Search results for "Polymer physics"
showing 9 items of 9 documents
On the polymer physics origins of protein folding thermodynamics
2016
A remarkable feature of the spontaneous folding of many small proteins is the striking similarity in the thermodynamics of the folding process. This process is characterized by simple two-state thermodynamics with large and compensating changes in entropy and enthalpy and a funnel-like free energy landscape with a free-energy barrier that varies linearly with temperature. One might attribute the commonality of this two-state folding behavior to features particular to these proteins (e.g., chain length, hydrophobic/hydrophilic balance, attributes of the native state) or one might suspect that this similarity in behavior has a more general polymer-physics origin. Here we show that this behavi…
3D Conformations of Thick Synthetic Polymer Chains Observed by Cryogenic Electron Microscopy.
2019
The backbone conformations of individual, unperturbed synthetic macromolecules have so far not been observed directly in spite of their fundamental importance to polymer physics. Here we report the dilute solution conformations of two types of linear dendronized polymers, obtained by cryogenic transmission electron stereography and tomography. The three-dimensional trajectories show that the wormlike chain model fails to adequately describe the scaling of these thick macromolecules already beyond a few nanometers in chain length, in spite of large apparent persistence lengths and long before a signature of self-avoidance appears. This insight is essential for understanding the limitations o…
Monte Carlo simulation in polymer physics: Some recent developments
1991
The computer simulation of macromolecular materials has to deal with phenomena on length scales from 1A to 100A, as well as with time scales ranging over many orders of magnitude, and thus still presents a challenge. With suitably coarse-grained models which disregard detailed information on chemical structure nevertheless collective phenomena can be described, such as unmixing of polymer blends, mesophase ordering of block-copolymer melts, “blob formation” in semidilute solutions, etc. Simulations of such models provide a sensitive test of approximate theories and give valuable hints for experiments.
Effects of solvent perturbation on gelation driven by spinodal demixing
1999
We study effects of solvent perturbation on kinetic competition between spinodal demixing and gelation in agarose solutions at a concentration of 5 g/l. Two different cosolutes (tert-butyl alcohol and trimethyl amine N-oxide) known for altering in opposite way solvent-mediated interactions are chosen. By rheometry, static and dynamic light scattering experiments, we show that the cosolute presence shifts the boundary of the instability region of solution leaving unaffected temperature and polymer concentration values required for percolation. Results suggest that an appropriate choice of quenching temperature and solvent allows controlling the gelation time and the gel structural properties.
Monte Carlo Simulations of Polymer Systems
1988
The impact of Monte Carlo “computer experiments” in polymer physics is described, emphasizing three examples taken from the author’s research group. The first example is a test of the classical Flory—Huggins theory for polymer mixtures, including a discussion of cricital phenomena. Also “technical aspects” of such simulations (“grand-canonical” ensemble, finite—size scaling, etc.) are explained briefly. The second example refers to configurational statistics and dynamics of chains confined to cylindrical tubes; the third example deals with the adsorption of polymers at walls. These simulations check scaling concepts developed along the lines of de Gennes.
Mechanical Properties of Single Molecules and Polymer Aggregates
2013
This chapter deals with the mechanical properties of single polymer chains, aggregates, and supramolecular complexes. The topics discussed cover a broad range from fundamental statistical mechanics of the equilibrium elastic properties of single polymer chains to details of the behavior of binding pockets in biomolecular assemblies as observed by force spectroscopy. The first section treats the equilibrium mechanical properties of single polymer chains in various environments, investigated via extensive simulations employing coarse-grained models that have proven extremely successful in many branches of polymer physics, namely the bond-fluctuation model and the self-avoiding walk model. Apa…
Theory and Simulation of Multiphase Polymer Systems
2010
The theory of multiphase polymer systems has a venerable tradition. The 'classical' theory of polymer demixing, the Flory-Huggins theory, was developed already in the forties of the last century. It is still the starting point for most current approaches -- be they improved theories for polymer (im)miscibility that take into account the microscopic structure of blends more accurately, or sophisticated field theories that allow to study inhomogeneous multicomponent systems of polymers with arbitrary architectures in arbitrary geometries. In contrast, simulations of multiphase polymer systems are relatively young. They are still limited by the fact that one must simulate a large number of lar…
Rapid small-angle and wide-angle x-ray studies of crystallization behavior in polymers
1976
Small-angle and wide-angle x-ray scattering measurements, using a position-sensitive detector, were made during melt-crystallization of linear polyethylenes and PEO–PS–PEO triblock copolymer. The scattering measurements indicated that the triblock copolymer grew by the enlargement of regions in which lamellae are regularly stacked. During primary crystallization at higher temperatures similar behavior is observed in two linear polyethylenes. At lower temperatures, changes in the shape of small-angle scattering curves during the primary stage of crystallization indicate that amorphous gaps within the lamellar stacking become filled in. During secondary crystallization at higher temperatures …
Insights into localized manipulation of organogel-related microcrystalline spherulite formation
2015
Abstract The formation processes of microcrystalline spherulitic fiber systems related to bile acid amides were determined to include dominant interface-related aspects, the role of which were studied in terms of potential manipulation and increased control over the overall structure of the networks. The nucleation and growth properties and aggregation of two lithocholyl amide derivatives were studied in several organic solvents using thermomicroscopy, as well as thermal control at macroscopic level. Nucleation/crystallization at interfaces was observed to act as the main route for the formation of microcrystalline fibers/solids in six gelator–solvent systems, in which spherulite formation …