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Dynamic Compression of in situ Grown Living Polymer Brush: Simulation and Experiment

A comparative dynamic Monte Carlo simulation study of polydisperse living polymer brushes, created by surface initiated living polymerization, and conventional polymer monodisperse brush, comprising linear polymer chains, grafted to a planar substrate under good solvent conditions, is presented. The living brush is created by end-monomer (de)polymerization reaction after placing an array of initiators on a grafting plane in contact with a solution of initially non-bonded segments (monomers). At equilibrium, the monomer density profile ϕ(z) of the LPB is found to decline as ϕ(z) ~ z^{-α} with the distance from the grafting plane z, while the distribution of chain lengths in the brush scales as c(N) ~ N^{-τ}. The measured values α= 0.64 and τ= 1.70 are very close to those, predicted within the framework of the Diffusion-Limited Aggregation theory, α= 2/3 and τ= 7/4. At varying mean degree of polymerization (from L = 28 to L = 170) and effective grafting density (from σ_g = 0.0625 to σ_g = 1.0), we observe a nearly perfect agreement in the force-distance behavior of the simulated LPB with own experimental data obtained from colloidal probe AFM analysis on PNIPAAm brush and with data obtained by Plunkett et. al., [Langmuir 2006, 22, 4259] from SFA measurements on same polymer.