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NUMBER  
AUTHOR Hyeon, Changbong,Liu, Lei
TITLE Compressing Theta-Chain in Slit Geometry
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JOURNAL NANO LETTERS, 2019
ABSTRACT When compressed in a slit of width D, a Theta-chain that displays the scaling of size R-0 (diameter) with respect to the number of monomers N, R-0 similar to aN(1/2), expands in the lateral direction as R-parallel to similar to aN(nu)(a/D)(2 nu-1). Provided that the Theta condition is strictly maintained throughout the compression, the well-known scaling exponent of Theta-chain in two dimensions, nu = 4/7, is anticipated in a perfect confinement. However, numerics shows that upon increasing compression from R-0/D < 1 to R-0/D >> 1, nu gradually deviates from nu = 1/2 and plateaus at nu = 3/4, the exponent associated with the self-avoiding walk in two dimensions. Using both theoretical considerations and numerics, we argue that it is. highly nontrivial to maintain the Theta condition under confinement because of two major effects. First, as the dimension is reduced from three to two dimensions, the contributions of higher order virial terms, which can be ignored in three dimensions at large N, become significant, making the perturbative expansion used in Flory-type approach inherently problematic. Second and more importantly, the geometrical confinement, which is regarded as an applied external field, alters the second virial coefficient (B-2) changes from B-2 = 0 (Theta condition) in free space to B-2 > 0 (good-solvent condition) in confinement. Our study provides practical insight into how confinement affects the conformation of a single polymer chain.
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