Search results for "MOLECULE"

Understanding the Electronic Reorganization along the Nonpolar [3+2] Cycloaddition Reactions of Carbonyl Ylides

2011

[EN] The nonpolar [3+2] cycloaddition (32CA) reaction of the carbonyl ylide (CY) 23 with tetramethylethylene (TME) 24 has been studied with DFT methods at the B3LYP/6-31G* level. This cycloaddition reaction, which has a very low activation energy of 4.7 kcal/mol, takes place through a synchronous transition structure. A topological analysis of the ELF along the 32CA reaction provides a new scope of the electronic structure of CY 23 as a pseudodiradical species offering a sound explanation of the high reactivity of this CY in nonpolar reactions. In addition, this analysis points to the nonparticipation of the oxygen lone pairs in the 32CA reaction. This cycloaddition can be seen as a pseudod…

Influence of polymer flexibility on nanoparticle dynamics in semidilute solutions

2018

The hierarchical structure and dynamics of polymer solutions control the transport of nanoparticles (NPs) through them. Here, we perform multi-particle collision dynamics simulations of solutions of semiflexible polymer chains with tunable persistence length lp to investigate the effect of chain stiffness on NP transport. The NPs exhibit two distinct dynamical regimes - subdiffusion on short time scales and diffusion on long time scales. The long-time NP diffusivities are compared with predictions from the Stokes-Einstein relation (SER), mode-coupling theory (MCT), and a recent polymer coupling theory (PCT). Increasing deviations from the SER as the polymer chains become more rigid (i.e. as…

Standard Definitions of Persistence Length Do Not Describe the Local “Intrinsic” Stiffness of Real Polymer Chains

2010

On the basis of extensive Monte Carlo simulations of lattice models for linear chains under good and Θ solvents conditions, and for bottle-brush polymers under good solvent conditions, different me...

Structure of bottle brush polymers on surfaces: weak versus strong adsorption.

2011

Large-scale Monte Carlo simulations are presented for a coarse-grained model of cylindrical molecular brushes adsorbed on a flat structureless substrate, varying both the chain length N of the side chains and the backbone chain length N(b). For the case of good solvent conditions, both the cases of weak adsorption (only 10 to 15% of the monomers being bound to the surface) and strong adsorption (~40% of the monomers being bound to the surface, forcing the bottle brush into an almost 2D conformation) are studied. We focus on the scaling of the total linear dimensions of the cylindrical brush with both chain lengths N and N(b), demonstrating a crossover from rod-like behavior (for not very la…

How Structure-Related Collapse Mechanisms Determine Nanoscale Inhomogeneities in Thermoresponsive Polymers

2012

Continuous wave electron paramagnetic resonance (CW EPR) spectroscopy on the amphiphilic spin probe TEMPO in solutions of selectively chosen functional, thermoresponsive poly(propylene oxide) (PPO)- and poly(ethylene oxide) (PEO)-based copolymers of both linear and branched structure is used to elucidate their host–guest interactions and inverse phase transitions. Three different fundamental types of host–guest interactions between probes and polymers could be correlated to the phase transition mechanisms (supported by MD simulations), evidencing that these proceed via nanoscale inhomogeneities of the polymers. Because of their ability to host small amphiphilic guest molecules, thermorespon…

Spinodal decomposition of chemically fueled polymer solutions

2021

Out-of-equilibrium phase transitions driven by dissipation of chemical energy are a common mechanism for morphological organization and temporal programming in biology. Inspired by this, dissipative self-assembly utilizes chemical reaction networks (CRNs) that consume high-energy molecules (chemical fuels) to generate transient structures and functionality. While a wide range of chemical fuels and building blocks are now available for chemically fueled systems, so far little attention has been paid to the phase-separation process itself. Herein, we investigate the chemically fueled spinodal decomposition of poly(norbornene dicarboxylic acid) (PNDAc) solution, which is driven by a cyclic che…

1984

Liquid-liquid phase equilibria in polymer solutions and polymer mixtures

2002

The pressure dependence of liquid-liquid equilibria in weakly interacting binary macromolecular systems (homopolymer solutions and blends) will be discussed. The common origin of the separate high-temperature/low-temperature and high-pressure/low-pressure branches of demixing curves will be demonstrated by extending the study into the region of metastable liquid states including the undercooled, overheated and stretched states (i.e. states at negative pressures). The seemingly different response of the UCST-branch of solutions and blends when pressurized (pressure induced mixing for most polymer solutions, pressure induced demixing for most blends) will be explained in terms of the location…

One- and two-component bottle-brush polymers: simulations compared to theoretical predictions

2007

Scaling predictions and results from self-consistent field calculations for bottle-brush polymers with a rigid backbone and flexible side chains under good solvent conditions are summarized and their validity and applicability is assessed by a comparison with Monte Carlo simulations of a simple lattice model. It is shown that under typical conditions, as they are also present in experiments, only a rather weak stretching of the side chains is realized, and then the scaling predictions based on the extension of the Daoud-Cotton blob picture are not applicable. Also two-component bottle brush polymers are considered, where two types (A,B) of side chains are grafted, assuming that monomers of …

Photoluminescence ZnO nanorod biosensors for medical and food safety applications

2017

Photoluminescence (PL) ZnO nanorods (NR) are prospect materials for biosensor applications. They can be deposited on solid state substrates and/or dispersed in liquid media. ZnO NRs demonstrate strong UV emission (3.28–3.3 eV), which depends on surface charge, formed by adsorbed molecules. In the present work we report on ZnO NRs, deposited on glass slides, used as biosensor templates for detection food pathogens. Change of ZnO PL after interaction with biomolecules was recorded. Dependence of PL intensity vs concentration of biomolecules was obtained. In the second part, ZnO nanorods were used as PL biomarkers. A suspension of ZnO NRs, conjugated with SSEA-4 antibodies (aSSEA-4) in PBS buf…