We present a Brownian dynamics simulation study on the diffusion of a neutral tracer particle confined in a regularly crosslinked polymer network, especially, when the tracer size is comparable to the mesh size of the network. Polymer networks with different mesh sizes are prepared and compressed to the extent that the total polymer densities become the same. Irrespective of the network mesh size, the tracer diffusion in the networks is slowed down, showing the subdiffusion on intermediate time scales followed by the normal diffusion at long times. However, the confinement effect on the tracer diffusion becomes more significant when network strands are tightly stretched with smaller mesh size. The time scales of dynamic transitions are analyzed in terms of the probability distribution of time-correlated particle displacements.

Polymer collapse transition에 대한 연구가 많이 진행되어왔다. 허나 각각의 microstate에 대한 entropy나 free energy에 대한 계산을 하지는 못하였다. 최근 local nonequilibrium thermodynamics와 관련한 논문이 발표되었는데 이는 비평형 상태에서의 각각의 microstate에 대한 확률 분포를 결정하는 물리량을 발견 및 특성을 규명하여 이 중 특별한 상태가 지니는 “information” 이라는 양이 내부에너지와 엔트로피와의 상관관계가 있음을 보였다. 또한, 이러한 information theory를 이용한 Shannon entropy를 사용하여 entropy를 정의하고 free energy와 같은 물리량을 계산하였다. 따라서 이를 이용하여 information theory를 이용한 Shannon entropy와 이로 정의된 free energy를 이용하여 polymer collapse중 entropy 및 free energy를 계산하였다.

Control of polymer conformations in heterogeneous confinement plays an important role in natural and engineering processes. We present a simulation study on the conformational structure and dynamics of a single, flexible polymer in a dense array of nanoposts with different sizes and separations, especially, when the volume of the interstitial space formed between four nanoposts is less than the size of the polymer chain. When a polymer is placed in the array of nanoposts, the size of polymer increases compared with that in the absence of nanoposts due to the confinement effect. It is shown that when a polymer is confined in the array of nanoposts the chain is elongated in the direction parallel to the nanoposts. As the interstitial volume between four nanoposts decreases either by increasing the nanopost diameter or by decreasing the separation between nanoposts, the chain elongation becomes more pronounced. On the contrary, the polymer size varies in a non-monotonic fashion, with an initial elongation followed by a chain contraction, as the interstitial volume is reduced both by increasing the nanopost diameter and decreasing the separation at the same time while keeping constant the width of the passageway between two nanoposts. The simulation analysis shows that the non-monotonic dependence of polymer size is determined by interplay between the chain alignment along the nanoposts in each interstitial volume and the chain spreading through passageways over several interstitial volume.