Diverse pore ordering in porous silica: synthesis and quantitative structural insights based on combining scattering and imaging techniques

Mesoporous silica exhibits a diverse range of applications owing to its pore structure and inter-pore correlation. Consequently, quantitative characterization of its mesoscopic structure is extremely crucial to reciprocate its potential applications. In this work, we utilized the chemical and aerosol routes to successfully synthesize granular, porous silica with an average pore size in the range of ∼5-10 nm and different degrees of structural correlation among its pores. To delve into their structural morphology, we employed complementary characterization techniques, including X-ray scattering, electron microscopy, and gas adsorption. Small-angle X-ray scattering (SAXS) was used to obtain statistically averaged quantitative information about their porous network. Field-emission scanning electron microscopy (FESEM) and high-resolution transmission electron microscopy (HRTEM) were used to identify their morphology and positional ordering. The information from these three different techniques was indeed complementary in nature. Thus, combining the comparative results from the detailed analyses using scattering, imaging and gas adsorption techniques is effective in providing an overall quantitative understanding about the morphology and pore correlations in this type of porous material with diverse pore structures.

A Platform Approach to Protein Encapsulates with Controllable Surface Chemistry

The encapsulation of proteins into core-shell structures is a widely utilised strategy for controlling protein stability, delivery and release. Despite the recognised utility of these microstructures, however, core-shell fabrication routes are often too costly or poorly scalable to allow for industrial translation. Furthermore, many scalable routes rely upon emulsion-techniques implicating denaturing or environmentally harmful organic solvents. Herein, we investigate core-shell protein encapsulation through single-feed, aqueous spray drying: a cheap, industrially ubiquitous particle-formation technology in the absence of organic solvents. We show that an excipient’s preference for the surface of the spray dried particle is well-predicted by its hydrodynamic diameter (Dh) under relevant feed buffer conditions (pH and ionic strength) and that the predictive power of Dh is improved when measured at the spray dryer outlet temperature compared to room temperature (R2 = 0.64 vs. 0.59). Lastly, we leverage these findings to propose an adaptable design framework for fabricating core-shell protein encapsulates by single-feed aqueous spray drying.

Confinement driven anomalous freezing in nano porous spray dried microspheres

One-step evaporative jamming of colloidal silica particles in contact-free spray droplets resulted in well-defined powder micro-granules with interstitial nanopores. This paper reports the anomalous freezing behaviour of confined water in the microspheres synthesized using spray drying. It has been revealed that the freezing point of water in these microspheres gets significantly lowered (∼-45 °C) owing to the confinement effect. Thermoporometry results are corroborated with the structural details obtained using complementary techniques of gas adsorption measurements and small-angle x-ray scattering.

Designing the shape of supraparticles by controlling the apparent contact angle and contact line friction of droplets

Surface-templated evaporation-driven supraparticle synthesis is a versatile method for supraparticle fabrication. A supraparticle is formed by drying droplet of a colloidal dispersion on liquid repellent surfaces, allowing precise control of the size and mean composition of the supraparticles. The crucial factor determining the morphology is the motion of the contact line of the dispersion droplet on the liquid repellent surface. Here, we study effects of (i) the apparent contact angle and (ii) the contact line friction of a droplet on the shape of the supraparticle. In order to change the initial apparent contact angle of the dispersion droplet a surfactant was added to decrease surface tension. In addition, two different liquid repellent surfaces were used: a polydimethysiloxane (PDMS) grafted surface and a lubricated surface. Both surfaces exhibited distinctly different contact line friction during evaporation. As the initial contact angle of a droplet decreases and friction of a contact line increases, flatter supraparticles are fabricated. By using this simple manipulation principle, eventually, various shapes of supraparticles can be obtained, such as mushroom, hemispherical, convex lens, and disk shapes. This study presents fundamental and critical information that allow us to manipulate the shape of a supraparticle via surface-templated evaporation-driven synthesis that increases the scalability of supraparticles for use in a wide range of applications.

Anisotropic interaction driven surface modulation on spray-dried microgranules

Rapid evaporation of solvent from spray colloidal droplets induces directed self-assembly among the nanoparticles, eventually interlocking them into correlated granular structures. In this work, it is demonstrated that anisotropy in colloidal interparticle interaction plays a key role in governing the surface topology of spray-dried granules. Colloidal dispersion comprised of spherical nanosilica (NS) and cylindrical carbon nanotubes (CNT) was chosen as a model system in this regard. For identical polarities of the colloidal components, granules with prominent wrinkle-like modulations are obtained, which is in drastic contrast with the case of opposite polarities. The extent of surface modulation depends on the relative concentration of CNT with respective to NS. A plausible mechanism for the formation of surface modulation is elucidated on the basis of the evolving anisotropic interparticle interactions during assembly. Electron microscopy, small-angle scattering, Raman spectroscopic techniques have been used for quantitative characterization of these micro-granules.

Supraparticles: Functionality from Uniform Structural Motifs

Under the right process conditions, nanoparticles can cluster together to form defined, dispersed structures, which can be termed supraparticles. Controlling the size, shape, and morphology of such entities is a central step in various fields of science and technology, ranging from colloid chemistry and soft matter physics to powder technology and pharmaceutical and food sciences. These diverse scientific communities have been investigating formation processes and structure/property relations of such supraparticles under completely different boundary conditions. On the fundamental side, the field is driven by the desire to gain maximum control of the assembly structures using very defined and tailored colloidal building blocks, whereas more applied disciplines focus on optimizing the functional properties from rather ill-defined starting materials. With this review article, we aim to provide a connecting perspective by outlining fundamental principles that govern the formation and functionality of supraparticles. We discuss the formation of supraparticles as a result of colloidal properties interplaying with external process parameters. We then outline how the structure of the supraparticles gives rise to diverse functional properties. They can be a result of the structure itself (emergent properties), of the colocalization of different, functional building blocks, or of coupling between individual particles in close proximity. Taken together, we aim to establish structure-property and process-structure relationships that provide unifying guidelines for the rational design of functional supraparticles with optimized properties. Finally, we aspire to connect the different disciplines by providing a categorized overview of the existing, diverging nomenclature of seemingly similar supraparticle structures.

Spray-Drying of Electrode Materials for Lithium- and Sodium-Ion Batteries

The performance of electrode materials in lithium-ion (Li-ion), sodium-ion (Na-ion) and related batteries depends not only on their chemical composition but also on their microstructure. The choice of a synthesis method is therefore of paramount importance. Amongst the wide variety of synthesis or shaping routes reported for an ever-increasing panel of compositions, spray-drying stands out as a versatile tool offering demonstrated potential for up-scaling to industrial quantities. In this review, we provide an overview of the rapidly increasing literature including both spray-drying of solutions and spray-drying of suspensions. We focus, in particular, on the chemical aspects of the formulation of the solution/suspension to be spray-dried. We also consider the post-processing of the spray-dried precursors and the resulting morphologies of granules. The review references more than 300 publications in tables where entries are listed based on final compound composition, starting materials, sources of carbon etc.

A deep look into the spray coating process in real-time-the crucial role of x-rays

Tailoring functional thin films and coating by rapid solvent-based processes is the basis for the fabrication of large scale high-end applications in nanotechnology. Due to solvent loss of the solution or dispersion inherent in the installation of functional thin films and multilayers the spraying and drying processes are strongly governed by non-equilibrium kinetics, often passing through transient states, until the final structure is installed. Therefore, the challenge is to observe the structural build-up during these coating processes in a spatially and time-resolved manner on multiple time and length scales, from the nanostructure to macroscopic length scales. During installation, the interaction of solid-fluid interfaces and between the different layers, the flow and evaporation themselves determine the structure of the coating. Advanced x-ray scattering methods open a powerful pathway for observing the involved processes in situ, from the spray to the coating, and allow for gaining deep insight in the nanostructuring processes. This review first provides an overview over these rapidly evolving methods, with main focus on functional coatings, organic photovoltaics and organic electronics. Secondly the role and decisive advantage of x-rays is outlined. Thirdly, focusing on spray deposition as a rapidly emerging method, recent advances in investigations of spray deposition of functional materials and devices via advanced x-ray scattering methods are presented.

Trends in small angle neutron scattering of actinide–trialkyl phosphate complexes: a molecular insight into third phase formation

SANS as a molecular probe was used to investigate and quantify the aggregation tendency of metal complexes, facilitating the prediction of third phase formation.

Nonuniform Growth of Composite Layer-by-Layer Assembled Coatings via Three-Dimensional Expansion of Hydrophobic Magnetite Nanoparticles

Nanocomposite coatings are promising for a range of practical applications, and layer-by-layer assembly (LbL) is a versatile tool for nanocomposite formation. However, conventional LbL is a quite laborious procedure taking a lot of time to reach a sufficient thickness of the coatings required for practical applications. Herein, we proposed a novel variant of the LbL approach based on the deposition of hydrophilic polyelectrolyte molecules from a polar solvent and hydrophobic magnetite nanoparticles (NPs) from a nonpolar dispersion medium with an intermediate washing in the same polar solvent. The composite multilayers formed in this way exhibit exponential growth of the thickness and mass. On the basis of quartz crystal microbalance (QCM), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), atomic force microscopy (AFM), and surface profile measurements, we propose a model describing the driving force of multilayer formation and the factors leading to nonlinear growth of their mass and thickness. The results allow one to expand the understanding of the mechanism of the LbL assembly in order to form multifunctional nanocomposites in a more efficient way.