Final Report Summary - COMPASS (Colloids with complex interactions: from model atoms to colloidal recognition and bio-inspired self assembly)
Self-assembly is the key construction principle that nature uses so successfully to fabricate its molecular machinery and often highly elaborate structures. In this project we followed nature’s strategies and made a concerted experimental and theoretical effort to study, understand and control self-assembly for a new generation of colloidal building blocks. The project combined synthesis of colloidal building blocks and complex assemblies, the experimental characterization of their size, shape and interactions as well as their self-assembly behavior, and the theoretical and computer modeling of these systems.
A key component of the project was the use of responsive or smart polymer microgels, i.e. colloidal particles made up of a cross-linked polymer network with diameters in the range of several hundred nm to 1-2 micrometers. We have established various synthesis and nanoengineering processes that allowed us to create an extended library of microgels in a variety of different shapes, compositions, patterns and functionalities. We have devoted a considerable effort to characterize and understand interactions between neutral and charged microgels of different shapes, which also includes the successful development of theoretical models for the influence of concentration, pH and salt on the interactions and swelling behavior of ionic microgels, and the effects of an external ac electric field.
Using responsive particles with complementary shapes (sphere and bowl-like), we have been able to implement colloidal lock-and-key mechanisms with a selectivity and specificity, that can be externally controlled through temperature and ionic strength. We could demonstrate that mixtures of such oppositely charged thermoresponsive particles can reversibly switch from unstructured dense liquids to well-defined molecule-shaped clusters with variable configuration, and thus provide a colloidal analogue of adaptive chemistry.
We have successfully developed different strategies for the assembly of “colloidal molecules” with well-defined and externally tunable binding sites using our library of thermoresponsive microgels as building blocks, for example using microfluidics-based fabrication principles, and investigated their externally tunable directional interactions.
Another major achievement has been the investigation of the self-assembly of thermoresponsive core-shell microgels with ellipsoidal shape in the presence of an alternating electrical field. Starting point was our discovery, that such particles can reversibly assemble into well-defined highly regular single-walled tubes under the influence of the field. We performed a systematic study of the self-assembly behavior and the resulting state diagram of these particles as a function of particle shape (i.e. axial ratio), concentration, and field strength. We subsequently developed a computer model in order to mimic thermoresponsive core-shell ellipsoidal particles in the presence of an external electric field. This has led to a better understanding of the mechanisms behind our astonishing observation of the reversible formation of well-defined tubular structures, which demonstrates that the formation of tubular structures through self-assembly requires much less geometrical and interaction specificity than previously thought, and advances our current understanding of the minimal requirements for self-assembly into regular virus-like structures. It also has established predictions for the phase diagram of these systems as a function of particle axial ratio and concentration and field strength.
A key component of the project was the use of responsive or smart polymer microgels, i.e. colloidal particles made up of a cross-linked polymer network with diameters in the range of several hundred nm to 1-2 micrometers. We have established various synthesis and nanoengineering processes that allowed us to create an extended library of microgels in a variety of different shapes, compositions, patterns and functionalities. We have devoted a considerable effort to characterize and understand interactions between neutral and charged microgels of different shapes, which also includes the successful development of theoretical models for the influence of concentration, pH and salt on the interactions and swelling behavior of ionic microgels, and the effects of an external ac electric field.
Using responsive particles with complementary shapes (sphere and bowl-like), we have been able to implement colloidal lock-and-key mechanisms with a selectivity and specificity, that can be externally controlled through temperature and ionic strength. We could demonstrate that mixtures of such oppositely charged thermoresponsive particles can reversibly switch from unstructured dense liquids to well-defined molecule-shaped clusters with variable configuration, and thus provide a colloidal analogue of adaptive chemistry.
We have successfully developed different strategies for the assembly of “colloidal molecules” with well-defined and externally tunable binding sites using our library of thermoresponsive microgels as building blocks, for example using microfluidics-based fabrication principles, and investigated their externally tunable directional interactions.
Another major achievement has been the investigation of the self-assembly of thermoresponsive core-shell microgels with ellipsoidal shape in the presence of an alternating electrical field. Starting point was our discovery, that such particles can reversibly assemble into well-defined highly regular single-walled tubes under the influence of the field. We performed a systematic study of the self-assembly behavior and the resulting state diagram of these particles as a function of particle shape (i.e. axial ratio), concentration, and field strength. We subsequently developed a computer model in order to mimic thermoresponsive core-shell ellipsoidal particles in the presence of an external electric field. This has led to a better understanding of the mechanisms behind our astonishing observation of the reversible formation of well-defined tubular structures, which demonstrates that the formation of tubular structures through self-assembly requires much less geometrical and interaction specificity than previously thought, and advances our current understanding of the minimal requirements for self-assembly into regular virus-like structures. It also has established predictions for the phase diagram of these systems as a function of particle axial ratio and concentration and field strength.