@article{powers_ryu_jhon_strickland_hall_genzer_2012, title={Determining the Polydispersity in Chemical Composition and Monomer Sequence Distribution in Random Copolymers Prepared by Postpolymerization Modification of Homopolymers}, volume={1}, ISSN={["2161-1653"]}, DOI={10.1021/mz300386g}, abstractNote={We report on establishing the polydispersity in chemical composition (PCC) and polydispersity in monomer sequence distribution (PMSD) in random copolymers of poly(styrene-co-4-bromostyrene) (PBrxS), where x = (0.385 ± 0.035) is the mole fraction of the 4-bromostyrene units (4-BrS), prepared by electrophilic substitution of bromine in the para-position of the phenyl ring of the parent polystyrene. Upon fixing the total number of repeating units, we tune the distribution of styrene and 4-BrS segments in PBrxS by carrying out the bromination reaction on polystyrene homopolymers in different solvents. While PBrxS with relatively random comonomer distribution is prepared in 1-chlorodecane, random-blocky sequences of 4-BrS in PBrxS are achieved by carrying out the bromination reaction in 1-chlorododecane. The PCC in both copolymers is established by fractionating both polymers using interaction chromatography (IC) and determining the chemical composition of the individual fractions by neutron activation analysis (NAA). The NAA data along with IC experiments reveal that the random-blocky sample possesses a narrowed PCC relative to a specimen with a more random comonomer sequence distribution. The full width at half-maximum (fwhm) in the chemical composition profile from IC is used to quantify PCC; the random mother sample possessed a 25% fwhm, while the random blocky mother sample has a fwhm equal to 8.7%. The change in the adsorption enthalpy per brominated segment due to adsorption is determined to be ≈1.5 times greater for the random-blocky than the relatively random sample, proving that more pronounced cooperative adsorption occurs in the case of the random-blocky sample relative to the random copolymer sample. Computer simulation employing the discontinuous molecular dynamic scheme further reveals that the distribution of comonomer sequences, that is, PMSD, in the random-blocky copolymer is narrower than that in the copolymer with a random distribution of both monomers.}, number={9}, journal={ACS MACRO LETTERS}, author={Powers, Wayne and Ryu, Chang Y. and Jhon, Young K. and Strickland, Lawrence A. and Hall, Carol K. and Genzer, Jan}, year={2012}, month={Sep}, pages={1128–1133} }
 @article{strickland_hall_genzer_2010, title={Controlling comonomer distribution in random copolymers by chemical coloring of surface-tethered homopolymers: An insight from discontinuous molecular dynamics simulation}, volume={26}, DOI={10.1021/la9045513}, abstractNote={Postpolymerization chemical modification ("coloring") of homopolymer brushes made of A units using B chemical moieties produces surface-anchored random copolymers (RCPs) A(1-x)B(x), where x is the degree of "coloring". We employ discontinuous molecular dynamics to study the "coloring" process in macromolecular tethers made of various lengths grafted at low and high densities on flat impenetrable surfaces. We demonstrate that the comonomer distribution in the A(1-x)B(x) RCPs depends on the interplay among (1) the length and the grafting density of the A-based homopolymer anchors, (2) the solubility of the parent homopolymer, and (3) the solubility of the B coloring units. Chemical modification of sparsely spaced chains on the surface leads to nearly random comonomer distribution in the A(1-x)B(x) RCPs regardless of the solubility of A and B. In contrast, the distribution of A and B units in A(1-x)B(x) RCPs prepared from homopolymers tethered at high grafting densities depends on the solubility of the parent homopolymer. Chemical modification of well-solvated A homopolymer grafts results in comonomer distributions that resemble those of diblock copolymers, comprising lightly modified blocks near the surface and heavily "colored" blocks at the top of the grafts. The relative lengths of the two blocks can be tuned by varying the solubility of B. Under poor solvent conditions, the distribution of A and B in the A(1-x)B(x) RCP is more complex; it is governed by the conformation of the parent A macromolecular anchors that form collapsed clusters before the coloring reaction.}, number={11}, journal={Langmuir}, author={Strickland, L. A. and Hall, C. K. and Genzer, Jan}, year={2010}, pages={8810–8820} }
 @article{strickland_hall_genzer_2010, title={Simulation of Mechanically-Assembled Monolayers In Poor Solvent Using Discontinuous Molecular Dynamics}, volume={43}, ISSN={["0024-9297"]}, DOI={10.1021/ma9026417}, abstractNote={We present and discuss the results of discontinuous molecular dynamics simulations of mechanically assembled polymer layers chemically attached to flexible substrates under poor solvent conditions. Square-well chains of lengths comprising 20 to 100 units end-grafted to a hard surface at low density are compressed laterally at varying rates. Brush thickness depends on the interplay between solvent quality and the substrate compression rate. Brushes formed in poor solvents at fast compression rates are thinner and exhibit more heterogeneity in coverage than brushes formed in good solvents at slow compression rates. End-monomer trapping increases with increasing compression rate and/or decreasing solvent quality. By varying relaxation/compression rate, we can modify the effects of brush thickness hysteresis. Finally, we suggest a general blueprint for efficient formation of defect-free monolayers that might be followed by experimenters.}, number={6}, journal={MACROMOLECULES}, author={Strickland, L. Anderson and Hall, Carol K. and Genzer, Jan}, year={2010}, month={Mar}, pages={3072–3080} }
 @article{strickland_hall_genzer_2009, title={Design of copolymers with tunable randomness using discontinuous molecular dynamics simulation}, volume={42}, DOI={10.1021/ma901605v}, abstractNote={We present the results of discontinuous molecular dynamics simulations of a “coloring” reaction performed on A-type homopolymers having length ranging from 100 to 300 units in implicit solvents. Th...}, number={22}, journal={Macromolecules}, author={Strickland, L. A. and Hall, C. K. and Genzer, Jan}, year={2009}, pages={9063–9071} }
 @article{strickland_hall_genzer_2008, title={Simulation of mechanically assembled monolayers and polymers in good solvent using discontinuous molecular dynamics}, volume={41}, ISSN={["0024-9297"]}, DOI={10.1021/ma8003218}, abstractNote={We present the results of discontinuous molecular dynamics simulations of mechanically assembled monolayers in good solvent. Polymers of chain lengths 5−100 were end-grafted to surfaces at low density and then compressed laterally at varying rates. Data for brush thickness and end-monomer density were collected as a function of surface density; they were shown to correspond well with theoretical predictions and simulation results performed at constant surface density. Brush thickness for all chain lengths could be controlled by judicious choice of the compression rate. Defects in the brush layer were dependent on chain length; it was shown that quick compression for relatively short chains allowed the layer no time to relax into coil form. Quick compression on long chain systems led to entanglement in the brush layer since the longer-chained system was not being afforded the long relaxation time required to form a fully relaxed brush. Hysteresis effects were examined by allowing the brush to relax to a lo...}, number={17}, journal={MACROMOLECULES}, author={Strickland, L. Anderson and Hall, Carol K. and Genzer, Jan}, year={2008}, month={Sep}, pages={6573–6581} }