Silicone Oil Surfaces Research Articles

Biofilm metagenomic characteristics behind high coulombic efficiency for propanethiol deodorization in two-phase partitioning microbial fuel cell

Hydrophobic volatile organic sulfur compounds (VOSCs) are frequently found during sewage treatment, and their effective management is crucial for reducing malodorous complaints. Microbial fuel cells (MFC) are effective for both VOSCs abatement and energy recovery. However, the performance of MFC on VOSCs remains limited by the mass transfer efficiency of MFC in aqueous media. Inspired by two-phase partitioning biotechnology, silicone oil was introduced for the first time into MFC as a non-aqueous phase (NAP) medium to construct two-phase partitioning microbial fuel cell (TPPMFC) and augment the mass transfer of target VOSCs of propanethiol (PT) in the liquid phase. The PT removal efficiency within 32 h increased by 11–20% compared with that of single-phase MFC, and the coulombic efficiency of TPPMFC (11.01%) was 4.32–2.68 times that of single-phase MFC owing to the fact that highly active desulfurization and thiol-degrading bacteria (e.g., Pseudomonas, Achromobacter) were attached to the silicone oil surface, whereas sulfur-oxidizing bacteria (e.g., Thiobacillus, Commonas, Ottowia) were dominant on the anodic biofilm. The outer membrane cytochrome-c content and NADH dehydrogenase activity improved by 4.15 and 3.36 times in the TPPMFC, respectively. The results of metagenomics by KEGG and COG confirmed that the metabolism of PT in TPPMFC was comprehensive, and that the addition of a NAP upregulates the expression of genes related to sulfur metabolism, energy generation, and amino acid synthesis. This finding indicates that the NAP assisted bioelectrochemical systems would be promising to solve mass-transfer restrictions in low solubility contaminates removal.

Free Arc Disperses-Sprays Carbon Nanotubes and Silicon Carbide, Preparing Thermal Silicone Grease

Thermal conductivity grease (TSG) is an important interface material for electronic devices’ heat dissipation. A continuous free-arc dispersion-spraying method of carbon nanotubes (CNTs) and nanocrystalline silicon carbide (SiC) for the preparation of TSG is reported. CNTs and SiC are dispersed and mixed by a free arc and are sprayed on the silicone oil surface (carried by the conveyor belt). Then, the silicon oil is separated from the conveyor belt, and the TSG composite (TSG-E) with highly dispersed CNTs@SiC is prepared. In this work, TSG-E has a CNTs@SiC network with CNTs as the frame and SiC as the node. Compared with untreated (TSG-N), grind (TSG-G), and ultrasonic (TSG-U) dispersion methods, TSG-E has better thermal conductivity (λ) and resistivity. CNTs@SiC network of the TSG-E series affects λ, the effect follows the thermal conductivity network theory and has a sudden change (greatly decreased) from TSG-E0.2 to TSG-E0.3. Besides, the sudden change of thermal stability for the TSG-E series is consistent with the change of λ.

Thermal Annealing Effect on Surface-Enhanced Raman Scattering of Gold Films Deposited on Liquid Substrates.

We prepare metal films with various thicknesses on liquid substrates by thermal evaporation and investigate the annealing effect on these films. Gold films deposited on a silicone oil surface consist of a large number of branched aggregates, which contains plenty of gold nanoparticles. This characteristic morphology is mainly attributed to the isotropic and free-sustained liquid substrate. Thermal annealing results in the reintegration of nanoparticles; thus, the surface morphology and microstructure of gold films change significantly. The dependence of annealing conditions on the surface-enhanced Raman scattering performance of gold films is studied, in which gold films show favorable Raman activity when annealed at certain annealing temperature and the experimental results are verified by simulation analysis. The study on the optimal annealing temperature of surface-enhanced Raman scattering substrate will pave the way for the potential application of films deposited on liquid surfaces in microfluidics and enhanced Raman detection.

Probing Molecular Interactions of Antibody Drugs, Silicone Oil, and Surfactant at Buried Interfaces In Situ.

Antibody drugs have been rapidly developed to cure many diseases including COVID-19 infection. Silicone oil is commonly used as a lubricant coating material for devices used in the pharmaceutical industry to store and administer antibody drug formulations. However, the interaction between silicone oil and antibody molecules could lead to the adsorption, denaturation, and aggregation of antibody molecules, impacting the efficacy of antibody drugs. Here, we studied the molecular interactions between antibodies and silicone oil in situ in real time. The effect of the surfactant on such interactions was also investigated. Specifically, the adsorption dynamics of a bispecific antibody (BsAb) onto a silicone oil surface without and with different concentrations of the surfactant PS80 in antibody solutions were monitored. Also the possible lowest effective PS80 concentrations that can prevent the adsorption of BsAb as well as a monoclonal antibody (mAb) onto silicone oil were measured. It was found that different concentrations of PS80 are required for preventing the adsorption of different antibodies. Both BsAB and mAB denature on silicone oil without a surfactant. However, for a low surfactant concentration in the solution, although the surfactant could not completely prevent the antibody from adsorption, it could maintain the native structures of adsorbed BsAb and mAb antibodies on silicone oil. This is important knowledge, showing that to prevent antibody aggregation on silicone oil it is not necessary to add surfactant to a concentration high enough to completely minimize protein adsorption.

Reduction of the water wettability of Cu films deposited on liquid surfaces by thermal evaporation

We report a facile approach for the wettability control of copper (Cu) films grown on a silicone oil surface by thermal evaporation. Characteristic aggregation of deposited Cu atoms was obtained due to the isotropic and free-sustained liquid substrates. Through the fine adjustment of deposition parameters in the growth process, Cu films with controlled morphology from ramified aggregates to continuous films can be prepared. Accompanied with the evolution of morphology, water wettability was effectively reduced and the hydrophilic-to-hydrophobic transition can be achieved. The relationship between the wettability and microstructure of Cu films was investigated. These films with characteristic morphology and controlled wettability may open lots of application avenues in the development of devices with modified surface properties.

Probing protein aggregation at buried interfaces: distinguishing between adsorbed protein monomers, dimers, and a monomer-dimer mixture in situ.

Protein adsorption on surfaces greatly impacts many applications such as biomedical materials, anti-biofouling coatings, bio-separation membranes, biosensors, antibody protein drugs etc. For example, protein drug adsorption on the widely used lubricant silicone oil surface may induce protein aggregation and thus affect the protein drug efficacy. It is therefore important to investigate the molecular behavior of proteins at the silicone oil/solution interface. Such an interfacial study is challenging because the targeted interface is buried. By using sum frequency generation vibrational spectroscopy (SFG) with Hamiltonian local mode approximation method analysis, we studied protein adsorption at the silicone oil/protein solution interface in situ in real time, using bovine serum albumin (BSA) as a model. The results showed that the interface was mainly covered by BSA dimers. The deduced BSA dimer orientation on the silicone oil surface from the SFG study can be explained by the surface distribution of certain amino acids. To confirm the BSA dimer adsorption, we treated adsorbed BSA dimer molecules with dithiothreitol (DTT) to dissociate these dimers. SFG studies on adsorbed BSA after the DTT treatment indicated that the silicone oil surface is covered by BSA dimers and BSA monomers in an approximate 6 : 4 ratio. That is to say, about 25% of the adsorbed BSA dimers were converted to monomers after the DTT treatment. Extensive research has been reported in the literature to determine adsorbed protein dimer formation using ex situ experiments, e.g., by washing off the adsorbed proteins from the surface then analyzing the washed-off proteins, which may induce substantial errors in the washing process. Dimerization is a crucial initial step for protein aggregation. This research developed a new methodology to investigate protein aggregation at a solid/liquid (or liquid/liquid) interface in situ in real time using BSA dimer as an example, which will greatly impact many research fields and applications involving interfacial biological molecules.

Investigating Thin Silicone Oil Films Using Four-Wave Mixing Spectroscopy and Sum Frequency Generation Vibrational Spectroscopy.

This article applies four-wave mixing (FWM) spectroscopy, a third-order nonlinear optical spectroscopic technique which is not intrinsically surface- or interface-sensitive, to study silicone oil thin films, supplemented by second-order nonlinear-optical sum frequency generation (SFG) vibrational spectroscopy. Although studies of thin organic films using coherent antistokes Raman spectroscopy (CARS), a special case of FWM, have been reported previously, in this study we demonstrate the feasibility of using a more general FWM process which involves three independent excitation laser beams to investigate silicone oil thin films. The results show that the FWM method has the potential to detect and provide molecular-level information on ultrathin silicone oil layers, down to a film thickness of 1 nm. This developed FWM methodology is widely applicable and can be utilized to study important issues in the biopharmaceutical field, e.g., to examine the distribution of silicone oil on syringe glass surfaces with subnanometer sensitivity. It can also be used to study the potentially slow reactions between silicone oil and glass surfaces as proposed in the literature but without direct molecular-level information.

Enhanced biodegradation of n-hexane in a two-phase partitioning bioreactor inoculated with Pseudomonas mendocina NX-1 under chitosan stimulation

Two-phase partitioning bioreactors (TPPBs) have been extensively used for volatile organic compounds (VOCs) removal. To date, most studies have focused on improving the mass transfer of gas phases/non-aqueous phases (NAPs)/aqueous phases, whereas the NAP/biological phases and gas/biological phases transfer has been neglected. Herein, chitosan was introduced into a TPPB to increase cell surface hydrophobicity (CSH) and improve the n-hexane mass transfer. The performance and stability of the TPPB with chitosan for n-hexane biodegradation were investigated, and it was found out that the TPPB with chitosan achieved maximum removal efficiency and elimination capacity of 80.6% and 26.5 g m−3 h−1, thereby reaching much higher values than those obtained without chitosan (61.3% and 15.2 g m−3 h−1). Chitosan not only obvio usly increased cell surface hydrophobicity and cell dry biomass on the surface of silicone oil, but might also allow hydrophobic cells in aqueous phases to directly capture and biodegrade n-hexane, resulting in an obvious improvement of mass transfer from the gas phase to biomass. Stability enhancement was another attractive advantage from chitosan addition. This study might provide a new strategy for the development of TPPB in the hydrophobic VOCs treatment.

A low-dimensional crystal growth model on an isotropic and quasi-free sustained substrate**Project supported by the National Natural Science Foundation of China (Grant Nos. 11374082 and 51671048) and the Ten Thousand Talents Plan of Zhejiang Province of China (Grant No. 2018R52003).

A new crystal growth theoretical model is established for the low-dimensional nanocrystals on an isotropic and quasi-free sustained substrate. The driven mechanism of the model is based on the competitive growth among the preferential growth directions of the crystals possessing anisotropic crystal structures, such as the hexagonal close-packed and wurtzite structures. The calculation results are in good agreement with the experimental findings in the growth process of the low-dimensional Zn nanocrystals on silicone oil surfaces. Our model shows a growth mechanism of various low-dimensional crystals on/in the isotropic substrates.

Interaction Mechanisms of Giant Unilamellar Vesicles with Hydrophobic Glass Surfaces and Silicone Oil-Water Interfaces: Adsorption, Deformation, Rupture, Dynamic Shape Changes, Internal Vesicle Formation, and Desorption.

Phospholipid monolayers at oil-water interfaces are often obtained via vesicle adsorption. However, the interaction mechanisms of vesicles with these oil-water interfaces remain unclear. Herein, we studied the adsorption of giant unilamellar vesicles (GUVs) of approximately 2-5 μm diameter onto silicone oil-water interfaces and glass surfaces modified with hexamethyldisilazane (HMDS) and octadecyltrimethoxysilane (ODTMS) using fluorescence microscopy. The GUVs exhibited various modes of interaction, adsorbing on the silanized glass surfaces without sizable deformation, whereas GUVs bound to the silicone oil-water interface exhibited large deformation. After adsorption, GUV rupture occurred within 350, 110, and 3 ms on HMDS-modified glass, ODTMS-modified glass, and silicone oil-water interface, respectively. On glass surfaces, GUV rupture was often initiated and proceeded with pore formation near the surface. The monolayer patches formed by GUV rupture on HMDS-modified glass remained for at least 1 h over an area approximately twice of that estimated from the original GUV. On the ODTMS-modified glass and silicone oil surfaces, the monolayer patch structures disappeared in milliseconds owing to lipid diffusion across the interface. When adsorbed on the oil-water interface, the GUVs spontaneously underwent dynamic shape changes, internal vesicle formation, and desorption without rupture. Thus, it can be concluded that these different pathways arose from different lipid-surface affinities.

Structure Evolution and Formation Mechanism of Wrinkled Fe Films on Liquid Surfaces

A characteristic wrinkled Fe film system has been prepared on silicone oil surfaces by a direct current magnetron sputtering method. The experiment shows that the Fe film is under a large compressive stress induced by the thermal contraction during deposition, which is relieved by the formation of wrinkling patterns. It is found that the wrinkling patterns, such as straight strips and herringbones, are formed in networked domains. The straight strips are perpendicular to the domain edges and the herringbones are located in the center of the domains. The morphologies of the wrinkled patterns are characterized by the optical microscopy and atomic force microscopy. It is found that the average length d of the domains remains nearly unchanged and the wavelength λ of the wrinkling patterns increases linearly with the film thickness h, which obeys an equation λ = 14h + 1440. The amplitude z of the herringbones increases firstly with the film thickness h for h ≤ 450 nm and decreases quickly for h > 450 nm. The characteristic, structure evolution and formation mechanisms of the wrinkled patterns have been described and discussed in detail.

Probing the Interfacial Interactions of Monoclonal and Bispecific Antibodies at the Silicone Oil-Aqueous Solution Interface by Using Sum Frequency Generation Vibrational Spectroscopy.

Silicone oil has been widely utilized in the pharmaceutical industry especially as a lubricant coating commonly used in syringes for the smooth delivery of drugs. Protein structure perturbation and aggregation have been reported upon protein contacting silicone oil by using indirect methods and ex-situ techniques. The conclusions derived from such indirect and ex-situ methods may not truly reflect the exact nature of the protein-silicone oil interfacial interactions. Recently, we have successfully demonstrated that sum frequency generation (SFG) vibrational spectroscopy can be used as a powerful and direct method of studying the fusion protein-silicone oil interfacial interactions in situ and in real time. In this article, we studied monoclonal and bispecific antibody interactions with the silicone oil surface by using SFG spectroscopy. Being structurally and functionally different in the nature of fusion proteins and antibodies, this study is important in enhancing our current understanding of protein-silicone oil interfacial interactions. Both types of antibodies investigated here readily and strongly adsorb onto the silicone oil surface and remain stable at least for 10 h. SFG spectra in the amide I region for monoclonal and bispecific antibodies centered at 1660 and 1665 cm-1, respectively, suggest the difference in their molecular structures. The absence of the antibody signals in the amide I region of time-dependent and static SFG spectra obtained for preadsorbed antibodies onto silicone oil after contacting polysorbate 80 (PS-80) surfactant suggests that PS-80 can effectively remove both types of antibodies from the silicone oil surface. This study demonstrated the feasibility of using SFG spectroscopy as a powerful tool for probing the antibody-interfacial interactions in situ and in real time.

Influence of post-annealing treatment on the morphology of Au films deposited on liquid surfaces

We report the annealing effects on the morphology of metallic films deposited on liquid surfaces, which was enabled by depositing Au atoms to a silicone oil surface by thermal evaporation at room temperature. Due to the isotropic characteristics of the liquid surface, the growth of Au films on silicone oil surfaces follows the two-stage growth model. Ramified aggregates consist of substantial nanoparticles exist in the Au film, which is different from films fabricated on solid substrates. After annealing at different temperatures, small nanoparticles started to melt first, and formed liquid layers covered on adjacent large nanoparticles. As the annealing temperature increased, more nanoparticles melt and the liquid layer became thicker, resulting in the increase of mean diameter of Au nanoparticles and film coverage. The dependence between film morphology and annealing temperature was investigated. This work provides a potential mechanism of annealing effect on the morphology of metallic films deposited on free-sustained substrates.

Theoretical study on the aggregation of aluminium clusters on a silicone oil surface

By using Amsterdam Density Functional (ADF) program based on first-principles, we have in detail investigated the formation mechanism of the aluminium (Al) nanoparticles (NPs) on a silicone oil surface. Our investigation shows that two moving Al clusters on liquid substrate meet to form a random initial structure. Collisions and interactions may make it become a more compact, more stable structure. As the deposition density increases, a discshaped morphology would be formed because of isotropy on the silicone oil surfaces. The structures built on the Face-Centered Cubic (FCC) units are not stable. Both atomic displacement and adsorption can almost destroy them. It is difficult to form Al crystals on the silicone oil surfaces.

Analysis of hemispherical vessel ablation failure involving natural convection by MPS method with corrective matrix

In a severe accident of a light water reactor, the reactor pressure vessel (RPV) lower head may fail due to ablation at the vessel wall boundary involving natural convection of molten core materials. Accurate prediction of RPV lower head failure is essential for assessing severe accident progression and improving accident management because it greatly influences the subsequent ex-vessel accident progressions. However, there have been still large uncertainties about RPV lower head failure mode in the Fukushima Daiichi Nuclear Accident in 2011. The Lagrangian based MPS (moving particle semi-implicit) method has advantage of analyzing such phenomena involving complex interfaces and liquid-solid phase changes over other Eulerian mesh-based method. In the preceding study, small-scale Pb–Bi hemisphere vessel ablation experiment, with silicone oil as simulated molten core, was reproduced qualitatively by original MPS method. However, ablation mechanism associated with natural convection of the high temperature liquid could not be discussed because of significant influence of numerical discretizing error. In this study, the improved MPS method coupling corrective matrix in the particle interaction model which largely suppress the numerical fluctuation was adopted to analyze the experiment. The results show that the ablated metal relocation may enhance convective heat transfer in the downstream. As a result, ablation of the vessel wall extends from the level, close to the silicone oil surface down to the bottom of the vessel rather than previously simulated localized ablation near the silicone oil surface.

Surface enhanced Raman scattering substrates prepared by thermal evaporation on liquid surfaces

We present an effective surface-enhancement Raman scattering (SERS) substrate enabled by depositing metallic film on a liquid surface at room temperature. Thermal evaporation is used to deposit Au atoms on silicone oil surface and then form quasi-continuous films. Due to the isotropic characteristics of the liquid surface, this film consists of substantial nanoparticles with uniform diameter, which is different from films fabricated on solid substrates and can be served as an applicable substrate for SERS detection. With the assistance of this substrate, SERS signals of rhodamine 6G were significantly enhanced, the dependence between SERS spectra and film thickness was investigated. Analytical simulation results confirm the experimental observations and the superiorities of our proposed method for preparation of SERS substrate. This work provides a potential application of metallic film deposition on free-sustained surface and holds promise as an efficient sensor in rapid trace detection of small molecule analytes.

Nucleation and growth of zinc crystals on a liquid surface

A catalyst-free preparation method for zinc nanocrystals on a silicone oil surface is developed at room temperature.

Understanding Protein-Interface Interactions of a Fusion Protein at Silicone Oil-Water Interface Probed by Sum Frequency Generation Vibrational Spectroscopy

Protein adsorbed at the silicone oil-water interface can undergo a conformational change that has the potential to induce protein aggregation on storage. Characterization of the protein structures at interface is therefore critical for understanding the protein-interface interactions. In this article, we have applied sum frequency generation (SFG) spectroscopy for studying the secondary structures of a fusion protein at interface and the surfactant effect on protein adsorption to silicone oil-water interface. SFG and chiral SFG spectra from adsorbed protein in the amide I region were analyzed. The presence of beta-sheet vibrational band at 1635 cm−1 implies the protein secondary structure was likely perturbed when protein adsorbed at silicone oil interface. The time-dependent SFG study showed a significant reduction in the SFG signal of preadsorbed protein when polysorbate 20 was introduced, suggesting surfactant has stronger interaction with the interface leading to desorption of protein from the interface. In the preadsorbed surfactant and a mixture of protein/polysorbate 20, SFG analysis confirmed that surfactant can dramatically prevent the protein adsorption to silicone oil surface. This study has demonstrated the potential of SFG for providing the detailed molecular level understanding of protein conformation at interface and assessing the influence of surfactant on protein adsorption behavior.

From Zinc Clusters to One-Dimensional Crystals on Quasi-Free Sustained Substrates

By using the Amsterdam density functional (ADF) program based on first-principles, we have in detail investigated the Zn n (n = 2–20) clusters, several series of stacked structures, and the growth mechanism of zinc nanorods on silicone oil surfaces, which are isotropic, and can be generally considered as quasi-free sustained substrates. For the Zn n (n = 2–20) clusters, some new ground-state structures are found. The additional boundary atoms can enhance the stability of the stacked structures containing unit cells. The structures from the transverse array of the unit cells on (002) crystal plane are more stable than those stacked along the [002] direction as atomic number increases. The transverse arrayed structures can grow along the [002] direction. However, there is an atomic dislocation between the (002) crystal planes. In fact, the dislocation forms its one side surface of (101). By means of a single point SCF calculation in the ADF program, the adsorption energies per atom on the (101) and (002) crystal planes are calculated. According to the Boltzmann distribution probability law, the adsorption probability on the (101) plane is larger than that on the (002) plane, and the ratio between them is about 24–900. This shows that the Zn nanorods grow preferentially along the [110] direction on the (101) planes. These are in good agreement with our experimental findings.

TEMPERATURE EFFECT ON MICROSTRUCTURE AND AGGREGATION BEHAVIOR OF GOLD ATOMIC AGGREGATES ON SILICONE OIL SURFACE

By thermal evaporation method, gold (Au) atomic aggregates were fabricated on a silicone oil surface and the aggregation mechanism was investigated. It is found that the apparent surface coverage ([Formula: see text]) of the Au aggregates dropped obviously, from 15% to 12% as the oil temperature (T) increased from 285[Formula: see text]K to 353[Formula: see text]K. Meanwhile, the average width of the aggregates gradually increased from 0.36[Formula: see text][Formula: see text]m to 0.50[Formula: see text][Formula: see text]m, indicating the aggregates combine with each other as T increased. By the atomic force microscopy observation, Au nanoparticles with diameter around 45.0 nm were observed in the aggregates, which were independent with T. Similarly, the average height of the aggregates found remain unchanged at around 10.0[Formula: see text]nm as T increased. The anomalous aggregation mechanism of Au aggregates suggests that a compact microstructure for Au aggregates is preferred at high T rather than three-dimensional (3D) growth, which is quite different from that of Ag aggregates.