Periodic Reporting for period 1 - CELICOIDS (Nanohelicoid metamaterials templated by cellulose nanocrystals with end-tethered polymers)
Reporting period: 2023-03-01 to 2025-08-31
Chirality plays a fundamental role in natural sciences and pharmacology. Circularly polarized light, a type of light wave that propagates on a helical path, is routinely used in chemical and biochemical instrumental analysis to characterize the three-dimensional structure of molecules. The main problem is that the optical responses of chiral molecules are inherently weak and new types of engineered materials are needed to enhance the detection of molecular chirality. Chiral metamaterials, which exhibit extraordinary electromagnetic properties not observed in nature, are fabricated with repeating patterns capable of enhancing such interactions. In order for a metamaterial to interact with ultraviolet or visible light, the scale of the repeating patterns needs to be on the order of hundreds of nanometers or less, which is extremely difficult and costly to fabricate using currently available technologies. This represents a significant challenge to be addressed in metamaterials engineering for future optical devices.
The CELICOIDS project responds to this growing need for simpler metamaterial fabrication technologies and proposes the development of new types of chiral nanostructures to control light-matter interactions. The project focuses on self-assembly of nanoparticles, which is a bottom-up fabrication technique that relies simply on physical interactions between particles in order to form the desired pattern, without the need of complex and expensive equipment.
The objective of CELICOIDS is to investigate the bottom-up self-assembly of end-modified nanorods to fabricate a new class of metamaterial, metallic nanohelicoids. The nanorods are obtained from cellulose, a natural polysaccharide extracted from paper, cotton or other plant fibres. When a suspension of the end-modified cellulose nanorods is poured onto a surface or confined within microdroplets, they self-assemble to form helical structures as they dry. Once these structures are impregnated with metals such as gold, they will guide the formation of metallic nanohelicoids. After removing the modified cellulose template, the ultimate goal is to achieve new metallic helicoidal structures. This nanostructure, when combined in a solution of chiral molecules, will likely amplify the interactions between circularly polarized light and chiral molecules through their anticipated electromagnetic properties. These properties will open new prospects for optical instruments routinely used in chemistry, biochemistry and pharmacology.
The CELICOIDS project responds to this growing need for simpler metamaterial fabrication technologies and proposes the development of new types of chiral nanostructures to control light-matter interactions. The project focuses on self-assembly of nanoparticles, which is a bottom-up fabrication technique that relies simply on physical interactions between particles in order to form the desired pattern, without the need of complex and expensive equipment.
The objective of CELICOIDS is to investigate the bottom-up self-assembly of end-modified nanorods to fabricate a new class of metamaterial, metallic nanohelicoids. The nanorods are obtained from cellulose, a natural polysaccharide extracted from paper, cotton or other plant fibres. When a suspension of the end-modified cellulose nanorods is poured onto a surface or confined within microdroplets, they self-assemble to form helical structures as they dry. Once these structures are impregnated with metals such as gold, they will guide the formation of metallic nanohelicoids. After removing the modified cellulose template, the ultimate goal is to achieve new metallic helicoidal structures. This nanostructure, when combined in a solution of chiral molecules, will likely amplify the interactions between circularly polarized light and chiral molecules through their anticipated electromagnetic properties. These properties will open new prospects for optical instruments routinely used in chemistry, biochemistry and pharmacology.
During the first 24 months of the CELICOIDS project, the research was primarily focused on the preparation, characterization, and functionalization of cellulose nanocrystals (CNCs), as well as the development of microfluidic systems for CNC-based microparticle fabrication. Cellulose nanocrystals are twisted rod-shaped nanoparticles that can be extracted from a variety of natural sources. CNCs of three distinct crystal structures (namely I, II and III) were successfully produced from multiple renewable sources, including cotton, sisal fibers, and bacterial cellulose by using combinations of chemical pretreatments and acid hydrolysis. After characterization of the surface chemistry and morphology of each CNC type, our team confirmed that the crystal structure, length of the CNCs, or aspect ratio, and surface chemical composition depend highly on the cellulose source and the chemical pretreatments applied. The CNC properties further change the characteristics of their self-assembled liquid crystal phases and provides us with a means to manipulate their interactions with polarized light.
The project team further synthesized a library of water-soluble polymers and explored chemical functionalization strategies to attach them to the ends of CNCs using water-based chemical reactions. Successful covalent attachment of a portion of the polymer library was confirmed with no disruption to CNC structural integrity and the reaction conditions are being adapted for each type of CNC and polymer.
To produce microparticles from droplets of CNC suspensions, a rapid and accessible PDMS casting method was developed to fabricate custom microfluidic devices. The impact of surfactant concentration on CNC suspension droplet drying was systematically investigated. Results showed that increasing surfactant content led to greater droplet shrinkage and maintained consistent drying rates. These findings demonstrate that surfactant concentration influences water diffusion during drying, impacting the final particle size and shape.
The project team further synthesized a library of water-soluble polymers and explored chemical functionalization strategies to attach them to the ends of CNCs using water-based chemical reactions. Successful covalent attachment of a portion of the polymer library was confirmed with no disruption to CNC structural integrity and the reaction conditions are being adapted for each type of CNC and polymer.
To produce microparticles from droplets of CNC suspensions, a rapid and accessible PDMS casting method was developed to fabricate custom microfluidic devices. The impact of surfactant concentration on CNC suspension droplet drying was systematically investigated. Results showed that increasing surfactant content led to greater droplet shrinkage and maintained consistent drying rates. These findings demonstrate that surfactant concentration influences water diffusion during drying, impacting the final particle size and shape.
The achievements during the first two years of the project have laid the groundwork for the production of hybrid chiral liquid crystal templates for chiral metamaterials fabrication. The optimization of the reaction steps required for the production of CNCs with a range of dimensions and crystal structures gives access to a vast library of liquid crystals for designing chiral metamaterial templates. Based on our understanding of the reaction conditions that permit the attachment of water-soluble polymers to the ends of CNCs with minimal disruption to their structural integrity will allow us to adapt the synthesis of liquid crystals to larger scales relevant to continuous manufacturing processes.
Our ongoing research on the formation of films and microparticles using the self-assembly of CNCs with different crystal structures and end-modified CNCs will be decisive in determining the optimal range of the parameters for the construction of templates for metallic nanohelicoids. These parameters include CNC twist, dimensions, end-tethered polymer chemical structure and their attachment to one end or both ends. For the formation of microparticle templates, recognizing the effect of surfactant concentration during microdroplet generation on the drying process provides a means to control the final particle size.
We anticipate that the CNC-based liquid crystals that we have produced will not only allow us to guide the formation of chiral metallic nanostructures, but also provide new experimental models for investigating the self-assembly of particles with surfaces having two or more distinct properties. The process of end-modified CNC self-assembly will be advantageous in terms of cost, processing time and adaptability to large scales, in comparison to techniques based on vapor deposition. We expect that the advancement of bottom-up self-assembly technologies for chiral metamaterial fabrication will boost the technological maturity of emerging chiroptical devices and chiral sensors for applications in biomedicine, pharmaceuticals and materials science.
Our ongoing research on the formation of films and microparticles using the self-assembly of CNCs with different crystal structures and end-modified CNCs will be decisive in determining the optimal range of the parameters for the construction of templates for metallic nanohelicoids. These parameters include CNC twist, dimensions, end-tethered polymer chemical structure and their attachment to one end or both ends. For the formation of microparticle templates, recognizing the effect of surfactant concentration during microdroplet generation on the drying process provides a means to control the final particle size.
We anticipate that the CNC-based liquid crystals that we have produced will not only allow us to guide the formation of chiral metallic nanostructures, but also provide new experimental models for investigating the self-assembly of particles with surfaces having two or more distinct properties. The process of end-modified CNC self-assembly will be advantageous in terms of cost, processing time and adaptability to large scales, in comparison to techniques based on vapor deposition. We expect that the advancement of bottom-up self-assembly technologies for chiral metamaterial fabrication will boost the technological maturity of emerging chiroptical devices and chiral sensors for applications in biomedicine, pharmaceuticals and materials science.