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Seong HG, Jin Z, Chen Z, Hu M, Emrick T, Russell TP. Bottlebrush Block Copolymers at the Interface of Immiscible Liquids: Adsorption and Lateral Packing. J Am Chem Soc 2024; 146:13000-13009. [PMID: 38710503 DOI: 10.1021/jacs.3c13817] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/08/2024]
Abstract
Amphiphilic bottlebrush block copolymers (BBCPs), having a hydrophilic bottlebrush polymer (BP) linked covalently to a hydrophobic BP, were found to segregate to liquid-liquid interfaces to minimize the free energy of the system. The key parameter influencing the outcome of the experiments is the ratio between the degree of polymerization of the backbone (NBB) and that of the side-chain brushes (NSC). Specifically, a spherical, star-like configuration results when NBB < NSC, while a cylindrical, bottlebrush-like shape is preferred when NBB > NSC. Dynamic interfacial tension (γ) and fluorescence recovery after photobleaching (FRAP) measurements show that the BBCP configuration influences the areal density and in-plane diffusion at the fluid interface. The characteristic relaxation times associated with BBCP adsorption (τA) and reorganization (τR) were determined by fitting time-dependent interfacial tension measurements to a sum of two exponential relaxation functions. Both τA and τR initially increased with NBB up to 92 repeat units, due to the larger hydrodynamic radius in solution and slower in-plane diffusivity, attributed to a shorter cross-sectional diameter of the side-chains near the block junction. This trend reversed at NBB = 190, with shorter τA and τR attributed to increased segregation strength and exposure of the bare water/toluene interface due to tilting and/or wiggling of the backbone chains, respectively. The adsorption energy barrier decreased with higher NBB, due to a reduced BBCP packing density at the fluid interface. This study provides fundamental insights into macromolecular assembly at fluid interfaces, as it pertains to unique bottlebrush block architectures.
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Affiliation(s)
- Hong-Gyu Seong
- Polymer Science & Engineering Department, Conte Center for Polymer Research, University of Massachusetts, 120 Governors Drive, Amherst, Massachusetts 01003, United States
| | - Zichen Jin
- Polymer Science & Engineering Department, Conte Center for Polymer Research, University of Massachusetts, 120 Governors Drive, Amherst, Massachusetts 01003, United States
| | - Zhan Chen
- Polymer Science & Engineering Department, Conte Center for Polymer Research, University of Massachusetts, 120 Governors Drive, Amherst, Massachusetts 01003, United States
| | - Mingqiu Hu
- Polymer Science & Engineering Department, Conte Center for Polymer Research, University of Massachusetts, 120 Governors Drive, Amherst, Massachusetts 01003, United States
| | - Todd Emrick
- Polymer Science & Engineering Department, Conte Center for Polymer Research, University of Massachusetts, 120 Governors Drive, Amherst, Massachusetts 01003, United States
| | - Thomas P Russell
- Polymer Science & Engineering Department, Conte Center for Polymer Research, University of Massachusetts, 120 Governors Drive, Amherst, Massachusetts 01003, United States
- Materials Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720, United States
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Carrillo JMY, Parambil V, Patra TK, Chen Z, Russell TP, Sankaranarayanan SKRS, Sumpter BG, Batra R. Accelerated Sequence Design of Star Block Copolymers: An Unbiased Exploration Strategy via Fusion of Molecular Dynamics Simulations and Machine Learning. J Phys Chem B 2024; 128:4220-4230. [PMID: 38648367 DOI: 10.1021/acs.jpcb.3c08110] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/25/2024]
Abstract
Star block copolymers (s-BCPs) have potential applications as novel surfactants or amphiphiles for emulsification, compatibilization, chemical transformations, and separations. s-BCPs have chain architectures where three or more linear diblock copolymer arms comprised of two chemically distinct linear polymers, e.g., solvophobic and solvophilic chains, are covalently joined at one point. The chemical composition of each of the subunit polymer chains comprising the arms, their molecular weights, and the number of arms can be varied to tailor the surface and interfacial activity of these architecturally unique molecules. This makes identification of the optimal s-BCP design nontrivial as the total number of plausible s-BCP architectures is experimentally or computationally intractable. In this work, we use molecular dynamics (MD) simulations coupled with a reinforcement learning-based Monte Carlo tree search (MCTS) to identify s-BCP designs that minimize the interfacial tension between polar and nonpolar solvents. We first validate the MCTS approach for the design of small- and medium-sized s-BCPs and then use it to efficiently identify sequences of copolymer blocks for large-sized s-BCPs. The structural origins of interfacial tension in these systems are also identified by using the configurations obtained from MD simulations. Chemical insights into the arrangement of copolymer blocks that promote lower interfacial tension were mined using machine learning (ML) techniques. Overall, this work provides an efficient approach to solve design problems via fusion of simulations and ML and provides important groundwork for future experimental investigation of s-BCPs for various applications.
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Affiliation(s)
- Jan-Michael Y Carrillo
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
| | - Vijith Parambil
- Department of Metallurgical and Materials Engineering, Indian Institute of Technology Madras, Chennai 600036, India
| | - Tarak K Patra
- Department of Chemical Engineering, Indian Institute of Technology Madras, Chennai 600036, India
- Center for Atomistic Modelling and Materials Design, IIT Madras, Chennai 600036, India
| | - Zhan Chen
- Polymer Science and Engineering Department, Conte Center for Polymer Research, University of Massachusetts, Amherst, Massachusetts 01003, United States
| | - Thomas P Russell
- Polymer Science and Engineering Department, Conte Center for Polymer Research, University of Massachusetts, Amherst, Massachusetts 01003, United States
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - Subramanian K R S Sankaranarayanan
- Center for Nanoscale Materials, Argonne National Laboratory, Lemont, Illinois 60439, United States
- Department of Mechanical and Industrial Engineering, University of Illinois, Chicago, Illinois 60607, United States
| | - Bobby G Sumpter
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
| | - Rohit Batra
- Department of Metallurgical and Materials Engineering, Indian Institute of Technology Madras, Chennai 600036, India
- Center for Nanoscale Materials, Argonne National Laboratory, Lemont, Illinois 60439, United States
- Center for Atomistic Modelling and Materials Design, IIT Madras, Chennai 600036, India
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Chen Z, Ribbe AE, Steinmetz C, Coughlin EB, Hu M, Gan X, Russell TP. Phase Behavior of Charged Star Block Copolymers at Fluids Interface. Angew Chem Int Ed Engl 2024; 63:e202400127. [PMID: 38206892 DOI: 10.1002/anie.202400127] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2024] [Revised: 01/08/2024] [Accepted: 01/09/2024] [Indexed: 01/13/2024]
Abstract
The phase behavior of block copolymers (BCPs) at the water-oil interface is influenced by the segmental interaction parameter ( χ ${\chi }$ ) and chain architecture. We synthesized a series of star block copolymers (s-BCPs) having polystyrene (PS) as core and poly(2-vinylpyridine) (P2VP) as corona. The interaction parameters of block-block ( χ ${\chi }$ PS-P2VP ) and block-solvent ( χ ${\chi }$ P2VP-solvent ) were varied by adjusting the pH of the aqueous solution. Lowering pH increased the fraction of quaternized-P2VP (Q-P2VP) with enhanced hydrophilicity. By transferring the equilibrated interfacial assemblies, morphologies ranging from bicontinuous films at pH of 7 and 3.1 to nanoporous and nanotubular structure at pH of 0.65 were observed. The nanoporous films formed hexagonally packed pores in s-BCP matrix, while nanotubes comprised Q-P2VP as corona and PS as core. Control over pore size, d-spacing between pores, and nanotube diameters was achieved by varying polymer concentration, molecular weight, volume fraction and arm number of s-BCPs. Large-scale nanoporous films were obtained by freeze-drying emulsions. Remarkably, the morphologies of linear BCPs were inverted, forming hexagonal-packed rigid spherical micelles with Q-P2VP as core and PS as corona in multilayer. This work provides insights of phase behaviors of BCP at fluids interface and offer a facile approach to prepare nanoporous film with well-controlled pore structure.
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Affiliation(s)
- Zhan Chen
- Department of Polymer Science and Engineering, University of Massachusetts Amherst, Amherst, MA 01003, USA
| | - Alexander E Ribbe
- Department of Polymer Science and Engineering, University of Massachusetts Amherst, Amherst, MA 01003, USA
| | - Christian Steinmetz
- Department of Polymer Science and Engineering, University of Massachusetts Amherst, Amherst, MA 01003, USA
| | - E Bryan Coughlin
- Department of Polymer Science and Engineering, University of Massachusetts Amherst, Amherst, MA 01003, USA
| | - Mingqiu Hu
- Department of Polymer Science and Engineering, University of Massachusetts Amherst, Amherst, MA 01003, USA
| | - Xuchen Gan
- Department of Polymer Science and Engineering, University of Massachusetts Amherst, Amherst, MA 01003, USA
| | - Thomas P Russell
- Department of Polymer Science and Engineering, University of Massachusetts Amherst, Amherst, MA 01003, USA
- Material Science Division, Lawrence Berkeley National Laboratory, Cyclotron Road, Berkeley, CA 94720, USA
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Chen Z, Seong HG, Hu M, Gan X, Ribbe AE, Ju J, Wang H, Doucet M, Emrick T, Russell TP. Janus bottlebrush compatibilizers. SOFT MATTER 2024; 20:1554-1564. [PMID: 38270211 DOI: 10.1039/d3sm01484c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2024]
Abstract
Bottlebrush random copolymers (BRCPs), consisting of a random distribution of two homopolymer chains along a backbone, can segregate to the interface between two immiscible homopolymers. BRCPs undergo a reconfiguration, where each block segregates to one of the homopolymer phases, adopting a Janus-type structure, reducing the interfacial tension and promoting adhesion between the two homopolymers, thereby serving as a Janus bottlebrush copolymer (JBCP) compatibilizer. We synthesized a series of JBCPs by copolymerizing deuterated or hydrogenated polystyrene (DPS/PS) and poly(tert-butyl acrylate) (PtBA) macromonomers using ruthenium benzylidene-initiated ring-opening metathesis polymerization (ROMP). Subsequent acid-catalyzed hydrolysis converted the PtBA brushes to poly(acrylic acid) (PAA). The JBCPs were then placed at the interface between DPS/PS homopolymers and poly(2-vinyl pyridine) (P2VP) homopolymers, where the degree of polymerization of the backbone (NBB) and the grafting density (GD) of the JBCPs were varied. Neutron reflectivity (NR) was used to determine the interfacial width and segmental density distributions (including PS homopolymer, PS block, PAA block and P2VP homopolymer) across the polymer-polymer interface. Our findings indicate that the star-like JBCP with NBB = 6 produces the largest interfacial broadening. Increasing NBB to 100 (rod-like shape) and 250 (worm-like shape) reduced the interfacial broadening due to a decrease in the interactions between blocks and homopolymers by stretching of blocks. Decreasing the GD from 100% to 80% at NBB = 100 caused an increase the interfacial width, yet further decreasing the GD to 50% and 20% reduced the interfacial width, as 80% of GD may efficiently increase the flexibility of blocks and promote interactions between homopolymers, while maintaining relatively high number of blocks attached to one molecule. The interfacial conformation of JBCPs was further translated into compatibilization efficiency. Thin film morphology studies showed that only the lower NBB values (NBB = 6 and NBB = 24) and the 80% GD of NBB = 100 had bicontinuous morphologies, due to a sufficient binding energy that arrested phase separation, supported by mechanical testing using asymmetric double cantilever beam (ADCB) tests. These provide fundamental insights into the assembly behavior of JBCPs compatibilizers at homopolymer interfaces, opening strategies for the design of new BCP compatibilizers.
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Affiliation(s)
- Zhan Chen
- Department of Polymer Science and Engineering, University of Massachusetts Amherst, Amherst, MA, 01003, USA.
| | - Hong-Gyu Seong
- Department of Polymer Science and Engineering, University of Massachusetts Amherst, Amherst, MA, 01003, USA.
| | - Mingqiu Hu
- Department of Polymer Science and Engineering, University of Massachusetts Amherst, Amherst, MA, 01003, USA.
| | - Xuchen Gan
- Department of Polymer Science and Engineering, University of Massachusetts Amherst, Amherst, MA, 01003, USA.
| | - Alexander E Ribbe
- Department of Polymer Science and Engineering, University of Massachusetts Amherst, Amherst, MA, 01003, USA.
| | - Jaechul Ju
- Department of Chemistry, The University of Texas at Austin, Austin, TX, 78712, USA
| | - Hanyu Wang
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA
| | - Mathieu Doucet
- Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA
| | - Todd Emrick
- Department of Polymer Science and Engineering, University of Massachusetts Amherst, Amherst, MA, 01003, USA.
| | - Thomas P Russell
- Department of Polymer Science and Engineering, University of Massachusetts Amherst, Amherst, MA, 01003, USA.
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, 37831, USA
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Carrillo JM, Wang Y, Kumar R, Sumpter BG. Coarse-grained explicit-solvent molecular dynamics simulations of semidilute unentangled polyelectrolyte solutions. THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER 2023; 46:92. [PMID: 37796422 DOI: 10.1140/epje/s10189-023-00342-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/22/2023] [Accepted: 08/28/2023] [Indexed: 10/06/2023]
Abstract
We present results from explicit-solvent coarse-grained molecular dynamics (MD) simulations of fully charged, salt-free, and unentangled polyelectrolytes in semidilute solutions. The inclusion of a polar solvent in the model allows for a more physical representation of these solutions at concentrations, where the assumptions of a continuum dielectric medium and screened hydrodynamics break down. The collective dynamic structure factor of polyelectrolytes, S(q, t), showed that at [Formula: see text], where [Formula: see text] is the polyelectrolyte peak in the structure factor S(q) and [Formula: see text] is the correlation length, the relaxation time obtained from fits to stretched exponential was [Formula: see text], which describes unscreened Zimm-like dynamics. This is in contrast to implicit-solvent simulations using a Langevin thermostat where [Formula: see text]. At [Formula: see text], a crossover region was observed that eventually transitions to another inflection point [Formula: see text] at length scales larger than [Formula: see text] for both implicit- and explicit-solvent simulations. The simulation results were also compared to scaling predictions for correlation length, [Formula: see text], specific viscosity, [Formula: see text], and diffusion coefficient, [Formula: see text], where [Formula: see text] is the polyelectrolyte concentration. The scaling prediction for [Formula: see text] holds; however, deviations from the predictions for [Formula: see text] and D were observed for systems at higher [Formula: see text], which are in qualitative agreements with recent experimental results. This study highlights the importance of explicit-solvent effects in molecular dynamics simulations, particularly in semidilute solutions, for a better understanding of polyelectrolyte solution behavior.
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Affiliation(s)
- Jan-Michael Carrillo
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA.
| | - Yangyang Wang
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA
| | - Rajeev Kumar
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA.
| | - Bobby G Sumpter
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA.
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