The mixing of polymers and nanoparticles is opening pathways for engineering flexible composites that exhibit advantageous electrical, optical, or mechanical properties. Recent advances reveal routes to exploit both enthalpic and entropic interactions so as to direct the spatial distribution of nanoparticles and thereby control the macroscopic performance of the material. For example, by tailoring the particle coating and size, researchers have created self-healing materials for improved sustainability and self-corralling rods for photovoltaic applications. A challenge for future studies is to create hierarchically structured composites in which each sublayer contributes a distinct function to yield a mechanically integrated, multifunctional material.

http://science.sciencemag.org/content/sci/314/5802/1107.full.pdf

Nanoparticle Polymer Composites: Where Two Small Worlds Meet

This paper provides a third update to the review of reversible deactivation radical polymerization (RDRP) achieved with thiocarbonylthio compounds (ZC(=S)SR) by a mechanism of reversible addition-fragmentation chain transfer (RAFT) that was published in June 2005 (Aust. J. Chem. 2005, 58, 379). The first update was published in November 2006 (Aust. J. Chem. 2006, 59, 669) and the second in December 2009 (Aust. J. Chem. 2009, 62, 1402). This review cites over 700 publications that appeared during the period mid 2009 to early 2012 covering various aspects of RAFT polymerization which include reagent synthesis and properties, kinetics and mechanism of polymerization, novel polymer syntheses, and a diverse range of applications. This period has witnessed further significant developments, particularly in the areas of novel RAFT agents, techniques for end-group transformation, the production of micro/nanoparticles and modified surfaces, and biopolymer conjugates both for therapeutic and diagnostic applications.

/pdf/living-radical-polymerization-by-the-raft-process-a-second-3rre2ur7xt.pdf

Living Radical Polymerization by the RAFT Process - A Second Update

Janus particles: synthesis, self-assembly, physical properties, and applications.

Templated Techniques for the Synthesis and Assembly of Plasmonic Nanostructures

Directing the self-assembly of block copolymers

A simple procedure is described to incorporate gold nanoparticles and control their location within symmetric poly(styrene-b-2 vinyl pyridine) (PS-PVP) diblock copolymers. Gold nanoparticles coated with thiol-terminated PS and/or PVP homopolymer chains (Mn approximately 1300 and 1500 g/mol, respectively) are incorporated into alternating lamellar layers of PS and PVP (total Mn approximately 196 500 g/mol). The location of the particles is controlled by varying the composition of ligands on the particle surfaces. In particular, gold particles coated with 100% PS or PVP reside near the center of the respective polymer domains, while particles coated with a mixture of both homopolymers reside at the interfaces between the two blocks.

/pdf/control-of-nanoparticle-location-in-block-copolymers-5354hbe87y.pdf

Control of nanoparticle location in block copolymers.

Incorporation of nanoparticles into self-assembled block copolymers has been explored as an efficient way for improving the mechanical strength, electrical conductivity, and optical properties of materials at the nanometer scale. Recent computer simulations predict that the cooperative self-organization of nanoparticles and block copolymers should yield a wide variety of structures with well-controlled particle arrangements. Such nanostructures may make it possible to fabricate novel functional materials, such as photonic bandgap materials, nanostructured solar cells, highly efficient catalysts, and high-density magnetic storage media. In particular, gold nanoparticles have attracted much interest for applications as catalysts as well as building blocks for electronic devices that operate at the single-electron level. Over the years, several experimental methods have been developed for incorporating inorganic nanoparticles into polymeric nanostructures. These can be divided into two approaches. The first approach involves synthesizing nanoparticles in situ within preformed block-copolymer structures. Preformed micelles of block copolymers containing metal precursors are used as nanoreactors to synthesize nanoparticles selectively in block copolymers. For example, Boontongkong et al. produced micropatterned silver nanoparticles in a poly(styrene-b-acrylic acid) block-copolymer template using this approach. Such an approach is simple and can be easily extended to yield large-area samples. However, controlling the arrangement of the nanoparticles within the periodic structure of the block copolymer is difficult. A second approach, recently proposed as a way to avoid some of the drawbacks of the method described above, uses cooperative self-organization of nanoparticles and block copolymers. Based on theoretical predictions of the morphology of inorganic–organic hybrid materials by Balazs and coworkers, Bockstaller et al. demonstrated hierarchical pattern formation using block copolymers and binary mixtures of different sized hydrophobic nanoparticles. More recently, our previous work showed how grafting different polymers to particle surfaces can be used to precisely control the placement of particles either at the center of one of the block-copolymer domains or at the interface dividing the two block-copolymer domains. This approach exploits enthalpic interactions between the block copolymer and functionalized nanoparticle surfaces to achieve precise particle placement. Such precise control of nanoparticle position in block-copolymer thin films is important for developing highly organized hybrid materials. A particularly interesting example is the work of Russell and co-workers, who showed that the orientation of block-copolymer domains in thin films could be controlled by introducing surface-active nanoparticles that preferentially segregated to the surface of high-surface-energy domains. However, the introduction of particles into block copolymers can also have profound effects on the overall morphology of nanocomposites, especially if the particle loading is high. Nevertheless, the effect of high particle loading on the overall composite morphology has not been explored in previous experimental studies. In this communication, we report a nanoparticle-induced phase transition in a block-copolymer thin film as well as the formation of different structures of gold nanoparticles. When gold nanoparticles are coated with short polymer chains that are chemically identical to one of the copolymer blocks (in what follows we refer to such particles as simply Au particles, but it should be understood that in all cases they are coated with short polymer chains), the particles can self assemble near the center of that copolymer domain, as shown in Figure 1a. In this case, due to the coating of polystyrene (PS) chains on gold particles, the interaction between gold particles and one of the polymer blocks (PS) is neutral, but the interaction between the gold particles and the other block (P2 VP) is very unfavorable. In this report, we show that the lamellar morphology remains unchanged only if the gold nanoparticle volume fraction, cau, is below some critical value, cau,cr. For cau > cau,cr, the local concentration of gold nanoparticles varies along the thickness of the film, and different coexisting morphologies emerge as a function of sample depth. For these experiments, symmetric block copolymers of polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP) with total molecular masses, Mn, of 59 kg mol –1 and 114 kg mol were used. Gold nanoparticles with an average diameter of 2.5 nm were stabilized by short thiol end-functionalized PS chains (PS-SH; Mn = 1.3 kg mol ) that were grafted to the nanoparticle surfaces to make them compatible with the PS block and to prevent aggregation. The transmission electron microscopy (TEM) image in Figure 1a shows the cross-sectional morphology of the film for cau = 0.14 (< cau,cr) cast from toluene. The lamellae lie parallel to the film surface, as expected. Since the P2VP was preferentially stained by iodine vapor, it appears darker than the PS in C O M M U N IC A TI O N S

Nanoparticle‐Induced Phase Transitions in Diblock‐Copolymer Films

Weacknowledge the support of theUCSB
Materials Research Lab (NSF-DMR-MRSEC Grant DMR05-
20415). Useful discussions with Prof. Glenn H. Fredrickson and
Dr. Gila E. Stein are greatly appreciated. S.G.J. and S.-M.Y.
appreciate support from the National CRI Center for Integrated
Optofluidic Systems and the BK-21 Program.

Creating Surfactant Nanoparticles for Block Copolymer Composites through Surface Chemistry

Polystyrene-coated gold nanoparticles (molecular weight (Mn) of PS ∼1300 g/mol, average particle diameter d (core + shell) ∼ 9.2 ± 2.2 nm, corresponding to a high areal chain density of PS) are incorporated into symmetric poly(styrene-b-2 vinylpyridine) diblock copolymers with total Mn ∼ 60 000−380 000 g/mol at volume fractions of 0.07−0.32. For all Mn of diblock copolymers and particle filling fractions examined, particles are centralized in the PS domains with Gaussian distribution profiles. The distribution width generally decreases as the PS domain size decreases or as the particle weight fraction increases. These observations are discussed in terms of the relative entropic contributions of the polymer chains and particles.

http://physics.nyu.edu/pine/reprints/2007-05-01-Macromolecules-Chiu.pdf

Julia J. Chiu

Papers

Control of nanoparticle location in block copolymers.

Nanoparticle‐Induced Phase Transitions in Diblock‐Copolymer Films

Creating Surfactant Nanoparticles for Block Copolymer Composites through Surface Chemistry

Distribution of Nanoparticles in Lamellar Domains of Block Copolymers