Abstract
Due to the ability of microgels to rapidly contract and expand in response to external stimuli, assemblies of interconnected microgels are promising for actuation applications, e.g., as contracting fibers for artificial muscles. Among the properties determining the suitability of microgel assemblies for actuation are mechanical parameters such as bending stiffness and mobility. Here, we study the properties of linear, one-dimensional chains of poly(N-vinylcaprolactam) microgels dispersed in water. They were fabricated by utilizing wrinkled surfaces as templates and UV-cross-linking the microgels. We image the shapes of the chains on surfaces and in solution using atomic force microscopy (AFM) and fluorescence microscopy, respectively. In solution, the chains are observed to execute translational and rotational diffusive motions. Evaluation of the motions yields translational and rotational diffusion coefficients and, from the translational diffusion coefficient, the chain mobility. The microgel chains show no perceptible bending, which yields a lower limit on their bending stiffness.
Highlights
The investigation of polymer materials with spatial dimensions from a few nanometers to several microns has become an important and established research field in nano-science [1].Improving the fundamental understanding of the mechanical, optical, electrical and magnetic properties of polymer-based nanoscale structures offers a high potential for developing future functional materials
The microgel chains show no perceptible bending, which yields a lower limit on their bending stiffness
Poly(N-vinylcaprolactam) (PVCL) based microgels with a hydrodynamic radius rh of approximately 250 nm and a volume phase transition temperature (VPTT) of 28 ◦ C were synthesized as described in previously published protocols [34]
Summary
The investigation of polymer materials with spatial dimensions from a few nanometers to several microns has become an important and established research field in nano-science [1].Improving the fundamental understanding of the mechanical, optical, electrical and magnetic properties of polymer-based nanoscale structures offers a high potential for developing future functional materials. Another interesting feature is their water swelling and deswelling properties. The swelling and deswelling of microgels can be triggered by external stimuli such as pH or temperature changes, and are much faster (microsecond and sub-microsecond time ranges) than swelling and deswelling of conventional macroscopic hydrogels. The reason for this difference is that the time required for diffusive transport of solvent into and out of the polymeric network scales with the network size [13]
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