Liquid Crystals in Flow: A New Era in Sensing and Diagnostics

Project Information

LCFlow

Grant agreement ID: 101039294

DOI

10.3030/101039294

EC signature date 26 April 2022

Start date 1 September 2022

End date 31 August 2027

Funded under

• European Research Council (ERC)

Total cost

€ 1 500 000,00

EU contribution

€ 1 500 000,00

Coordinated by

MIDDLE EAST TECHNICAL UNIVERSITY
Türkiye

Periodic Reporting for period 1 - LCFlow (Liquid Crystals in Flow: A New Era in Sensing and Diagnostics)

Reporting period: 2022-09-01 to 2025-02-28

Summary of the context and overall objectives of the project

Liquid crystals (LCs) are the delicate phases of matter that exhibit molecular order, fluidic nature and birefringent optical properties. LCs have been developed as materials suitable for energy- and label-free reporting of the chemical changes occurring at their interfaces. Important examples of such changes include the presence of biomolecular, gaseous or nano-/microscopic species or chemical or biochemical interactions/reactions involving these species. LC-water interfaces were employed in most promising sensors as a medium to facilitate the interaction of the LCs with the species. Although promising, the studies reported were limited to the stagnant LC systems, limiting their use in continuous sensing and diagnostic applications.

This project is designed to open a new era in the sensing and diagnostic systems involving the use of LCs by introducing a microfluidic flow. The system of interest differs significantly from its counterparts by introducing LC-water interfaces that facilitate the exchange of analytical species during flow. However, the design of such a system is challenging, and critical understanding is required to proceed toward the next generation LCFlow platforms.

This project aims to design highly sensitive, dynamically tunable, and label-free LC-based fluidic sensing platforms and it is structured to understand:

1) The effect of the presence of the “soft” interfaces and the LC interfacial anchoring on the flow regimes, and the LC director profiles,
2) The role of the type, scale, shape and the symmetry of the chemical heterogeneity at the contacting surfaces on the LC flow and configurations,
3) The dynamic influences of the changes occurring at the contact interfaces on the configuration and the optical appearance of the LC medium,

The context of the project is positioned at the intersection of fundamental knowledge generation and application. It is highly interdisciplinary involving physics, chemistry, materials science and engineering.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The fabrication of the microfluidic platform was performed which allows stable flow of the LCs while forming an interface with aqueous phases. The device is stable enough for multiple modes of operation including co-current and counter-current flow configurations of the LC and aqueous phases, and weak and strong shear conditions at the bulk and interfaces. The results obtained so far showed that the stability will provide flexibility in the future designs of the sensing devices. The characterization of the flow-induced structural transitions at the interfaces of the LCs was performed. Microscopic methods were used and sixteen LC configurations maintained in the microchannels as a function of the flow, configurations, and interfacial shearing strength were identified. Remarkable configuration transitions were observed to occur in channels that indicated significant elastic distortions with the application of less than 1 Pa of shear stress. The influence of the interfacial shear on the flow resistances and LC configurations was also studied and found that the interfacial shear is significantly reducing the flow resistances of the LCs as it results in straining of the LCs at the vicinity of the interfaces. Patterned chemical heterogeneities were fabricated on solid interfaces of the flowing LCs such that the pure LC material exhibits alternating homeotropic and planar anchoring conditions along or orthogonal to the flowing LCs. Such designs allowed the investigation of how the alternating anchoring conditions influenced the flow configurations, LC director profiles, configuration transitions, and flow resistances of LCs in microchannels. These observations will form a basis for understanding how the LC configurations influence the flow in the channel and tune the response of the LCs. The LC-aqueous interfaced microfluidic platform also allowed tracking of the adsorbates at the interfaces. The experiments with the amphiphilic species in aqueous phases showed that Lc interfaces can be used to track their presence and amount. This observation is a significant achievement that shows the promising use of the LCFlow concept in the quantification of the analytical species in the aqueous medium.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The development of an LC-aqueous interfaced responsive microfluidic platform in LCFlow project will provide a basis to combine the past approaches of LC-based responsive platforms (sensors and actuators) towards developing advanced automated applications including high-throughput analysis and sensing applications. The platform is stable enough to tailor for specific analytes and simple and flexible enough to upgrade for high-throughput analysis of complex mixtures. Thus, the LCFlow platform will be a breakthrough to proceed toward the next generation of sensing platforms led by liquid crystalline materials.

The LC-aqueous multiphase flow platform that is capable of applying bulk and interfacial shear independently in a controlled environment is of critical importance and is a breakthrough in studying the role of shear on structures of the LCs at their responsive interfaces. We identified the fundamental set of the maintained nematic LC structures and transitions as a function of shearing and found a critical dependence of the shear strength and the orthogonality of the interfacial and bulk nematic directors on the LC structures maintained. This progress opened a field for studying the role of shear experimentally for various systems (including more complex anchoring conditions and LC phases) that will also trigger additional studies on the theory and simulations of flowing LCs. Future progress in this direction will serve in the engineering of LC-based flow systems for responsive applications.

We developed experimental methods to study the influence of the heterogenous interfacial anchoring of LCs at hard and soft interfaces on their flow properties. Our system is composed of LCs with soft, active interfaces that allows to modify the chemical and physical state of the LC interfaces in a controlled environment. Such an approach is novel and beyond the state-of-the-art because it is the first time the influence of heterogeneity and shear conditions at LC interfaces are being explored. Such approaches will provide additional modality in the design of LC-based optical systems.