Coil to globule transition of homo- and block-copolymer with different topological constraint and chain stiffness

Thermal properties of knotted block copolymer rings with charged monomers subjected to short-range interactions

The thermal properties of coarse-grained knotted copolymer rings fluctuating in a highly screening solution are investigated on a simple cubic lattice using the Wang-Landau Monte Carlo algorithm. The rings contain two kinds of monomers A and B with opposite charges that are subjected to short-range interactions. In view of possible applications in medicine and the construction of intelligent materials, it is shown that the behavior of copolymer rings can be tuned by changing both their monomer configuration and topology. We find several phase transitions depending on the monomer distribution. They include the expansion and collapse of the knotted polymer as well as rearrangements leading to metastable states. The temperatures at which these phase transitions are occurring and other features can be tuned by changing the topology of the system. The processes underlying the observed transitions are identified. In knots formed by diblock copolymers, two different classes of behaviors are detected depending on whether there is an excess of monomers of one kind or not. Moreover, we find that the most stable compact states are formed by copolymers in which units of two A monomers are alternated by units of two B monomers. Remarkably, these compact states are in a lamellar phase. The transition from the lamellar to the expanded state produces in the specific heat capacity a narrow and high peak that is centered at temperatures that are much higher than those of the peaks observed in all other monomer distributions.

Enhancement of surface nonwettability by grafting loops

We present a computer simulation study on the nonwettability of a flat surface tethered with deformable looped polymer chains.

Understanding the wettability of a hairy surface: effect of hair rigidity and topology

We present a computer simulation study on the wettability of a hairy surface with different topological structures such as single hairs, hair bundles and network structure. Superficially, for end-tethered rigid hairs or flexible hairs, the nonwettability of the substrate should be analyzed in completely different ways. For rigid hairs, the contact angle is dominantly dependent on the top layer density of hairs. A larger top layer density leads to a larger interaction between droplet and surface, as well as a lower contact angle. For flexible hairs, the nonwettability is determined by the typical properties of hairs right below the droplet, e.g., the chemistry of the surface, the topography and strength of the hair bundle/network or nonwetted area below the projection of the droplet. Nevertheless, it is also possible to generalize these aspects into a uniform procedure, which implies an intrinsic consistent mechanism of the dewetting behavior for droplets on such hairy surfaces. Counterintuitively, we also suggest that the surface which can strongly resist the transition to the Wenzel state does not necessarily lead to a large contact angle, especially in a system where the droplet is treated as liquid bulk. This study helps to build up guidelines for the design of nonwetting surface materials.

Control globular structure formation of a copolymer chain through inverse design

A copolymer chain in dilute solution can exhibit various globular structures with characteristic morphologies, which makes it a potentially useful candidate for artificial materials design. However, the chain has a huge conformation space and may not naturally form the globular structure we desire. An ideal way to control globular structure formation should be inverse design, i.e., starting from the target structure and finding out what kind of polymers can effectively generate it. To accomplish this, we propose an inverse design procedure, which is combined with Wang-Landau Monte Carlo to fully and precisely explore the huge conformation space of the chain. Starting from a desired target structure, all the geometrically possible sequences are exactly enumerated. Interestingly, reasonable interaction strengths are obtained and found to be not specified for only one sequence. Instead, they can be combined with many other sequences and also achieve a relatively high yield for target structure, although these sequences may be rather different. These results confirm the possibility of controlling globular structure formation of a copolymer chain through inverse design and pave the way for targeted materials design.