13 results on '"James J. Semler"'
Search Results
2. Effect of Comonomer Sequence Distribution on the Adsorption of Random Copolymers onto Impenetrable Flat Surfaces
- Author
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Jan Genzer, Martin S. Beevers, Pavel G. Khalatur, Young K. Jhon, Alexei R. Khokhlov, James J. Semler, and Olga Guskova
- Subjects
Polymers and Plastics ,Chemistry ,Comonomer ,Organic Chemistry ,Monte Carlo method ,Thermodynamics ,Mole fraction ,Inorganic Chemistry ,Solvent ,chemistry.chemical_compound ,Adsorption ,Polymer chemistry ,Materials Chemistry ,Copolymer ,Solvent effects ,Macromolecule - Abstract
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...
- Published
- 2009
3. Effect of Solvent Quality and Chain Confinement on the Kinetics of Polystyrene Bromination
- Author
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Young K. Jhon, Jan Genzer, and James J. Semler
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Polymers and Plastics ,Organic Chemistry ,Kinetics ,Photochemistry ,Inorganic Chemistry ,Nitrobenzene ,Solvent ,Reaction rate ,chemistry.chemical_compound ,Reaction rate constant ,chemistry ,Polymer chemistry ,Materials Chemistry ,Polystyrene ,Solvent effects ,Solubility - Abstract
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.
- Published
- 2008
4. Facile Method of Controlling Monomer Sequence Distributions in Random Copolymers
- Author
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James J. Semler, Martin S. Beevers, Alan E. Tonelli, Ramanan Krishnamoorti, Jan Genzer, and Young K. Jhon
- Subjects
chemistry.chemical_classification ,Materials science ,Mechanical Engineering ,Polymer ,chemistry.chemical_compound ,Monomer ,chemistry ,Mechanics of Materials ,Covalent bond ,Polymer chemistry ,Copolymer ,Partition (number theory) ,General Materials Science ,Long chain - Abstract
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
- Published
- 2007
5. Monte Carlo Simulations of Copolymer Adsorption at Planar Chemically Patterned Surfaces: Effect of Interfacial Interaction
- Author
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James J. Semler and Jan Genzer
- Subjects
Work (thermodynamics) ,Lattice model (finance) ,Polymers and Plastics ,Chemistry ,media_common.quotation_subject ,Organic Chemistry ,Monte Carlo method ,Frustration ,Substrate (chemistry) ,Condensed Matter Physics ,Critical value ,Inorganic Chemistry ,Adsorption ,Chemical physics ,Polymer chemistry ,Materials Chemistry ,Copolymer ,media_common - Abstract
Monte Carlo simulation utilizing the bond fluctuation model in conjunction with single and configurational biased Monte Carlo moves is used to study the adsorption of diblock (A-block-B) and alternating (A-alt-B) copolymers at flat, chemically heterogeneous surfaces comprising C and D domains. The main objective of this work is to address the effect of the strength of attraction between the adsorbing surface domains, D, and the copolymer adsorbing segments, B, on the copolymer's ability to recognize the chemical pattern on the surface. The results of our simulations reveal that both block and alternating copolymers have the ability to recognize the surface motif and transcribe it into the bulk material. The extent to which diblock copolymers transfer the chemical pattern from the surface to the bulk is relatively unaffected when the attractive B-D potential is increased beyond a certain critical value. This behavior stems from the brush-like conformation adopted by the diblock copolymer at the substrate. In contrast to the diblock copolymer, the adsorption of the alternating copolymer is influenced by the strength of the attraction between the copolymer's adsorbing segments and the adsorbing domains on the surface. Since the B segments are distributed evenly along the backbone, the alternating copolymers are more likely to adopt conformations in which the whole chain is zipped to the surface. The resultant entropic frustration is then alleviated through an increased formation of loops with little change to their length. Such conformational changes endow the alternating copolymer with the ability to invert the substrate pattern as the distance away from the surface is increased.
- Published
- 2004
6. Monte Carlo simulations of copolymer adsorption at planar chemically patterned surfaces: Effect of surface domain sizes
- Author
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Jan Genzer and James J. Semler
- Subjects
Materials science ,Monte Carlo method ,General Physics and Astronomy ,Radius ,chemistry.chemical_compound ,Planar ,Adsorption ,Monomer ,chemistry ,Chemical physics ,Computational chemistry ,Copolymer ,Dynamic Monte Carlo method ,Polymer blend ,Physical and Theoretical Chemistry - Abstract
We present results of Monte Carlo simulation studies utilizing the bond fluctuation model in conjunction with single and configurational biased Monte Carlo moves to investigate the adsorption of diblock (A–b–B) and alternating (A–alt–B) copolymers at physically flat surfaces made of an equal number of two chemically different sites, C and D. The adsorption of the copolymer to the surface is driven by the repulsion between the A and B segments along the copolymer and the attraction between the B segments and the D sites on the surface. We address the critical role of the commensurability between the copolymer’s monomer sequence distribution and the size and spatial distribution of the surface adsorbing sites on the copolymer adsorption. We show that both copolymer architectures have the ability to recognize the surface motif and transcribe it into the bulk material. Diblock copolymers can transfer the pattern once the heterogeneous domain sizes match the size of the parallel component to the radius of gyra...
- Published
- 2003
7. ABA Triblock Copolymer Gels Modified with an A-Compatible Semicrystalline Homopolymer
- Author
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Richard J. Spontak, Teri A. Walker, Guillermo J. van Maanen, Donovan N. Leonard, James J. Semler, and and Rudolf R. Bukovnik
- Subjects
Materials science ,Modulus ,Surfaces and Interfaces ,Condensed Matter Physics ,Micelle ,Solvent ,Crystallinity ,Differential scanning calorimetry ,stomatognathic system ,Chemical engineering ,Rheology ,Polymer chemistry ,Electrochemistry ,Copolymer ,General Materials Science ,Elastic modulus ,Spectroscopy - Abstract
In the presence of a midblock-selective solvent, ABA triblock copolymers form physical gels in which bridged and entangled B-chains establish a swollen network stabilized by A-microdomains. Here, we seek to improve the properties of an ABA gel through the addition of an A-compatible, high-molecular-weight semicrystalline homopolymer (shA). Dynamic rheology indicates that the elastic modulus increases substantially, and far beyond that achievable with an inert filler, with increasing shA content at constant solvent concentration. Transmission electron micrographs reveal the existence of nanoscale shA filaments and sheets dispersed in a micelle-stabilized gel network. The shape of the nanoscale shA objects, which are partially crystalline according to differential scanning calorimetry, and their apparent interaction with the A-rich micelles enhance network development and are responsible for the pronounced modulus increase.
- Published
- 2002
8. Macromol. Rapid Commun. 18/2009
- Author
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James J. Semler, Young K. Jhon, Chang Y. Ryu, Byung Ho Jeon, Jan Genzer, and Junwon Han
- Subjects
Polymers and Plastics ,Organic Chemistry ,Materials Chemistry - Published
- 2009
9. Discriminating Among Co-monomer Sequence Distributions in Random Copolymers Using Interaction Chromatography
- Author
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Junwon, Han, Byung Ho, Jeon, Chang Y, Ryu, James J, Semler, Young K, Jhon, and Jan, Genzer
- Abstract
Interaction chromatography has been employed to validate that adsorption of poly[styrene-co-(4-bromostyrene)] (PBr(x) S) random copolymers, where x denotes the mole fraction of 4-bromostyrene (4-BrS) in PBr(x) S in solution depends on the average number of adsorptive segments, the type of adsorbing substrate, and on the co-monomer sequence distribution in PBr(x) S.
- Published
- 2009
10. Monte Carlo Simulations of Copolymer Adsorption from Copolymer / Homopolymer Melts at Planar Chemically Patterned Surfaces
- Author
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Jan Genzer and James J. Semler
- Subjects
chemistry.chemical_classification ,Planar ,Adsorption ,Materials science ,chemistry ,Chemical physics ,Monte Carlo method ,Polymer chemistry ,Copolymer ,Substrate (chemistry) ,Sequence (biology) ,Polymer ,Microstructure - Abstract
We investigate the adsorption of copolymers from copolymer / homopolymer mixtures at planar chemically patterned surfaces. The Monte Carlo bond fluctuation model is used in conjunction with configurational biased Monte Carlo moves to study the effect of: i) the copolymer microstructure, ii) the size and spatial distribution of chemical heterogeneities on the substrate, and iii) the polymer/substrate interactions on the ability of the copolymer to recognize the substrate chemical pattern. Our results confirm that the surface pattern recognition occurs whenever the characteristic size of the copolymer distribution sequence matches that of the surface heterogeneity domain. Moreover, the copolymer sequence distribution plays a crucial role in determining the extent of the surface pattern transfer into the bulk material. Our results reveal that more pronounced surface pattern transfer into the bulk occurs for small attractions of the adsorbing species to particular surface domains relative to the large attractions.
- Published
- 2001
11. Design of random copolymers with statistically controlled monomer sequence distributions via Monte Carlo simulations
- Author
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Jan Genzer and James J. Semler
- Subjects
chemistry.chemical_classification ,Work (thermodynamics) ,Materials science ,Monte Carlo method ,General Physics and Astronomy ,Thermodynamics ,Sequence (biology) ,Polymer ,chemistry.chemical_compound ,Monomer ,Distribution (mathematics) ,chemistry ,Polymer chemistry ,Dynamic Monte Carlo method ,Copolymer ,Physical and Theoretical Chemistry - Abstract
We use Monte Carlo simulations to model the formation of random copolymers with tunable monomer sequence distributions. Our scheme is based on the original idea proposed a few years ago by Khokhlov and Khalatur [Physica A 249, 253 (1998); Phys. Rev. Lett. 82, 3456 (1999)], who showed that the distribution of species B in A-B random copolymers can be regulated by (a) adjusting the coil size of a homopolymer A and (b) chemically modifying ("coloring") monomers that reside at (or close to) the periphery of the coil with species B. In contrast to Khokhlov and Khalatur's work, who modeled the polymer modification by performing the coloring instantaneously, we let the chemical coloring reaction progress over time using computer simulations. We show that similar to Khokhlov and Khalatur's work, the blockiness (i.e., number of consecutive monomers) of the B species along the A-B copolymer increases with increasing degree of collapse of the parent homopolymer A. A simple analysis of the A-B monomer sequences in the copolymers reveals that monomer sequence distributions in homopolymers "colored" under collapsed conformations possess certain degrees of self-similarity, while there is no correlation found among the monomer sequence distributions formed by coloring homopolymers with expanded conformations.
- Published
- 2006
12. Cover Picture: Macromol. Theory Simul. 3/2004
- Author
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James J. Semler and Jan Genzer
- Subjects
Inorganic Chemistry ,Polymers and Plastics ,Organic Chemistry ,Materials Chemistry ,Cover (algebra) ,Condensed Matter Physics ,Geology ,Remote sensing - Published
- 2004
13. Effect of Comonomer Sequence Distribution on the Adsorption of Random Copolymers onto Impenetrable Flat Surfaces.
- Author
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Young K. Jhon, James J. Semler, Jan Genzer, Martin Beevers, Olga A. Gus’kova, Pavel G. Khalatur, and Alexei R. Khokhlov
- Subjects
- *
ABSORPTION & adsorption of polymers , *COPOLYMERS , *MONOMERS , *POLYSTYRENE , *SURFACE chemistry , *BROMINATION , *SIMULATION methods & models - Abstract
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 xdenotes 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: (1) Increasing the degree of “blockiness” in comonomer distribution enhances the adsorption of macromolecules dissolved in a good solvent. (2) Near the adsorption transition, the amount of adsorbed segments in “random-blocky” copolymers is larger relative to their regular multiblock counterparts. (3) Lowering the solvent quality facilitates copolymer adsorption. Overall, the findings from computer modeling are found to be in a good agreement with the experimental data. [ABSTRACT FROM AUTHOR]
- Published
- 2009
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