Atom transfer radical polymerization.

Responsive polymer materials can adapt to surrounding environments, regulate transport of ions and molecules, change wettability and adhesion of different species on external stimuli, or convert chemical and biochemical signals into optical, electrical, thermal and mechanical signals, and vice versa. These materials are playing an increasingly important part in a diverse range of applications, such as drug delivery, diagnostics, tissue engineering and 'smart' optical systems, as well as biosensors, microelectromechanical systems, coatings and textiles. We review recent advances and challenges in the developments towards applications of stimuli-responsive polymeric materials that are self-assembled from nanostructured building blocks. We also provide a critical outline of emerging developments.

Emerging applications of stimuli-responsive polymer materials

Self-organization in many solution-processed, semiconducting conjugated polymers results in complex microstructures, in which ordered microcrystalline domains are embedded in an amorphous matrix1. This has important consequences for electrical properties of these materials: charge transport is usually limited by the most difficult hopping processes and is therefore dominated by the disordered matrix, resulting in low charge-carrier mobilities2 (⩽10-5 cm2 V-1 s-1). Here we use thin-film, field-effect transistor structures to probe the transport properties of the ordered microcrystalline domains in the conjugated polymer poly(3-hexylthiophene), P3HT. Self-organization in P3HT results in a lamella structure with two-dimensional conjugated sheets formed by interchain stacking. We find that, depending on processing conditions, the lamellae can adopt two different orientations—parallel and normal to the substrate—the mobilities of which differ by more than a factor of 100, and can reach values as high as 0.1 cm2 V-1 s-1 (refs 3, 4). Optical spectroscopy of the field-induced charge, combined with the mobility anisotropy, reveals the two-dimensional interchain character of the polaronic charge carriers, which exhibit lower relaxation energies than the corresponding radical cations on isolated one-dimensional chains. The possibility of achieving high mobilities via two-dimensional transport in self-organized conjugated lamellae is important for applications of polymer transistors in logic circuits5 and active-matrix displays4,6.

Two-dimensional charge transport in self-organized, high-mobility conjugated polymers

http://experimentationlab.berkeley.edu/sites/default/files/AFMImages/butt_AFM.pdf

Force measurements with the atomic force microscope: Technique, interpretation and applications

We discuss in this review how the roughness of a solid impacts its wettability. We see in particular that both the apparent contact angle and the contact angle hysteresis can be dramatically affected by the presence of roughness. Owing to the development of refined methods for setting very well-controlled micro- or nanotextures on a solid, these effects are being exploited to induce novel wetting properties, such as spontaneous filmification, superhydrophobicity, superoleophobicity, and interfacial slip, that could not be achieved without roughness.

Wetting and Roughness

We report on the radical-chain polymerization of styrene using self-assembled monolayers of azo initiators covalently bound to high surface area silica gels. In this process monolayers of poly(styrene) molecules terminally attached to the surface of the inorganic substrate are obtained. As the initiator molecules are immobilized at the surfaces in a one-step reaction, well-reproducible layers can be prepared and the surface concentration of the initiator can be adjusted in a wide range between the limit of detection and full surface coverage. In the subsequent polymerization reactions polymer monolayers with high, controlled graft density can be obtained. The synthesis of the attached layers and the characterization by X-ray photoelectron spectroscopy, diffuse reflectance infrared spectroscopy (DRIFT), and elemental analysis are described. After cleavage of an ester group that connects the polymers to the surface, the molecular weights of the polymers were determined. The results of the study show that th...

Synthesis of Poly(styrene) Monolayers Attached to High Surface Area Silica Gels through Self-Assembled Monolayers of Azo Initiators

Preface. List of Contributors. Polymer Brushes: On the Way to Tailor-Made Surfaces (Jurgen Ruhe). 1 Growth of Polymer Molecules at Surfaces: Introductory Remarks. 2 Coatings: From First Principles to High-Tech Applications. 3 Surface-Coating Techniques. 4 Surface-Attached Polymers. 5 Polymer Brushes: General Features. 6 Theory of Polymer Brushes. 7 Synthesis of Polymer Brushes. 8 Polymer Brushes as Functional Materials. 9 Microstructured Polymer Brushes. 10 Surface-Initiated Polymerization: The Overall Picture. Part I Synthesis. 1 Recent Advances in Polymer Brush Synthesis (Anthony M. Granville and William J. Brittain). 1.1 Introduction. 1.2 "Grafting To" Synthesis Technique. 1.3 "Grafting From" Synthesis Technique. 2 Polymer Brushes by Atom Transfer Radical Polymerization (Jeffrey Pyun, Tomasz Kowalewski, and Krzysztof Matyjaszewski). 2.1 Introduction. 2.2 Polymer Brushes on Flat Surfaces. 2.3 Polymer Brushes from Particles. 2.4 Molecular Brushes. 3 Polymer Brushes by Atom Transfer Radical Polymerization Initiated from Macroinitiator Synthesized on the Surface (Viktor Klep, Bogdan Zdyrko, Yong Liu, and Igor Luzinov). 3.1 Introduction. 3.2 Experimental. 3.3 Results and Discussion. 4 Synthesis of Polypeptide Brushes (Henning Menzel and Peter Witte). 4.1 Introduction. 4.2 Preparation of Peptide Brushes by "Grafting To". 4.3 Preparation of Peptide Brushes by Grafting From Polymerization. 4.4 Preparation of Peptide Brushes by Living Grafting From Polymerization. 5 Bottle Brush Brushes: Ring-Opening Polymerization of Lactide from Poly(hydroxyethyl methacrylate) Surfaces (Jong-Bum Kim, Wenxi Huang, Chun Wang, Merlin Bruening, and Gregory L. Baker). 5.1 Introduction. 5.2 Synthesis of PHEMA-g-PLA. 5.3 Conclusions and Implications for Future Studies. 5.4 Experimental Section. 6 Preparation of Well-Defined Organic-Inorganic Hybrid Nanostructures using Living Cationic Surface-Initiated Polymerization from Silica Nanoparticles (Il-Jin Kim, Su Chen, and Rudolf Faust). 6.1 Introduction. 6.2 Experimental Section. 6.3 Results and Discussion. 7 Photoinitiated Polymerization from Self-Assembled Monolayers (Daniel J. Dyer, Jianxin Feng, Charles Fivelson, Rituparna Paul, Rolf Schmidt, and Tongfeng Zhao). 7.1 Introduction. 7.2 Substrates. 7.3 Photoinitiated Radical Polymerization Mechanisms. 7.4 Polymerization from AIBN-type SAMs. 7.5 Conclusions and Future Studies. 7.6 Experimental. 8 Recent Advances in the Synthesis and Rearrangement of Block Copolymer Brushes (Stephen G. Boyes, Anthony M. Granville, Marina Baum, Bulent Akgun, Brian K. Mirous, and William J. Brittain). 8.1 Introduction and Background. 8.2 Controlled/"Living" Free Radical Polymerization. 8.3 Synthesis of Block Copolymer Brushes. 8.4 Rearrangement of Block Copolymer Brushes. 9 Surface-Grafted Hyperbranched Polymers (Hideharu Mori and Axel H. E. Muller). 9.1 Introduction. 9.2 "Grafting To" Approach. 9.3 Multi-Step Grafting Approach. 9.4 "Grafting From" Approach. Part II Characterization. 10 The Analysis and Characterization of Polymer Brushes: From Flat Surfaces to Nanoparticles (Rigoberto C. Advincula). 10.1 Introduction. 10.2 Characterization of Ultrathin Polymer Films and Polymer Brushes. 10.3 Investigating Polymer Brush Systems. 10.4 The Importance of Characterizing Particles and Nanoparticles. 10.5 Characterization and Analysis Methods for Polymer Brushes on Particles. 11 Characterization of Polymer Brushes on Nanoparticle Surfaces (Thomas A. P. Seery, Mark Jordi, Rosette Guino, and Dale Huber). 11.1 Introduction. 11.2 Experimental. 11.3 Results and Discussion. 12 Spherical Polyelectrolyte Brushes (Matthias Ballauff). 12.1 Introduction. 12.2 Synthesis and Characterization. 12.3 Experimental Verification of Theoretical Predictions. 12.4 Flow Behavior. 12.5 Applications. 13 Weak Polyelectrolyte Brushes: Complex Formation and Multilayer Build-up with Oppositely Charged Polyelectrolytes (Rupert Konradi, Haining Zhang, Markus Biesalski, and Jurgen Ruhe) 13.1 Introduction. 13.2 Synthesis and Data Evaluation. 13.3 Swelling Behavior of Weak Polyelectrolyte Brushes in Aqueous Environments. 13.4 Interaction Between Polyelectrolyte Brushes and Oppositely Charged Polyelectrolytes in Solution. 14 Structure and Properties of High-Density Polymer Brushes (Yoshinobu Tsujii, Muhammad Ejaz, Shinpei Yamamoto, Kohji Ohno, Kenji Urayama, and Takeshi Fukuda). 14.1 Introduction. 14.2 Controlled Synthesis of High-Density Polymer Brush by ATRP. 14.3 Structure and Properties of High-Density PMMA Brushes. 14.4 Application of High-Density Polymer Brushes. 15 Behavior of Surface-Anchored Poly(acrylic acid) Brushes with Grafting Density Gradients on Solid Substrates (Tao Wu, Jan Genzer, Peng Gong, Igal Szleifer, Petr Vlcek, and Vladimir Subr) Glossary. 15.1 Introduction. 15.2 Experimental Section. 15.3 Theory Section. 15.4 Experimental Results. 15.5 Discussion. 16 Kinetics of Polymer Brush Formation With and Without Segmental Adsorption (Lynn S. Penn, Heqing Huang, Roderic P. Quirk, and Tae H. Cheong). 16.1 Introduction. 16.2 Experimental. 16.3 Results and Discussion. Part III Applications. 17 Applications of Polymer Brushes and Other Surface-Attached Polymers (Kenneth C. Caster). 17.1 Introduction. 17.2 Surface Modification and Functionalization. 17.3 Applications. 17.4 Future Prospects. Appendix. 18 Polymer Brushes: Towards Applications (Gregory L. Whiting, Tamer Farhan, and Wilhelm T. S. Huck). 18.1 Introduction. 18.2 Experimental. 18.3 Results and Discussion. 19 Polymerization, Nanopatterning and Characterization of Surface-Confined, Stimulus-Responsive Polymer Brushes (Marian Kaholek, Woo-Kyung Lee, Bruce LaMattina, Kenneth C. Caster, and Stefan Zauscher). 19.1 Introduction. 19.2 Experimental. 19.3 Results and Discussion. 20 Mixed Polymer Brushes: Switching of Surface Behavior and Chemical Patterning at the Nanoscale (Sergiy Minko, Marcus Muller, Valeriy Luchnikov, Mikhail Motornov, Denys Usov, Leonid Ionov, and Manfred Stamm). 20.1 Introduction. 20.2 Theory of Mixed Polymer Brushes. 20.3 Synthesis of Mixed Brushes. 20.4 Experimental Study of Phase Segregation in Mixed Brushes. 20.5 Adaptive Responsive Behavior: Regulation of Wetting and Adhesion. 20.6 Patterning of Mixed Brushes. 21 Local Chain Organization of Switchable Binary Polymer Brushes in Selective Solvents (Melbs C. LeMieux, Denys Usov, Sergiy Minko, Manfred Stamm, and Vladimir V. Tsukruk). 21.1 Introduction. 21.2 Experimental. 21.3 Results and Discussion. 22 Motion of Nano-Objects Induced by a Switchable Polymer Carpet (Svetlana Prokhorova, Alexey Kopyshev, Ayothi Ramakrishnan, and Jurgen Ruhe). 22.1 Introduction. 22.2 Materials. 22.3 Results and Discussion. 23 Photochemical Strategies for the Preparation and Microstructuring of Densely Grafted Polymer Brushes on Planar Surfaces (Oswald Prucker, Rupert Konradi, Martin Schimmel, Jorg Habicht, In-Jun Park, and Jurgen Ruhe). 23.1 Introduction. 23.2 General Features of Surface-Initiated Polymerization from Monolayers of Azo Initiators. 23.3 Photolithographic Procedures for the Generation of Microstructured Polymer Brushes on Planar Surfaces. 23.4 Multifunctional Patterns. 23.5 Applications of Photostructured Polymer Brushes. Index.

Polymer brushes : synthesis, characterization, applications

The kinetics and mechanism of a radical chain polymerization reaction initiated from a self-assembled monolayer of an azo initiator attached to the surfaces of silica particles are investigated. The rate of the decomposition of the surface-attached initiator is followed by differential scanning calorimetry and volumetry. The kinetics of formation of the terminally attached polymer is studied by dilatometry. After polymerization the polymer is removed from the surfaces and the molecular weight averages and molecular weight distribution of the degrafted polymer are studied as a function of reaction parameters during polymerization. From the molecular weight, the mass of the attached polymer, and the specific surface area, the number of polymer molecules per area (or the distance between the anchoring sites) can be calculated and compared to the corresponding values of the initiator monolayers. The mechanism of a polymerization with surface-attached radicals is compared to that of conventional radical chain ...

Mechanism of Radical Chain Polymerizations Initiated by Azo Compounds Covalently Bound to the Surface of Spherical Particles

We report a simple and yet effective way to photochemically attach thin polymeric layers to solid surfaces. The system is based on a photoreactive benzophenone derivative that is bound to SiO2 surfaces via a silane anchor. This substrate is then covered with a polymer film that is reacted with the benzophenone moieties by illumination with UV light (λ > 340 nm). As a result of the photochemical reaction, a thin layer of the polymer is covalently bound to the surface. Nonattached polymer is removed by extraction. As examples, we have successfully attached thin layers of poly(styrene) and poly(ethyloxazoline). The thickness of the layer is a function of the illumination time and the molecular weight of the polymer. The film thickness increases linearly with the radius of gyration of the polymers used for attachment. Using this system, we were able to photochemically attach up to 16 nm thick films of poly(styrene).

Photochemical Attachment of Polymer Films to Solid Surfaces via Monolayers of Benzophenone Derivatives

Surface roughness has a profound influence on the wetting properties of a material. This fact is especially true with respect to the wetting of superhydrophobic surfaces. As a result of a special surface structure, a drop of water brought into contact with such a material forms an almost perfect sphere and even a very slight tilting of the superhydrophobic object is sufficient to cause the drop to roll off. For the description of the behavior of drops on rough surfaces two theories, namely those of Cassie and Wenzel, are often employed. However, it is currently becoming well established that both models explain the wetting behavior more from a qualitative or practical point of view rather than giving a quantitative description. For a prediction of actual contact angles, a more complex description is required that, next to thermodynamics, takes into account the kinetics of wetting. In this article, we focus on a few key aspects of superhydrophobic wetting, namely the characterization of superhydrophobic surfaces, models for the movement of drops, transitions between the Cassie and Wenzel states, and the behavior of superhydrophobic materials under condensation.

Jürgen Rühe

Papers

Synthesis of Poly(styrene) Monolayers Attached to High Surface Area Silica Gels through Self-Assembled Monolayers of Azo Initiators

Polymer brushes : synthesis, characterization, applications

Mechanism of Radical Chain Polymerizations Initiated by Azo Compounds Covalently Bound to the Surface of Spherical Particles

Photochemical Attachment of Polymer Films to Solid Surfaces via Monolayers of Benzophenone Derivatives

Some thoughts on superhydrophobic wetting