Nanostructure Explains the Behavior of Slippery Covalently Attached Liquid Surfaces

Slippery covalently-attached liquid surfaces (SCALS) with low contact angle hysteresis (CAH, <5°) and nanoscale thickness display impressive anti-adhesive properties, similar to lubricant-infused surfaces. Their efficacy is generally attributed to the liquid-like mobility of the constituent tethered chains. However, the precise physico-chemical properties that facilitate this mobility are unknown, hindering rational design. This work quantifies the chain length, grafting density, and microviscosity of a range of polydimethylsiloxane (PDMS) SCALS, elucidating the nanostructure responsible for their properties. Three prominent methods are used to produce SCALS, with characterization carried out via single-molecule force measurements, neutron reflectometry, and fluorescence correlation spectroscopy. CO₂ snow-jet cleaning was also shown to reduce the CAH of SCALS via a modification of their grafting density. SCALS behavior can be predicted by reduced grafting density, Σ, with the lowest water CAH achieved at Σ≈2. This study provides the first direct examination of SCALS grafting density, chain length, and microviscosity and supports the hypothesis that SCALS properties stem from a balance of layer uniformity and mobility.     

具有微纳米结构超疏水表面润湿性的研究

本文综述了近年来具有微纳米结构超疏水表面的研究进展。介绍了具有微纳米结构超疏水表面的制备方法,表面结构对超疏水性能的影响,周期性结构表面超疏水的条件,超疏水表面接触角滞后以及功能化超疏水表面等方面的研究,探讨了这一领域存在的问题及可能的发展方向。     

梯度接触角表面的构建与应用

梯度接触角是梯度表面张力的反映,固体表面的润湿性由表面化学组成和表面微观形貌共同决定。通过表面化学组成和表面微观形貌的梯度化,可制备接触角变化范围不同的梯度接触角表面。本文综述了梯度接触角表面在液滴移动、微流体流动和生物吸附等领域中的应用。梯度接触角表面具有的不平衡杨氏力是促进液滴移动的主要原因,而表面所产生的接触角滞后则阻碍液滴移动;在生物学领域,梯度接触角表面会造成蛋白质和细胞选择性吸附或黏附。最后,简要探讨了梯度接触角表面存在的问题和发展方向。     

Manipulation of Structure on Silicon Surfaces via Chemical Adsorption

Via chemical adsorption, various films were assembled onto silicon surfaces. The structures and properties of the monolayer‐ or bilayer‐modified silicon surfaces, such as Si‐C₁₀H₂₀ CH₂OC(O)CF₃, Si‐C₁₀H₂₀CH₂OH, and Si‐C₁₀H₂₀‐CH₂‐NH‐C₁₈H₃₇, were investigated by various techniques. x‐ray photoelectron spectroscopy (XPS) gave clear proofs of the formation of octadecylamine layer and other kinds of layers on silicon surfaces. The contact angle measurements showed that the wettability of silicon surfaces was dominated by the terminal functional groups of the attached layers. Atomic force microscopy (AFM) observations showed that interesting patterns have formed on the monolayer‐ or bilayer‐modified silicon surfaces. Electrochemical impedance spectra (EIS) measurements showed that the Si‐C₁₀H₂₀CH₂‐NH‐C₁₈H₃₇ has a better ability to prevent charge transfer as compared with that of Si‐C₁₀H₂₀CH₂OH, which may find applications in the area of surface passivations.     

Wettability of Polyhedral Oligomeric Silsesquioxane Nanostructured Polymer Surfaces

Summary: Some model structures of waterborne polyurethane anionomers containing various amounts (ca. 3–20%) of a diol functionalized polyhedral oligomeric silsesquioxane (POSS) nanofiller were prepared. X‐ray diffraction showed the formation of a nanocrystalline structure in all copolymers considered. Static contact angle measurements indicated a significant enhancement of surface hydrophobicity as well as reduction in surface tension components even at the least POSS level (3%). Dynamic contact angle cycles allowed the evaluation of the hysteresis, which was found to be large and kinetically increasing in POSS‐modified samples. Film topography was analyzed by AFM, showing a more pronounced roughness in the nanostructured surface.

The AFM image showing a moderate roughness increase.     

超疏水表面的研究进展

表面的浸润性是决定材料应用的一个重要性质,许多物理化学过程,如吸附、润滑、黏合、分散和摩擦等均与表面的浸润性密切相关.近年来,由于超疏水表面在自清洁表面、微流体系统和生物相容性等方面的潜在应用,有关超疏水表面的研究引起了极大的关注.本文综述了超疏水表面研究的新进展:简单介绍了表面浸润性的表征手段和影响因素,归纳了超疏水表面的制备方法和相关的理论分析,对超疏水表面研究的发展进行了展望.     

Dehydrogenative Homocoupling of Terminal Alkenes on Copper Surfaces: A Route to Dienes

Homocouplings of hydrocarbon groups including alkynyl (sp¹), alkyl (sp³), and aryl (sp²) have recently been investigated on surfaces with the interest of fabricating novel carbon nanostructures/nanomaterials and getting fundamental understanding. Investigated herein is the on‐surface homocoupling of an alkenyl group which is the last elementary unit of hydrocarbons. Through real‐space direct visualization (scanning tunneling microscopy imaging) and density functional theory calculations, the two terminal alkenyl groups were found to couple into a diene moiety on copper surfaces, and is contrary to the common dimerization products of alkenes in solution. Furthermore, detailed DFT‐based transition‐state searches were performed to unravel this new reaction pathway.     

Ion‐Specific Oil Repellency of Polyelectrolyte Multilayers in Water: Molecular Insights into the Hydrophilicity of Charged Surfaces

Surface wetting on polyelectrolyte multilayers (PEMs), prepared by alternating deposition of polydiallyldimethylammonium chloride (PDDA) and poly(styrene sulfonate) (PSS), was investigated mainly in water‐solid‐oil systems. The surface‐wetting behavior of as‐prepared PEMs was well correlated to the molecular structures of the uncompensated ionic groups on the PEMs as revealed by sum frequency generation vibrational and X‐ray photoelectron spectroscopies. The orientation change of the benzenesulfonate groups on the PSS‐capped surfaces causes poor water wetting in oil or air and negligible oil wetting in water, while the orientation change of the quaternized pyrrolidine rings on the PDDA‐capped surfaces hardly affects their wetting behavior. The underwater oil repellency of PSS‐capped PEMs was successfully harnessed to manufacture highly efficient filters for oil‐water separation at high flux.     

The Effect of Pristine and Hydroxylated Oxide Surfaces on the Guaiacol HDO Process: A DFT Study

The acid-base character of oxide supports is crucial for catalytic reactions. In this work, the acid-base properties of five oxide surfaces common in heterogeneous catalysis were investigated and related to their interaction with monolignol compounds derived from lignin. We have used density functional theory simulations also to understand the role of the surfaces’ hydroxylation state. The results show that moderate hydroxyl coverage on the amphoteric γ-Al₂O₃ (110) slightly strengthens the oxy-compounds’ adsorption due to an increase in Lewis acidity. Similarly, low hydroxyl coverage on the reducible TiO₂ (101) enlarges its adsorption capacity by up to 42 % compared with its clean surface. The higher affinity is attributed to the more favourable interaction between the surface-OH groups and the aromatic rings. Overall, the results indicate that hydroxyl coverage enhances the amphoteric and reducible adsorption capacity towards aromatic species.     

Shear‐Controlled Micro/Nanometer‐Scaled Super‐Hydrophobic Surfaces with Tunable Sliding Angles from Single Component Isotactic Poly(propylene)

Summary: With the proper selection of shear and thermal conditions, super‐hydrophobic polymeric surfaces (contact angle > 150°) with tunable sliding angles (from less than 1° to higher than 90°) can be prepared from pure isotactic poly(propylene) (iPP) without any further modification with low‐surface‐energy components under ambient atmosphere. The formed surfaces have naturally good thermal properties, chemical and moisture resistance, low density, and potentially low manufacturing cost.

SEM images of formed super‐hydrophobic surfaces and related two extreme sliding angles (contact angles of these surfaces are higher than 150°).     

Calculation of Adsorption Isotherms on Hard Solid Surfaces Using Measurements of Surface Tensions and Contact Angles

The adsorption excess isotherms of binary mixtures adsorbed on hard solids were calculated by means of surface tension and contact angle measurements using the Gibbs adsorption isotherm equation. The calculation procedure is described in detail using the authors' own measurements of mixtures containing ethylene glycol(1)/water(2) on Teflon and poly(vinyl chloride), and water(1)/n-propanol(2) on Teflon. On the basis of these results and also from surface tensions and contact angles on hard solids published by other authors, all types of isotherms were found as given for porous adsorbents in the classification of Schay and Nagy. In addition to those, new isotherm types are proposed.     

Preferential Formation of SiOC over SiC Linkage upon Thermal Grafting on Hydrogen‐Terminated Silicon (111)

In a stringent and near oxygen‐free environment, Si?H surfaces were introduced to a trifluoroalkyne, an alcohol‐derivatized alkyne, as well as an equal mixture of both alkynes at a temperature of 130 °C. Contact angle measurements, high‐resolution X‐ray photoelectron spectroscopy (XPS), and angle‐resolved XPS were performed to examine the system. Si?H surfaces were found to have a strong preference towards the formation of Si?O?C rather than Si?C bonds when the alcohol and alkyne reactivities were compared.     

Surface modification and characterization of SEBS films obtained by in situ and ex situ oxidization with potassium permanganate

The surface morphologies and compositions of the asymmetric films of polystyrene‐b‐poly(ethylene‐co‐butylene)‐b‐polystyrene (SEBS) prepared by in situ and ex situ oxidization with the KMnO₄ aqueous solution and KMnO₄/H₂SO₄ mixed solution were investigated by using scanning electron microscope, atomic force microscope (AFM), X‐ray photoelectron spectroscopy (XPS) and attenuated total reflectance infrared spectroscopy (ATR‐FTIR). The effect of the oxidization reagents on morphological changes and the influence of in situ and ex situ preparation methods on surface compositions were discussed. Different from the in situ oxidation by degrading the copolymers to form a gradient film, the ex situ oxidation preferentially degraded the uppermost layer of the film. Although both the KMnO₄ oxidation and the KMnO₄/H₂SO₄ oxidation gave hierarchical structures, distinctive differences were found that large ridges and smaller granules were fabricated in the former film and the latter produced large and deep ravines and fine sponge‐like morphologies. Additionally, the oxygen concentration and the oxo‐species implanted by these oxidation treatments were characterized and evaluated to provide a quantitative comparison. Oxygen, as well as manganese was found to be implanted in the surface layer of the oxidized film, forming predominantly O? C and O? C?O groups, as well as a small fraction of O? H and Mn? O compounds. Changes in contact angle of water on these films and total surface oxygen content are related but not directly. The hystereses of water contact angle at a value of 119 ± 3° due primarily to surface roughness and at a value of 63 ± 3° due primarily to chemical heterogeneity are led by different oxidation degrees and oxidation methods. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

Asymmetrically Functionalized,Four‐Armed,Poly(ethylene glycol) Compounds for Construction of Chemically Functionalizable Non‐Biofouling Surfaces

Asymmetrically functionalized, four‐armed, Tween 20 derivatives that formed stable monomolecular films on solid substrates were designed and synthesized. Thiol‐modified Tween 20 was used for forming self‐assembled monolayers (SAMs) on gold, and maleimide‐modified Tween 20 was introduced onto SiO₂ surfaces with SAMs of (3‐mercaptopropyl)trimethoxysilane through Michael addition. These structurally modified Tween 20 compounds gave the original characteristics of Tween 20, non‐biofouling (from ethylene glycol groups) and functionalizable (from OH groups) properties, to each substrate. The non‐biofouling properties of the Tween 20‐coated gold and SiO₂ surfaces were investigated by surface plasmon resonance spectroscopy and ellipsometry, and these surfaces showed strong resistance against nonspecific adsorption of proteins. In addition, the biospecific binding of streptavidin was achieved after coupling of (+)‐biotinyl‐3,6,9‐trioxaundecanediamine onto the non‐biofouling surfaces through amide‐bond formation.