Linear polymers in shear flow display a dominant mode of dynamics known as tumbling, around the vorticity axis, whereby the two ends exchange their places, accompanied by a temporary compression of the chain in the gradient direction. We will demonstrate that topological polymers respond to shear in dramatically different ways, emerging from a coupling between topology and hydrodynamics. In particular, we will discuss ring polymers as well as rings connected either chemically (bonded rings, BR) or mechanically (catenated rings, CR). Rings display vorticity swelling and an inflated phase that suppresses tumbling and Brownian motion. BRs tumble around an axis parallel to the gradient direction, whereas CRs show slip tumbling while maintaining their overall orientation and shape. These unusual phenomena all result from proper consideration of hydrodynamic interactions and they disappear if the latter are (artificially) switched off.

Single molecule and super-resolution fluorescence microscopy have pushed investigations of the structure and dynamics of systems in life and materials sciences far beyond the diffraction limit. Recent studies have shown that exploiting observables beyond localization can provide unprecedented insights into the local environment in such systems. Apart from spectral information to probe local polarity,[1] fluorescence lifetime information can access valuable insights. Fürstenberg and coworkers found that the quenching of red-emitting dyes by water can be used to determine the local water content around dyes,[2] allowing the amount of water molecules to be estimated using fluorescence lifetime imaging microscopy (FLIM). In our study, the fluorescence dye ATTO 655 was covalently embedded into aqueous hydrogel particles known as microgels. Its fluorescence lifetimes were measured using fluorescence lifetime single molecule localization microscopy imaging (FL–SMLM),[3] a recently developed localization-based super-resolution method performed on a confocal scanning microscope. Stern-Volmer analysis allowed us to determine the local water content in microgels at different temperatures and thus to exploit the different environmental properties in these microgels. Furthermore, the combination of FLIM with localization-based super-resolution microscopy allows for the estimation of the spatial distribution of water within microgels.[4] Apart from that, FLIM measurements can be used as nanoscopic moisture sensors.[5]

Polyethylene (PE) may be a chemically simple polymer, with only one monomeric unit (ethylene) present, but it can present a complex molecular structure containing short chain (SCB) and long chain (LCB) branching [1]. This topological complexity leads to a rich rheological behavior, of great interest in order to design novel PE materials for industrial application. In this work we have applied a model based on reptation concepts called the Branch-on-Branch model (BoB). The BoB model can be used to delve into the molecular architecture and is capable of predicting the expected experimental properties of any of our selected architectures [2]. A collection of PEs synthesised using heterogeneous metallocene catalysts (mPE) have been selected [3]. Small angle oscillatory shear (SAOS) experiments have been performed to obtain the linear response. Meanwhile the nonlinear viscoelastic response was studied using start-up stress growth shear and uniaxial extensional measurements. Then, the BoB model was applied to fit the experimental data and find the matching molecular topology for each material, following the scheme shown in Figure 1. Using this methodology, a strong asymmetry in the LCB distribution was predicted in some samples containing a characteristic non-linear fingerprint. Furthermore, two different LCB populations have been found to describe one same LVE, building upon Janzen and Colby findings [4].
Combining an in-depth rheological characterization with molecular computational models is a powerful tool for the exhaustive study of complex polymeric topologies, paving the way for the design of novel material architectures.

Acrylamide-based microgels have garnered significant attention in recent decades due to their numerous properties. Among these, poly(N-isopropylacrylamide) (PNIPAM) microgels have been extensively studied for academic purposes, while polyacrylamide (PAm) microgels, despite their broad industrial utility, remain comparatively underexplored. These microgels, with their responsive polymeric networks, can be synthesized via various techniques, primarily precipitation polymerization (PP) and inverse emulsion polymerization (IEP). However, a detailed comparison of the impact of these synthesis methods on microgel properties under isochemical conditions has been lacking.
In this study, we compared PAm microgels synthesized using these two widely employed methods, highlighting significant differences in their structural and rheological behavior. The results indicate that precipitation polymerization leads to heterogeneous, highly branched polymers, whereas inverse emulsion polymerization produces more defined microgel structures, minimizing interpenetration effects. This comparative analysis provides insights into tailoring microgel properties for specific applications by selecting the appropriate synthesis method.

In this communication, we present our efforts to investigate the physical chemistry of specific small molecule functional moieties and their impact on the macroscopic behavior of dynamic polymer networks with well-defined architectures. Our recent work focuses on self-assembling and liquid crystal polymers [1], [2], which have expanded the possibilities for designing materials with predictable stimuli-responsive properties, particularly thermo- and chemoresponsive behavior.

Notably, equipping star polymers with molecular receptors for boron-assisted imine formation, an approach aligned with the principles of internally catalyzed dynamic covalent chemistry, [3], [4], enables the development of stimuli-responsive, self-assembling polymer hydrogels [5]. The use of boron-assisted imine formation and related exchange reactions represents a novel strategy in polymer science, yielding highly dynamic materials with chemoresponsive properties. Indeed, the viscoelastic behavior and gelation kinetics of these materials can be tuned by biological species such as glucose and cysteine in biologically relevant environments. Our understanding of the thermodynamics and kinetics of small molecule dynamic covalent binding motifs, along with neighboring group participation effects, provides fundamental insights for designing network polymers with a la carte stimuli-responsive behavior. This family of soft materials holds promise for emerging applications in, for example, soft robotics and drug delivery.

Adhesion in aqueous environment is one of the topics that gains increasing attention. The water screening effect at the interface of adhesives and substrates tremendously reduces their efficiency and limits their use in underwater applications. While significant experimental and theoretical advances have been made on adhesion of synthetic materials,¹ there is still clear lack of knowledge on more complex bio-adhesion processes in wet and underwater conditions. In this work, mechanisms and factors affecting underwater adhesion were studied using homemade probe tack test allowing the characterization of the underwater adhesion properties between a tough hydrogel adhesive and surface-attached hydrogels designed with macro/micro-patterns. This configuration allows the separation of the bulk effects (cohesion) from surface properties.² Macroscopic tough bio-based double network (DN) hydrogels of negatively-charged κ-carrageenan/agarose and poly(acrylamide) were developed. Model hydrogel thin films (~100 nm) and microscopic hexagonal hydrogel patterns from positively-charged poly((dimethylamino)ethyl methacrylate) (PDMAEMA) were prepared on solid substrates via cross-linking and grafting (CLAG) strategy using photolithography.³ The effects of the aqueous environment and surface topography by changing the hexagonal side length (20 and 200 μm) and the distance between the hexagon patterns (20 and 200 μm) on adhesion energy were investigated. While the adhesion energy between unpatterned PDMAEMA hydrogel thin film and tough DN hydrogel is about 8.5 J/m² as a result of strong electrostatic interactions. The surface topography greatly increases the underwater adhesive properties, adhesion energies as high as 37 J/m² have been obtained as a result of the improved water drainage and the reduction of crack propagation.