辛基三乙氧基硅烷/十八烷基三氯硅烷均相混合自组装单分子膜的表征及其形成机制

使用接触角、原子力显微镜(AFM)、静电力显微镜(EFM)和傅里叶变换红外(FTIR)光谱对辛基三乙氧基硅烷(C8TES)/十八烷基三氯硅烷(OTS)均相混合自组装单分子膜(SAM)及其形成过程中样品表面的润湿性、表面形貌、表面电势和膜内分子的有序度进行了表征,对采用分步法利用C8TES分子空间位阻制备C8TES/OTS均相混合SAM的反应机制进行了研究.结果表明,C8TES/OTS均相混合SAM表面接触角为105°,样品表面平整、光滑;对样品表面电势进行分析后发现,混合SAM表面电势分布均匀,电势频率分布为典型的正态分布;在均相混合SAM的形成过程中,样品表面电势的分布始终十分均匀,电势频率分布均为典型的正态分布;C8TES/OTS均相混合SAM是一种具有上下两层分子排列密度不同的膜结构的单分子膜,其内部结构至少在500 nm×500 nm到20μm×20μm尺度上是高度均匀一致的,膜内没有明显的特征结构,具有典型的均相混合SAM特征.     

Step-growth synthesis and interfacial friction properties of surface dendron coatings

We report a new procedure for synthesizing self-assembled two-tiered coatings comprised of a tethered carbosilane dendron canopy layer over an alkylsilane sublayer. The sublayer is anchored to a silicon substrate, and the areal density of the canopy can be controlled by changing the concentration of reactive vinyl groups on the sublayer surface. The structure of the dendron layer is characterized by angle-resolved X-ray photoelectron spectroscopy (ARXPS), water contact angle, and ellipsometry. Steric hindrance due to close packing of functional groups has a strong effect on the reaction efficiency, and dendron structure can be obtained only in canopies with low areal densities. Lateral force microscopy (LFM) is used to study interfacial friction and adhesion properties of the coatings. Structural variations in the canopy layer are found to play a crucial role in interfacial friction properties of these coatings.     

辛基三乙氧基硅烷/十八烷基三氯硅烷均相混合自组装单分子膜的表征及其形成机制

使用接触角、原子力显微镜（AFM）、静电力显微镜（EFM）和傅里叶变换红外（FTIR）光谱对辛基三乙氧基硅烷（C8TES）/十八烷基三氯硅烷（OTS）均相混合自组装单分子膜（SAM）及其形成过程中样品表面的润湿性、表面形貌、表面电势和膜内分子的有序度进行了表征,对采用分步法利用C8TES分子空间位阻制备C8TES/OTS均相混合SAM的反应机制进行了研究. 结果表明,C8TES/OTS均相混合SAM表面接触角为105°,样品表面平整、光滑;对样品表面电势进行分析后发现,混合SAM表面电势分布均匀,电势频率分布为典型的正态分布;在均相混合SAM的形成过程中,样品表面电势的分布始终十分均匀,电势频率分布均为典型的正态分布;C8TES/OTS均相混合SAM是一种具有上下两层分子排列密度不同的膜结构的单分子膜,其内部结构至少在500 nm×500 nm到20 μm×20 μm尺度上是高度均匀一致的,膜内没有明显的特征结构,具有典型的均相混合SAM特征.     

Self-assembled monolayers derived from alkoxyphenylethanethiols having one, two, and three pendant chains

This article describes the design, synthesis, and study of alkoxyphenylethanethiol-based adsorbates with one (R1ArMT), two (R2ArMT), and three (R3ArMT) pendant octadecyloxy chains substituted at the 4-, 3,5-, and 3,4,5-positions, respectively, of the phenylethanethiol group. These adsorbates are being developed for use in the preparation of compositionally versatile "mixed" self-assembled monolayer (SAM) coatings. The resultant SAMs were characterized by ellipsometry, contact angle goniometry, polarization modulation infrared reflection-absorption spectroscopy (PM-IRRAS), and X-ray photoelectron spectroscopy (XPS). The studies revealed that R1ArMT generates a well-ordered monolayer film, while R2ArMT and R3ArMT generate monolayer films with diminished conformational order in which the degree of crystallinity decreases as follows: C18 ～ R1ArMT > R3ArMT > R2ArMT. In addition, comparison of the molecular and chain packing densities of SAMs derived from these new adsorbates reveals that the R2ArMT and R3ArMT adsorbates give rise to SAMs with reduced chain tilt and smaller surface area per chain when compared to the SAMs derived from C18 and R1ArMT.     

Stability of mixed PEO-thiol SAMs for biosensing applications

The secret of a successful affinity biosensor partially hides in the chemical interface layer between the transducer system and the biological receptor molecules. Over the past decade, several methodologies for the construction of such interface layers have been developed on the basis of the deposition of self-assembled monolayers (SAMs) of alkanethiols on gold. Moreover, mixed SAMs of polyethylene oxide (PEO) containing thiols have been applied for the immobilization of biological receptors. Despite the intense research in the field of thiol SAMs, relatively little is known about their biosensing properties in correlation with their long-term stability. Especially the impact of the storage conditions on their biosensing characteristics has not been reported before to our knowledge. To address these issues, we prepared mixed PEO SAMs and tested their stability and biosensing performance in several storage conditions, i.e., air, N2, ethanol, phosphate buffer, and H2O. The quality of the SAMs was monitored as a function of time using various characterization techniques such as cyclic voltammetry, contact angle, grazing angle Fourier-transform infrared spectroscopy, and X-ray photoelectron spectroscopy. In addition, the impact of the different storage conditions on the biosensor properties was investigated using surface plasmon resonance. Via the latter technique, the receptor immobilization, the analyte recognition, and the nonspecific binding were extensively studied using the prostate specific antigen as a model system. Our experiments showed that very small structural differences in the SAM can have a great impact in their final biosensing properties. In addition it was shown that the mixed SAMs stored in air or N2 are very stable and retain their biosensor properties for at least 30 days, while ethanol appeared to be the worst storage medium due to partial oxidation of the thiol headgroup. In conclusion, care must be taken to avoid SAM degradation during storage to retain typical SAM characteristics, which is very important for their general use in many proposed applications.     

Mixed self-assembled monolayers of semirigid tetrahydro-4H-thiopyran end-capped oligo(cyclohexylidenes)

Single-component and mixed self-assembled monolayers (SAMs) of one- and three-ring semirigid tetrahydro-4H-thiopyran end-capped oligo(cyclohexylidenes)-that is, thiopyran (1), 4-(4-cyclohexylidene-cyclohexylidene)tetrahydro-4H-thiopyran (2), and 4-(tetrahydro-4H-thiopyran-4-cyclohexylidene-4'-ylidene)tetrahydro-4H-thiopyran (3)--on Au(111) substrates have been prepared and studied by cyclic voltammetry (CV), atomic force microscopy (AFM), and scanning tunneling microscopy (STM). It was found that the shortest adsorbate 1 more readily forms a SAM than 2 or 3. Notwithstanding, the SAMs of 2 or 3 are thermodynamically more stable due to favorable intermolecular attractions. Holes were made with the AFM tip establishing tilt angles of 30-50 degrees with respect to the surface normal for all SAMs. STM imaging showed well-ordered, line-shaped packing patterns with molecular resolution for the SAM of 2. Similar patterned structures were not observed for 1 and 3. Mixed SAMs were prepared by exposing a SAM of 1 to ethanol solutions of either 2 or 3. STM imaging revealed that domains of molecules of 2 or 3 amidst a monolayer of 1 are formed in both cases. Whereas in the mixed SAM of 1 and 2 the domains are irregularly shaped, circular islands of uniform size are found in the mixed SAM of 1 and 3.     

Molecular tilting and its impact on frictional properties of n-alkane self-assembled monolayers

Hydrophobic, methyl-terminated self-assembled monolayer (SAM) surfaces can be used to reduce friction. Among methyl-terminated SAMs, the frictional properties of alkanethiol SAMs and silane SAMs have been well-studied. In this research, we investigated friction of methyl-terminated n-hexatriacontane (C36) SAM and compared its friction properties with the alkanethiol and silane SAMs. Alkane SAM does not have an anchoring group. The alkane molecules stand on the surface by physical adsorption, which leads to a higher surface mobility of alkane molecules. We found that C36 SAM has a higher coefficient of friction than that of octadecyltrichlorosilane (OTS) silane. When an atomic force microscope (AFM) tip was swiped across the alkane SAM with a loading force, we found that the alkane SAM can withstand the tip loading pressure up to 0.48 GPa. Between 0.48 and 0.49Ga, the AFM tip partially penetrated the SAM. When the tip moved away, the deformed SAM healed and maintained the structural integrity. When the loading pressure was higher than 0.49 GPa, the alkane SAM was shaved into small pieces by the tip. In addition, we found that the molecular tilting of C36 molecules interacted with the tribological properties of the alkane SAM surface. On one hand, a higher loading force can push the rod-like alkane molecules to a higher tilting angle; on the other hand, a higher molecular tilting leads to a lower friction surface.     

Effect of intramonolayer hydrogen bonding of carboxyl groups in self-assembled monolayers on a single force with phenylurea on an AFM probe tip.

The molecular interaction force of the intermonolayer hydrogen bonding between phenylurea groups on a probe tip and carboxyl groups in self-assembled monolayers was measured directly by means of atomic force microscopy in ethanol. Gold-coated AFM probe tips were modified chemically with 2-(N'-phenylureido)ethanethiol possessing a terminal urea moiety, which is a well-known powerful functionality for forming stable hydrogen bondings with neutral and anionic species. Adhesion force measurements were carried out on gold substrates coated with a COOH-terminated SAM composed of 6-mercaptohexanoic acid in ethanol using the phenylurea-functionalized probe tip. The adhesion force observed was decreased in the presence of H2PO4(-) in the measurement bath, indicating that the intermonolayer hydrogen bonding between the phenylurea moieties and carboxyl groups attached covalently to the probe tip and substrate, respectively, is suppressed by the anion added to the measurement solution. The specific hydrogen-bonding force was measured on binary mixed SAMs prepared by mixing 6-mercaptohexanoic acid with 1-hexanethiol. The individual hydrogen-bonding force between the phenylurea-modified tip and the binary mixed SAMs with various fractions of MHA was evaluated by repetitive force measurements and their statistical analyses by an autocorrelation method. We discuss the effect of diluting the COOH-terminated component in the mixed SAM on the adhesion force and the single force between the phenylurea and carboxyl groups in terms of competition between intermonolayer and intramonolayer hydrogen bonding.     

Chemical force microscopy of mixed self-assembled monolayers of alkanethiols on gold: evidence for phase separation

Mixed self-assembled monolayers formed by the coadsorption of hydroxyl- and methyl-terminated alkanethiols with similar chain lengths have been characterized by friction force microscopy. Friction coefficients have been determined by assuming a fit to Amonton's law. The friction coefficients vary linearly with the fraction of polar-terminated adsorbates in the self-assembled monolayer (SAM). With carboxylic acid-terminated tips, the coefficient of friction increases with the fraction of hydroxyl-terminated thiols, while with methyl-terminated tips it decreases. Similar trends are observed for pull-off forces, which increase and decrease as a function of the fraction of polar-terminated adsorbates for carboxylic acid- and methyl-terminated adsorbates, respectively. Analysis of histograms of adhesion forces has yielded insights into the phase structure of mixed SAMs. Single-component monolayers yield histograms that may be fitted to symmetric Gaussian distributions, irrespective of the nature of the terminal group on either the tip or the SAM. However, mixed monolayers yield broad, asymmetric distributions that could not be fitted with a Gaussian distribution. The best explanation for these data is that mixed SAMs of hydroxyl- and methyl-terminated alkanethiols of similar chain length form phase-separated structures.     

Stability of self-assembled monolayers on titanium and gold

Methyl- and hydroxyl-terminated phosphonic acid self-assembled monolayers (SAMs) were coated on Ti from aqueous solution. Dodecyl phosphate and dodecyltrichlorosilane SAMs were also coated on Ti using solution-phase deposition. The stability of SAMs on Ti was investigated in Tris-buffered saline (TBS) at 37 degrees C using X-ray photoelectron spectroscopy, contact angle goniometry, and atomic force microscopy. For comparison purposes, a hydroxyl-terminated thiol SAM was coated on Au, and its stability was also investigated under similar conditions. In TBS, a significant proportion of phosphonic acid or phosphate molecules were desorbed from the Ti surface within 1 day, while the trichlorosilane SAM on Ti or thiol SAM on Au was stable for up to 7 days under similar conditions. The stability of hydroxyl-terminated phosphonic acid SAM coated Ti and thiol SAM coated Au was investigated in ambient air and ultraviolet (UV) light. In ambient air, the phosphonic acid SAM on Ti was stable for up to 14 days, while the thiol SAM on Au was not stable for 1 day. Under UV-radiation exposure, the alkyl chains of the phosphonic acid SAM were decomposed, leaving only the phosphonate groups on the Ti surface after 12 h. Under similar conditions, decomposition of alkyl chains of the thiol SAM was observed on the Au surface accompanied by oxidation of thiolates.     

Chemical stability of nonwetting, low adhesion self-assembled monolayer films formed by perfluoroalkylsilanization of copper

A self-assembled monolayer (SAM) has been produced by reaction of 1H,1H,2H,2H-perfluorodecyldimethylchlorosilane (PFMS) with an oxidized copper (Cu) substrate and investigated by x-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), friction force microscopy (FFM), a derivative of AFM, and contact angle measurement. FFM showed a significant reduction in the adhesive force and friction coefficient of PFMS modified Cu (PFMS/Cu) compared to unmodified Cu. The perfluoroalkyl SAM on Cu is found to be extremely hydrophobic, yielding sessile drop static contact angles of more than 130 degrees for pure water and a "surface energy" (which is proportional to the Zisman critical surface tension for a Cu surface with 0 rms roughness) of 14.5 mJm2(nMm). Treatment by exposure to harsh conditions showed that PFMS/Cu SAM can withstand boiling nitric acid (pH=1.8), boiling water, and warm sodium hydroxide (pH=12, 60 degrees C) solutions for at least 30 min. Furthermore, no SAM degradation was observed when PFMS/Cu was exposed to warm nitric acid solution for up to 70 min at 60 degrees C or 50 min at 80 degrees C. Extremely hydrophobic (low surface energy) and stable PFMS/Cu SAMs could be useful as corrosion inhibitors in micro/nanoelectronic devices and/or as promoters for antiwetting, low adhesion surfaces or dropwise condensation on heat exchange surfaces.     

Nanotribological properties of alkanephosphonic acid self-assembled monolayers on aluminum oxide: effects of fluorination and substrate crystallinity

Two phosphonic acid (PA) self-assembled monolayers (SAMs) are studied on three aluminum oxide surfaces: the C and R crystallographic planes of single crystal alpha-alumina (sapphire) and an amorphous vapor-deposited alumina thin film. SAMs are either fully hydrogenated CH3(CH2)17PO3H2 or semifluorinated CF3(CF2)7(CH2)11PO3H2. Atomic force microscope (AFM) topographic imaging reveals that the deposited films are homogeneous, atomically smooth, and stable for months in the laboratory environment. Static and advancing contact angle measurements agree with previous work on identical or similar films, but receding measurements suggest reduced coverage here. To enable reproducible nanotribology measurements with the AFM, a scanning protocol is developed that leads to a stable configuration of the silicon tip. Adhesion for the semifluorinated films is either comparable to or lower than that for the hydrogenated films, with a dependence on contact history observed. Friction between each film and the tips depends strongly upon the type of molecule, with the fluorinated species exhibiting substantially higher friction. Subtle but reproducible differences in friction are observed for a given SAM depending on the substrate, revealing differences in packing density for the SAMs on the different substrates. Friction is seen to increase linearly with load, a consequence of the tip's penetration into the monolayer.     

Local packing environment strongly influences the frictional properties of mixed CH3- and CF3-terminated alkanethiol SAMs on Au(111)

Compositionally mixed, self-assembled monolayers (SAMs) derived from 16,16,16-trifluorohexadecanethiol and a normal alkanethiol, either hexadecanethiol or pentadecanethiol, were formed on Au(111) substrates. The relative composition of the films was determined using X-ray photoelectron spectroscopy and was found to approximately equal the equimolar composition of the isooctane solution from which they were formed. The frictional properties of the mixed films were measured on the nanometer scale using atomic force microscopy and were observed to decrease when the chain length of the CH(3)-terminated component was shortened by one methylene unit (i.e., when hexadecanethiol was replaced by pentadecanethiol). For comparison, the frictional properties of a mixed-chain-length CH(3)-terminated SAM derived from hexadecanethiol and pentadecanethiol in a 1:1 ratio was also examined. In contrast to the mixed CF(3)/CH(3) system, the latter mixed-chain-length system exhibited relatively higher friction when compared to single-component SAMs derived solely from either hexadecanethiol or pentadecanethiol. For both types of mixed films, the change in frictional properties that occurs as a result of modifying the position of neighboring terminal groups with respect to the surface plane is discussed in terms of the influence of local packing environments on interfacial energy dissipation (friction).     

Interfacial friction of thin PDMS network films

This study focuses on developing dry, surface‐tethered polymeric lubricant coatings capable of significantly decreasing friction and wear of nano‐ and micrometer scale machines. Vinyl‐terminated polydimethylsiloxane chains are spin‐coated with a crosslinking agent and platinum catalyst onto silicon wafers functionalized with a self‐assembling monolayer containing reactive vinyl groups. Lateral force microscopy (LFM) measurements employing a bead probe are used to quantify the coefficient of friction (COF) and adhesion characteristics of the PDMS‐SAM surface tethered networks. The combined polymer network and SAM layer manifest extremely low friction coefficients, μ = 4 × 10^?3, which is nearly one order of magnitude lower than the friction coefficient of the bare silicon substrate. The lowest friction forces are measured using silicon substrates covered with nanometer thick, peroxide crosslinked PDMS networks; though poorly crosslinked, these networks display COFs as much as ten‐times lower than a solitary SAM coating layer. Micrometer thick end‐linked optimal networks also manifest attractive interfacial friction properties, with COFs approximately three times larger than the thinner, imperfect networks. These observations are discussed in terms of the structure of the polymer networks and the role of adhesion forces on interfacial friction. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1773–1787, 2008     

Nanografting of alkanethiols by tapping mode atomic force microscopy

Nanografting, an atomic force microscopy (AFM) based nanolithography technique, is becoming a popular method for patterning self-assembled monolayers (SAMs). In this technique, a nanoscale patch of a thiol-on-gold SAM is exchanged with a different thiol by the action of an AFM tip operated in contact mode at high load. The results are then imaged in topographic or lateral force microscopy again at low values of the load. One of the problems of contact mode nanografting is that monolayers of large molecules such as proteins are likely to be deformed, damaged, or even removed from the surface by contact mode imaging even when small loads are used. Furthermore, we need to note that the stiffness of the cantilevers used in contact mode is different than that of the cantilevers used in tapping mode and that tip changing in the course of an experiment can be quite inconvenient. Here, we show that a monolayer on a gold substrate can be nanografted using tapping mode AFM (also referred to as amplitude modulation AFM) rather than the commonly used contact mode. While the grafting parameters are somewhat trickier to choose, the results demonstrate that nanografting in tapping mode can make patches of the same quality as those made by contact mode, therefore allowing for gentle imaging of the grafted molecules and the whole SAM without changing the microscope tip.     

Spectroscopic analysis of the tribological behavior of a model boundary layer lubricant

Highly ordered alkanethiol self-assembled monolayers (SAMs) on gold substrates are suitable models of boundary layer lubricants and may be used in actual nanoscale device applications. Here, such monolayers were studied by spectroscopic methods as a function of tribological wear (rubbing) using a pin-on-disk microtribometer. The coefficient of friction (COF) (ratio of the frictional force to the load) was measured with the tribometer, and reflectance infrared spectra and X-ray photoelectron spectra were obtained as the monolayer film failed and the COF changed. The results show that it is possible to correlate disorder in the monolayer film with tribological failure of the film, and that continued rubbing produces a chemical change in the monolayer film. Disorder in the monolayer is distinct from the influence of wear in the underlying gold substrate. Aged SAMs, having sulfonate rather than thiol headgroups and initially less well ordered, behave differently to the well-ordered freshly prepared SAMs. Interestingly, they show a lower COF over many more cycles of exposure to the rubbing pin. The impact of the mechanism of film failure in boundary layer lubrication is discussed.     

Langmuir and Langmuir-Blodgett films of N-(4-octadecyloxy-2-hydroxybenzylidene) derivatives of amino acids

Langmuir and Langmuir-Blodgett monolayers of N-(4-octadecyloxy-2-hydroxybenzylidene) derivatives of glycine, tyrosine, and phenylalanine were studied using pi-A isotherms and photoelastic modulated FTIR (PEM-FTIR). Based on compression modulus and interaction parameters, mixed monolayers of these compounds with stearylamine (SAM) showed well-organized monolayers compared to mixed systems with stearic acid (SA) and stearyl alcohol (SAL). The pure amphiphiles exhibited fairly well-ordered packing in the films, and in the mixtures, the ordering increased and showed a triclinic packing arrangement. For the phenylalanine amphiphile the packing showed slight disorder compared to the other two compounds. Surface properties of the LB films of these compounds on solid substrates were analyzed using static and dynamic contact angles of a series of liquids. The surface tension of coated substrates reflected clearly the highly acidic character. Fluidlike monolayers having a molecularly rough surface indicated high wettability for n-alkanes. In contrast, the monolayer containing well-ordered, well-packed alkyl chains indicated low wettability and small hysteresis.     

Chemically transformable configurations of mercaptohexadecanoic acid self-assembled monolayers adsorbed on Au(111)

Carboxyl-terminated self-assembled monolayers (SAMs) are commonly used in a variety of applications, with the assumption that the molecules form well-ordered monolayers. In this work, near-edge X-ray absorption fine structure measurements verify that well-ordered monolayers can be formed using acetic acid in the solvent. Disordered monolayers with unbound molecules present in the film result using only ethanol. A stark reorientation occurs upon deprotonation of the end group by rinsing in a KOH solution. This reorientation of the end group is reversible with tilted-over, hydrogen-bound carboxyl groups while the carboxylate ion end groups are upright. C(1s) photoemission shows that SAMs formed and rinsed with acetic acid in ethanol have protonated end groups, while SAMs formed without acetic acid have a large fraction of carboxylate-terminated molecules.     

Effect of humidity and temperature on nano/microtribolgical properties of perfluorinated carboxylic acid and hydrogenated carboxylic acid self‐assembled monolayers deposited on aluminum‐coated silicon substrate

Two series of perfluorinated carboxylic acid (FC) and hydrogenated carboxylic acid (HC) self‐assembled monolayer (SAM) films were prepared on aluminum surfaces separately by chemical vapor deposition. The formation, structure and morphology of these films were characterized by measuring contact angle with ellipsometric method, x‐ray photoelectron spectrometry, and atomic force microscopy, respectively. FC and HC SAMs with long chains formed more densely packed films than those with short chains did. The comparative micro/nanoscale friction and adhesive properties of FC and HC SAMs, with various chain lengths on aluminum‐coated silicon substrate, were investigated. The influence of environmental conditions, such as relative humidity (RH) and temperature, on the friction and adhesion behavior was studied. Micro/nanotribological properties of the films were greatly influenced by their backbones and terminal groups. FC SAMs with long chain exhibited adhesion‐resistance, friction reduction, and environmental independence. Copyright © 2009 John Wiley & Sons, Ltd.     

Surface characterization and platelet compatibility evaluation of the binary mixed self-assembled monolayers

This report describes a technique that used mixed self-assembled monolayer (SAM) as a model surface to evaluate the effect of steric hindrance on the SAM packing quality and its platelet compatibility. Two series of binary mixed SAMs were formed by mixing the bulky terminated alkanethiol (HS(CH2)10PO3H2) with a smaller terminated one (HS(CH2)9CH3 and HS(CH2)11OH) respectively. Surface characterization results showed the hydrophilicity on these two series of mixed SAMs changed with the solution mole fraction of PO3H2 terminated thiol, chi(PO3H2,soln), and reached to a nearly constant value as chi(PO3H2,soln) was 0.6 for PO3H2+CH3 SAM and 0.4 for PO3H2+OH SAM. This finding should be due to the gradual saturation of surface PO3H2 functionality on these mixed SAMs. The XPS analysis indicated the addition of the CH3 and OH terminated thiol could reduce the steric hindrance effect of PO3H2 functionality on monolayer formation and, henceforth, improve the SAM packing quality. In vitro platelet adhesion assay revealed the platelet compatibility on the PO3H2+OH SAMs was better than that on the PO3H2+CH3 and the pure PO3H2 ones. Moreover, the PO3H2+OH SAM with a low chi(PO3H2,soln) value exhibited the least platelet activating property of these two mixed SAM systems. These findings suggested that material's surface wettability and surface charge density should act collectively in affecting its platelet compatibility.