Tejero R.,CSIC - Institute of Polymer Science and Technology |
Arbe A.,Materials Physics Center |
Fernandez-Garcia M.,CSIC - Institute of Polymer Science and Technology |
Lopez D.,CSIC - Institute of Polymer Science and Technology
Macromolecules | Year: 2015
Amphiphilic polymers are tunable systems to construct supramolecular hierarchically self-assembled structures. Six families of heterocyclic polymethacrylates (PMTAs) bearing 1,3-thiazole and 1,2,3-triazole pendant groups with alkyl and succinate spacers were chemically modified by quaternization reaction of the azole heterocycles with five alkylating agents (methyl, butyl, octyl, dodecyl, and hexadecyl iodide) leading to a library of 30 different amphiphilic poly(ionic liquid)s (PMTAs-RI). These polymers have been characterized in bulk by small- and wide-angle X-ray scattering (SAXS, WAXS) and differential scanning calorimetry (DSC). Quaternization induces a dramatic effect (increase) on the glass-transition temperature Tg, being strongest for methyl iodide members. Increasing the length of the quaternizing agent, plasticization is first observed, followed by a further increase of Tg. This effect, together with evidence of a second Tg and crystallization for the members with the longest quaternizing agents, could be attributed to the presence of well-developed alkyl nanodomains evidenced by the structural investigation. WAXS and SAXS results have been consistently interpreted by assuming nanostructuration driven by the amphiphilicity balance of poly(ionic liquid)s. The different morphologies revealed by SAXS have been characterized, assigning a plausible chemical nature to the phases involved in each case. The nonpolar fraction has been considered as the control parameter defining the main features of the achieved morphology. By increasing this parameter, structures ranging from hexagonally packed nonpolar cylinders in a polar matrix to the inverse situation have been found, passing through lamellar phases. Under some conditions, within the polar lamellae a third phase formed by cylinders of heterocycles has even been determined. We have checked the validity of the scenario proposed by comparing the sizes deduced from the SAXS analysis with the expected characteristic lengths of the associated moieties, inferring thereby how alkyl side groups arrange within the nanodomains. On the basis of the complete picture achieved, the type of nanostructures formed by this class of polymers can be predicted, if the chemical composition including the quaternization degree is known. © 2015 American Chemical Society.
Lo Verso F.,Johannes Gutenberg University Mainz |
Lo Verso F.,Materials Physics Center |
Yelash L.,Johannes Gutenberg University Mainz |
Binder K.,Johannes Gutenberg University Mainz
Macromolecules | Year: 2013
Spherical polymer brushes have a structure intermediate between star polymers and polymer brushes on flat substrates, and are important building blocks of polymer nanoparticles. Molecular dynamics simulations are presented for isolated spherical polymer brushes under good solvent conditions, varying the grafting density as well as the chain length, using a coarse-grained bead-spring model of flexible chains. We complement previous work on the static properties of the same model by analyzing the chain dynamics, studying the motions of monomers in relation to their position along the grafted chains, and extract suitable relaxation times. A qualitative discussion in terms of the Rouse model is given, as well as a comparison to corresponding work on planar brushes. We find that the end monomers relax faster than monomers further inside along the chain, as previously observed for planar brushes, but at variance with theoretical expectations. The relevance of our findings for experimental work is briefly discussed. © 2013 American Chemical Society.
Capone B.,University of Vienna |
Coluzza I.,University of Vienna |
Blaak R.,University of Vienna |
Verso F.L.,Materials Physics Center |
Likos C.N.,University of Vienna
New Journal of Physics | Year: 2013
The design of self-assembling materials in the nanometer scale focuses on the fabrication of a class of organic and inorganic subcomponents that can be reliably produced on a large scale and tailored according to their vast applications for, e.g. electronics, therapeutic vectors and diagnostic imaging agent carriers, or photonics. In a recent publication (Capone et al 2012 Phys. Rev. Lett. 109 238301), diblock copolymer stars have been shown to be a novel system, which is able to hierarchically self-assemble first into soft patchy particles and thereafter into more complex structures, such as the diamond and cubic crystal. The self-aggregating single star patchy behavior is preserved from extremely low up to high densities. Its main control parameters are related to the architecture of the building blocks, which are the number of arms (functionality) and the fraction of attractive end-monomers. By employing a variety of computational and theoretical tools, ranging from the microscopic to the mesoscopic, coarse-grained level in a systematic fashion, we investigate the crossover between the formation of microstructure versus macroscopic phase separation, as well as the formation of gels and networks in these systems. We finally show that telechelic star polymers can be used as building blocks for the fabrication of open crystal structures, such as the diamond or the simple-cubic lattice, taking advantage of the strong correlation between single-particle patchiness and lattice coordination at finite densities. © IOP Publishing and Deutsche Physikalische Gesellschaft.
Berthier L.,Montpellier University |
Moreno A.J.,University of the Basque Country |
Moreno A.J.,Materials Physics Center |
Szamel G.,Colorado State University
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2010
We use theory and simulations to investigate the existence of amorphous glassy states in ultrasoft colloids. We combine the hypernetted chain approximation with mode-coupling theory to study the dynamic phase diagram of soft repulsive spheres interacting with a Hertzian potential, focusing on low temperatures and large densities. At constant temperature, we find that an amorphous glassy state is entered upon compression, as in colloidal hard spheres, but the glass unexpectedly melts when density increases further. We attribute this reentrant fluid-glass transition to particle softness and correlate this behavior to previously reported anomalies in soft systems, thus emphasizing its generality. The predicted fluid-glass-fluid sequence is confirmed numerically. © 2010 The American Physical Society.
Cangialosi D.,Materials Physics Center
Journal of Physics Condensed Matter | Year: 2014
The fate of matter when decreasing the temperature at constant pressure is that of passing from gas to liquid and, subsequently, from liquid to crystal. However, a class of materials can exist in an amorphous phase below the melting temperature. On cooling such materials, a glass is formed; that is, a material with the rigidity of a solid but exhibiting no long-range order. The study of the thermodynamics and dynamics of glass-forming systems is the subject of continuous research. Within the wide variety of glass formers, an important sub-class is represented by glass forming polymers. The presence of chain connectivity and, in some cases, conformational disorder are unfavourable factors from the point of view of crystallization. Furthermore, many of them, such as amorphous thermoplastics, thermosets and rubbers, are widely employed in many applications. In this review, the peculiarities of the thermodynamics and dynamics of glass-forming polymers are discussed, with particular emphasis on those topics currently the subject of debate. In particular, the following aspects will be reviewed in the present work: (i) the connection between the pronounced slowing down of glassy dynamics on cooling towards the glass transition temperature (Tg) and the thermodynamics; and, (ii) the fate of the dynamics and thermodynamics below Tg. Both aspects are reviewed in light of the possible presence of a singularity at a finite temperature with diverging relaxation time and zero configurational entropy. In this context, the specificity of glass-forming polymers is emphasized. © 2014 IOP Publishing Ltd.