arXiv subjects

Ludwik Leibler

Publications and source records attributed to Ludwik Leibler.

9 recordsLinked to original sources

arXiv2026

Residual semi-crystalline particles released during enzymatic degradation of plastics

Enzymatic recycling of plastics is limited by the presence of semi-crystalline spherulites that are recalcitrant to enzymatic depolymerization. Depending on the quality of the waste stream and its treatment history, a large volume fraction of the material actually remains in form of connected clusters of such spherulites. We build on a recently published numeric method to predict the number, the connectivity, and the morphology of these clusters as an outcome of enzymatic degradation. When applied to PET waste, our method predicts that the resulting aggregates are loosely connected, "fluffy" structures with a high surface-to-volume ratio, accompanied by smaller clusters following a continuous size distribution. By providing a quantitative framework for understanding the microparticle production during the depolymerization, these findings should assist choosing a suitable downstream treatment, such as filtering or flocculation. This work could thus help to advance the enzymatic depolymerization technologies.

cond-mat.soft↗

arXiv2026

Theory for enzymatic degradation of semi-crystalline polymer particles

In enzymatic recycling or biodegradation of semi-crystalline plastic waste, crystalline spherulites embedded into an amorphous matrix hinder and slow down depolymerisation. When the enzymatic depolymerisation temperature exceeds the glass transition temperature, these spherulites tend to grow. The depolymerisation process is thus controlled by a competition between erosion of the amorphous matrix from the particle surface and the growth of recalcitrant spherulites within the particle bulk and at its surface. We present a geometric model that captures this competition, together with an algorithm to solve the equations numerically. Our algorithm introduces a new extension of Voronoi/Delaunay tessellation in space. We extract the parameters for the model from experimental data on the enzymatic depolymerization by hydrolase LCC-ICCG of PET bottle flakes and textile waste, in order to make a prediction of the observed degradation yield as a function of time. Both the final yield and the degradation kinetics are correctly predicted. Most importantly, the model clarifies how and to which extent nucleating agents, impurities, additives, and/or rapid crystal growth present in the waste can undermine pretreatment efforts aiming to initiate depolymerisation from a material with a low initial crystallinity.

physics.chem-ph↗

arXiv2024

Dynamic Heterogeneity of Short Semi-crystalline Polymer Chains during Recrystallization

The instant crystallization of semi-crystalline polymers have become possible following the recent advances in Fast Scanning Calorimetry (FSC) and enables to make a bridge between the time scale available experimentally with those accessible with computer simulations. Although the FSC observations have provided new information on the crystallization kinetics and evolution of the crystals, the molecular details on the chain exchange events between ordered and disordered domains of crystals have remained elusive. Using molecular dynamics simulations, we examined the detailed chain dynamics and thermodynamics of polyamide 6 (PA6) system under two heating treatments. (i) Quenching PA6 melt deeply below the melting temperature T m and (ii) annealing the resulting quenched system to a temperature close to T m . We categorized the chains into mobile amorphous fraction (MAF) and rigid amorphous fraction (RAF), based on the length of consecutive chain's bond angles in trans state. In the deep quenched system close to the glass transition temperature T g , the mobility of the MAF chains are strongly suppressed and they remain in glassy state. However, upon rising the temperature close to melting temperature, the system undergoes recrystallization leading to coexistence of RAF and supercooled liquid MAF chains. The highly mobile unentangled MAF chains explore the interphase domains, and during the late-stage of crystallization, they are thermally translocated into the lamellae by reducing the fold number of RAF chains. The chain mobility in the annealed system could potentially lead to improved biodegradation in semi-crystalline chains.

cond-mat.soft↗

arXiv2023

Mechanical activation of reversible bonds by low amplitude high frequencies excitations

Reversible covalent or supramolecular bonds play an important role in materials science and in biological systems. The equilibrium between open and closed bonds and the association rate can be controlled thermally, chemically, by mechanical pulling, ultrasound or catalysts. In practice, these intrinsic equilibrium methods either suffer from a limited range of tunability or may damage the system. Here, we present a non-equilibrium strategy that exploits the dissipative properties of the system to control and change the dynamic properties of sacrificial and reversible networks. We show theoretically and numerically how high-frequency mechanical oscillations of very low amplitude can open or close bonds. This mechanism indicates how reversible bonds could alleviate mechanical fatigue of materials especially at low temperatures where they are fragile. In another area, it suggests that the system can be actively modified by the application of ultrasound to induce gel-fluid transitions and to activate or deactivate adhesion properties.

cond-mat.soft↗

arXiv2018

Phase separation and self-assembly in vitrimers: hierarchical morphology of molten and semi-crystalline polyethylene/dioxaborolane maleimide systems

Vitrimers - a class of polymer networks which are covalently crosslinked and insoluble like thermosets, but flow when heated like thermoplastics - contain dynamic links and/or crosslinks that undergo an associative exchange reaction. These dynamic crosslinks enable vitrimers to have interesting mechanical/rheological behavior, self-healing, adhesive, and shape memory properties. We demonstrate that vitrimers can self-assemble into complex meso- and nanostructures when crosslinks and backbone monomers strongly interact. Vitrimers featuring polyethylene (PE) as the backbone and dioxaborolane maleimide as the crosslinkable moiety were studied in both the molten and semi-crystalline states. We observed that PE vitrimers macroscopically phase separated into dioxaborolane maleimide rich and poor regions, and characterized the extent of phase separation by optical transmission measurements. This phase separation can explain the relatively low insoluble fractions and overall crystallinities of PE vitrimers. Using synchrotron-sourced small-angle X-ray scattering (SAXS), we discovered that PE vitrimers and their linear precursors micro-phase separated into hierarchical nanostructures. Fitting of the SAXS patterns to a scattering model strongly suggests that the nanostructures - which persist in both the melt and amorphous fraction of the semi-crystalline state - may be described as dioxaborolane maleimide rich aggregates packed in a mass fractal arrangement. These findings of hierarchical meso- and nanostructures point out that incompatibility effects between network components and resulting self-assembly must be considered for understanding behavior and the rational design of vitrimer materials.

cond-mat.soft↗

arXiv2007

Phase-separation of miscible liquids in a centrifuge

We show that a liquid mixture in the thermodynamically stable homogeneous phase can undergo a phase-separation transition when rotated at sufficiently high frequency $ω$. This phase-transition is different from the usual case where two liquids are immiscible or where the slow sedimentation process of one component (e.g. a polymer) is accelerated due to centrifugation. For a binary mixture, the main coupling is due to a term $\propto Δρ(ωr)^2$, where $Δρ$ is the difference between the two liquid densities and $r$ the distance from the rotation axis. Below the critical temperature there is a critical rotation frequency $ω_c$, below which smooth density gradients occur. When $ω>ω_c$, we find a sharp interface between the low density liquid close to the center of the centrifuge and a high density liquid far from the center. These findings may be relevant to various separation processes and to the control of chemical reactions, in particular their kinetics.

cond-mat.soft↗

arXiv2007

Phase-separation in ion-containing mixtures in electric fields

When a liquid mixture is subjected to external electric fields, ionic screening leads to field gradients. We point out that if the mixture is initially in the homogeneous phase, this screening can bring about a robust phase-separation transition with two main features: (i) the phase separation is expected to occur in any electrode geometry, and (ii) the voltage required is typically of the order of 1 V and even less. We discuss several applications of the effect relevant to the field of microfluidics, focusing on the creation of a nanometer-scale lubrication layer in the phase-separation process.

cond-mat.soft↗

arXiv2005

Electrostatic Cancellation of Gravity Effects in Liquid Mixtures

We point out that a spatially-varying electric field can be used to cancel the effect of gravity in liquid mixtures by coupling to the different components' permittivities. Cancellation occurs if the system under consideration is small enough. For a simple ``wedge'' electrode geometry we show that the required system size and voltage are practical, easily realizable in the Lab. Thus this setup might be a simple alternative to more expensive or hazardous options such as the space-shuttle, drop-tower, or magnetic levitation experiments.

cond-mat.stat-mech↗

arXiv2002

Structural changes in block copolymers: coupling of electric field and mobile ions

We consider the coupling between an external electric field and dissociated ions embedded in anisotropic polarizable media such as block copolymers. We argue that the presence of such ions can induce strong morphological changes and even lead to a structural phase transition. We investigate, in particular, diblock copolymers in the body centered cubic (bcc) phase. In pure dielectric materials (no free charges), a dielectric breakdown is expected to occur for large enough electric fields, preempting any structural phase transition. On the other hand, dissociated ions can induce a phase transition for fields of about 10 V/$μ$m or even lower. This transition is from an insulator state, where charges are preferentially localized inside bcc spherical domains, to a conducting state where charges can move along the long axis of oriented cylinders (forming a hexagonal phase). The cylinders diameter is small and is determined by the volume fraction of the minority copolymer component. The strength of this mechanism can be tuned by controlling the amount of free ions present as is observed by our experiments. These theoretical predictions support recent experimental findings on the bcc to hexagonal phase transition in copolymer systems.

cond-mat.soft↗