Periodic Reporting for period 3 - [LC]2 ('Living' Colloidal Liquid Crystals)
Reporting period: 2022-02-01 to 2023-07-31
Living organisms are composed of biological materials with striking physical properties. Biological matter can autonomously grow, self-organise, heal and move, while synthetically manufactured materials tend to be static, non-responsive and passive. This project aims to design a class of materials that are soft, self-assembled and self-motile—in other words, life-like. Such biomimetic materials have the potential to replicate the way living systems actively, adaptively and autonomously interact with their environment, and so transform the way we approach manufacturing and engineering our world. The goal of this specific research programme is to combine qualities of active liquid crystals and colloidal liquid crystals to design hierarchical and intrinsically out-of-equilibrium structures, which we call ‘Living’ Colloidal Liquid Crystals, or [LC]2.
The first, ‘living’ part of [LC]2 involves active liquid crystals, which are fluids that spontaneously flow without being driven from the outside. Many spontaneously flowing active fluids are biological, such as groups of bacteria or other cells that are self-motile and tend to align. This alignment is what makes them liquid crystals. The second, Colloidal part of [LC]2 involves adding small particles, called colloids, to these fluids. The liquid crystal background then forces the colloids to arrange themselves into precisely controlled patterns, a phenomenon called self-assembly. Together, the colloidal aspect of [LC]2 can generate self-assembly, while the active aspect can endow autonomous and functional dynamics. However, [LC]2 materials are complex and so designing ‘living’ metamaterials requires new models of active liquid crystals that can deal with the complexities of adding freely moving colloids. The [LC]2 project has developed multiscale coarse-grained simulations and new theories of liquid crystals that now allow us to study these dynamically complex, life-like fluids.
The first, ‘living’ part of [LC]2 involves active liquid crystals, which are fluids that spontaneously flow without being driven from the outside. Many spontaneously flowing active fluids are biological, such as groups of bacteria or other cells that are self-motile and tend to align. This alignment is what makes them liquid crystals. The second, Colloidal part of [LC]2 involves adding small particles, called colloids, to these fluids. The liquid crystal background then forces the colloids to arrange themselves into precisely controlled patterns, a phenomenon called self-assembly. Together, the colloidal aspect of [LC]2 can generate self-assembly, while the active aspect can endow autonomous and functional dynamics. However, [LC]2 materials are complex and so designing ‘living’ metamaterials requires new models of active liquid crystals that can deal with the complexities of adding freely moving colloids. The [LC]2 project has developed multiscale coarse-grained simulations and new theories of liquid crystals that now allow us to study these dynamically complex, life-like fluids.
The [LC]2 research programme is divided into three work packages, each of which has produced notable results to date. The first is concerned with the development of novel approaches to modelling active fluids. It has successfully developed, implemented and quantified a coarse-grained numerical algorithm for simulating spontaneously flowing active fluids, which is ideal for embedding colloids within. Furthermore, the project has advanced methods for simulating active systems, including motile bacteria, epithelial tissues and layered liquid crystals. By advancing the ability of researchers to model different types of active materials, work package one (WP1) has increased our capacity to design animate materials. These mesoscale models have now been employed to simulate how active fluids flow when confined in microfluidic geometries.
While WP1 advanced the ‘living’ aspect of [LC]2, work package two (WP2) tackles the ‘colloidal’ facet of ‘Living’ Colloidal Liquid Crystals. The [LC]2 project has developed an algorithm for simulating passive composite colloidal/liquid crystal materials. These include small particles, called colloids, embedded in nematic-type liquid crystals, which are fluids composed of aligned, rod-like molecules and so have orientational order. The [LC]2 team has quantified the interactions between different colloids and how they entangle within the nematic liquid crystal. Furthermore, embedded flexible polymers chains in nematics have been studied to discover how their sudden turns, or hairpins, can untangle in time.
Finally, these ideas have been brought together (work package three [WP3]). The [LC]2 team has built simulations to model rotating 2D colloids above an active fluid and compared this directly to experiments. The team has also designed particles with different north and south hemispheres, called Janus particles. These particles can steal surrounding activity to propel themselves, thus becoming self-propelled particles. The [LC]2 team is currently simulating how the activity-driven dynamics of rods differs from spherical particles and how fixing colloids in an active flow can either disrupt ordered flows or reinforce them.
Thus, foundational work has been accomplished, results obtained and discoveries disseminated as a result of [LC]2. In particular, the groundwork for achieving ‘living’ colloidal liquid crystals has been laid by developing codes for active nematics and colloidal liquid crystals, which have been quantified and merged into a single simulation package. From these, [LC]2 has produced initial results leading to multiple conference presentations, invited lectures, international collaborations and scientific publications.
While WP1 advanced the ‘living’ aspect of [LC]2, work package two (WP2) tackles the ‘colloidal’ facet of ‘Living’ Colloidal Liquid Crystals. The [LC]2 project has developed an algorithm for simulating passive composite colloidal/liquid crystal materials. These include small particles, called colloids, embedded in nematic-type liquid crystals, which are fluids composed of aligned, rod-like molecules and so have orientational order. The [LC]2 team has quantified the interactions between different colloids and how they entangle within the nematic liquid crystal. Furthermore, embedded flexible polymers chains in nematics have been studied to discover how their sudden turns, or hairpins, can untangle in time.
Finally, these ideas have been brought together (work package three [WP3]). The [LC]2 team has built simulations to model rotating 2D colloids above an active fluid and compared this directly to experiments. The team has also designed particles with different north and south hemispheres, called Janus particles. These particles can steal surrounding activity to propel themselves, thus becoming self-propelled particles. The [LC]2 team is currently simulating how the activity-driven dynamics of rods differs from spherical particles and how fixing colloids in an active flow can either disrupt ordered flows or reinforce them.
Thus, foundational work has been accomplished, results obtained and discoveries disseminated as a result of [LC]2. In particular, the groundwork for achieving ‘living’ colloidal liquid crystals has been laid by developing codes for active nematics and colloidal liquid crystals, which have been quantified and merged into a single simulation package. From these, [LC]2 has produced initial results leading to multiple conference presentations, invited lectures, international collaborations and scientific publications.
By this mid-way point, the [LC]2 project has already advanced the state of the art in multiple ways.
Most importantly, [LC]2 has developed a first truly mesoscopic algorithm for simulating active nematics, and has numerically implemented and quantified the algorithm. This approach is particle-based, which gives it a number of advantages. For instance, it reproduces results from both macroscopic theories and microscopic simulations. Additionally, it is ideal for simulating the dynamics of embedded particles, such as colloids, filaments or polymers —making it ideal for simulating ‘Living’ Colloidal Liquid Crystals. The success of this approach suggests the method can be extended to simulate other types of active fluids by the end of the project. This will include variations with suppressed giant number fluctuations. The [LC]2 project has also extended the state of the art for modelling other soft materials, which may prove to be potential active fluids in which colloids can be embedded. These include new approaches to modelling layered liquid crystals with suspended colloids, numerically modelling tissues using mesoscale approaches with a degree of detail not been done before, and simulating bacterial microcolonies to quantify the degree of order generated by activity.
Additionally, [LC]2 has resulted in multiple discoveries that advanced the field of active matter. In some cases, the team has worked with international experimental collaborators to discover new methods for controlling active flows. These include using submersed micropatterned structures below active fluids to guide flows, and driving disk-shaped colloids to cause topological transitions to vortices that don’t otherwise exist. These collaborations will continue to provide the potential to experimentally realise [LC]2 designs. Models from the project have also produced predictions that have yet to be experimentally realised, including discovering persistent helicity, which is a first instant of spontaneous but steady-state helicity in 3D active nematics. The existence of active helicity expands the range of possible emergent flows. The [LC]2 project will determine if embedded colloids protect such spontaneously ordered flows or destroy them.
Furthermore, [LC]2 has led to predictions for the behaviour of engineered Janus colloids. By the end of the project, the behaviour of Janus colloids will be understood in its entirety, including its hydrodynamic effects. This work will extend to consider non-spherical colloids in active nematics and simulate multiple colloids interacting through the active nematic fluid, producing further advancements of the state of the art.
Most importantly, [LC]2 has developed a first truly mesoscopic algorithm for simulating active nematics, and has numerically implemented and quantified the algorithm. This approach is particle-based, which gives it a number of advantages. For instance, it reproduces results from both macroscopic theories and microscopic simulations. Additionally, it is ideal for simulating the dynamics of embedded particles, such as colloids, filaments or polymers —making it ideal for simulating ‘Living’ Colloidal Liquid Crystals. The success of this approach suggests the method can be extended to simulate other types of active fluids by the end of the project. This will include variations with suppressed giant number fluctuations. The [LC]2 project has also extended the state of the art for modelling other soft materials, which may prove to be potential active fluids in which colloids can be embedded. These include new approaches to modelling layered liquid crystals with suspended colloids, numerically modelling tissues using mesoscale approaches with a degree of detail not been done before, and simulating bacterial microcolonies to quantify the degree of order generated by activity.
Additionally, [LC]2 has resulted in multiple discoveries that advanced the field of active matter. In some cases, the team has worked with international experimental collaborators to discover new methods for controlling active flows. These include using submersed micropatterned structures below active fluids to guide flows, and driving disk-shaped colloids to cause topological transitions to vortices that don’t otherwise exist. These collaborations will continue to provide the potential to experimentally realise [LC]2 designs. Models from the project have also produced predictions that have yet to be experimentally realised, including discovering persistent helicity, which is a first instant of spontaneous but steady-state helicity in 3D active nematics. The existence of active helicity expands the range of possible emergent flows. The [LC]2 project will determine if embedded colloids protect such spontaneously ordered flows or destroy them.
Furthermore, [LC]2 has led to predictions for the behaviour of engineered Janus colloids. By the end of the project, the behaviour of Janus colloids will be understood in its entirety, including its hydrodynamic effects. This work will extend to consider non-spherical colloids in active nematics and simulate multiple colloids interacting through the active nematic fluid, producing further advancements of the state of the art.