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We propose a free-space density functional theory for polymer adsorption. The derivation within the framework of density functional theory leads to the splitting of the intrinsic free energy into an ideal-gas term and a residual term responsible for the intrinsic energy and the nonbonded interactions between monomers, respectively. A more reasonable treatment is adopted for the residual free energy to count for the monomer-monomer correlation underestimated by the local density approximation. An approach using propagators is proposed to calculate the single-chain partition function and the segment-density distributions, the three adsorption conformations as trains, loops, and tails are further described by propagators. Dirac's bra-ket notation used makes the derivation simpler and provides clearer physical meanings. The theoretical calculations for the adsorption of hard-sphere chains onto a nonadsorbing and an adsorbing hard wall show that the structure of the adsorption layer is strongly affected by the packing effect which has been underestimated by the previous lattice adsorption theory. [ABSTRACT FROM AUTHOR]

The driving force for channel formation by triheteropolymers confined in hydrophobic nanocylinders was investigated by lattice Monte Carlo simulations. A variety of conditions, such as the interactions between different kinds of segments, the interactions between segments and the nanocylindrical walls, and the structure of the polymer, were considered. It was found that for a channel to be generated, the attractive interaction between one kind of segments and the nanocylindrical wall should be larger than a minimum value. The cross-sectional radius of a channel seen from above or below the ends of the nanotube as a function of the interactions between the segments and the wall as well as of the interactions between different kinds of segments was determined. The succession in the chain of different kinds of segments (the chain connectivity) also plays a significant role in channel formation. The present treatment may provide some insight regarding the formation of protein channels in the phospholipid bilayers of the cell membrane. [ABSTRACT FROM AUTHOR]

The recognition of homopolymer at nanopatterned surface has been investigated by density functional theory (DFT). Chain conformation and pattern transfer parameter predicted from the DFT are in good agreement with Monte Carlo simulation results. The theory describes satisfactorily the transition from depletion at low packing fractions to adsorption and double-layer adsorption at high packing fractions and also accounts for the crucial effect of the segment-wall interaction. It is found that homopolymer is better recognized at a low bulk density and a stronger interaction with the surface. The polymer can not only recognize the surface but also invert the surface at high bulk densities. The chain in the solution-wall interface exhibits a typical “brush” conformation with a length approximated by half the length of polymer chain. [ABSTRACT FROM AUTHOR]

A density functional theory (DFT) is developed for polymer mixtures with shorted-ranged attractive interparticle interactions confined in a slit. Different weighting functions are used separately for the repulsive part and the attractive part of the excess free energy functional by applying the weighted density approximation. The predicted results by DFT are in good agreement with the corresponding simulation data indicating the reliability of the theory. Furthermore, the center-of-mass profiles and the end-to-end distance distributions are obtained by the single chain simulation; the predictions also agree well with simulation data. The results reveal that both the attraction of the slit wall and the temperature has stronger effect on longer chains than on shorter ones because the intrasegment correlation of chains increases with increasing chain length. [ABSTRACT FROM AUTHOR]

By employing dissipative particle dynamics simulations, we investigated the cooperative phase behavior of composites containing diblock copolymer molecules and nanoparticles. The nanoparticles and their aggregates are located either in the domains generated by each of the two kinds of segments of the block copolymer and/or at their interface. Various conditions, such as the interactions between nanoparticles, the interactions between them and the segments of the block copolymer, the interactions between the segments of the block copolymer, and the volume ratio of nanoparticles to block copolymer, have been changed to gather information about nanoparticle aggregation and block copolymer/nanoparticles morphology building. The dynamics of nanoparticles aggregation and the evolution of the morphology of the block copolymer have been followed. Our findings have identified two critical repulsive interactions regarding nanoparticle aggregation, one between nanoparticles and the other between the segments of the block copolymer and nanoparticles. Aggregates have been generated for repulsive interactions larger than the former critical value or smaller than the latter one.

Monte Carlo simulations are employed to obtain information about the radius and the roughness of the inner surface of the channels, which are generated by a family of block copolymer solutions confined in nanotubes. The fluctuations of the above quantities also have been calculated. The simulations have been carried out by varying the interactions between various kinds of segments and those between segments and the wall of the nanotubes, as well as the chemical structure of the copolymer and the nanotube diameter. The present simulations provide insight regarding the structure of ionic and water channels formed by protein in the phospholipid bilayers of the cell membrane.

A density functional theory is developed for copolymers confined in a nanoslit on the basis of our previous work for homopolymers. The theory accurately captures the structural characteristics for diblock and alternating copolymers composed of hard-sphere or square-well segments. Satisfactory agreement is obtained between the theoretical predictions and simulation results in segment density profiles, segment fractions, and partition coefficients. Structures under confinement strongly depend on the substituent segment sizes for the hard-sphere copolymers and also on the segment-wall attractions for the square-well copolymers. Alternating copolymers are found to behave as homopolymers with effective segment size, and effective segment-segment and segment-wall interactions.