1
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Teunissen LW, Smulders MMJ, Zuilhof H. Modular and Substrate-Independent Grafting-To Procedure for Functional Polymer Coatings. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2023. [PMID: 37216307 DOI: 10.1021/acs.langmuir.3c00280] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
The ability to tailor polymer brush coatings to the last nanometer has arguably placed them among the most powerful surface modification techniques currently available. Generally, the synthesis procedures for polymer brushes are designed for a specific surface type and monomer functionality and cannot be easily employed otherwise. Herein, we describe a modular and straightforward two-step grafting-to approach that allows introduction of polymer brushes of a desired functionality onto a large range of chemically different substrates. To illustrate the modularity of the procedure, gold, silicon oxide (SiO2), and polyester-coated glass substrates were modified with five different block copolymers. In short, the substrates were first modified with a universally applicable poly(dopamine) primer layer. Subsequently, a grafting-to reaction was performed on the poly(dopamine) films using five distinct block copolymers, all of which contained a short poly(glycidyl methacrylate) segment and longer segment of varying chemical functionality. Ellipsometry, X-ray photoelectron spectroscopy, and static water contact angle measurements confirmed successful grafting of all five block copolymers to the poly(dopamine)-modified gold, SiO2, and polyester-coated glass substrates. In addition, our method was used to provide direct access to binary brush coatings, by simultaneous grafting of two different polymer materials. The ability to synthesize binary brush coatings further adds to the versatility of our approach and paves the way toward production of novel multifunctional and responsive polymer coatings.
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Affiliation(s)
- Lucas W Teunissen
- Laboratory of Organic Chemistry, Wageningen University, Stippeneng 4, Wageningen 6708 WE, The Netherlands
| | - Maarten M J Smulders
- Laboratory of Organic Chemistry, Wageningen University, Stippeneng 4, Wageningen 6708 WE, The Netherlands
| | - Han Zuilhof
- Laboratory of Organic Chemistry, Wageningen University, Stippeneng 4, Wageningen 6708 WE, The Netherlands
- School of Pharmaceutical Sciences and Technology, Tianjin University, 92 Weijin Road, Tianjin 300072, People's Republic of China
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2
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Butt HJ, Berger R, Steffen W, Vollmer D, Weber SAL. Adaptive Wetting-Adaptation in Wetting. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2018; 34:11292-11304. [PMID: 30110544 DOI: 10.1021/acs.langmuir.8b01783] [Citation(s) in RCA: 54] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
Many surfaces reversibly change their structure and interfacial energy upon being in contact with a liquid. Such surfaces adapt to a specific liquid. We propose the first order kinetic model to describe dynamic contact angles of such adaptive surfaces. The model is general and does not refer to a particular adaptation process. The aim of the proposed model is to provide a quantitative description of adaptive wetting and to link changes in contact angles to microscopic adaptation processes. By introducing exponentially relaxing interfacial energies and applying Young's equation locally, we predict a change of advancing and receding contact angles depending on the velocity of the contact line. Even for perfectly homogeneous and smooth surfaces, a dynamic contact angle hysteresis is obtained. As possible adaptations, we discuss changes and reconstruction of polymer surfaces or monolayers, diffusion and swelling, adsorption of surfactants, replacement of contaminants, reorientation of liquid molecules, or formation of an electric double layer.
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Affiliation(s)
- Hans-Jürgen Butt
- Max Planck Institute for Polymer Research , Ackermannweg 10 , 55128 Mainz , Germany
| | - Rüdiger Berger
- Max Planck Institute for Polymer Research , Ackermannweg 10 , 55128 Mainz , Germany
| | - Werner Steffen
- Max Planck Institute for Polymer Research , Ackermannweg 10 , 55128 Mainz , Germany
| | - Doris Vollmer
- Max Planck Institute for Polymer Research , Ackermannweg 10 , 55128 Mainz , Germany
| | - Stefan A L Weber
- Max Planck Institute for Polymer Research , Ackermannweg 10 , 55128 Mainz , Germany
- Department of Physics , Johannes Gutenberg University , Staudingerweg 10 , 55128 Mainz , Germany
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3
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Michalek L, Barner L, Barner-Kowollik C. Polymer on Top: Current Limits and Future Perspectives of Quantitatively Evaluating Surface Grafting. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2018; 30:e1706321. [PMID: 29512237 DOI: 10.1002/adma.201706321] [Citation(s) in RCA: 46] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/31/2017] [Revised: 12/01/2017] [Indexed: 05/15/2023]
Abstract
Well-defined polymer strands covalently tethered onto solid substrates determine the properties of the resulting functional interface. Herein, the current approaches to determine quantitative grafting densities are assessed. Based on a brief introduction into the key theories describing polymer brush regimes, a user's guide is provided to estimating maximum chain coverage and-importantly-examine the most frequently employed approaches for determining grafting densities, i.e., dry thickness measurements, gravimetric assessment, and swelling experiments. An estimation of the reliability of these determination methods is provided via carefully evaluating their assumptions and assessing the stability of the underpinning equations. A practical access guide for comparatively and quantitatively evaluating the reliability of a given approach is thus provided, enabling the field to critically judge experimentally determined grafting densities and to avoid the reporting of grafting densities that fall outside the physically realistic parameter space. The assessment is concluded with a perspective on the development of advanced approaches for determination of grafting density, in particular, on single-chain methodologies.
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Affiliation(s)
- Lukas Michalek
- School of Chemistry, Physics and Mechanical Engineering, Institute for Future Environments, Queensland University of Technology (QUT), 2 George Street, Brisbane, QLD, 4000, Australia
| | - Leonie Barner
- School of Chemistry, Physics and Mechanical Engineering, Institute for Future Environments, Queensland University of Technology (QUT), 2 George Street, Brisbane, QLD, 4000, Australia
- Institute for Biological Interfaces, Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, 76344, Eggenstein-Leopoldshafen, Germany
| | - Christopher Barner-Kowollik
- School of Chemistry, Physics and Mechanical Engineering, Institute for Future Environments, Queensland University of Technology (QUT), 2 George Street, Brisbane, QLD, 4000, Australia
- Macromolecular Architectures, Institut für Technische Chemie und Polymerchemie, Karlsruhe Institute of Technology (KIT), Engesserstr. 18, 76131, Karlsruhe, Germany
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4
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Chen C, Tang P, Qiu F. Binary hairy nanoparticles: Recent progress in theory and simulations. ACTA ACUST UNITED AC 2014. [DOI: 10.1002/polb.23528] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Affiliation(s)
- Cangyi Chen
- Department of Macromolecular Science; State Key Laboratory of Molecular Engineering of Polymers, Fudan University; Shanghai 200433 China
| | - Ping Tang
- Department of Macromolecular Science; State Key Laboratory of Molecular Engineering of Polymers, Fudan University; Shanghai 200433 China
| | - Feng Qiu
- Department of Macromolecular Science; State Key Laboratory of Molecular Engineering of Polymers, Fudan University; Shanghai 200433 China
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5
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Li W, Bao C, Wright RAE, Zhao B. Synthesis of mixed poly(ε-caprolactone)/polystyrene brushes from Y-initiator-functionalized silica particles by surface-initiated ring-opening polymerization and nitroxide-mediated radical polymerization. RSC Adv 2014. [DOI: 10.1039/c4ra02429j] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
This article reports the synthesis of mixed brushes by ring-opening polymerization of ε-caprolactone and nitroxide-mediated radical polymerization of styrene from Y-initiator-functionalized silica particles.
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Affiliation(s)
- Weikun Li
- Department of Chemistry
- University of Tennessee
- Knoxville, USA
| | - Chunhui Bao
- Department of Chemistry
- University of Tennessee
- Knoxville, USA
| | | | - Bin Zhao
- Department of Chemistry
- University of Tennessee
- Knoxville, USA
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6
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Wang ZL, Xu JT, Du BY, Fan ZQ. Preparation and characterization of V-shaped PS-b-PEO brushes anchored on planar gold substrate through the trithiocarbonate junction group. J Colloid Interface Sci 2012; 384:29-37. [DOI: 10.1016/j.jcis.2012.06.067] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2012] [Revised: 06/15/2012] [Accepted: 06/18/2012] [Indexed: 11/29/2022]
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7
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Bao C, Tang S, Horton JM, Jiang X, Tang P, Qiu F, Zhu L, Zhao B. Effect of Overall Grafting Density on Microphase Separation of Mixed Homopolymer Brushes Synthesized from Y-Initiator-Functionalized Silica Particles. Macromolecules 2012. [DOI: 10.1021/ma301300k] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Affiliation(s)
- Chunhui Bao
- Department of Chemistry, University of Tennessee, Knoxville, Tennessee 37996,
United States
| | - Saide Tang
- Department
of Macromolecular
Science and Engineering, Case Western Reserve University, Cleveland, Ohio 44106, United States
| | - Jonathan M. Horton
- Department of Chemistry, University of Tennessee, Knoxville, Tennessee 37996,
United States
| | - Xiaoming Jiang
- Department of Chemistry, University of Tennessee, Knoxville, Tennessee 37996,
United States
| | - Ping Tang
- Department of Macromolecular Science, Fudan University, Shanghai 200433, China
| | - Feng Qiu
- Department of Macromolecular Science, Fudan University, Shanghai 200433, China
| | - Lei Zhu
- Department
of Macromolecular
Science and Engineering, Case Western Reserve University, Cleveland, Ohio 44106, United States
| | - Bin Zhao
- Department of Chemistry, University of Tennessee, Knoxville, Tennessee 37996,
United States
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8
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Ionov L, Minko S. Mixed polymer brushes with locking switching. ACS APPLIED MATERIALS & INTERFACES 2012; 4:483-9. [PMID: 22220904 DOI: 10.1021/am201736t] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
Mixed polymer brushes, made of two different kinds of polymers randomly grafted to the same solid substrate, were introduced as switchable interfaces for a number of promising applications. The switching properties of the mixed polymer brushes are substantially dependent on grafting density, molecular weight, compatibility of two distinct grafted polymers, and their interaction with the solvent. This work reports the mixed polymer brushes with the property of locking switching. The wetting properties of such a mixed brush can be switched between the wetting properties of individual constituting polymers by appropriate selection of solvent. However, the mixed polymer brushes wetting behavior can be locked in the hydrophobic state. This kinetically frozen methastable state, however, can be unlocked via treatment by proper "unlocking" solvent. This locking and unlocking of the hydrophobic state of the mixed brush with specific solvents could find useful applications for the development of functional materials.
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Affiliation(s)
- Leonid Ionov
- Department of Chemistry and Biomolecular Science, Clarkson University, Potsdam, New York 13699, USA.
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9
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10
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Li A, Benetti EM, Tranchida D, Clasohm JN, Schönherr H, Spencer ND. Surface-Grafted, Covalently Cross-Linked Hydrogel Brushes with Tunable Interfacial and Bulk Properties. Macromolecules 2011. [DOI: 10.1021/ma2006443] [Citation(s) in RCA: 86] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Ang Li
- Laboratory for Surface Science and Technology, Department of Materials, ETH Zurich, Wolfgang-Pauli-Strasse 10, 8093 Zurich, Switzerland
| | - Edmondo M. Benetti
- Laboratory for Surface Science and Technology, Department of Materials, ETH Zurich, Wolfgang-Pauli-Strasse 10, 8093 Zurich, Switzerland
| | - Davide Tranchida
- Department of Physical Chemistry I, University of Siegen, Adolf-Reichwein-Strasse 2, 57076 Siegen, Germany
| | - Jarred N. Clasohm
- Laboratory for Surface Science and Technology, Department of Materials, ETH Zurich, Wolfgang-Pauli-Strasse 10, 8093 Zurich, Switzerland
| | - Holger Schönherr
- Department of Physical Chemistry I, University of Siegen, Adolf-Reichwein-Strasse 2, 57076 Siegen, Germany
| | - Nicholas D. Spencer
- Laboratory for Surface Science and Technology, Department of Materials, ETH Zurich, Wolfgang-Pauli-Strasse 10, 8093 Zurich, Switzerland
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11
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Zdyrko B, Luzinov I. Polymer Brushes by the “Grafting to” Method. Macromol Rapid Commun 2011; 32:859-69. [DOI: 10.1002/marc.201100162] [Citation(s) in RCA: 225] [Impact Index Per Article: 17.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2011] [Indexed: 11/08/2022]
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12
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Griffiths GH, Vorselaars B, Matsen MW. Unit-Cell Approximation for Diblock−Copolymer Brushes Grafted to Spherical Particles. Macromolecules 2011. [DOI: 10.1021/ma2003745] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- G. H. Griffiths
- School of Mathematical and Physical Sciences, University of Reading, Whiteknights, Reading, RG6 6AX, United Kingdom
| | - B. Vorselaars
- School of Mathematical and Physical Sciences, University of Reading, Whiteknights, Reading, RG6 6AX, United Kingdom
| | - M. W. Matsen
- School of Mathematical and Physical Sciences, University of Reading, Whiteknights, Reading, RG6 6AX, United Kingdom
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13
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Orski SV, Fries KH, Sontag SK, Locklin J. Fabrication of nanostructures using polymer brushes. ACTA ACUST UNITED AC 2011. [DOI: 10.1039/c1jm11039j] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
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14
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Jiang X, Zhao B, Zhong G, Jin N, Horton JM, Zhu L, Hafner RS, Lodge TP. Microphase Separation of High Grafting Density Asymmetric Mixed Homopolymer Brushes on Silica Particles. Macromolecules 2010. [DOI: 10.1021/ma101518a] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Affiliation(s)
- Xiaoming Jiang
- Department of Chemistry, University of Tennessee, Knoxville, Tennessee 37996
| | - Bin Zhao
- Department of Chemistry, University of Tennessee, Knoxville, Tennessee 37996
| | - Ganji Zhong
- Department of Macromolecular Science and Engineering, Case Western Reserve University, Cleveland, Ohio 44106
- College of Polymer Science and Engineering, Sichuan University, Chengdu 610065, People’s Republic of China
| | - Naixiong Jin
- Department of Chemistry, University of Tennessee, Knoxville, Tennessee 37996
| | - Jonathan M. Horton
- Department of Chemistry, University of Tennessee, Knoxville, Tennessee 37996
| | - Lei Zhu
- Department of Macromolecular Science and Engineering, Case Western Reserve University, Cleveland, Ohio 44106
| | - Robert S. Hafner
- The Characterization Facility of the College of Science and Engineering, University of Minnesota, Minneapolis, Minnesota 55455
| | - Timothy P. Lodge
- Department of Chemistry, University of Minnesota, Minneapolis, Minnesota 55455
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15
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Jiang X, Zhong G, Horton JM, Jin N, Zhu L, Zhao B. Evolution of Phase Morphology of Mixed Poly(tert-butyl acrylate)/Polystyrene Brushes Grafted on Silica Particles with the Change of Chain Length Disparity. Macromolecules 2010. [DOI: 10.1021/ma100716n] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Affiliation(s)
- Xiaoming Jiang
- Department of Chemistry, University
of Tennessee, Knoxville, Tennessee 37996
| | - Ganji Zhong
- Department of Macromolecular Science and Engineering, Case Western Reserve University, Cleveland, Ohio 44106
- College of Polymer Science and Engineering, Sichuan University, Chengdu 610065, People’s Republic of China
| | - Jonathan M. Horton
- Department of Chemistry, University
of Tennessee, Knoxville, Tennessee 37996
| | - Naixiong Jin
- Department of Chemistry, University
of Tennessee, Knoxville, Tennessee 37996
| | - Lei Zhu
- Department of Macromolecular Science and Engineering, Case Western Reserve University, Cleveland, Ohio 44106
| | - Bin Zhao
- Department of Chemistry, University
of Tennessee, Knoxville, Tennessee 37996
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16
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Sui X, Zapotoczny S, Benetti EM, Schön P, Vancso GJ. Characterization and molecular engineering of surface-grafted polymer brushes across the length scales by atomic force microscopy. ACTA ACUST UNITED AC 2010. [DOI: 10.1039/b924392e] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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17
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CHARACTERIZATION OF FERROELELECTRIC ULTRATHIN FILMS FABRICATED BY ELECTROSTATIC SELF-ASSEMBLY. ACTA POLYM SIN 2009. [DOI: 10.3724/sp.j.1105.2009.01091] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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18
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Zhao B, Zhu L. Mixed Polymer Brush-Grafted Particles: A New Class of Environmentally Responsive Nanostructured Materials. Macromolecules 2009. [DOI: 10.1021/ma902042x] [Citation(s) in RCA: 181] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Affiliation(s)
- Bin Zhao
- Department of Chemistry, University of Tennessee, Knoxville, Tennessee 37996
| | - Lei Zhu
- Department of Macromolecular Science and Engineering, Case Western Reserve University, Cleveland, Ohio 44106
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19
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Vyas MK, Nandan B, Schneider K, Stamm M. Nanowear studies in chemically heterogeneous responsive polymeric brushes by surface force microscopy. Eur Polym J 2009. [DOI: 10.1016/j.eurpolymj.2009.01.034] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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20
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Vyas MK, Nandan B, Schneider K, Stamm M. Nanowear studies in reversibly switchable polystyrene–poly(acrylic acid) mixed brushes. J Colloid Interface Sci 2008; 328:58-66. [DOI: 10.1016/j.jcis.2008.09.009] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2008] [Revised: 08/11/2008] [Accepted: 09/01/2008] [Indexed: 11/17/2022]
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21
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Zhu L, Zhao B. Transmission Electron Microscopy Study of Solvent-Induced Phase Morphologies of Environmentally Responsive Mixed Homopolymer Brushes on Silica Particles. J Phys Chem B 2008; 112:11529-36. [DOI: 10.1021/jp8048026] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Lei Zhu
- Polymer Program, Institute of Materials Science and Department of Chemical, Materials and Biomolecular Engineering, University of Connecticut, Storrs, Connecticut 06269 and Department of Chemistry, University of Tennessee, Knoxville, Tennessee 37996
| | - Bin Zhao
- Polymer Program, Institute of Materials Science and Department of Chemical, Materials and Biomolecular Engineering, University of Connecticut, Storrs, Connecticut 06269 and Department of Chemistry, University of Tennessee, Knoxville, Tennessee 37996
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22
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Kumar Vyas M, Schneider K, Nandan B, Stamm M. Switching of friction by binary polymer brushes. SOFT MATTER 2008; 4:1024-1032. [PMID: 32907135 DOI: 10.1039/b801110a] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Surface force studies on polystyrene-poly(2-vinylpyridine) (1 : 1) mixed polymer brushes and corresponding monobrushes were carried out in dried state under a controlled environment. The aim was to explore possibilities to control adhesion and friction between inorganic or polymeric surfaces by use of polymer brushes. The effect of switching of chemical composition of binary brush surfaces (on treatment with suitable solvents) on wettability, surface roughness, and hence the adhesion and friction properties of the surfaces were determined. Atomic force microscopy (AFM) with silicon tips, silicon nitride tips, and colloidal probes with silica particles were employed to investigate the interactions between inorganic surfaces and polymer brushes. To study the interactions between different polymer brush surfaces colloidal probes were covered with polystyrene and poly(acrylic acid) brushes on the surface. For all the dry polymer brushes samples, surface roughness values were in the range of 0.35-1.0 nm only. Adhesion and friction forces of polymer brush samples were reduced in comparison to the silicon wafer and were correlated with each other (except for the silicon tip). Switching in adhesion and friction forces up to a factor of 4.5 was possible by switching of the conformation of mixed brushes on treatment with selective solvents. The friction force on a PS + P2VP gradient polymer brush layer varied laterally and increased with increase in the P2VP content. Friction depends on wettability, scan velocity of the AFM tip, grafting density, and composition gradient of polymer brushes. Moreover, for PS and P2VP monobrushes, friction forces were shown to increase with increasing grafting density. Polymer brush layers thus may be used to control the adhesion and friction behavior of solid surfaces in different ways.
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Affiliation(s)
- Mukesh Kumar Vyas
- Leibniz Institute of Polymer Research Dresden, Hohe Strasse 6, 01069 Dresden, Germany.
| | - Konrad Schneider
- Leibniz Institute of Polymer Research Dresden, Hohe Strasse 6, 01069 Dresden, Germany.
| | - Bhanu Nandan
- Leibniz Institute of Polymer Research Dresden, Hohe Strasse 6, 01069 Dresden, Germany.
| | - Manfred Stamm
- Leibniz Institute of Polymer Research Dresden, Hohe Strasse 6, 01069 Dresden, Germany.
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23
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Luzinov I, Minko S, Tsukruk VV. Responsive brush layers: from tailored gradients to reversibly assembled nanoparticles. SOFT MATTER 2008; 4:714-725. [PMID: 32907173 DOI: 10.1039/b718999k] [Citation(s) in RCA: 163] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
We present a condensed overview of the recent developments of novel responsive thin polymer films from end-tethered chains (polymer brushes), which are different from conventional, uniform, and planar brush layers. For this discussion, we selected two types of recently introduced surface layers: binary brush layers with variable chemical composition forming a controllable gradient of composition and properties in a selected direction and brush layers either grafted directly to inorganic nanoparticles to form hybrid core-shell structures or combined with inorganic nanoparticles embedded into this layer. Unlike traditional brush layers, such a design brings a novel set of responsive surface properties allowing for capillary-driven microfluidic motion, combinatorial-like multiplexing response, reversible aggregation and dis-assembly of nanoparticles, fabrication of ultrahydrophobic coatings, and switchable mass transport across interfaces.
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Affiliation(s)
- Igor Luzinov
- School of Materials Science and Engineering and Center for Optical Materials Science and Engineering Technologies, Clemson University, Clemson, SC 29634, USA.
| | - Sergiy Minko
- Department of Chemistry and Biomolecular Science, Clarkson University, Potsdam, NY 13699, USA.
| | - Vladimir V Tsukruk
- School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA.
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24
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Limpoco FT, Advincula RC, Perry SS. Solvent dependent friction force response of polystyrene brushes prepared by surface initiated polymerization. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2007; 23:12196-12201. [PMID: 17949015 DOI: 10.1021/la701272a] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
Polystyrene (PS) brushes were prepared on oxide passivated silicon by the surface initiated polymerization (SIP) technique. From an AIBN-type free radical initiator, which was silanized and immobilized on silicon wafers, styrene brushes were directly polymerized and grafted from the surface. The formation of the initiator monolayer and, subsequently, the polymer brush on the surface were monitored by X-ray photoelectron spectroscopy (XPS) and ellipsometry. Friction force measurements were performed by atomic force microscopy (AFM), using a 5 microm SiO2 colloidal sphere tip and under systematically varied solvent environments (nonpolar to polar), to demonstrate the dependence of brush lubricity on solvation. The relative uptake of solvents in the PS brush was determined by quartz crystal microbalance (QCM), and it correlates well with friction data. It is surmised that, in poor solvent environments, the polymer brush exists in a collapsed conformation, giving rise to the higher observed friction response.
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Affiliation(s)
- F T Limpoco
- Department of Chemistry, University of Florida, Gainesville, FL 32611-7200, USA
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25
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Liberelle B, Giasson S. Chemical end-grafting of homogeneous polystyrene monolayers on mica and silica surfaces. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2007; 23:9263-70. [PMID: 17663570 DOI: 10.1021/la700478r] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/16/2023]
Abstract
Homogeneous polystyrene monolayers covalently end-attached on mica and silica surfaces were obtained using a "graft to" methodology. The grafting was achieved via nucleophilic substitution between silanol groups (Si-OH) containing surface and monochlorosilyl terminated polystyrene (PS). Different parameters, such as surface activation, grafting reaction time, polymer concentration, nature of solvent, and presence of catalyst, were investigated to determine the optimal conditions for creating very homogeneous and stable polymer monolayers. Ellipsometry, atomic force microscopy (AFM), surface forces apparatus (SFA), and contact angle measurements were used to characterize the polymer-grafted layers. An efficient plasma activation procedure was established to create a maximum number of silanol groups on mica surfaces without increasing the surface roughness. Surface reactivity was investigated by grafting trimethylchlorosilane (TMS) on OH-activated mica and silica. The maximum TMS surface coverage on activated mica is similar to that observed for silica. The stability of covalently attached TMS and PS layers in toluene and water were investigated. Both grafted layers (TMS and PS) partially detached from the mica and silica surfaces when immersed in water. Hydrolysis of the siloxane bond between the monochlorosilyl groups and the surface is the most probable cause of layer degrafting. The degrafting was much slower with the long PS polymer chains, compared to the small TMS molecules, which may act as a protective layer against hydrolysis.
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Affiliation(s)
- Benoît Liberelle
- Department of Chemistry, Université de Montréal, C.P. 6128, succursale Centre-ville, Montréal, Québec, Canada
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26
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Yin Y, Sun P, Li B, Chen T, Jin Q, Ding D, Shi AC. A Simulated Annealing Study of Diblock Copolymer Brushes in Selective Solvents. Macromolecules 2007. [DOI: 10.1021/ma070393n] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Yuhua Yin
- College of Physics, and the Key Laboratory of Functional Polymer Materials, Ministry of Education, and College of Chemistry, Nankai University, Tianjin, 300071, People's Republic of China, and Department of Physics and Astronomy, McMaster University, Hamilton, Ontario L8S 4M1, Canada
| | - Pingchuan Sun
- College of Physics, and the Key Laboratory of Functional Polymer Materials, Ministry of Education, and College of Chemistry, Nankai University, Tianjin, 300071, People's Republic of China, and Department of Physics and Astronomy, McMaster University, Hamilton, Ontario L8S 4M1, Canada
| | - Baohui Li
- College of Physics, and the Key Laboratory of Functional Polymer Materials, Ministry of Education, and College of Chemistry, Nankai University, Tianjin, 300071, People's Republic of China, and Department of Physics and Astronomy, McMaster University, Hamilton, Ontario L8S 4M1, Canada
| | - Tiehong Chen
- College of Physics, and the Key Laboratory of Functional Polymer Materials, Ministry of Education, and College of Chemistry, Nankai University, Tianjin, 300071, People's Republic of China, and Department of Physics and Astronomy, McMaster University, Hamilton, Ontario L8S 4M1, Canada
| | - Qinghua Jin
- College of Physics, and the Key Laboratory of Functional Polymer Materials, Ministry of Education, and College of Chemistry, Nankai University, Tianjin, 300071, People's Republic of China, and Department of Physics and Astronomy, McMaster University, Hamilton, Ontario L8S 4M1, Canada
| | - Datong Ding
- College of Physics, and the Key Laboratory of Functional Polymer Materials, Ministry of Education, and College of Chemistry, Nankai University, Tianjin, 300071, People's Republic of China, and Department of Physics and Astronomy, McMaster University, Hamilton, Ontario L8S 4M1, Canada
| | - An-Chang Shi
- College of Physics, and the Key Laboratory of Functional Polymer Materials, Ministry of Education, and College of Chemistry, Nankai University, Tianjin, 300071, People's Republic of China, and Department of Physics and Astronomy, McMaster University, Hamilton, Ontario L8S 4M1, Canada
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27
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Peleshanko S, Anderson KD, Goodman M, Determan MD, Mallapragada SK, Tsukruk VV. Thermoresponsive reversible behavior of multistimuli pluronic-based pentablock copolymer at the air-water interface. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2007; 23:25-30. [PMID: 17190480 DOI: 10.1021/la061547f] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
Surface behavior of the pH- and thermoresponsive amphiphilic ABCBA pentablock copolymer has been studied with respect to the environmental conditions. We demonstrate that the pentablock copolymer poly((diethylaminoethyl methacrylate)-b-(ethylene oxide)-b-(propylene oxide)-b-(ethylene oxide)-b-(diethylaminoethyl methacrylate)) possesses reversible temperature changes at the air-water interface in a narrow pH range of the water subphase. Significant diversity in the surface morphology of pentablock copolymer monolayers at different pH and temperatures observed were related to the corresponding reorganization of central and terminal blocks. Remarkable reversible variations of the surface pressure observed for the Langmuir monolayers at pH 7.4 in the course of heating and cooling between 27 and 50 degrees C is associated with conformational transformations of terminal blocks crossing the phase line in the vicinity of the lower critical solution temperature point. The observed thermoresponsive surface behavior can be exploited for modeling of the corresponding behavior of pentablock copolymers adsorbed onto various biointerfaces for intracellular delivery for deeper understanding of stimuli-responsive transformations relevant to controlled drug and biomolecules release and retention.
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Affiliation(s)
- Sergiy Peleshanko
- Department of Materials Science and Engineering, Iowa State University, Ames, Iowa 50011, USA
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28
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LeMieux MC, Peleshanko S, Anderson KD, Tsukruk VV. Adaptive nanomechanical response of stratified polymer brush structures. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2007; 23:265-73. [PMID: 17190513 DOI: 10.1021/la061723k] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
We have fabricated a stratified polymer surface film with tunable thickness (within 17-34 nm) through facile, room-temperature, UV-initiated polymerization with a temperature-sensitive pNIPAAM layer confined beneath a hydrophobic layer. AFM morphology and ellipsometric measurements were measured at each grafting step, along with XPS measurements of the overall layer to verify layer growth. The strong characteristic LCST behavior of pNIPAAM was observed in water, with a 100% change in thickness above and below this transition. The AFM nanomechanical results demonstrate vertical gradients of the elastic response tunable to a desired state by the external temperature. These temperature-sensitive, adaptive polymer structures with the pNIPAAM layer "hidden" beneath the rubbery, hydrophobic PBA topmost layer represent an interesting example of nanoengineering surfaces with properties such as adhesion, elastic modulus, and multi-level structural reorganization responsive to fluidic and temperature variations that can be important for biological purposes such as implant coatings, cell-surface mimicry, and drug delivery vehicles.
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Affiliation(s)
- M C LeMieux
- Department of Materials Science and Engineering, Iowa State University, Ames, Iowa 50011, USA
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29
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Santer S, Kopyshev A, Donges J, Rühe J, Jiang X, Zhao B, Müller M. Memory of surface patterns in mixed polymer brushes: simulation and experiment. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2007; 23:279-85. [PMID: 17190515 DOI: 10.1021/la0629577] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
The correlation between the morphology of mixed polymer brushes and fluctuations of the grafting points is investigated by single-chain-in-mean-field simulations and experiments. The local topography of two types of mixed polystyrene-polymethylmethacrylate (PS-PMMA) brushes that differ in their modes of attachment has been studied during repeated microphase separation into laterally structured and homogeneous morphologies upon changing solvents. In the first type of brush (conventional), each of the surface-attached initiator groups starts the growth of either a PS or a PMMA chain in a random fashion. In the second case (Y-shaped mixed brushes), two chains of different types are attached to the same anchor group on the substrate. Whereas in the first case statistical fluctuations of the chemical composition occur on a local scale, such composition fluctuations are strongly suppressed in the latter case. The microphase-separated morphology is similar in both cases, but Y-shaped brushes exhibit a significantly weaker domain memory than do conventional PS-PMMA mixed brushes. The results of the experiment are compared with simulations, and a simple phenomenological argument and qualitative agreement are found. The observations demonstrate that small fluctuations in the grafting points are amplified by the microphase separation and nucleate the location of the domains in the mixed brush.
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Affiliation(s)
- Svetlana Santer
- Department of Microsystems Engineering (IMTEK), University of Freiburg, Georges-Koehler-Allee 103, D-79110 Freiburg, Germany.
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30
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Cuenot S, Gabriel S, Jérôme R, Jérôme C, Fustin CA, Jonas AM, Duwez AS. First Insights into Electrografted Polymers by AFM-Based Force Spectroscopy. Macromolecules 2006. [DOI: 10.1021/ma060824m] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Stéphane Cuenot
- Unité POLY and CeRMiN, Université catholique de Louvain, Place Croix du Sud 1, B-1348 Louvain-la-Neuve, Belgium; CERM, Université de Liège, B6 Sart-Tilman, B-4000 Liège, Belgium; and Unité CMAT and CeRMiN, Université catholique de Louvain, Place L. Pasteur 1, B-1348 Louvain-la-Neuve, Belgium
| | - Sabine Gabriel
- Unité POLY and CeRMiN, Université catholique de Louvain, Place Croix du Sud 1, B-1348 Louvain-la-Neuve, Belgium; CERM, Université de Liège, B6 Sart-Tilman, B-4000 Liège, Belgium; and Unité CMAT and CeRMiN, Université catholique de Louvain, Place L. Pasteur 1, B-1348 Louvain-la-Neuve, Belgium
| | - Robert Jérôme
- Unité POLY and CeRMiN, Université catholique de Louvain, Place Croix du Sud 1, B-1348 Louvain-la-Neuve, Belgium; CERM, Université de Liège, B6 Sart-Tilman, B-4000 Liège, Belgium; and Unité CMAT and CeRMiN, Université catholique de Louvain, Place L. Pasteur 1, B-1348 Louvain-la-Neuve, Belgium
| | - Christine Jérôme
- Unité POLY and CeRMiN, Université catholique de Louvain, Place Croix du Sud 1, B-1348 Louvain-la-Neuve, Belgium; CERM, Université de Liège, B6 Sart-Tilman, B-4000 Liège, Belgium; and Unité CMAT and CeRMiN, Université catholique de Louvain, Place L. Pasteur 1, B-1348 Louvain-la-Neuve, Belgium
| | - Charles-André Fustin
- Unité POLY and CeRMiN, Université catholique de Louvain, Place Croix du Sud 1, B-1348 Louvain-la-Neuve, Belgium; CERM, Université de Liège, B6 Sart-Tilman, B-4000 Liège, Belgium; and Unité CMAT and CeRMiN, Université catholique de Louvain, Place L. Pasteur 1, B-1348 Louvain-la-Neuve, Belgium
| | - Alain M. Jonas
- Unité POLY and CeRMiN, Université catholique de Louvain, Place Croix du Sud 1, B-1348 Louvain-la-Neuve, Belgium; CERM, Université de Liège, B6 Sart-Tilman, B-4000 Liège, Belgium; and Unité CMAT and CeRMiN, Université catholique de Louvain, Place L. Pasteur 1, B-1348 Louvain-la-Neuve, Belgium
| | - Anne-Sophie Duwez
- Unité POLY and CeRMiN, Université catholique de Louvain, Place Croix du Sud 1, B-1348 Louvain-la-Neuve, Belgium; CERM, Université de Liège, B6 Sart-Tilman, B-4000 Liège, Belgium; and Unité CMAT and CeRMiN, Université catholique de Louvain, Place L. Pasteur 1, B-1348 Louvain-la-Neuve, Belgium
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31
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Roan JR. Soft nanopolyhedra as a route to multivalent nanoparticles. PHYSICAL REVIEW LETTERS 2006; 96:248301. [PMID: 16907284 DOI: 10.1103/physrevlett.96.248301] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/09/2006] [Indexed: 05/11/2023]
Abstract
Computer simulations show that end-grafted immiscible homopolymers can confer multivalence to nanoparticles, resulting in soft nanopolyhedra with structures identical to those found in small clusters of colloidal microspheres. Unprecedented structure tunability is demonstrated by several structure transition sequences, including a reentrant transition, induced by varying composition, polymer lengths, or grafting patterns. These results suggest a new method for fabricating nanoparticles with precisely controlled numbers and locations of functional sites (i.e., multivalent nanoparticles).
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Affiliation(s)
- Jiunn-Ren Roan
- Department of Physics, National Chung Hsing University, 250 Kuo-Kuang Road, Taichung 40227, Taiwan
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32
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Santer S, Kopyshev A, Donges J, Yang HK, Rühe J. Domain memory of mixed polymer brushes. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2006; 22:4660-7. [PMID: 16649779 DOI: 10.1021/la060134b] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
The nano-phase-separation in mixed polymer brushes consisting of polystyrene and poly(methyl methacrylate) (PS-PMMA) chains attached to a silicon surface is studied. The topographies of the mixed brushes are examined after they have been exposed to solvents which induce or erase nano-phase-separation. It is discussed whether the brush locally forms the same pattern every time the transition from the smooth and featureless to the nanopatterned state occurs ("domain memory") or if the local assembly of the domains emerges in a different arrangement after each cycle of topography switching. A memory measure parameter is introduced, which characterizes quantitatively the domain memory effect in the nanopattern. It is shown that at constant grafting density but with increasing molecular weight of the brush chains the memory measure parameter decreases. In contrast to this, brushes with constant molecular weight, but differing in grafting density, all have a similar domain memory. We discuss a possible origin of the domain memory effect in the mixed brush systems studied and point out its impact on the motion of nanoparticles adsorbed on top of such systems.
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Affiliation(s)
- Svetlana Santer
- Department of Microsystems Engineering (IMTEK), University of Freiburg, Georges-Koehler-Allee 103, D-79110 Freiburg, Germany.
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33
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Santer S, Kopyshev A, Yang HK, Rühe J. Local Composition of Nanophase-Separated Mixed Polymer Brushes. Macromolecules 2006. [DOI: 10.1021/ma060092y] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Svetlana Santer
- Department of Microsystems Engineering (IMTEK), University of Freiburg, Georges-Koehler-Allee 103, D-79110 Freiburg, Germany
| | - Alexey Kopyshev
- Department of Microsystems Engineering (IMTEK), University of Freiburg, Georges-Koehler-Allee 103, D-79110 Freiburg, Germany
| | - Hyun-Kwan Yang
- Department of Microsystems Engineering (IMTEK), University of Freiburg, Georges-Koehler-Allee 103, D-79110 Freiburg, Germany
| | - Jürgen Rühe
- Department of Microsystems Engineering (IMTEK), University of Freiburg, Georges-Koehler-Allee 103, D-79110 Freiburg, Germany
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34
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Ye M, Zhang D, Han L, Tejada J, Ortiz C. Synthesis, preparation, and conformation of stimulus-responsive end-grafted poly(methacrylic acid-g-ethylene glycol) layers. SOFT MATTER 2006; 2:243-256. [PMID: 32646151 DOI: 10.1039/b510894b] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Here we report the formation of stimulus-responsive chemically end-grafted "brush-brushes" by synthesizing, mono thiol(end)-functionalized poly(methacrylic acid--ethylene glycol) or poly(MAA--EG) comb-type graft copolymers a combination of protecting group chemistry and atom transfer radical polymerization using the initiator 2-(2,4-dinitrophenylthio)ethyl 2-bromo-2-methyl propionate. The polymers were synthesized with three different molecular weights (15 k, 17 k and 27 k), PEG side chain graft densities (EG/MAA mole ratio = 2.2, 0.4 and 1.9, respectively), and a PEG molecular weight = 1100 and then chemically end-grafted to gold substrates chemisorption, resulting in molecular separation distances of ∼3-4 nm. pH-Dependent swelling was confirmed to take place gradually above pH 4-5 and quantified by heights measured by contact mode AFM imaging of microcontact printed (µCP) samples. Swelling factors (maximum height/minimum height) were fairly large (3.6-7.3) and a decrease in molecular weight by ∼2× and side chain graft density by ∼4× resulted in a decrease in swelling factor by ∼2×. Layer height normal force for all three polymers measured by contact mode atomic force microscope imaging on µCP samples at pH 9 showed a nonlinearly decreasing relationship and complete compression ∼<2 nm for forces >10 nN. At pH 4, all polymer layers were largely collapsed (heights ∼<4 nm) and incompressible (, heights were independent of normal force).
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Affiliation(s)
- Miao Ye
- Department of Materials Science and Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA.
| | - Dong Zhang
- Department of Materials Science and Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA.
| | - Lin Han
- Department of Materials Science and Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA.
| | - Jonathon Tejada
- Department of Materials Science and Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA.
| | - Christine Ortiz
- Department of Materials Science and Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA.
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35
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Li D, Sheng X, Zhao B. Environmentally Responsive “Hairy” Nanoparticles: Mixed Homopolymer Brushes on Silica Nanoparticles Synthesized by Living Radical Polymerization Techniques. J Am Chem Soc 2005; 127:6248-56. [PMID: 15853330 DOI: 10.1021/ja0422561] [Citation(s) in RCA: 265] [Impact Index Per Article: 13.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
This article reports on the preparation of environmentally responsive "hairy" nanoparticles by growth of mixed poly(tert-butyl acrylate) (PtBA)/polystyrene (PS) brushes from silica particles using living radical polymerization techniques and subsequent hydrolysis of PtBA to produce amphiphilic mixed poly(acrylic acid) (PAA)/PS brushes. Silica particles were synthesized by the Stober process and were functionalized with an asymmetric difunctional initiator-terminated monolayer. Surface-initiated atom transfer radical polymerization of tBA was carried out in the presence of a free initiator. Kinetics study showed that the polymerization was well controlled. By cleaving PtBA off the particles, the molecular weights of the grafted and free polymers were found to be essentially identical. Mixed PtBA/PS brushes were obtained by the nitroxide-mediated radical polymerization of styrene from PtBA particles. The M(n) of the grafted PS was found to be the same as that of the free PS formed in the solution from the free initiator. Amphiphilic mixed PAA/PS brush-coated nanoparticles were synthesized from mixed PtBA/PS particles by hydrolysis of PtBA with iodotrimethylsilane. Tyndall scattering experiments and (1)H NMR study showed that the mixed PAA/PS particles can be dispersed and form a stable suspension in CHCl(3), a selective solvent for PS, and also in CH(3)OH, a selective solvent for PAA, demonstrating the capability of these hairy nanoparticles to undergo chain reorganization in response to environmental changes.
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Affiliation(s)
- Dejin Li
- Department of Chemistry, University of Tennessee, Knoxville, Tennessee 37996, USA
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