Ring comb copolymer brushes

The equilibrium conformations of isolated comb copolymer ring molecules in an athermal solution are investigated by off-lattice Monte Carlo simulations. The molecules considered consist of a closed flexible backbone densely grafted with flexible or rigid side chains. The study focuses on the influence of the length of the side chains on the conformational behavior. As a function of the side chain length the structure gradually stiffens until the size of the side chains approaches the diameter of the ring. Longer side chains do not influence the backbone conformation any further. The results are compared with the large body of knowledge available for linear cylindrical comb copolymer brushes.

Strongly adsorbed comb copolymers with rigid side chains

We study the conformational behavior in a plane of a comb copolymer molecule, consisting of a semiflexible backbone and rigid side chains interacting via a van der Waals potential. Using a mean-field approach, two different regimes are distinguished depending on the strength of the attraction between the side chains. In the weak attraction limit the side chains are oriented preferably perpendicular to the backbone. The persistence length λ of the comb copolymer molecule scales as the second power of the length of the side chain L: λ ∝L2. In the strong attraction limit all side chains become strongly tilted and the persistence length scales as λ ∝L4. The nonlinear bending regime is also studied and characterized by a change in structure and a decreasing moment of bending force as a function of curvature, i.e., bending becomes easier.

Comb Copolymer Brush with Chemically Different Side Chains

An investigation of side chain microphase separation within a single comb copolymer molecule containing chemically different A and B side chains has been carried out. Expressions for the transition point χ*AB in a good (χ*AB ~ N-3/8), marginal (χ*AB ~ N-1/2), θ (χ*AB ~ N-2/3), and poor (χ*AB ~ N-1) solvent are derived both by a mean field calculation and by scaling arguments. Properties of the system below and above the transition point are described. Some unusual “bowlike” conformations are predicted for a single molecule in the microphase separated state in a good solvent.

Spontaneous Curvature of Comb Copolymers Strongly Adsorbed at a Flat Interface: A Computer Simulation Study

Using a modified bond fluctuation model, with only excluded-volume interactions, we demonstrate spontaneous curvature of 2D comb copolymer molecules, provided the side chains are allowed to flip from one side of the backbone to the other. When the side chains are not allowed to flip, the polymer conformations are very stiff. Once flipping is allowed, the polymers display a distinct curvature. We illustrate the curvature by presenting randomly selected snapshots. In addition, bond angle correlation analysis shows that in this case the polymer does not behave like a persistent wormlike chain. In connection to this we outline a model that incorporates curvature and is able to fit the correlation data. Further evidence for spontaneous curvature is given by scattering data displaying a pronounced peak that can be connected to conformational characteristics. Our findings are in good agreement with recent theoretical and experimental studies.

Size dependence of the elastic modulus of thin polymer fibers – modeling

The problem of the size dependence of physical properties is one of the most intriguing when we transit to the nano-level. Experiments have shown that this effect is characteristic of the elastic modulus of many polymeric nanofibers obtained by electrospinning. Existing explanations of this effect did not offer a general understanding of the physical nature of this phenomenon. In this study, we propose a universal model of this phenomenon. We consider the structure of fibers within the framework of the core-shell model, in which the shell is approximated by a thin elastic surface. The analysis of deformation is based on the fundamental laws of the mechanics of deformation of twisted thin shells and, unlike the theories proposed earlier, does not require any additional artificial arguments. This approach made it possible to obtain a simple analytical expression for the size dependence of the elastic modulus, which represents it as the sum of the bulk modulus of the core and two additional moduli proportional to D–1 and D–3, respectively. The resulting model corresponds to all available (from published sources) experimental data, related to polymer of very different chemical structure, and therefore can be considered as universal

Lamellar-in-lamellar self-assembled C–b–(B–b–A)m–b–B–b–C multiblock copolymers: Alexander–de Gennes approach and dissipative particle dynamics simulations

A simple theoretical analysis of the lamellar-in-lamellar self-assembled state of ternary C–b–(B–b–A)m–b–B–b–C multiblock copolymer melts in the strong segregation limit is presented using the Alexander–de Gennes approximation. For a given value of m, the influence of the chain length of the various blocks and the value of the Flory–Huggins χAB and χBC interaction parameters on the number k of internal domains is discussed in detail. The theoretically predicted tendencies are corroborated by computer simulations using the dissipative particle dynamics technique.

Comb copolymer cylindrical brushes containing semiflexible side chains: a Monte Carlo study

The off-lattice Monte Carlo method is applied to investigate the equilibrium conformations of isolated comb copolymer cylindrical brushes in an athermal solution. The molecules considered consist of a flexible backbone, which is densely grafted with semiflexible side chains. The study focuses on the influence of the degree of intrinsic stiffness, λside, of the side chains on the conformational behavior of the molecules. It is demonstrated that with a fixed side chain length, M, the local length scale conformational fluctuations of the backbone increase as a function of λside. However, the persistence length, λ, of the cylindrical brush increases considerably with the side chain stiffness, indicating that the backbone becomes more extended at the large length scale. Moreover, as a function of λside, there is an increase in the ratio λ/D of the persistence length and the diameter, D, of the brush. This behavior is in good agreement with recent theoretical predictions and provides important new insight in the latest experimental observations.

Cylindrical Brushes of Comb Copolymer Molecules Containing Rigid Side Chains

An analysis of the cylindrical brush of an isolated comb copolymer molecule, consisting of a semiflexible backbone and rodlike side chains, is presented. Using a mean-field approach and a simplyfying assumption, which is tested by computer simulations, we find that the persistence length of the brush, λ, scales as λ ∝ L2/ln L for large values of the side chain length L. In the cylindrical brush regime the order parameter of the rods is negative, implying that the rods orient normal to the cylindrical axis.

Effect of Side Chain Rigidity on the Elasticity of Comb Copolymer Cylindrical Brushes: A Monte Carlo Simulation Study

We report the results of a Monte Carlo simulation study of isolated comb copolymer cylindrical brushes. The conformational characteristics of molecules consisting of a flexible backbone densely grafted with side chains strongly depend on the rigidity of the side chains, which is exemplified by using both fully flexible and totally rigid side chains. The short length scale fluctuations of the backbone are not affected by the presence of rigid rod side chains, whereas flexible side chains induce local stretching of the backbone. However, at the large length scale, the persistence length λ of the cylindrical brush is considerably larger for rigid rod side chains than for flexible side chains. Moreover, for rigid side chains the ratio between the persistence length λ and the diameter D of the brush increases approximately linearly as a function of the rod length L, thus supporting the possibility of lyotropic behavior. In contrast to this, in the case of flexible side chains, λ/D is approximately independent of the side chain length M.