Solution study of novel diblock copolymers: Morphology and structural transition

The solution behavior and morphology of the nanostructures formed by novel block copolymers based on 1-cetyl[2-(acryloyloxy)ethyl]dimethylammonium bromide (ADHA) and 2-hydroxyethylacrylate (HEA) or N-isopropylacrylamide (NIPAM) have been studied using small angle X-ray scattering (SAXS), dynamic light scattering (DLS), and transmission electron microscopy (TEM). In these block copolymers the pADHA block consists of long hydrophobic C₁₆ tails connected to a positively charged quaternary ammonium group, making it amphiphilic, while the second block is either fully hydrophilic (pHEA) or thermoresponsive (pNIPAM). Using SAXS, we demonstrate that the morphology of block copolymer nanostructures is dependent on the solute concentration and on the length and composition of the blocks. In the case of thermoresponsive pADHA-b-pNIPAM, two types of ordered structures are formed and their characteristics are also defined by the temperature. Complementary information is obtained from DLS, showing large particles with the size up to 280 nm, which is beyond the resolution of the SAXS data. Loss of ordering around the lower critical solution temperature followed by ordering restoration at the higher temperature was observed for the pADHA-b-pNIPAM block copolymers. The differences in the structural order in the block copolymer solutions are directly related to their ability to coat hydrophobic metal nanoparticles.     

Analysis of HNBR-Montmorillonite Nanocomposites

Summary Morphologies and dynamic mechanical properties of hydrogenated acrylonitrile butadiene rubber (HNBR) filled with organophilic layered silicates (OLS) were investigated. The results from transmission electron microscopy (TEM), small angle X-ray scattering (SAXS, especially X-ray diffraction on larger structures) and dynamic mechanical analysis (DMA) favor the notion of local filler-filler network-like clusters consisting of exfoliated silicate layers. Especially, processing under high shear forces leads to an anisotropic structure of the network. Due to the orientation of the clusters the aspect ratio (at small deformations) increases. This is in accord with the large reinforcing effect observed for these materials. For example, the stress at 50% elongation from tensile test can be increased at 33% with 5 phr OLS compared to the unfilled reference. We estimate the activation energy of the immobilized polymer layer around the filler structures and show that the values depend on the spatial direction (the values are between 3.4 kJ/mol and 4 kJ/mol). As a result, the DMA–analysis could be used as a supporting method to evaluate orientation effects of the filler structures. Furthermore, from SAXS experiments, measured in the three directions in space, and from TEM analysis one could conclude that small amounts of intercalated structures are still present. These structures are orientated, too. The results make evident that the orientation of intercalated structures should be taken into account, especially if SAXS is used to estimate the degree of exfoliation.     

Structural changes during the deformation of thermoplastics in relation to impact resistance

Plain and rubber-modified polymers deform by shearing, crazing, and voiding. The structural changes during deformation were studied by density measurements, small-angle X-ray scattering (SAXS), and electron microscopy (EM). The consequences of these deformation processes for impact resistance are briefly discussed.     

Fold recognition aided by constraints from small angle X-ray scattering data

We performed a systematic exploration of the use of structural information derived from small angle X-ray scattering (SAXS) measurements to improve fold recognition. SAXS data provide the Fourier transform of the histogram of atomic pair distances (pair distribution function) for a given protein and hence can serve as a structural constraint on methods used to determine the native conformational fold of the protein. Here we used it to construct a similarity-based fitness score with which to evaluate candidate structures generated by a threading procedure. In order to combine the SAXS scores with the standard energy scores and other 1D profile-based scores used in threading, we made use both of a linear regression method and of a neural network-based technique to obtain optimal combined fitness scores and applied them to the ranking of candidate structures. Our results show that the use of SAXS data with gapless threading significantly improves the performance of fold recognition.     

Mesoscale Characterization of Supramolecular Transient Networks Using SAXS and Rheology

Hydrogels and, in particular, supramolecular hydrogels show promising properties for application in regenerative medicine because of their ability to adapt to the natural environment these materials are brought into. However, only few studies focus on the structure-property relationships in supramolecular hydrogels. Here, we study in detail both the structure and the mechanical properties of such a network, composed of poly(ethylene glycol), end-functionalized with ureido-pyrimidinone fourfold hydrogen bonding units. This network is responsive to triggers such as concentration, temperature and pH. To obtain more insight into the sol-gel transition of the system, both rheology and small-angle X-ray scattering (SAXS) are used. We show that the sol-gel transitions based on these three triggers, as measured by rheology, coincide with the appearance of a structural feature in SAXS. We attribute this feature to the presence of hydrophobic domains where cross-links are formed. These results provide more insight into the mechanism of network formation in these materials, which can be exploited for tailoring their behavior for biomedical applications, where one of the triggers discussed might be used.     

Characterization of Nanodomains in Polymer-Derived SiCN Ceramics Employing Multiple Techniques

A combination of methods, Bragg diffraction, small-angle X-ray scattering (SAXS), and transmission electron microscopy, is applied to the characterization of nanodomains and nanocrystals in polymer-derived ceramics (PDCs). Detailed study of two materials, silicon carbonitride (SiCN) and a SiCN–zirconia nanocomposite, is presented. The first contains domains which can be measured only by SAXS. However, the nanocrystallites of zirconia in the second material can be quantatively studied by all three techniques. In both instances, we find the SAXS to be particularly useful because these data provide detailed information regarding the size distribution of the domains and the crystallites. This information can be valuable in understanding the materials science of PDCs: e,g., the change in the distribution and the average size of the nanoclusters can be modeled to understand the kinetic mechanisms of coarsening at high temperatures.     

Structure and morphology of segmented polyurethanes: 4. Domain structures of different scales and the composition heterogeneity of the polymers

The morphology of polybutadiene containing polyurethanes has been studied by using small-angle light scattering (SALS), small-angle X-ray scattering (SAXS), phase contrast microscopy and electron microscopy. Domain structures having sizes of 1000, 100 and 10 nm are observed within these samples and are explained as the results of segregation on the molecular level, subchain level and segmental level, respectively. These phenomena are related to the molecular heterogeneity in chemical composition and average hard segment length. It has been found that because of the analogy in molecular structure with SBS block copolymers, segmented polyurethanes may form microdomains of soft and hard segments with more or less uniform size and regular arrangements in space.     

A step forward towards the structural characterization of Na2Ti2O5·H2O nanotubes and their correlation with optical and electric transport properties

In this work we present the synthesis, structural, morphological, optical and electrochemical characterization of sodium titanate nanotubes (NaNT) obtained by hydrothermal means. According to our detailed structural study, we found that a Na₂Ti₂O₅·H₂O layered crystalline phase with [TiO₅] pyramidal square base coordination, utilized as a building block of the nanotubes, explains satisfactorily the experimental results. This is a very important aspect, since the bibliography does not always provide structural information about titanate nanotubes. With respect to the formation mechanism we highlight the crucial role of the post treatment washing in the final crystalline structure of the nanotubes. Simulated X-rays powder diffraction patterns (XRPD), based on real size nanotubes models, were refined with experimental data. Building blocks for the NaNT model were inferred from computational simulations, by means of Density Functional Theory. The obtained tube's model characteristic dimensions were also consistent with SAXS and TEM analysis. In addition, our SAXS analysis suggested that the presence of humidity in the cavities of titanate nanotubes is progressively lost at the 80–100 °C temperature range, in good agreement with thermogravimetric analysis. Electrochemical impedance spectroscopy analysis for dried samples in the temperature range, studied under cooling conditions, revealed a single ionic transport mechanism, probably associated to the in-between [TiO₅] layers ion transport. However, a secondary process was observed for non-dried samples, during heating conditions, that could be associated to the ionic transport along the water filled tube's cavity, consistent with SAXS analysis. In summary, this work shows an integral approach, through theory and experiment, in order to understand the effect of the structure on the physical and electronic properties of the system.     

Effect of hard segment content and carbon-based nanostructures on the kinetics of flexible polyurethane nanocomposite foams

Reactive flexible polyurethane (PU) foams were synthesized with two contents of hard segments (HS) and filled with multi-walled carbon nanotubes (MWCNTs), functionalized MWCNTs (f-MWCNTs) and functionalized graphene sheets (FGS). The effect of the HS content and the carbon nanofillers on the kinetics of polymerization and the kinetics of phase-separation have been studied by Fourier transform infrared spectroscopy (FT-IR) and synchrotron small-angle X-ray scattering (SAXS). A slow down on the rate of polymerization and on the development of the polymer structure due to the increase of the HS content and the inclusion of the nanoparticles was observed. Therefore, this work demonstrates that there is a relationship between the kinetics of polymerization and the kinetics of phase separation in flexible PU nanocomposite foams. SAXS data was used to generate 3D microstructures of PU nanocomposite foams and the phase-separated morphology was observed by atomic force microscopy (AFM).     

SAXS characterization of the Nafion membrane nanostructure modified by radiation cross-linkage

The present study employs small-angle X-ray scattering (SAXS) to investigate the water-swollen structures of two types of Nafion membranes, commercial Nafion 117 membranes and the membranes synthesized from the Nafion precursor, subjected to gamma radiation. The membrane structure can be characterized by two-length scales, comprised the long-range order of lamellar crystalline domains in the matrix and the local order of ionic cluster domains. Both the long-range order lamella and local order cluster in the membranes are significantly affected by the radiation-induced cross-linking. We have extended a local order model to take into account the polydispersity effect, which can more satisfactorily reproduce the ionomer SAXS peak than other existing models. The structural parameters determined from the SAXS model analysis are self-consistent with those obtained from the model-independent Porod analysis. The modified membrane structure by the radiation cross-linking is very helpful for developing a high performance and low cost of direct methanol fuel cells.     

Structural changes in non-isothermal crystallization process of melt-cooled polyoxymethylene[II] evolution of lamellar stacking structure derived from SAXS and WAXS data analysis

Structural change occurring in the cooling process of polyoxymethylene from the molten state has been investigated by carrying out the temperature dependent measurements of small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS). In the SAXS experiment the generation of lamellar stacking structure with long period of ca. 14 nm was detected at first and then the new lamellae were inserted in between the already-existing lamellae to give the long period of 7 nm below 140 °C. The SAXS data were analyzed on the basis of lamellar insertion model by taking into account the second kind of paracrystalline disorder about the lamellar stacking mode. The thus obtained results were combined with the previously published infrared spectral data, and the structural change was deduced concretely. The generation of taut tie chains passing through the adjacent lamellae was proposed, which could reasonably explain the observation of infrared bands characteristic of extended-chain-crystal-like morphology.     

Transmission electron microtomography in polymer research

This feature article summarizes recent advances in an emerging three-dimensional (3D) imaging technique, transmission electron microtomography (TEMT), and its applications to polymer-related materials, such as nanocomposites and block copolymer morphologies. With the recent developments made in TEMT, it is now possible to obtain truly quantitative 3D data with sub-nanometer resolution. A great deal of new structural information, which has never been obtained by conventional microscopy or various scattering methods, can be directly evaluated from the 3D volume data. It has also been demonstrated that, with the combination of TEMT and scattering methods, it becomes possible to study structures that have not yet been characterized. The structural information obtained from such 3D imaging provides a good opportunity not only to gain essential insight into the physics of self-assembling processes and the statistical mechanics of long chain molecules, but also to establish the “structure-property” relationship in polymeric materials.     

The application of small angle scattering techniques to porosity characterization in carbons

Small angle scattering (SAS) techniques offer a number of advantages for the investigation of the nature and behavior of porous materials. In particular, with respect to carbons, the essentially non-intrusive nature of SAS means that along with the more traditional, pre- and post-treatment characterization of carbons, in principle, characterization can also be performed in situ during adsorption and activation processes. In the current communication, the application of the techniques of small angle X-ray (SAXS) and neutron (SANS) scattering is reviewed specifically with respect to porosity characterization in carbons. First, the basis of these techniques is presented. More recent applications of SAXS and SANS to carbon porosity are presented, and their relative attributes are contrasted, including the related technique of contrast matching with SANS to distinguish “closed” from “open” porosity, and its application to elucidation of pore development mechanisms. Applications of other related techniques, such as μSAXS and TGA/SAXS, to carbon characterization and porosity development are also discussed.     

Taking “Nothing” into Consideration: Supported Metal Catalysts by SAXS

The analysis of the X‐ray diffraction patterns scattered at small‐angles (SAXS) by porous materials is a powerful analytical tool providing relevant structural information on supported metals used as heterogeneous catalysts. In particular, the technique offers valuable structural insights on the interphases which govern the chemical behaviour of these materials. Using a series of silica‐supported palladium catalysts we show how SAXS experiments address the crucial importance of porosity (or “nothing”) in affecting the structure of these catalysts.     

Self-assembled multicompartment liquid crystalline lipid carriers for protein, peptide, and nucleic acid drug delivery

Lipids and lipopolymers self-assembled into biocompatible nano- and mesostructured functional materials offer many potential applications in medicine and diagnostics. In this Account, we demonstrate how high-resolution structural investigations of bicontinuous cubic templates made from lyotropic thermosensitive liquid-crystalline (LC) materials have initiated the development of innovative lipidopolymeric self-assembled nanocarriers. Such structures have tunable nanochannel sizes, morphologies, and hierarchical inner organizations and provide potential vehicles for the predictable loading and release of therapeutic proteins, peptides, or nucleic acids. This Account shows that structural studies of swelling of bicontinuous cubic lipid/water phases are essential for overcoming the nanoscale constraints for encapsulation of large therapeutic molecules in multicompartment lipid carriers. For the systems described here, we have employed time-resolved small-angle X-ray scattering (SAXS) and high-resolution freeze-fracture electronic microscopy (FF-EM) to study the morphology and the dynamic topological transitions of these nanostructured multicomponent amphiphilic assemblies. Quasi-elastic light scattering and circular dichroism spectroscopy can provide additional information at the nanoscale about the behavior of lipid/protein self-assemblies under conditions that approximate physiological hydration. We wanted to generalize these findings to control the stability and the hydration of the water nanochannels in liquid-crystalline lipid nanovehicles and confine therapeutic biomolecules within these structures. Therefore we analyzed the influence of amphiphilic and soluble additives (e.g. poly(ethylene glycol)monooleate (MO-PEG), octyl glucoside (OG), proteins) on the nanochannels' size in a diamond (D)-type bicontinuous cubic phase of the lipid glycerol monooleate (MO). At body temperature, we can stabilize long-living swollen states, corresponding to a diamond cubic phase with large water channels. Time-resolved X-ray diffraction (XRD) scans allowed us to detect metastable intermediate and coexisting structures and monitor the temperature-induced phase sequences of mixed systems containing glycerol monooleate, a soluble protein macromolecule, and an interfacial curvature modulating agent. These observed states correspond to the stages of the growth of the nanofluidic channel network. With the application of a thermal stimulus, the system becomes progressively more ordered into a double-diamond cubic lattice formed by a bicontinuous lipid membrane. High-resolution freeze-fracture electronic microscopy indicates that nanodomains are induced by the inclusion of proteins into nanopockets of the supramolecular cubosomic assemblies. These results contribute to the understanding of the structure and dynamics of functionalized self-assembled lipid nanosystems during stimuli-triggered LC phase transformations.     

Regulating dual temperature- and pH-responsibility constructed from core-shell mesoporous hybrid silica (P(NIPAM-co-AA)@BMMs) via adjusting AA incorporation onto NIPAM

The mesoporous hybrid silicas (P@BMMs) with core-shell structure were successfully synthesized via seed polymerization method using bimodal mesoporous silica materials (BMMs) as core and dual pH- and temperature-responsive poly(N-isopropylacryl-acrylamide)-co-poly(acrylic acid) (P(NIPAM-co-AA)) copolymer as shell. Meanwhile, the obtained P@BMMs were physicochemically and morphologically characterized via X-ray diffraction, N₂ adsorption-desorption isotherms, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared, ultraviolet visible diffused reflection spectrum, small angle X-ray scattering (SAXS), dynamic light scattering, and thermogravimetric analysis techniques. The results indicated that P(NIPAM-co-AA) was successfully coated onto the mesoporous surface of used BMMs, while the uniform mesoporous structure of obtained P@BMMs was still preserved. Using ibuprofen (IBU) as a model drug, the influence of the P(NIPAM-co-AA) shell on the release kinetics of IBU was explored, and its performances elucidated that the P@BMMs nanoparticles presented an apparent thermo/pH-responsive properties, which could be regulated via adjusting mass ratio of AA to NIPAM, and their IBU-release kinetic profiles were favorable to Korsmeyer-Peppas model. Specially, SAXS patterns were employed to evaluate the fractal evolution of P@BMMs along with releasing time, showing the decline tendency for mass fractal value from 2.89 to 2.56 during the release time of 0.25–24?h.     

Interface morphology and phase separation in polymer-dispersed liquid crystal composites

It is widely appreciated that electro-optic activity in polymer-dispersed liquid crystals (PDLCs) depends on separation of the polymer and liquid crystal (LC) phases. Since the phase structure develops in a non-equilibrium system, the morphology of the LC domains depends on the details of the chemical and physical processes active during domain formation. The nature of the interface between the polymer and liquid crystal phases is of particular interest. This work discusses the two-phase morphology in an acrylate-based system that develops during polymerization-induced phase separation (PIPS). Using small-angle X-ray scattering (SAXS) and ultra-small-angle X-ray scattering (USAXS), we find that interfaces in PDLCs developed from an acrylate-based recipe are more disordered than generally appreciated. Information gained from SAXS and USAXS is compared to data from scanning electron microscopy (SEM) and transmission electron microscopy (TEM). To elucidate the apparent discrepancies between imaging and scattering, we investigated the effects of SEM sample preparation. We observe significant alteration of the interface morphology due to the leaching of the LC phase.     

Structure of poly (p-phenylenebenzobisoxazole) (PBZO) and poly (p-phenylenebenzobisthiazole) (PBZT) for proton exchange membranes (PEMs) in fuel cells

The structures of membranes of PBZO and PBZT extruded with counter rotating dies (CRD) were studied by wide angle X-ray diffraction (WAXD), small angle X-ray scattering (SAXS), atomic force, scanning electron and transmission electron microscopy (AFM, SEM, and TEM). The structure of CRD-extruded PBZO was compared with that of a solution-cast membrane. The extruded membranes have sheet structures typical of rigid-rod polymers. The heterocyclic rings of the extruded membranes are oriented approximately parallel to the membrane surface, while those of the cast membrane are oriented perpendicular to the surface. The parallel orientation of the rings of the extruded membranes may be due to the normal force exerted during extrusion. The polymer molecules near the surfaces of the extruded membranes are oriented along the shear directions of the extruder, while those in the middle are oriented randomly. There is little cholesteric nature. These materials have potential as microporous PEMs holding ion conducting polymers (ICPs).