A non‐Gaussian theory of rubberlike elasticity based on rotational isomeric state simulations of network chain configurations. I. Polyethylene and polydimethylsiloxane short‐chain unimodal networks

Fabrication and characterization of microporous soft templated photoactive 3D materials for water disinfection in batch and continuous flow

Water cleaning can be provided in batch mode or in continuous flow. For the latter, some kind of framework must withhold the cleaning agents from washout. Porous structures provide an ideal ratio of surface to volume for optimal access of the water to active sites and are able to facilitate rapid and efficient fluid transport to maintain a constant flow. When functionalized with suitable photoactive agents, they could be used in solar photocatalytic disinfection. In this study, we have used the sugar cube method to fabricate PDMS-based materials that contain three different classes of photosensitizers that differ in absorption wavelength and intensity, charge as well as in ability to generate singlet oxygen. The obtained sponges are characterized by scanning electron microscopy and digital microscopy. Archimede's method was used to measure porosity and density. We show that the materials can absorb visible light and generate Reactive Oxygen Species (ROS) that are required to kill bacteria. The disinfection ability was tested by examining how irradiation time and operation mode (batch vs. flow) contribute to the performance of the material. The current strategy is highly adaptable to other (medium) pressure-driven flow systems and holds promising potential for various applications, including continuous flow photoreactions.

Nanoparticles can modulate network topological defects during multimodal elastomer formation

We experimentally show that nanoparticles (NPs) can significantly regulate the network topological defects during a molecularly controlled elastomeric synthesis. Using positron annihilation lifetime spectroscopy, we demonstrate this on well-defined model systems of poly(dimethyl siloxane) elastomers and layered silicate nanoparticles (NPs). The evolutions of topological defects in elastomeric networks prepared from unimodal, bimodal, and NP dispersed bimodal elastomers are sequentially investigated. The extent of NP induced defect regulation is identified by varying the particle concentration from moderately low to an approximate upper limit. The fraction of free volume hole defects present between packed chains in the network generated by molecular control is significantly reduced. The fraction of smaller interstitial cavities near the cross-link sites shows a moderate increase at the lowest NP concentration. However, this fraction decreases at a high NP concentration and is nearly the same as that of bimodal networks that are devoid of NP infusion. Despite the variations in their fractions with NP infusion, the sizes of both these types of defects that remain in the network are minimally affected. The collective topological defects arising from chain induced heterogeneity also show a qualitative reduction upon NP infusion.

Stable Freestanding Thin Films of Copolymer Melts Far from the Glass Transition

Thin polymer films have attracted attention because of both their broad range of applications and of the fundamental questions they raise regarding the dynamic response of confined polymers. These films are unstable if the temperature is above their glass transition temperature T_g. Here, we describe freestanding thin films of centimetric dimensions made of a comb copolymer melt far from its glass transition that are stable for more than a day. These long lifetimes allowed us to characterize the drainage dynamics and the thickness profile of the films. Stratified regions appear as the film drains. We have evidence that the stability, thinning dynamics, and thickness profile of the films result from structural forces in the melt. Understanding the key mechanisms behind our observations may lead to new developments in polymeric thin films, foams, and emulsions without the use of stabilizing agents.

Elasticity and photoelasticity relationships for polyethylene terephthalate fiber networks by molecular simulation

We present a framework for the development of elasticity and photoelasticity relationships for polyethylene terephthalate fiber networks, incorporating aspects of the primary molecular structure. Semicrystalline polymeric fiber networks are modeled as sequentially arranged crystalline and amorphous regions. Rotational isomeric states-Monte Carlo simulations of amorphous chains of up to 360 bonds (degree of polymerization, DP=60), confined between and bridging infinite impenetrable crystalline walls, have been characterized by Omega, the probability density of the intercrystal separation h, and Deltabeta, the polarizability anisotropy. ln Omega and Deltabeta have been modeled as functions of h, yielding the chain deformation relationships. The development has been extended to the fiber network to yield the photoelasticity relationships. We execute our framework by fitting to experimental stress-elongation data and employing the single fitted parameter to directly predict the birefringence-elongation behavior, without any further fitting. Incorporating the effect of strain-induced crystallization into the framework makes it physically more meaningful and yields accurate predictions of the birefringence-elongation behavior.

A non-Gaussian model in polymeric network

We investigate a finite chain approximation, the non-Gaussian Tsallis distribution, to the polymeric network, which gives an improvement to the Gaussian model. This distribution presents some necessary characteristics, like a cutoff to the maximum chain length and a continuous limit to the Gaussian one for a large number of monomers. It also presents a simple quadratic structure that allows to generalize the Gaussian properties such as exact-moments calculation and Wick theorem. We obtain the free-energy density in its full tensorial structure.

A Unified Approach to Conformational Statistics of Classical Polymer and Polypeptide Models

We present a unified method to generate conformational statistics which can be applied to any of the classical discrete-chain polymer models. The proposed method employs the concepts of Fourier transform and generalized convolution for the group of rigid-body motions in order to obtain probability density functions of chain end-to-end distance. In this paper, we demonstrate the proposed method with three different cases: the freely-rotating model, independent energy model, and interdependent pairwise energy model (the last two are also well-known as the Rotational Isomeric State model). As for numerical examples, for simplicity, we assume homogeneous polymer chains. For the freely-rotating model, we verify the proposed method by comparing with well-known closed-form results for mean-squared end-to-end distance. In the interdependent pairwise energy case, we take polypeptide chains such as polyalanine and polyvaline as examples.