Evaporative Self-assembly Research Articles

Polymer-Mediated Crack Suppression in Deposit of Nanoellipsoids.

Uniform distribution of particles and crack suppression in dried particulate deposits are major challenges for applications in coating and printing technologies. To address this, we investigated the impact of the addition of a water-soluble polymer, poly(vinyl alcohol) (PVA), on the evaporative self-assembly and kinetics of crack formation in deposits of anisotropic colloids. The fluid flow inside the drying drop is significantly altered due to polymer-mediated adsorption of ellipsoids to the drop surface. The competition between outward capillary flow and Marangoni flow developed in the drying colloid-polymer dispersion drop dictates the distribution of particles in the final dried patterns. The deposits formed by drying drops of ellipsoids dispersed in PVA solutions show three distinct patterns depending on the PVA concentration. A transition from ring-like deposit to uniform deposition with intermittent cracks was observed for a critical PVA concentration of 0.3 wt %. Radial as well as annular cracks were observed in the case of no PVA, while only annular cracks were formed in the dried patterns as the PVA content increased, thus indicating the change of capillary stresses in the films. Analyses of the particle dynamics and deposition patterns confirmed the effectiveness of gelation-driven crack prevention. This method offers a facile and straightforward solution for obtaining crack-free coatings in drying-mediated colloidal nanoparticle assembly.

Deep-eutectic-solvent modulation of self-assembled multi-responsive films based on polyvinyl alcohol/cellulose nanocrystal and grape skin red for highly sensitive food monitoring

To enhance the mechanics performance, sensitivity and response range of multi-responsive photonic films, herein, a facile method for fabricating multi-responsive films is demonstrated using the evaporative self-assembly of a mixture of grape skin red (GSR), cellulose nanocrystal (CNC), polyvinyl alcohol (PVA) and deep eutectic solvent (DES). The prepared materials exhibited excellent thermal stability, strain properties, solvent resistance, ultraviolet (UV) resistance and antioxidant activity. Compared to a pure PVA film, the presence of GSR strengthened the antioxidant property of the film by 240.1 % and provided excellent UV barrier capability. The additional cross-linking of DES and CNC promoted more efficient phase fusion, yielding a film strain of 41.5 %. The addition of hydrophilic compound GSR, wetting and swelling due to the DES and the surface inhomogeneity of the films rendered the multi-responsive films high sensitivity, wide response range and multi-cyclic stability in environments with varying pH and humidity. A sample application showed that a PVA/CNC/DES film has the potential to differentiate between fresh, sub-fresh and fully spoiled shrimps. The above results help in designing intelligent thin film materials that integrate antioxidant properties, which help in monitoring the changes in food freshness and food packaging.

Drying behaviour of nanofluid sessile droplets on self-affine vis-à-vis corrugated nanorough surfaces.

In recent years, evaporative self-assembly of sessile droplets has gained considerable attention owing to its wide applicability in many areas. While the phenomenon is well studied for smooth and isotropically rough (self-affine) surfaces, investigations comparing the outcomes on self-affine vis-à-vis corrugated surfaces remains to be done. In this experimental work, we compare the wetting and evaporation dynamics of nano-colloidal microlitre droplets on self-affine and corrugated nanorough surfaces having identical roughnesses and interface properties. The coupled influence of particle size, concentration, and surface structuring has been explored. Differences in wettability and evaporation dynamics are observed, which are explained via the interaction between wetting fluid and anisotropic surface roughness. Our findings exhibit different temporal behaviour of contact radius and angle in the evaporation process of the droplets. Further, the corrugated surface exhibits anisotropic wettability with a monotonic change in droplet shape as evaporation proceeds, finally giving rise to irregular dried patterns. The scaled rim width and crack spacing of the particulate deposits are examined. Our results can inspire fabrication of surfaces that can facilitate direction-dependent droplet motion for specific applications.

Insights into Permanent Encodings of Macroscopic Spike Patterns by Magnetic-Field-Directed Evaporative Self-Assembly from Ferrofluids.

Field-directed assembly has the potential to make large hierarchically ordered structures from nanoscale objects. Shear forces and optical, electric, and magnetic fields have been used for this purpose. Ferrofluids consist of magnetic nanoparticles hosted in mobile liquids. Though they exhibit rich structures and lattice patterns in response to an applied magnetic field, the patterns collapse when the field is removed. Recently, we adapted evaporation-induced self-assembly to obtain permanent encodings of the complex field response of magnetite nanoparticles in alkane media. The encodings are characterized by order that culminates in macrostructures comprising kinetically trapped spike patterns. The present work examines a number of variables that control pattern formation associated with this encoding. Control variables include applied magnetic field strength, magnetic field gradient, nanoparticle concentration, solvent evaporation conditions, and alkane solvent chain length. The pattern formation process is captured in six stages of evolution until the solvent host has evaporated and the pattern is permanently fixed. The macropatterns consist of hexagonal arrays that coexist with different pentagonal and heptagonal defects. The Voronoi entropy is calculated for different patterns that arise due to changes in the control parameters. Insight into order in the lattice patterns is achieved by extracting measurables like peak-to-peak spike wavelength, spike population, spike height, and base diameter from the patterns. The pattern measurables depend nonlinearly on the magnetic field gradient, solvent evaporation rate, and solvent chain length. Nanoparticle concentration does not impact the measurables significantly. Nonetheless, the results agree qualitatively with a linear expression for the critical magnetization and wavelength that explicitly contains the field gradient and surface tension.

The control of dry-out patterns using bubble-containing droplets

Hypothesis: For an evaporating nanofluid droplet that contains a bubble inside, we suspect the bubble boundary remains pinned during evaporation whereas the droplet perimeter recedes. Thus, the dry-out patterns are mainly determined by the presence of the bubble and their morphology can be tuned by the size and location of the added bubble.Experiments: Bubbles with varying base diameters and lifetimes are added into evaporating droplets that contain nanoparticles with different types, sizes, concentrations, shapes, and wettability. The geometric dimensions of the dry-out patterns are measured.Findings: For a droplet containing a long-lifetime bubble, a complete ring-like deposit forms, and its diameter and thickness increases and decreases with the bubble base diameter, respectively. The ring completeness, i.e., the ratio of actual ring length to its imaginary perimeter, decreases with the decrease in bubble lifetime. The pinning of droplet receding contact line by particles near the bubble perimeter has been found to be the key factor leading to ring-like deposits. This study introduces a strategy of producing ring-like deposit and allows a control of the ring morphology in a simple, cheap, and impurity-free fashion, which is applicable to various applications associated with evaporative self-assembly.

Large-scale production of high-quality elastic structural color films based on hydrogen bond and colloidal charge co-driven silica microsphere self-assembly

Photonic crystals (PCs) could revolutionize the modern engineering field. However, the commonly used large-scale roll-to-roll fabrication techniques are limited by the utilization of complex materials and devices. In this work, a method combining evaporative self-assembly and roll-to-roll precision printing was used for the ultrafast fabrication of large-area colloidal crystals. In this process, hydrogen bonding and colloidal charge cooperate to promote the formation of highly ordered colloidal crystals from SiO2 particles with virtually crack-free textures. The as-fabricated PCs films exhibits excellent optical and mechanical properties, including uniform and saturated colors (1 > ΔE·ab for 27 orthogonal points), long service life (>12 months), a wide operating temperature range (25–90 °C), superior bending resistance (>190,000 cycles), good folding resistance (>320 cycles), and excellent reversibility (>27,000 cycles). This work provides new insights into the self-assembly of colloidal SiO2 particles that will enable the application of PCs films in the back covers of mobile phones and multicolor displays.

Evaporation induced self-assembly of silica nanoparticles on ITO substrates in a confined cell for vertical alignment of liquid crystals and performance analysis

The work reported herein advances the approach to achieve the vertical alignment (VA) of liquid crystals (LCs) by directly forming the multilayer self-assembly of nanoparticles (NPs) on the indium tin oxide (ITO) substrates in a confined cell. In this method, for confined evaporative self-assembly of NPs, the colloidal solution of uniformly dispersed 0.3 wt% silica NPs (SNPs) in deionized (DI) water was injected in between the two ITO coated glass substrates by capillary method. The ITO cell filled with colloidal solution was kept at a fixed temperature of 60°C for uniform thermal evaporation of water to deposit the multilayer of NPs on ITO substrates. The multilayered self-assembly of SNPs on ITO substrates was confirmed through field emission scanning electron microscopy (FESEM) and fourier transform infrared (FTIR) spectroscopy studies. The surface roughness profile of the deposited SNPs-multilayer was analysed by atomic force microscopy (AFM). Further, the contact angle (CA) and surface energy values of SNPs-multilayer deposited ITO substrates were also measured and analyzed comparatively with the values of polyimide (PI) coated ITO substrates. After complete evaporation of water, a negative dielectric anisotropy nematic LC was filled in to the cell using capillary method again and the versatility of prepared substrates was assessed for the VA of the liquid crystal (LC). Inquisitively, confirmation of VA of LC in the present approach was found similar with the PI coated VA (conventional approach) using polarized optical microscopy (POM) and conoscopy studies. In addition, effects of external applied electric field were observed well in order with the orientation of LCs to switch vertically aligned LC (VALC) cells from opaque OFF state to transparent ON state, under crossed polarizers. Also, the obtained results in terms of transmission, threshold voltage, operating voltage, and contrast ratio (CR) of VALC cell prepared with this easy and new approach were found comparable to the conventional approach.

Spatially Ordered Arrays of Colloidal Inorganic Metal Halide Perovskite Nanocrystals via Controlled Droplet Evaporation in a Confined Geometry.

Inorganic metal halide perovskite nanocrystals, such as quantum dots (QDs), have emerged as intriguing building blocks for miniaturized light-emitting and optoelectronic devices. Although conventional lithographic approaches and printing techniques allow for discrete patterning at the micro/nanoscale, it is still important to utilize intrinsic QDs with the concomitant retaining of physical and chemical stability during the fabrication process. Here, we report a simple strategy for the evaporative self-assembly to produce highly ordered structures of CsPbBr3 and CsPbI3 QDs on a substrate in a precisely controllable manner by using a capillary-bridged restrict geometry. Quantum confined CsPbBr3 and CsPbI3 nanocrystals, synthesized via a modified hot-injection method with excess halide ions condition, were readily adapted to prepare colloidal QD solutions. Subsequently, the spatially patterned arrays of the perovskite QD rings were crafted in a confirmed geometry with high fidelity by spontaneous solvent evaporation. These self-organized concentric rings were systemically characterized regarding the center-to-center distance, width, and height of the patterns. Our results not only facilitate a fundamental understanding of assembly in the perovskite QDs to enable the solution-printing process but also provide a simple route for offering promising practical applications in optoelectronics.

Effect of Particles of Irregular Size on the Microstructure and Structural Color of Self-Assembled Colloidal Crystals.

Self-assembled colloidal crystals can exhibit structural colors, a phenomenon of intense reflection within a range of wavelengths caused by constructive interference. Such diffraction effects are most intense for highly uniform crystals; however, in practice, colloidal crystals may include particles of irregular size, which can reduce the quality of the crystal. Despite its importance in realizing high-quality structural colors, a quantitative relationship between particles of irregular size, crystal quality, and the resultant structural color response remains unclear. This study systematically and quantitatively investigates the effect of adding particles of irregular size on the microstructural quality and structural color reflectivity of colloidal crystals formed by evaporative self-assembly via experiment and simulation. We examine two sizes of irregular particles─those which are 1.9 times larger and 0.4 times smaller than the host crystal. We find that small irregular particles are more detrimental to surface crystal quality and structural color reflectivity than large irregular particles. When incorporated with 10% volume fraction of irregularly sized particles, the reflectivity of crystal films with large (small) irregularly sized particles decreases by 18.4 ± 5.6% (27.5 ± 5.8%), and a measure of surface crystal quality derived from Fourier analysis of scanning electron microscopy images reduces by 40.0 ± 4.5% (48.8 ± 6.0%). By modeling colloidal films incorporated with irregular particles via molecular dynamics simulation and computing the reflection spectra of the modeled crystals via the finite-difference time-domain method, we find that the peak reflectivity of the assembled structures increases monotonically with overall crystallinity, and that overall crystallinity is correlated with the volume fraction of incorporated irregular particles. The quantitative relationships developed in this study can be applied to predict the level of irregularly sized particles that can be tolerated in colloidal films before significant degradation in crystal quality and reflectivity occurs.

Morphological and Orientational Controls of Self-Assembly of Gold Nanorods Directed by Evaporative Microflows.

Evaporative self-assembly of noble metal nanoparticles into ordered structures holds great promise for fabricating optical and plasmonic devices by virtue of its low cost, high efficiency, and ease of operation. However, poor control of Marangoni flows is one of the challenges accounting for realizing a well-defined assembly. Herein, based on the theoretical analysis of the influence of evaporative intensity on the assembly, two simple but reliable flow-field-confinement platforms are designed to control the evaporative microflows and to work concurrently with depletion forces to enable the regulated self-assembly of gold nanorods. Orientationally ordered assemblies are realized by the designed strong unidirectional microflow in a capillary, and a device-scale assembly of monolayer membrane is obtained by the created weak convection in homemade glass cells. Morphologically diversified superstructure assemblies, such as spherulite-like, boundary-twisted, chiral spiral assemblies, and merging membranes with a π-twisted domain wall, are obtained due to the spontaneous symmetry breaking or in the presence of defects, such as surface steps and screw dislocations. Optical anisotropy and polarization-dependent behaviors of these assemblies are further revealed, implying the potential applications in plasmonic coupling devices and optoelectronic components. An understanding of the entropy-driven assembly behaviors and control of evaporative microflows to guide the self-assembly of gold nanorods provides insights into the general bottom-up approach that is helpful for constructing complex yet robust nanosuperstructures.

Random photoluminescence emission base-on droplet evaporative segregation of All-inorganic perovskite for All-photonic cryptographic primitive

Segregation is a phenomenon of inhomogeneous distribution of constituent elements during crystallization and could be found in alloy, polymers, colloid, etc. Some researchers have also found component segregation in perovskite crystals. Until now, the existing research reports are all about the halogen segregation of perovskite at the micro level, while the research about the component segregation of perovskite at the macro level is blank, leaving no relevant application developed. Therefore, we can broaden the PUFs-based application of perovskite crystals by employing the multi-wavelength emission property arising from component macrosegregation. We synthesized perovskite crystal arrays with macroscopic composition segregation in one step by surface-tension-confined evaporative self-assembly. The macrosegregation in perovskite crystals prepared with different halogen ratios and temperature was surveyed. The photoluminescence spectra of perovskite crystals were investigated. Perovskite crystals with composition segregation could generate physically unclonable cryptographic primitives, which were made by a simple and random process and difficult to replicate. According to the number of peaks in the spectrum, we converted the optical response into quaternary cryptographic keys, and demonstrated the randomness and stability of the system. This study excavated the application prospect of macroscopic component segregation perovskite in all-photonic cryptographic primitives.

Rational design of multi-walled carbon nanotube-reduced graphene oxide hierarchical porous paper toward superior electromagnetic interference shielding

The ever-intensifying electromagnetic (EM) pollution drives the intense demand for EM shielding materials. Through evaporative self-assembly and hydrazine hydrate vapor reduction strategy, intricate multiwalled carbon nanotube (MWCNT) ingeniously anchors on the porous reduced graphene oxide (RGO) paper. The synthesized MWCNT-RGO composite paper manifests a better EMI shielding performance compared with pure RGO. Typically, S5-15 (5 wt% MWCNT, 15 g mixture) furnishes the maximum electromagnetic shielding effectiveness up to 47.88 dB with a thickness of 1.04 mm in the X band. These ingenious bicomponent microstructures possess abundant heterointerfaces and defects. Consequently, they synergistically balance the impedance matching, and contribute to conduction loss, polarization relaxation and multiple reflection and scattering. This work supplies the inspiration for the facile preparation of carbon composite with high EM shielding efficiency and thin lamellation by consolidating MWCNT and RGO to form porous heterostructure.

(Invited) Globally Aligned, Wafer-Scale Deposition of Carbon Nanotubes Via Interfacial Assembly

Floating evaporative self-assembly (FESA) is a solution-based technique for fabricating highly-aligned semiconducting carbon nanotube films.1,2 Field-effect transistors (FETs) based on carbon nanotubes aligned via FESA have exhibited current densities exceeding that of GaAs and Si, demonstrating the promise of this technique.3 However, the global uniformity of FESA films is poor, as the films are composed of stripes of aligned and randomly oriented carbon nanotubes. Additionally, this technique is inherently difficult to scale. In the work presented here, we demonstrate a scalable technique to overcome the shortcomings of FESA and to achieve globally uniform films of aligned carbon nanotubes at desirable packing densities for FETs.In our technique, carbon nanotubes are continuously aligned across target substrates by lifting the substrates through a flowing nanotube ink/water interface. The ink/water interface collects and confines the nanotubes, which is vital to achieving a high degree of alignment. Polarized Raman spectroscopy mapping is used to quantify the degree of alignment in the resulting aligned nanotube films. The full width at half maximum (FWHM) of the alignment distribution within the films is 6.0° measured across a 1 mm2 area. We control the aligned carbon nanotube packing density from 0.2 to 59 µm-1 by varying the ink concentration from 0.1 to 100 µg mL-1. Using optimized conditions, we demonstrate the scalability of this technique by aligning carbon nanotubes across a 100 mm wide wafer. Charge transport measurements are performed using FETs with the aligned carbon nanotube films as the active channels, and the performance is compared to FETs based on FESA films.1. Jinkins, K., R. et al. Nanotube Alignment Mechanism in Floating Evaporative Self-Assembly. Langmuir 33, 13407–13414 (2017).2. Joo, Y., Brady, G. J., Arnold, M. S. & Gopalan, P. Dose-Controlled, Floating Evaporative Self-assembly and Alignment of Semiconducting Carbon Nanotubes from Organic Solvents. Langmuir 30, 3460–3466 (2014).3. Brady, G. J. et al. Quasi-ballistic carbon nanotube array transistors with current density exceeding Si and GaAs. Sci. Adv. 2, (2016).

Facile fabrication of porous fire-resistant graphene macro-assembly with outstanding electromagnetic interference shielding performance

Free-standing bifunctional reduced graphene oxide paper (RGOP) was facilely fabricated by evaporative self-assembly and hydrazine hydrate vapor reduction. The RGOP integrates remarkable fire resistance and outstanding electromagnetic interference (EMI) shielding performance with a total shielding effectiveness value of 41.5 dB at 0.49 mm thickness in the X band. This research provides a facile pathway to fabricate graphene macro-assembly for fire safety and EMI shielding applications.

Highly Aligned Array of Heterostructured Polyflourene-Isolated Boron Nitride and Carbon Nanotubes.

Boron nitride nanotubes (BNNTs) have attracted increasing attention for their exceptional thermal, electronic, and optical properties. However, the progress in BNNTs applications has largely been limited by the low purity of as-synthesized BNNTs and inefficient solution-processing protocols due mainly to the instability of BNNTs in most of the solvents. Therefore, fabrication of highly pure, stable, and fully individualized BNNTs in a rational manner is required. Here, we report a significant improvement in the preparation of well-dispersed BNNTs, utilizing conjugated polymers that interact with BNNTs, allowing selective sorting and individualization of the nanotubes. Evidence of strong interactions between the polymers and BNNTs was observed by optical absorption and photoluminescence spectroscopies, while effective individualization was observed by electron microscopy. The sorted BNNTs were successfully used in a solution-processing protocol called dose-controlled, floating evaporative self-assembly (DFES) previously established for single-walled carbon nanotubes (SWCNT) array fabrication. A device fabricated via DFES from the sorted BNNTs mixed with polymer-wrapped, semiconducting single-walled carbon nanotubes (s-SWCNTs) exhibited an on-state conductance of 253 ± 6 μS μm-1 and an on/off ratio of 106.6±0.4 for a gate voltage of -0.1 V. This breakthrough in BNNT dispersion and isolation is a significant advancement toward the exploitation of BNNTs in future applications.

Opaque and translucent films from aqueous microfiber suspensions by evaporative self-assembly

Films were prepared by casting microfiber (MF) suspensions on hydrophobic and hydrophilic substrates at controlled conditions (23 °C and 50% relative humidity). It was found that opaque films are formed on the hydrophilic surface, while translucent films are formed on the hydrophobic one. The physical and mechanical properties of the MF films were found to be comparable to those of nano-fibrillated cellulose and microfibrillated cellulose films. The observations from the microfiber film formation on the two substrates of different wettability are discussed in the context of the evaporation of water from sessile droplets containing nanoparticles.

Enabling the Selective Detection of Endocrine-Disrupting Chemicals via Molecularly Surface-Imprinted "Coffee Rings".

Molecularly imprinted polymers (MIPs) represent an intriguing class of synthetic materials that can selectively recognize and bind chemical or biological molecules in a variety of value-added applications in sensors, catalysis, drug delivery, antibodies, and receptors. In this context, many advanced methods of implementing functional MIP materials have been actively studied. Herein, we report a robust strategy to produce highly ordered arrays of surface-imprinted polymer patterns with unprecedented regularity for MIP-based sensor platform, which involves the controlled evaporative self-assembly process of MIP precursor solution in a confined geometry consisting of a spherical lens on a flat Si substrate (i.e., sphere-on-flat geometry) to synergistically utilize the "coffee-ring" effect and repetitive stick-slip motions of the three-phase contact line simply by solvent evaporation. Highly ordered arrays of the ring-patterned MIP films are then polymerized under UV irradiation to achieve semi-interpenetrating polymer networks. The extraction of templated target molecules from the surface-imprinted ring-patterned MIP films leaves behind copious cavities for the recognizable specific "memory sites" to efficiently detect small molecules. As a result, the elaborated surface structuring effect, sensitivity, and specific selectivity of the coffee-ring-based MIP sensors are scrutinized by capitalizing on an endocrine-disrupting chemical, 2,4-dichlorophenoxyacetic acid (2,4-D), as an example. Clearly, the evaporative self-assembly of nonvolatile solutes in a confined geometry renders the creation of familiar yet ordered coffee-ring-like patterns for a wide range of applications, including sensors, scaffolds for cell motility, templates, substrates for neuron guidance, etc., thereby dispensing with the need of multistep lithography techniques and external fields.

Evaporative self-assembly of the binary mixture of soft colloids.

We have reported experimental studies on the self-assembly and degree of ordering of a binary mixture of soft colloids in monolayer deposits obtained by controlled evaporation. A sessile drop containing soft colloids is evaporated on a solid surface to achieve a loosely-packed two-dimensional deposit with a hexagonal arrangement. The soft microgel particles possess a hard core with a compliant corona, which plays a crucial role in retaining the crystallinity of the binary particle monolayer. The ordered arrangement of the binary mixture is observed even when the bulk diameter of one type of particle is 25% higher than the other, irrespective of their mixing ratio (1 : 3, 1 : 1, and 3 : 1). The microgel particles of both sizes are found to be homogeneously distributed throughout the deposit, completely suppressing the size-dependent particle segregation. Furthermore, in contrast to the self-assembly of bidisperse hard colloids, wherein the lattice distorts to accommodate particles of disparate sizes, in soft colloids, the particles deform at the interface to preserve the crystalline lattice. Moreover, unlike the gradual order-to-disorder transition observed in the deposits consisting of monodisperse microgel particles, the deposits of a binary mixture of microgels exhibit no noticeable trend. The areal disorder parameter, pair correlation function and the shape factor which quantifies the local ordering of particles in the deposit indicate the absence of a distinct order-to-disorder transition for the binary mixtures.

Evaporative self-assembly of soft colloidal monolayers: the role of particle softness.

We investigate the sessile drop evaporation aided self-assembly of microgel particles by varying their softness. Evaporation of sessile drops containing amphiphilic microgel particles at suitable concentrations results in uniform monolayer deposits that span the entire drop area. At lower concentrations, the deposits are in the form of monolayer coffee rings whose width scales with particle concentration. Using softer microgels synthesised with a lower quantity of crosslinker, we show that the monolayer coffee rings do not form at low particle concentrations. The microgels adsorbed at the interface deform, and the extent of deformation depends on the softness of the microgels as well as their concentration at the interface. Upon complete evaporation of the solvent, the microgel-laden interface is transferred to the substrate. The final deposit shows hexagonal particle arrays where the interparticle separation increases with increasing microgel softness and decreases with particle concentration in the drop. Further insight into the role of microgel softness in the microstructure of the particulate deposits is obtained by measuring the viscoelasticity of the particle-laden interface. Interestingly, the interface loaded with lesser crosslinked microgels exhibits viscoelastic nature even at lower particle concentrations, whereas the higher crosslinked microgels show viscous behaviour.

Link among array non-uniformity, threshold voltage, and subthreshold swing degradation in aligned array carbon nanotube field effect transistors

Threshold voltage variation is a problem in field effect transistors (FETs) fabricated from arrays of aligned semiconducting carbon nanotubes. Moreover, the subthreshold swing of FETs fabricated from arrays of nanotubes is often several times larger than the subthreshold swing of FETs fabricated from a single nanotube or nanotube bundle. Here, we experimentally quantify the impact of nanotube bundling and array non-uniformity on threshold voltage variation and subthreshold swing degradation in arrays of aligned semiconducting nanotubes deposited by floating evaporative self-assembly. The height (and, therefore, degree of bundling) and array morphology of more than one hundred back-gated FETs (with the nanotube channel exposed) are mapped via atomic force microscopy. Both threshold voltage and subthreshold swing significantly increase as the degree of bundling increases—showing a clear link between the physical characteristics of an array and electrical properties. Modeling shows that much of the subthreshold swing degradation in arrays can be attributed to the bundling–threshold voltage link, in which polydispersity in bundle size within an array causes a bundle-by-bundle shift in threshold voltage and a gradual turn-on of the FET. Increased off-current also plays a role in increasing the sub-threshold swing. These findings highlight the importance of synthesizing and assembling arrays of aligned nanotubes that are highly ordered, with uniform and repeatable morphology.