Precise control of the spatial organization of nanoscopic building blocks, such as nanoparticles, over multiple length scales is a bottleneck in the 'bottom-up' generation of technologically important materials. Only a few approaches have been shown to achieve nanoparticle assemblies without surface modification. We demonstrate a simple yet versatile approach to produce stimuli-responsive hierarchical assemblies of readily available nanoparticles by combining small molecules and block copolymers. Organization of nanoparticles into one-, two- and three-dimensional arrays with controlled inter-particle separation and ordering is achieved without chemical modification of either the nanoparticles or block copolymers. Nanocomposites responsive to heat and light are demonstrated, where the spatial distribution of the nanoparticles can be varied by exposure to heat or light or changing the local environment. The approach described is applicable to a wide range of nanoparticles and compatible with existing fabrication processes, thereby enabling a non-disruptive approach for the generation of functional devices.

The wetting transition from the Cassie-Baxter state to the Wenzel state on textured surfaces was investigated. Nano- to microscale hexagonal pillared lattices were prepared by nanoimprint lithography on fluorinated cycloolefin polymer substrates. The transition was clearly observed for water and some ionic liquids through contact angle measurements and optical microscopy. A simple model clearly demonstrated that the energy barrier in the wetting transition from the Cassie-Baxter state to the Wenzel state was dominated by the competition between the energy barrier and external forces, particularly the Laplace pressure in the present case.

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Lamella-, cylinder-, and sphere-forming block copolymers (BCPs) of polystyrene-b-polybutadiene (PS-b-PBD) were drawn into the pores of anodized aluminum oxide (AAO) membranes in the melt by capillary forces. After thermal annealing, the nanorods of the BCP were removed by dissolution of the AAO with a weak acid, and transmission electron microscopy (TEM) was used to investigate the resultant morphologies of the confined BCPs. The diameters of the pores in the AAO and the molecular weight of the block copolymers were varied to investigate the effect of confinement on the microphase separation of the BCP. Concentric cylinders were observed for the lamella-forming BCPs under 2D confinement, and deviations of the lamella repeat period were measured as a function of AAO pore diameter. In addition, torus-like morphologies were observed as the degree of confinement increased. For the bulk cylinder-forming BCPs, a rich variety of morphologies, not seen in the bulk, were observed that included stacked torus-like morphologies and single-, double-, and triple-helical morphologies The specific morphology depended on D/L 0, where D is the AAO pore diameter and L 0 is the period of the BCP in the bulk. D/L 0 was varied from 0.92 to 2.22. For bulk sphere-forming BCPs, core−shell cylindrical morphologies, single columns of spherical microdomains, and spirals of doubly and triply paired spherical microdomains were observed. Transmission electron microscopy was also performed in tomography mode (TEMT) to quantitatively determine a 3-D description of the morphologies. The morphologies found were consistent with recent simulations of confined BCPs.

In a block-selective solvent, the insoluble block or blocks of a block copolymer agglomerate to form nanometer-sized micelle-like aggregates, which are stabilized against further agglomeration by the soluble block(s). Depending on the composition of the copolymer, the interfacial tension between the solvent and the insoluble block(s), and other factors, the shape of the aggregates formed can be spherical, [1] vesicular, [2][3][4][5] tubular, [6][7][8] cylindrical, [9][10][11][12][13][14][15] etc. The shape diversity of such aggregates facilitates their applications in nanofabrication, lithography, cell culturing, and drug delivery.Most of the previous solution self-assembly studies of block copolymers were performed for AB diblock copolymers. The natural choices for solvents have been blockselective solvents, which solubilize one block of an AB diblock copolymer, but not the other. With ABC triblock copolymers, the solvent choice becomes much more interesting. Traditionally, solvents selective for one terminal block (A or C) or for two consecutive blocks (A and B or B and C) were used. [16,17] With rare exceptions, [13,14,[18][19][20][21][22] the use of such solvents led to core-shell-corona spherical or cylindrical aggregates. More recently, solvents selective for the A and C terminal blocks have been used, and the use of such solvents has led to aggregates with interesting coronal-chain segregation patterns. [8,23,24] We report in this paper the self-assembly of an ABC triblock copolymer in solvents that are good for C, poor for B, and marginal for A. We report also our surprising discovery that, after a long period of sample ageing, the selfassembled aggregates were double and sometimes triple helices. Even more surprising, such structures were formed in three different solvent systems that we have tested so far.The triblock copolymer used was poly(n-butyl methacrylate)-block-poly(2-cinnamoyloxyethyl methacrylate)-blockpoly(tert-butyl acrylate) or PBMA 350 -b-PCEMA 160 -bPtBA 160 consisting of 350 BMA units, 160 CEMA units, and 160 tBA units. The precursor to this polymer was prepared by anionic polymerization and had a low polydispersity index of 1.06 (see the Supporting Information).The marginal solvent mixtures were prepared from dichloromethane and methanol, tetrahydrofuran (C 4 OH with f M = 77 %, and CHCl 3 / CH 3 OH with f M = 83 % as the marginal mixtures for PBMA for the self-assembly of the triblock copolymer.Aggregate preparation was performed by first dissolving the polymer in CH 2 Cl 2 , C 4 H 8 O, or CHCl 3 and then adding CH 3 OH over a period of 1 min until the desired f M value was reached. At this stage, our transmission electron microscopy (TEM) analyses indicated that the triblock copolymer formed mostly spherical aggregates. Our NMR analysis suggested that the PtBA and PBMA chains were not segregated but were well mixed in the corona of the spherical aggregates (see the Supporting Information).Our suspicion was that the spherical aggregates were formed at f M % 50 %, when PCEMA first seg...

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This Perspective summarizes the recent advances and perspective in three-dimensional (3D) imaging techniques and their applications to polymer nanostructures, e.g., microphase-separated structures of block copolymers. We place particular emphasis on the method of transmission electron microtomography (TEMT). As a result of some recent developments in TEMT, it is now possible to obtain truly quantitative 3D images of polymer nanostructures with subnanometer resolution. The introduction of scanning optics in TEMT has made it possible to obtain large volumes of 3D data from a micrometer thick polymer specimens using conventional electron microscopes at relatively low acceleration voltage, 200 kV. Thus, TEMT covers structures over a wide range of thicknesses from a few nanometers to several hundred nanometers, which corresponds to quite an important spatial range for hierarchical polymer nanostructures. TEMT provides clear 3D images and a wide range of new structural information, which cannot be obtained using other methods, e.g., conventional microscopy or scattering methods, can be directly evaluated from the 3D volume data. In addition, when combined with other characterization methods, e.g., scattering and computer simulations, TEMT can yield even better results. The single chain conformation of block copolymers inside microdomains may be virtually visualized by TEMT. TEMT is a versatile technique that is not only restricted to polymer applications but can also be used as a powerful characterization tool in energy applications, e.g., fuel cells, etc.

Nanoparticles with concentric layered structures were generated from a lamellae-forming poly(styrene-b-isoprene) diblock copolymer using controlled precipitation from a tetrahydrofuran/water mixture. Chloroform, a good solvent for both blocks, was used to swell and anneal the nanoparticles suspended in aqueous media. The three-dimensional morphologies of particles were reconstructed by transmission electron microtomography throughout the process of solvent annealing. A transition from concentric lamellae to PI cylinders in a PS matrix occurred upon annealing, presumably due to a slight selectivity of chloroform for PS. These cylindrical microdomains were further divided into PS-core-PI-shell spherical structures in a PS matrix upon extended annealing, a structure that is unique among reported microphase separated morphologies of diblock copolymers.