Random Sequential Adsorption: From Continuum to Lattice and Pre-Patterned Substrates

The random sequential adsorption (RSA) model has served as a paradigm for diverse phenomena in physical chemistry, as well as in other areas such as biology, ecology, and sociology. In the present work, we survey aspects of the RSA model with emphasis on the approach to and properties of jammed states obtained for large times in continuum deposition versus that on lattice substrates, and on pre-patterned surfaces. The latter model has been of recent interest in the context of efforts to use pre-patterning as a tool to improve selfassembly in micro- and nanoscale surface structure engineering

Bionanomaterials from plant viruses

Plant virus capsids have emerged as useful biotemplates for material synthesis. All plant virus capsids are assembled with high-precision, three-dimensional structures providing nanoscale architectures that are highly monodisperse, can be produced in large quantities and that cannot replicate in mammalian cells (so are safe). Such exceptional characteristics make plant viruses strong candidates for application as biotemplates for novel and new material synthesis

Fabrication of planar colloidal clusters with template-assisted interfacial assembly.

The synthesis of nanoparticle clusters, also referred to as colloidal clusters or colloidal molecules, is being studied intensively as a model system for small molecule interactions as well as for the directed self-assembly of advanced materials. This paper describes a technique for the interfacial assembly of planar colloidal clusters using a combination of top-down lithographic surface modification and bottom-up Langmuir-Blodgett deposition. Micrometer sized polystyrene latex particles were deposited onto a chemically modified substrate from a decane-water interface with Langmuir-Blodgett deposition. The surface of the substrate contained hydrophilic domains of various size, spacing, and shape, while the remainder of the substrate was hydrophobic. Particles selectively deposited onto hydrophilic regions from the decane-water interface. The number of deposited particles depended on the size of each patch, thereby demonstrating that tuning cluster size is possible by engineering patch geometry. Following deposition, the clusters were permanently bonded with temperature annealing and then removed from the substrate via sonication. The permanently bonded planar colloidal clusters were stable in an aqueous environment and at a decane-water interface laden with isotropic colloidal particles. The method is a simple and fast way to synthesize colloidal clusters with few limitations on particle chemistry, composition, and shape.The authors thank Professor Luis M. Liz-Marzan, head of the Colloidal Chemistry Group at Universidade de Vigo, Spain, for the gold nanorod suspension. The research was performed as part of the IAP program MICROMAST financed by BELSPO. The FWO Vlaanderen, projects G.0554.10 and G.0697.11, as well as the ERC starting grant 337739 - HIENA are gratefully acknowledged for their financial support.This is the accepted manuscript. The final version is available from ACS at http://pubs.acs.org/doi/abs/10.1021/la504383m

Three-dimensional microscale simulation of colloidal particle transport and deposition in chemically heterogeneous capillary tubes

The effect of surface chemical heterogeneity and hydrodynamics on particle transport and deposition in porous media was investigated by microscale simulations using a colloidal particle tracking model, called 3D-PTPO (Three-dimensional particle tracking model by Python® and OpenFOAM®) code. This work is aimed as a step toward modeling of transport and deposition in porous media idealized as a bundle of straight capillary tubes. Therefore, our focus is put upon a three-dimensional capillary with periodically repeating chemically heterogeneous surfaces namely crosswise strips patterned and chess board patterned. The main feature of this recent model is to renew the flow field by reconstructing the pore structure, to take the pore surface modification induced by the volume of the deposited particles into account. The dependency of the deposition probability and the dimensionless surface coverage (Γ/ΓRSA) on the frequency of the pitches (λ), the Péclet number (Pe) and the favorable area fraction (θ), as well as the distribution of the spatial density of deposited particles along the capillary tube were studied. The results indicate that particles tend to deposit at the leading and trailing edges of the favorable strips, and the deposition is more uniform along the patterned capillary compared to the homogeneous one. In addition, for the chemically heterogeneous capillary, in a similar manner as for the homogeneous one, a definite plateau exists for the Γ/ΓRSA at low Péclet values. For high Pe values, the declining trend for Γ/ΓRSA versus Pe is in good agreement with the derived power law dependence already observed in the literature for fully adsorbing surfaces. Moreover, for fixed θ the deposition probability is linearly correlated with λ and for given λ, such a deposition probability is also a linear function of θ

Particle Deposition in Microfluidic Devices at Elevated Temperatures

In microchannels, interaction and transport of micro-/nanoparticles and biomolecules are crucial phenomena for many microfluidic applications, such as nanomedicine, portable food processing devices, microchannel heat exchangers, etc. The phenomenon that particles suspended in liquid are captured by a solid surface (e.g., microchannel wall) is referred to as particle deposition. Particle deposition is of importance in numerous practical applications and is also of fundamental interest to the field of colloid science. This chapter presents researches on fouling and particle deposition in microchannels, especially the effects of temperature and temperature gradient, which have been frequently ‘ignored’ but are important factors for thermal-driven particle deposition and fouling processes at elevated temperatures

Electrical double layer interactions with surface charge heterogeneities

Particle deposition at solid-liquid interfaces is a critical process in a diverse number of technological systems. The surface forces governing particle deposition are typically treated within the framework of the well-known DLVO (Derjaguin-Landau-Verwey-Overbeek) theory. DLVO theory assumes of a uniform surface charge density but real surfaces often contain chemical heterogeneities that can introduce variations in surface charge density. While numerous studies have revealed a great deal on the role of charge heterogeneities in particle deposition, direct force measurement of heterogeneously charged surfaces has remained a largely unexplored area of research. Force measurements would allow for systematic investigation into the effects of charge heterogeneities on surface forces. A significant challenge with employing force measurements of heterogeneously charged surfaces is the size of the interaction area, referred to in literature as the electrostatic zone of influence. For microparticles, the size of the zone of influence is, at most, a few hundred nanometers across. Creating a surface with well-defined patterned heterogeneities within this area is out of reach of most conventional photolithographic techniques. Here, we present a means of simultaneously scaling up the electrostatic zone of influence and performing direct force measurements with micropatterned heterogeneously charged surfaces by employing the surface forces apparatus (SFA). A technique is developed here based on the vapor deposition of an aminosilane (3-aminopropyltriethoxysilane, APTES) through elastomeric membranes to create surfaces for force measurement experiments. This vapor deposition technique produces surfaces with well-defined micropatterned charge heterogeneities consisting of APTES monolayers on both flat and curved mica substrates. Characterization of these surfaces reveals highly charged APTES patches with minimal topographical variations. Force measurements between these micropatterned surfaces and mica results in interaction force profiles intermediate between mica-mica and APTES-mica. These force profiles are compared to a simple linear approximation for calculating forces with charge heterogeneities, expanded here to account for arbitrary charge heterogeneities. Our findings indicate a simple additive contribution between the APTES patches and surrounding mica to the measured force profile and suggest surface forces with charge heterogeneities can be predicted from a simple linear approximation based on the surface coverage of heterogeneities within the zone of influence

Directing Interfacial Events Using Biomimetic Polymer Brushes

Polymer brushes are versatile surface modification tools, wherein composition, architecture and biological functionality can be controlled precisely and independently. By growing biomimetic polymer chains from substrate-bound initiator sites through atom transfer radical polymerization (ATRP), engineered biointerfaces were developed for four application areas. Spatioselective deactivation of ATRP initiator coatings made via chemical vapor deposition polymerization was demonstrated to synthesize micropatterned polymer brushes in a substrate-independent, modular and facile manner. Exposure of 2-bromoisobutyryl groups to UV light resulted in the loss of the bromine atom and effectively inhibited polymer brush growth. Microstructured brushes were selectively grown from those areas on the initiator that were protected from UV exposure, as confirmed by atomic force microscopy (AFM), Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) and imaging ellipsometry. Protein patterns based on specific as well as non-specific adsorption can be created on technologically relevant substrates such as polystyrene, PDMS, polyvinyl chloride and steel. Model surfaces can aid in examining different hypotheses relevant to viral adsorption and formulating design rules for virus-resistant coatings. Thermodynamic models predicted that the extent of viral adsorption is shaped by the interplay between electrostatic attraction offered by binding sites and steric and hydration repulsions arising from surrounding polymer brushes. To verify these predictions, electrostatically heterogeneous carbohydrate-functional brushes were developed. Experimental results confirmed model predictions and offered guidelines for designing virus-resistant surfaces in realistic scenarios where electrostatically attractive defects are prevalent. By allowing the carbohydrate brushes to attain brush thicknesses between 3-5 nm, low levels of protein and viral adsorption could be achieved, even when the defect density was as high as 25-30%. The development of polymeric materials that facilitate the culture of large numbers of human pluripotent stem cells in fully defined conditions, poses a critical engineering challenge. Prior work had indicated that modifying the extent of zwitterionic self-association of PMEDSAH coatings could enhance the propagation rate of human embryonic stem cells (hESCs). Moderately self-associated PMEDSAH coatings were reported to be capable of expanding an initial population of 20,000 hESCS to 4.7 billion pluripotent cells at the end of five weeks, which is 2-fold and 12-fold higher than the estimated propagation rates for unassociated and highly associated coatings respectively. It was hypothesized that a property-prediction tool based on statistical design of experiments could identify reaction parameters that would yield targeted gel architectures. Model predictions were used to decrease the critical thickness at which the wettability transition occurs by merely increasing the catalyst quantity from 1 mol% to 3 mol%. Pro-regenerative M2 macrophages (M2 Mps) have the potential to remediate chronic inflammation in a spectrum of disorders pertaining to macrophage polarization, such as diabetic wounds. By targeting the CD206 receptor on these cells using mannose molecules presented in multivalent architectures, we could engineer coatings that preferentially adhered to M2 cells over pro-inflammatory M1 cells. While a selectivity ratio (for M2 over M1) between 6 to 7 was observed on mannosylated surfaces, the control glucosylated surfaces did not discriminate between M1 and M2 phenotypes, exhibiting a selectivity ratio between 0.4 to 0.7. By applying insights from polymer chemistry, surface science, and thermodynamics, an intimate understanding of biomedically relevant interfacial phenomena was acquired. This enabled the development of a platform based on multifunctional polymer brushes to address diverse problems at the interface of polymers and biology.PHDChemical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/144127/1/rmykmr_1.pd

Scanning Probe Investigations of the Surface Self-Assembly of Organothiols and Organosilanes Using Nanoscale Lithography

Particle lithography and scanning probe lithography were applied to study the kinetics and mechanisms of surface self-assembly processes. Organothiols on Au(111) and organosilane on Si(111) were chosen as model systems for investigations at the nanoscale using atomic force microscopy (AFM). Fundamental insight of structure/property interrelationships and understanding the properties of novel materials are critical for developments with molecular devices. Methods using an AFM probe for nanofabrication have been applied successfully to prepare sophisticated molecular architectures with high reproducibility and spatial precision. The established capabilities of AFM-based nanografting were reviewed for inscribing patterns of diverse composition, to generate complicated surface designs with well-defined chemistries. Nanografting provides a versatile tool for generating nanostructures of organic and biological molecules, as well as nanoparticles. Protocols of nanografting are accomplished in liquid media, providing a mechanism for introducing new reagents for successive in situ steps for 3-D fabrication of designed nanopatterns. Because so many chemical reactions can be accomplished in solution, there are rich possibilities for chemists to design studies of other surface reactions. Surface assembly and self-polymerization of chloromethylphenyltrichlorosilane (CMPS) were investigated using test platforms of organosilanes fabricated with particle lithography. A thin film of octadecyltrichlorosilane (OTS) with well-defined nanopores was prepared on Si(111) to spatially confine the surface assembly of CMPS within nanopores of OTS. Time-dependent changes during the self-polymerization of CMPS was visualized ex situ using AFM. Molecular-level details of CMPS nanostructures were obtained from high resolution AFM images to track the growth of organosilanes on Si(111). Measurements of the heights and diameters of CMPS nanostructures provided quantitative information of the kinetics of CMPS self-polymerization. Scanning probe-based methods of nanolithography were applied to investigate the self-assembly of a tridentate organothiol, 1,1,1-tris(mercaptomethyl)heptadecane (TMMH). Multidentate adsorbates can address problems with long-term stability to oxidation observed with monothiolated n-alkylthiols. Multidentate thiol ligands demonstrate improved resistance to oxidation, thermal desorption and UV exposure. Progressive changes in surface morphology for TMMH assembly onto Au(111) was studied in situ with time-lapse AFM, monitoring changes in surface coverage at different time intervals. Nanoshaving and nanografting were used as molecular rulers to evaluate the thickness of films of TMMH