28 research outputs found
Effect of Chain Stiffness on the Structure of Single-Chain Polymer Nanoparticles
Polymeric single-chain nanoparticles (SCNPs) are soft nano-objects
synthesized by purely intramolecular cross-linking of single polymer chains. By
means of computer simulations, we investigate the conformational properties of
SCNPs as a function of the bending stiffness of their linear polymer
precursors. We investigate a broad range of characteristic ratios from the
fully flexible case to those typical of bulky synthetic polymers. Increasing
stiffness hinders bonding of groups separated by short contour distances and
increases looping over longer distances, leading to more compact nanoparticles
with a structure of highly interconnected loops. This feature is reflected in a
crossover in the scaling behaviour of several structural observables. The
scaling exponents change from those characteristic for Gaussian chains or rings
in -solvents in the fully flexible limit, to values resembling fractal
or `crumpled' globular behaviour for very stiff SCNPs. We characterize domains
in the SCNPs. These are weakly deformable regions that can be seen as
disordered analogues of domains in disordered proteins. Increasing stiffness
leads to bigger and less deformable domains. Surprisingly, the scaling
behaviour of the domains is in all cases similar to that of Gaussian chains or
rings, irrespective of the stiffness and degree of cross-linking. It is the
spatial arrangement of the domains which determines the global structure of the
SCNP (sparse Gaussian-like object or crumpled globule). Since intramolecular
stiffness can be varied through the specific chemistry of the precursor or by
introducing bulky side groups in its backbone, our results propose a new
strategy to tune the global structure of SCNPs.Comment: 20 pages, 17 figure
Mapping the “Extra Solvent Power, ESP” of Ionic Liquids for Monomers, Polymers and Globular Nanoparticles
Understanding the miscibility behavior of ionic
liquid (IL) / monomer, IL / polymer and IL / nanoparticle mixtures is critical
for the use of ILs as green solvents in polymerization processes, and to
rationalize recent observations concerning the superior solubility of some
proteins in ILs when compared to standard solvents. In this work, the most
relevant results obtained in terms of a three-component Flory-Huggins theory
concerning the “Extra Solvent Power, ESP” of ILs when compared to traditional
non-ionic solvents for monomeric solutes (case I), linear polymers (case II)
and globular nanoparticles (case III) are presented. Moreover, useful ESP maps
are drawn for the first time for IL mixtures corresponding to case I, II and
III. Finally, a potential pathway to improve the miscibility of non-ionic
polymers in ILs is also proposed
Electrical characterization of new electrochromic devices
Electrochromic devices change their color and optical properties with applied voltage. A new symmetrical electrochromic configuration was constructed in previous works, where PEDOT acted as electrochromic layer or as counter electrode layer, depending on the polarity of the applied voltage. Devices of around 500mm2 and switching voltages from 0,5V to 2V are used in this work. Measured electrochemical impedance is fitted to an equivalent circuit based on a Randles cell, with Warburg impedance simulating ionic diffusion at low frequencies. Voltage dependence is analyzed for the first time in this kind of devices. Results show homogeneity problems in the contact layers, not seen in normal operation, and the voltage dependence on some construction parameters. This will be used to improve the devices construction, but improvements in the equivalent circuit should also be made. The proposed equivalent circuit is not valid after the redox reaction, from 1.5 to 2V.<br /