@article{13395, abstract = {Metallic nanoparticles co-functionalised with monolayers of UV- and CO2-sensitive ligands were prepared and shown to respond to these two types of stimuli reversibly and in an orthogonal fashion. The composition of the coating could be tailored to yield nanoparticles capable of aggregating exclusively when both UV and CO2 were applied at the same time, analogously to the behaviour of an AND logic gate.}, author = {Lee, Ji-Woong and Klajn, Rafal}, issn = {1364-548X}, journal = {Chemical Communications}, keywords = {Materials Chemistry, Metals and Alloys, Surfaces, Coatings and Films, General Chemistry, Ceramics and Composites, Electronic, Optical and Magnetic Materials, Catalysis}, number = {11}, pages = {2036--2039}, publisher = {Royal Society of Chemistry}, title = {{Dual-responsive nanoparticles that aggregate under the simultaneous action of light and CO2}}, doi = {10.1039/c4cc08541h}, volume = {51}, year = {2015}, } @article{13396, abstract = {Photoswitching in densely packed azobenzene self-assembled monolayers (SAMs) is strongly affected by steric constraints and excitonic coupling between neighboring chromophores. Therefore, control of the chromophore density is essential for enhancing and manipulating the photoisomerization yield. We systematically compare two methods to achieve this goal: First, we assemble monocomponent azobenzene–alkanethiolate SAMs on gold nanoparticles of varying size. Second, we form mixed SAMs of azobenzene–alkanethiolates and “dummy” alkanethiolates on planar substrates. Both methods lead to a gradual decrease of the chromophore density and enable efficient photoswitching with low-power light sources. X-ray spectroscopy reveals that coadsorption from solution yields mixtures with tunable composition. The orientation of the chromophores with respect to the surface normal changes from a tilted to an upright position with increasing azobenzene density. For both systems, optical spectroscopy reveals a pronounced excitonic shift that increases with the chromophore density. In spite of exciting the optical transition of the monomer, the main spectral change in mixed SAMs occurs in the excitonic band. In addition, the photoisomerization yield decreases only slightly by increasing the azobenzene–alkanethiolate density, and we observed photoswitching even with minor dilutions. Unlike in solution, azobenzene in the planar SAM can be switched back almost completely by optical excitation from the cis to the original trans state within a short time scale. These observations indicate cooperativity in the photoswitching process of mixed SAMs.}, author = {Moldt, Thomas and Brete, Daniel and Przyrembel, Daniel and Das, Sanjib and Goldman, Joel R. and Kundu, Pintu K. and Gahl, Cornelius and Klajn, Rafal and Weinelt, Martin}, issn = {1520-5827}, journal = {Langmuir}, keywords = {Electrochemistry, Spectroscopy, Surfaces and Interfaces, Condensed Matter Physics, General Materials Science}, number = {3}, pages = {1048--1057}, publisher = {American Chemical Society}, title = {{Tailoring the properties of surface-immobilized azobenzenes by monolayer dilution and surface curvature}}, doi = {10.1021/la504291n}, volume = {31}, year = {2015}, } @article{13399, abstract = {Nature has long inspired scientists with its seemingly unlimited ability to harness solar energy and to utilize it to drive various physiological processes. With the help of man-made molecular photoswitches, we now have the potential to outperform natural systems in many ways, with the ultimate goal of fabricating multifunctional materials that operate at different light wavelengths. An important challenge in developing light-controlled artificial molecular machines lies in attaining a detailed understanding of the photoisomerization-coupled conformational changes that occur in macromolecules and molecular assemblies. In this issue of ACS Nano, Bléger, Rabe, and co-workers use force microscopy to provide interesting insights into the behavior of individual photoresponsive molecules and to identify contraction, extension, and crawling events accompanying light-induced isomerization.}, author = {Kundu, Pintu K. and Klajn, Rafal}, issn = {1936-086X}, journal = {ACS Nano}, keywords = {General Physics and Astronomy, General Engineering, General Materials Science}, number = {12}, pages = {11913--11916}, publisher = {American Chemical Society}, title = {{Watching single molecules move in response to light}}, doi = {10.1021/nn506656r}, volume = {8}, year = {2014}, } @article{13406, abstract = {Dual-responsive nanoparticles are designed by functionalizing magnetic cores with light-responsive ligands. These materials respond to both light and magnetic fields and can be assembled into various higher-order structures, depending on the relative contributions of these two stimuli.}, author = {Das, Sanjib and Ranjan, Priyadarshi and Maiti, Pradipta Sankar and Singh, Gurvinder and Leitus, Gregory and Klajn, Rafal}, issn = {0935-9648}, journal = {Advanced Materials}, keywords = {Mechanical Engineering, Mechanics of Materials, General Materials Science}, number = {3}, pages = {422--426}, publisher = {Wiley}, title = {{Dual-responsive nanoparticles and their self-assembly}}, doi = {10.1002/adma.201201734}, volume = {25}, year = {2013}, } @article{13408, abstract = {Well-defined metallic nanobowls can be prepared by extending the concept of a protecting group to colloidal synthesis. Magnetic nanoparticles are employed as “protecting groups” during the galvanic replacement of silver with gold. The replacement reaction is accompanied by spontantous dissociation of the protecting groups, leaving behind metallic nanobowls.}, author = {Ridelman, Yonatan and Singh, Gurvinder and Popovitz-Biro, Ronit and Wolf, Sharon G. and Das, Sanjib and Klajn, Rafal}, issn = {1613-6829}, journal = {Small}, keywords = {Biomaterials, Biotechnology, General Materials Science, General Chemistry}, number = {5}, pages = {654--660}, publisher = {Wiley}, title = {{Metallic nanobowls by galvanic replacement reaction on heterodimeric nanoparticles}}, doi = {10.1002/smll.201101882}, volume = {8}, year = {2012}, } @article{13411, abstract = {Photoresponsive gold nanoparticles dispersed in a solid/frozen matrix provide a basis for sensors that “remember” whether the sample has ever exceeded the melting temperature of the matrix. The operation of these sensors rests on the ability to photoinduce metastable electric dipoles on NP surfaces – upon melting, these dipoles drive NP aggregation, precipitation, and crosslinking. These events are manifested by a pronounced color change.}, author = {Klajn, Rafal and Browne, Kevin P. and Soh, Siowling and Grzybowski, Bartosz A.}, issn = {1613-6829}, journal = {Small}, keywords = {Biomaterials, Biotechnology, General Materials Science, General Chemistry}, number = {13}, pages = {1385--1387}, publisher = {Wiley}, title = {{Nanoparticles that “remember” temperature}}, doi = {10.1002/smll.200902272}, volume = {6}, year = {2010}, } @article{10390, abstract = {We use numerical simulations to study the phase behavior of a system of purely repulsive soft dumbbells as a function of size ratio of the two components and their relative degree of deformability. We find a plethora of different phases, which includes most of the mesophases observed in self-assembly of block copolymers but also crystalline structures formed by asymmetric, hard binary mixtures. Our results detail the phenomenological behavior of these systems when softness is introduced in terms of two different classes of interparticle interactions: (a) the elastic Hertz potential, which has a finite energy cost for complete overlap of any two components, and (b) a generic power-law repulsion with tunable exponent. We discuss how simple geometric arguments can be used to account for the large structural variety observed in these systems and detail the similarities and differences in the phase behavior for the two classes of potentials under consideration.}, author = {Šarić, Anđela and Bozorgui, Behnaz and Cacciuto, Angelo}, issn = {1520-5207}, journal = {The Journal of Physical Chemistry B}, keywords = {materials chemistry}, number = {22}, pages = {7182--7189}, publisher = {American Chemical Society}, title = {{Packing of soft asymmetric dumbbells}}, doi = {10.1021/jp107545w}, volume = {115}, year = {2010}, } @article{13414, abstract = {Supraspherical aggregates of crosslinked metal nanoparticles are transformed into pancakes and nanorods by mechanical stresses and shears imparted by macroscopic objects (see image). The dimensions of both types of nanostructures can be controlled by the pressures applied.}, author = {Browne, Kevin P. and Klajn, Rafal and Villa, JulieAnn and Grzybowski, Bartosz A.}, issn = {1613-6829}, journal = {Small}, keywords = {Biomaterials, Biotechnology, General Materials Science, General Chemistry}, number = {23}, pages = {2656--2658}, publisher = {Wiley}, title = {{Mechanofabrication of pancake and rodlike nanostructures from deformable nanoparticle aggregates}}, doi = {10.1002/smll.200900902}, volume = {5}, year = {2009}, } @article{13416, abstract = {The reversible molecular template-directed self-assembly of gold nanoparticles (AuNPs), a process which relies solely on noncovalent bonding interactions, has been demonstrated by high-resolution transmission electron microscopy (HR-TEM). By employing a well-known host−guest binding motif, the AuNPs have been systemized into discrete dimers, trimers, and tetramers. These nanoparticulate twins, triplets, and quadruplets, which can be disassembled and reassembled either chemically or electrochemically, can be coalesced into larger, permanent polygonal structures by thermal treatment using a focused HR-TEM electron beam.}, author = {Olson, Mark A. and Coskun, Ali and Klajn, Rafal and Fang, Lei and Dey, Sanjeev K. and Browne, Kevin P. and Grzybowski, Bartosz A. and Stoddart, J. Fraser}, issn = {1530-6992}, journal = {Nano Letters}, keywords = {Mechanical Engineering, Condensed Matter Physics, General Materials Science, General Chemistry, Bioengineering}, number = {9}, pages = {3185--3190}, publisher = {American Chemical Society}, title = {{Assembly of polygonal nanoparticle clusters directed by reversible noncovalent bonding interactions}}, doi = {10.1021/nl901385c}, volume = {9}, year = {2009}, } @article{13419, abstract = {Reaction-diffusion (RD) processes initiated from the surfaces of mesoscopic particles can fabricate complex core-and-shell structures. The propagation of a sharp RD front selectively removes metal colloids or nanoparticles from the supporting gel or polymer matrix. Once fabricated, the core structures can be processed “remotely” via galvanic replacement reactions, and the composite particles can be assembled into open-lattice crystals.}, author = {Wesson, Paul J. and Soh, Siowling and Klajn, Rafal and Bishop, Kyle J. M. and Gray, Timothy P. and Grzybowski, Bartosz A.}, issn = {1521-4095}, journal = {Advanced Materials}, keywords = {Mechanical Engineering, Mechanics of Materials, General Materials Science}, number = {19}, pages = {1911--1915}, publisher = {Wiley}, title = {{“Remote” fabrication via three-dimensional reaction-diffusion: Making complex core-and-shell particles and assembling them into open-lattice crystals}}, doi = {10.1002/adma.200802964}, volume = {21}, year = {2009}, } @article{13422, abstract = {Make like a leaf: The synthesis and characterization of a family of “flowerlike” Au/Fe3O4 nanoparticles is described, whereby Fe3O4 “leaves” adhere to a gold core (see image). The size and numbers of iron oxide domains can be adjusted flexibly by changing the proportion of the starting materials and the reaction time.}, author = {Wei, Yanhu and Klajn, Rafal and Pinchuk, Anatoliy O. and Grzybowski, Bartosz A.}, issn = {1613-6829}, journal = {Small}, keywords = {Biomaterials, Biotechnology, General Materials Science, General Chemistry}, number = {10}, pages = {1635--1639}, publisher = {Wiley}, title = {{Synthesis, shape control, and optical properties of hybrid Au/Fe3O4 “nanoflowers”}}, doi = {10.1002/smll.200800511}, volume = {4}, year = {2008}, } @article{13423, abstract = {Supraspheres (SS) composed of hundreds to thousands of metal nanoparticles (NPs) and crosslinked by dithiol linkers are assembled into larger structures, which are subsequently converted into nanoporous metals (NMs). Conversion is achieved by heating which removes organic molecules stabilizing the NPs and allows for NP fusion. Heating of SS solutions leads to NMs of overall macroscopic dimensions; localized radiation using collimated electron beam is used to prepare metallized surface micropatterns. Depending on the composition of supraspherical precursors, nanoporous materials composed of up to three metals can be obtained. Strategies for controlling pore size and nanoscale surface roughness of these materials are discussed.}, author = {Klajn, Rafal and Gray, Timothy P. and Wesson, Paul J. and Myers, Benjamin D. and Dravid, Vinayak P. and Smoukov, Stoyan K. and Grzybowski, Bartosz A.}, issn = {1616-3028}, journal = {Advanced Functional Materials}, keywords = {Electrochemistry, Condensed Matter Physics, Biomaterials, Electronic, Optical and Magnetic Materials}, number = {18}, pages = {2763--2769}, publisher = {Wiley}, title = {{Bulk synthesis and surface patterning of nanoporous metals and alloys from supraspherical nanoparticle aggregates}}, doi = {10.1002/adfm.200800293}, volume = {18}, year = {2008}, } @article{9149, abstract = {The interaction of tidal currents with sea-floor topography results in the radiation of internal gravity waves into the ocean interior. These waves are called internal tides and their dissipation due to nonlinear wave breaking and concomitant three-dimensional turbulence could play an important role in the mixing of the abyssal ocean, and hence in controlling the large-scale ocean circulation. As part of on-going work aimed at providing a theory for the vertical distribution of wave breaking over sea-floor topography, in this paper we investigate the instability of internal tides in a very simple linear model that helps us to relate the formation of unstable regions to simple features in the sea-floor topography. For two-dimensional tides over one-dimensional topography we find that the formation of overturning instabilities is closely linked to the singularities in the topography shape and that it is possible to have stable waves at the sea floor and unstable waves in the ocean interior above. For three-dimensional tides over two-dimensional topography there is in addition an effect of geometric focusing of wave energy into localized regions of high wave amplitude, and we investigate this focusing effect in simple examples. Overall, we find that the distribution of unstable wave breaking regions can be highly non-uniform even for very simple idealized topography shapes.}, author = {Bühler, Oliver and Muller, Caroline J}, issn = {0022-1120}, journal = {Journal of Fluid Mechanics}, keywords = {mechanical engineering, mechanics of materials, condensed matter physics}, pages = {1--28}, publisher = {Cambridge University Press}, title = {{Instability and focusing of internal tides in the deep ocean}}, doi = {10.1017/s0022112007007410}, volume = {588}, year = {2007}, } @article{13426, abstract = {Photoswelling of thin films of dichromated gelatin provides a basis for fabrication of multilevel surface reliefs via sequential UV illumination through different photomasks. The remarkable feature of this simple, benchtop technique is that by adjusting irradiation times, film thickness, or its hydration state the heights of the developed features can be varied from few nanometers to tens of microns. After UV exposure, the surface structures can be replicated faithfully into either soft or hard PDMS stamps.}, author = {Paszewski, Maciej and Smoukov, Stoyan K. and Klajn, Rafal and Grzybowski, Bartosz A.}, issn = {1520-5827}, journal = {Langmuir}, keywords = {Electrochemistry, Spectroscopy, Surfaces and Interfaces, Condensed Matter Physics, General Materials Science}, number = {10}, pages = {5419--5422}, publisher = {American Chemical Society}, title = {{Multilevel surface nano- and microstructuring via sequential photoswelling of dichromated gelatin}}, doi = {10.1021/la062982c}, volume = {23}, year = {2007}, } @article{13430, abstract = {Dynamic self-assembly (DySA) processes occurring outside of thermodynamic equilibrium underlie many forms of adaptive and intellligent behaviors in natural systems. Relatively little, however, is known about the principles that govern DySA and the ways in which it can be extended to artificial ensembles. This article discusses recent advances in both the theory and the practice of nonequilibrium self-assembly. It is argued that a union of ideas from thermodynamics and dynamic systems' theory can provide a general description of DySA. In parallel, heuristic design rules can be used to construct DySA systems of increasing complexities based on a variety of suitable interactions/potentials on length scales from nanoscopic to macroscopic. Applications of these rules to magnetohydrodynamic DySA are also discussed.}, author = {Fialkowski, Marcin and Bishop, Kyle J. M. and Klajn, Rafal and Smoukov, Stoyan K. and Campbell, Christopher J. and Grzybowski, Bartosz A.}, issn = {1520-6106}, journal = {The Journal of Physical Chemistry B}, keywords = {Materials Chemistry, Surfaces, Coatings and Films, Physical and Theoretical Chemistry}, number = {6}, pages = {2482--2496}, publisher = {American Chemical Society}, title = {{Principles and implementations of dissipative (dynamic) self-assembly}}, doi = {10.1021/jp054153q}, volume = {110}, year = {2006}, } @article{13431, abstract = {Hydrogel stamps can microstructure solid surfaces, i.e., modify the surface topology of metals, glasses, and crystals. It is demonstrated that stamps soaked in an appropriate etchant can remove material with micrometer-scale precision. The Figure shows an array of concentric circles etched in glass using the immersion wet stamping process described (scale bar: 500 μm).}, author = {Smoukov, S. K. and Bishop, K. J. M. and Klajn, Rafal and Campbell, C. J. and Grzybowski, B. A.}, issn = {1521-4095}, journal = {Advanced Materials}, keywords = {Mechanical Engineering, Mechanics of Materials, General Materials Science}, number = {11}, pages = {1361--1365}, publisher = {Wiley}, title = {{Cutting into solids with micropatterned gels}}, doi = {10.1002/adma.200402086}, volume = {17}, year = {2005}, } @article{13432, abstract = {A new experimental technique is described that uses reaction−diffusion phenomena as a means of one-step microfabrication of complex, multilevel surface reliefs. Thin films of dry gelatin doped with potassium hexacyanoferrate are chemically micropatterned with a solution of silver nitrate delivered from an agarose stamp. Precipitation reaction between the two salts causes the surface to deform. The mechanism of surface deformation is shown to involve a sequence of reactions, diffusion, and gel swelling/contraction. This mechanism is established experimentally and provides a basis of a theoretical lattice-gas model that allows prediction surface topographies emerging from arbitrary geometries of the stamped features. The usefulness of the technique is demonstrated by using it to rapidly prepare two types of mold for passive microfluidic mixers.}, author = {Campbell, Christopher J. and Klajn, Rafal and Fialkowski, Marcin and Grzybowski, Bartosz A.}, issn = {1520-5827}, journal = {Langmuir}, keywords = {Electrochemistry, Spectroscopy, Surfaces and Interfaces, Condensed Matter Physics, General Materials Science}, number = {1}, pages = {418--423}, publisher = {American Chemical Society}, title = {{One-step multilevel microfabrication by reaction−diffusion}}, doi = {10.1021/la0487747}, volume = {21}, year = {2005}, } @article{13434, abstract = {Thin films of ionically doped gelatin have been color-patterned with submicrometer precision using the wet-stamping technique. Inorganic salts are delivered onto the gelatin surface from an agarose stamp, and diffuse into the gelatine layer, producting deeply colored precipitates. Reaction fronts originating from different features of the stamp cease within < 1 μm of each other, leaving sharp, transparent regions in between.}, author = {Campbell, C. J. and Fialkowski, M. and Klajn, Rafal and Bensemann, I. T. and Grzybowski, B. A.}, issn = {1521-4095}, journal = {Advanced Materials}, keywords = {Mechanical Engineering, Mechanics of Materials, General Materials Science}, number = {21}, pages = {1912--1917}, publisher = {Wiley}, title = {{Color micro- and nanopatterning with counter-propagating reaction-diffusion fronts}}, doi = {10.1002/adma.200400383}, volume = {16}, year = {2004}, } @article{13435, abstract = {Micropatterning of surfaces with several chemicals at different spatial locations usually requires multiple stamping and registration steps. Here, we describe an experimental method based on reaction–diffusion phenomena that allows for simultaneous micropatterning of a substrate with several coloured chemicals. In this method, called wet stamping (WETS), aqueous solutions of two or more inorganic salts are delivered onto a film of dry, ionically doped gelatin from an agarose stamp patterned in bas relief. Once in conformal contact, these salts diffuse into the gelatin, where they react to give deeply coloured precipitates. Separation of colours in the plane of the surface is the consequence of the differences in the diffusion coefficients, the solubility products, and the amounts of different salts delivered from the stamp, and is faithfully reproduced by a theoretical model based on a system of reaction–diffusion partial differential equations. The multicolour micropatterns are useful as non-binary optical elements, and could potentially form the basis of new applications in microseparations and in controlled delivery.}, author = {Klajn, Rafal and Fialkowski, Marcin and Bensemann, Igor T. and Bitner, Agnieszka and Campbell, C. J. and Bishop, Kyle and Smoukov, Stoyan and Grzybowski, Bartosz A.}, issn = {1476-4660}, journal = {Nature Materials}, keywords = {Mechanical Engineering, Mechanics of Materials, Condensed Matter Physics, General Materials Science, General Chemistry}, pages = {729--735}, publisher = {Springer Nature}, title = {{Multicolour micropatterning of thin films of dry gels}}, doi = {10.1038/nmat1231}, volume = {3}, year = {2004}, }