Shear-induced orientation in polymer/clay dispersions via in situ X-ray scattering

Determination of the In-Plane Exciton Radius in 2D CdSe Nanoplatelets via Magneto-optical Spectroscopy

Colloidal, two-dimensional semiconductor nanoplatelets (NPLs) exhibit quantum confinement in only one dimension, which results in an electronic structure that is significantly altered compared to that of other quantum-confined nanomaterials. Whereas it is often assumed that the lack of quantum confinement in the lateral plane yields a spatially extended exciton, reduced dielectric screening potentially challenges this picture. Here, we implement absorption spectroscopy in pulsed magnetic fields up to 60 T for three different CdSe NPL thicknesses and lateral areas. Based on diamagnetic shifts, we find that the exciton lateral extent is comparable to NPL thickness, indicating that the quantum confinement and reduced screening concomitant with few-monolayer thickness strongly reduces the exciton lateral extent. Atomistic electronic structure calculations of the exciton size for varying lengths, widths, and thicknesses support the substantially smaller in-plane exciton extent.

Polymer nanocomposites having a high filler content: synthesis, structures, properties, and applications

The recent development of nanoscale fillers, such as carbon nanotubes, graphene, and nanocellulose, allows the functionality of polymer nanocomposites to be controlled and enhanced. However, conventional synthesis methods of polymer nanocomposites cannot maximise the reinforcement of these nanofillers at high filler content. Approaches for the synthesis of high content filler polymer nanocomposites are suggested to facilitate future applications. The fabrication methods address the design of the polymer nanocomposite architecture, which encompasses one, two, and three dimensional morphologies. Factors that hamper the reinforcement of nanostructures, such as alignment, dispersion of the filler and interfacial bonding between the filler and polymer, are outlined. Using suitable approaches, maximum potential reinforcement of nanoscale fillers can be anticipated without limitations in orientation, dispersion, and the integrity of the filler particle-matrix interface. High filler content polymer composites containing emerging materials such as 2D transition metal carbides, nitrides, and carbonitrides (MXenes) are expected in the future.

Structural Reorganization of CNC in Injection-Molded CNC/PBAT Materials under Thermal Annealing

Composite materials were prepared by extrusion and injection molding from polybutyrate adipate terephthalate (PBAT) and high aspect ratio cellulose nanocrystals (CNCs) extracted from capim dourado fibers. Three CNC contents were used, corresponding to 0.5, 1, and 2 times the theoretical percolation threshold. Small-amplitude oscillary shear (SAOS) experiments show that as the CNC content increases, a more elastic behavior is observed but no percolating network can form within the polymeric matrix as a result of the high shear rates involved during the injection-molding process. Annealing of the samples at 170 °C was performed, and the possible reorganization of the nanofiller was investigated. This reorganization was further elucidated using 2D-SAOS and creep experiments.

Evaluation of flow-induced nanoclay orientation and microstructural stability in polyethylene/clay nanocomposites via melt rheological and thermal analysis

The effects of shear rate upon the flow-induced nanoclay orientation and morphological stability in film blown polyethylene clay nanocomposites were studied by means of linear and nonlinear rheological characterization parallel with differential scanning calorimetry and X-ray diffraction (XRD) analyses. Nanocomposite samples were prepared using a modular twin screw extruder followed by film processing technique. XRD analysis performed on film samples showed that the samples exhibited intercalated/exfoliated microstructure. The 3D physical networks were formed by the clay nanolayers in the structures of undrawn samples. However, the breakdown of the clay physical networks during film processing as a result of the imposed shear field within the die area and also an elongational flow field was evidenced. Time sweep test performed at various shear rates and shearing times using a rheometric mechanical spectrometer showed that, in all samples, the time required for the restructurization of the clay nanolayers during relaxation of the melt was found to be higher than 3600 s.

Using Small-Angle Scattering Techniques to Understand Mechanical Properties of Biopolymer-Based Biomaterials

The design and engineering of innovative biopolymer-based biomaterials for a variety of biomedical applications should be based on the understanding of the relationship between their nanoscale structure and mechanical properties. Down the road, such understanding could be fundamental to tune the properties of engineered tissues, extracellular matrices for cell delivery and proliferation/differentiation, etc. In this tutorial review, we attempt to show in what way biomaterial structural data can help to understand the bulk material properties. We begin with some background on common types of biopolymers used in biomaterials research, discuss some typical mechanical testing techniques and then review how others in the field of biomaterials have utilized small-angle scattering for material characterization. Detailed examples are then used to show the full range of possible characterization techniques available for biopolymer-based biomaterials. Future developments in the area of material characterization by small-angle scattering will undoubtedly facilitate the use of structural data to control the kinetics of assembly and final properties of prospective biomaterials.

Hydrogen bonding-driven rheological modulation of chemically reduced graphene oxide/poly(vinyl alcohol) suspensions and its application in electrospinning

Rheology of graphene oxide (GO) and chemically reduced graphene oxide (RGO) nanosheets suspended in poly(vinyl alcohol) (PVA) solution were investigated by altering nanosheet loading and reduction time of RGO in a wide range. A small amount (0.5 wt%) of GO and RGO in the dilute regime of filler resulted in a threefold increase and a fourfold decrease in steady viscosity at 0.01 s(-1), respectively; increasing GO and RGO loadings in the semi-dilute regime of filler caused steady viscosity to increase to different degrees. Meanwhile, the steady viscosity of the suspension decreased gradually by more than one order of magnitude with increasing reduction time of RGO. By characterizing the microstructure in suspensions, the style and relative density of H-bonding between PVA chains and nanosheets were confirmed to account for the suspension rheology. Modulation of viscosity in a wide range via simply control of the loading and reduction time of RGO was hydrogen bonding-driven, which was successfully applied to electrospinning to prepare nanocomposite nanofibers. The addition of 1 wt% GO and RGO with respect to the polymer mass significantly improved PVA fibrous uniformity and fineness, and the spinnable concentration range of PVA was greatly broadened from (8.5-11.3 wt%) to (5-18 wt%). Meanwhile, the thermal stability of the nanofibers was also enhanced by GO or RGO addition.

Rheological behavior of clay-nanoparticle hybrid-added bentonite suspensions: specific role of hybrid additives on the gelation of clay-based fluids

Two different types of clay nanoparticle hybrid, iron oxide nanoparticle clay hybrid (ICH) and Al(2)O(3)-SiO(2) nanoparticle clay hybrid (ASCH), were synthesized and their effects on the rheological properties of aqueous bentonite fluids in steady state and dynamic state were explored. When ICH particles were added, bentonite particles in the fluid cross-link to form relatively well-oriented porous structure. This is attributed to the development of positively charged edge surfaces in ICH that leads to strengthening of the gel structure of the bentonite susensions. The role of ASCH particles on the interparticle association of the bentonite fluids is different from that of ICH and sensitive to pH. As pH of ASCH-added bentonite suspensions increased, the viscosity, yield stress, storage modulus, and flow stress decreased. In contrast, at low pH, the clay suspensions containing ASCH additives were coagulated and their rheological properties become close to those of ICH added bentonite fluids. A correlation between the net surface charge of the hybrid additives and the rheological properties of the fluids indicates that the embedded nanoparticles within the interlayer space control the variable charge of the edge surfaces of the platelets and determine the particles association behavior of the clay fluids.

Rheo-SAXS investigation of shear-thinning behaviour of very anisometric repulsive disc-like clay suspensions

Aqueous suspensions of swelling clay minerals exhibit a rich and complex rheological behaviour. In particular, these repulsive systems display strong shear-thinning at very low volume fractions in both the isotropic and gel states. In this paper, we investigate the evolution with shear of the orientational distribution of aqueous clay suspensions by synchrotron-based rheo-SAXS experiments using a Couette device. Measurements in radial and tangential configurations were carried out for two swelling clay minerals of similar morphology and size, Wyoming montmorillonite and Idaho beidellite. The shear evolution of the small angle x-ray scattering (SAXS) patterns displays significantly different features for these two minerals. The detailed analysis of the angular dependence of the SAXS patterns in both directions provides the average Euler angles of the statistical effective particle in the shear plane. We show that for both samples, the average orientation is fully controlled by the local shear stress around the particle. We then apply an effective approach to take into account multiple hydrodynamic interactions in the system. Using such an approach, it is possible to calculate the evolution of viscosity as a function of shear rate from the knowledge of the average orientation of the particles. The viscosity thus recalculated almost perfectly matches the measured values as long as collective effects are not too important in the system.