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.Comment: 5 pages, one figur

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

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.Comment: 1.5 pages, one figure. Accepted to PRE brief report

Dynamic covalent chemistry in polymer networks : a mechanistic perspective

The incorporation of dynamic covalent linkages within and between polymer chains brings new properties to classical thermosetting polymer formulations, in particular in terms of thermal responses, processing options and intrinsic recycling abilities. Thus, in recent years, there has been a rapidly growing interest in the design and synthesis of monomers and cross-linkers that can be used as robust but at the same time reactive organic building blocks for dynamic polymer networks. In this perspective, a selection of such chemistries is highlighted, with a particular focus on the reaction mechanisms of molecular network rearrangements, and on how various mechanistic profiles can be related to the mechanical and physicochemical properties of polymer materials, in particular in relation with vitrimers, the recently defined third category of polymer materials. The recent advances in this area are not only expected to help direct promising emerging polymer applications, but also point towards the need for a better fundamental understanding of chemical reactivity within a macromolecular context

Chemical control of the viscoelastic properties of vinylogous urethane vitrimers

International audienc

Etude de l'autoréparation d'élastomères supramoléculaires

National audienceDes travaux récents ont permis de développer un nouveau type d'élastomère constitué d'un réseau de molécules associées entre elles via des liaisons hydrogènes faibles et réversibles. Cet élastomère supramoléculaire présente un pouvoir autoréparant remarquable : les surfaces formées par pressage ou moulage sont peu autoadhésives ; en revanche, une pièce rompue peut retrouver ses propriétés mécaniques d'origine en mettant simplement en contact les surfaces de fracture. Nous montrons ici au moyen d'une expérience de type « tack » que l'autoréparation de surfaces de fracture et l'autoadhésion de surfaces mises en forme mettent en jeu des mécanismes distincts impliquant des énergies d'adhésion et des échelles de temps très différentes. En particulier, des traitements thermiques révèlent que la désactivation de ce pouvoir autoréparant est fortement accélérée par un recuit des surfaces endommagées. Ces résultats suggèrent l'existence de mécanismes de reconstruction des surfaces gouvernés par la mobilité moléculaire

On Sorption of Gases and Liquids in Glassy Polymers

この論文は国立情報学研究所の電子図書館事業により電子化されました

Control of reactions and network structures of epoxy thermosets

International audienc

Orienting Ion-Containing Block Copolymers Using Ac Electric Fields

ABSTRACT: We consider orientation mechanisms for block copolymers in an electric field. Theoretical and experimental studies have shown that nonuniformity of the dielectric constant gives rise to a preferred orientation of the melt with respect to the applied field. We show that the presence of ions, as found in anionically prepared copolymers, may increase the alignment effect markedly. Time-varying (ac) and static (dc) fields are considered within a unified framework. We find that orientation of block copolymers can in principle be achieved without a dielectric contrast if there is a mobility contrast. The presence of ions is especially important at small field frequencies, as is in most experiments. Unlike the no-ions case, it is found that orienting forces depend on the polymer chain lengths. The mobile-ions mechanism suggested here can be used to reduce the magnitude of orienting fields as well as to discriminate between block copolymers of different lengths