@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{gallow_jhon_genzer_loo_2012, title={Influence of gradient strength and composition profile on the onset of the cloud point transition in hydroxyethyl methacrylate/dimethylaminoethyl methacrylate gradient copolymers}, volume={53}, ISSN={["1873-2291"]}, DOI={10.1016/j.polymer.2012.01.027}, abstractNote={We examined the onset of the cloud point in dilute aqueous solutions of gradient copolymers of 2-hydroxyethyl methacrylate and dimethylaminoethyl methacrylate. Dynamic Light Scattering (DLS) and transmittance measurements both indicate that the copolymer solution cloud point decreases with increasing copolymer gradient strength, defined as the largest difference in the instantaneous composition along the copolymer. While transmittance measurements suggest that macroscopic clouding does not set in until 30% of the polymer chain becomes insoluble, DLS experiments, which are more sensitive to the onset of aggregation, indicate that the onset of aggregation occurs at the point where the least soluble polymer chain end becomes insoluble. Collectively, our data indicate that the macroscopic cloud point transition is highly sensitive to co-monomer sequence distribution of the copolymers, with its onset and transition breadth tunable through copolymer gradient strength.}, number={5}, journal={POLYMER}, author={Gallow, Keith C. and Jhon, Young K. and Genzer, Jan and Loo, Yueh-Lin}, year={2012}, month={Feb}, pages={1131–1137} }
 @article{gallow_jhon_tang_genzer_loo_2011, title={Cloud Point Suppression in Dilute Solutions of Model Gradient Copolymers with Prespecified Composition Profiles}, volume={49}, ISSN={["1099-0488"]}, DOI={10.1002/polb.22226}, abstractNote={AbstractGradient copolymers of 2‐hydroxyethyl methacrylate (HEMA) and 2‐(dimethylamino)ethyl methacrylate (DMAEMA) having prescribed linear, parabolic, and hyperbolic composition profiles were synthesized with the guidance of a numerical model that determines the instantaneous comonomer feed rate. These materials exhibit low polydispersity indices (<1.1); the evolution of the overall DMAEMA content and the absolute molecular weight of the copolymers are all in good agreement with the quantities predicted by our model. Compared to random copolymers of HEMA and DMAEMA, the cloud points of dilute buffered aqueous solutions of gradient copolymers decrease with increasing gradient strength; where the gradient strength is defined as the largest difference in the instantaneous composition along the copolymer. The temperature range over which the solutions transition from transparent to turbid also broadens significantly with increasing gradient strength. Both observations suggest the onset of transition to be dictated by the least soluble ends of the polymer chains. These correlations point to the importance of monomer sequence distribution in determining the macroscopic physical properties of copolymers. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011}, number={9}, journal={JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS}, author={Gallow, Keith C. and Jhon, Young K. and Tang, Wei and Genzer, Jan and Loo, Yueh-Lin}, year={2011}, month={May}, pages={629–637} }
 @article{tonelli_jhon_genzer_2010, title={Glass Transition Temperatures of Styrene/4-BrStyrene Copolymers with Variable Co-Monomer Compositions and Sequence Distributions}, volume={43}, ISSN={["0024-9297"]}, DOI={10.1021/ma101355f}, abstractNote={In both equations WA and WB are the weight fractions of comonomer units A and B. In eq 1 TgA and TgB are the glass transition temperatures of homopolymers poly-A and poly-B, and in eq 2 PAA, PAB =PBA, PBB and TgAA, TgAB, TgBB are the probabilities/populations of and glass-transitions temperatures contributed by each distinct comonomer diad. Figure 1 illustrates both behaviors, as observed in methacrylate (MA) copolymers with vinyl chloride (VC) and vinylidene chloride (VDC). While VC-MA copolymers follow the weightadditive relation (eq 1) of Fox et al., VDC-MA copolymers deviate strongly, with observed Tgps far above those given by the Fox equation, even though the Tgs of PMA and PVDC homopolymers are nearly identical. This is particularly evident when comparing the Tgps of random and regularly alternating VDCMA copolymers, each having the same overall 50:50 molar composition. The 50:50 random VDC-MA copolymer has a Tgp some 35 C above that predicted by the Fox relation (eq 1), while the regularly alternating sample’sTgp is an additional 15 C higher than that of the 50:50 random copolymer. The contrasting Tgp behavior evidenced byVC-MAandVDC-MAcopolymers was previously suggested to be the consequence of the conformational flexibilities of their individual copolymer chains. Therewe put forward the following relationship to describe the deviation between the glass-transition temperatures observed for copolymers Tgp(obs) and those predicted by the Fox Relation (eq 1), Tgp(Fox), dependent solely upon the overall weight-average chemical composition of comonomers:}, number={16}, journal={MACROMOLECULES}, author={Tonelli, Alan E. and Jhon, Young K. and Genzer, Jan}, year={2010}, month={Aug}, pages={6912–6914} }
 @article{cho_lee_jhon_genzer_char_2010, title={Polymer Nanotubules Obtained by Layer-by-Layer Deposition within AAO-Membrane Templates with Sub-100-nm Pore Diameters}, volume={6}, ISSN={["1613-6829"]}, DOI={10.1002/smll.201001212}, abstractNote={The preparation and features of nanotubes consisting of various materials have attracted signifi cant attention over the past few years because of their potential applications in microelectronics, biosensors, drug-delivery systems, and many other fi elds. The layer-by-layer (LbL) deposition technique on templates has been one of the most popular methods for the formation of nanotubes. Any size and shape of template can be utilized and the desired amount of various materials including polyelectrolytes, [ 1,2 ] biomolecules, [ 3,4 ]}, number={23}, journal={SMALL}, author={Cho, Younghyun and Lee, Woo and Jhon, Young Kuk and Genzer, Jan and Char, Kookheon}, year={2010}, month={Dec}, pages={2683–2689} }
 @article{han_jeon_ryu_semler_jhon_genzer_2009, title={Discriminating Among Co-monomer Sequence Distributions in Random Copolymers Using Interaction Chromatography}, volume={30}, ISSN={["1521-3927"]}, DOI={10.1002/marc.200900282}, abstractNote={AbstractInteraction chromatography has been employed to validate that adsorption of poly[styrene‐co‐(4‐bromostyrene)] (PBrxS) random copolymers, where x denotes the mole fraction of 4‐bromostyrene (4–BrS) in PBrxS in solution depends on the average number of adsorptive segments, the type of adsorbing substrate, and on the co‐monomer sequence distribution in PBrxS.magnified image
}, number={18}, journal={MACROMOLECULAR RAPID COMMUNICATIONS}, author={Han, Junwon and Jeon, Byung Ho and Ryu, Chang Y. and Semler, James J. and Jhon, Young K. and Genzer, Jan}, year={2009}, month={Sep}, pages={1543–1548} }
 @article{jhon_semler_genzer_beevers_gus'kova_khalatur_khokhlov_2009, title={Effect of Comonomer Sequence Distribution on the Adsorption of Random Copolymers onto Impenetrable Flat Surfaces}, volume={42}, ISSN={["1520-5835"]}, DOI={10.1021/ma8027936}, abstractNote={We study the effect of comonomer sequence distributions in random copolymers (RCPs) on RCP adsorption on flat impenetrable surfaces. RCP poly(styrene-co-4-bromostyrene) (PBrxS), where x denotes the mole fraction of 4-bromostryrene (4-BrS), is prepared by bromination of parent homopolystyrene. By varying the solvent quality during the bromination, either “truly random” (good solvent) or “random-blocky” (poor solvent) PBrxS RCPs are prepared. Adsorption studies of PBrxS from various solvents at silica surfaces reveal that the adsorption of PBrxS increases with (1) increasing blockiness of the macromolecule, (2) increasing content of 4-BrS in PBrxS, and (3) decreasing solvent quality. Additionally, the effect of comonomer sequence distribution on RCP adsorption is modeled in detail using a coarse-grained statistical mechanical model and fully atomistic simulations based on configurational-biased grand-canonical Monte Carlo (CB-GCMC) technique. The main result from the simulations can be summarized as follows...}, number={7}, journal={MACROMOLECULES}, author={Jhon, Young K. and Semler, James J. and Genzer, Jan and Beevers, Martin and Gus'kova, Olga A. and Khalatur, Pavel G. and Khokhlov, Alexei R.}, year={2009}, month={Apr}, pages={2843–2853} }
 @article{jhon_semler_genzer_2008, title={Effect of solvent quality and chain confinement on the kinetics of polystyrene bromination}, volume={41}, DOI={10.1021/ma8011653}, abstractNote={We report on the kinetics of the bromination of free polystyrene (PS) chains in bulk solution and those anchored on flat solid substrates by performing the bromination reaction in different solvents, including nitrobenzene (NB), 1-chlorodecane (CD), 1-chloroundecane (CUD), and 1-chlorododecane (CDD), at various temperatures. We find that bulk bromination of PS follows the second-order kinetic in bromine and the reaction rate increases with increasing dielectric constant of the solvent (e). In spite of eCDD > eCD, the bulk bromination kinetics of PS in CDD is slower than that in CD because of lower solubility of PS in CDD than in CD. In addition, we demonstrate that the reaction rates for brominating PS brushes anchored to flat solid substrates are much slower than those for brominating free PS chains in bulk solution. We attribute this behavior to steric hindrance due to PS confinement on the substrate.}, number={18}, journal={Macromolecules}, author={Jhon, Y. K. and Semler, J. J. and Genzer, Jan}, year={2008}, pages={6719–6727} }
 @article{semler_jhon_tonelli_beevers_krishnamoorti_genzer_2007, title={Facile method of controlling monomer sequence distributions in random copolymers}, volume={19}, DOI={10.1002/adma.200602359}, abstractNote={Inthis report, we present a simple methodology facilitating theformation of A-B random copolymers with tunable sequencedistributions. We demonstrate that varying the degree ofblockiness in the sequence distribution of A and B monomershas a profound impact on the partition of random copolymersat interfaces.Random copolymers (RCPs) are long chain moleculesmade of covalently bound monomers comprising at least twodifferent chemical moieties (say, A and B). In addition to theoverall molecular weight, RCPs are characterized by theircomposition and monomer sequence distribution. The abilityof A-B RCPs to act as “homopolymers with tunable composi-tion”, ranging between A and B homopolymers, has recentlyattracted considerable attention in controlling polymer misci-bility}, number={19}, journal={Advanced Materials}, author={Semler, J. J. and Jhon, Y. K. and Tonelli, A. and Beevers, M. and Krishnamoorti, R. and Genzer, Jan}, year={2007}, pages={2877-} }
 @article{jhon_bhat_jeong_rojas_szleifer_genzer_2006, title={Salt-induced depression of lower critical solution temperature in a surface-grafted neutral thermoresponsive polymer}, volume={27}, ISSN={["1521-3927"]}, DOI={10.1002/marc.200600031}, abstractNote={AbstractSummary: Quartz crystal microbalance with dissipation monitoring (QCM‐D) is employed to determine the effect of salt on the volume phase transition of thermoresponsive polymer brushes. Changes in mass and viscoelasticity of poly(N‐isopropylacrylamide) (PNIPAM) layers grafted from a QCM‐D crystal are measured as a function of temperature, upon contact with aqueous solutions of varying salt concentrations. The phase‐transition temperature of PNIPAM brushes, TC,graft, quantified from the QCM‐D measurements is found to decrease as the concentration of salt is increased. This phenomenon is explained by the tendency of salt ions to affect the structure of water molecules (Hofmeister effect). However, in contrast to the linear decrease in phase‐transition temperature upon increasing salt concentration observed for free PNIPAM, the trend in TC,graft for PNIPAM brushes is distinctively non‐linear.Schematic representation of the effect of salt concentration on the phase transition behavior of thermoresponsive polymer brushes.magnified imageSchematic representation of the effect of salt concentration on the phase transition behavior of thermoresponsive polymer brushes.
}, number={9}, journal={MACROMOLECULAR RAPID COMMUNICATIONS}, author={Jhon, Young K. and Bhat, Rajendra R. and Jeong, Changwoo and Rojas, Orlando J. and Szleifer, Igal and Genzer, Jan}, year={2006}, month={May}, pages={697–701} }