Reorientation kinetics of superparamagnetic nanostructured rods

The attractive interactions between oppositely charged species (colloids, macromolecules etc) dispersed in water are strong, and the direct mixing of solutions containing such species generally yields to a precipitation, or to a phase separation. We have recently developed means to control the electrostatically-driven attractions between nanoparticles and polymers in water, and at the same time to preserve the stability of the dispersions. We give here an account of the formation of supracolloidal aggregates obtained by co-assembly of 7 nm particles with copolymers. Nanostructured rods of length comprised between 5 and 50 microns and diameter 500 nm were investigated. By application of a magnetic field, the rods were found to reorient along with the magnetic field lines. The kinetics of reorientation was investigated using step changes of the magnetic field of amplitude 90 degrees. From the various results obtained, among which an exponential decay of the tangent of the angle made between the rod and the field, we concluded that the rods are superparamagnetic.Comment: 12 pages - 452kB 7 - figures - 1 Table will be published in Journal of Physics : Condensed Matte

Electrostatic co-assembly of iron oxide nanoparticles and polymers : towards the generation of highly persistent superparamagnetic nanorods

A paradigm proposed recently by Boal et al. (A.K. Boal et al., Nature 404, 746-748, 2000) deals with the possibility to use inorganic nanoparticles as building blocks for the design and fabrication of colloidal and supracolloidal assemblies. It is anticipated that these constructs could be made of different shapes, patterns and functionalities and could constitute the components of future nanodevices including sensors, actuators or nanocircuits. Here we report a protocol that allowed us to fabricate such nanoparticle aggregates. The building blocks of the constructs were anionically coated iron oxide nanocrytals (superparamagnetic, size 7 nm) and cationic-neutral block copolymers. We have shown that the electrostatic interactions between charged species can be controlled by tuning the ionic strength of the dispersion. Under appropriate conditions, the control of electrostatics resulted in the elaboration of spherical or elongated aggregates at the micrometer length scale. The elongated aggregates were found to be rod-like, with diameters of a few hundred nanometers and lengths between 1 and 50 micrometers. In addition to their remarkable stiffness, the nanostructured rods were found to reorient along with an externally applied magnetic field, in agreement with the laws of superparamagnetism.Comment: 6 pages, 5 figures, appeared in Advanced materials in September 2008, reference

Research data supporting "Controlling the Photonic Properties of Cholesteric Cellulose Nanocrystal Films with Magnets"

The data are organized and grouped in dedicated .zip files for each Figure they contribute to. All figures (ToC, Figures 1-4 and SI_1-17) are present in high resolution in each sub-folder. Software for file extensions: .mi (Gwyddion), .mat, .m and .fig (MATLAB), .blend (Blender). The following Info is also available in README_OpenData.pdf: *** ToC. Original photographs (.jpg) Figure 1. Original photographs (.jpg) Figure 2. Original graphics 2A-F (.png, .fig) spectrometer settings (.mat) Original photographs (Figure 2K) Figure 3. Original microscopy photographs (Figures 3A-L) (.png) and scale bar (.png) Bertrand lens and k-space calibration with grating (.png, .xlsx, xls) Figure 4. Original SEM photographs (.tif) Figure S1. AFM (.tiff, .mi) Figure S2. Titration file (.xlsx, xls, .png) Figure S3. Original photographs (.jpg) Sample preparation and Phase diagram (.xlsx, xls) Figure S4. Original photographs (.jgp) evaporation rate (.xlsx, xls) Figure S5. Original photographs (.jgp) Figure S6. Original photographs (.jgp) Figure S7. Original photographs (.jgp) Figure S8. Original photographs and schematics (.png) Figure S9. Original photographs and schematics (.jpg, .png) Figure S10. Original SEM images (.tif) Figure S11. Original SEM images (.tif) Figure S12. Original SEM images (.tif) Figure S13. Original SEM images (.tif) Figure S14. Experimental magnetic field mapped of the tilted field geometry (.xlsx, .xls) Visualization of the magnetic field for tilted field geometries (.m, .png, .fig) 3D schematic of the two magnets with the iron plate (.png, .blend) Visualization of the magnetic field for simple geometries (.pdf, .png) Figure S15. Computing of the magnetic field for the tilted field geometry (magnetic_field_calculated_mapping.xlsx, .xls) Computed magnetic field for the tilted field geometry (TwoMagVertAndTwoMagUpsideDown.xlsx, .xls) Script in MATLAB to create the figures (.m) Original graphic files (.fig, .png) Figure S16. Original figures (.fig, .png) Script in MATLAB illustrating the formula used to create the fits (.m) fit datapoints (.txt) Figure S17. Original photography (.jpg

Aggregation of Antibody Drug Conjugates at Room Temperature: SAXS and Light Scattering Evidence for Colloidal Instability of a Specific Subpopulation

Coupling a hydrophobic drug onto monoclonal antibodies via lysine residues is a common route to prepare antibody–drug conjugates (ADC), a promising class of biotherapeutics. But a few chemical modifications on protein surface often increase aggregation propensity, without a clear understanding of the aggregation mechanisms at stake (loss of colloidal stability, self-assemblies, denaturation, etc.), and the statistical nature of conjugation introduces polydispersity in the ADC population, which raises questions on whether the whole ADC population becomes unstable. To characterize the average interactions between ADC, we monitored small-angle X-ray scattering in solutions of monoclonal IgG1 human antibody drug conjugate, with average degree of conjugation of 0, 2, or 3 drug molecules per protein. To characterize stability, we studied the kinetics of aggregation at room temperature. The intrinsic Fuchs stability ratio of the ADC was estimated from the variation over time of scattered light intensity and hydrodynamic radius, in buffers of varying pH, and at diverse sucrose (0% or 10%) and NaCl (0 or 100 mM) concentrations. We show that stable ADC stock solutions became unstable upon pH shift, well below the pH of maximum average attraction between IgGs. Data indicate that aggregation can be ascribed to a fraction of ADC population usually representing less than 30 mol % of the sample. In contrast to the case of (monodisperse) monoclonal antibodies, our results suggest that a poor correlation between stability and average interaction parameters should be expected as a corollary of dispersity of ADC conjugation. In practice, the most unstable fraction of the ADC population can be removed by filtration, which affects remarkably the apparent stability of the samples. Finally, the lack of correlation between the kinetic stability and variations of the average inter-ADC interactions is tentatively attributed to the uneven nature of charge distributions and the presence of patches on the drug-modified antibodies

Biocompatible and Sustainable Optical Strain Sensors for Large-Area Applications

By a simple two-step procedure, large photonic strain sensors using a biocompatible cellulose derivative are fabricated. Transient color shifts of the sensors are explained by a theoretical model that consideres the deformation of cholesteric domains, which is in agreement with the experimental results. The extremely simple fabrication method is suitable for both miniaturization and large-sale manufacture, taking advantage of inexpensive and sustainable materials.Biotechnology and Biological Sciences Research Council (David Phillips fellowship (Grant ID: BB/K014617/1)), The Isaac Newton Trust Cambridge (Grant ID: 76933), European Research Council (Grant ID: ERC-2014-STG H2020 639088

Hyperspectral Imaging of Photonic Cellulose Nanocrystal Films: Structure of Local Defects and Implications for Self-Assembly Pathways

Cellulose nanocrystals (CNCs) can spontaneously assemble into chiral nematic films capable of reflecting circularly polarized light in the visible range. As many other photonic materials obtained by bottom-up approaches, CNC films often display defects that greatly impact their visual appearance. Here, we study the optical response of defects in photonic CNC films, coupling optical microscopy with hyperspectral imaging, and we compare it to optical simulations of discontinuous cholesteric structures of increasing complexity. Cross-sectional SEM observations of the film structure guided the choice of simulation parameters and showed excellent agreement with experimental optical patterns. More importantly, it strongly suggests that the last fraction of CNCs to self-assemble, upon solvent evaporation, does not undergo the typical nucleation and growth pathway, but a spinodal decomposition, an alternative self-assembly pathway so far overlooked in cast films and that can have far-reaching consequences on choices of CNC sources and assembly conditions

Hyperspectral Imaging of Photonic Cellulose Nanocrystal Films: Structure of Local Defects and Implications for Self-Assembly Pathways

Cellulose nanocrystals (CNCs) can spontaneously assemble into chiral nematic films capable of reflecting circularly polarized light in the visible range. As many other photonic materials obtained by bottom-up approaches, CNC films often display defects that greatly impact their visual appearance. Here, we study the optical response of defects in photonic CNC films, coupling optical microscopy with hyperspectral imaging, and we compare it to optical simulations of discontinuous cholesteric structures of increasing complexity. Cross-sectional SEM observations of the film structure guided the choice of simulation parameters and showed excellent agreement with experimental optical patterns. More importantly, it strongly suggests that the last fraction of CNCs to self-assemble, upon solvent evaporation, does not undergo the typical nucleation and growth pathway, but a spinodal decomposition, an alternative self-assembly pathway so far overlooked in cast films and that can have far-reaching consequences on choices of CNC sources and assembly conditions

Universal scattering behavior of co-assembled nanoparticle-polymer clusters

Water-soluble clusters made from 7 nm inorganic nanoparticles have been investigated by small-angle neutron scattering. The internal structure factor of the clusters was derived and exhibited a universal behavior as evidenced by a correlation hole at intermediate wave-vectors. Reverse Monte-Carlo calculations were performed to adjust the data and provided an accurate description of the clusters in terms of interparticle distance and volume fraction. Additional parameters influencing the microstructure were also investigated, including the nature and thickness of the nanoparticle adlayer.Comment: 5 pages, 4 figures, paper published in Physical Review

Shape Memory Cellulose-Based Photonic Reflectors.

Biopolymer-based composites enable to combine different functionalities using renewable materials and cost-effective routes. Here we fabricate novel thermoresponsive photonic films combining cellulose nanocrystals (CNCs) with a polydiolcitrate elastomer exhibiting shape memory properties, known as hydroxyl-dominant poly(dodecanediol-co-citrate) (PDDC-HD). Iridescent films of CNCs are first made by evaporation-induced self-assembly, then embedded in the PDDC-HD prepolymer, and finally cured to obtain a cross-linked composite with shape memory properties. The fabricated samples are characterized by polarized optical microscopy, scanning electron microscopy, and thermomechanical cycling. The obtained hybrid material combines both intense structural coloration and shape memory effect. The association of stiff cellulose nanocrystals and soft polydiolcitrate elastomer enhances the overall mechanical properties (increased modulus and reduced brittleness). This hybrid nanocomposite takes advantage of two promising materials and expands their possibilities to cover a wide range of potential applications as multiresponsive devices and sensors. As they perform from room to body temperatures, they could be also good candidates for biomedical applications.EU FP7 NoE Nanophotonics4Energy Grant No. 248855, the Spanish MINECO project MAT2015-68075 (SIFE), and Comunidad de Madrid S2013/MIT-2740 (PHAMA_2.0) program. All the authors acknowledge the Royal Society (2014/R2-IE140719). A.E. was supported by the FPI PhD program from the MICINN. S.V., B.F.P., and A.G.P. are funded by the BBSRC David Phillips fellowship [BB/K014617/1] and the ERC-2014-STG H2020 639088. G.G. acknowledges the EPSRC [1525292]. M.C.S. acknowledges the Instituto de Salud Carlos III of Spain for a Miguel Servet I contract (MS13/00060)