arXiv subjects

Steven van Kesteren

Publications and source records attributed to Steven van Kesteren.

4 recordsLinked to original sources

arXiv2026

PACSim: A Flexible Simulation Framework for Polymer-Attenuated Coulombic Self-Assembly

Polymer-Attenuated Coulombic Self-Assembly (PACS) is a flexible experimental approach for generating crystals from simple colloidal building blocks. The central components are charged spherical particles coated with a polymer brush that prevents irreversible aggregation. Whether oppositely charged colloids crystallize, and which structures they form, depends on several factors, including colloid concentration, charge, and size, as well as the salt concentration of the solution. Molecular dynamics (MD) simulations are a powerful tool for predicting the outcomes of PACS assembly experiments and also provide particle-level insight into the assembly processes. Here, we present an open-source simulation framework, PACSim, that enables MD simulation studies of assembly by PACS across a range of experimentally relevant scenarios. PACSim is built on top of OpenMM, a flexible MD simulation framework that readily supports the implementation of different interaction potentials, as well as integration with other tools such as enhanced-sampling and machine-learning frameworks. We describe the motivation for PACSim, outline its features, report methodological advancements inspired by this framework, and provide examples of its use.

cond-mat.soft↗

arXiv2022

Self-propelling colloidal finite state machines

Endowing materials with physical intelligence holds the key for a progress leap in robotic systems. In spite of the growing success for macroscopic devices, transferring these concepts to the microscale presents several challenges connected to the lack of suitable fabrication and design techniques, and of internal response schemes that connect the materials' properties to the function of an autonomous unit. Here, we realize self-propelling colloidal clusters which behave as simple finite state machines, i.e. systems built to possess a finite number of internal states connected by reversible transitions and associated to distinct functions. We produce these units via capillary assembly combining hard polystyrene colloids with two different types of thermo-responsive microgels. The clusters, actuated by spatially uniform AC electric fields, adapt their shape and dielectric properties, and consequently their propulsion, via reversible temperature-induced transitions controlled by light. The different transition temperatures for the two microgels enable three distinct dynamical states corresponding to three illumination intensity levels. The sequential reconfiguration of the microgels affects the velocity and shape of the active trajectories according to a pathway defined by tailoring the clusters' geometry during assembly. The demonstration of these simple systems indicates an exciting route to build more complex units with broader reconfiguration schemes and multiple responses towards the realization of autonomous systems with physical intelligence at the colloidal scale.

cond-mat.soft↗

arXiv2022

Printing on particles: combining two-photon nanolithography and capillary assembly to fabricate multi-material microstructures

Additive manufacturing at the micro- and nanoscale has seen a recent upsurge to suit the increasing demand for more elaborate structures. However, the integration and precise placement of multiple distinct materials at small scales remain a challenge. To this end, we combine here the directed capillary assembly of colloidal particles and two-photon direct laser writing (DLW) to realize a new class of multi-material microstructures. We use DLW both to fabricate 3D micro-templates to guide the capillary assembly of soft- and hard colloids, and to link well-defined arrangements of polystyrene or silica particles produced with capillary assembly, a process we term "printing on particles". The printing process is based on automated particle recognition algorithms and enables the user to connect colloids into one- and two-dimensional tailored structures, including particle clusters and lattices of varying symmetry and composition, using commercial photo-resists (IP-L or IP-PDMS). Once printed and developed, the structures can be easily harvested and re-dispersed in water. The flexibility of our method allows the combination of a wide range of materials into complex structures, which we envisage will boost the realization of new systems for a broad range of fields, including microrobotics, micromanipulation and metamaterials.

cond-mat.soft↗

arXiv2020

Direct evidence of stress-induced chain proximity in a macromolecular complex

The mechanical properties of many supramolecular materials are often determined by non-covalent interactions that arise from an interplay between chemical composition and molecular microstructural organization. The reversible nature of non-covalent interactions gives supramolecular materials responsive properties that are otherwise difficult to obtain, such as becoming rigid as a response to mechanical stress. How exactly non-covalent interactions emerge from microstructure, how they might change in response to applied force or deformation is not understood. Here we combine Nuclear Magnetic Resonance (NMR) and rheology to directly probe the role of chain proximity in polymer complexes. We observe an increase in chain proximity in response to imposed flow, which we hypothesize to originate from enhanced hydrogen bonding. The chain proximity is directly correlated to rod climbing and shear banding. Flow persists only when applied stresses are low, suggesting a stress-induced thickening mechanism. We verify that hydrogen bond disruptors can turn off both the non-trivial flow behavior and the spectroscopic evidence of chain proximity. The combined rheo-NMR approach shows that it is possible to directly observe the molecular origins behind supramolecular mechanics, paving the way for further study into mechano-chemical properties of supramolecular materials.

cond-mat.soft↗