InterNano Nanomanufacturing Repository
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Controlled Aggregation of Colloidal Particles for Toner Applications
No full textMicrometer-sized particles were formed by controlled aggregation of carboxylated polystyrene colloidal spheres having a mean diameter of about 200 nm with a commercial cationic coagulant. To identify the parameters governing the size and structure of the aggregates, the aggregate size distribution was studied over a period of time with dynamic light scattering. The effect of the particle concentration, pH, and ionic strength on the aggregation behavior was investigated. The coagulant concentration used for present studies was 5 parts per hundred on the basis of the polystyrene particles and the particle concentrations used were 10-15%. The particle size distribution for the latex suspensions was also investigated with a 10% aluminum sulfate [Al(2)(SO4)(3)center dot 14H(2)O] solution as a model coagulant. With the commercial coagulant, aggregation was found to be slower at lower pH than at neutral pH. At pH 6, the particles started to aggregate within minutes and form aggregates of about 1000 nm. We expected that lowering the pH would reduce interparticle repulsive forces and enhance the collision efficiency. However, at a lower pH of 2, the aggregation process slowed down. Increasing the ionic strength at neutral pH led to a broader aggregate size distribution, and the population of larger aggregates increased. The suspensions with the model coagulant showed similar behavior. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 122: 1358-1363, 201
Interaction of Cationic Proteins and Polypeptides with Biocompatible Cationically-Anchored PEG Brushes
No full textPolyetheylene glycol (PEG) brushes, for instance, physically tethered to a surface via the adsorbing portion of a PEG-containing copolymer, are a popular protein-resistant surface treatment. Though physisorbed brushes might be displaced by competing species, they continue to dominate diagnostic chips and other applications. In this work, we examine the interactions of two cationic species, poly L-lysine (PLL) and lysozyme, with a popular type of PEG brush, formed by the adsorption of a graft copolymer of PLL PEG on negative silica. Here, 20K molecular weight (MW) PLL comprises the main backbone that adsorbs to the silica and the PEG side chains (2K or SK, in different samples) form tethers. This work examines variations in brush heights and densities, still confining the study to brush architectures (near 30% functionalization of the PLL by PEG side chains) that completely prevent the adsorption of blood proteins such as fibrinogen and albumin. It is found that lysozyme adsorbs to interfaces passivated with these PLL PEG copolymers in amounts that increase with the amount of PEG in the brush. This suggests attractions between the PEG tethers and lysozyme itself. When PLL PEG brushes are challenged by homopolymer PLL (a random coil at the physiological pH studied here), the PLL PEG is almost completely displaced from the silica substrate. The rapid displacement kinetics (with complete loss of protein repellence) for all brush architectures suggest the absence of a steric barrier against PLL penetration of the PEG brush. A small overshoot in surface coverage prior to the displacement of the PLL PEG chains demonstrates the adsorption of PLL on regions of silica at the base of the brush prior to chain displacement, further arguing for the accessibility of the substrate despite the presence of the brush. Differences between the interactions of lysozyme or PLL with the brush suggest an important role of the globular nature of folded proteins compared with random coil polypeptides in protein brush interactions and brush penetration. The results emphasize the technological challenge of retaining seemingly robust brushes adsorbed to interfaces, and eliminating protein adhesion from the brush itself
Metallization of Branched DNA Origami for Nanoelectronic Circuit Fabrication
No full textThis work examines the metallization of folded DNA, known as DNA origami, as an enabling step toward the use of such DNA as templates for nanoelectronic circuits. DNA origami, a simple and robust method for creating a wide variety of shapes and patterns, makes possible the increased complexity and flexibility needed for both the design and assembly of useful circuit templates. In addition, selective metallization of the DNA template is essential for circuit fabrication. Metallization of DNA origami presents several challenges over and above those associated with the metallization of other DNA templates such as λ-DNA. These challenges include (1) the stability of the origami in the processes used for metallization, (2) the enhanced selectivity required to metallize small origami structures, (3) the increased difficulty of adhering small structures to the surface so that they will not be removed when subject to multiple metallization steps, and (4) the influence of excess staple strands present with the origami. This paper describes our efforts to understand and address these challenges. Specifically, the influence of experimental conditions on template stability and on the selectivity of metal deposition was investigated for small DNA origami templates. These templates were seeded with Ag and then plated with Au via an electroless deposition process. Both staple strand concentration and the concentration of ions in solution were found to have a significant impact. Selective continuous metal deposition was achieved, with an average metallized height as small as 32 nm. The shape of branched origami was also retained after metallization. These results represent important progress toward the realization of DNA-templated nanocircuits
Highly Ordered Assembly of Single-Domain Dichloropentacene over Large Areas on Vicinal Gold Surfaces
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Post-CMOS hybrid spin-charge nanofabrics
No full textWe propose a hybrid spin-charge fabric with computation in spin domain and communication in charge domain. In nanofabrics based on non-equilibrium physical phenomenon like interference of spin waves, switching times are lower than the thermal relaxation times leading to fast multi-value logic at high fan-in without the exponential performance degradation noticeable in CMOS. While computation is much more efficient than in CMOS, these benefits can be lost due to the communication requirements between spin-wave blocks, when implemented with wave guides. This inspired a new type of hybrid nanofabric with spin wave high fan-in functions connected to an interconnect stack similar to CMOS: our analysis shows a delay reduction of up to 10X (8.64ns) along the critical path for a (511;9) parallel counter implemented in this fabric vs. spin-wave only. Similar benefits are also shown for a CLA adder with ~4.2ns delay reduction for 1024 bit CLA adder
Optical Measurement of Thermal Conductivity Using Fiber Aligned Frequency Domain Thermoreflectance
No full textFiber aligned frequency domain thermoreflectance (FAFDTR) is a simple noncontact optical technique for accurately measuring the thermal conductivity of thin films and bulk samples for a wide range of materials, including electrically conducting samples. FAFDTR is a single-sided measurement that requires minimal sample preparation and no microfabrication. Like existing thermoreflectance techniques, a modulated pump laser heats the sample surface, and a probe laser monitors the resultant thermal wave via the temperature dependent reflectance of the surface. Via the use of inexpensive fiber coupled diode lasers and common mode rejection, FAFDTR addresses three challenges of existing optical methods: complexity in setup, uncertainty in pump-probe alignment, and noise in the probe laser. FAFDTR was validated for thermal conductivities spanning three orders of magnitude (0.1-100 W/m K), and thin film thermal conductances greater than 10 W/m(2) K. Uncertainties of 10-15% were typical, and were dominated by uncertainties in the laser spot size. A parametric study of sensitivity for thin film samples shows that high thermal conductivity contrast between film and substrate is essential for making accurate measurements. DOI: 10.1115/1.400354