DOI 10.1140/epje/i200101124 Eur. Phys. J. E 7, 65–71 (2002) T HE EUROPEAN P HYSICAL JOURNAL E c  EDP Sciences Societ`a Italiana di Fisica Springer-Verlag 2002 Drift of a polymer chain in a porous medium —A Monte Carlo study K. Avramova a and A. Milchev Institute for Physical Chemistry, Bulgarian Academy of Sciences, G. Bonchev Str., Block 11, 1113 Sofia, Bulgaria Received 20 August 2001 and Received in final form 19 November 2001 Abstract. We investigate the drift of an end-labeled telehelic polymer chain in a frozen disordered medium under the action of a constant force applied to the one end of the macromolecule by means of an off-lattice bead spring Monte Carlo model. The length of the polymers N is varied in the range 8 <N< 128, and the obstacle concentration in the medium C is varied from zero up to the percolation threshold C ≈ 0.75. For field intensities below a C-dependent critical field strength B c, where jamming effects become dominant, we find that the conformational properties of the drifting chains can be interpreted as described by a scaling theory based on Pincus blobs. The variation of drag velocity with C in this interval of field intensities is qualitatively described by the law of Mackie-Meares. The threshold field intensity B c itself is found to decrease linearly with C. PACS. 36.20.-r Macromolecules and polymer molecules – 36.20.Ey Conformation (statistics and dynamics) – 82.45.-h Electrochemistry and electrophoresis 1 Introduction The explosive development of physical methods and con- cepts related to problems of biological interest in recent years might be viewed as one of the major trends in contemporary statistical physics. The behavior of large flexible molecules like DNA, RNA, denaturated proteins, polysaccharides and synthetic polyelectrolytes in disor- dered media, usually under the influence of external fields, constitutes the basis of numerous applications [1] and therefore a principle target of scientific investigations. Electrophoresis is one of the most widely used tech- niques for separating charged macromolecules according to their size [1,2]. During electrophoresis, charged chains, such as nuclei acids or synthetic polyelectrolytes, are driven through random media by an external electric field. The obstacles in the medium are usually fibers of gel-agarose polyacrilamid, etc. More recently, litographi- cally etched arrays of silicon have been proposed as elec- trophoretic medium [3,4]. In gas chromatography the driv- ing force is the gas flow and it causes the migration through the sieving media and the separation. Despite the large interest in these problems and numerous studies both theoretically [5–11] and by means of computer simu- lations [12–16], no complete understanding of the complex macromolecular behavior has been achieved so far. One of the main targets of investigation thereby is the impact of the surrounding medium of obstacles [17] on the config- a e-mail: kati@ipc.bas.bg urational properties and specific dynamics of the drifting species. In an earlier investigation [18] we used dynamic Monte Carlo simulation to study the structure and mobility of a polyelectrolyte chain protruding through a porous medium in a uniform external field. A characteristic maxi- mum of the drift velocity upon increasing the external field intensity, indicating the onset of “trapping” processes, was observed. The critical magnitude of the field intensity at which the velocity goes through a maximum was found to be weakly dependent on the density of the random me- dia. This behavior was interpreted as due to the formation of “hairpin” configurations whereby the polymer chain is trapped for some “capture” time, the latter growing ex- ponentially with the intensity of the field. A special case of polyelectrolytes which may formally be considered as a particular case of block polyelectrolytes is that of end-labeled macromolecules in which part of the chain is uniformly charged whereas the rest is neutral. Typically these are various telehelic block ionomers. In the present study we examine the configurational properties and dynamic behavior of such end-labeled polymers with only one charged end, referred to as class “c” [19], which are subject to a uniform field in a porous medium [19, 20]. The structure properties of such telehelic ionomers in the bulk have been studied earlier by Wu and Slater [19] within the framework of a reptation model. An at- tempt to understand the influence of the porous environ- ment has been tried later by Stepanow and Schulz [20] who treated analytically the case of electrophoresis of end-