Adsorption and pinning of multiblock copolymers on chemically heterogeneous patterned surfaces

Simulation study on the critical adsorption and diffusion of polymer chains on heterogeneous surfaces with random adsorption sites

The critical adsorption and diffusion of a linear polymer chain on a heterogeneous surface with randomly distributed adsorption sites are studied using dynamic Monte Carlo simulations. Results show that the critical fraction of the adsorption sites at which critical adsorption takes place decreases exponentially with the increasing polymer-surface attraction strength and, at the same time, decreases with the increasing intra-polymer attraction strength. For adsorbed polymers with large intra-polymer attraction strength, we also find an adsorption-induced structural transition from a three-dimensional compact globule to a two-dimensional compacted pancake with an increasing fraction of adsorption sites. Anomalous sub-diffusion is observed for the adsorbed polymer diffusion on heterogeneous surfaces, in contrast to the normal diffusion on a homogeneous surface. The polymer on heterogeneous surfaces shows larger fluctuation in the total surface attraction energy and a longer waiting time.

Interactions of complex polymers with nanoporous substrate

With the advance of polymer synthesis, polymers that possess unique architectures such as stars or cyclic chains, and unique chemical composition distributions such as block copolymers or statistical copolymers have become frequently encountered. Characterization of these complex polymer systems drives the development of interactive chromatography where the adsorption of polymers on the porous substrate in chromatography columns is finely tuned. Liquid Chromatography at the Critical Condition (LCCC) in particular makes use of the existence of the Critical Adsorption Point (CAP) of polymers on solid surfaces and has been successfully applied to characterization of complex polymer systems. Interpretation and understanding of chromatography behaviour of complex polymers in interactive chromatography motivates theoretical/computational studies on the CAP of polymers and partitioning of these complex polymers near the CAP. This review article covers the theoretical questions encountered in chromatographic studies of complex polymers.

PNIPAmx–PPO36–PNIPAmx thermo-sensitive triblock copolymers: chain conformation and adsorption behavior on a hydrophobic gold surface

The presence of the PNIPAm block is not a sufficient condition for the complex adsorption behavior of PNIPAm_x–PPO₃₆–PNIPAm_x triblock copolymers.

Critical adsorption of a flexible polymer on a stripe-patterned surface

The adsorption and dynamics of a polymer chain on a stripe-patterned surface composed of periodical attractive and neutral stripes are studied by using Monte Carlo simulation. The critical adsorption temperature Tc and pattern-recognition temperature Tr are estimated from the desorption probability, surface contact number, and bridge number. A phase diagram presenting three polymer states, including a desorbed state above Tc, a multi-stripe adsorbed state at an intermediate temperature Tr < T < Tc, and a single-stripe adsorbed state below Tr, is provided for infinitely long chains. Normal diffusion is always observed for a polymer in the direction parallel to the stripe even at low temperature. But in the direction perpendicular to the stripe, the polymer can freely diffuse above Tc, whereas the polymer is confined to one attractive stripe below Tr. However, the adsorbed polymer can hop from one attractive stripe to another at the intermediate temperature Tr < T < Tc.

Interplay of Coil-Globule Transition and Surface Adsorption of a Lattice HP Protein Model

An end-grafted hydrophobic-polar (HP) model protein chain with alternating H and P monomers is studied to examine interactions between the critical adsorption transition due to surface attraction and the collapse transition due to pairwise attractive H–H interactions. We find that the critical adsorption phenomenon can always be observed; however, the critical adsorption temperature T_CAP is influenced by the attractive H–H interactions in some cases. When the collapse temperature T_c is lower than T_CAP, the critical adsorption of the HP chain is similar to that of a homopolymer without intrachain attractions and T_CAP remains unchanged, whereas the collapse transition is suppressed by the adsorption. In contrast, for cases where T_c is close to or higher than T_CAP, T_CAP of the HP chain is increased, indicating that a collapsed chain is more easily adsorbed on the surface. The strength of the H–H attraction also influences the statistical size and shape of the polymer, with strong H–H attractions resulting in adsorbed and collapsed chains adopting two-dimensional, circular conformations.

Competitive adsorption and assembly of block copolymer blends on nanopatterned surfaces

By employing off-lattice Monte Carlo simulations, the competitive adsorption and assembly of block copolymer blends on a nanopatterned surface were investigated. The segment distributions and polymer configurations are examined by varying the chemical structures of polymers, the interactions between segments and adsorbing stripe domains of the nanopatterned surface, and the width of stripe domains in the nanopatterned surface. The simulation results show that by modulating the affinities between a copolymer and the adsorbing stripe domain, one can adjust the density distributions and adsorption properties of block copolymer blends. With decorating the chemical structure of a surface, the targeted molecules would be actively recognized and separated. This offers a versatile way for novel separation materials and for the fabrication of nanomaterials.