Mode Atomic Force Microscopy Research Articles

Adsorbed Organic Material and Its Control on Wettability

Laboratory core flood and field scale tests have demonstrated that 5–40% more oil can be released from sandstone reservoirs by injecting low salinity water, rather than high salinity fluids, such as seawater or formation water. The effect has been explained by a change in wettability of the minerals that form the pore surfaces, as a result of the decrease in divalent cation concentration. We have previously demonstrated that, even for solvent cleaned core samples, mineral surfaces retain a significant quantity of carbon containing material and this affects wettability and response to changed salinity. Here we quantified the response of sandstone core plug material in its preserved state (i.e., after storage in kerosene) and after the same core plug material was treated with ethanol and ozone to remove adsorbed organic compounds. We used the chemical force microscopy (CFM) mode of atomic force microscopy (AFM) to directly measure the adhesion force for two types of molecules on pore surfaces of individual sand grains that were plucked from an oil reservoir core plug. We functionalized AFM tips with alkane or carboxylate, so they resembled tiny oil droplets and measured adhesion to the sand grain surfaces in artificial seawater (ASW; 35,600 ppm) and in ASW diluted to ∼1,500 ppm (ASW-low). Both before and after the ethanol/ozone treatment, and for both the alkane and the carboxylate functionalized tips, the adhesion was lower in ASW diluted to ∼1,500 ppm than in ASW. For both alkane and carboxylate, the difference in adhesion between ASW and ASW-low was higher before the ethanol/ozone treatment. We attribute this change in response to the salinity dependent force caused mainly by the electric double layer (EDL) at the sand grain surfaces. We interpret the higher adhesion difference, before a very thorough ethanol/ozone treatment, to be a result of the loss of the organic material that was originally adsorbed on these surfaces, which adds to the charge density and thereby to the salinity dependent EDL force. Investigating the same area on the same pore surface, before and after removal of the organic material, demonstrates without doubt that it is organic material that causes the low salinity response, not the underlying mineral surface.

Nano-mechanical Behavior of Calcium Silicate Hydrate and Calcium Hydroxide in Cement Paste: Elevated Peak-Force Study

In this paper, the mechanical behavior of calcium–silicate–hydrate (C–S–H) and calcium–hydroxide (CH) was investigated at the nano-level. This study aims to propose a new method of evaluating nano-mechanical behavior of the two main cement paste components of C–S–H and CH. Nano-mechanical behavior of cement paste components is assessed, utilizing novel peak-force tapping mode of atomic force microscope and new proposed technique of elevated peak-forces. Another aim of this study is to investigate the early age properties of cement during the initial setting time by atomic force microscope. As a result, it is indicated that mostly C–S–H colloids treated as ductile materials comparing to brittle behavior of CH mono-layer sheet. However, multilayer of CH behaves like semi-ductile and plastic materials in very small increments of deflection. It was found that the trend of Young’s modulus is divided to three major intervals. Preliminary, the values were decreased within 20 min after the beginning of hydration and then it seems to be constant up to about 45 min after hydration (the initial setting time of cement). After that, Young’s modulus gradually increased up to 2 h after hydration to a relatively higher value. The roughness trend can be divided into three different phases as well as the Derjaguin, Muller, and Toporov modulus. First, at early 10 min, the values are increased drastically. Second, the average values are decreased sharply at 20 min after hydration and also reduced gradually up to around 60 min after hydration.

Effect of water and nano-silica solution on the early stages cement hydration

The nanoscopic young’s modulus of cement paste during early ages of hydration in water and nano-silica was investigated by the application of atomic force microscopy (AFM). Peak-Force Quantitative Nano-Mechanical (PFQNM) imaging mode in atomic force microscopy was used to determine elastic modulus of cement paste before and after immersion in water and nano-silica solution. The results clearly show how mechanical and physical properties of cement grains changes progressively to higher values during the hydration process in water and nano-silica.Moreover, an empirical theory on mechanism of hydration development is proposed in the current study based on experimental observations. Average Young’s modulus of condensed cement powder was changed from about 15GPa, for unhydrated state, to 11.3GPa after two hours of hydration in water environment. The average roughness trend was also altered from 8.31nm to 18.2nm during hydration process. Results show that the cement hydration rate in nano-silica solution is much higher than water environment. Moreover transition zone between C-S-H colonies have much higher mechanical properties than the hardest colonies in every ages. In the presence of nano-silica, transition zone has a width of less than 10nm and a surface area of 5% of the overall surface area.

Size-Dependent Stiffness of Nanodroplets: A Quantitative Analysis of the Interaction between an AFM Probe and Nanodroplets.

The interfacial properties of nanodroplets are very significant for the exploration of the basic law governing the fluid behavior at the nanoscale and also the applications in some important processes in novel materials fabrication by forming a special and local reaction environment. However, many basic factors such as the interfacial tension or stiffness of nanodroplets are still lacking, partially because of the difficulty of making quantitative measurements of the interfacial interactions at the nanometer scale. Here, we used a novel atomic force microscopy (AFM) mode, PeakForce mode, to control the interaction between an AFM probe and nanodroplets, by which we could obtain the morphology and stiffness of nanodroplets simultaneously. The change in the stiffness with the size of the nanodroplets was observed where the smaller nanodroplets usually had a larger stiffness. To explain this phenomenon, we then established a theoretical model based on the Young-Laplace equation in which the deformation and size-dependent stiffness could be described quantitatively and the experimental observations could be explained with our numerical calculations very well. The general methodology presented here could also be extended to analyze the relevant behavior of nanobubbles and other wetting phenomena at the nanoscale.

Precise positioning of cancerous cells on PDMS substrates with gradients of elasticity.

In this work the novel method to create PDMS substrates with continuous and discrete elasticity gradients of different shapes and dimensions over the large areas was introduced. Elastic properties of the sample were traced using force spectroscopy (FS) and quantitative imaging (QI) mode of atomic force microscopy (AFM). Then, fluorescence microscopy was applied to investigate the effect of elastic properties on proliferation of bladder cancer cells (HCV29). Obtained results show that cancerous cells proliferate significantly more effective on soft PDMS, whereas the stiff one is almost cell-repellant. This strong impact of substrate elasticity on cellular behavior is driving force enabling precise positioning of cells.

Imaging latex–carbon nanotube composites by subsurface electrostatic force microscopy

Electrostatic modes of atomic force microscopy have shown to be non-destructive and relatively simple methods for imaging conductors embedded in insulating polymers. Here we use electrostatic force microscopy to image the dispersion of carbon nanotubes in a latex-based conductive composite, which brings forth features not observed in previously studied systems employing linear polymer films. A fixed-potential model of the probe-nanotube electrostatics is presented which in principle gives access to the conductive nanoparticle’s depth and radius, and the polymer film dielectric constant. Comparing this model to the data results in nanotube depths that appear to be slightly above the film–air interface. This result suggests that water-mediated charge build-up at the film–air interface may be the source of electrostatic phase contrast in ambient conditions.

Sol-gel derived bioactive coating on zirconia: Effect on flexural strength and cell proliferation.

The purpose of this study was to evaluate the effect of sol-gel derived bioactive coatings on the biaxial flexural strength and fibroblast proliferation of zirconia, aimed to be used as an implant abutment material. Yttrium stabilized zirconia disc-shaped specimens were cut, ground, sintered, and finally cleansed ultrasonically in each of acetone and ethanol for 5 minutes. Three experimental groups (n = 15) were fabricated, zirconia with sol-gel derived titania (TiO2 ) coating, zirconia with sol-gel derived zirconia (ZrO2 ) coating, and non-coated zirconia as a control. The surfaces of the specimens were analyzed through images taken using a scanning electron microscope (SEM), and a non-contact tapping mode atomic force microscope (AFM) was used to record the surface topography and roughness of the coated specimens. Biaxial flexural strength values were determined using the piston-on-three ball technique. Human gingival fibroblast proliferation on the surface of the specimens was evaluated using AlamarBlue assay™. Data were analyzed using a one-way analysis of variance (ANOVA) followed by Tukey's post-hoc test. Additionally, the biaxial flexural strength data was also statistically analyzed with the Weibull distribution. The biaxial flexural strength of zirconia specimens was unaffected (p > 0.05). Weibull modulus of TiO2 coated and ZrO2 coated groups (5.7 and 5.4, respectively) were lower than the control (8.0). Specimens coated with ZrO2 showed significantly lower fibroblast proliferation compared to other groups (p < 0.05). In conclusion, sol-gel derived coatings have no influence on the flexural strength of zirconia. ZrO2 coated specimens showed significantly lower cell proliferation after 12 days than TiO2 coated or non-coated control. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 2401-2407, 2017.

Alterations in Platelet Activity and Elastic Modulus of Healthy Subjects, Carriers of G20210A Polymorphism in the Prothrombin Gene

Summary Platelet activation is a complex process in which platelet reorganization takes place associated with changes in the cell shape, topology, membrane elasticity and microparticle production. The aim of this study was to investigate the changes/aberrations in the platelet activity, elasticity and morphology in healthy subjects, carriers of A allele of prothrombin G20210A polymorphism. Blood samples from 18 healthy subjects were used for platelet analysis by force-mode atomic force microscopy. Restriction analysis was used to investigate the carriage of G20210A polymorphism in the prothrombin gene. Flow- cytometry was applied to evaluate platelet activation. Young’s modulus of the plasma membranes of platelets derived from healthy subjects, carriers of variant A allele of prothrombin 20210G&gt;A polymorphism (407±69 kPa) is two times higher than the one determined for non­carriers (195.4±48.7 kPa; p&lt;0.05). The background activity of platelets measured as an interrelation of Cd41/Cd61 and CD62 by flow cytometry was also higher in carriers of variant A allele of prothrombin 20210G&gt;A polymorphism (5.0%) than in non-carriers (1.3%). Platelets isolated from healthy carriers of variant A allele of prothrombin 20210G&gt;A polymorphism exhibited a higher level of activity and a higher degree of stiffness at the stage of spreading as compared to platelets from non­carriers.

Environmentally Conscious Pretreatment Process for Plating on PPS Resins

<Introduction>Polyphenylene sulfide (PPS) is a heat-resistance material partially crystalline polymer with a simple chemical construction. The PPS has a high melting point of about 280°C, outstanding chemical resistance and non-combustibility established by an industry flammability test without any flame retardant chemical. Furthermore, the PPS is widely used in the replacement of high-functional insulation and various metals from their properties. When the PPS is plated, surface roughening is treated with a mixed solution of Nitric acid and hydrofluoric acid conventionally. However, the solution is difficult in waste water treatment. So the correspondence to these problems is demanded.Therefore we reported a formation technology of the plating film superior in adhesion strength for pretreatment of the insulation resin until now. In this study, we applied the atmospheric UV irradiation method for PPS resins and investigated the plating process. <Experimental>PPS substrates was annealed at 80 °C for 1 h in order to relax the internal stress. The substrate was irradiated using ultraviolet (UV) irradiation equipment (KOL1-300S, KOTO Electric Co., LTD) in the atmosphere. After the atmospheric UV irradiation, the substrate was plated about 0.3 μm metal film by electroless NiP plating bath. After electroless NiP plating and after electrolytic copper plating bath, samples were heated at 80 °C for 1 h in order to improve adhesion.The condition of the deposited NiP film after electroless plating was visually observed. Wettability testing of the substrate after atmospheric UV irradiation and proceeding alkaline treatment was performed by water contact angle.Adhesion strength of the plated film to the substrate after electrolytic plating was measured by 90° peel test according to the JIS H 8630-2006 procedure with a pull speed of 50 mm min-1. Adhesion strength was measured on an Orient Precision Machine Factory Strike Log Rough E2-L05. The measurement involved peeling the plated film from the substrate at three different locations for which the average was calculated.Surface morphologies of the untreated substrate, the substrate after atmospheric UV irradiation were observed by scanning probe microscope (SPM) using the atomic force microscopy (AFM) mode. The surface roughness (Ra) of the samples was measured over a 10 μm2 area. Similarly, surface morphologies of the substrate after atmospheric UV irradiation and proceeding alkaline treatment was observed by scanning electron microscope (SEM).Fourier transform infrared spectroscopy (FT-IR) of the substrate before and after atmospheric UV irradiation was performed using the attenuated total reflection (ATR) method. Therefore, the similar samples was confirmed the change of functional groups on the substrate before and after atmospheric UV irradiation by X-ray photoelectron spectroscopy (XPS). For samples prepared for FT-IR analysis and XPS analysis, atmospheric UV irradiation time was 5 min, 10 min, and 30 min. <Results and Discussion>The high-quality electroless NiP plating was visually confirmed on the PPS resin surface by surface modification using atmospheric UV irradiation. Adhesion strength of about 0.8 kN m-1 was obtained for the treatment. Similarly, as a result of having measured the water contact angle, it was decreased with 31.2° for the treatment of 20 min whereas the untreated substrate was 79.4°. It is thought that a hydrophilicity of the PPS resin surface improved by atmospheric UV irradiation. The change in substrate morphology and surface roughness using atmospheric UV irradiation was observed by SPM. The Ra of untreated PPS and PPS after atmospheric UV irradiation were almost no change, a smoothness of the substrate had been kept. Furthermore after the atmospheric UV irradiation, the dimples was formed on the modified surface. The dimples is considered that the elastomers component in PPS resins was eluted. Subsequently, we confirmed the increase in the adsorption of O-H, C=O and C-O groups increasing the UV irradiation time by FT-IR spectroscopy. In addition, as a result of analyzed by XPS, C-C and C-S bonds were confirmed in the untreated substrate, subsequently by UV irradiation we confirmed that C-C bonding peak decreased and the detection of C-O and COO bonding peaks due to the hydrophilic increased. <Summary>From the above results, the plating on PPS resins was possible to applying the atmospheric UV irradiation method that is environmentally friendly. Furthermore, a smoothness of the substrate had been kept with superior to adhesion strength. Acknowledgement: This study was aided by “MEXT-supported Program for the Strategic Research Foundation at Private Universities”.

Examining Electrical Properties of Solid Electrolyte Interface on Silicon Electrodes

The complex surface reactions contribute to the formation of solid-electrolyte interphases (SEI), and cause the irreversible capacity loss of silicon (Si) electrodes. The chemical and mechanical instability of the interphases finally leads to performance degradation. A microscopic characterization of the electrical properties at the interface is expected to gain information to understand the physical and chemical evolution caused by the formation of SEI, and provide the guidance for improvements in performance. The microscopic electrical characterization techniques, including Kelvin probe force microscopy (KPFM) and scanning spreading resistance microscopy (SSRM), have been applied to silicon electrodes. The nanoelectrical probes have been developed in one atomic force microscopy (AFM)-based platform, and the complementary electrical characterizations can be performed on the same sample area in nm-scale. Based on the contact potential difference method, KPFM maps the work function (WF) on electrode surfaces, which is expected to largely change with lithiation and delithiation. WF is sensitive to Li-ion distribution and diffusion, which can be highly inhomogeneous in nm-scale and can be assessed and evaluated from the KPFM mapping. Local conductivity/resistivity of Li-ion electrodes has been studied by SSRM. Based on the contact mode of AFM, SSRM maps of local resistivity in 10-nm resolutions have been acquired by applying a voltage between the probe and a sample and measuring the current through the probe. Ex-situ measurements along the Lithiation/delithiation process have been performed to understand the formation of SEI and the impact of electrochemical reaction on the electrical properties of SEI. Figure 1 shows the SSRM resistance changes before and after lithiation of Si electrode. The inhomogeneity with grain and domain sizes of 200-500 nm is observed at the surface of Si electrode. Surface modification by using atomic layer deposition and molecular layer deposition has also been used to modify the surface chemistry of silicon electrodes. This presentation will discuss the evolution in nm-scale resistance of SEI during electrochemical reactions, and the impact of surface coating materials on the electrical properties of SEI. Figure 1

AFM study of hydrodynamics in boundary layers around micro- and nanofibers

The description of hydrodynamic interactions between a particle and the surrounding liquid, down to the nanometer scale, is of primary importance since confined liquids are ubiquitous in many natural and technological situations. In this paper we combine three nonconventional atomic force microscopes to study hydrodynamics around micro and nanocylinders. These complementary methods allow the independent measurement of the added mass and friction terms over a large range of probe sizes, fluid viscosities,and solicitation conditions. A theoretical model based on an analytical description of the velocity field around the probe shows that the friction force depends on a unique parameter, the ratio of the probe radius to the thickness of the viscous boundary layer.We demonstrate that the whole range of experimental data can be gathered in a master curve, which is well reproduced by the model. This validates the use of these atomic force microscopy modes for a quantitative study of hydrodynamics and opens the way to the investigation of other sources of dissipation in simple and complex fluids down to the submicron scale.

Mapping of Nanoscale Mechanical Properties of Polymers in Quasi-static and Oscillatory Atomic Force Microscopy Modes

ABSTRACTRecent advances in studies of local mechanical properties of polymers with different atomic force microscopy techniques (contact, Hybrid and amplitude modulation modes) are described in interplay between experiment and theory. Analysis of force curves and time dependencies of probe response to sample compliance, which were recorded on a number of polymer materials at various temperatures, leads to quantitative mapping of specific mechanical properties (elastic modulus, work of adhesion, etc). High spatial resolution of elastic modulus mapping (10-20 nm) is illustrated in measurements of lamellar structures of several polymers. Challenges of examination of viscoelastic properties are pointed out and a possible solution is presented.

Calibration of higher eigenmodes of cantilevers.

A method is presented for calibrating the higher eigenmodes (resonant modes) of atomic force microscopy cantilevers that can be performed prior to any tip-sample interaction. The method leverages recent efforts in accurately calibrating the first eigenmode by providing the higher-mode stiffness as a ratio to the first mode stiffness. A one-time calibration routine must be performed for every cantilever type to determine a power-law relationship between stiffness and frequency, which is then stored for future use on similar cantilevers. Then, future calibrations only require a measurement of the ratio of resonant frequencies and the stiffness of the first mode. This method is verified through stiffness measurements using three independent approaches: interferometric measurement, AC approach-curve calibration, and finite element analysis simulation. Power-law values for calibrating higher-mode stiffnesses are reported for several cantilever models. Once the higher-mode stiffnesses are known, the amplitude of each mode can also be calibrated from the thermal spectrum by application of the equipartition theorem.

Dynamic nano-triboelectrification using torsional resonance mode atomic force microscopy.

Understanding the mechanism of charge generation, distribution, and transfer between surfaces is very important for energy harvesting applications based on triboelectric effect. Here, we demonstrate dynamic nanotriboelectrification with torsional resonance (TR) mode atomic force microscopy (AFM). Experiments on rubbing the sample surface using TR mode for the generation of triboelectric charges and in-situ characterization of the charge distribution using scanning Kelvin probe microcopy (SKPM) were performed. This method allows the tip to perform lateral oscillation and maintains the tip-sample interaction in the attractive region to ensure high efficiency of the charge generation during the rubbing process. The measured efficiency of generating triboelectric charges can achieve ~10.53 times higher than conventional static/contact mode in the triboelectrification experiments. In addition to the charge generation, local discharging experiments were also performed. This work would provide a new method to generate patterned charges and also be helpful in understanding the mechanism of nanotriboelectrification.

Wide range local resistance imaging on fragile materials by conducting probe atomic force microscopy in intermittent contact mode

An imaging technique associating a slowly intermittent contact mode of atomic force microscopy (AFM) with a home-made multi-purpose resistance sensing device is presented. It aims at extending the widespread resistance measurements classically operated in contact mode AFM to broaden their application fields to soft materials (molecular electronics, biology) and fragile or weakly anchored nano-objects, for which nanoscale electrical characterization is highly demanded and often proves to be a challenging task in contact mode. Compared with the state of the art concerning less aggressive solutions for AFM electrical imaging, our technique brings a significantly wider range of resistance measurement (over 10 decades) without any manual switching, which is a major advantage for the characterization of materials with large on-sample resistance variations. After describing the basics of the set-up, we report on preliminary investigations focused on academic samples of self-assembled monolayers with various thicknesses as a demonstrator of the imaging capabilities of our instrument, from qualitative and semi-quantitative viewpoints. Then two application examples are presented, regarding an organic photovoltaic thin film and an array of individual vertical carbon nanotubes. Both attest the relevance of the technique for the control and optimization of technological processes.

Understanding Failure Mechanisms of Solid Electrolyte Interphase on Silicon Anodes: An in-Situ AFM Approach

The formation and evolution of solid electrolyte interphase (SEI) directly governs the lifetime and performance of rechargeable Lithium-ion batteries. There are lots of studies dealing with chemistry of the SEI layer but very little information is available in terms of its mechanical behavior for example fracture behavior, strength etc. To enable utilization of high capacity anode materials such as Silicon which goes through large volume changes (~300%) during cycling, a mechanistic understanding of SEI layer is of critical importance. In this study we have used in-situ atomic force microscopy (AFM) to monitor the formation, evolution and failure of the SEI layer on patterned Si island electrodes. The unique PeakForce tapping mode was used to image the extremely fragile SEI layer, which is very challenging for conventional AFM modes in organic solvent. Our in situ studies show for the first time the in operando cracking of SEI layer and its evolution during cycling. Based on a succession of AFM images showing failure of SEI layer, we were able to calculate the critical strain at which this failure starts. A classical energy release rate approach was used to get a bound of fracture energy values of SEI layer for a range of elastic moduli of SEI layer. This study not only provides an in-depth understanding of failure modes of SEI layer but also offer guidance towards tailoring passivation layers for optimal battery performance.

SU‐F‐SPS‐08: Measuring the Interaction Of DDR Cell Receptors and Extracellular Matrix Collagen in Prostate Cells

Purpose:Discoidin domain receptors (DDR) have recently been recognized as important players in cancer progression. DDRs are cell receptors that interact with collagen, an extracellular matrix (ECM) protein. However the detailed mechanism of their interaction is unclear. Here we attempted to examine their interaction in terms of structural (surface topography), mechanical (rupture force), and kinetic (binding probability) information on the single molecular scale with the use of atomic force microscopy (AFM).Methods:The Quantitative Nano‐mechanical property Mapping (QNM) mode of AFM allowed to assess the cells in liquid growth media at their optimal physiological while being viable. Human benign prostate hyperplasia (BPH‐1) cell line was genetically regulated to suppress DDR expression (DDR‐ cells) and was compared with naturally DDR expressing cells (DDR+).Results:Binding force measurements (n = 1000) were obtained before and after the two groups were treated with fibronectin (FN), an integrin‐inhibiting antibody to block the binding of integrin. The quantification indicates that cells containing DDR bind with collagen at a most probable force of 80.3–83.0 ±7.6 pN. The probability of them binding is 0.167 when other interactions (mainly due to integrin‐collagen binding) are minimized.Conclusion:Together with further force measurements at different pulling speeds will determine dissociation rate, binding distance and activation barrier. These parameters in benign cells provides some groundwork in understanding DDR's behavior in various cell microenvironments such as in malignant tumor cells.Funding supported by Richard Barber Interdisciplinary Research Program of Wayne State University

Automated force controller for amplitude modulation atomic force microscopy.

Atomic Force Microscopy (AFM) is widely used in physics, chemistry, and biology to analyze the topography of a sample at nanometer resolution. Controlling precisely the force applied by the AFM tip to the sample is a prerequisite for faithful and reproducible imaging. In amplitude modulation (oscillating) mode AFM, the applied force depends on the free and the setpoint amplitudes of the cantilever oscillation. Therefore, for keeping the applied force constant, not only the setpoint amplitude but also the free amplitude must be kept constant. While the AFM user defines the setpoint amplitude, the free amplitude is typically subject to uncontrollable drift, and hence, unfortunately, the real applied force is permanently drifting during an experiment. This is particularly harmful in biological sciences where increased force destroys the soft biological matter. Here, we have developed a strategy and an electronic circuit that analyzes permanently the free amplitude of oscillation and readjusts the excitation to maintain the free amplitude constant. As a consequence, the real applied force is permanently and automatically controlled with picoNewton precision. With this circuit associated to a high-speed AFM, we illustrate the power of the development through imaging over long-duration and at various forces. The development is applicable for all AFMs and will widen the applicability of AFM to a larger range of samples and to a larger range of (non-specialist) users. Furthermore, from controlled force imaging experiments, the interaction strength between biomolecules can be analyzed.

Solid Electrolyte Interphase Formation and Failure Mechanisms in Lithium Ion Batteries: In Situ and in Operado AFM Imaging

The lifetime and performance of lithium-ion batteries depend significantly on the formation and evolution of the solid electrolyte interphase (SEI) layer. A stable SEI is necessary for utilization of high specific capacity anode materials such as Si which goes through huge volume changes (upto ~400%) during cycling. In this study we report in situ atomic force microscopy (AFM) investigation on the formation and failure mechanisms of SEI layer using patterned Si island structures. Due to the shear lag effect [1], these patterned Si islands go through lateral expansion and contraction. This puts the SEI layer on the top of the island in tension and compression during lithiation and delithiation, respectively. We performed the studies in a glovebox at the environment with < 1 ppm O2 and H2O. In addition, the unique PeakForce tapping mode was used to image the extremely fragile SEI layer, which is very challenging for conventional AFM modes in organic solvent. Our in situ studies show for the first time the in operando cracking of SEI layer and its evolution during cycling. To understand the mechanics of the SEI layer, the critical strain at which this cracking starts to evolve was derived from a progression of the AFM images. This observation will be complemented with coin cell data on comparison of irreversible capacities of continuous film and patterned island samples which differ in their mode of deformation. We are also using Scanning electrochemical microscopy (SECM) to detect local electrochemical differences at stable and unstable SEI sites. Our comprehensive studies not only provide a new in-depth understanding of the in operando SEI formation, evolution and its mechanical response, but also offer guidance to tailor passivation layers for optimal battery performance. Reference: [1] Tokranov et. al. ACS Appl. Mater. Interfaces, 2014, 6, 6672

Studies of Grafted and Sulfonated Spiro Poly(isatin-ethersulfone) Membranes by Super Acid-Catalyzed Reaction.

Spiro poly(isatin-ethersulfone) polymers were prepared from isatin and bis-2,6-dimethylphenoxyphenylsulfone by super acid catalyzed polyhydroxyalkylation reactions. We designed and synthesized bis-2,6-dimethylphenoxyphenylsulfone, which is structured at the meta position steric hindrance by two methyl groups, because this structure minimized crosslinking reaction during super acid catalyzed polymerization. In addition, sulfonic acid groups were structured in both side chains and main chains to form better polymer chain morphology and improve proton conductivity. The sulfonation reactions were performed in two steps which are: in 3-bromo-1-propanesulfonic acid potassium salt and in con. sulfuric acid. The membrane morphology was studied by tapping mode atomic force microscope (AFM). The phase difference between the hydrophobic polymer main chain and hydrophilic sulfonated units of the polymer was shown to be the reasonable result of the well phase separated structure. The correlations of proton conductivity, ion exchange capacity (IEC) and single cell performance were clearly described with the membrane morphology.