Abstracts for Publications 61-80

81. Q. X. Nguyen, T. G. Belgard, J. J. Taylor, V. S. Murthy, N. J. Halas, and M. S. Wong, "Water-Phase Synthesis of Cationic Silica/Polyamine Nanoparticles," Chem. Mater. 24 (8), 1426–1433 (2012) DOI:10.1021/cm203132m

Abstract:

Silica particles are commonly functionalized with amine groups on their surface through the hydrolytic condensation of aminotrialkoxysilanes for use in bioimaging, enzyme immobilization, and other applications. Eliminating this aminotrialkoxysilane condensation step could simplify and improve the efficiency of the synthesis of amine-functionalized silica. Here, we describe a one-pot, ambient-condition, water-phase method to synthesize silica-based nanoparticles (NPs) that present surface amine groups. The formation mechanism involves the electrostatic cross-linking of cationic polyallylamine hydrochloride by citrate anions and the infusion of the resulting polymer/salt aggregates by silicic acid. The particles were unimodal with average diameters in the range of 40 to 100 nm, as determined by the size of the templating polymer-salt aggregates. Colorimetric analysis using Coomassie brilliant blue and zeta potential measurements confirmed the presence of surface amine groups on the hybrid silica/polymer NPs. The point of zero-charge value for these NPs was 5, between the corresponding values of unfunctionalized and aminopropyltriethoxysilane-functionalized silica particles (~2 and ~10, respectively). Surface charge calculations indicated the hybrid NPs had a lower amine surface density than aminopropyltriethoxysilane-functionalized silica (0.057 #/nm2 vs 0.169 #/nm2 at pH 7). The polymer-salt aggregate synthesis chemistry is a new approach toward controlling the amine surface density and point of zero-charge of hybrid silica/polymer NPs.

80. L. Y. Zhu, W.-J. An, J. W. Springer, L. B. Modesto-Lopez, S. Gullapalli, D. Holten, M. S. Wong and P. Biswas, "Linker-free quantum dot sensitized TiO2 photoelectrochemical cells," Int. J. Hydrogen Energy, 37 (8), 6422–6430 (2012). DOI:10.1016/j.ijhydene.2012.01.028

Abstract:

Aerosol based techniques were used to characterize and deposit quantum dots (QDs). Using an electrospray-assisted characterization technique, the mobility diameter of CdSe QDs was successfully measured in real-time. The electrospray technique was also used to deposit CdSe QDs onto nanostructured TiO2 films. Compared to conventional methodologies such as dip coating with linker-containing molecules or chemical bath deposition, an electrospray system enabled uniform deposition of QDs over the nanostructured TiO2 surface in a short processing time. As-deposited films were annealed to enhance binding between the QDs and TiO2 surface. These QD-decorated TiO2 films were used in photoelectrochemical cells, for which the photoenergy conversion efficiencies were tested. Optimization of the deposition time of the QDs resulted in increased efficiencies. Multiple layers of QDs caused a decrease in energy-conversion efficiency, likely due to inhibition of the transportation of photogenerated electrons into the TiO2 structure. The energy-conversion efficiency trends were supported by time-resolved photoluminescence decay data.

79. M. Thakur, M. Isaacson, S. L. Sinsabaugh, M. S. Wong, and S. L. Biswal, "Gold-Coated porous silicon films as anodes for lithium ion batteries," J. Power. Sources., 205, 426-432 (2012). DOI:10.1016/j/jpowsour.2012.01.058

Abstract:

Silicon has the highest known theoretical charge capacity for lithium, making it a promising material for rechargeable lithium ion batteries (LIB). A significant drawback of silicon anodes is the large volume change associated with the insertion and extraction of lithium, which oftentimes leads to cracking and pulverization of the anode, limiting its cycle life. We present a layered architecture consisting of a gold-coated porous silicon film attached to a bulk silicon substrate. This structure demonstrates an enhanced ability to alloy with lithium ions over several charge/discharge cycles while maintaining mechanical integrity. With this structure we show that a specific capacity of over 3000 mAh g-1 can be achieved for over 50 charge–discharge cycles at 100 μA cm-2, and 2500 mAh g-1 can be achieved for over 75 cycles with coulombic efficiencies over 95%. This is a significant improvement over a gold-coated, non-porous silicon sample, which had a maximum capacity of 1 mAh g-1 before failing after 10 cycles at 0.25 mAh g-1 when cycled at a constant current of 100 μA cm-2, illustrating the benefit of internal pores. Gold-coated porous silicon out-performed non-gold-coated porous silicon, which had a first cycle discharge capacities of 500 mAh g-1, which quickly faded to 76 mAh g-1 after the 10th cycle when cycled at a constant current of 50 μA cm-2. The combination of internal pores and a gold-coating points to a new approach to improving the long-term cycleability and high-capacity performance metrics of LIB anodes.

78. K.-S. Lee, I. Kim, S. Gullapalli, M. S. Wong, and G. E. Jabbour, "Enhanced performance of hybrid solar cells using longer arms of quantum cadmium selenide tetrapods," Appl. Phys. Lett., 99, 223515 (2011). DOI:10.1063/1.3662839

Abstract:

We demonstrate that enhanced device performance of hybrid solar cells based on tetrapod (TP)-shaped cadmium selenide (CdSe) nanoparticles and conjugated polymer of poly (3-hexylthiophene) (P3HT) can be obtained by using longer armed tetrapods which aids in better spatial connectivity, thus decreasing charge hopping events which lead to better charge transport. Longer tetrapods with 10 nm arm length lead to improved power conversion efficiency of 1.12% compared to 0.80% of device having 5 nm short-armed tetrapods:P3HT photoactive blends.

77. S. Gullapalli and M. S. Wong, "Nanotechnology: A Guide to Nano-objects," Chem. Eng. Prog., 107(5), 28-32 (2011). http://www.aiche.org/downloads/exchange/apr11.html

Abstract:

Rapid change in the field of nanotechnology can make it hard to keep track of the latest nanomaterial developments. Here's a primer on the most common shapes, sizes, and compositions of nano-objects.

76. H. G. Bagaria and M. S. Wong, "Polyamine–salt aggregate assembly of capsules as responsive drug delivery vehicles," J. Mater. Chem., 21 (26), 9454-9466 (2011). DOI: 10.1039/C1JM10712G (Feature Article)

Abstract:

Responsive capsular delivery systems that can partly mimic the complexity of cellular systems hold great promise for the future of medicine. Simple self-assembled systems like liposomes are already in clinical use and others like polymeric micelles are under clinical trials. Unlike these self-assembled systems, the greater flexibility and versatility offered by template-based routes will likely drive the development of sophisticated capsules. The focus of this review is to introduce one such template-based route, which is based on polyamine–salt aggregate or ‘PSA’ assembly. The basic synthesis premise involves the assembly of cationic polymer (like poly-L-lysine) by ionic crosslinking with multivalent anionic salts (like citrate) into metastable templates for cargo encapsulation and shell material deposition. The technique offers several benefits: (i) the synthesis procedure involves simple mixing at ambient conditions, (ii) the capsule size is easy to control in the sub-100 nm to micron range, and (iii) a wide range of formulations is readily available with the use of different polymer, salt, cargo, and shell-forming precursors. In this review, the current state of this technique, the materials chemistry of the capsule assembly, and the demonstrated applications, including photothermal therapy, MRI contrast agent development and protease-responsive NIR imaging, will be discussed.

75. H. G. Bagaria, M. R. Dean, C. A. Nichol, and M. S. Wong, "Self-Assembly and Nanotechnology: Real-Time, Hands-On, and Safe Experiments for K-12 Students," J. Chem. Educ., 88 (5), 609-614 (2011). DOI: 10.1021/ed100598y

Abstract:

What students and teachers often ask is, how are nano-sized materials made when they are so small? One answer is through the process of self-assembly in which molecules, polymers, and nanoparticles connect to form larger objects of a defined structure and shape. Two hands-on experiments are presented in which students prepare capsules in real time using simple and safe ingredients and study the materials for encapsulation and release of food coloring dye. These experiments are visual and interactive demonstrations of self-assembly (as a synthesis tool) and nanotechnology (in which nanomaterial can be made to perform useful functions), and build on the concepts of acid−base chemistry and electrostatic interaction.

74. N. X. Zhao, H. G. Bagaria, M. S. Wong, and Y. L. Zu, "A nanocomplex that is both tumor cell-selective and cancer gene-specific for anaplastic large cell lymphoma," J Nanobiotechnol, 9, 2 (2011). DOI: 10.1186/1477-3155-9-2

Abstract:

Many in vitro studies have demonstrated that silencing of cancerous genes by siRNAs is a potential therapeutic approach for blocking tumor growth. However, siRNAs are not cell type-selective, cannot specifically target tumor cells, and therefore have limited in vivo application for siRNA-mediated gene therapy.

73. Y. L. Fang, K. N. Heck, P. Alvarez, and M. S. Wong, "Kinetics Analysis of Palladium/Gold Nanoparticles as Colloidal Hydrodechlorination Catalysts," ACS Catal., 1 (2), 128-138 (2011). DOI: 10.1021/cs100067k

Abstract:

The aqueous-phase hydrodechlorination (HDC) of trichloroethene (TCE) is an important chemical reaction for water pollution control, for which unsupported palladium-on-gold and palladium nanoparticles (Pd/Au and Pd NPs) definitively show the beneficial effects of gold on palladium catalysis. The observed batch reactor kinetics can be erroneously oversimplified when concentration and mass transfer effects are neglected. A comprehensive treatment of NP catalysis is presented here using Pd-based NPs as the catalytic colloid and TCE HDC as the model reaction. Mass transfer effects were quantified for three specific compositions (Pd/Au NPs with 30% and 60% Pd surface coverages, and pure Pd NPs) by analyzing the observed reaction rates as functions of stirring rate and initial catalyst charge. The largest effect on observed reaction rates came from gas−liquid mass transfer. The TCE HDC reaction was modeled as a Langmuir−Hinshelwood mechanism involving competitive chemisorption of dihydrogen and TCE for all three NP compositions. Differences in adsorption affinities of the reactant molecules for the Pd/Au and Pd surfaces are suggested as responsible for the observed difference in TCE reaction order at high TCE concentrations; that is, first-order for Pd/Au NPs and non-first-order for Pd NPs.

72. H. G. Bagaria, S. B. Kadali, and M. S. Wong, "Shell Thickness Control of Nanoparticle/Polymer Assembled Microcapsules," Chem. Mater., 23 (2), 301-308 (2011). DOI: 10.1021/cm102472h

Abstract:

Organic/inorganic composite microcapsules can be produced in water through a two-step charge-driven assembly of polyallylamine, citrate anions, and 13 nm silica nanoparticles. The shell is composed of nanoparticles intermixed with polymer, and is thick enough (100s of nm) to provide structural stability before or after drying. Controlling shell thickness, however, is currently difficult to perform. Presented here is a new method in which the shell wall can be thickened by contacting the as-synthesized capsules with silicic acid. This shell thickening was observed and quantified for a moderately broad, unimodal size distribution of capsular particles, through a combination of transmission electron and confocal fluorescence microscopies. Thermogravimetric analysis confirmed the deposition of additional silica, and Coulter counter measurements showed the mean capsule diameter of 4.5 ± 2.2 μm changed negligibly with silicic acid treatment. The shell-thickening process occurred in an inward direction, in which the nanosized silicic acid oligomers most likely diffused through the permeable capsule wall and deposited within the wall and on the inner shell wall surface. Adjustable shell wall thicknesses in hybrid microcapsules provide enhanced capability for chemical encapsulation, storage, and release applications.

71. J. M. Berlin, J. Yu, W. Lu, E. E. Walsh, L. L. Zhang, P. Zhang, Wei. Chen, A. T. Kan, M. S. Wong, M. B. Tomson, and J. M. Tour, "Engineered nanoparticles for hydrocarbon detection in oil-field rocks," Energy Environ. Sci., 4 (2), 505-509 (2011). DOI: 10.1039/C0EE00237B

Abstract:

Polyvinyl alcohol functionalized oxidized carbon black efficiently carries a hydrophobic compound through a variety of oil-field rock types and releases the compound when the rock contains hydrocarbons.

70. L. A. Pretzer, Q. X. Nguyen, and M. S. Wong, "Controlled Growth of Sub-10 nm Gold Nanoparticles Using Carbon Monoxide Reductant," J. Phys. Chem. C, 114 (49), 21226-21233 (2010). DOI: 10.1021/jp107945d

Abstract:

There is a need to develop aqueous-phase synthesis methods of sub-10-nm Au nanoparticles (NPs), given their many exciting possibilities in catalysis, sensing, biomedical, and other water-based applications. Synthesizing Au NPs by reducing Au salt onto preformed NPs as seeds is a useful approach because final particle size can be finely predicted and controlled, though few studies have reported successful synthesis of Au NPs in the 1 and 10 nm size range. Here we report that water-suspended Au particles with a diameter ~2.8 nm can be grown as large as ~12 nm with sub-nanometer control, as verified through detailed ultraviolet−visible spectroscopy, small-angle X-ray scattering, and transmission electron microscopy measurements. With carbon monoxide as the reducing agent, this seeded-growth method results in colloidally stable Au sols. The reaction mechanism most likely involves the catalyzed oxidation of CO into CO2 accompanied by electron transfer to the gold hydroxide-chloride ionic species through the growing particle.

69. H. G. Bagaria, G. C. Kini, and M. S. Wong, "Electrolyte Solutions Improve Nanoparticle Transfer from Oil to Water," J. Phys. Chem. C, 114 (47), 19901-19907 (2010). DOI: 10.1021/jp106140j

Abstract:

Many techniques to transfer NPs from the oil phase into the water phase have been developed, but all have limitations that remain to be addressed, specifically low transfer yields and partial NP aggregation. One of the transfer processes involves emulsifying an oil suspension of NPs in water with surfactants, followed by evaporation of the oil to produce water suspensions of surfactant-encapsulated NPs. We show here that using salt solutions instead of deionized water significantly improves this emulsion-based transfer process. With oleate-coated CdSe quantum dots as a model NP system, hexane as the oil phase, sodium bis(2-ethylhexyl) sulfosuccinate (AOT) as the emulsifying surfactant, and NaCl solution as the water phase, the resultant aqueous suspensions exhibit months-long photoluminescence stability, near 100% phase-transfer yield, and nonaggregation. These benefits are attributed to a more laterally packed AOT layer surrounding the NP, as supported by zeta-potential measurements, surface-charge calculations, thermogravimetry, and Nile Red fluorescence analysis. The new phase-transfer method is general for a variety of NP, surfactant, and salt types.

68. J. Yu, J. M. Berlin, W. Lu, L. Zhang, A. T. Kan, P. Zhang, E. E. Walsh, S. N. Work, W. Chen, J. M. Tour, M. S. Wong, and M. B. Tomson, "Transport study of nanoparticles for oilfield application," SPE 131158, 2010 SPE International Conference on Oilfield Scale, Aberdeen, UK, May 26-27., (online) DOI: 10.2118/131158-MS

Abstract:

Recently, the revolution of nanotechnology has been noticed for its many potential applications in the oil & gas industry such as enhanced oil recovery process and subsurface mapping. Understanding the transport and retention of nanoparticles (NPs) in an oilfield environment, such as high salinity, high temperature, high pressure, and heterogeneous pore distribution is critical to their application. The objective of this study is to investigate the fundamental transport and retention properties of NPs in the challenging oilfield conditions.
In this work, dolomite core material from an oil well in Kuwait and Berea sandstone were used. Carbon NPs were used as model nanomaterials. The core sample was washed with toluene to remove residual oil, ground to 106 – 250 μm grains, and packed into columns. Carbon NP breakthrough curves were collected in synthetic seawater at room temperature. The results showed that the existence of salt ions dramatically delayed NP breakthrough time and increased NP retention. Effects of different types of salts and salt concentrations are discussed. NP transport appears to be highly dependent on the degree of interaction between the NPs, salt ions in solution, and porous medium surface, which affects retardation and retention. NP breakthrough can be significantly improved by avoiding this interaction via NP surface modification. Our preliminary results provided helpful guidelines for NP transport in oil & gas applications. The results are discussed in detail. Furthermore, the experimental results were fitted with a 1-D advective and dispersion equation combined with a first-order removal term to obtain important transport parameters for NPs that did not aggregate. More complicated models are being developed to capture the unusual breakthrough curves associated with NP aggregation.

66. N. Soultanidis, W. Zhou, A. C. Psarras, A. J. Gonzalez, E. F. Iliopoulou, C. J. Kiely, I. E. Wachs, and M. S. Wong, "Relating n-Pentane Isomerization Activity to the Tungsten Surface Density of WOx/ZrO2," J. Am. Chem. Soc., 132 (38), 13462-13471 (2010). DOI: 10.1021/ja105519y

Abstract:

Zirconia-supported tungsten oxide (WOx/ZrO2) is considered an important supported metal oxide model acid catalyst, for which structure−property relationships have been studied for numerous acid-catalyzed reactions. The catalytic activity for xylene isomerization, alcohol dehydration, and aromatic acylation follows a volcano-shape dependence on tungsten surface density. However, WOx/ZrO2 has not been studied for more acid-demanding reactions, like n-pentane isomerization, with regard to surface density dependence. In this work, WOx/ZrO2 was synthesized using commercially available amorphous ZrOx(OH)4−2x and model crystalline ZrO2 as support precursors. They were analyzed for n-pentane isomerization activity and selectivity as a function of tungsten surface density, catalyst support type, and calcination temperature. Amorphous ZrOx(OH)4−2x led to WOx/ZrO2 (WZrOH) that exhibited maximum isomerization activity at 5.2 W·nm−2, and the crystalline ZrO2 led to a material (WZrO2) nearly inactive at all surface densities. Increasing the calcination temperature from 773 to 973 K increased the formation of 0.8−1 nm Zr-WOx clusters detected through direct imaging on an aberration-corrected high-resolution scanning transmission electron microscope (STEM). Calcination temperature further increased catalytic activity by at least two times. Brønsted acidity was not affected but Lewis acidity decreased in number, as quantified via pyridine adsorption infrared spectroscopy. WOx/ZrO2 exhibited isomerization activity that peaked within the first 2 h time-on-stream, which may be due to Zr-WOx clusters undergoing an activation process.

65. Y. L. Fang, J. T. Miller, N. Guo, K. N. Heck, Pedro. J. J. Alvarez, and M. S. Wong, "Structural Analysis of Palladium-decorated Gold Nanoparticles as Colloidal Bimetallic Catalysts," Catal. Today, 160 (1), 96-102 (2011). DOI: 10.1016/j.cattod.2010.08.010

Abstract:

Bimetallic palladium-decorated gold nanoparticle (Pd/Au NP) catalysts are significantly more active than palladium-only catalysts, but the mechanism for enhancement is not completely clear for most reactions, like the aqueous-phase hydrodechlorination of trichloroethene. In this study, we conducted X-ray absorption spectroscopy on carbon-supported Pd/Au NPs to obtain information about the local atomic environment (i.e., oxidation states, coordination numbers, and bond distances) of the two metals under different treatment conditions. The as-synthesized NPs were confirmed to have a Pd-shell/Au-core nanostructure, in which the Pd was found as surface ensembles. Upon exposure to room temperature in air, a portion of the Pd, but not the Au, was oxidized. In comparison, nearly the entire surface of monometallic Pd NPs was oxidized, suggesting that Au in Pd/Au NPs imparts oxidation resistance to Pd atoms. The surface Pd was found randomly distributed, presumably as a PdAu surface alloy, after reduction at 300 °C. X-ray absorption spectroscopy provides direct evidence for the Pd-shell/Au-core structure of Pd/Au NPs, and suggests that metallic Pd in the Pd/Au NPs is a source for higher catalytic activity for aqueous-phase trichloroethene hydrodechlorination.

64. J. A. Jamison, E. L. Bryant, S. B. Kadali, M. S. Wong, V. L. Colvin, K. Matthews, and M. K. Calabretta, "Altering Protein Surface Charge with Chemical Modification Modulates Protein-Gold Nanoparticle Aggregation," J. Nanopart. Res., 13 (2), 625-636 (2010). DOI:10.1007/s11051-010-0057-5

Abstract:

Gold nanoparticles (AuNP) can interact with a wide range of molecules including proteins. Whereas significant attention has focused on modifying the nanoparticle surface to regulate protein–AuNP assembly or influence the formation of the protein “corona,” modification of the protein surface as a mechanism to modulate protein–AuNP interaction has been less explored. Here, we examine this possibility utilizing three small globular proteins—lysozyme with high isoelectric point (pI) and established interactions with AuNP; α-lactalbumin with similar tertiary fold to lysozyme but low pI; and myoglobin with a different globular fold and an intermediate pI. We first chemically modified these proteins to alter their charged surface functionalities, and thereby shift protein pI, and then applied multiple methods to assess protein–AuNP assembly. At pH values lower than the anticipated pI of the modified protein, AuNP exposure elicits changes in the optical absorbance of the protein–NP solutions and other properties due to aggregate formation. Above the expected pI, however, protein–AuNP interaction is minimal, and both components remain isolated, presumably because both species are negatively charged. These data demonstrate that protein modification provides a powerful tool for modulating whether nanoparticle–protein interactions result in material aggregation. The results also underscore that naturally occurring protein modifications found in vivo may be critical in defining nanoparticle–protein corona compositions.

63. T. Y. Liu, J. A. Eukel, H. Bagaria, M. S. Wong, M. Pasquali, and H. K. Schmidt, "Performance of CdSe tetrapods-gold as nanostructure electrochemical materials in photovoltaic cells," Photovoltaic Specialists Conference (PVSC), 2009 34th IEEE, vol., no., pp.002074-002079, 7-12 June 2009. DOI:10.1109/PVSC.2009.5411448 (Link)

Abstract:

Nanoscale rectennae (rectifying antennae) have been fabricated by combining rectifying organic self-assembled monolayers (SAM) with plasmonic materials because of their surface plasmon resonance (SPR) properties of capturing light. Gold antenna arrays are assembled by coating on CdSe tetrapod templates; the rectifying barrier is formed by self-assembled monolayer (SAM) of gold and electrolyte which contains alkylthiolate. Photocurrent measurements showed that electric currents can be induced at different wavelengths within visible range that strongly depend on the aspect ratio of the tetrapod. Adding gold layer can increase the generated photocurrents due to the rectification. Multiple mechanisms among the semiconductors, metals and electrolytes in response of photocurrent are indicated and analyzed.

62. G. C. Kini, S. L. Biswal, and M. S. Wong, "Non-LBL Assembly and Encapsulation Uses of Nanoparticle-Shelled Hollow Spheres," Adv Polym Sci, 229, 175-200 (2010). DOI:10.1007/12_2010_53

Abstract:

Nanoparticles (NPs, diameter range of 1–100nm) can have size-dependent physical and electronic properties that are useful in a variety of applications. Arranging them into hollow shells introduces the additional functionalities of encapsulation, storage, and controlled release that the constituent NPs do not have.This chapter examines recent developments in the synthesis routes and properties of hollow spheres formed out of NPs. Synthesis approaches reviewed here are recent developments in the electrostatics-based tandem assembly and interfacial stabilization routes to the formation of NP-shelled structures. Distinct from the well-established layer-by-layer (LBL) synthesis approach, the former route leads to NP/polymer composite hollow spheres that are potentially useful in medical therapy, catalysis, and encapsulation applications. The latter route is based on interfacial activity and stabilization by NPs with amphiphilic properties, to generate materials like colloidosomes, Pickering emulsions, and foams. The varied types of NP shells can have unique materials properties that are not found in the NP building blocks, or in polymer-based, surfactant-based, or LBL-assembled capsules.

61. T.-C. Tseng, E. S. McGarrity, J. W. Kiel, P. M. Duxbury, M. E. Mackay, A. L. Frischknecht, S. Asokan, and M. S. Wong, "Three-dimensional Liquid Surfaces through Nanoparticle Selfassembly," Soft Matter, 6, 1533-1538 (2010).DOI:10.1039/b918429e

Abstract:

Nanoparticles blended into thin polymer films are driven to assemble at interfaces by both entropic and enthalpic forces. When nanoparticles assemble at a substrate–polymer film interface, these forces are so large that they enable the film to follow surface protrusions and form a three-dimensional surface, instead of dewetting from the substrate. In other words, disassembling the nanoparticle layer requires more energy than that gained by the film dewetting from the rough surface. Here we studied blends of linear polystyrene and CdSe nanoparticles spin coated onto silicon substrates containing sparsely distributed SiO2 particles (ca. 120 nm diameter). The films were then thermally annealed for periods of up to 24 h, well above the glass transition temperature of the polymer. The profiles of different film thicknesses (40–180 nm) were characterized using atomic force microscopy (AFM) before and after being annealed and were found to become much smoother, yet remain three-dimensional after annealing with a profile that gradually decayed away from the SiO2 particles. Calculations based on a continuum theory using a balance of assembly, dispersion and surface tension forces were performed and found to be in agreement with the AFM profile data demonstrating the strength of the assembly forces.