A general approach to controlling the surface composition of poly(ethylene oxide)-based block copolymers for antifouling coatings

Sulfobetaine Zwitterions with Embedded Fluorocarbons: Synthesis and Interfacial Properties

We describe the preparation of a new set of fluorinated sulfobetaine (FSB) zwitterionic polymers in which fluorocarbon moieties are attached directly to the zwitterionic components. An efficient two-step modification to the conventional sulfobetaine methacrylate monomer synthesis gave access to a series of polymer zwitterions containing varying extents of fluorocarbon character. FSB methacrylates proved amenable to homo- and copolymerizations using reversible addition-fragmentation chain transfer (RAFT) conditions, affording polymers with molecular weights ranging from 5 to 20 kDa and with low molecular weight distributions. Thin films of FSB homopolymers on glass proved stable to aqueous environments and exhibited increasing hydrophobicity with fluorocarbon content, as well as remarkably large water contact angle hysteresis values that enable pinning of water droplets on hydrophobic surfaces, reminiscent of the "petal effect" found in nature. FSB-containing copolymers in aqueous media demonstrated markedly reduced oil-water interfacial tension values, even with moderate (20-50 mol %) FSB incorporation.

Effects of Amphiphilic Polypeptoid Side Chains on Polymer Surface Chemistry and Hydrophilicity

Polymers are commonly used in applications that require long-term exposure to water and aqueous mixtures, serving as water purification membranes, marine antifouling coatings, and medical implants, among many other applications. Because polymer surfaces restructure in response to the surrounding environment, in situ characterization is crucial for providing an accurate understanding of the surface chemistry under conditions of use. To investigate the effects of surface-active side chains on polymer surface chemistry and resultant interactions with interfacial water (i.e., water sorption), we present synchrotron ambient pressure X-ray photoelectron spectroscopy (APXPS) studies performed on poly(ethylene oxide) (PEO)- and poly(dimethylsiloxane) (PDMS)-based polymer surfaces modified with amphiphilic polypeptoid side chains, previously demonstrated to be efficacious in marine fouling prevention and removal. The polymer backbone and environmental conditions were found to affect polypeptoid surface presentation: due to the surface segregation of its fluorinated polypeptoid monomers under vacuum, the PEO-peptoid copolymer showed significant polypeptoid content in both vacuum and hydrated conditions, while the modified PDMS-based copolymer showed increased polypeptoid content only in hydrated conditions due to the hydrophilicity of the ether monomers and polypeptoid backbone. Polypeptoids were found to bind approximately 2.8 water molecules per monomer unit in both copolymers, and the PEO-peptoid surface showed substantial water sorption that suggests a surface with a more diffuse water/polymer interface. This work implies that side chains are ideal for tuning water affinity without altering the base polymer composition, provided that surface-driving groups are present to ensure activity at the interface. These types of systematic modifications will generate novel polymers that maximize bound interfacial water and can deliver surface-active groups to the surface to improve the effectiveness of polymer materials.

Surface Design of Liquid Separation Membrane through Graft Polymerization: A State of the Art Review

Surface modification of membranes is an effective approach for imparting unique characteristics and additional functionalities to the membranes. Chemical grafting is a commonly used membrane modification technique due to its versatility in tailoring and optimizing the membrane surface with desired functionalities. Various types of polymers can be precisely grafted onto the membrane surface and the operating conditions of grafting can be tailored to further fine-tune the membrane surface properties. This review focuses on the recent strategies in improving the surface design of liquid separation membranes through grafting-from technique, also known as graft polymerization, to improve membrane performance in wastewater treatment and desalination applications. An overview on membrane technology processes such as pressure-driven and osmotically driven membrane processes are first briefly presented. Grafting-from surface chemical modification approaches including chemical initiated, plasma initiated and UV initiated approaches are discussed in terms of their features, advantages and limitations. The innovations in membrane surface modification techniques based on grafting-from techniques are comprehensively reviewed followed by some highlights on the current challenges in this field. It is concluded that grafting-from is a versatile and effective technique to introduce various functional groups to enhance the surface properties and separation performances of liquid separation membranes.

Expanding the Potential of the Solvent-Assisted Method to Create Bio-Interfaces from Amphiphilic Block Copolymers

Artificial membranes, as materials with biomimetic properties, can be applied in various fields, such as drug screening or bio-sensing. The solvent-assisted method (SA) represents a straightforward method to prepare lipid solid-supported membranes. It overcomes the main limitations of established membrane preparation methods, such as Langmuir-Blodgett (LB) or vesicle fusion. However, it has not yet been applied to create artificial membranes based on amphiphilic block copolymers, despite their enhanced mechanical stability compared to lipid-based membranes and bio-compatible properties. Here, we applied the SA method on different amphiphilic di- and triblock poly(dimethylsiloxane)-block-poly(2-methyl-2-oxazoline) (PDMS-b-PMOXA) copolymers and optimized the conditions to prepare artificial membranes on a solid support. The real-time membrane formation, the morphology, and the mechanical properties have been evaluated by a combination of atomic force microscopy and quartz crystal microbalance. Then, selected biomolecules including complementary DNA strands and an artificial deallylase metalloenzyme (ADAse) were incorporated into these membranes relying on the biotin-streptavidin technology. DNA strands served to establish the capability of these synthetic membranes to interact with biomolecules by preserving their correct conformation. The catalytic activity of the ADAse following its membrane anchoring induced the functionality of the biomimetic platform. Polymer membranes on solid support as prepared by the SA method open new opportunities for the creation of artificial membranes with tailored biomimetic properties and functionality.

Review of silicone surface modification techniques and coatings for antibacterial/antimicrobial applications to improve breast implant surfaces

Silicone implants are widely used in the medical field for plastic or reconstructive surgeries for the purpose of soft tissue issues. However, as with any implanted object, healthcare-associated infections are not completely avoidable. The material suffers from a lack of biocompatibility and is often subject to bacterial/microbial infections characterized by biofilm growth. Numerous strategies have been developed to either prevent, reduce, or fight bacterial adhesion by providing an antibacterial property. The present review summarizes the diverse approaches to deal with bacterial infections on silicone surfaces along with the different methods to activate/oxidize the surface before any surface modifications. It includes antibacterial coatings with antibiotics or nanoparticles, covalent attachment of active bacterial molecules like peptides or polymers. Regarding silicone surfaces, the activation step is essential to render the surface reactive for any further modifications using energy sources (plasma, UV, ozone) or chemicals (acid solutions, sol-gel strategies, chemical vapor deposition). Meanwhile, corresponding work on breast silicone prosthesis is discussed. The latter is currently in the line of sight for causing severe capsular contractures. Specifically, to that end, besides chemical modifications, the antibacterial effect can also be achieved by physical surface modifications by adjusting the surface roughness and topography for instance.

Omni-Directional Protected Nanofiber Membranes by Surface Segregation of PDMS-Terminated Triblock Copolymer for High-Efficiency Oil/Water Emulsion Separation

An excellent antifouling membrane with high permeate flux is required for oil/water emulsion separation due to ever-increasing oily industrial wastewater. Thus, an intriguing integration of the Omni-directional protected porous membrane that combines a high porosity nanofiber membrane with a surface segregation mechanism is established for the first time. By applying polydimethylsiloxane(PDMS)-terminated triblock copolymer, the enrichment of the hydrophilic poly(ethylene oxide) (PEO) segment and the nonpolar PDMS segment on the surface of the nanofiber endowed the nanofiber membrane with underwater oleophobicity and low oil adhesion force, exhibiting oil resistance as well as oil release property. An ultrahigh permeate flux of ∼7115 L m^-2 h^-1 with a separation efficiency of ∼97.88% is achieved under the driving force of gravity (∼0.9 kPa), which is the highest permeate flux ever reported under similar conditions. Moreover, the surface segregation nanofiber membrane shows excellent reusability and ultrahigh permeate flux with the assistance of stirring in a long-term test, revealing the promising performances for the further particular application of oily wastewater.

In-Situ Surface Modification of Terpinen-4-ol Plasma Polymers for Increased Antibacterial Activity

Surface modification of thin films is often performed to enhance their properties. In this work, in situ modification of Terpinen-4-ol (T4) plasma polymer is carried out via simultaneous surface functionalization and nanoparticle immobilization. Terpinen-4-ol plasma polymers surface were decorated with a layer of ZnO nanoparticles in an oxygen plasma environment immediately after polymer deposition. A combination of hydrophilic modification and ZnO nanoparticle functionalization of the T4 polymer surface led to an enhancement in antibacterial properties by factor of 3 (from 0.75 to 0.25 CFU.mm-2). In addition, ZnO nanoparticle-modified coatings demonstrated improved UV absorbing characteristics in the region of 300-400 nm by 60% relative to unmodified coatings. The ZnO modified coatings were transparent in the visible region of 400-700 nm. The finding points towards the potential use of ZnO nanoparticle-modified T4 plasma polymers as optically transparent UV absorbing coatings.

Noncovalent Aqua Materials Based on Perylene Diimides

Most robust functional organic materials are currently based on polymers. These materials exhibit high stability, but once formed they are difficult to modify, adapt to their environment, and recycle. Materials based on small molecules that are held together by noncovalent interactions can offer an alternative to conventional polymer materials for applications that require adaptive and stimuli-responsive features. However, it is challenging to engineer macroscopic noncovalent materials that are sufficiently robust for practical applications. This Account summarizes progress made by our group towards the development of noncovalent "aqua materials" based on well-defined organic molecules. These materials are uniquely assembled in aqueous media, where they harness the strength of hydrophobic and π-π interactions between large aromatic groups to achieve robustness. Despite their high stability, these supramolecular systems can dynamically respond to external stimuli. We discuss design principles, fundamental properties, and applications of two classes of aqua materials: (1) supramolecular gels and (2) nanocrystalline arrays. The materials were characterized by a combination of steady-state and time-resolved spectroscopic techniques, electrical measurements, molecular modeling, and high-resolution microscopic imaging, in particular cryogenic transmission electron microscopy (cryo-TEM) and cryogenic scanning electron microscopy (cryo-SEM). All investigated aqua materials are based on one key building block, perylene diimide (PDI). PDI exhibits remarkably stable intermolecular bonds, together with useful chemical and optoelectronic properties. PDI-based amphiphiles carrying poly(ethylene glycol) (PEG) were designed to form linear supramolecular polymers in aqueous media. These one-dimensional arrays of noncovalently linked molecules can entangle and form three-dimensional supramolecular networks, leading to soft gel-like materials. Tuning the strength of interactions between fibers enables dynamic adjustment of viscoelastic properties and functional characteristics. Besides supramolecular gels, we show that simple PDI-based molecules can self-assemble in aqueous medium to form robust organic nanocrystals (ONCs). The mechanical and optoelectronic properties of ONCs are distinctly different from gel-phase materials. ONCs are excellent building blocks for macroscopic free-standing materials that can be used in dry state, unlike hydrogels. Being constructed from small molecules, ONC materials are easy to fabricate and recycle. High thermal robustness, good mechanical properties, and modular design render ONC materials versatile and suitable for a variety of applications. In the future, noncovalent aqua materials can become a sustainable alternative to conventional polymer materials. Examples from our research include stimuli-responsive and recyclable filtration membranes for preparative nanoparticle separation, water purification and catalysis, light-harvesting hydrogels for solar energy conversion, and nanocrystalline films for switchable surface coatings and electronic devices.

Upcycling aromatic polymers through C-H fluoroalkylation

The unique properties imparted by planar, rigid aromatic rings in synthetic polymers make these macromolecules useful in a range of applications, including disposable packaging, aerospace materials, flexible electronics, separation membranes, and engineering thermoplastics. The thermal and chemical stability of aromatic polymers, however, makes it difficult to alter their bulk and/or surface properties and results in challenges during recycling. In response, we report a platform approach for the C-H functionalization of aromatic polymers by taking advantage of their innate reactivity with electrophilic radical intermediates. The method uses mild reaction conditions to photocatalytically generate electrophilic fluoroalkyl radicals for the functionalization of an array of commercially relevant polyaromatic substrates, including post-industrial and post-consumer plastic waste, without altering their otherwise attractive thermomechanical properties. The density of fluorination, and thus the material properties, is tuned by either increasing the reagent concentration or incorporating longer perfluoroalkyl species. Additionally, the installation of versatile chemical functionality to aromatic polymers is demonstrated through the addition of a bromodifluoromethyl group, which acts as an initiator for atom transfer radical polymerization (ATRP) grafting of vinyl polymers. The method described herein imparts new and versatile chemical functionality to aromatic polymers, enabling an efficient approach to diversify the properties of these otherwise recalcitrant commodity plastics and demonstrating a viable pathway to upcycle post-consumer plastic waste.

Antifouling membranes for sustainable water purification: strategies and mechanisms

One of the greatest challenges to the sustainability of modern society is an inadequate supply of clean water. Due to its energy-saving and cost-effective features, membrane technology has become an indispensable platform technology for water purification, including seawater and brackish water desalination as well as municipal or industrial wastewater treatment. However, membrane fouling, which arises from the nonspecific interaction between membrane surface and foulants, significantly impedes the efficient application of membrane technology. Preparing antifouling membranes is a fundamental strategy to deal with pervasive fouling problems from a variety of foulants. In recent years, major advancements have been made in membrane preparation techniques and in elucidating the antifouling mechanisms of membrane processes, including ultrafiltration, nanofiltration, reverse osmosis and forward osmosis. This review will first introduce the major foulants and the principal mechanisms of membrane fouling, and then highlight the development, current status and future prospects of antifouling membranes, including antifouling strategies, preparation techniques and practical applications. In particular, the strategies and mechanisms for antifouling membranes, including passive fouling resistance and fouling release, active off-surface and on-surface strategies, will be proposed and discussed extensively.

De Novo Synthesis of Phosphorylated Triblock Copolymers with Pathogen Virulence-Suppressing Properties That Prevent Infection-Related Mortality

Phosphate is a key and universal "cue" in response to which bacteria either enhance their virulence when local phosphate is scarce or downregulate it when phosphate is adundant. Phosphate becomes depleted in the mammalian gut following physiologic stress and serves as a major trigger for colonizing bacteria to express virulence. This process cannot be reversed with oral supplementation of inorganic phosphate because it is nearly completely absorbed in the proximal small intestine. In the present study, we describe the de novo synthesis of phosphorylated polyethylene glycol compounds with three defined ABA (hydrophilic/-phobic/-philic) structures, ABA-PEG10k-Pi10, ABA-PEG16k-Pi14, and ABA-PEG20k-Pi20, and linear polymer PEG20k-Pi20 absent of the hydrophobic block. The 10k, 16k, and 20k demonstrate the molecular weights of the poly(ethylene glycol) block, and Pi10, Pi14, and Pi20 represent the repeating units of phosphate. Polymers were tested for their efficacy against Pseudomonas aeruginosa virulence in vitro and in vivo by assessing the expression of the phosphate sensing protein PstS, the production of key virulence factor pyocyanin, and Caenorhabditis elegans killing assays. Results indicate that all phosphorylated polymers suppressed phosphate sensing, virulence expression, and lethality in P. aeruginosa. Among all of the phosphorylated polymers, ABA-PEG20k-Pi20 displayed the greatest degree of protection against P. aeruginosa. To define the role of the hydrophobic core in ABA-PEG20k-Pi20 in the above response, we synthesized PEG20k-Pi20 in which the hydrophobic core is absent. Results indicate that the hypdrophobic core of ABA-PEG20k-Pi20 is a key structure in its protective effect against P. aeruginosa, in part due to its ability to coat the surface of bacteria. Taken together, the synthesis of novel polymers with defined structures and levels of phosphorylation may elucidate their antivirulence action against clinically important and lethal pathogens such as P. aeruginosa.

Model Amphiphilic Block Copolymers with Tailored Molecular Weight and Composition in PDMS-Based Films to Limit Soft Biofouling

A set of controlled surface composition films was produced utilizing amphiphilic block copolymers dispersed in a cross-linked poly(dimethylsiloxane) network. These block copolymers contained oligo(ethylene glycol) (PEGMA) and fluoroalkyl (AF6) side chains in selected ratios and molecular weights to control surface chemistry including antifouling and fouling-release performance. Such properties were assessed by carrying out assays using two algae, the green macroalga Ulva linza (favors attachment to polar surfaces) and the unicellular diatom Navicula incerta (favors attachment to nonpolar surfaces). All films performed well against U. linza and exhibited high removal of attached sporelings (young plants) under an applied shear stress, with the lower molecular weight block copolymers being the best performing in the set. The composition ratios from 50:50 to 60:40 of the AF6/PEGMA side groups were shown to be more effective, with several films exhibiting spontaneous removal of the sporelings. The cells of N. incerta were also removed from several coating compositions. All films were characterized by surface techniques including captive bubble contact angle, atomic force microscopy, and near edge X-ray absorption fine structure spectroscopy to correlate surface chemistry and morphology with biological performance.

Heterogeneous surfaces to repel proteins

The nonspecific adsorption of proteins is usually undesirable on solid surfaces as it induces adverse responses, such as platelet adhesion on medical devices, negative signals of biosensors and contamination blockage of filtration membranes. Thus, an important scheme in material science is to design and fabricate protein-repulsive surfaces. Early approaches in this field focused on homogeneous surfaces comprised of single type functionality. Yet, recent researches have demonstrated that surfaces with heterogeneities (chemistry and topography) show promising performance against protein adsorption. In this review, we will summarize the recent achievements and discuss the new perspectives in the research of developing and characterizing heterogeneous surfaces to repel proteins. The protein repulsion mechanisms of different heterogeneous surfaces will also be discussed in details, followed by the perspective and challenge of this emerging field.

Copolymer films containing amphiphilic side chains of well-defined fluoroalkyl-segment length with biofouling-release potential

Novel methacrylate copolymers containing polysiloxane (SiMA) and mixed poly(ethyleneglycol)-perfluorohexyl side chains (MEF) were synthesised and dispersed as surface-active additives in crosslinked PDMS films.

Zwitterionic Antifouling Coatings for the Purification of High-Salinity Shale Gas Produced Water

Fouling refers to the undesirable attachment of organic molecules and microorganisms to submerged surfaces. It is an obstacle to the purification of shale gas produced water and is currently without an effective solution due to the highly contaminated nature of produced water. Here, we demonstrate the direct vapor application of a robust zwitterionic coating to a variety of substrates. The coating remains unprecedentedly hydrophilic, smooth, and effectively antifouling in extremely high salinity solutions (with salt concentration of 200,000 ppm). The fouling resistance is assessed rapidly and quantitatively with a molecular force spectroscopy-based method and corroborated using quartz crystal microbalance system with dissipation monitoring. Grazing angle attenuated total reflectance Fourier transform infrared is used in combination with X-ray photoelectron spectroscopy, atomic force microscope, and in situ spectroscopic ellipsometry to lend insight into the underlying mechanism for the exceptional stability and effectiveness of the zwitterionic coating under high-salinity conditions. A unique coating architecture, where the surface is concentrated with mobile zwitterionic moieties while the bulk is cross-linked to enhance coating durability, was discovered to be the origin of its stable fouling resistance under high salinity. Combined with previously reported exceptional stability in highly oxidative environments and strong fouling resistance to oil and grease, the zwitterionic surface here has the potential to enable low-cost, membrane-based techniques for the purification of produced water and to eventually balance the favorable economics and the concerning environmental impacts of the hydraulic fracturing industry.

Surface Structure and Hydration of Sequence-Specific Amphiphilic Polypeptoids for Antifouling/Fouling Release Applications

Amphiphilic polypeptoids can be designed with specific sequences of hydrophilic and hydrophobic units, which determine their surface properties for antifouling/fouling release purposes. Although the sequence-dependent surface structures of polypeptoids have been extensively investigated, e.g., with X-ray spectroscopy, their molecular structures under the aqueous conditions relevant to marine fouling have not been studied. In this work, we applied sum frequency generation (SFG) vibrational spectroscopy to study the surface structures and hydration of a series of amphiphilic polypeptoid coatings with different sequences in air and water. SFG spectra, in agreement with X-ray spectroscopy studies, revealed that the surface coverage of the hydrophilic N-(2-methoxyethyl)glycine (Nme) units in air is affected by both the number and position of the hydrophobic N-(heptafluorobutyl)glycine (NF) units in the peptoid chain and is negatively correlated with the surface concentration of the fluorine element. Our ability to probe the SFG signals of water molecules at the peptoid surface provides new information on the hydrated film properties. From these SFG signals and the time evolution of water contact angles on the polymers, we see that the hydrated film properties are also dependent upon the peptoid sequence. This work indicates that the surface presence of the Nme groups and the ability of the polymers to order and strongly hydrogen bond with interfacial water molecules determine their antifouling properties, whereas the surface restructuring rate upon contact with water affects their fouling release behaviors.

Microphase Structure, Crystallization Behavior, and Wettability Properties of Novel Fluorinated Copolymers Poly(perfluoroalkyl acrylate-co-stearyl acrylate) Containing Short Perfluorohexyl Chains

Novel fluorinated copolymers of stearyl acrylate (SA) and (perfluorohexyl)ethyl acrylate (C6A), (perfluorohexyl)ethyl methacrylate (C6MA), 2-[[[[2-(perfluorohexyl)]-sulfonyl]methyl] amino]ethyl acrylate (C6SA), and methacrylate (C6SMA) were synthesized via miniemulsion copolymerization. The extremely hydrophobic monomers perfluoroalkyl acrylate (FA) and SA acted as the reactive costabilizer in the miniemulsion system. The microstructure and surface wetting properties of the copolymers were characterized by (1)H NMR, FT-IR, and dynamic contact angle test. The crystallization behaviors and fine surface structures of the copolymer films were determined by differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) analysis. The self-assembled aggregation and roughness of the copolymer films were investigated by atomic force microscopy (AFM). The results showed that the fluorinated side chains interrupted and impeded the crystallizable side chains of SA from forming complete crystals. And the Tm and ΔHf of the copolymers were decreased as a consequence of this effect. The fluorinated side chains in P(C6A/SA) and P(C6MA/SA) arranged between the crystallizable hydrocarbon side chains of SA, while the crystallization structure of fluorinated and nonfluorinated pendant groups existed all at once in copolymers P(C6SA/SA) and P(C6SMA/SA). The four copolymers exhibited very low surface free energy and excellent dynamic water repellency attributed to the restriction of perfluoroalkyl groups combined with crystallization of stearyl pendant groups.

Fluorous Cylindrical Micelles of Controlled Length by Crystallization-Driven Self-Assembly of Block Copolymers in Fluorinated Media

Fluorous solvents have recently found broad applications in medical treatments as well as catalytic transformations, yet the controlled self-assembly of nanomaterials in fluorinated media has remained a challenge. Herein, we report the synthesis of block copolymers containing a crystalline polyferrocenylsilane metalloblock and a highly fluorinated coil block and their controlled self-assembly in fluorinated media. Using the crystallization-driven self-assembly approach, cylindrical micelles have been prepared with controlled lengths and narrow length polydispersities by self-seeding. Finally, by partial functionalization of these block copolymers with fluorescent dye molecules, we show that well-defined, functional nanomaterials can be obtained in the fluorous phase.

A synthetic strategy for the preparation of sub-100 nm functional polymer particles of uniform diameter

An amphiphilic block copolymer surfactant is used to impart modifiable surface functionality to polymer nanoparticles synthesized via emulsion polymerization.

Perfluoropolyether/poly(ethylene glycol) triblock copolymers with controllable self-assembly behaviour for highly efficient anti-bacterial materials

A series of perfluoropolyether/poly(ethylene glycol) (PFPE/PEG) triblock copolymers PEG/PFPE/PEG (P1–P3) and PFPE/PEG/PFPE (P4–P5) were prepared via thiol–ene click reaction in high yields.

Hyperbranched polymers: advances from synthesis to applications

This review summarizes the advances in hyperbranched polymers from the viewpoint of structure, click synthesis and functionalization towards their applications in the last decade.

Adsorption of "soft" spherical particles onto sinusoidally-corrugated substrates

We utilize a Monte Carlo simulation scheme based on the bond fluctuation model to simulate settlement of "soft" adhesive particles onto sinusoidally-corrugated substrates. Particles are composed of a hard inner core with a "soft" adhesive shell made of surface-grafted polymer chains. These chains adhere to surface lattice sites via pair wise non-specific interactions acting between the substrate and the last two segments of the polymer grafts on the particle. This simulation scheme is aimed at comprehending single particle adsorption behavior to find the highest adhesion energy locations for given test surfaces and elucidate test surfaces that reduce adhesion energy. Parameters in this study are set by the particle, the substrate and an interaction parameter between the two. Particle parameters include core diameter (D), grafting density of polymer (σ) and length of grafted polymer (N). Substrate parameters include wavelength (λ) and amplitude (A). Our results show that the wavelength of substrate features plays a significant role in the settlement of single particle systems. At λ = D/2 we observe a minimum in the adhesion energy and at λ = D we observe a uniform settlement location of the particles. Increasing N leads to a reduction in the effectiveness of substrate topography to direct the settlement of individual particles into specific sites on the substrate.