Into the Facet-Selectivity of Sequenced Amphiphilic Peptoids at the Au-Water Interface

Shape-controlled colloidal nanocrystal syntheses often require aid from facet-selective solution-phase chemical additives to regulate atom addition/migration fluxes or oriented particle attachment. Because of their highly tunable chemical property and robustness to a wide range of experimental conditions, peptoids contribute to a very promising group of next-generation functional chemical additives. To generalize the design philosophy, it is critical to understand the origin of facet selectivity at the molecular level. We employ molecular dynamics simulations and biased sampling methods to investigate the origin of Au(111)-favored adsorption of a peptoid, Nce3Ncp6, that is evidenced to assist the formation of five-fold twinned nanostructures. We find that the facet-selectivity is achieved through a synergistic effect of both molecule-surface and solvent-surface interactions. Extending beyond the single-chain scenario, the order of peptoid-peptoid and peptoid-surface energetics, i.e., peptoid-Au(100) < peptoid-peptoid < peptoid-Au(111), further amplifies the distinct behavior of Nce3Ncp6 chains on different Au surfaces. Our studies set the stage for future peptoid design in shape-controlled nanocrystal syntheses by probing the facet selectivity from various perspectives.

Dynamics of Monolayer Growth in Vapor–Liquid–Solid GaAs Nanowires Based on Surface Energy Minimization

The vapor–liquid–solid growth of III-V nanowires proceeds via the mononuclear regime, where only one island nucleates in each nanowire monolayer. The expansion of the monolayer is governed by the surface energetics depending on the monolayer size. Here, we study theoretically the role of surface energy in determining the monolayer morphology at a given coverage. The optimal monolayer configuration is obtained by minimizing the surface energy at different coverages for a set of energetic constants relevant for GaAs nanowires. In contrast to what has been assumed so far in the growth modeling of III-V nanowires, we find that the monolayer expansion may not be a continuous process. Rather, some portions of the already formed monolayer may dissolve on one of its sides, with simultaneous growth proceeding on the other side. These results are important for fundamental understanding of vapor–liquid–solid growth at the atomic level and have potential impacts on the statistics within the nanowire ensembles, crystal phase, and doping properties of III-V nanowires.

Surface energetics to assess influence of biomass-type and biomass–adsorbent interactions in expanded beds

In integrated bioprocessing applications, expanded bed adsorption (EBA) chromatography presents an opportunity to harvest biomolecules directly from the crude feedstock. However, unfavorable biomass interactions with adsorbent usually leads to fouling, which reduces its protein binding capacity as it alters column hydrodynamics and binding site availability. In this work, a detailed study on biomass adhesion behavior of four different industrially relevant microorganisms on 26 different, most commonly occurring adsorbent surfaces with varying degrees of surface energy and surface charge has been conducted. The results showed the derivation of a relative “stickiness” factor for every microorganism, which further classifies each organism based on their general degree of adhesion to surfaces with respect to one another. The obtained results can help to better understand the effect of biomass homogenization on biomass–adsorbent interactions in EBA. The data of surface energy and charge for the surfaces investigated in this work can be used to calculate the stickiness factor of other microorganisms of interest and may assist in the development of novel adsorbent materials for EBA chromatography.

Convenient Screening of Antifouling Agents for Direct Recovery of Bioproducts Employing a Fast Microplate Assay

Major limitations in direct recovery of bioproducts from unclarified feedstock are predominantly associated with the presence of suspended whole and lysed biomass in processing systems. Most commonly, biomass interaction with adsorbent beads, synthetic membranes, and other processes surfaces causes fouling. This phenomenon is usually detrimental to bioprocess performance. This study focused on the development of a simple, easy to implement, economical and robust technique to evaluate biomass deposition and screening for chemical agents able to prevent such phenomenon. The results were confirmed by linking biomass deposition with surface energetics according to the extended Derjaguin, Landau, Verwey and Overbeek (xDLVO) theory. Assay development involved the modification of the inside surface of microwell polystyrene plates with diethyl-aminoethyl (DEAE) functional groups. The resulting microplate surface mimics commercial chromatographic anion-exchangers matrices that are prone to biomass fouling. Two biomass types, Saccharomyces cerevisiae and Chinese hamster ovary (S. cerevisiae and CHO, respectively) cells and twenty-five polyelectrolytes or amphiphilic compounds were employed. Results showed that DEAE-modified surface had the highest cell deposition while agent-coated wells showed varying degrees. Direct experimental observations and calculations performed based on xDLVO approach indicated that polyacrylic acid, polymethacrylic acid, and poly(vinyl sulfate) could prevent CHO cells and yeast deposition. On the other hand, polysulphonic acid and poly(sodium 4-styrenesulfonate) were only effective to prevent yeast deposition. Microscopic visualization of polymer-coated beads in the presence of biomass confirmed the mentioned results.

Enhanced Surface Energetics of CNT-Grafted Carbon Fibers for Superior Electrical and Mechanical Properties in CFRPs

Surface enhancement of components is vital for achieving superior properties in a composite system. In this study, carbon nanotubes (CNTs) were grown on carbon fiber (CF) substrates to improve the surface area and, in turn, increase the adhesion between epoxy-resin and CFs. Nickel (Ni) was used as the catalyst in CNT growth, and was coated on CF sheets via the electroplating method. Surface energetics of CNT-grown CFs and their work of adhesion with epoxy resin were measured. SEM and TEM were used to analyze the morphology of the samples. After the optimization of surface energetics by catalyst weight ratio (15 wt.% Ni), CF-reinforced plastic (CFRP) samples were prepared using the hand lay-up method. To validate the effect of chemical vapor deposition (CVD)-grown CNTs on CFRP properties, samples were also prepared where CNT powder was added to epoxy prior to reinforcement with Ni-coated CFs. CFRP specimens were tested to determine their electrical resistivity, flexural strength, and ductility index. The electrical resistivity of CNT-grown CFRP was found to be about 9 and 2.3 times lower than those of as-received CFRP and CNT-added Ni-CFRP, respectively. Flexural strength of CNT-grown Ni-CFRP was enhanced by 52.9% of that of as-received CFRP. Interestingly, the ductility index in CNT-grown Ni-CFRP was 40% lower than that of CNT-added Ni-CFRP. This was attributed to the tip-growth formation of CNTs and the breakage of Ni coating.