Interacting Trimagnetic Ensembles for Enhanced Magnetic Resonance Transverse Relaxivity.

An ensemble of nanosystems can be considered to improve magnetic resonance imaging (MRI) transverse relaxivity. Herein, an interacting superparamagnetic competing structure of an isotropic-anisotropic trimagnetic hybrid nanosystem, γ-Fe2O3@δ-MnO2@NiFe2O4, is considered for MRI relaxivity exploration. The interacting superparamagnetic system reveals fascinating dynamic magnetic behavior, where flower-shaped two-dimensional flakes are decorated over nanoparticles. The hybrid nanosystem exhibits modulated shape anisotropy with spin blocking and energy barrier broadening, which help in achieving faster MR transverse relaxivity. The hierarchical architecture ensemble of the trimagnetic landscape shows effective MR transverse relaxivity with a transverse (r2)/longitudinal (r1) relaxivity of 61.5 and potential cell viability. The competing trimagnetic system with regulated activation energy is found to be the underlying reason for such signal enhancement in MRI contrast efficiency. Hence, this study displays a novel pathway correlating MR transverse relaxivity with dynamic magnetic behavior and competing landscape of hierarchical trimagnetic ensembles.

Modulating a model membrane of sphingomyelin by a tricyclic antidepressant drug.

Tricyclic medicine such as amitriptyline (AMT) hydrochloride, initially developed to treat depression, is also used to treat neuropathic pain, anxiety disorder, and migraines. The mechanism of functioning of this type of drugs is ambiguous. Understanding the mechanism is important for designing new drug molecules with higher pharmacological efficiency. Hence, in the present study, biophysical approaches have been taken to shed light on their interactions with a model cellular membrane of brain sphingomyelin in the form of monolayer and multi-lamellar vesicles. The surface pressure-area isotherm infers the partitioning of a drug molecule into the lipid monolayer at the air water interface, providing a higher surface area per molecule and reducing the in-plane elasticity. Further, the surface electrostatic potential of the lipid monolayer is found to increase due to the insertion of drug molecule. The interfacial rheology revealed a reduction of the in-plane viscoelasticity of the lipid film, which, depends on the adsorption of the drug molecule onto the film. Small-angle X-ray scattering (SAXS) measurements on multilamellar vesicles (MLVs) have revealed that the AMT molecules partition into the hydrophobic core of the lipid membrane, modifying the organization of lipids in the membrane. The modified physical state of less rigid membrane and the transformed electrostatics of the membrane could influence its interaction with synaptic vesicles and neurotransmitters making higher availability of the neurotransmitters in the synaptic cleft.

Advances in Understanding and Managing Alzheimer's Disease: From Pathophysiology to Innovative Therapeutic Strategies.

Alzheimer's disease (AD) is a debilitating neurodegenerative disorder characterized by the presence of amyloid-ß (Aß) plaques and tau-containing neurofibrillary tangles, leading to cognitive and physical decline. Representing the majority of dementia cases, AD poses a significant burden on healthcare systems globally, with onset typically occurring after the age of 65. While most cases are sporadic, about 10% exhibit autosomal forms associated with specific gene mutations. Neurofibrillary tangles and Aß plaques formed by misfolded tau proteins and Aß peptides contribute to neuronal damage and cognitive impairment. Currently, approved drugs, such as acetylcholinesterase inhibitors and N-methyl D-aspartate receptor agonists, offer only partial symptomatic relief without altering disease progression. A promising development is using lecanemab, a humanized IgG1 monoclonal antibody, as an immune therapeutic approach. Lecanemab demonstrates selectivity for polymorphic Aß variants and binds to large soluble Aß aggregates, providing a potential avenue for targeted treatment. This shift in understanding the role of the adaptive immune response in AD pathogenesis opens new possibilities for therapeutic interventions aiming to address the disease's intricate mechanisms. This review aims to summarize recent advancements in understanding Alzheimer's disease pathology and innovative therapeutic approaches, providing valuable insights for both researchers and clinicians.

Comprehensive Insights into Pathophysiology of Alzheimer's Disease: Herbal Approaches for Mitigating Neurodegeneration.

Alzheimer's disease [AD] is a progressive neurodegenerative disorder characterized by cognitive decline, memory loss, and functional impairment. Despite extensive research, the exact etiology remains elusive. This review explores the multifaceted pathophysiology of AD, focusing on key hypotheses such as the cholinergic hypothesis, hyperphosphorylated Tau Protein and Amyloid ß hypothesis, oxidative stress hypothesis, and the metal ion hypothesis. Understanding these mechanisms is crucial for developing effective therapeutic strategies. Current treatment options for AD have limitations, prompting the exploration of alternative approaches, including herbal interventions. Cholinesterase inhibitors, targeting the cholinergic hypothesis, have shown modest efficacy in managing symptoms. Blocking Amyloid ß [Aß] and targeting hyperphosphorylated tau protein are under investigation, with limited success in clinical trials. Oxidative stress, implicated in AD pathology, has led to the investigation of antioxidants. Natural products, such as Punica granatum Linn, Radix Scutellariae, and Curcuma longa have demonstrated antioxidant properties, along with anti-inflammatory effects, offering potential neuroprotective benefits. Several herbal extracts, including Ginkgo biloba, Bacopa monnieri, and Withania somnifera, have shown promise in preclinical studies. Compounds like Huperzine A, Melatonin, and Bryostatin exhibit neuroprotective effects through various mechanisms, including cholinergic modulation and anti-inflammatory properties. However, the use of herbal drugs for AD management faces limitations, including standardization issues, variable bioavailability, and potential interactions with conventional medications. Additionally, the efficacy and safety of many herbal products remain to be established through rigorous clinical trials. This review also highlights promising natural products currently in clinical trials, such as Resveratrol and Homotaurine, and their potential impact on AD progression. DHA, an omega-3 fatty acid, has shown cognitive benefits, while Nicotine is being explored for its neuroprotective effects. In conclusion, a comprehensive understanding of the complex pathophysiology of AD and the exploration of herbal interventions offer a holistic approach to managing this devastating disease. Future research should address the limitations associated with herbal drugs and further evaluate the efficacy of promising natural products in clinical settings.

Integrative Modulation of Magnetic Resonance Transverse and Longitudinal Relaxivity in a Cell-Viable Bimagnetic Ensemble, γ-Fe2O3@ZnFe2O4.

The potential application of magnetic nanosystems as magnetic resonance imaging (MRI) contrast agents has been thoroughly investigated. This work seeks to attain robust MRI-contrast efficiency by designing an interacting landscape of a bimagnetic ensemble of zinc ferrite nanorods and maghemite nanoparticles, γ-Fe2O3@ZnFe2O4. Because of competing spin clusters and structural anisotropy triggered by isotropic γ-Fe2O3 and anisotropic ZnFe2O4, γ-Fe2O3@ZnFe2O4 undergoes the evolution of cluster spin-glass state as evident from the critical slowing down law. Such interacting γ-Fe2O3@ZnFe2O4 with spin flipping of 1.2 × 10-8 s and energy barrier of 8.2 × 10-14 erg reflects enhanced MRI-contrast signal. Additionally, γ-Fe2O3@ZnFe2O4 is cell-viable to noncancerous HEK 293 cell-line and shows no pro-tumorigenic activity as observed in MDA-MB-231, an extremely aggressive triple-negative breast cancer cell line. As a result, γ-Fe2O3@ZnFe2O4 is a feasible option for an MRI-contrast agent having longitudinal relaxivity, r1, of 0.46 s-1mM-1 and transverse relaxivity, r2, of 15.94 s-1mM-1, together with r2/r1 of 34.65 at 1.41 T up to a modest metal concentration of 0.1 mM. Hence, this study addresses an interacting isotropic/anisotropic framework with faster water proton decay in MR-relaxivity resulting in phantom signal amplification.

Interparticle interaction-dependent jamming in colloids: insights into glass transition and morphology modulation during rapid evaporation-induced assembly.

Understanding the role of interparticle interactions in jamming phenomena is essential for gaining insights into the intriguing glass transition behavior observed in atomic and molecular systems. In this study, we investigate the jamming behavior of colloids with tunable interparticle interactions during evaporation-induced assembly (EIA). By manipulating the interaction among charged colloids using cationic polyethyleneimine (PEI) through electro-sorption and subsequent free polymer induced repulsion, we observe distinct jamming behavior in silica colloids during EIA, depending on the interparticle interactions. Silica colloids with strong repulsive interactions exhibit a repulsive colloidal glass state with a volume fraction of silica colloids in supraparticle ϕ ∼ 0.70. On the other hand, PEI-mediated attractive interactions among silica colloids lead to an attractive colloidal glass phase with a significantly lower ϕ ∼ 0.43. Free polymer induced repulsion of colloids at higher PEI concentration once again results in a repulsive glassy state with ϕ ∼ 0.61. Furthermore, we revealed that interparticle interactions not only influence the jamming behavior but also play a significant role in shaping the morphology of self-assembled structures during EIA, and the assembled structure undergoes a morphological reentrant transition from a doughnut-like shape to a spherical form and again back to a doughnut-like configuration. Jamming-dependent evolution of micropores and dynamics of the confined PEI have been probed using positron annihilation lifetime spectroscopy (PALS) and broadband dielectric spectroscopy (BDS). PALS reveals distinct variations in the micropores of the supraparticles with different PEI loadings, confirming the impact of jamming on the evolution of the micropores within the supraparticles. BDS measurements uncover non-monotonic dynamics of PEI molecules confined in the evolved pore network. It is revealed that the reentrant jamming behavior of colloids, modulated by PEI, holds profound significance for the long-term stability of supraparticles.

Performance of small- and wide-angle x-ray scattering beamline at Indus-2 synchrotron.

A Small- and Wide-Angle X-ray Scattering (SWAXS) beamline (BL-18) is installed and commissioned at a 1.5 T bending magnet port (5°) of Indus-2 synchrotron at RRCAT, Indore, India. The ∼40-m-long beamline has tunable x-ray energy in the range of 5-20 keV by using a double crystal monochromator. A 1.5-m-long toroidal mirror is used to focus the x-ray beam at the detector position. The beamline is equipped with a 6-m-long movable detector stage to access different wave-vector transfer ranges. At present, an online image plate area detector and a linear position-sensitive gas detector are installed for Small-Angle X-ray Scattering (SAXS) and Wide-Angle X-ray Scattering (WAXS) measurements, respectively. The beamline is operational in simultaneous SAXS/WAXS mode to probe the mesoscopic as well as molecular level structure over a wide range of wave-vector transfer. The specification of the beamline and its performance are reported here. A few recent experimental results, as obtained from BL-18, are also described in brief.

Evidence of Size Stratification in Colloidal Glass Microgranules Realized by Rapid Evaporative Assembly.

Evaporation is a ubiquitous phenomenon. Rapid evaporation of the continuous phase from micrometric colloidal droplets can be used to realize nanostructured microgranules, constituting the assembled nanoparticles. One of the important aspects of such nonequilibrium assembly is the nature of the packing of nanoparticles in the microgranules. The present work demonstrates the evidence of size stratification of the nanoparticles in such far-from-equilibrium configurations. Small-angle X-ray scattering, in combination with particle packing simulation, reveals the "large on top"-type stratification in such assembled microgranules, where the larger particles get concentrated at the outer shell of the granules while the smaller particles reside in the core region. It also reveals the presence of local clusters in such a rapid evaporative assembly in aerosolized colloidal droplets.

Probing Microscale Structuring-Induced Phase Separation with Fluorescence Recovery Diffusion Dynamics in Poly(ethylene glycol) Solutions.

Apart from biocompatibility, poly(ethylene glycol) (PEG)-based biomedical constructs require mechanical tunability and optimization of microscale transport for regulation of the release kinetics of biomolecules. This study illustrates the role of inhomogeneities due to aggregates and structuring in the PEG matrix in the microscale diffusion of a fluorescent probe. Comparative analysis of fluorescence recovery after photobleaching (FRAP) profiles with the help of diffusion half-time is used to assess the diffusion coefficient (D). The observations support a nontrivial dependence of diffusion dynamics on polymer concentration (volume fraction, φ) and that of fillers carboxymethyl cellulose (CMC) and nanoclay bentonite (B). D values follow the Rouse scaling D ∼ φ-0.54 in PEG solutions. The diffusion time of the fluorescent probe in the PEG+bentonite matrix reveals the onset of depletion interaction-induced phase separation with an increase in bentonite concentration in the PEG matrix beyond 0.1 wt %. Beyond this concentration, structure factors obtained from prebleach FRAP images show a rapid increase at low Q. The two-phase system (PEG-rich and bentonite-rich) was characterized by the hierarchical structural topology of bentonite aggregates, and aggregate sizes were obtained at different length scales with phase contrast imaging, small-angle neutron scattering, and small-angle X-ray scattering. The microscale transport detection presented captures sensitively the commencement of phase separation in the PEG + bentonite matrix, as opposed to the PEG or PEG + CMC matrix, which are observed to be one-phase systems. This method of diffusion half-time and prebleach image analysis can be used for the fast, high-throughput experimental investigation of microscale mechanical response and its correlation with structuring in the polymer matrix.

Polyethyleneimine-assisted formation of Ag-SiO2 hybrid microspheres for H2O2 sensing and SERS applications.

Herein, we report a simple, cost-effective, and eco-friendly approach for producing polyethyleneimine (PEI)-assisted silver nanoparticle-supported silica microspheres through evaporation-induced assembly (EIA). The silica-PEI microspheres obtained through EIA consisted of highly trapped PEI molecules owing to their electrosorption onto oppositely charged silica colloids. The trapped PEI molecules in the microspheres played a crucial role in linking silver ions to form silver ion-PEI complexes, which were then reduced to form silver nanoparticles. Further, the complex interactions between PEI and silica colloids led to enhanced porosity in the microspheres, enabling the efficient adsorption of Ag ions. The characterization of the Ag-SiO2 microspheres was carried out using various techniques, including field-emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDX) spectroscopy, X-ray diffraction (XRD), small-angle X-ray scattering (SAXS), and Fourier transform infrared (FTIR) spectroscopy, which confirmed the successful formation of Ag nanoparticles on microspheres, and a plausible formation mechanism is elucidated. The Ag-SiO2 microspheres exhibited good sensing properties for hydrogen peroxide (H2O2), with an estimated limit of detection of 1.08 mM and a sensitivity of 0.033 µA mM-1 mm-2. The microspheres were also used as a surface-enhanced Raman scattering (SERS) substrate, which demonstrated high sensitivity in detecting rhodamine 6G down to a concentration of 2 × 10-6 M. The present approach elucidates a promising alternative to conventional methods that face challenges, such as scalability issues, complex and cumbersome synthesis procedures, and the use of strong reducing agents. With the potential for industrial-level scalability, this method offers a viable strategy for producing Ag-SiO2 microspheres with possible applications in biomedical and sensing technologies.

Nucleation-Growth Versus Spinodal Decomposition in Fe-Cr Alloys: An Experimental Verification by Atom Probe Tomography and Small Angle Neutron Scattering.

Identifying the operative mode of phase separation [spinodal decomposition (SD) or nucleation-growth (NG)] remains an extremely important area of research. The present work examines this critically in the Fe-Cr system using atom probe tomography (APT) and small angle neutron scattering (SANS), and establishes the framework to distinguish the two different modes of α' phase separation in thermally aged Fe-35 at% Cr and Fe-20 at% Cr alloys. Independent APT analysis determines the mode of phase separation on the basis of (i) the presence/absence of periodic chemical fluctuation through radial distribution function analysis and (ii) interphase interface characteristics (diffuse/sharp). SANS analysis, in contrast, yields virtually indistinguishable correlation peaks for both the modes, which necessitates further investigation of the several different aspects of SANS profiles in the light of APT results. For the first time, key features of SANS profiles have been identified that can unambiguously distinguish SD from NG in the Fe-Cr system: (i) nature of temporal evolution of FWHM of the correlation peak and (ii) appropriate value of γ for fitting with the dynamic scaling model (γ = 6 for SD, Fe-35 at% Cr alloy; γ = 4 for NG, Fe-20 at% Cr alloy).

Temperature-dependent anomalous viscosity of aqueous solutions of imidazolium-based ionic liquids.

Ionic liquids (ILs) are organic salts with a low melting point compared to inorganic salts. Room temperature ILs are of great importance for their widespread potential industrial applications. The viscosity of aqueous solutions of two imidazolium-based ILs, investigated in the present study, exhibits an anomalous temperature variation. Unlike conventional molecular fluids, the viscosity of 1-methyl-3-octyl imidazolium chloride [OMIM Cl] and 1-methyl-3-decyl imidazolium chloride [DMIM Cl] solutions is found to increase with temperature and then depress. The Small Angle X-ray Scattering (SAXS) data suggest that the lattice parameter of the body-centered cubic lattice formed by the spherical micelles of these ILs, and the morphology of the micelles remain intact over the measured temperature range. The molecular dynamics simulation shows the micelles to be more refined with their integrated structure on increasing the temperature. On further increase of the temperature, the structure is found to be loosened, which is corroborated by the simulation work. The ionic conductivity of these IL solutions shows a trend that is opposite to that of the viscosity. The observed anomalous nature of the viscosity is attributed to the trapped dissociated ions in the network of the micellar aggregates.

Amphiphilic interaction-mediated ordering of nanoparticles in Pickering emulsion droplets.

For various industrial processes, the stabilization of an oil phase is crucial and demands a proper balance of complex interactions in an emulsion system. In Pickering emulsions, this is achieved by introducing nanoparticles, which become organized at the oil-water interface. The influence of interparticle interactions towards the formation of a stable emulsion and the ordering of the stabilizing nanoparticles is intriguing and needs attention. In this work, the role of amphiphilic interactions between hydrophilic silica nanoparticles and the Pluronic F127 tri-block co-polymer towards the spontaneous formation of a fairly stable Pickering emulsion has been studied using small-angle X-ray scattering. Unlike the usual random arrangements of the nanoparticles in a conventional Pickering emulsion, we observed highly organized silica nanoparticles at the oil-water interface. The established standard raspberry structural model of the Pickering emulsion fails to explain such strong ordering as observed in the present case. A plausible formation mechanism of the present Pickering emulsion with a high on-surface silica correlation is elucidated on the basis of the combined interactions of the block co-polymer and silica particles. A computer model is developed to elucidate the effects of size and distribution of the surface-decorating nanoparticles and their positional correlation.

Hollow TiO2/SiO2 composite microspheres through reactive assembly across immiscible liquid interfaces.

Titania (TiO2) based photocatalysts have shown tremendous potential in tackling important issues related to energy, the environment, and water purification. The tunable morphologies of the TiO2 based multicomponent composites are promising for the improvement of photocatalytic characteristics for practical applications. In this work, we report a one-step facile approach to achieve hollow silica/titania microspheres through the process of reactive assembly at the immiscible interface of micrometer-sized droplets. Scanning electron microscopy and small-angle neutron scattering revealed the hierarchal structure of the microspheres. Elemental mapping of the composite microspheres provided direct evidence of the incorporation of silica nanoparticles into the microspheres. The diffusion of reactant molecules and hydrolysis/condensation reactions across the phase boundary of the interface of two immiscible liquids controls the morphology of the microspheres and the size of TiO2 nanoparticles. The silica/titania composite microspheres show excellent thermal stability against the anatase to rutile phase transition caused by inhibition of the growth of TiO2 nanoparticles due to proximity of the silica nanoparticles. The photoelectrochemical measurements show that TiO2-SiO2 microspheres exhibit superior photocatalytic characteristics compared to the TiO2 microspheres. The kinetics of dye degradation for TiO2-SiO2 microspheres is found to be significantly faster compared to TiO2 microspheres which confirms the superior photocatalytic properties of the composite microspheres.

Unravelling the polyethylenimine mediated non-monotonic stability behaviour of silica colloids: the role of competing electrostatic and entropic interactions.

Polymer-mediated interactions play an important role in the stability of colloids and are therefore paramount for both fundamental as well as scientific interests. The stability of colloids in the presence of neutral polymers depends on several parameters such as the adsorbing/non-adsorbing nature, molecular weight, concentration and temperature, and such systems are well studied. However, the stability behaviour of charged colloids in the presence of charged polyelectrolyte involves complex interaction mechanisms and hence needs attention. The present work reports the study of the stability behaviour of negatively charged silica colloids in the presence of cationic polyethylenimine (PEI) polyelectrolyte using small-angle neutron and X-ray scattering. The intriguing non-monotonic stability behaviour of silica colloids is observed with varying concentrations of PEI. In the low and intermediate PEI concentration regimes, electrosorption of PEI on the silica colloids causes partial screening of charges, leading to aggregation of colloids. The DLVO interaction potential at low and intermediate concentrations of PEI exhibit a reduced repulsion barrier which is responsible for aggregation. In the high concentration regime, the entropic interaction between the free PEI molecules and PEI decorated silica colloids leads to depletion re-stabilization. The combination of DLVO potential and adsorbed PEI mediated enhanced depletion repulsion in the presence of free PEI gives rise to an increased repulsion barrier responsible for the re-stabilization at high PEI concentrations.

Effect of Oleylamine on the Surface Chemistry, Morphology, Electronic Structure, and Magnetic Properties of Cobalt Ferrite Nanoparticles.

The influence of oleylamine (OLA) concentration on the crystallography, morphology, surface chemistry, chemical bonding, and magnetic properties of solvothermal synthesized CoFe2O4 (CFO) nanoparticles (NPs) has been thoroughly investigated. Varying OLA concentration (0.01-0.1 M) resulted in the formation of cubic spinel-structured CoFe2O4 NPs in the size-range of 20-14 (±1) nm. The Fourier transform spectroscopic analyses performed confirmed the OLA binding to the CFO NPs. The thermogravimetric measurements revealed monolayer and multilayer coating of OLA on CFO NPs, which were further supported by the small-angle X-ray scattering measurements. The magnetic measurements indicated that the maximum saturation (MS) and remanent (Mr) magnetization decreased with increasing OLA concentration. The ratio of maximum dipolar field (Hdip), coercivity (HC), and exchanged bias field (Hex) (at 10 K) to the average crystallite size (Dxrd), i.e., (Hdip/Dxrd), (HC/Dxrd), and (Hex/Dxrd), increased linearly with OLA concentration, indicating that OLA concurrently controls the particle size and interparticle interaction among the CFO NPs. The results and analyses demonstrate that the OLA-mediated synthesis allowed for modification of the structural and magnetic properties of CFO NPs, which could readily find potential application in electronics and biomedicine.

Structure-Correlated Magnetic Resonance Transverse Relaxivity Enhancement in Superparamagnetic Ensembles with Complex Anisotropy Landscape.

The aim of the work is to explore structure-relaxivity relationship by observing transverse relaxivity enhancement in magnetic resonance imaging (MRI) of differently organized superparamagnetic complex ensembles of zinc ferrite isotropic/anisotropic nanosystems. We observe that superparamagnetic systems show a correlation of MRI-transverse relaxivity, r2/r1, with spatial arrangement of nanoparticles, as well as magnetic easy axes and thermal-energy-dependent anisotropy energy landscape. The presence of highly random/partially aligned easy axes with enhanced anisotropy constant leads to modulation in transverse relaxation. As a result, we achieve highest contrast efficiency in compact ensemble of isotropic nanoparticles and hollow core ensemble. Indeed, core-shell ensemble with combined effect of aligned and randomly oriented easy magnetic axes shows a reduction in MRI contrast efficiency. However, we address a hypothesis for transverse contrast efficiency where we depict the correlation among MRI-transverse contrast efficiency with structural complexity of ensembles, differently arranged primary nanoparticles/magnetic easy axes, anisotropy constant, and collective magnetic behavior. In consequence, we simplify the limitation of quantum mechanical outer-sphere diffusion model of magnetic resonance relaxivity by neglecting the contribution of magnetization and introducing an anisotropy constant contribution with complex structure landscape of easy axes.

Pattern of an Evaporated Colloidal Droplet on a Porous Membrane Dictated by Competitive Processes of Flow and Absorption.

Understanding the deposition pattern formed by an evaporated colloidal drop is of fundamental and technological interest. Such an evaporative process is important in various applications starting from inkjet printing to disease diagnosis. In this work, it is shown that the deposit pattern on a porous membrane can be tuned by varying the colloidal viscosity and membrane pore size. We have used small-angle X-ray scattering (SAXS) in scanning mode for profiling of deposit morphology and also for estimation of the interparticle correlation. It is demonstrated that low viscosity and small pore size favor a centrally dipped pattern owing to the coffee ring effect, which can be modified to a contrasting centrally peaked pattern by increasing the viscosity and pore size. To comprehend the experimental observations, a computer model has been developed using a continuity equation that well corroborates the experimental observations on the final deposited pattern and also provides the time evolution of the pattern. The work provides a way to tune the pattern of colloidal stain on a porous substrate by controlling flow and absorption.

Polyethylenimine assisted non-monotonic jamming of colloids during evaporation induced assembly and its implication on CO2 sorption characteristics.

We report a detailed study of hierarchically organized silica-polyethylenimine (PEI) microspheres achieved through evaporation-induced assembly. Due to complex interactions between oppositely-charged silica nanoparticles and PEI, non-monotonic jamming of the colloidal particles is manifested. With an increase in the polymer concentration, the local volume fraction of the silica particles decreases from 0.68 to 0.43 and then increases to 0.55 with further increase. The unusual jamming behaviour of the silica colloids in the presence of PEI provides an avenue for immobilizing PEI without reducing the porosity and specific area in contrast to the conventional impregnation approach. The resultant composite microspheres show good thermal stability and CO2 sorption characteristics. For a 33 wt% PEI loading, the microspheres exhibit a significant CO2 capture capacity of 65 mg g-1 even at room temperature and it is increased to 90 mg g-1 at 75 °C. The variation in the CO2 capture capacity at 0 °C as a function of PEI loading also demonstrated the signature of non-monotonicity owing to the structural modification in the silica-PEI microspheres. The composite microspheres demonstrated fast adsorption kinetics reaching 70% of the total capture capacity in one minute during the CO2 capture. The CO2 cycling adsorption-desorption studies showed good regeneration capability up to 20 cycles.

Jamming of Nano-Ellipsoids in a Microsphere: A Quantitative Analysis of Packing Fraction by Small-Angle Scattering.

The packing of particles is ubiquitous, and it is of fundamental importance, particularly in materials science in the nanometric length scale. It becomes more intriguing when constituent particles deviate from spherical symmetry owing to the inherent complexity in quantifying their positional and rotational correlation. For quantitative estimation of packing fraction, it requires a thorough analysis of the positional correlation of jammed particles. This article adopts a novel approach for determination of the packing fraction of strongly correlated nano-ellipsoids in a microsphere using small-angle scattering. The method has been elucidated through a quantitative analysis of structural correlation of nano-hematite ellipsoids in 3D micrometric granules, which are realized using rapid evaporative assembly. Owing to the deviation from spherical symmetry, the conventional analysis of scattering data fails to interpret the actual packing fraction of the anisotropic particles. The structural correlation gets smeared out because of orientation distribution among the packed anisotropic particles, which leads to an anomaly in the estimation of packing fraction using the conventional analysis approach. It is illustrated that consideration of an interparticle distance distribution function of the correlated nano-ellipsoids becomes indispensable in determining their packing fraction.