Desorption Force Research Articles

Novel strategy for improved sylvite flotation through controlled crystallization

By understanding minerals as crystals, a crystallization-controlled methodology was performed to enhance the floatability of soluble minerals. Here, aimed strategies were applied to modulate the crystallization of KCl salt to grow crystals with various shapes as cubic-, hopper- and needle-like structure. Stereoscope and scanning electronic microscopy (SEM) helped to unveil the morphologies where X ray diffraction (XRD) characterized their high crystallinities. Afterwards, Atomic Force Microscope (AFM) was performed to research the crystallizing behaviors that cubic-like structure was obtained by turbid fast growth, while hopper-like structure formation was due to the constant high supersaturation and needle-like crystal occurred under still fast crystallization. Flotation tests with octadecylamine hydrochloride (ODA) as collector demonstrated the floatability of samples obeyed the order as needle-like (96.19 %) > hopper-like (81.59 %) > cubic-like (80.08 %) KCl samples. The mechanism was studied by surface area and related interaction tests. BET result demonstrated the highest surface area of needle-like structure than that of hopper-like and cubic-like structure. Besides, induction time combined with adhesion & desorption force tests further explained the better interaction of needle-like sample with bubble than cubic-like sample. While the special structure of hopper-like structure with lower weight but inner filled solution resulted in its near equivalent floatability with cubic-like sample. In conclusion, a new strategy for promoting flotation behavior by designing the crystallization of soluble KCl was proposed, shedding some light on further application on other soluble or semi-soluble minerals.

Conceptualizing flexible papers using cellulose model surfaces and polymer particles.

Cellulose, as a naturally abundant and biocompatible material, is still gaining interest due to its high potential for functionalization. This makes cellulose a promising candidate for replacing plastics. Understanding how cellulose interacts with various additives is crucial for creating composite materials with diverse properties, as it is the case for plastics. In addition, the mechanical properties of the composite materials are assumed to be related to the mobility of the additives against the cellulose. Using a well-defined cellulose model surface (CMS), we aim to understand the adsorption and desorption of two polymeric particles (core-shell particles and microgels) to/from the cellulose surface. The nanomechanics of particles and CMS are quantified by indentation measurements with an atomic force microscope (AFM). AFM topography measurements quantified particle adsorption and desorption on the CMS, while peak force AFM measurements determined the force needed to move individual particles. Both particles and the CMS exhibited pH-dependent charge behavior, allowing a tunable interaction between them. Particle adsorption was irreversible and driven by electrostatic forces. In contrast, desorption and particle mobility forces are dominated by structural morphology. In addition, we found that an annealing procedure consisting of swelling/drying cycles significantly increased the adhesion strength of both particles. Using the data, we achieve a deeper understanding of the interaction of cellulose with polymeric particles, with the potential to advance the development of functional materials and contribute to various fields, including smart packaging, sensors, and biomedical applications.

Native Silicon Oxide Properties Determined by Doping.

The physico-chemical properties of native oxide layers, spontaneously forming on crystalline Si wafers in air, can be strictly correlated to the dopant type and doping level. In particular, our investigations focused on oxide layers formed upon air exposure in a clean room after Si wafer production, with dopant concentration levels from ≈1013 to ≈1019 cm-3. In order to determine these correlations, we studied the surface, the oxide bulk, and its interface with Si. The surface was investigated using the contact angle, thermal desorption, and atomic force microscopy measurements which provided information on surface energy, cleanliness, and morphology, respectively. Thickness was measured with ellipsometry and chemical composition with X-ray photoemission spectroscopy. Electrostatic charges within the oxide layer and at the Si interface were studied with Kelvin probe microscopy. Some properties such as thickness, showed an abrupt change, while others, including silanol concentration and Si intermediate-oxidation states, presented maxima at a critical doping concentration of ≈2.1 × 1015 cm-3. Additionally, two electrostatic contributions were found to originate from silanols present on the surface and the net charge distributed within the oxide layer. Lastly, surface roughness was also found to depend upon dopant concentration, showing a minimum at the same critical dopant concentration. These findings were reproduced for oxide layers regrown in a clean room after chemical etching of the native ones.

Regenerability of fly‐ash derived zeolite NaP1: Evaluation via copper recovery

AbstractEffective regeneration of adsorbents is considered as one of the essential qualities for commercial use. However, most of the studies have only reported the adsorption properties and overlooked the reuse of adsorbents. In this study, we determined the regenerability and reusability of fly‐ash derived zeolite (FADZ) NaP1. These adsorbents have become popular to remove pollutants from water, including toxic metals, since they are less expensive, compared to their counterparts, and can be synthesized from a waste product. We evaluated the efficiency of copper (Cu2+) ions recovery from water using multiple regeneration solutions due to medium adsorption selectivity towards Cu2+. We determined the time required for the regeneration using acid, base, and salt solutions. The suitable pH and solution while maintaining the structure of the zeolite were studied. Up to 90% recovery was achieved via three successive regenerations, each taking 3 h using 3 M KCl and 3 M NaCl solutions. X‐ray diffraction (XRD) and fluorescence showed changes in structure after regeneration at pH < 5 and contact time <6 h. The desorption kinetics using KCl solutions can be described by pseudo‐second order model. Freundlich model represents the desorption of Cu2+ ions better than the Langmuir model due to regression coefficient (R2) values in the range of 0.998–1.0. Results suggest a strong ion exchange mechanism as the main driving force for desorption. The type of anions (such as Cl− and OH−) in solution influences regeneration in addition to the exchanging cation.

Mechanical Stability of DNA Corona Phase on Gold Nanospheres.

Noncovalent adsorption of biopolymers on the surface of gold nanoparticles (AuNPs) forms a corona phase that drastically diversify AuNP functions. However, mechanical stabilities of such corona phase are still obscure, hindering the application of biopolymer-coated AuNPs. Here, using optical tweezers, we have observed, for the first time, that DNA corona phase adsorbed on a 5 nm AuNP via two (dA)21 strands in proximity can withstand an average desorption force of 40 pN, which is higher than the stall force of DNA/RNA polymerases. This suggests a new role for AuNPs to modulate replications or transcriptions after binding to prevalent poly(dA) segments in eukaryotic genomes. We have also revealed that with increasing AuNP size (1.8-10 nm), DNA corona becomes harder to remove, likely due to the larger surfaces and flatter facets on bigger AuNPs. These findings provide guidance to design AuNP corona that can withstand harsh environments for biological and materials applications.

(Digital Presentation) Electrochemical Regeneration of Spent Alkaline Absorbent from Direct Air Capture

The atmospheric carbon dioxide (CO2) concentration has increased by nearly 49% compared to preindustrial levels. This increase is primarily ascribed to anthropogenic activities and has caused rapid climate change in recent years. Direct air capture (DAC) technologies, aiming to remove CO2 directly from the atmosphere, are indispensable for mitigating the climate risks.One of the most studied DAC technologies is wet scrubbing with alkaline hydroxide solutions (e.g., KOH). Recently, we developed an electrochemical system that can regenerate spent alkaline absorbents from DAC and desorb high-purity CO2 gas under atmospheric pressure. The electrochemical cell consisted of three compartments, i.e., an anode compartment, an “acidifying” compartment, and a cathode compartment (Figure 1). During the operation, protons (H+) produced from the H2 oxidation at the anode are transported to the acidifying compartment where the spent absorbent coming from the air contactor is fed. The decreasing pH of the acidifying solution facilitates the conversion of bicarbonate/carbonate ions to carbonic acid (H2CO3 *, including dissolved CO2). When the chemical potential of oversaturated H2CO3 * is higher than the partial pressure of CO2 in the gas phase, CO2 can be desorbed. In the cathode compartment, the K+ from acidifying compartment combines with the locally produced hydroxides (OH−) to regenerate the alkaline absorbent. Overall, the electrochemical cell creates a pH swing in two adjacent compartments. CO2 gas is desorbed at low pH while the alkaline absorbent is regenerated at high pH.In the acidifying compartment, the cations changed from K+ to H+ that can displace the equilibrium of the carbon species towards the desorption of CO2 gas. However, this phenomenon brings two limitations to large-scale application of the system. Firstly, the depleting of K+ and HCO3 -/CO3 2- leads to the decrease of conductivity of the acidifying solution, which induces the increase of ohmic losses in the cell. Moreover, the desorbed CO2 gas bubbles in the cell also contributes to the electrical resistance of the cell. Therefore, the current work investigates optimization strategies to reduce the energy consumption of the system.The first strategy is to desorb CO2 into a lower CO2 partial pressure gas phase instead of atmospheric pressure. A decrease in the CO2 partial pressure from 0.9 to 0.3 bar displayed a maximum increase of 13% in gas production due to higher driving force for desorption and a maximum decrease of 7% in cell potential due to reduced gas bubble presence in the cell. The second strategy adds background electrolyte (phosphate or sulfate) into the absorbent. The adding of background electrolyte provided extra conductivity in the acidifying solution when most of the K+ and CO2 have been removed. Furthermore, the background electrolyte reduced the pH of the acidifying solution, which benefits the desorption of CO2. The lowest specific energy consumption achieved in this study was 249 kJ mol-1 CO2 captured under 150 A m-2. This low energy consumption makes the technology competitive among its counterparts. Finally, an equilibrium model has been developed that simulates the performance of the system and indicates further improvement potentials.This work demonstrates the proof of concept of a novel electrochemical direct air capture process. Our main conclusions show that the process has a competent energy consumption and potential for upscaling with the tested optimization strategies. Figure 1

Quantitative Explanation of Basic Compound Retention Mechanisms in Reversed-Phase Mode Liquid Chromatography

The quantitative analysis of the chromatographic behavior of basic compounds measured with pentyl-, hexenyl-, and octyl-bonded silica gels were analyzed in silico employing model phases. The main retention force was the van der Waals (VW) interaction, and the main desorption force was an electrostatic (ES) interaction. The contribution of hydrogen bonding (HB) was weak compared to that for acidic compounds. The quantitative explanation was achieved utilizing the calculated VW, HB, and ES energy values obtained from a molecular mechanics program. The electron localization was observed at the molecular interaction-site calculated MOPAC program. This fundamental approach was like that of explaining chemical reactions. The difference was electron localization in chromatography or electron transfer in a chemical reaction.

Single-Molecule Desorption Studies of Poly(acrylic acid) at Electrolyte/Oxide/TiAlN Interfaces.

The presented studies correlate the surface chemistry of electrochemically oxidized TiAlN hard coatings with the desorption forces of poly(acrylic acid) (PAA) at the electrolyte/oxide/TiAlN interface. Atomic force microscopy (AFM)-based single-molecule force spectroscopy (SMFS) was performed at different pH values to investigate surface chemistry-induced changes in desorption force. The chemical state was characterized by X-ray photoemission spectroscopy and electrochemical analysis. The results show that the desorption forces continuously decrease with increasing pH in the range from pH 5 to 9. The comparison of the desorption forces on rf-sputtered titanium dioxide and aluminum oxide films shows that the electrochemically oxidized surface of TiAlN, in agreement with the revealed surface composition, shows interfacial adhesive properties in contact with PAA and water that resemble a pure titanium oxide layer. Load rate-dependent measurements were performed to analyze both the free energy barrier and the transition state distance.

Covalent Attachment of Single Molecules for AFM-based Force Spectroscopy.

Atomic force microscopy (AFM)-based single molecule force spectroscopy is an ideal tool for investigating the interactions between a single polymer and surfaces. For a true single molecule experiment, covalent attachment of the probe molecule is essential because only then can hundreds of force-extension traces with one and the same single molecule be obtained. Many traces are in turn necessary to prove that a single molecule alone is probed. Additionally, passivation is crucial for preventing unwanted interactions between the single probe molecule and the AFM cantilever tip as well as between the AFM cantilever tip and the underlying surface. The functionalization protocol presented here is reliable and can easily be applied to a variety of polymers. Characteristic single molecule events (i.e., stretches and plateaus) are detected in the force-extension traces. From these events, physical parameters such as stretching force, desorption force and desorption length can be obtained. This is particularly important for the precise investigation of stimuli-responsive systems at the single molecule level. As exemplary systems poly(ethylene glycol) (PEG), poly(N-isopropylacrylamide) (PNiPAM) and polystyrene (PS) are stretched and desorbed from SiOx (for PEG and PNiPAM) and from hydrophobic self-assembled monolayer surfaces (for PS) in aqueous environment.

Thin Polymer Film Force Spectroscopy: Single Chain Pull-out and Desorption.

Atomic force microscopy (AFM) was utilized to investigate the force associated with chain pull-out and single chain desorption of poly(styrene-co-butadiene) random copolymer thin films on mica, silicon, and graphite substrates. Chain pull-out events were common and produced a force of 20-25 pN. The polymer desorption force was strongest on the graphite substrate and weakest on the mica, which agreed with the calculated work of adhesion for each system and the substrate hydrophobicity. Furthermore, it was demonstrated that there was a systematic order to when each of these phenomena occurred during the tip retraction from the surface, which provided information about the structure of the thin films.

A study of the microstructure modification of a space crawling robot adhesive feet based on discrete element method

According to the on-orbit maintenance mission requirements of a proposed space cooperative spacecraft, a new type of space crawling robot, which can be mounted on a grasping manipulator, is proposed. After the active spacecraft and the faulty target form a connection, the crawling robot can move to the spot on the faulty target that requires maintenance to be performed using fine operations. In this paper, the adhesion technology of space crawling robots was studied, and an adhesive microarray structure, which imitates gecko setae, was proposed. The simulation model was established using the discrete element software EDEM. The effects of the structural parameters, such as the contact area, length–diameter ratio, length, diameter, and density, on the adhesion characteristics of the microarrays in zero-gravity space environment were analysed using simulation. Based on the simulation results, a plasma deep etching process was used to process the microarray specimens. The desorption process was tested in the ground environment using the water droplet method, and the tangential desorption force was tested. The experimental data show that the tangential adhesion decreases with an increase in the spacing and the length–diameter ratio. The experimental results are very consistent with the simulation results, which further demonstrated the correctness of the discrete element simulation with respect to the desorption process and the rationality of the optimal design of the microarray structure.

Adhesion and desorption characteristics of high-temperature condensed flue gas dust on filter material surface

This study is based on high-temperature flue gas containing condensed dust and the dust removal of granular bed. The effects of adhesion temperature, filter plate material (99% and 85% corundum), and dust materials (tin, ferric oxide, and fly ash mixed with sodium chloride) on the desorption stress of dust on the filter surface are explored through desorption stress tests. Results show that the desorption force of tin peaks at 800 °C. Adhesion at <900 °C is not observed for ferric oxide but occurs at >900 °C for fly ash blended with sodium chloride. The mixture adheres on the filter surface at >800 °C, and desorption force increases as adhesion temperature and sodium chloride proportion increase. Large desorption stress occurs on the extremely rough surface of the filter material.

Angle-Dependent Atomic Force Microscopy Single-Chain Pulling of Adsorbed Macromolecules from Planar Surfaces Unveils the Signature of an Adsorption-Desorption Transition.

The adsorption–desorption behavior of polymer chains is at the heart of macromolecular surface science and technology. With the current developments in atomic force microscopy (AFM), it has now become possible to address the desorption problem from the perspective of a single macromolecule. Here, we report on desorption of single polymer chains on planar surfaces by AFM-based single molecule force spectroscopy (SMFS) as a function of the pulling angle with respect to the surface-normal direction. SMFS experiments were performed in water with various substrates using different polymers covalently attached to the AFM probe tip. End-grafting at the AFM tip was achieved by surface-initiated polymerization using initiator functionalized tips. We found that the desorption force increases with a decreasing pulling angle, i.e., an enhanced adhesion of the polymer chain was observed. The magnitude of the desorption force shows a weak angular dependence at pulling angles close to the surface normal. A significant increase of the force is observed at shallower pulling from a certain pulling angle. This behavior carries the signature of an adsorption–desorption transition. The angular dependence of the normalized desorption force exhibits a universal behavior. We compared and interpreted our results using theoretical predictions for single-chain adsorption–desorption transitions.

Detachment of Rough Colloids from Liquid–Liquid Interfaces

Particle surface roughness and chemistry play a pivotal role in the design of new particle-based materials. Although the adsorption of rough particles has been studied in the literature, desorption of such particles remains poorly understood. In this work, we specifically focus on the detachment of rough and chemically modified raspberry-like microparticles from water/oil interfaces using colloidal-probe atomic force microscopy. We observe different contact-line dynamics occurring upon particle detachment (pinning vs sliding), depending on both the particle roughness and surface modification. In general, surface roughness leads to a reduction of the desorption force of hydrophobic particles into the oil and provides a multitude of pinning points that can be accessed by applying different loads. Our results hence suggest future strategies for stabilization and destabilization of Pickering emulsions and foams.

Analysis of acid-base interactions at Al2O3 (11-20) interfaces by means of single molecule force spectroscopy

Single molecule force spectroscopy (SMFS) was employed to investigate the interaction forces between aliphatic amino, hydroxyl and ether groups and aluminum oxide single crystal surfaces in an aqueous electrolyte at pH=6. The force studies were based on the variation of the terminal group of polyethylene glycol which was bound via a SAu bond to the gold coated AFM tip. X-ray Photoelectron Spectroscopy (XPS) was performed to characterize the surface chemistry of the substrate. Force distance curves were measured between the PEG-NH2, OH and OCH3 functionalized atomic force microscope (AFM) tip and the non-polar single crystalline Al2O3(11-20) surface. The experimental results exhibit non-equilibrium desorption events which hint at acid-base interactions of the electron donating hydroxyl and amino groups with Al-ions in the surface of the oxide. The observed desorption forces for the NH2, OH/Al2O3(11-20) were in the range of 100–200pN.

Pulling angle-dependent force microscopy.

In this paper, we describe a method allowing one to perform three-dimensional displacement control in force spectroscopy by atomic force microscopy (AFM). Traditionally, AFM force curves are measured in the normal direction of the contacted surface. The method described can be employed to address not only the magnitude of the measured force but also its direction. We demonstrate the technique using a case study of angle-dependent desorption of a single poly(2-hydroxyethyl methacrylate) (PHEMA) chain from a planar silica surface in an aqueous solution. The chains were end-grafted from the AFM tip in high dilution, enabling single macromolecule pull experiments. Our experiments give evidence of angular dependence of the desorption force of single polymer chains and illustrate the added value of introducing force direction control in AFM.

Experimental study on freeze drying of Loy Yang lignite and inhibiting water re-adsorption of dried lignite

Loy Yang lignite with a high water content was dewatered by freeze drying (FD). The drying kinetics of FD was calculated using thin-layer drying models given in the literature. Residual water content, re-adsorption or desorption behaviors, and pore size distributions of all of the samples were investigated. Furthermore, coating with different amounts of kerosene by direct mixing or adsorption methods to restrain water re-adsorption was also investigated. The results showed that FD dewatering contained three steps: a fast dewatering period (∼2h), followed by a reduced drying-rate period (2–3h) and an apparently falling-rate period (>3h). The Midilli-Kucuk model described the drying process perfectly and could be employed to predict residual water content in the sample at any time during the FD dewatering process. The moisture holding capacity (MHC) of the FD-treated samples was lower than that of raw lignite, which is because of the effect of the water–lignite bond strength and the diffusion adsorption or desorption force. Moreover, adding kerosene by either adsorption or direct-mixing methods can both decrease MHC because kerosene is coated on the surface and in the pores of the lignite. These prevent water re-adsorption. The adsorption method is better than the direct-mixing method because it consumes less kerosene.

Electromagnetophoretic Dynamic Force Measurement of Particle-Wall Interaction in Solution; Effects of pH and Metal Ions

The electromagnetophoretic buoyancy exerted on a carboxylated polystyrene particle in an electrolyte solution was utilized for the measurements of the desorption force of the particles from the car...

Forced Desorption of Bovine Serum Albumin and Lysozyme from Graphite: Insights from Molecular Dynamics Simulation.

We use molecular dynamics (MD) simulation to study the adsorption and desorption of two widely different proteins, bovine serum albumin (BSA) and lysozyme, on a graphite surface. The adsorption is modeled using accelerated MD to allow the proteins to find optimum conformations on the surface. Our results demonstrate that the "hard protein" lysozyme retains much of its secondary structure during adsorption, whereas BSA loses it almost completely. BSA has a considerably larger adsorption energy compared to that of lysozyme, which does not scale with chain length. Desorption simulations are carried out using classical steered MD. The BSA molecule becomes fully unzipped during pull-off, whereas several helices survive this process in lysozyme. The unzipping process shows up in the force-distance curve of BSA as a series of peaks, whereas only a single or few, depending on protein orientation, force peaks occur for lysozyme. The maximum desorption force is larger for BSA than for lysozyme, but only by a factor of about 2.3.

Mechanism of Reversible Peptide-Bilayer Attachment: Combined Simulation and Experimental Single-Molecule Study.

The binding of peptides and proteins to lipid membrane surfaces is of fundamental importance for many membrane-mediated cellular processes. Using closely matched molecular dynamics simulations and atomic force microscopy experiments, we study the force-induced desorption of single peptide chains from phospholipid bilayers to gain microscopic insight into the mechanism of reversible attachment. This approach allows quantification of desorption forces and decomposition of peptide-membrane interactions into energetic and entropic contributions. In both simulations and experiments, the desorption forces of peptides with charged and polar side chains are much smaller than those for hydrophobic peptides. The adsorption of charged/polar peptides to the membrane surface is disfavored by the energetic components, requires breaking of hydrogen bonds involving the peptides, and is favored only slightly by entropy. By contrast, the stronger adsorption of hydrophobic peptides is favored both by energy and by entropy and the desorption forces increase with increasing side-chain hydrophobicity. Interestingly, the calculated net adsorption free energies per residue correlate with experimental results of single residues, indicating that side-chain free energy contributions are largely additive. This observation can help in the design of peptides with tailored adsorption properties and in the estimation of membrane binding properties of peripheral membrane proteins.