight of PS 3.5 × 103 g/mol and P4VPQ 11.6 × 103 g/mol forms core-shell polymer micelles in aqueous solution. The cationic brush shell of the polymer micelle can be used to accommodate hydrophilic drugs and biomolecules, such as DNA, for biomedical applications. It is essential to understand how biomolecules are adsorbed within the brush layer. Here we investigated the interaction of the cationic brush of the polymer micelle with DNA by small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). It is found when adding only relatively small amounts of on average 30 base pairs (bp) DNA, at 19.6 and 39.2 μM for 0.1 mM PS-b-P4VPQ, most of the polymer micelle/DNA complexes remain well dispersed. The brush layer of the polymer micelles are slightly swelled due to the adsorption of DNA within the brush layer. When the DNA concentration is increased to 58.8 μM or higher, the polymer micelle/DNA complexes form closely packed agglomerates. At high DNA concentrations, some adsorbed DNA will start to build up at the edge or surface of the brush layer which could induce aggregation of the polymer micelle/DNA complexes. This means that it is possible to prepare mostly dispersed polymer/DNA complexes by keeping the DNA concentration below the aggregation concentration. The well dispersed polymer micelle/DNA complexes are advantageous for many DNA related biomedical applications.

The binary P123 + F108, + F98, + F88, + F68, + F87 and + P84 systems were used to systematically explore the effect of molecular weight and hydrophobicity of Pluronic on the tendency of cooperative binding between parent copolymers and solubility of drug (ibuprofen) in these mixed Pluronic systems. Temperature-dependent co-micellization process in these systems was carefully investigated by using high sensitivity differential scanning calorimeter (HSDSC), dynamic light scattering (DLS) and small angle X-ray scattering (SAXS). All the HSDSC thermograms for these systems consistently exhibit two endothermic (micellization) peaks apart by at least 13.3 °C. It was evidenced that micelles are mainly formed by P123, the copolymer with a lower critical micelle temperature (CMT), at low temperatures. Raising temperature would dehydrate the other Pluronic with a higher CMT to be integrated into the neat P123 micelles developed at low temperatures. When the temperature is further increased beyond the second endothermic peak, the mixed micelles with a two-shell structure and characteristic corona lengths of their parent copolymers are observed to prove the existence of cooperative binding between parent copolymers. All the binary mixed Pluronic systems used in this study exhibit cooperative binding to form unimodal distribution of mixed micelles, except the P123 + F68 system. The SAXS results show that P123 + F68 system at 65 °C exhibits bimodal distribution of aggregates with coexisting of neat F68 micelles (65% in number) and P123 + F68 mixed micelles (35% in number). It is interesting to find out that P123 and F68 with distinct polypropylene oxide (PPO) moieties (i.e., a difference of 37 PO units) would exhibit very weak cooperative binding to partially form mixed micelles. Addition of ibuprofen in the P123 + F68 system would substantially enhance the cooperative binding between P123 and F68 to form bimodal distribution of aggregates with coexisting of neat F68 micelles (drops down to 30% in number) and P123 + F68 mixed micelles (increases up to 70% in number). For the systems with ibuprofen incorporated, SAXS results demonstrate that the drug is mainly encapsulated in the core of neat micelles developed at low temperatures. The solubility of ibuprofen in the 0.5 wt% P123 + 0.368 wt% P84 system is as high as 2.62 mg/ml, which is 114 times more than that in pure water at 37 °C.

The β-amyloid peptide (Aβ) (1–40) is one of the major components that form Alzheimer's amyloid deposits. Studies of the membrane insertion of amyloid showed that amyloid is surface active and can insert into lipid monolayers [Ji et al. (2002). Biochemistry (Moscow), 67, 1283–1288; Ege & Lee (2004). Biophys. J. 87, 1732–1740]. The interaction between the peptide and a lipid monolayer or bilayer is critical to the understanding of the formation of amyloid peptide deposits on the membrane. In this paper, we have studied the structural transition of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) multibilayers with the insertion of amyloid peptide 1–40 by grazing-incidence small-angle X-ray scattering at different bilayer hydration levels (changing the relatively humidity). We mixed the DPPC and amyloid peptide in an organic solvent at a 10 to 1 weight ratio, then cast it onto a silicon wafer to form the mixed lipid multibilayer film. In this study of the pure DPPC multibilayer film and the DPPC multibilayer film inserted with amyloid peptide, it was found that the hydration process was bimodal with a better-hydrated top layer and a less-hydrated bottom layer. The gel-to-ripple phase transition suffers a strong confinement effect due to the presence of the solid substrate. With the insertion of the amyloid peptide, the ripple phase of the membrane bilayers was suppressed at high humidity and the whole film can be swollen more uniformly at lower incubation time than the pure DPPC film supported on a silicon wafer. This means water vapor can penetrate more easily into the DPPC bilayers inserted with Aβ than into the pure DPPC bilayers. Amyloid peptides were found to form clusters in the bilayer and possess in-plane correlation. From analyzing the diffuse scattering around the Bragg peak in the lateral direction, the amyloid peptides are found to form clusters in the bilayer with a radius of about 9 nm. It is also estimated that the number of Aβ molecules in one cluster is about 12 and on average each Aβ molecule occupies an interface area of about 22 nm2. As the relative humidity exceeds about 94%, the Aβ clusters seem to develop an ordered structure with a spacing of about 300 A.

Small-angle X-ray scattering was used to characterize the size and aggregation behavior of the Pt nanoparticles synthesized by the polyol process and the unusual poly(N-vinyl-2-pyrrolidone) (PVP) reduction. With formaldehyde (HCHO) as the reduction agent, the Pt nanoparticles synthesized in aqueous solutions with a high PVP/PtCl4 weight ratio were characterized by short rods with a 70% polydispersity in rod length. The size and size distribution of the rod-like Pt nanoparticles (3 nm in rod length and 2 nm in rod diameter) are consistent with the corresponding transmission electron microscopy image. With a comparable PVP/PtCl4 weight ratio in the aqueous solution containing HCHO, the high number density of reduced Pt nanoparticles led to a fractal-like aggregation with a fractal dimension of 2.1 and a correlation length of ~30 nm. We also demonstrated that Pt nanoparticles can be synthesized by PVP reduction at 323 K without HCHO. The particle size and the clustering behavior of the Pt nanoparticles reduced by PVP are closely related to the PVP concentration in the solution. Both the Pt nanoparticles synthesized in the commonly used polyol process and the unusual PVP reduction form fractal-like clusters via the PVP–metal nanoparticle association when the number density of the Pt nanoparticles in the solutions is high.

A SWAXS (small- and wide-angle X-ray scattering) instrument was recently installed at the wiggler beamline BL17B3 of the National Synchrotron Radiation Research Center (NSRRC), Taiwan. The instrument, which is designed for studies of static and dynamic nanostructures and correlations between the nano (ormeso) structure (SAXS) and crystalline structure (WAXS), provides a flux of 1010–1011photon s−1at the sample at energies between 5 and 14 keV. With a SAXS area detector and a WAXS linear detector connected to two data acquisition systems operated in master–slave mode, the instrument allows one to perform time-resolved as well as anomalous scattering measurements. Data reduction algorithms have been developed for rapid processing of the large SWAXS data sets collected during time-resolved measurements. The performance of the instrument is illustrated by examples taken from different classes of ongoing projects: (i) time-resolved SAXS/WAXS/differential scanning calorimetry (DSC) with a time resolution of 10 s on a semicrystalline poly(hexamethylene terephthalate) sample, (ii) anomalous SAXS/WAXS measurements on a nanoparticulate PtRu catalyst, and (iii) grazing-incidence SAXS of a monolayer of oriented semiconductor quantum wires, and humidity-controlled ordering of Alamethicin peptides embedded in an oriented lipid membrane.

Nonisothermal crystallizations of polycaprolactone (PCL) in the presence of poly(vinyl chloride) (PVC) at a cooling rate of 0.5 °C/min from 90 to 30 °C under supercritical CO2 at a constant pressure 304 atm were investigated. DSC and SAXS data found that the nonisothermal crystallizations of the PCL/PVC blends under supercritical CO2 resulted in decrease in thickness of the crystalline layers in the lamellar stacks. These nonisothermal supercritical CO2 treatments also generated a morphological heterogeneity with size (13.8 nm for pure PCL) larger than the long period (12.1 nm) of the lamellar stacks. The size of this heterogeneity was slightly enhanced from 13.8 nm for pure PCL to 15.2 and 16.3 nm for the blends containing 10 and 25 wt % PVC, respectively.

Structural characteristics of optical quality poly(2-methoxy-5-(2'-ethylhexyloxy)-1,4-phen- ylenevinylene) (MEH-PPV) films drop-cast from toluene solutions have been examined by use of wide- angle (WAXS) and small-angle X-ray scattering (SAXS) as well as field-emission scanning electron microscopy. For the as-cast film SAXS and WAXS patterns clearly suggest existence of nanodomains of mesomorphic order. Under grazing incidence, both SAXS and WAXS patterns of the as-cast film exhibit impressive uniaxial symmetry with strong scattering along the film normal; however, the corresponding normal-incidence patterns are circularly isotropic, implying in-plane random orientation. A structural model consisting of preferentially uniaxial-oriented nanodomains and disordered matrix is therefore proposed for the as-cast film. Annealing at 210 °C results in disorientation of nanodomains: this decrease in structural asymmetry upon heat treatment correlates well with concomitant changes in charge transport behavior determined from time-of-flight measurements, manifesting dramatically decreased charge mobility as well as transition from nondispersive to dispersive modes.

We have studied the structure and phase transition characteristics of the fullerenes (C 60 )-embedded lipid bilayers. With small-angle neutron scattering (SANS), we have observed a degradation of bilayer ordering and a suppression effect on the phase transitions of the host vesicle bilayers of dipalmitoylphosphatidylcholine (DPPC), due to the embedment of fullerenes. The fullerene-embedded lipid system with substrate-oriented bilayers is also investigated using X-ray reflectivity and grazing incident small-angle X-ray scattering (GISAXS). In the depth direction, the multilamellar peaks observed in the X-ray reflectivity profile for the oriented DPPC/C 60 bilayers reveal a larger head-to-head distance D HH of 50.6 A and a bilayer spacing D of 59.8 A, compared to the D HH =47.7 A and D =59.5 A for a pure DPPC membrane measured at the same conditions. Furthermore, the lipid head layers and water layers in the extracted electron density profile for the complex system are highly smeared, implying a fluctuating or corrugated structure in this zone. Correspondingly, GISAXS for the oriented DPPC/C 60 membrane reveals stronger diffuse scatterings along the membrane plane than that for the pure DPPC system, indicating a higher in-plane correlation associated with the embedded fullerenes.

Lamellar morphologies of melt-crystallized blends of syndiotactic polystyrene (sPS, weight-average molecular weight M w =200 k ) and atactic polystyrene (aPS, Mw=100k) have been investigated using small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). sPS/aPS blends with various compositions were prepared and crystallized isothermally at 250 °C prior to morphological studies. Due to the proximity in the densities of the crystal and amorphous phases, a weak SAXS reflection associated with lamellar microstructure was obtained at room temperature. In addition, strong diffuse scattering at low scattering vectors was evidently observed and its appearance may obscure the intensity maximum associated with the lamellar features, leading to the difficulties in determining the microstructure of the blends. To enhance the density contrast, SAXS intensities at an elevated temperature of 150 °C were measured as well to deduce the morphological results with better precision. Based on the Debye–Bueche theory, the intensities of the diffuse scattering were estimated and subtracted from the observed intensities to obtain the scattering contribution exclusively from the lamellar microstructure. Morphological parameters of the sPS/aPS blends were derived from the one-dimensional correlation function. On addition of aPS, no significant changes in the lamellar thickness have been found and the derived lamellar thicknesses are in good agreement with TEM measurements. Segregation of rejected aPS components during sPS crystallization was evidently observed from TEM images which showed aPS pockets located between sPS lamellar stacks and distributed uniformly in the bulk samples, leading to the interfibrillar segregation.

The effect of supercritical CO2 on the morphological structure of compatible crystalline/amorphous poly(ethylene oxide) (PEO)/poly(methyl methacrylate)(PMMA) blends was investigated by means of small angle X-ray scattering (SAXS) with the measurement of absolute scattering intensity. The morphological structure of PEO/PMMA exhibited a considerable change upon CO2 treatment as demonstrated by the drastic increase of scattering intensity, or the enhancement of electron density contrast between the crystalline and amorphous layers in the lamellar stacks, resulting from the swelling of amorphous PEO via the incorporation of CO2 into the interlamellar (IL) regions. Upon CO2 treatment, both the crystal and amorphous layer thickness (lc and la, respectively) were increased with the extents depending on the blend composition. The increasing of la upon CO2 treatment was decreased with increasing PMMA content, suggesting that PEO was much easier to be swollen by CO2 than PMMA. Compared with the increase of la, the increase of lc was much more significant and was attributed to the occurrence of melting and recrystallization during CO2 treatment that led to thicker PEO crystals caused by an increased crystal surface free energy. The measured electron density contrast revealed that the distance of segregation in the PEO/PMMA blends involved the extralamellar segregation before CO2 treatments and the swelling of IL region dominated the drastic increase of scattering intensity after CO2 treatments. The finding of extralamellar morphology was consistent with the magnitude of volume fraction of lamellar stacks in the blends. The CO2 treatment could increase the distance of segregation for neat PEO and PEO-rich blends. The lamellar size distribution appeared to be broader and the lamellar stacks more disorganized for the blends after CO2 treatments according to SAXS one-dimensional correlation function profiles.

While the aging temperature is increased to low undercooling, 180 °C for Al–9.7 at.% Li alloy, the transitions of both the coarsening mechanism and the size distribution of δ′ precipitates in Al–Li alloy are found and studied using small-angle X-ray scattering (SAXS) technique. A modified precipitation mechanism considering this transition is explored with respect to both the determined precipitate size distribution and the growth rate constant. Additionally, a more adequate method is established for estimating the growth rate constant as a function of aging temperature and Li concentration, and those results are compared with corresponding measurement results.

We have studied the interactions of a lipophilic C60-derivative, synthesized recently for potential biomedical applications, with phospholipid monolayers and bilayers. The results of surface pressure–area isotherms, atomic force microscopic images, and neutron and X-ray scattering show consistently that the lipophilic C60 can intercalate into monolayers as well as vesicle bilayers of the phospholipids studied. In general, the lipophilic C60 can incorporate into the lipid membranes better in the liquid crystal phase, and modify the bending and compression modulus of the host lipid membranes significantly.

We studied the self-assembly behavior in the bulk complexes of poly(ethylene oxide) (PEO) with an amphiphilic dodecylbenzenesulfonic acid (DBSA) formed through hydrogen bonding. In the hydrate state, PEO−DBSA complexes self-organized into a lamellar morphology consisting of alternating stacks of polar and nonpolar layers. The interlamellar distance increased with decreasing binding fraction of DBSA due to increasing inclusion of unbound monomer units into the polar layers. In the disordered state the comblike structure persisted and a “correlation hole” peak was present in the corresponding small-angle X-ray scattering (SAXS) profile. Complexation with PEO greatly promoted the thermal stability of the mesophase and the dynamics of mesophase formation as compared with those in pure DBSA. The faster mesophase formation in the complexes was proposed to stem from the higher isotropization temperature as well as the existence of comblike structure in the disordered melt.

Lamellar morphology and thickness of syndiotactic polystyrene (sPS) samples melt-crystallized at various temperatures were probed using transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS). In addition, the melting temperature and enthalpy of the crystallized samples were characterized with differential scanning calorimetry. Under appropriate thermal treatments, all the samples investigated in this study were crystallized into β′ crystal modification, as revealed by wide-angle X-ray diffraction. From the SAXS intensity profiles, a scattering peak (or shoulder) associated with lamellar features as well as the presence of anomalous scattering at the zero-scattering vector were evidently observed. The peculiar zero-angle scattering was successfully described by the Debye–Bueche model, and subtraction of its contribution from the raw intensity profiles was carried out to deduce the intensity profile merely associated with the lamellar feature. The lamellar thickness obtained from Lorentz-corrected intensity profiles in this manner agrees with that measured from the TEM images, provided that the two-phase model is applied. On the basis of the Gibbs–Thomson equation, the modest estimations of equilibrium melting temperature and the surface free energy of the fold lamellar surface are 292.7 ± 2.7 °C and 20.2 ± 2.6 erg/cm2, respectively, when lamellar thicknesses measured by TEM are applied. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1626–1636, 2002

We systematically studied the effects of composition and crystallization temperature (Tc) on the morphological patterns of poly(vinylidene fluoride) (PVDF)/poly(vinyl acetate) (PVAc) blends by means of small angle X-Ray scattering (SAXS). The absolute intensity was measured so that the morphological structures can be resolved from the intensity perturbation. The scattering intensity associated with the PVDF lamellar stacks was strongly enhanced upon blending with PVAc. This was due to the presence of amorphous PVAc in the interlamellar regions that enhanced the electron density contrast between the crystalline and amorphous layers. Except for an intermediate Tc of 110°C where the systems attained the maximum crystal growth rate, partial extralamellar segregation of PVAc became prevalent when the PVAc composition exceeded 20 or 30 wt%. Even crystallization at as low as 20°C (where the diluent mobility was expected to be sluggish) produced a large extent of extralamellar segregation due to slow crystal growth. The results suggested that the crystal growth kinetics has dominated over the diluent mobility in controlling the average distance of diluent segregation in PVDF/PVAc with the prescribed molecular weight combination.

Extensive morphological studies on a syndiotactic polystyrene (sPS) sample prepared from compression molding were carried out using small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). SAXS was conducted at 25 ○C as well as at 150 ○C to enhance the scattering contrast in order to obtain more reliable morphological parameters. The compression-molded sample was crystallized into a β′ orthorhombic crystal lattice characterized by wide-angle X-ray diffraction (WAXD). A similar weight fraction of crystallinity, ca. 0.37, was obtained from both WAXD and differential scanning calorimetry measurements.

This study reports the creation of star-like chain architecture through complexation of a mono-amino terminated poly(ethylene oxide) (PEO-NH2) with a macrocyclic compound, 4-sulfonic calix[n]arene (n=4 and 8) (SCA-n). The complexes were prepared in aqueous solution to render proton transfer from the sulfonic acid groups in SCA-n to the amino groups in PEO-NH2, and thereby generated 4- and 8-arm star-like complexes with the PEO arms attached to the SCA-n cores via ionic bonding. Formation of the complexes was verified by titration, solubility test, and dilute solution viscometry. The intrinsic viscosities ([η]) of the complexes in toluene were 60% higher than that of neat PEO-NH2, showing that the star-like structure retained in nonpolar solvents. On the other hand, PEO arms dissociated from the cores in water, so that the complexes and neat PEO-NH2 displayed similar [η]. The star-like supramolecules showed a SAXS peak associated with the core-core correlation in the melt with the inter-core distance of 7.3 nm. The concentration fluctuation in the melt was completely destroyed upon the crystallization of PEO arms. In the semicrystalline state, the SCA-n cores were excluded from the crystal lattice and resided in the interlamellar amorphous regions. Measurements of the crystal thickness by SAXS indicated that the PEO chains in the crystals were once- and twice-folded in neat PEO-NH2 and the complexes crystallized at 40 °C, respectively.

Disc-shaped bicelles are formed by mixing long-chain lipids with short-chain lipids at suitable molar ratios and they have a relatively uniform size, typically around a few tens of nanometers in diameter. Different from the typically formulated cationic or anionic liposome–DNA complexes, which are used as nonviral vectors for improving the transfection efficiency of gene therapy, a novel way of packing the DNA can be developed by using the much smaller disc-like bicelles. We demonstrate that anionic lipid bicelle-ion–DNA (AB–DNA) complexes can be formed with the help of divalent ions. Multi-stacked AB–DNA complexes can be formed with diameters of around 50–100 nm and lengths of around 50–150 nm as revealed by TEM. Using the anionic lipid–DNA complexes has the advantage of lower cytotoxicity than using cationic lipids. The interaction of DNA with anionic bicelles was investigated by SAXS. It was found that the anionic bicelle could not form stable complexes with DNA at low calcium ion concentrations, such as 1 mM. The AB–DNA complexes can be formed in the investigated range of 10 mM to 100 mM calcium ion concentrations. However, for an equal anionic lipid charge and DNA charge system, an ion-membrane phase (multilamellar vesicles) would gradually appear as the calcium ion concentration is increased above a critical concentration. It indicates that DNA could be packed closer at above the critical divalent ion concentration. If more DNA is added to such a two-phase coexistence system (originally with the total anionic lipid charge equal to that of DNA), the ion-membrane phase could be transformed into the AB–DNA complexes. As a result, more DNA can be packed in the form of AB–DNA complexes at above the critical calcium ion concentration.

Polyester based polyurethanes were synthesized from 4,4′-methylene bis(phenyl isocyanate) (MDI) with butanediol as a chain extender and low molecular weight polyester-diol as a soft segment. Three polyesters were used in the synthesis of polyurethanes. Two of the polyesters, with molecular weight Mn = 2,660 and 2,155, were synthesized from adipic acid and 1,6-hexanediol, which had an even number of carbon atoms (polyester-6-6-1 and polyester-6-6-2). The other polyester with Mn = 2,770 was synthesized from pimelic acid and 1,5-pentanediol, which had an odd number of carbon atoms (polyester-7-5). Polyester-6-6-1 and polyester-6-6-2 consisting of even carbon monomers, had a higher degree of crystallinity at room temperature than polyester-7-5, which consists of an odd number of carbon monomers. The effect of polyester molecular weight and soft and hard-segmental geometric structure on the soft-and hard-segmental phase segregation was studied using differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and small angle X-ray scattering (SAXS).

We have synthesized fullerene derivatives, C60[CO(CH2)5O(CH2)4SO3Na]6 (FC10S), which consists of a C60 cage covalently bonded with six sulfonated arms for a high water solubility. We study the aggregation structures of the novel C60-derivatives in 0.1 M NaCl aqueous solutions by small angle X-ray scattering (SAXS). In the concentration range studied, 0.5 wt% to 2 wt %, the rod-like structure of FC10S aggregates has a radius of 20 A and a rod-length about 150 A at 25°C, and the aggregation structure is insensitive to the concentration change. The aggregates, however, grow in length as the temperature increases, while the radius increases slightly with increasing temperature.

A modified method for small-angle X-ray scattering (SAXS) analysis was developed to reconstruct the free-form particle size distribution of precipitates by including the interparticle interference effect. In this paper, the known indirect Fourier transform method (ITM) is extended to include the hard-sphere (HS) model which considers the interaction between the precipitates. This method is tested by analyzing simulated SAXS data and shows a better agreement than other similar studies. Then this modified method is applied to analyze several experimental SAXS data from δ′ (Al 3 Li particles) precipitation in Al-7.9at%Li alloys aged at various conditions. The variation of average radii with aging time was found to follow the kinetic power law. The SAXS results are used to investigate the kinetic model of the δ′ coarsening (Ostwald ripening) with volume fraction effect. When comparing both experimentally obtained asymptotic size distributions of δ′ particles with those predicted by the kinetic theories, the MLSW theory is found to be in better agreement with the experimental results. This work gives a more clear interpretation of the coarsening mechanism than other experimental results. The dynamic scaling behavior of this phase separation is also investigated.

Polyester-based polyurethanes containing 60 wt % of polyester were synthesized from low molecular weight polyester (M n 2000) and 4,4'-methylene bis-(phenyl isocyanate) (MDI), with butanediol as a chain extender and glycerol as a crosslinker. The triol crosslinker was used in substitution for the 1,4-butanediol chain extender; thus, the crosslinker was chemical bonded to the hard segments of polyurethane. The morphologies of these polyurethanes were studied by differential scanning calorimetry (DSC), small-angle X-ray scattering (SAXS), TMA (thermal mechanical analysis), and FTIR (Fourier transform infrared spectroscopy). Owing to the highly steric hindrance, the presence of triol crosslinker in the hard segments resulted in a decrease in the aggregation of hard segments through hydrogen bonding. The experimental results revealed that the degree of phase segregation of soft and hard segments decreased with increasing the triol crosslinker content in the hard segments.

The semicrystalline morphology of poly(3-hydroxy butyrate) (PHB)/poly(vinyl acetate) (PVAc) blends at four crystallization temperatures (Tc = 70, 90, 110, and 125 °C) was probed by small-angle X-ray scattering (SAXS). Morphological parameters including the crystal thickness (lc) and the amorphous layer thickness (la) were deduced from the interphase distribution function. Blending with PVAc thickened the PHB crystals. The amorphous layers were also swollen upon blending, but la displayed a maximum in its variation with PVAc composition. A zero-angle scattering was observed in the Lorentz-corrected SAXS profiles of PHB/PVAc 60/40 blend crystallized at 110 and 125 °C and 50/50 composition crystallized at 90−125 °C. Such a zero-angle scattering was attributed to the presences of amorphous domains between the lamellar stacks so as to generate gaps in the sequential stacking of lamellae. These amorphous domains were generated by the interfibrillar segregation of PVAc, where PVAc was expelled beyond several lay...

This study presents a novel method for small-angle X-ray scattering (SAXS) to reconstruct the particle size distribution using the indirect transform method plus hard-sphere model. Effectiveness of the proposed method is demonstrated by a simulation case study, in which our results correlate well with simulation results. The method proposed herein, which is an improvement over the conventional one, is then applied to analyze a series of experimental SAXS intensities from δ′ precipitation in Al–9.7at%Li alloy. More accurate parameters involving structural and thermodynamic information are obtained. Moreover, SAXS analysis is performed to investigate the kinetic model of δ′ particle coarsening. Comparing the experimentally obtained asymptotic size distributions of δ′ particles with those predicted by the theoretical models and other experimental results demonstrates that MLSW theory is more appropriate than the others. The experimental results indicate the MLSW model interprets more accurately than the other SAXS studies. Dynamic scaling is used to examine the time-dependent SAXS profiles during this phase separation.

We study the aggregation behaviors of polyhydroxylated fullerenes (fullerenols) in aqueous solutions using small angle X-ray scattering (SAXS). The scattering results show that the highly water soluble C60(OH)18 form mainly small aggregates of a few tens A in size. The structure of the aggregates for the concentrations studied, from 0.625 wt % to 10 wt %, can be characterized with a fractal dimension of 2.5.

An improved method for small-angle X-ray scattering (SAXS) data analysis is developed to reconstruct the free-form particle size distribution of δ′ precipitation in an Al–Li alloy. This improved method consists of four iterative steps; the interparticle interference is also included. The indirect transform method (ITM) plus a hard-sphere (HS) model which considers the depleted zones are used in the analysis of δ′ precipitation in an Al–Li alloy. Two parameters, namely the hard-sphere volume fraction, ηHS, and the ratio of hard-sphere radius to the particle radius,RHS/R, which determine the structure factor of the interparticle effect, are iteratively calculated using the monodisperse assumption and Gaussian size distribution. These two parameters are finally used in reconstructing the particle size distribution by the ITM + HS method. This method is tested by analysing simulated SAXS data and shows a better agreement than found in similar studies. This improved method is applied to analyse a set of experimental SAXS intensities from δ′ (Al3Li particles) precipitation in an Al–9.7 at.% Li alloy. The monodisperse results are compared with the polydisperse ITM + HS results. The current ITM + HS method fits the SAXS data better than the other methods. The variations of average radii with aging time were found to follow the kinetic power law. The SAXS results are used to investigate the theoretical kinetic model of the volume-fraction effect on late-stage coarsening (Ostwald ripening). By comparing both experimentally obtained asymptotic size distributions of δ′ particles as well as coarsening rate constants with those predicted by the various kinetic models, the modified Lifshitz–Slyozov–Wagner (MLSW) theory is found to be in better agreement with the experimental results than the other theories.

Polyester based polyurethanes were synthesized from a low molecular weight polyester (Mn∼2000) and 4,4′-methylene bis(phenyl isocyanate) (MDI) with butanediol as a chain extender and glycerol as crosslinker. The polyester was synthesized from adipic acid and glycol, a mixture of 1,6-hexanediol and 1,2-propanediol. The effect of the crosslinker content on the phase segregation of soft- and hard-segments was studied by DSC (differential scanning calorimetry) and SAXS (small angle X-ray scattering). The introducing of triol functional group into the hard segments increased the aggregation of hard segments through crosslink covalent bonds. Owing to highly steric hindrance, the presence of tri-ol crosslinker in the hard segments decreased the aggregation of hard segments through hydrogen bonding. The phase segregation of soft- and hard-segments is thus due to the aggregation of hard-segments through crosslinked covalent bonds and H-bonding.

The importance of crystal growth rate in the morphological formation of strongly interacting crystalline/amorphous polymer blends has been assessed by considering polycaprolactone (PCL)/poly(4-vinylphenol) (PVPh) systems. The effects of composition and molecular weight (MW) on the morphological structure were investigated by small-angle X-ray scattering (SAXS). Blending with PVPh increased the long period associated with the alternating crystalline−amorphous layers. The long period increase was characterized by the thickening of PCL crystals upon blending instead of the swelling of amorphous layers. The extent of extralamellar segregation of PVPh was revealed from the volume fraction of lamellar stacks. Despite the relatively high Tg of PVPh, significant extralamellar segregation of PVPh was observed. The extent of extralamellar segregation increased with PVPh composition for a given molecular weight combination of PCL and PVPh. For a given composition, the blends with PCL molecular weight (MPCL) of 15 80...

Solid-state complexes of flexible polymers with long-tail surfactants (surf) exhibit mesomorphic phase and microphase-separated lamellar morphology consisting of alternating polymer and surf layers. The alkyl tails in the surf layers are highly stretched and closely packed due to the excluded volume effect. In this study, the self-assembled structure of a new polymer(surf) complex system based on complexation between poly(N-vinyl pyrrolidone) (PVP) and dodecyl benzene sulfonic acid (DBSA) was investigated by optical microscopy and small-angle X-ray scattering (SAXS). Both mesomorphic phases and microphase-separated lamellar morphology were observed in PVP(DBSA) complexes. The thicknesses of polymer and surf layers were determined from the one-dimensional correlation function. Both types of thickness are dependent on complex composition. The interplay between chain conformational entropy and interaction energies (repulsive and attractive) is suggested to control the self-organized structure in the complexes. Complexation with DBSA reduced the thermal stability of PVP, which was in contrast with poly(ethyleneimine)-DBSA complexes reported previously.

In a melt-miscible crystalline/amorphous polymer blend, crystallization is accompanied with the segregation of amorphous diluent. Depending on the distance of segregation, various types of segregation morphology, including interlamellar, interfibrillar, and interspherulitic, may be created. In this study, we systematically investigated the effects of molecular weight (MW) of both crystalline and amorphous component on the formation of segregation morphology in polycaprolactone (PCL)/poly(vinyl chloride) (PVC) blends. Optical microscopy and small-angle X-ray scattering (SAXS) revealed that the extent of interfibrillar morphology increased with decreasing MW of PCL (MPCL). However, in the blends containing oligomeric PCL, interfibrillar segregation also involved the exclusion of uncrystallizable PCL short chains. The volume fraction of PVC expelled into the interfibrillar regions was calculated from SAXS linear crystallinity and bulk crystallinity. The results indicated that the transport of PVC into interf...

A polyurethane (PU) elastomer film based on segmented poly(tetramethylene oxide) (PTMO) has been studied using wide-angle X-ray scattering (WAXS), and small-angle X-ray and neutron scattering (SAXS and SANS). The broad WAXS peaks measured for the PU elastomer reveal a low crystallinity of the soft segments PTMO and no crystalline domains for the hard segments, methylene bis(4-isocynatobenzene) (MDI), at 20 °C. Whereas small-angle scattering indicates the existence of hard-segment-rich aggregates. Using the contrast variation provided by the SANS and SAXS, we have extracted detailed structural information of the aggregates, including the shape, size, and the aggregation numbers.

Three segmented polyurethane block copolymers PU-M, PU-X and PU-T containing different diisocynates, diphenylmethane-4,4'-diisocyanate (MDI), xylene diisocyanate (XDI) and 2,4-toluene diisocyanate (TDI) respectively with the same chain extender 1,4-butanediol (BD) and soft segment polyester-diol were investigated by small-angle X-ray scattering (SAXS). Microphase separation transition (MST) occurred due to the thermodynamic incompatibility between the soft and hard segments. The long domain spacing, interfacial thickness (or transition layer thickness), core zone, and lamellar thickness were determined for these three different polyurethanes from one dimension correlation function after the Fourier transformation of small-angle X-ray scattered intensity curve based on the Strobl and Schneider model. The structural parameters for these three polyurethanes determined from the scattering measurements indicate that the degrees of microphase separation are in the following sequence: PU-M > PU-X > PU-T.

Water solutions of fullerene-based ionomers, C 60 [(CH 2 ) 4 SO 3 Na] 6 (star-ionomer), have been studied by small angle neutron scattering (SANS) and small angle X-ray scattering (SAXS). The scattering profiles indicate clearly the existence of small aggregates of star-ionomers. The structural information of the aggregates is extracted from the SANS and SAXS data using a hard sphere model. By the contrast between neutron and X-ray scattering, the average aggregation number is determined to be 8.5 for 1 wt.% sample solutions. The spherical-like aggregates are nearly monodisperse in the investigated concentration range from 0.25 to 4%.

Biological applications of water-soluble hexa(sulfobutyl)fullerene (FC 4 S) are reviewed. It was synthesized in a yield of 80–85% by the treatment of C 60 in dimethoxyethane (DME) with sodium naphthalide (10 equiv.) at 25 °C, followed by reacting the resulting hexa-anionic fullerene intermediates with an excess of 1,4-butane sultone (15 equiv.). FC 4 S showed an enhanced superoxide radical (O 2 −. ) scavenging activity and suppression efficiency against the superoxide-induced ferricytochrome c reduction under physiologic conditions, as compared with those of fullerenols at a dose level of 100 μ m. For example, a profound suppression efficiency of 60 and 96% was detected at a dose level of 50 and 100 μ m, respectively. Aggregation behaviors of FC 4 S molecules in aqueous solution were investigated using SAXS (small-angle X-ray scattering) and SANS (small-angle neutron scattering) techniques. We concluded that the aggregation size and shape of FC 4 S nanoparticles with the radius of gyration,R g of 18.9–19.1 A remain relatively unchanged with the variation of concentration in the concentration range of 0.35–26.0 mM. The phenomena were correlated to a high total surface area of nanoparticles and interfacial accessability of fullerene cages to reactive oxygen radical species.

Cationic lipid–DNA (CL–DNA) complexes can be used as non-viral vectors to improve transfection efficiency in gene therapy. It is greatly desirable to develop new ways of packing DNA in order to make breakthroughs on the development of highly efficient DNA delivery systems. Different from the widely-studied vesicle based CL–DNA complexes, we have developed a novel cationic bicelle–DNA complex system by mixing cationic bicelles with DNA to form alternating stacks of disc bilayered plates and DNA arrays with a repeat distance of 7.5 nm. SAXS and TEM studies revealed that the DNA molecules encapsulated between the disc bilayered plates form ordered arrays with a spacing of around 4–5 nm. The number of stacking layers can be easily tuned from just a few layers to more than one hundred layers by adjusting the doping percentage of the charged lipids. This CB–DNA complex is quite stable against increases in temperature above the chain-melting temperature of the long chain lipids. Due to the flexible size tunability (number of stacking layers) and the unique structure of the packing of the DNA arrays with 50–100 nm size disc bilayered plates, the CB–DNA complexes are promising as novel non-viral vectors for gene delivery.

Using small-angle X-ray scattering (SAXS) and small-angle neutron scattering (SANS) with contrast variation, we have studied the complex aggregation of Alzheimer amyloid-β(1–40) (Aβ) peptides with sodium dodecyl sulfate (SDS). With the addition of 0.115 mM Aβ peptide into an aqueous solution containing 6 mM SDS, time-dependent SAXS indicates the formation of a globular SDS–Aβ complex with a core–shell structure. The emergence of the complex aggregates, however, lags significantly behind the fast transition of the secondary structure of Aβ peptides from random coil to α-helical structure observed by circular dichroism (CD). With scattering contrast varied by SDS and deuterated SDS, SANS results reveal the coexistence of Aβ aggregates and the SDS–Aβ complex, which together form clusters of a mass fractal structure. Based on the changes of the zero-angle scattering intensity with the contrast variation, a molecular association ratio, ∼30 : 1, of SDS to Aβ is extracted for the globular complex micelle. With a concentration (20 mM) above the critical micelle concentration (CMC) of SDS, time-dependent SAXS and CD reveal a better synchronization between the formation of the SDS–Aβ complex and the changes in Aβ secondary structure. Using an ellipsoid model with a core–shell structure in the SAXS data analysis, we have extracted detailed structural information of the prolate, core-shelled SDS–Aβ complex, having size and shape resembling pure SDS micelles. The significantly larger electron density of the shell of the complex, as compared to that of pure SDS micelles, suggests that the hydrophilic parts of Aβ peptides can situate well with the sulfate headgroups of SDS in the shell region. Delicate differences in the micellar structure and the formation pathway of the two types of SDS–Aβ complexes, respectively formed in aqueous solutions containing SDS concentrations below and above its CMC, are discussed in terms of the dissimilar association efficiencies of Aβ peptides with SDS monomers and SDS micelles. The morphology, association ratio, and clustering behavior of the SDS–Aβ complex obtained in this study may have implications in interpreting the related spectroscopy and SDS–PAGE results of the protein.

Zircaloy-4 through beta quenching treatment has been extensively used as cladding and core structure material in water-cooled nuclear reactors, due to its high nodular corrosion resistance and mechanical strength. Research shows that corrosion resistance is highly related to the sites and size distribution of the second phase precipitate particles after quenching. The nodular corrosion resistance decreases as particle size increases, while uniform corrosion resistance increases. The existence of a large amount of quenched-in vacancies enhances the nucleation and growth of precipitates during the quench process. The microstructure of zircaloy-4 transforms from beta phase (bcc) to Widmanstaetten alpha phase (hcp) with a lathe structure by martensitic transformation. The main intermetallic precipitates, Zr{sub 4}(Fe,Cr), with a fcc phase mostly precipitated at the lathe boundaries, having sizes from 4 to 35 nm. These particles can be considered as a polydispersive system. SAXS (Small-Angle X-ray Scattering) technique, which is used in this study, is a powerful tool to determine the size distribution of fine particles. The IFT (Indirect Fourier Transformation) method is used in this study to analyze the measured scattering intensity distribution which comes from the scattering of all particles (below 50 nm) within the specimen. This work attempts to more accurately reconstructmore » or determine the size distribution of the second phase particles in beta-quenched zircaloy-4 without prior assumption of the shape of size distribution. The results can be used in future work to explore the mechanism of growth kinetics of Zr{sub 4}(Fe,Cr) precipitate.« less