Nanoscale Morphology of Water in Silica Colloidal Crystals

Cohesion Gain Induced by Nanosilica Consolidants for Monumental Stone Restoration

Mineral nanoparticle suspensions with consolidating properties have been successfully applied in the restoration of weathered architectural surfaces. However, the design of these consolidants is usually stone-specific and based on trial and error, which prevents their robust operation for a wide range of highly heterogeneous monumental stone materials. In this work, we develop a facile and versatile method to systematically study the consolidating mechanisms in action using a surface forces apparatus (SFA) with real-time force sensing and an X-ray surface forces apparatus (X-SFA). We directly assess the mechanical tensile strength of nanosilica-treated single mineral contacts and show a sharp increase in their cohesion. The smallest used nanoparticles provide an order of magnitude stronger contacts. We further resolve the microstructures and forces acting during evaporation-driven, capillary-force-induced nanoparticle aggregation processes, highlighting the importance of the interactions between the nanoparticles and the confining mineral walls. Our novel SFA-based approach offers insight into nano- and microscale mechanisms of consolidating silica treatments, and it can aid the design of nanomaterials used in stone consolidation.

Capillary-Enhanced Immobilization of Nanoparticles

The contact between a spherical nanoparticle and a planar substrate is surrounded by an annular wedge cavity. In adsorption processes, this acts like a small pore. Interfacial/capillarity effects lead to an accumulation of adsorbate in this region ("capillary condensation"). This effectively increases the contact area between the particles and the substrate. Thus, capillary-enhanced adsorbate accumulation increases the adhesion between the nanoparticles and the planar surface, which effectively immobilizes the particles.

Colloidal crystals and water: Perspectives on liquid-solid nanoscale phenomena in wet particulate media

Solid colloidal ensembles inherently contain water adsorbed from the ambient moisture. This water, confined in the porous network formed by the building submicron spheres, greatly affects the ensemble properties. Inversely, one can benefit from such influence on collective features to explore the water behavior in such nanoconfinements. Recently, novel approaches have been developed to investigate in-depth where and how water is placed in the nanometric pores of self-assembled colloidal crystals. Here, we summarize these advances, along with new ones, that are linked to general interfacial water phenomena like adsorption, capillary forces, and flow. Water-dependent structural properties of the colloidal crystal give clues to the interplay between nanoconfined water and solid fine particles that determines the behavior of ensembles. We elaborate on how the knowledge gained on water in colloidal crystals provides new opportunities for multidisciplinary study of interfacial and nanoconfined liquids and their essential role in the physics of utmost important systems such as particulate media.

Identification of Dewetting Stages and Preparation of Single Chain Gold Nanoparticle Rings by Colloidal Lithography

Massively parallel nanoparticle assembly was carried out by means of colloidal lithographic experiments over a silicon substrate supported (sub)microparticle Langmuir-Blodgett monolayer, using high purity aqueous solution of PEGylated gold nanoparticles. The size of the polystyrene template particles in the monolayer was varied between 608 nm and 2.48 μm, while gold nanoparticles with diameters between 18 and 65 nm were used. Thanks to the PEGylation of the gold nanoparticles, they could be used as tracer objects to follow the drying process. In this way, different dewetting stages could be identified in the confined space between and underneath the template polystyrene spheres. Depending on the concentration of the nanoparticles, the presented approach allows the preparation of single-particle width necklace structures composed of gold particles. At the same time, the high purity of the substrate as well as of the evolved particle rings is preserved and unwanted particle deposition on the substrate surface is minimized.

Exploration and exploitation of water in colloidal crystals

Water on solid surfaces is ubiquitously found in nature, in most cases due to mere adsorption from ambient moisture. Because porous structures have large surfaces, water may significantly affect their characteristics. This is particularly obvious in systems formed by separate particles, whose interactions are strongly influenced by small amounts of liquid. Water/solid phenomena, like adsorption, condensation, capillary forces, or interparticle cohesion, have typically been studied at relatively large scales down to the microscale, like in wet granular media. However, much less is known about how water is confined and acts at the nanoscale, for example, in the interstices of divided systems, something of utmost importance in many areas of materials science nowadays. With novel approaches, in-depth investigations as to where and how water is placed in the nanometer-sized pores of self-assembled colloidal crystals have been made, which are employed as a well-defined, versatile model system with useful optical properties. In this Progress Report, knowledge gained in the last few years about water distribution in such nanoconfinements is gathered, along with how it can be controlled and the consequences it brings about to extract new or enhance existing material functionalities. New methods developed and new capabilities of standard techniques are described, and the water interplay with the optical, chemical, and mechanical properties of the ensemble are discussed. Some lines for applicability are also highlighted and aspects to be addressed in the near future are critically summarized.