Final Report Summary - NEMCODE (Controlled Assembly and Stabilisation of Functionalised Colloids in Nematic Liquid Crystals)
NEMCODE was an interdisciplinary project putting together organic synthesis and applied physics. The main goal of the NEMCODE was to develop new methods of manipulation of the surfaces of silica colloids in order to generate 2D colloidal crystals assembled in liquid crystals. The specific properties conferred by the molecular materials prepared in the chemistry laboratory can lead to the fabrication of stable colloidal crystals with specific characteristics. Moreover, the flexibility given by the fact that the fellow was preparing himself the molecular materials allowed for a prompt tackling of problems in addition to explore new features that arose during the experiments. Besides, the fellow had the possibility of learning a variety of techniques that are not generally related to the organic chemistry realm.
The initial main goal was the creation of 2D colloidal crystals with selectively created defects. This materials could be in theory used as photonic light guides, creating selective paths for a light beam. However, under the guidance of the Scientist in Charge it was possible to widen this topic embracing other aspects of soft matter physics e.g. liquid crystalline emulsions, liquid crystal alignment, chiral nematic liquid crystals etc.
Colloidal crystals have been studied for long time since their photonic properties – i.e. they selectively interact with electromagnetic radiations of wavelength comparable to the size of the colloids that form the assemblies. This phenomenon is observable in colloidal crystals formed by colloids with a size comparable to the wavelength of visible light; e.g. opal. The iridescent colour of these materials depends on the selective scattering of certain wavelengths (colour) that is subtracted from the transmitted light. From a technological point of view these materials could be used for photonic informatics where the electricity is substituted by light and the semiconductor substituted by photonic crystals. Computer based on photonics instead of electronics are theorized to be faster and to consume less energy since the will not undergo the overheating that characterize the computers as we know them.
On the other hand the field of liquid crystals (LCs) offers great opportunities from a technological point of view due to the specific properties of these materials which flow like liquids but diffract light like crystals. From a molecular point of view LCs are characterized by molecules with one dimension much longer (or much shorter than the other two). The molecules therefore are geometrically anisotropic and in bulk tend to align all in the same direction. This confers optical anisotropy to the system – i.e. the light is affected by different refractive indices depending on the incident direction. Moreover, some LCs phases have photonic properties. In particular, in chiral nematic phases the molecules orient in helices, the light of a wavelength comparable to the pitch of the helix is selectively diffracted.
Therefore, the synthesis of liquid crystalline materials with specific characteristics e.g. specific crystalline phases displayed, in addition to materials for silica functionalization have been of great importance for the whole project.
More in general NEMCODE allowed Dr Giorgio Mirri to learn new techniques in a soft matter physics lab which are not in the background of an organic chemist. Besides, learning to determine what properties specific molecular units could confer to a material in order to obtain specific bulk effects and synthesising the molecular materials in the chemistry laboratory using organic synthesis and assess the physical properties of the modified materials were also part of this interdisciplinary project.
Work performed and main results achieved
- The key of the success of the project resides in the fact that the materials studied were not commercially available but tailor made directly by the fellow in a chemistry laboratory.
The synthesis of the polymerizable materials and of the photoinitiator was performed for the different materials needed as described in Scheme 1 in the attached document.
Attaching the fluorescent tag required the design of a different approach, due to the sensitivity of the BODIPY unit to the thiol-ene radical click reaction initially chosen to attach this unit to the trimethoxysilane moiety. This that might appear as a drawback allowed to develop a new approach to the functionalization of BODIPY by exploiting the electrophilic susceptibility of the lateral positions. This approach will be described in an article which is currently under preparation.
Results: synthesis of molecular materials for silica functionalization; development of a methodology for BODIPY functionalization
- During the fellowship the fellow demonstrated a new approach for stabilizing colloidal assemblies prepared in liquid crystal matrices. The assembly can be performed in a reactive liquid crystal and when complete the polymerization is initiated by UV irradiation. The reactive mesogens generate a polymeric network which retains the optical characteristic of the liquid crystal. The polymerisation of the LC stabilizes the assemblies to high temperatures and allows for the extraction of the assembly.
Results: This work was published in Soft Matter (RSC publishing, impact factor 4.151 doi: 10.1039/C4SM00358F).
- Another important result achieved is the definition of a new applied method for the total control of the surface memory effect of a liquid crystalline material. This innovative method could find application in the fabrication of LCDs. Results: Preliminary results were published in Soft Matter (impact factor 4.151 doi: 10.1039/C5SM00282F). The further development of this technique was not divulgated and we are exploring the possibility of filing a patent, in addition to further publications. The high interest on this topic is demonstrated by the fact that the paper was listed as HOT Paper 2015 by the Soft Matter Blog and highlighted by Physics Today (‘Laser beam remodels liquid crystals on the fly' in an article by Ashley Smart Physics Today 2015, 68, 6, p. 12).
- As a variation to one of the objectives of the project the fellow studied another approach to photonic materials studying liquid crystal emulsions between discotic and rod-like liquid crystals. The alignment in the liquid crystal droplets and optical properties of the mixtures are currently under investigation and at least one publication is expected on this topic.
Expected Final Results and Impact
Final results of the fellowship can be resumed as a significant step forwards toward the stabilization of photonic objects assembled in liquid crystal media, only using molecular materials with specific characteristics and using rather inexpensive soft matter applied techniques.
During this Fellowship we developed a method for the stabilization of colloidal assemblies in LCs that can then be extracted from the medium they are assembled and used for other applications (Soft Matter, 2014, 10, 5797). This method can be applied to stabilize a variety of photonic objects created in LCs which have the same problems of stability of the colloidal crystals (e.g. 3D LC lasers), therefore it can have an impact on photonic industry. Moreover, a new method for the control of the surface alignment of LCs was developed (Soft Matter, 2015, 11, 3347). The impact of this method can be important, since it gives the possibility of controlling the alignment of a LC material using a laser to modify the surface alignment of a nematic LC in a fully assembled cell. The realignment can be performed to areas down to 10 x 10 µm. The method could have an impact on the LCD industry since it could be used to generate pixels with specific orientation and to correct mistakes in the alignment generated during the production. The impact of this method is demonstrated by the fact that the article was listed as a Soft Matter 2015 Hot Article and that was highlighted by Physics Today the magazine of the American Institute of Physics.
The impact of NEMCODE on the fellow is that he learnt several new techniques and built a professional profile that is bridging the gap between organic chemistry and applied physics. The impact on the group is that the fellow prepared new materials that can be used in the physics lab, in addition to gaining a new point of view for tackling problems. The impact on the ERA is the formation of interdisciplinary figures which will contribute to the European research community either in academia or in industry.
The initial main goal was the creation of 2D colloidal crystals with selectively created defects. This materials could be in theory used as photonic light guides, creating selective paths for a light beam. However, under the guidance of the Scientist in Charge it was possible to widen this topic embracing other aspects of soft matter physics e.g. liquid crystalline emulsions, liquid crystal alignment, chiral nematic liquid crystals etc.
Colloidal crystals have been studied for long time since their photonic properties – i.e. they selectively interact with electromagnetic radiations of wavelength comparable to the size of the colloids that form the assemblies. This phenomenon is observable in colloidal crystals formed by colloids with a size comparable to the wavelength of visible light; e.g. opal. The iridescent colour of these materials depends on the selective scattering of certain wavelengths (colour) that is subtracted from the transmitted light. From a technological point of view these materials could be used for photonic informatics where the electricity is substituted by light and the semiconductor substituted by photonic crystals. Computer based on photonics instead of electronics are theorized to be faster and to consume less energy since the will not undergo the overheating that characterize the computers as we know them.
On the other hand the field of liquid crystals (LCs) offers great opportunities from a technological point of view due to the specific properties of these materials which flow like liquids but diffract light like crystals. From a molecular point of view LCs are characterized by molecules with one dimension much longer (or much shorter than the other two). The molecules therefore are geometrically anisotropic and in bulk tend to align all in the same direction. This confers optical anisotropy to the system – i.e. the light is affected by different refractive indices depending on the incident direction. Moreover, some LCs phases have photonic properties. In particular, in chiral nematic phases the molecules orient in helices, the light of a wavelength comparable to the pitch of the helix is selectively diffracted.
Therefore, the synthesis of liquid crystalline materials with specific characteristics e.g. specific crystalline phases displayed, in addition to materials for silica functionalization have been of great importance for the whole project.
More in general NEMCODE allowed Dr Giorgio Mirri to learn new techniques in a soft matter physics lab which are not in the background of an organic chemist. Besides, learning to determine what properties specific molecular units could confer to a material in order to obtain specific bulk effects and synthesising the molecular materials in the chemistry laboratory using organic synthesis and assess the physical properties of the modified materials were also part of this interdisciplinary project.
Work performed and main results achieved
- The key of the success of the project resides in the fact that the materials studied were not commercially available but tailor made directly by the fellow in a chemistry laboratory.
The synthesis of the polymerizable materials and of the photoinitiator was performed for the different materials needed as described in Scheme 1 in the attached document.
Attaching the fluorescent tag required the design of a different approach, due to the sensitivity of the BODIPY unit to the thiol-ene radical click reaction initially chosen to attach this unit to the trimethoxysilane moiety. This that might appear as a drawback allowed to develop a new approach to the functionalization of BODIPY by exploiting the electrophilic susceptibility of the lateral positions. This approach will be described in an article which is currently under preparation.
Results: synthesis of molecular materials for silica functionalization; development of a methodology for BODIPY functionalization
- During the fellowship the fellow demonstrated a new approach for stabilizing colloidal assemblies prepared in liquid crystal matrices. The assembly can be performed in a reactive liquid crystal and when complete the polymerization is initiated by UV irradiation. The reactive mesogens generate a polymeric network which retains the optical characteristic of the liquid crystal. The polymerisation of the LC stabilizes the assemblies to high temperatures and allows for the extraction of the assembly.
Results: This work was published in Soft Matter (RSC publishing, impact factor 4.151 doi: 10.1039/C4SM00358F).
- Another important result achieved is the definition of a new applied method for the total control of the surface memory effect of a liquid crystalline material. This innovative method could find application in the fabrication of LCDs. Results: Preliminary results were published in Soft Matter (impact factor 4.151 doi: 10.1039/C5SM00282F). The further development of this technique was not divulgated and we are exploring the possibility of filing a patent, in addition to further publications. The high interest on this topic is demonstrated by the fact that the paper was listed as HOT Paper 2015 by the Soft Matter Blog and highlighted by Physics Today (‘Laser beam remodels liquid crystals on the fly' in an article by Ashley Smart Physics Today 2015, 68, 6, p. 12).
- As a variation to one of the objectives of the project the fellow studied another approach to photonic materials studying liquid crystal emulsions between discotic and rod-like liquid crystals. The alignment in the liquid crystal droplets and optical properties of the mixtures are currently under investigation and at least one publication is expected on this topic.
Expected Final Results and Impact
Final results of the fellowship can be resumed as a significant step forwards toward the stabilization of photonic objects assembled in liquid crystal media, only using molecular materials with specific characteristics and using rather inexpensive soft matter applied techniques.
During this Fellowship we developed a method for the stabilization of colloidal assemblies in LCs that can then be extracted from the medium they are assembled and used for other applications (Soft Matter, 2014, 10, 5797). This method can be applied to stabilize a variety of photonic objects created in LCs which have the same problems of stability of the colloidal crystals (e.g. 3D LC lasers), therefore it can have an impact on photonic industry. Moreover, a new method for the control of the surface alignment of LCs was developed (Soft Matter, 2015, 11, 3347). The impact of this method can be important, since it gives the possibility of controlling the alignment of a LC material using a laser to modify the surface alignment of a nematic LC in a fully assembled cell. The realignment can be performed to areas down to 10 x 10 µm. The method could have an impact on the LCD industry since it could be used to generate pixels with specific orientation and to correct mistakes in the alignment generated during the production. The impact of this method is demonstrated by the fact that the article was listed as a Soft Matter 2015 Hot Article and that was highlighted by Physics Today the magazine of the American Institute of Physics.
The impact of NEMCODE on the fellow is that he learnt several new techniques and built a professional profile that is bridging the gap between organic chemistry and applied physics. The impact on the group is that the fellow prepared new materials that can be used in the physics lab, in addition to gaining a new point of view for tackling problems. The impact on the ERA is the formation of interdisciplinary figures which will contribute to the European research community either in academia or in industry.