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Electric field driven propulsion and collective dynamics of homogeneous and patchy colloidal capsules.

Periodic Reporting for period 1 - PaCDoC (Electric field driven propulsion and collective dynamics of homogeneous and patchy colloidal capsules.)

Reporting period: 2017-04-01 to 2019-03-31

The research project studied capsules that were made by covering oil droplets with nano- and micrometer sized particles. The overall objective of the project was to achieve electric field-induced propulsion of homogenous (made out of same type of particles) and patchy capsules (capsules with domains of different chemical or physical properties) over millimeter distances, both in carrier fluids and at boundaries. Enabling capsule propulsion extend the capsules’ capabilities, applications and potential for performing multiple tasks. To realize, understand and control capsule propulsion is therefore highly desirable in fields such as biology, medicine, environmental science and material science. Benefits from capsule propulsion in these fields include: targeted drug delivery, cargo transport, forming nanomachines, removing toxic materials from water or human bodies, or actively controlling material behavior. Particle capsules, and especially patchy particle capsules are challenging to fabricate. To realize the potential applications of these capsules, it is also important to consistently produce capsules with tailored physical and mechanical properties. One of the objectives of this action was therefore to combine microfluidic devices and electric fields for high-throughput fabrication of patchy capsules. Realizing this objective was also necessary to study the collective dynamics of multiple propelling capsules which was the last objective of this research project. While single capsules can be used for encapsulation and controlled release for cargo transport, a larger number of capsules can additionally self-assemble into complex materials, form remarkable large-scale patterns and exhibit swarming behavior or coherent motion. Understanding and imitating these phenomena are helpful in many aspects, for example, for the control of rheological properties, diffusion of bacteria suspensions, to lower human infertility, as models for active complex systems and control of microbial infections.
In the first part of the project, we investigated the behavior of particle capsules that were suspended in bulk fluid and their behavior when subjected to an electric field. At the host institution, Adam Mickiewicz University (AMU) and at the Slovak Academy of Sciences (SAS) we studied and measured the material properties of the particle and fluids used for fabricating capsules. The work resulted in a publication on structuring of modified polystyrene particles at droplet surfaces and important knowledge on properties of particles intended for forming particle capsules.Using a novel approach that combined microfluidics and electric fields, we managed to consistently fabricate patchy particle capsules. To improve the control over the capsules’ particle concentration and composition, we performed experiments on capsules that extended the knowledge on electric field-induced flows and how such flows can be used to structure and manipulate particles at droplet interfaces. Part of this work was performed at the University of Oslo (UiO). We also found how particles affect the electric and mechanical properties of droplets. Three articles were published on studies of particle-covered droplets in electric field. At AMU and UiO we also performed deformation experiments on droplets covered by particles of different properties, and investigated the effect of electric field-induced flows on particle capsules. From the research, we figured out which particles are suitable for a propulsion system and studied the behaviour of capsules during deformation. A manuscript on this research was published, while a second paper is submitted and currently in a review process. Based on these investigations, we demonstrated a new method for propelling patchy capsules through deformation. Another method for capsule propulsion was investigated and accomplished by counter-rotating capsules. However, we had problems controlling the direction of the capsule propulsion. One of the major challenges were openings at the capsule particle layer. This was thoroughly investigated and we discovered how the applied electric field and liquid viscosity of the droplets affected opening and closing of particle capsules. We also demonstrated three examples of applications for this phenomena. A manuscript on these findings was recently published. Due to delays with other objectives, there was little time left to study propulsion of capsules on boundaries and their collective behavior. In addition to 7 published articles (one more in review process), the scientific results from this project has also been disseminated at various conferences, meetings and seminars.
Patchy capsules are challenging to produce and the research on such capsules is therefore limited. This research project has developed a novel method for fabricating patchy particle capsules based on microfluidic equipment and electric fields. The method combined with our investigations on capsules in electric field will lay solid foundations for further development and applications within the field, and ultimately, for commercialization and products within biology, food, medicine, environmental science and material science. By employing external electric field, we have also developed new methods for propelling capsules. The propulsion methods differ from previous methods by using an electric field as the driving mechanism. Propelling capsules can perform a multitude task, for example cargo transport, driving nanomachines, removing toxic materials from water or human bodies, or actively controlling material behavior. Capsules with increased functionalities such as propulsion allow for improved products and processes through their impact on areas such as: material safety; reducing production costs; increasing material versatility and complexity; reducing system weight, power consumption and size. These impacts may in turn lead to great financial profit due to direct and positive impact on life quality, the environment, economic growth and sustainability. The results from this project will encourage more experimental research on particle capsules and move the field forward towards the ultimate goal of tailoring advanced microrobots that possess multiple functions, patent and economic market potential, as well as applications with social significance within soft-matter physics, medicine science, biotechnology, food science, materials science and applied sciences. The research project has also had an impact on my scientific career. Through various interdisciplinary experiments and scientific discussions with collaborators I have broadened my scientific expertise and increased my competitiveness among researchers within soft-matter physics, but also within other fields, e.g. chemical physics, biophysics, spectroscopy and scattering techniques. The project allowed me to develop my own ideas, gain versatile research experience, and to build a solid publication record and international reputation that will ultimately help me to set up an international research team. Through supervising MSc and PhD students, I have also developed my teaching, supervising and leadership skills. Morover, by attending special courses and workshops, I have developed my communication, networking and project management skills.
Deformation of a patchy capsule.