Final Report Summary - JANUS FERROELECTRICS (Janus Nanoparticles as Novel Ferroelectric Materials)
Janus Ferroelectrics is a project that aims to explore the potential utility of nanostructured monolayers on inorganic particles to create useful electronically responsive materials. Taking inspiration from recent discoveries in the field of nanostructured monolayers on gold nanoparticles, heterogeneous monolayers were utilized to create and study "Janus" biphasic monolayer systems on spherical particles. The individual faces of the spherical particle could be tuned to have variable electronic properties. Differences between the two bound faces would provide the foundation of the response to electrical stimuli.
As specified in the planning and work packages, the first main objective was to determine and define the parameters responsible for the formation of the Janus nanoparticles. We chose to use a platform of thiol-terminated molecules to form the monolayer on gold nanoparticles. The reason for this was twofold: first, this chemistry is the simplest, cleanest, and most consistent way of studying monolayer organization on spherical surfaces. Other chemistries pose significant problems in simplicity, robustness, and reproducibility. The second reason was existing expertise: both the fellow and the scientist in charge had developed extensive expertise in the area of generating and studying thiol-monolayer-protected gold nanoparticles. A combination of multiple techniques were utilized for this work, including ion mobility-mass spectrometry, nuclear magnetic resonance spectroscopy, scanning tunneling microscopy, and high-performance liquid chromatography, among others. Extensive study and collaboration yielded some useful information concerning the question of design parameters. However, it became clear that extensive complexity was inherent to the system. Even in a relatively simple and highly refined system such as this, broad diversity in monolayer morphology was found. Systems which were expected to generate Janus structure were found to create striped monolayers, randomly mixed monolayers, or a mixture of the two. In some cases Janus morphologies were detected in quantities too low to manifest a useful electronic response. Thus it became very difficult to properly parameterize the design of Janus structured monolayers.
The project progressed using monolayer systems which consistently produced Janus morphologies, or were suspected to be Janus nanoparticles but could not be positively confirmed. The large majority of systems which consistently produced Janus morphologies had similar electronic properties on both faces, reducing their usefulness to this project. Thus many monolayer components that were unconfirmed to form Janus monolayers were explored in this stage. Some promising properties were found, particularly in the realm of their physicochemical interactions with the media. Some of these nanoparticles manifested unusual solubility, many more would spontaneously and unexpectedly aggregation. However, no properly ferroelectric responsive nanoparticles were found. A significant amount of time was spent exploring this issue, generating several possible answers but none could be confirmed entirely. For each of the systems, it is suspected that the Janus morphologies were too dilute within the structurally diverse system, reducing any measurable effects. Second, in many cases the monolayer components may have been too electronically similar to generate a measurable response. It is likely that these two factors, among other minor factors, acted together. Unfortunately, attempts to “purify” the Janus morphologies from the other structures did not meet with success.
The focus of the project was then honed toward the unusual solubility and self-assembly properties of the nanoparticles. “Like dissolves like,” a common maxim in chemistry education, expresses the idea that the solubility of a molecule can be predicted by examining the structural similarity between that molecule and a given solvent. Though typically applied to small organic molecules in organic solvents or water, nanoscale particles with organic coatings follow the same maxim. This is so fundamental that it barely draws mention in the modern scientific literature. Solubility can generally be presumed when there are strong similarities in molecular structure between solute and solvent. When an organic coating featuring more than one type of chemistry is randomly spread across the surface of the colloid, the “like dissolves like” maxim is broadly valid as long as any featured chemistry is considered together. We are now providing an example of an important exception. When organic coating forms an organized monolayer on the colloid surface, the different functionalities can be organized in such a way that only one chemistry becomes dominant in determining the particle’s solubility. This effect generates unusual and surprisingly complex solubility properties of small gold colloids protected by a mixture of alkanethiol and fluorinated alkanethiols, which combine polar and omniphobic functionalities. Depending on the size of these colloids, the coating organizes differently, producing size-dependent dissolution in a range of fluorinated, perfluorinated, or non-fluorinated polar organic solvents. Fluorinated and partially-fluorinated solvents preferentially dissolve the smallest nanoparticles (mean diameter 2.5-3 nm), while non-fluorinated solvents preferentially dissolve larger nanoparticles (mean diameter >4.5 nm). New computational methods were developed to explore the atomic-level interactions between surface coatings and solvents. These methods generally agreed with experimental results, leading to possible insights into coating-led solvent orientation through electrostatic interactions. A novel approach was envisioned and partially developed to make the characterization of organic coatings more precise, robust, and accessible. New methods were also employed to investigate the ability of nanoscale measurement techniques to “push the envelope” in imaging these nanoparticles. Computational techniques were employed to model and predict the images obtained through these microscopic techniques, allowing for comparison with and validation of experimental results.
These results each serve to boost the state of the art within the European Union, through collaboration with European laboratories, European researchers, and disseminating knowledge though European institutions. The unique curvature-dependent properties of these nanoparticles serves as a powerful example of deviation from the “like dissolves like” maxim. The role of surface curvature on dipole-driven wetting effects also has implications for numerous fields of research in nanotechnology and materials. The results can be used to advance intellectual property in the development of new, smart nanomaterials with novel wetting properties, as well as the development of vital characterization methods for organic coatings on colloids.
As specified in the planning and work packages, the first main objective was to determine and define the parameters responsible for the formation of the Janus nanoparticles. We chose to use a platform of thiol-terminated molecules to form the monolayer on gold nanoparticles. The reason for this was twofold: first, this chemistry is the simplest, cleanest, and most consistent way of studying monolayer organization on spherical surfaces. Other chemistries pose significant problems in simplicity, robustness, and reproducibility. The second reason was existing expertise: both the fellow and the scientist in charge had developed extensive expertise in the area of generating and studying thiol-monolayer-protected gold nanoparticles. A combination of multiple techniques were utilized for this work, including ion mobility-mass spectrometry, nuclear magnetic resonance spectroscopy, scanning tunneling microscopy, and high-performance liquid chromatography, among others. Extensive study and collaboration yielded some useful information concerning the question of design parameters. However, it became clear that extensive complexity was inherent to the system. Even in a relatively simple and highly refined system such as this, broad diversity in monolayer morphology was found. Systems which were expected to generate Janus structure were found to create striped monolayers, randomly mixed monolayers, or a mixture of the two. In some cases Janus morphologies were detected in quantities too low to manifest a useful electronic response. Thus it became very difficult to properly parameterize the design of Janus structured monolayers.
The project progressed using monolayer systems which consistently produced Janus morphologies, or were suspected to be Janus nanoparticles but could not be positively confirmed. The large majority of systems which consistently produced Janus morphologies had similar electronic properties on both faces, reducing their usefulness to this project. Thus many monolayer components that were unconfirmed to form Janus monolayers were explored in this stage. Some promising properties were found, particularly in the realm of their physicochemical interactions with the media. Some of these nanoparticles manifested unusual solubility, many more would spontaneously and unexpectedly aggregation. However, no properly ferroelectric responsive nanoparticles were found. A significant amount of time was spent exploring this issue, generating several possible answers but none could be confirmed entirely. For each of the systems, it is suspected that the Janus morphologies were too dilute within the structurally diverse system, reducing any measurable effects. Second, in many cases the monolayer components may have been too electronically similar to generate a measurable response. It is likely that these two factors, among other minor factors, acted together. Unfortunately, attempts to “purify” the Janus morphologies from the other structures did not meet with success.
The focus of the project was then honed toward the unusual solubility and self-assembly properties of the nanoparticles. “Like dissolves like,” a common maxim in chemistry education, expresses the idea that the solubility of a molecule can be predicted by examining the structural similarity between that molecule and a given solvent. Though typically applied to small organic molecules in organic solvents or water, nanoscale particles with organic coatings follow the same maxim. This is so fundamental that it barely draws mention in the modern scientific literature. Solubility can generally be presumed when there are strong similarities in molecular structure between solute and solvent. When an organic coating featuring more than one type of chemistry is randomly spread across the surface of the colloid, the “like dissolves like” maxim is broadly valid as long as any featured chemistry is considered together. We are now providing an example of an important exception. When organic coating forms an organized monolayer on the colloid surface, the different functionalities can be organized in such a way that only one chemistry becomes dominant in determining the particle’s solubility. This effect generates unusual and surprisingly complex solubility properties of small gold colloids protected by a mixture of alkanethiol and fluorinated alkanethiols, which combine polar and omniphobic functionalities. Depending on the size of these colloids, the coating organizes differently, producing size-dependent dissolution in a range of fluorinated, perfluorinated, or non-fluorinated polar organic solvents. Fluorinated and partially-fluorinated solvents preferentially dissolve the smallest nanoparticles (mean diameter 2.5-3 nm), while non-fluorinated solvents preferentially dissolve larger nanoparticles (mean diameter >4.5 nm). New computational methods were developed to explore the atomic-level interactions between surface coatings and solvents. These methods generally agreed with experimental results, leading to possible insights into coating-led solvent orientation through electrostatic interactions. A novel approach was envisioned and partially developed to make the characterization of organic coatings more precise, robust, and accessible. New methods were also employed to investigate the ability of nanoscale measurement techniques to “push the envelope” in imaging these nanoparticles. Computational techniques were employed to model and predict the images obtained through these microscopic techniques, allowing for comparison with and validation of experimental results.
These results each serve to boost the state of the art within the European Union, through collaboration with European laboratories, European researchers, and disseminating knowledge though European institutions. The unique curvature-dependent properties of these nanoparticles serves as a powerful example of deviation from the “like dissolves like” maxim. The role of surface curvature on dipole-driven wetting effects also has implications for numerous fields of research in nanotechnology and materials. The results can be used to advance intellectual property in the development of new, smart nanomaterials with novel wetting properties, as well as the development of vital characterization methods for organic coatings on colloids.