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Stochastic thermodynamics and the associated fluctuation relations provide the means to extend the fundamental laws of thermodynamics to small scales and systems out of equilibrium. The fluctuating thermodynamic variables are usually treated in the context of either isolated Hamiltonian evolution, or Markovian dynamics in open systems. However, there is no reason a priori why the Markovian approximation should be valid in driven systems under nonequilibrium conditions. In this work, we introduce an explicitly non-Markovian model of dynamics of an open system, where the correlations between the system and the environment drive a subset of the environment out of equilibrium. Such an environment gives rise to a new type of non-Markovian entropy production term. Such non-Markovian components must be taken into account in order to recover the fluctuation relations for entropy. As a concrete example, we explicitly derive such modified fluctuation relations for the case of an overheated single electron box.

Advances in precise focusing of colloidal particles in microfluidic systems open up the possibility of using microfluidic junctions for particle separation and filtering applications. We present a comprehensive numerical study of the dynamics of solid and porous microparticles in T-shaped junctions. Good agreement with experimental data is obtained on the location of particle-separating streamlines for single solid particles with realistic parameters corresponding to the experiments. We quantify the changes in the position of the separating line for porous, partially penetrable colloids. A prediction of the full phase diagram for particle separation is presented in the case of two successive particles entering a T-junction. Our results suggest the intriguing possibility of using the one- and two-particle T-junctions as logic gates.

We study the structural and dynamical mechanisms of reinforcement of a polymer nanocomposite (PNC) via coarse-grained molecular dynamics simulations. In a regime of strong polymer-filler interactions, the stress at failure of the PNC is clearly correlated to structural quantities, such as the filler loading, the surface area of the polymer-filler interface, and the network structure. Additionally, we find that small fillers, of the size of the polymer monomers, are the most effective at reinforcing the matrix by surrounding the polymer chains and maximizing the number of strong polymer-filler interactions. Such a structural configuration is correlated to a dynamical feature, namely, the minimization of the relative mobility of the fillers with respect to the polymer matrix.

We study polymer translocation through a nanopore subject to conformational differences created by putting two different solvents at the cis and trans compartments using Langevin dynamics in three dimensions (3D). Initially a fraction of the chain is placed in a good solvent at the cis side and the rest of the chain at the trans side is immersed in a bad solvent where it forms a globule. We study several aspects of the translocating chain as a function of the strength of the interaction ɛ/k(B)T for the bad solvent, where the temperature T is kept below the Θ temperature for the specific bead-spring model that we have used to describe the chain. For ɛ/k(B)T≥1 we find the mean first passage time (τ)~(ɛ/k(B)T)(-1) and (τ)~N(1.1±0.05). In that regard, translocation under solvent asymmetry is similar to the case of driven translocation under a bias inside the pore. However, the globule formed at the trans in the immediate vicinity of the pore readily absorbs the incoming particles making the translocation process faster than the driven translocation. Our simulation results for long chains and ɛ/k(B)T≥1 agree well with a theoretical prediction by Muthukumar [M. Muthukumar, J. Chem. Phys. 111, 10371 (1999).].

We consider the dynamics of polymer translocation out of confined environments. Analytic scaling arguments lead to the prediction that the translocation time scales like tau approximately N(beta+nu(2D))R(1+(1-nu(2D))/nu) for translocation out of a planar confinement between two walls with separation R into a three-dimensional (3D) environment, and tau approximately N(beta+1)R for translocation out of two strips with separation R into a two-dimensional (2D) environment. Here, N is the chain length, nu and nu(2D) are the Flory exponents in 3D and 2D, and beta is the scaling exponent of translocation velocity with N , whose value for the present choice of parameters is beta equals approximately 0.8 based on Langevin dynamics simulations. These scaling exponents improve on earlier predictions.

We investigate the dynamics of single-stranded DNA translocation through a nanopore driven by an external force using Langevin dynamics simulations in two dimensions to study how the translocation dynamics depend on the details of the DNA sequences. We consider a coarse-grained model of DNA built from two bases A and C, having different base-pore interactions, e.g., a strong (weak) attractive force between the pore and the base A (C) inside the pore. From a series of studies on hetero-DNAs with repeat units AmCn, we find that the translocation time decreases exponentially as a function of the volume fraction fC of the base C. For longer A sequences with fC

Using Langevin dynamics simulations, we investigate the influence of polymer-pore interactions on the dynamics of biopolymer translocation through nanopores. We find that an attractive interaction can significantly change the translocation dynamics. This can be understood by examining the three components of the total translocation time tau approximately tau1+tau2+tau3 corresponding to the initial filling of the pore, transfer of polymer from the cis side to the trans side, and emptying of the pore, respectively. We find that the dynamics for the last process of emptying of the pore changes from nonactivated to activated in nature as the strength of the attractive interaction increases, and tau3 becomes the dominant contribution to the total translocation time for strong attraction. This leads to nonuniversal dependence of tau as a function of driving force and chain length. Our results are in good agreement with recent experimental findings, and provide a plausible explanation for the different scaling behavior observed in solid state nanopores vs that for the natural alpha-hemolysin channel.

We determine the scaling exponents of polymer translocation (PT) through a nanopore by extensive computer simulations of various microscopic models for chain lengths extending up to N=800 in some cases. We focus on the scaling of the average PT time tau approximately Nalpha and the mean-square change of the PT coordinate, approximately tbeta. We find alpha=1+2nu and beta=2/alpha for unbiased PT in two dimensions (2D) and three dimensions (3D). The relation alphabeta=2 holds for driven PT in 2D, with a crossover from alpha approximately 2nu for short chains to alpha approximately 1+nu for long chains. This crossover is, however, absent in 3D where alpha=1.42+/-0.01 and alphabeta approximately 2.2 for N approximately 40-800.

We investigate polymer translocation through a nanopore under a pulling force using Langevin dynamics simulations. We concentrate on the influence of the chain length N and the pulling force F on the translocation time tau . The distribution of tau is symmetric and narrow for strong F . We find that tau approximately N{2} and translocation velocity v approximately N{-1} for both moderate and strong F . For infinitely wide pores, three regimes are observed for tau as a function of F . With increasing F , tau is independent of F for weak F , and then tau approximately F{-2+nu{-1}} for moderate F, where nu is the Flory exponent, which finally crosses over to tau approximately F{-1} for strong force. For narrow pores, even for moderate force tau approximately F{-1}. Finally, the waiting time, for monomer s and monomer s+1 to exit the pore, has a maximum for s close to the end of the chain, in contrast to the case where the polymer is driven by an external force within the pore.