Search results for "Field Theory"

Interfaces between coexisting phases of polymer mixtures: Comparison between Monte Carlo simulations and theoretical predictions

1997

Large scale Monte Carlo investigations of the interface between A-rich and B-rich phases of symmetric binary (AB) polymer mixtures are presented, using the bond fluctuation model of flexible chains with NA=NB=N=32 effective monomers. The temperature range studied, 0.144<T/Tc0.759, includes both the strong and the weak segregation limit. Interfacial free energy and interfacial structure are studied, and compared to predictions based on the selfconsistent field theory. Also the broadening of the interfacial width due to capillary waves is considered, and finite size effects due to the confinement of interfaces in thin films of polymer blends are discussed.

Static properties of end-tethered polymers in good solution: A comparison between different models

2004

We present a comparison between results, obtained from different simulation models, for the static properties of end-tethered polymer layers in good solvent. Our analysis includes data from two previous studies--the bond fluctuation model of Wittmer et al. [J. Chem. Phys. 101, 4379 (1994)] and the off-lattice bead-spring model of Grest and Murat [Macromolecules 26, 3108 (1993)]. Additionally, we explore the properties of a similar off-lattice model simulated close to the Theta temperature. We show that the data for the bond fluctuation and the Grest-Murat model can be analyzed in terms of scaling theory because chains are swollen inside the Pincus blob. In the vicinity of the Theta point th…

Boosting Vis/NIR Charge-Transfer Absorptions of Iron(II) Complexes by N-Alkylation and N-Deprotonation in the Ligand Backbone.

2017

Reversing the 3MLCT / 3MC excited state order in iron(II) complexes is a challenging objective, yet would finally result in longsought luminescent transition metal complexes with an earthabundant central ion. One approach to achieve this goal is based on low-energy charge transfer absorptions in combination with a strong ligand field. Coordinating electron rich and electron poor tridentate oligopyridine ligands with large bite angles at iron(II) enables both low-energy MLCT absorption bands around 590 nm and a strong ligand field. Variations of the electron rich ligand by introducing longer alkyl substituents destabilizes the iron(II) complex towards ligand substitution reactions while hard…

Synthesis, crystal structure and properties of two acetazolamide (5-acetamido-1,3,4-thiadiazole-2-sulfonamide) complexes: bis(5-acetamidato- 1,3,4-th…

1992

Abstract The diverse coordination chemistry exhibited by acetazolamide (H2acm), a potent inhibitor of the carbonic anhydrase metalloenzyme, is highlighted in two new copper(II) complexes of this ligand: [Cu(Hacm)2(en)2] (I) and [Cu(Hacm)2(tn)2] (II). The synthesis, crystal structure and spectroscopic properties of both compounds are reported in this paper. The structures of both compounds consist of discrete units of [Cu(Hacm)2(en)2] (I) and [Cu(Hacm)2(tn)2] (II), respectively, interacting through van der Waals contacts and hydrogen bonds only. Hacm, however, binds differently in each compound. In both cases, the Cu(II) ions, lying on the symmetry centers, show an elongated octahedral geome…

Spin state switching in iron coordination compounds

2013

The article deals with coordination compounds of iron(II) that may exhibit thermally induced spin transition, known as spin crossover, depending on the nature of the coordinating ligand sphere. Spin transition in such compounds also occurs under pressure and irradiation with light. The spin states involved have different magnetic and optical properties suitable for their detection and characterization. Spin crossover compounds, though known for more than eight decades, have become most attractive in recent years and are extensively studied by chemists and physicists. The switching properties make such materials potential candidates for practical applications in thermal and pressure sensors …

Anisotropic diffusion in etched particle tracks studied by field gradient NMR

1994

Etched particle tracks produced after heavy ion irradiation of polymer foils are used as model systems to test the performance of NMR in a newly developed ultrahigh magnetic field gradient system. The stimulated NMR echo decay of molecules diffusing in the channels, formulated in terms of the self part of the intermediate scattering function, is anisotropic and yields the form factor of the channels.

Effects of inhomogeneities of cross-links on a microphase separation of polymer mixtures

1994

We generalize de Gennes' theory of the microphase separation of cross-linked polymer mixtures to take into account the spatial fluctuations of the elasticity constant c, preventing the mixture from complete segregation. Within a mean-field analysis we found that the spatial fluctuations of c(r), which are assumed to obey the Poisson distribution, enlarge the size of the domains. The latter is obtained to be temperature dependent.


Role of Solvent Compatibility in the Phase Behavior of Binary Solutions of Weakly Associating Multivalent Polymers

2021

AbstractCondensate formation of biopolymer solutions, prominently those of various intrinsically disordered proteins (IDPs), is determined by “sticky” interactions between associating residues, multivalently present along the polymer backbone. Using a ternary mean field “stickers-and-spacers” model, we demonstrate that if sticker association is of the order of a few times the thermal energy, a delicate balance between specific binding and non-specific polymer-solvent interactions gives rise to a particularly rich ternary phase behavior under physiological circumstances. For a generic system represented by a solution comprising multi-associative scaffold and client polymers, the difference i…

Calculation of the Phase Behavior of Lipids

1998

The self-assembly of monoacyl lipids in solution is studied employing a model in which the lipid's hydrocarbon tail is described within the Rotational Isomeric State framework and is attached to a simple hydrophilic head. Mean-field theory is employed, and the necessary partition function of a single lipid is obtained via a partial enumeration over a large sample of molecular conformations. The influence of the lipid architecture on the transition between the lamellar and inverted-hexagonal phases is calculated, and qualitative agreement with experiment is found.

1995

Surfaces have a profound effect on the structure and related properties of multiphase polymeric materials, such as polymer mixtures and block copolymer mesophases. In particular, phase transitions in the bulk (unmixing, microphase separation, etc.) may be complemented by surface-induced transitions (formation of wetting layers, surface-directed spinodal decomposition, surface-induced ordering). This review gives a brief introduction to the phenomenological theories of such phenomena, emphasizing the simplest approach based on Flory—Huggins—de Gennes free energy functionals and associated Monte Carlo simulations. More sophisticated theories and recent experiments are mentioned briefly.