Interfaces chain conformation

The randomization stage refers to the equilibration of the nonequilibrium conformations of the chains near the surfaces and in the case of crack healing and processing, the restoration of the molecular weight distribution and random orientation of chain segments near the interface. The conformational relaxation is of particular importance in the strength development at incompatible interfaces and affects molecular connectivity at polymer-solid interfaces. 

I. Bitsanis, G. ten Brinke. A lattice Monte Carlo study of long chain conformations at a solid polymer-melt interface. J Chem Phys 99 3100-3111, 1993. 

Even from those first remarks it is evident that our knowledge of polymers at surfaces and interfaces depends largely on analytical techniques. They should yield information on chemical composition, density, roughness, chain conformation, end distribution etc. across the interface with subnanometer resolution. In Sect. 2... 

While thin polymer films may be very smooth and homogeneous, the chain conformation may be largely distorted due to the influence of the interfaces. Since the size of the polymer molecules is comparable to the film thickness those effects may play a significant role with ultra-thin polymer films. Several recent theoretical treatments are available [136-144,127,128] based on Monte Carlo [137-141,127, 128], molecular dynamics [142], variable density [143], cooperative motion [144], and bond fluctuation [136] model calculations. The distortion of the chain conformation near the interface, the segment orientation distribution, end distribution etc. are calculated as a function of film thickness and distance from the surface. In the limit of two-dimensional systems chains segregate and specific power laws are predicted [136, 137]. In 2D-blends of polymers a particular microdomain morphology may be expected [139]. Experiments on polymers in this area are presently, however, not available on a molecular level. Indications of order on an... 

In the case of t < Lo, it has been suggested that perpendicular lamellae are favored in the boundary-symmetric confined film because they avoid the entropic penalty associated with the compressed chain conformations in parallel-oriented microdomains [109]. In boundary-asymmetric substrate-supported films, various kinds of morphologies, including hybrid morphologies that combine surface-parallel and surface-perpendicular components, are predicted, as well as observed, depending on the film thickness difference and surface/interface energies [14,41,120]. 

The above conclusion may imply that adsorbed macromolecules at liquid-solid interface take a looped chain conformation in which only a small fraction of their monomeric units are attached to adsorbent surface, as suggested by Rowland eta/.63. Kamiyama et al. explained the difference in chromatographic behavior by chain architecture, assuming that the arrangement of monomeric sequences attached to... 

Discussion. We can now propose a coarse description of the paraffinic medium in a lamellar lyotropic mesophase (potassium laurate-water). Fast translational diffusion, with D 10"6 at 90 °C, occurs while the chain conformation changes. The characteristic times of the chain deformations are distributed up to 3.10"6 sec at 90 °C. Presence of the soap-water interface and of neighboring molecules limits the number of conformations accessible to the chains. These findings confirm the concept of the paraffinic medium as an anisotropic liquid. One must also compare the frequencies of the slowest deformation mode (106 Hz) and of the local diffusive jump (109 Hz). When one molecule wants to slip by the side of another, the way has to be free. If the swinging motions of the molecules, or their slowest deformation modes, were uncorrelated, the molecules would have to wait about 10"6 sec between two diffusive jumps. The rapid diffusion could then be understood if the slow motions were collective motions in the lamellae. In this respect, the slow motions could depend on the macroscopic structure (lamellar or cylindrical, for example)... 

ASi all A-segments are present in an A-domain and all B-segments in a B-domain A 2 All A-B connections are situated in the interface between A and B-domains AS3 Within a domain the chain conformations are restricted in comparison with a random flight situation. 

This microscopic interaction model can be used to explain more specific interactions between drug molecules and lipids. Such specific interactions could be a selective coupling between a drag molecule and a particular chain conformation of the lipid (kink excitation). This could have a dramatic effect on the fluctuation system. The drug molecule would then control the formation of interfaces between lipid domains and bulk phase in the neighborhood of the transition. First results on an extended model of this type [50] have confirmed this view and demonstrated that the partition coefficient can develop non-classical behavior by displaying a maximum near the transition. And such a maximum has in fact been observed experimentally... 

Chain Conformation of Grafted Polymer Chains at Interfaces. 171... 

Alkyl chain conformation was examined at the CCI4/D2O and air/water interfaces and compared to sodium dodecylsulfonate (DDS), which has the same chain length, at the same interfaces. DDS exhibits typical simple surfactant behaviour at both interfaces. 

The proportion of a-helix in native proteins is variable and sometimes not very great. It is a mistake to over emphasize its role in interfacial structures, but where it is present its radial distribution of side chains means that its orientation in the interface will be governed by its over-all hydrophobicity. The presence of hydrophobic groups directed into the water is then possible as well as others contributing to cohesion between adjacent molecules as in the monolayers considered here. Those directed into the water may function as sites for the binding of other molecules in the aqueous phase. This is also a possibility for the p conformation but not for extended chain conformations where under pressure the hydrophobic side chains are directed away from the surface and the hydrophilic ones into the water. While this latter model has been accepted by surface chemists 37), the conformation appears unlikely both from a biological and a stereochemical standpoint. Indeed except where there is a regular alternation of hydrophobic and hydrophilic side chains, the conformation is probably not one acceptable within the usual criteria for polypeptide structures (5). 

In fig. 3.18a and b two situations are depicted where the coverage is so low that the individual chains do not feel each other. When the affinity of the segments for the interface (as expressed by the adsorption parameter x < defined in [II.5.4.11) is very close to the critical value the typical chain conformation is that of a... 

Beyond neat liquid water sum-frequency vibrational spectroscopy allowed the study of the alkyl chain conformation of surfactants such as dodecyl sulfate described in Ch. 9, that mediates the interfaces between water and CCI4 when the head group or the cations of these amphiphile molecules varied (77, 78). It also gave experimental evidence that the water surface favours the presence of anions rather than cations (79). This effect is at the origin of the oxidative power of sea water, which is ascribed to Cl anions positioned on surfaces of liquid-water droplets. It has also been applied to other H-bonded liquid water, such as methanol, where it could be demonstrated that the CH3 groups point away from the liquid at the interface with vapour (73). This is also the case for CH3 groups of acetic acid (80). Also the surface of liquid water could be shown (81) to be disrupted by even such a small amount as 0.3% of acetic acid, which does not ionize, even at this low... 

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