Multiscale Effects of Interfacial Polymer Confinement in Silica Nanocomposites

Dispersing hydrophilic nanofillers in highly hydrophobic polymer matrices is widely used to tune the mechanical properties of composite material systems. The ability to control the dispersion of fillers is closely related to the mechanical tunability of such composites. In this work, we investigate the physical–chemical underpinnings of how simple end-group modification to one end of a styrene–butadiene chain modifies the dispersion of silica fillers in a polymer matrix. Using surface-sensitive spectroscopies, we directly show that polymer molecular orientation at the silica surface is strongly constrained for silanol functionalized polymers compared to nonfunctionalized polymers because of covalent interaction of silanol with silica. Silanol functionalization leads to reduced filler aggregation in composites. The results from this study demonstrate how minimal chemical modifications of polymer end groups are effective in modifying microstructural properties of composites by inducing molecular ordering of polymers at the surface of fillers

Fluorescent Staining of Silicone Micro- and Nanopatterns for Their Optical Imaging

Performance of engineered surfaces can be enhanced by making them hydrophobic or superhydrophobic via coating them with low-surface-energy micro- and nanopatterns. However, the wetting phenomena of particularly irregular shape and spacing (super)hydrophobic patterns such as polysiloxane coatings are not yet fully understood from a microscopic perspective. Here, we show a new method to collect 3D confocal images from irregular polysiloxane micro- and nanorods from a single rod resolution to discuss their wetting response over long liquid/solid interaction times and quantify the length and diameter of these rods. To collect such 3D confocal images, fluorescent dye containing water droplets were left on our superhydrophobic and hydrophobic polysiloxane coated surfaces. Then their liquid/solid interfaces were imaged at different staining scenarios: (i) using different fluorescent dyes, (ii) when the droplets were in contact with surfaces, or (iii) after the droplets were taken away from the surface at the end of staining. Using such staining strategies, we could resolve the micro- and nanorods from root to top and determine their length and diameter, which were then found to be in good agreement with those obtained from their electron microscopy images. 3D confocal images in this paper, for the first time, present the long-time existence of more than one wetting state under the same droplet in contact with surfaces, as well as external and internal three-phase contact lines shifting and pinning. In the end, these findings were used to explain the time-dependent wetting kinetics of our surfaces. We believe that the proposed imaging strategy here will, in the future, be used to study many other irregular patterned (super)antiwetting surfaces to describe their wetting theory, which is today impossible due to the complicated surface geometry of these irregular patterns

Droplet size assisted polysiloxane architecting

(Super)antiwetting shielding around engineering materials and protecting them against harsh environmental conditions has been achieved in recent years via growing various geometry polysiloxane (or silicone) patterns around them by using droplet assisted growth (DAGS) method, where the polymerization takes place inside of the water droplets acting as reaction vessels. The size and distribution of these reaction vessels are the main factors in making different geometry silicone patterns; however, very little is known about the fate of these droplets throughout the polymerization. Here, we proposed keeping the relative humidity (% RH) inside the reactor stable throughout the polymerization as a new coating parameter to force the size of the reaction vessel water droplets to be the same for building simple shape silicone rods with controlled geometry and distribution. In this manner, we grew simple geometry cylindric micro-rods on surfaces and could tune their length, diameter, inter-rod spacings, and thus the (super)hydrophobicity. Beyond fabricating simple geometry cylindrical micro rods, here, we also demonstrate that by changing the amplitude and the stability of the % RH, it is possible to fabricate different (super)hydrophobic nano-grasses, conical silicone micro-rods, and isotropic silicone nanofilaments (SNF). In the end, the proposed new way of tuning initial and in-situ reaction vessel droplet size can be used as a single factor to formulate different geometry silicone patterns with tunable dimensions, leading to different roughness and thus different degrees of hydrophobicity and superhydrophobicity. Due to its simplicity, silicone patterning with irregular spacing and size is preferred among other coating techniques, but the mathematical description of these irregular patterns is not trivial to explain their (super)hydrophobicity. To a certain extent, the droplet-size-assisted silicone shaping in this work provides a new way to control the length, diameter, morphology, inter-rod spacing, and thus the (super)hydrophobicity of the silicone patterns, especially those in the shape of simple cylindrical micro-rods. This control over silicone architecting will help to prepare new (super)hydrophobic coatings with more controlled morphology and thus wettability; on the other hand, it will support surface scientists modeling the connection between surface geometry and (super)antiwetting of such irregular pillared surfaces that remain elusive

Fluorescent Staining of Silicone Micro-and Nano-patterns for Their Optical Imaging

Performance of engineered surfaces can be enhanced by making them hydrophobic or superhydrophobic via coating them with low-surface-energy micro-and nano-patterns. However, the wetting phenomena of particularly irregular shape and spacing (super)hydrophobic patterns such as polysiloxane coatings are not yet fully understood from a microscopic perspective. Here, we show a new method to collect 3D confocal images from irregular polysiloxane micro-and nanorods from a single rod resolution to discuss their wetting response over long liquid/solid interaction times and quantify the length and diameter of these rods. To collect such 3D confocal images, fluorescent dye containing water droplets were left on our superhydrophobic and hydrophobic polysiloxane coated surfaces. Then their liquid/solid interfaces were imaged at different staining scenarios: (i) using different fluorescent dyes, (ii) when the droplets were in contact with surfaces, or (iii) after the droplets were taken away from the surface at the end of staining. Using such staining strategies, we could resolve the micro-and nanorods from root to top and determine their length and diameter, which were then found to be in good agreement with those obtained from their electron microscopy images. 3D confocal images in this paper, for the first time, present the long-time existence of more than one wetting state under the same droplet in contact with surfaces, as well as external and internal three-phase contact lines shifting and pinning. In the end, these findings were used to explain the time-dependent wetting kinetics of our surfaces. We believe that the proposed imaging strategy here will, in the future, be used to study many other irregular patterned (super)antiwetting surfaces to describe their wetting theory, which is today impossible due to the complicated surface geometry of these irregular patterns

Droplet Size-Assisted Polysiloxane Architecting

(Super)antiwetting shielding around engineering materials and protecting them against harsh environmental conditions has been achieved via growing various geometry polysiloxane (or silicone) patterns around them by using droplet assisted growth (DAGS) method, where the polymerization takes place inside of the water droplets acting as reaction vessels. The size and distribution of these reaction vessels are the main factors in making different geometry silicone patterns; however, very little is known about the fate of these droplets throughout the polymerization. Here, we proposed keeping the relative humidity (% RH) inside the reactor stable throughout the polymerization as a new coating parameter to force the size of the reaction vessel water droplets to be the same for building simple shape silicone rods with controlled geometry and distribution. In this manner, we grew simple geometry cylindric micro-rods on surfaces and could tune their length, diameter, inter-rod spacings, and thus the (super)hydrophobicity. Here, we also demonstrate that by changing the amplitude and the stability of the % RH, it is possible to fabricate different (super)hydrophobic nano-grasses, conical silicone micro-rods, and isotropic silicone nanofilaments (SNF). The proposed new way of tuning initial and in-situ reaction vessel droplet size can be used as a single factor to formulate different geometry silicone patterns with tunable dimensions, leading to different roughness and hydrophobicity. To a certain extent, the droplet-size-assisted silicone shaping in this work provides a new way to control the length, diameter, morphology, inter-rod spacing, and thus the (super)hydrophobicity of the silicone patterns, especially those in the shape of simple cylindrical micro-rods. This control over silicone architecting will help to prepare new (super)hydrophobic coatings with more controlled morphology and thus wettability; on the other hand, it will support surface scientists modeling the connection between surface geometry and (super)antiwetting of such irregular pillared surfaces that remain elusive

Ligand‐Binding Mediated Gradual Ionic Transport in Nanopores

Selective binding of metal ions to their receptors at the cell membranes is essential for immune reactions, signaling, and opening/closing of the ion channels. Such ligand‐binding‐based pore activities inspire scientists to build metal‐ion‐responsive mesoporous films that can interact with metal ions to tune the ionic nanopore transport. However, to apply these mesoporous films in novel sensing and separation applications, their ligand‐binding‐triggered ionic pore transport needs to be understood fundamentally toward programming the transport of both anions and cations simultaneously and gradually. Herein, it is shown how Ca²⁺ ion concentration and attachment to the different chemistry silica nanopores tunes finely the nanopore transport of both anions and cations, especially for phosphate‐containing polyelectrolyte (PMEP) functionalized mesopores. This biased ligand binding can gradually regulate the transport of anions and cations, whereas pores without polymers can gradually regulate only the anionic transport. Last, pore polymer functionality related to Ca²⁺ ion binding also diverts the pores’ adsorption/desorption (reversibility) response. Almost fully reversible Ca²⁺ binding is observed in non‐functional pores and non‐reversible Ca²⁺ binding at the PMEP‐modified pores. It is also demonstrated that non/functional pores, even at sub‐µm concentrations, bind only divalent Ca²⁺ ions, but they are not selective to trivalent Al³⁺ ions

Ligand‐Binding Mediated Gradual Ionic Transport in Nanopores

Abstract Selective binding of metal ions to their receptors at the cell membranes is essential for immune reactions, signaling, and opening/closing of the ion channels. Such ligand‐binding‐based pore activities inspire scientists to build metal‐ion‐responsive mesoporous films that can interact with metal ions to tune the ionic nanopore transport. However, to apply these mesoporous films in novel sensing and separation applications, their ligand‐binding‐triggered ionic pore transport needs to be understood fundamentally toward programming the transport of both anions and cations simultaneously and gradually. Herein, it is shown how Ca2+ ion concentration and attachment to the different chemistry silica nanopores tunes finely the nanopore transport of both anions and cations, especially for phosphate‐containing polyelectrolyte (PMEP) functionalized mesopores. This biased ligand binding can gradually regulate the transport of anions and cations, whereas pores without polymers can gradually regulate only the anionic transport. Last, pore polymer functionality related to Ca2+ ion binding also diverts the pores’ adsorption/desorption (reversibility) response. Almost fully reversible Ca2+ binding is observed in non‐functional pores and non‐reversible Ca2+ binding at the PMEP‐modified pores. It is also demonstrated that non/functional pores, even at sub‐µm concentrations, bind only divalent Ca2+ ions, but they are not selective to trivalent Al3+ ions

Crystallization at Nanodroplet Interfaces in Emulsion Systems: A Soft-Template Strategy for Preparing Porous and Hollow Nanoparticles

A heterophase method to prepare hollow and/or porous crystalline nanoparticles of metal oxides at room temperature is presented, taking cerium(IV) oxide and \u3b3-iron(III) oxide (i.e., maghemite) as representative cases. The crystallization begins at the oil\u2013water interface in aqueous nanodroplets of the precursor in inverse (water-in-oil) miniemulsion systems, and it may continue toward the inner part of the droplets. A poly(styrene-b-acrylic acid) block copolymer is used as a structuring agent because the ability of the carboxylic groups to bind metal ions improves the inorganic shell formation. A precipitating base is added from the continuous phase, generating hydroxide species at the interface that begin the crystallization. We analyze the effects of the synthetic parameters in terms of colloidal stability and morphology of the resulting materials. In the case of maghemite samples, the prepared dispersions of hollow particles present a distinct magnetofluidic behavior