Tapered block polymers are an emerging class of macromolecules with unique and diverse self-assembly behavior and properties. Herein, we directly examine the manipulation of self-assembled interfaces in poly(isoprene-b-styrene) (I-S)-based block polymers (BPs) by synthesizing non-tapered (I-S), normal tapered (I-IS-S), and inverse tapered (I-SI-S) BPs with controlled monomer segment distributions. We provide the first direct measurements of interfacial mixing for these tapered polymers through X-ray reflectivity (XRR). The density profiles from XRR are compared to results from fluids density functional theory (fDFT) with good agreement. We find that our normal tapered BPs (30 vol % tapering) have similar interfacial mixing to diblock polymers, while our inverse tapered BPs (30 vol % tapering) have much wider interfaces. Additionally, differential scanning calorimetry (DSC) studies elucidate the influence of tapering on the glass transition temperature (T g) and change of heat capacity (ΔC P ) for each BP phase, and quantitative analysis from ΔC P also indicates enhanced mixing in the inverse tapered I-SI-S BPs. Finally, we investigate the free surface morphologies of these tapered polymers in thin film geometries. The inverse tapered BP form larger island/hole structures likely due to decreased surface elasticity from mixing as a result of the modified interblock interfacial characteristics. These results demonstrate that BPs with similar molecular weights and compositions can exhibit different thermodynamic properties and free surface morphologies in thin film geometries, as influenced by monomer sequence.
Block polymers (BPs) potentially can be used to template large arrays of nanopatterns for advanced nanotechnologies. However, the practical utilization of directed BP self-assembly typically requires guide patterns of relatively small size scales. In this work, the macroscopic alignment of block polymer cylinders on a template-free substrate is achieved through raster solvent vapor annealing combined with soft shear (RSVA-SS). Spatial control over nanoscale structures is realized by using a solvent vapor delivery nozzle, poly(dimethylsiloxane) shearing pad, and motorized stage. Complex patterns including dashes, crossed lines, and curves are demonstrated, along with the ability for large area alignment and scale-up for industry applications. The unique ability to directly write macroscopic patterns with microscopically aligned BP nanostructures will open new avenues of applied research in nanotechnology.T he macroscopic alignment of nanoscale periodic structures in block polymer (BP) thin films is attracting increased attention due to its necessity for unlocking various applications in materials chemistry and nanotechnology. 1−7 For example, spherical or cylindrical nanostructures formed by self-assembled BPs have been used successfully to pattern semiconductors, fabricate ultradense arrays of metal nanowires, and template magnetic storage media; 8−13 however, progress in the widespread adoption of BPs for these applications has been impeded by the lack of a versatile and efficient technique for inducing the long-range order and orientation of nanostructures in a predetermined direction. One major difficulty is that BPs tend to self-assemble in an isotropic manner in the absence of surface forces and external fields. 14−16 Thus, many techniques have been developed to guide BP self-assembly with varying degrees of success. Graphoepitaxy creates single-crystalline ordered structures, but the required substrate prepatterning can limit the size of the arrays that can be fabricated. 17,18 Additionally, valuable substrate area is lost due to patterning. Chemical prepatterning can direct BP alignment over large areas, but it requires substrate modification at the nanometer scale; this process can be prohibitively slow. 19,20 Electric fields, magnetic fields, and polarized light also have been explored but are limited to specialized polymer systems. 21−23 To address these above limitations, researchers are actively developing new and more universal methods to efficiently direct BP selfassembly on template-free substrates through cost-effective means.Shear fields are an established approach to align BPs in bulk 24,25 and have been employed to align single-layer BP thin films (∼30 nm) as demonstrated by Register and Chaikin. 26,27 In these works, shear stress was applied by the deformation and displacement of a cross-linked poly(dimethylsiloxane) (PDMS) pad placed on top of a cylinder-forming BP thin film, and the BP domain orientation was correlated strongly with the shear direction after thermal annealing under shear for...
Osteoblast-like and osteoclast-like cells freed from neonatal calvaria by sequential enzymatic digestion after 6-7 days in culture were placed in diffusion chambers and implanted in the peritoneal cavities of CD-1 mice. About half of the chambers also contained a dead calvarium to test for the need of an "inducer." After 20 days, 11 of 18 chambers containing to osteoblast-like cells formed large foci of mineralized bone that corresponded to alkaline phosphatase activity throughout the chambers. Moreover, only type I (i.e., bone) collagen was formed. Occasional deposits of bone were found in only 3 of 22 chambers containing the osteoclast-like cells. The presence of dead bone did not affect any of the results. These data confirm the osteoblast-like nature of the isolated cell populations and demonstrate that these cells retain their differentiated function in culture.
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