Mechanochemically Responsive Viscoelastic Elastomers

Mechanochemically responsive (MCR) polymers have been designed to possess unconventional properties such as changing colors, self-healing, and releasing catalysts under deformation. These properties of MCR polymers stem from a class of molecules, referred to as mechanophores, whose chemical reactions can be controlled by mechanical forces. Although extensive studies have been devoted to the syntheses of MCR polymers by incorporating various mechanophores into polymer networks, the intricate interactions between mechanical forces and chemical reactions in MCR polymers across multiple length and time scales are still not well understood. In this paper, we focus on mechanochemical responses in viscoelastic elastomers and develop a theoretical model to characterize the coupling between viscoelasticity and chemical reactions of MCR elastomers. We show that the kinetics of viscoelasticity and mechanophore reactions introduce different time scales into the MCR elastomers. The model can consistently represent experimental data on both mechanical properties and chemical reactions of MCR viscoelastic elastomers. In particular, we explain recent experimental observations on the increasing chemical activation during stress relaxation of MCR elastomers, which cannot be explained with existing models. The proposed model provides a theoretical foundation for the design of future MCR polymers with desirable properties.

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Internal and external catalysis in boronic ester networks

10.33774/chemrxiv-2021-kwjg1 ◽

2021 ◽

Author(s):

Boyeong Kang ◽

Julia Kalow

Keyword(s):

Mechanical Properties ◽

Binding Affinity ◽

Polymer Networks ◽

Model Systems ◽

Self Healing ◽

Dynamic Materials ◽

Boronic Ester ◽

Rate Acceleration ◽

Exchange Spectroscopy ◽

Kinetics Of

In dynamic materials, the reversible condensation between boronic acids and diols provides adaptability, self-healing ability, and responsiveness to small molecules and pH. Recent work has shown that the thermodynamics and kinetics of bond exchange determine the mechanical properties of dynamic polymer networks. However, prior studies have focused on how structural and environmental factors influence boronic acid–diol binding affinity, and design rules for tuning the kinetics of this dynamic bond are lacking. In this work, we investigate the effects of diol (or polyol) structure and salt additives on the rate of bond exchange, binding affinity, and the mechanical properties of the corresponding polymer networks. To better mimic the environment of polymer networks in our small-molecule model systems, we incorporated proximal amide groups, which are used to conjugate diols to polymers, and included salts commonly found in buffers. Using one-dimensional selective exchange spectroscopy (1D EXSY), we find that both proximal amides and buffering anions induce significant rate acceleration consistent with internal and external catalysis, respectively. This rate acceleration is reflected in the stress relaxation of gels formed using PEG modified with different alcohols, and in the presence of salts containing acetate or phosphate. These findings contribute to the fundamental understanding of the boronic ester dynamic bond and offer new molecular strategies to tune the macromolecular properties of dynamic materials.

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EFFECT OF AZOINITIATORS OF METHYL METHACRYLATE POLYMERIZATION ON THE FORMATION PROCESS AND MORFOLOGY OF POLYURETHANE /POLYMETHYL METHACRYLATE INTERPENETRATING POLYMER NETWORKS

Ukrainian Chemistry Journal ◽

10.33609/2708-129x.86.9.2020.39-54 ◽

2020 ◽

Vol 86 (9) ◽

pp. 39-54

Author(s):

Liudmyla Kosynchuk ◽

Oksana Antonenko ◽

Volodymyr Grishchenko ◽

Nataliia Busko ◽

Taisa Ignatova ◽

...

Keyword(s):

Phase Separation ◽

Methyl Methacrylate ◽

Chemical Reactions ◽

Polymer Networks ◽

Heterogeneous Systems ◽

Interpenetrating Polymer Networks ◽

Methyl Methacrylate Polymerization ◽

Negative Effect ◽

Kinetics Of

Interpenetrating polymer networks (IPN) are mixtures of two cross-linked polymers formed as a result of chemical reactions of in situ synthesis of components from single-phase initial mixtures. As a rule, due to the incompatibility of the components, a physical process of phase separation takes place with the formation of heterogeneous systems with insignificant interphase adhesion, which can have a negative effect on the physicochemical properties. To increase the compatibility of the components and to stabilize the systems, compatibilizers are introduced into the reaction mixtures. In this work the kinetics of the in situ formation of the components of polyurethane/poly(methyl methacrylate) interpenetrating polymer networks and the phase separation induced by chemical reactions in the presence of methyl methacrylate polymerization oligoazoinitiators in the reaction mixture were studied. Oligoazoinitiators contained fragments of a polyurethane chain also. It has been shown that the introduction of oligoazoinitiators of various chemical natures can control the process of IPN formation due to the formation of block copolymers during synthesis, which are compatibilizers of the mixture. They slow down the phase separation process and favor the formation of a finer IPN structure.

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Persistent Photoconductivity And Thermal Recovery Kinetics Of Low Energy Ar + Bombarded GaAs

MRS Proceedings ◽

10.1557/proc-223-203 ◽

1991 ◽

Vol 223 ◽

Author(s):

A. Vaseashta ◽

L. C. Burton

Keyword(s):

Deep Level Transient Spectroscopy ◽

Deep Level ◽

Thermal Recovery ◽

Low Energy ◽

Persistent Photoconductivity ◽

Transport Parameters ◽

Excellent Correlation ◽

Proposed Model ◽

Transient Spectroscopy ◽

Kinetics Of

ABSTRACTKinetics of persistent photoconductivity, photoquenching, and thermal and optical recovery observed in low energy Ar+ bombarded on (100) GaAs surfaces have been investigated. Rate and transport equations for these processes were derived and simulated employing transport parameters, trap locations and densities determined by deep level transient spectroscopy. Excellent correlation was obtained between the results of preliminary simulation and the experimentally observed values. The exponential decay of persistent photoconductivity response curve was determined to be due to metastable electron traps with longer lifetime and is consistent with an earlier proposed model.

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Agent-Based Computational Model

10.23943/princeton/9780691158884.003.0003 ◽

2017 ◽

Cited By ~ 2

Author(s):

Joshua M. Epstein

Keyword(s):

Computational Model ◽

Bounded Rationality ◽

Time Scales ◽

Spatially Explicit ◽

Agent Based ◽

Affective Component ◽

Elementary Type ◽

Social Component ◽

Different Time Scales

This part describes the agent-based and computational model for Agent_Zero and demonstrates its capacity for generative minimalism. It first explains the replicability of the model before offering an interpretation of the model by imagining a guerilla war like Vietnam, Afghanistan, or Iraq, where events transpire on a 2-D population of contiguous yellow patches. Each patch is occupied by a single stationary indigenous agent, which has two possible states: inactive and active. The discussion then turns to Agent_Zero's affective component and an elementary type of bounded rationality, as well as its social component, with particular emphasis on disposition, action, and pseudocode. Computational parables are then presented, including a parable relating to the slaughter of innocents through dispositional contagion. This part also shows how the model can capture three spatially explicit examples in which affect and probability change on different time scales.

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Faculty Opinions recommendation of Influence of gene action across different time scales on behavior.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.1006517.81506 ◽

2002 ◽

Author(s):

Randolf Menzel

Keyword(s):

Time Scales ◽

Gene Action ◽

Different Time Scales

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Response of normalized difference vegetation index in main vegetation types to climate change and their variations in different time scales along a North-South Transect of Eastern China

Chinese Journal of Plant Ecology ◽

10.3724/sp.j.1258.2011.01117 ◽

2011 ◽

Vol 35 (11) ◽

pp. 1117-1126

Author(s):

Zhen YU ◽

Peng-Sen SUN ◽

Shi-Rong LIU

Keyword(s):

Climate Change ◽

Time Scales ◽

Vegetation Index ◽

Normalized Difference Vegetation Index ◽

Eastern China ◽

Vegetation Types ◽

Different Time Scales

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New highly efficient coulometric cell with homogenous potential distribution on the working electrode

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19860636 ◽

1986 ◽

Vol 51 (3) ◽

pp. 636-642

Author(s):

Michal Németh ◽

Ján Mocák

Keyword(s):

Chemical Reactions ◽

Potential Distribution ◽

Anaerobic Conditions ◽

Highly Efficient ◽

Working Electrode ◽

Constant Potential ◽

Quantitative Analyses ◽

Mechanism And Kinetics ◽

Kinetics Of

A highly efficient coulometric cell was designed and constructed, ensuring a constant potential over the whole surface of the working electrode and suitable for very rapid electrolysis. It consists of concentric cylindrical Teflon parts; also the working and auxiliary electrodes are cylindrical and concentric. Electrolysis can be carried out under anaerobic conditions. Functioning of the cell was tested on the oxidation of hexacyanoferrate(II) and chlorpromazine and reduction of hexacyanoferrate(III). The new cell is suitable for routine quantitative analyses and in studying the mechanism and kinetics of moderately rapid chemical reactions.

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