Search results for "MOLECULE"
showing 10 items of 5162 documents
Laponite clay in homopolymer and tri-block copolymer matrices
2007
Macromolecule/laponite nanomaterials were studied by DSC and X-ray diffraction techniques. The matrices are poly(ethylene) glycols at various molecular masses and poly(ethylene oxides)-poly(propylene oxides)-poly(ethylene oxides) tri-block copolymers. The latter were tuned by modulating the molecular masses, at constant hydrophilic/hydrophobic ratio, and the hydrophilicity. For all the investigated systems, the enthalpy of melting (ΔH m) is nearly constant up to a given composition thereafter it increases monotonically reaching the value of the pure macromolecule. We proposed a model to interpret the DSC data. Briefly, it was invoked a mechanism of interaction following which some segments …
The Crystalline State of Macromolecular Substances
1974
Unlike low molecular weight substances, high polymers do not crystallize completely. However long the crystallization process is continued, they still consist of a mixture of crystalline and non crystalline regions. In the undrawn material, these regions form larger units which are known as spherulites. Questions that are of special interest concern the arrangement of the chains in the noncrystalline regions, the causes of chain folding, and the imperfections in the crystals. The incomplete crystallization is a consequence of kinetic inhibitions. This can be deduced from the fact that the crystalline fraction increases with rising crystallization temperature. If polymerization is carried ou…
Detection of polymer compatibility by means of self-organization: poly(ethylene oxide) and poly(sodium 4-styrenesulfonate)
2021
Information on the miscibility of different polymers A and B on a molecular level is important in many ways. However, along the traditional lines this knowledge is difficult and time consuming to achieve. The current study presents a simple alternative, based on the determination of the intrinsic viscosities (specific hydrodynamic volume of isolated coils) for blend solutions in a common solvent. In the case of incompatible polymers, isolated coils contain one macromolecule only, either A or B. In contrast, compatible polymers form mixed isolated coils, because of favorable interactions. The present investigation was carried out for the system water/poly(ethylene oxide)/poly(sodium 4-polyst…
Effect of an organoclay on the photochemical transformations of a PBAT/PLA blend and morpho-chemical features of crosslinked networks
2021
Abstract In this work, we report the effect of an organoclay on the photochemical weathering of nanocomposites based on a poly(butylene adipate-co-terephthalate) (PBAT)/poly(lactic acid) (PLA) blend. The evolution of physicochemical properties was monitored by integrating spectroscopic, mechanical, and morphological analyses. A robust relationship was found between the molecular transformations of the polymer macromolecules and the morpho-mechanical properties of irradiated films. Moreover, the analysis of insoluble fractions extracted from nanocomposites pointed out that free-standing, porous structures, displaying an unprecedented thickness as great as 100 µm, were formed, thus unambiguou…
Polymer brushes under flow and in other out-of-equilibrium conditions
2011
Polymer brushes are formed from flexible linear macromolecules tethered at one chain end to a solid substrate, forming a dense polymeric layer of polymer chains which are more or less stretched in the direction perpendicular to the substrate surface. These systems find interest also due to numerous applications (colloid stabilization, improvement of lubrication properties when the surfaces are exposed to shear, protection of the surface against adsorption of nanoparticles or proteins, etc.), for which often the dynamic non-equilibrium response of these brushes to external perturbation is important. The present review summarizes recent computer simulation studies pertinent to these questions…
Magnetic molecular nanostructures: Design of magnetic molecular materials as monolayers, multilayers and thin films
2007
In this paper we summarize the importance and versatility of the molecular approach in the design and development of novel magnetic molecular materials. These materials processing, in order to obtain controlled molecular structures at the nanoscale, will also be remarked.
Minimizing geminate recombination losses in small-molecule-based organic solar cells
2019
Small-molecule-based organic solar cells (OSCs) are a recurrent alternative to polymer-based OSCs. Due to the higher purity and definition of small molecules compared to polymers, the morphological requirements can be more relaxed. Here, we present a series of novel rhodanine-based small-molecule electron donors and blend them with the standard acceptor PC70BM. By performing a target analysis on femtosecond spectroscopy data, we quantify the rates of geminate charge recombination. We are able to reproduce these rates by applying the Marcus–Levich–Jortner equation, using results from quantum chemical calculations. This shows that in a series of differently substituted compounds, one can corr…
Sanidics: A new class of mesophases, displayed by highly substituted rigid-rod polyesters and polyamides
1990
Abstract The structure of rigid-chain polyesters and polyamides which possess flexible side chains consisting of methylene or 1,4,7-trioxaoctyl oxide units have been investigated by means of X-ray scattering. The X-ray studies were performed on fibres and monodomains. Additional information was gained from calorimetric, dilatometric and microscopic studies. The investigations revealed that these polymers display mesophases and that the structures of the mesophases differ from those observed for discotic and calamitic phases. They are characterized by the fact that in the ordered and disordered phases board-like molecules are stacked parallel on top of each other and that these stacks of mol…
One is Enough: Influencing Polymer Properties with a Single Chromophoric Unit
2011
1) Institute for Technical and Macromolecular Chemistry, University of Hamburg, Bundesstrasse 45, D-‐20146 Hamburg, Germany 2) WCU program of C2E2, School of Chemical and Biological, Engineering, College of Engineering, Seoul National University, Seoul, Korea Designing a polymer usually involves the incorporation of multiple functional units into a polymer chain, which mutually determine the polymer properties. By combining various functional units, a myriad of polymer properties can be fine-‐ tuned. Classical polymer chemistry teaches us that a single functional group -‐-‐ in particular the end-‐group of a polymer chain -‐-‐ does not contribute to the polymer properties, as is indee…
Direct Surface Relief Formation in Polymer Films
2013
Due to active development of nanoelectronics, the studies of methods of nanorelief surface formation in different materials, in particular polymers are very important. Organic polymer films in consequence of their dielectric and optical properties have been used as basis of these devices. In this paper, the possibility of UV optical record and electron beam lithography in different type of polymeric films was studied. Mechanisms of molecular structure changes: photoisomerization, destruction, cross-linking and oxidation have been discussed. The results of UV illumination of polyurethanes, polyacrylates, and some block-copolymers were described. The element analysis of polybutadiene block co…