Dynamics of a Confined Polymer Chain

Structure and Dynamics of a Confined Polymer Chain Studied by Spatially and Temporally Resolved Fluorescence Techniques... 

At very close tip-substrate separation, an unpredicted peak was observed in the current response. Analysis of the force curve and random walk simulations of the chain conformation enabled this peak to be attributed to compression-induced conformational change of the end-grafted chains overcompressed chains elongate to escape confinement. These results illustrate the power of SECM-AFM in being able to characterize, in situ, the dynamics of end-grafted polymer chains. Moreover, as SECM-AFM allows the force and current responses associated with chain compression to be simultaneously measured, the interplay between chain conformation and dynamics and their modulation upon confinement can be explored. Additionally, as SECM-AFM is a local probe... 

The theoretical background of the confinement effect in (artificial) tubes was recently examined in detail with the aid of an analytical theory as well as with Monte Carlo simulations [70]. The analytical treatment referred to a polymer chain confined to a harmonic radial tube potential. The computer simulation mimicked the dynamics of a modified Stockmayer chain in a tube with hard pore walls. In both treatments, the characteristic laws of the tube/reptation model were reproduced. Moreover, the crossover from reptation (tube diameter equal to a few Kuhn segment lengths) to Rouse dy-... 

Essential Dynamics In most applications details of individual MD trajectories are of only minor interest. An illustrative example due to Grubmuller [10] is documented in Figure 3. It describes the dynamics of a polymer chain of 100 CH2 groups. Possible stepsizes for numerical integration are confined... 

For the investigation of polymer systems under spatial confinement, fluorescence microscopy is a powerful method providing valuable information with high sensitivity. A fluorescence microscopy technique with nanometric spatial resolution and nanosecond temporal resolution has been developed, and was used to study the structure and dynamics of polymer chains under spatial confinement a polymer chain in an ultra-thin film and a chain grafted on a solid substrate. Studies on the conformation of the single polymer chain in a thin film and the local segmental motion of the graft polymer chain are described herein. 

In the previous chapter, we discussed the dynamics of a polymer in a fixed network. We shall now discuss the polymer dynamics in concentrated solutions and melts. In these systems, though aU polymers are moving simultaneously it can be argu that the reptation picture will also hold. Consider the motion of a certain test polymer arbitrarily chosen in melts. If the test polymer moves perpendicularly to its own contour, it drags many other chains surrounother hand the movement of the test polymer along its contour will be much easier. It will be thus plausible to assume that the polymer is confined in a tube-like region, and the major mode of the dynamics is reptation. 

Experiments in confined geometries, particularly in the case of polymers, require several considerations. Besides the existence or absence of interfaces, the geometry itself plays an important role. ID confinement geometiy (thin films) and 2D confinement (nanotubes and nanorods) implies that the polymer chain has to accommodate in an anisotropic fashion, whereas in 3D (nanospheres) the confinement is isotropic. In each of the above mentioned experiments, interfaces play a fundamental role. In the particular case of ID confinement, as for supported thin films, it has been demonstrated that there is a strong impact of interfaces on the static and dynamical properties of the polymer [38]. These interfaces also appear in the case of polymers confined in cylindrical pores. Tanaka and coworkers demonstrated that the slower dynamics near a substrate is related to a wall-induced enhancement of glassy structural order , which is a manifestation of strong interparticle correlations [39]. The presence of the solid interface favours the presence of clusters with a preferential bond orientational order. When the polymer system under these circumstances is semicrystaUine, the crystallization process is modified in two different ways. On one hand, the slower dynamics due to the polymer-chain interactions delays the crystallization process [12, 20]. On the other... 

A. Milchev, K. Binder. Dynamics of polymer chains confined in slit-like pores. J Physique 7/5 21-31, 1996. 

---