The 2000 perspective article by Gert Strobl, “From the melt via mesomorphic and granular crystalline layers to lamellar crystallites: A major route followed in polymer crystallization?”, proposed a revolutionary multistep mechanism for polymer crystallization from the quiescent melt, fundamentally challenging the dominant single-step models of the time. Two decades later, this perspective revisits Strobl’s conceptual framework to assess its legacy, its limitations, and its continuing relevance to modern polymer science. We examine the three-stage pathway—mesomorphic layer formation, cooperative transition to a granular crystalline layer, and block merging into lamellar crystallites—through the lens of subsequent experimental, theoretical, and simulation advances. While the model’s central premise of intermediate states has stimulated extensive research, key elements remain debated. The distinction between crystal-fixed and crystal-mobile polymers has emerged as a critical factor, reinterpreting the stabilization phenomena Strobl observed and challenging the universality of his proposed pathway. Simulation studies have provided complementary insights into precursor states; yet, the direct detection of the granular crystalline layer and the mesomorphic precursor remains elusive. We identify open questions regarding the molecular origins of early stage ordering, the factors determining lamellar thickness, and the universality of granular crystalline states. Strobl’s model was important not because it provided definitive answers, but because it forced the field to confront its assumptions and inspired a generation of research that continues to advance our understanding of polymer crystallization.
The drying of complex fluids, such as colloidal or polymer solutions, is filled with fascinating dynamics as a consequence of evaporation-driven inhomogeneities of the suspended material, which can result in an “elastic skin” at the liquid–air interface and dense deposits at the contact line, both of which can lead to significant mechanical stresses. As a consequence, drops of a colloidal solution or a polymer solution may undergo shape changes during drying and cracks can form, after which a deposited drop or film can even delaminate from the substrate. Understanding the rates of different transport processes helps to understand and organize the different material responses. We look back at the well-cited 2018 contribution in EPJE by Giorgiutti-Dauphiné and Pauchard who provided an organized view and many insights on this topic, highlight some more recent research, and look towards future developments. As a colloidal solution dries, typically the concentration of suspended particles increases near the liquid-air interface, which produces elastic effects and (fascinating) shape changes in response to the reduction in volume. Here this shape change is shown on the left, with a cross-sectional microscope image displayed on the right indicating the spatial variations inconcentration. note: this image is from Figure 13 of is from reference 6 in the paperAs a colloidal solution dries, typically the concentration of suspended particles increases near the liquid-air interface, which produces elastic effects and (fascinating) shape changes in response to the reduction in volume. Here this shape change is shown on the left, with a cross-sectional microscope image displayed on the right indicating the spatial variations inconcentration.
Microrobotic swarms are promising candidates for targeted drug delivery in complex physiological environments, including blood, mucus, and extracellular matrices. In such biomedical scenarios, collective motion is strongly influenced by low-Reynolds-number drag, crowding, confinement, viscoelasticity, and non-Newtonian rheology. This article envisages a mechanics-based computational framework for microrobotic swarms in viscoelastic (gel-like) media. Starting from Langevin dynamics, we derive the overdamped description appropriate for microscale agents and extend it to active Brownian particles with self-propulsion, local alignment, and short-range interparticle interactions. Cohesive and purely repulsive collective regimes are represented through Lennard-Jones and Weeks-Chandler-Andersen potentials, respectively. To model gel-like rheology, we introduce a fractional Kelvin–Voigt description of drag that incorporates power-law memory effects. The resulting stochastic dynamics are mapped to an explicit Euler–Maruyama algorithm with truncated-history fractional convolution, documented stabilizers, and diagnostic observables for polarization, clustering, trajectories, and transport. Beyond the model itself, the present study synthesizes recent work on bacterial living fluids, externally driven colloidal and microrobotic swarms, fish-school hydrodynamics, neural-network control of collective patterns, and cross-scale magnetic catheter-swarm thrombus removal. That microrobotic-swarm transport in biomedical media should not be treated only as a soft-matter problem is the primary takeaway. We believe that it is rather a coupled mechanics problem in which propulsion, interaction, memory, disorder, hydrodynamic communication, and clinical deliverability must be taken into consideration. At the same time, the preliminary simulations suggest a practically important biomedical trend: whereas Newtonian transport is more prone to collective aggregation, viscoelastic transport can preserve a more distributed swarm morphology, which is encouraging for controllable delivery, broader spatial coverage, and aggregation-resistant payload transport in complex bodily fluids.
Biological membranes are dynamic soft interfaces in which molecular interactions govern their structure and organization across multiple length and time scales. Processes such as structural remodelling, fusion and curvature generation arise from collective molecular rearrangements within these highly complex environments. Despite the widespread use of simplified membrane models, establishing meaningful links between (two-dimensional) interfacial systems and three-dimensional membrane behaviour remains a major challenge. In this perspective, we discuss how studies on Langmuir monolayers may provide access not only to equilibrium membrane thermodynamics, but also to the relaxation phenomena underlying membrane transformations. Focusing on interfacial rheology, with particular attention to mechanical hysteresis, we discuss how dynamic interfacial observables may provide experimentally accessible indicators of how lipid assemblies accumulate, dissipate, and reorganize lateral stresses, and how such responses may become linked to membrane organization and remodelling. Beyond their role as simplified membrane mimics, we discuss recent literature on Langmuir monolayers, and we explore the possibility that dilatational and shear relaxation modes measured in monolayers (2D relaxation) contain information relevant to membrane self-assembly (3D remodelling).
We investigate the dynamics of an actively driven semiflexible polymer confined by a soft harmonic potential. Our study is inspired by in-vitro motility assays where cytoskeletal filaments are propelled by motor proteins under controlled confinement. Using coarse-grained simulations that couple polymer elasticity with stochastic motor attachment, detachment, and force generation, we obtain distinct dynamical regimes ranging from fully confined to freely escaping states, separated by a region of intermittent coexistence. The transitions between these regimes are governed by the combined effects of activity, filament stiffness, confinement strength, and motor processivity. Moderate confinement stabilizes compact spiral conformations through a balance between active forcing and bending elasticity. Stronger activity promotes escape. The motion of the center-of-mass of the polymer exhibits diffusive–ballistic–localized crossovers and oscillations characteristic of trapped chiral active Brownian particles. Our results establish a minimal physical framework for understanding how activity and geometric confinement interact to regulate the transport and morphology of active filaments. A diagram depicting the model setup: a polymer in a harmonic trap embedded on a motor assay, followed by a time series showing three di9erent states of the system.
Two-dimensional coalescence of holes (regions with thickness less than the surrounding film) in free-standing Smectic A films was studied. Investigations were made on two types of domains: circular holes and holes with a thin sheet of the external film between holes. Direct evidence was found that before start of coalescence a long, thin sheet of external film can exists between holes. This sheet determines the early mechanism of coalescence. It is shown that the existence of the sheet essentially elongates the linear temporal dependence of the size of the bridge connecting the two holes rb(t) t. Later when the thin sheet disappears the crossover to the conventional dependence rb(t) (t)1/2 was observed. Our results can explain numerous data on two-dimensional and quasi-two-dimensional coalescence at the early and later stages of coalescence.
Equilibration in liquids and glasses can proceed through multiple pathways, mediated by relaxation processes that remain active even when structural α -relaxation is strongly suppressed. Two prominent candidates are the Johari–Goldstein (JG) relaxation and the recently discovered slow Arrhenius process (SAP), both of which persist in the glassy state and exhibit a weaker temperature dependence than the structural relaxation. Their coexistence raises a central challenge: how to identify which localized process governs a given nonequilibrium kinetics. Here we compare the microscopic signatures of these two mechanisms and discuss practical strategies for their attribution. In particular, we argue that activation-energy matching provides only a first empirical indication, whereas SAP-driven kinetics can be identified more stringently within the collective small displacement (CSD) framework. The JG-controlled kinetics, on the contrary, should be assessed through consistency criteria tied to thermodynamic state of the system and α -dynamics. We believe that establishing such discriminating frameworks will be crucial for the next generation of experiments, simulations, and theoretical descriptions of nonequilibrium glassy dynamics.
Population density strongly affects the internal organization and movement dynamics of fish schools. Here, we investigate density-dependent collective motion in zebrafish (Danio rerio) schools with group sizes ranging from 2 to 30 individuals. Using trajectories measured relative to the school center of mass, we show that individual motion is superdiffusive at low densities and progressively approaches Brownian-like behavior as density increases. Step-length distributions are well described by truncated power laws: for N ≤ 15 , the fitted exponents are compatible with a Lévy-walk regime, whereas larger groups show a transition toward Brownian motion. In parallel, q-Gaussian fits of the signed radial displacement increments reveal heavy-tailed, non-Gaussian fluctuations at low densities and a gradual convergence toward Gaussian-like behavior at high densities. These results support a density-driven transition from a polarized, strongly correlated schooling state to a more disordered shoaling state, suggesting that increased density reorganizes local interactions within the group.
We investigate how breaking the geometric axisymmetry of fibers alters their dynamics when suspended in wall turbulence, using intrinsic curvature as a controlled proxy for symmetry loss. The study is based on a series of large-scale direct numerical simulations of turbulent channel flow laden with flexible fibers with varying lengths and intrinsic curvatures. We find that curved fibers tend to accumulate in the near-wall region of the flow. Analyzing their orientation dynamics, we recorded a marked shift in dynamics in comparison to their straight counterparts as they tend to have a preferential alignment even in the near-isotropic region of the flow. They also tend to tumble at larger rates with increasing curvatures. Furthermore, we also find that fiber dynamics become less sensitive to their curvature with increasing length.
This work systematically investigates the wetting properties of electrochemically doped poly(3-hexylthiophene) (P3HT) films at different oxidation states. In situ spectroelectrochemistry and ex situ opto-electronic characterization of the doped films confirm that the polaron and bipolaron states have successfully been obtained through electrochemical doping. Sessile drop and dynamic water contact angle measurements yield reproducible results that strongly depend on the applied electrochemical doping potential, with a maximum water contact angle variation of up to 43° from the neutral to the fully doped state. The evolution of wettability correlates with the doping states and is heavily influenced by morphological changes upon doping. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) reveal that wrinkle-like structures appear at high doping levels which is consistent with predominant bipolaron formation accompanied by doping-induced swelling followed by drying. Complementary grazing-incidence wide-angle X-ray scattering (GIWAXS) shows that doping to the polaronic state leads to lamellar expansion with a contraction of the π–π stacking distance within crystalline domains. Despite these lattice changes, the edge-on orientation is largely preserved, indicating that the overall crystalline texture remains stable even at the highest studied doping levels.
The wetting processes of polymer brushes, embedded with a fluorescent probe, were investigated with time-correlated single photon counting. A suitable aurone dye was synthesized, which exhibits moderate fluorescence in aprotic solvents, poor fluorescence in protic solvents and practically no fluorescence in aqueous solution. Poly(diethylene glycol methyl ether methacrylate) (PDEGMA) brushes of ca. 200 nm thickness were obtained by polymerization from a Ti surface by surface-initiated atom transfer radical polymerization (SI-ATRP). The dye-loaded brushes show fluorescence of the dye comparable with the autofluorescence of the PDEGMA brushes and the subjacent α-bromoisobutyryl bromide (BiBB) functionalized polydopamine (PDA) layer. With a global analysis of fluorescence decays, the lifetimes of the complex multicomponent materials were deconvoluted. The dry polymer loaded with the dye possesses a five-exponential fluorescence decay with the characteristic decay times of 3.0 ns for the dye, and 6.0, 1.8 and 0.45 ns for PDEGMA brushes as well as < 0.05 ns for the PDA-BiBB layer. Because of the strong decrease of the fluorescence lifetime of the dye down to 2.4 ns when submersed in water and a concomitant decrease of the lifetimes of the matrix to 4.5, 1.3 and 0.40 ns, both dye and matrix fluorescence are feasible reporter probes for the analysis of wetting processes of polymers with fluorescence lifetime imaging. The contrast of the intensity images of the aurone, which is low because of background fluorescence, increases by a factor of 3.1 in the time-resolved imaging at certain time delay after excitation. Hence, the incorporation of the aurone in the polymer brushes is a promising and versatile system for the investigation of (de)wetting dynamics employing fluorescence lifetime imaging and nanosecond time-resolved fluorescence imaging microscopy.
In this paper, various aspects of the Poisson-Boltzmann (PB) equation, focusing on the roles of structural confinement and ionic conservation have been addressed. Specifically, this paper provides an analytical and well-behaved solution of the PB equation in finite and infinite structures for open and isolated electrolytic environments. A structure-dependent Debye length for confined systems and a generalized Debye length appropriate for isolated electrolytes are introduced. For an isolated symmetric (1:1) electrolyte, a generalized PB equation has been derived. In the literature, the solution to this equation within a finite region is often presented as complex mathematical expressions, typically constrained to particular scenarios. In this paper, a general solution to the PB equation is derived using a novel mathematical function yielding a simpler closed-form solution than existing analytical approaches. This solution is expressed explicitly in a fully analytical, closed form, and approximation free manner. The results presented yield a simple and general algorithm for treating the PB model under various conditions. Finally, using this framework, we examine the validity range of the Debye model, determine, through pressure analysis, when two immersed electrodes become effectively non-interacting and analyze the stored electrostatic energy in different geometries, highlighting the effect of system isolation on the stored energy.
A common, but not the only method for the spectral resonance shift in a microresonator is to change the cavity’s optical path. A fundamentally different approach to separate polarized modes at the fixed optical path consists in inhomogeneous twisting of a medium within the cavity, which allows for the creation of high-sensitivity devices such as sensors, filters, microlasers, modulators, phase shifters, etc. An experimental and theoretical study of the polarization and spectral properties of a Fabry–Pérot microresonator formed by a pair of flat metallic mirrors with a planar-oriented nematic liquid crystal layer between them has been carried out. The specific chirality of the liquid crystal structure is induced by a magnetic field in the T-effect regime and is characterized by inhomogeneous twisting and the presence of a plane at the center of the nematic layer where the local director reverses the twist sign. Despite the small resulting deformation, these factors enhance the nonadiabatic propagation of light waves in the resonator, which, in turn, leads to significant anomalous shifts of the polarized resonant modes in the transmittance spectrum. The obtained experimental spectral shifts of the modes are consistent with the data of the numerical simulation using the 4 × 4 transfer matrix method and are explained by the contribution of the geometric phase, which paves the way to novel topological photonics devices. Metallic microresonator with a specific chirality of the nematic liquid crystal in magnetic field
The study "On dense granular flows" by GDR MiDi, published in 2004 in The European Physical Journal E 14, 341–365, stands as a seminal collective work that significantly advanced the understanding of dense granular materials. Remarkably, the names of the contributing authors are not listed; only the name of the consortium is given—a brave statement for joint efforts like this!. The GDR Midi (Groupement de Recherche sur les Milieux Divisés) was a CNRS-led consortium of French laboratories. Its mission was to bring together diverse scientific communities—including solid mechanics, fluid mechanics, physics, and geophysics—around the study of granular media, in order to promote collaboration through frequent, informal meetings held typically four times per year (see group photograph of a meeting in Carry Le Rouet in 2005). This approach enabled the identification of key scientific challenges as the need to compare and consolidate data across different configurations, between experiments and simulations, and across different research groups, ultimately inspiring the work that led to the collective GDR Midi paper.
We perform three-dimensional simulations of SAW-driven spreading of silicone oil drops on flat substrates and over solid obstacles. The resulting model takes the form of a three-dimensional long-wave thin-film equation incorporating capillary, gravitational, and SAW-induced acoustic stresses. A key feature of the formulation is a smooth attenuation function that localizes acoustic forcing within the bulk drop while avoiding spurious transverse discontinuities. Comparisons with results of earlier 2D formulations demonstrate qualitatively similar dynamics, albeit the additional spatial dimension permits transverse mass redistribution driven by capillarity, which leads to slower streamwise spreading and slightly lower drop apexes than predicted by 2D models. The model is applied to SAW induced dynamic wetting of flat substrates and solid obstacles and is representative of experimental geometries. Quantitative comparisons with experimental observations show good agreement for front propagation and obstacle climbing dynamics. In particular, improved agreement with the experimentally observed dependence of the liquid climbing time over obstacles on SAW amplitude is obtained when the fully three-dimensional formulation is used.
Chemical graph theory facilitates the understanding of the complex structure of molecules. Researchers can achieve a thorough understanding of the physical science, chemical properties, and bio-organic characteristics of pharmaceuticals through the calculation of resolvability and topological parameters in drug design. The resolvability constraints for graph G=(V, E) constitute a complex domain in which the framework is structured so that each vertex (atom) or edge (bond) denotes a distinct position. This study aims to utilize molecular graph theory to identify specific graph-theoretic parameters associated with the molecular graphs of eight medications used in malaria treatment. This paper presents resolvability parameters, including metric dimension (MD) and edge metric dimension (EMD), for eight medications used in malaria treatment. We demonstrate that the resolvability parameters for the specified drugs are both bounded and constant. This property facilitates molecular identification, verifies graph isomorphism, and functions as a valuable topological descriptor in QSAR/QSPR modeling. Furthermore, it improves chemical database indexing and feature generation for machine learning, facilitating efficient structure-based analysis in drug discovery and material design. Resolvability Parameters in Anti-Malarial Drugs
The study of red blood cell (RBC) deformability remains an active area of research due to its linkage to health and normal physiological functions of RBCs in the circulatory system. RBC deformability is commonly analyzed using force-based experimental and theoretical approaches. Complementary to these methods, geometric descriptions of RBC shape provide insight into curvature redistribution and bending energetics independent of explicit constitutive modeling. In this work, we present a semi-analytical, surface-based framework to study RBC deformation under axial stretching by imposing an affine geometric strain on a triangulated biconcave membrane, with volume conservation enforced throughout. Linear strain and a non-linear Hencky-type strain are compared. While linear strain reproduces experimental trends only for small deformations, nonlinear strain yields global shape variations—axial and transverse diameters and elongation index—that are consistent with reported optical tweezers data over a wide deformation range. The surface formulation enables detailed mapping of Gaussian and mean curvature redistribution during elongation. Evaluation of the Helfrich bending energy, including spontaneous curvature treated as an effective geometric parameter, yields energetically consistent values when non-linear strain is employed. Analysis of the curvature-bending energy of the RBC subjected to axial stretching suggests that nonlinear strain and spontaneous curvature should be the primary considerations to ensure that the membrane bending energy remains within the range of 10–100 eV during RBC biomechanical deformation. The framework does not resolve force balance or membrane constitutive behavior, but provides a computationally efficient geometric surrogate linking imposed deformation to curvature and bending energetics.
We investigate the influence of drop volume on partial wetting of sessile drops on a horizontal solid substrate for up to large Bond numbers, considering water on both polymethyl methacrylate (PMMA) and aluminum-coated substrates, as well as glycerol on PMMA. The horizontal orientation of the substrate, along with methods for creating sessile drops, facilitated the rotational symmetry of drops to perform controlled and reproducible experiments. In particular, we explore the manner in which the statistic macroscopic contact angle (MCA) depends on the sessile drop volume or related Bond numbers, whether the drop is injected via a syringe positioned above the substrate (DSA30 Krüss equipment) or from below the substrate through a tiny hole drilled in it. In both cases, experimental results exhibit that as the drop volume is increased spanning Bond numbers in the range [0.1–14], the contact line advances on the substrate and the MCA significantly decreases down to an asymptotic value.
We investigate the kinetics of wetting ridge growth and droplet cloaking on lubricant-infused polymer brushes using a combination of experiments, molecular dynamics simulations, and theoretical modeling. We focus on three representative systems: DMSO-water on hexadecane-swollen PLMA (D-H), water on hexadecane-swollen PLMA (W-H), and water on PDMS (W-S). The dynamics are governed by the interplay between interfacial thermodynamics, brush elasticity, and transport of lubricant within the brush. Ridge growth is accompanied by the formation of depletion zones both beneath and outside the drop. This leads to a progressive slowdown governed by the need to transport lubricant through the brush. At sufficiently high swelling, we observe local separation of oil from the brush within the ridge, providing an additional mechanism for lubricant depletion. To rationalize these observations, we develop a continuum diffusion model based on the free energy of the brush and its coupling to the contact line. The model quantitatively captures the growth of the wetting ridge at intermediate and late times, demonstrating that the kinetics are largely controlled by diffusive transport within the brush.
Shadowgraph experiments have been performed on giant nonequilibrium fluctuations in solutions of polystyrene in toluene with polymer molar masses between 2.1 and 90.9 kg/mol and mass fractions ranging from 0.002 up to 0.6. Due to the large Soret coefficient of the polymer and the applied temperature difference of 50 K, a linear model is not sufficient to describe the time-dependent and static structure functions. Nonlinearities stemming mainly from the highly nonlinear concentration profile, as well as from the temperature and concentration dependence of various thermophysical parameters, are taken into account using a previously developed layer model. This model enables a detailed analysis of the signal generation within the shadowgraph cell. The thermal structure function mainly emerges from the hot top plate. For short polymer chains and/or low concentrations, the solutal structure function is dominated by the cold side. However, due to the complicated interplay between the Soret effect, the viscosity, and the gravitational quench, this can change for long chains and high concentrations, with the strongest solutal signal emerging from the hot side. Situations involving a non-monotonous layer sequence are also possible. The simulated structure functions agree reasonably with experimental data. Dispersion of the structure functions due to nonlinearities in strong temperature gradients
