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Eingeladener Vortrag
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Luminescent lanthanides(III) offer exceptional optical properties that can overcome issues often encountered with other fluorophores (e.g. organic dyes). Their long lifetimes up to milliseconds, low photobleaching and sharp and characteristic emission peaks make the lanthanides extremely valuable for the development of advanced luminescent materials. Previous work on Ru(II) and Ir(III) gold surfaces further highlights the potential of employing the luminescence of metal complexes for the fabrication of sensing platforms and devices.
Here, we incorporate visible and NIR-emitting lanthanide(III) complexes Ln2L3 (Ln = Eu(III), Nd(III), Yb(III)) to gold and plasmonic surfaces, translating the unique optical properties of the lanthanides(III) to practical devices. The Ln2L3 complexes are deposited on the surfaces with different methods, ranging from polymer aided physisorption to the covalent attachment on the gold surface. Furthermore, we exploit the high sensitivity to the coordination environment of lanthanides(III) to design and prepare a sensing platform.
We report a new sequence selective terpolymerisation in which three monomers (butylene oxide (BO) A, PhNCS B and phtalic thioanhydride (PTA) C) are selectively enchained into an (ABA′C)n sequence. PTA/PhNCS/BO ring-opening terpolymerisation ROTERP can be coupled with CS2 ROTERP to generate tetrapolymers and with εDL ROP in switchable catalysis for blockpolymer synthesis.
Supramolecular copolymerization driven by integrative self-sorting of hydrogen-bonded rosettes
(2020)
Molecular recognition to preorganize noncovalently polymerizable supramolecular complexes is a characteristic process of natural supramolecular polymers, and such recognition processes allow for dynamic self-alteration, yielding complex polymer systems with extraordinarily high efficiency in their targeted function. We herein show an example of such molecular recognition-controlled kinetic assembly/disassembly processes within artificial supramolecular polymer systems using six-membered hydrogen-bonded supramolecular complexes (rosettes). Electron-rich and poor monomers are prepared that kinetically coassemble through a temperature-controlled protocol into amorphous coaggregates comprising a diverse mixture of rosettes. Over days, the electrostatic interaction between two monomers induces an integrative self-sorting of rosettes. While the electron-rich monomer inherently forms toroidal homopolymers, the additional electrostatic interaction that can also guide rosette association allows helicoidal growth of supramolecular copolymers that are comprised of an alternating array of two monomers. Upon heating, the helicoidal copolymers undergo a catastrophic transition into amorphous coaggregates via entropy-driven randomization of the monomers in the rosette.
The application of inorganic nanoparticles as reinforcement agent for polymer composites is constantly growing. Improving the performance of the material with desirable properties requires understanding of the interaction between polymer chains and nanoparticles and the properties of the interphase as well. Boehmite, a mineral of aluminum with basic unit of AlO(OH), is a novel and promising nanofiller which leads to enhanced performance of polymer composites. It has been recently reported that boehmite nanoparticles have reinforcing effect on epoxy matrix in carbon-fiber composites. It was primarily assumed that these improvements are due to very high Young’s modulus of boehmite particles. However, in our latest study we presented new values for the Young’s modulus of boehmite much lower than those reported earlier. This brings up the importance of interphase properties, e.g. the crosslink density, which can have the dominant role in the overall material property. Nevertheless, due to resolution limitations of conventional nanoprobing approaches, characterization of the interphase between individual particles and matrix is a challenge.
In this study, the main goal is to investigate the interphase of the epoxy/boehmite nanocomposites using AFM-based methods. We simplify the three-dimensional nanocomposite system to a two-dimensional horizontally layered sample with a large and easy to access interphase area. For this purpose, 1µm coatings of hydrothermally synthesized boehmite are prepared as the substrate on which the epoxy is later molded and cured. AFM surface potential and force maps were obtained on the cross-sectional cut of epoxy/ boehmite sample. The results show unexpectedly a large interphase area (approx. 1 µm) with different electrical and mechanical properties comparing to bulk epoxy. The average force-distance curves from this region showed more elastic behavior compared to bulk. The underlying mechanism of this influence is not fully understood yet. Thus, further investigation on the interphase region using the novel Nano-IR approach provides more information about the chemical characteristics. Numerical simulation will give complementary information to understand the effect of nanoparticles on the crosslinking density of the interphase. This can be different to bulk epoxy due to either different local temperature gradients or due to a surface selectivity of boehmite towards the monomer molecules.
One aim of the EMPIR nPSize project 17NRM04 was to develop and validate three classes of candidate reference (test) materials (RTMs), with i) well-defined non-spherical shape, ii) relatively high polydispersity index, and iii) accurate particle concentrations.
To fulfil the requirements of the project, 11 different types of materials were prepared. Following the initial assessment of the materials suitability, nPSize5_PT_UNITO, nPSize6_AC_UNITO and nPSize7_GN_CEA materials were found unsuitable for the project, due to various reasons. PT material was deemed unsuitable due to its predominantly agglomerated nature. AC material contained relatively high amount of impurities (other particle forms). GN material was found too heterogeneous in both the length and width for the purpose of the project. The remaining 8 candidate RTMs were assessed for their homogeneity and stability and used for successful delivery of the associated activities within the nPSize project.
he main objective of the nPSize project is to improve the measurement capabilities for nanoparticle size based on both measurement methods traceable to SI units and new reference materials. Two basic approaches have been used in order to develop measurement procedures resulting in traceable results of the nanoparticle size distribution: physical modelling for the methods used in the project (TSEM, SEM, AFM and SAXS) and machine learning.
Physical modelling: In this part, the physical models associated with different shape measurements for the techniques TSEM, SEM, AFM and SAXS have been collected and further developed with the aim to simulate the resulting signal as measured by the individual methods. Uncertainties and traceability associated with each model were investigated and evaluated. In the following, the progress on these physical models is reported for each individual method.
Machine Learning modelling: The aim of this part is to use machine learning to enable automatic measurement of nanoparticle shape from expert a-priori information only. No physical model will be used as a-priori information in this task.
The accuracy and traceability of the size results obtained by each technique will be analyzed and compared with the physical modelling. A machine learning database will then be used to create automatic detection algorithms.
Aluminium is still one of the most important contact metallisations for power electronic chips like MOSFETs or IGBTs. With a large difference in thermal expansion coefficients (CTEs) between aluminium and silicon and the temperatures generated in hot-spots during high power transients, these layers are prone to failure due to thermo-mechanical fatigue. Usually lifetime assessment is done by subjecting dedicated test specimens to standardised stress tests as e.g. active or passive thermal cycling. This paper proposes a novel method for accelerated stress testing and lifetime modelling of thin aluminium films in the high-cycle fatigue regime by isothermal mechanical loading. The proposed novel test method is suggested to complement or replace resource-demanding thermal cycling tests and allow simple in-situ monitoring of failure.
The progress of the VAMAS Project 16 "Measurement of (relative) number concentration of bimodal silica nanoparticles including deposition from liquid suspension" in TWA 34 Nanoparticle Populations is presented. Follwowing points are discusssed:
- Validate the performance of imaging methods to measure the relative number concentration
• electron microscopy (SEM, TEM) and atomic force microscopy (AFM)
• two modes of bimodal (30 and 60 nm) silica nanoparticles
- Validate the performance of small angle X-ray scattering (SAXS) for the traceable measurement of the number concentration of the two modes.
The progress in the VAMAS Project #15" Measurement of particle size and shape distribution of bipyramidal titania including deposition from liquid suspension" within TWA 34 Nanoparticle Populations is presented with highlight of the following points:
- Determine and compare particle size and shape distribution by means of:
• electron microscopy (SEM, TEM, STEM-in-SEM)
• atomic force microscopy (AFM)
• small angle X-ray scattering (SAXS)
- Determine uncertainty induced by deposition protocol from liquid suspension with comparison to known values from a prior ILC with already deposited nanoparticles on TEM grids.
- Provide comparative validation of protocols for the techniques other than TEM.
The optical properties of semiconductor nanocrystals (SCNCs) depend on constituent material, particle size, and surface chemistry, with the size of the photoluminescence (PL) quantum yield (QY) and the PL decay kinetics being largely controlled by the number of dangling bonds, which have to be properly passivated for high quality materials. Hence, PL measurements can provide insight not only in SCNC photophysics, yet can be also used for quality control of SCNC synthesis and surface modification. In this respect, steady state and time-resolved fluorometry and confocal microscopy with time correlated single photon counting were used to study the PL properties of core-shell CdSe SCNCs with different shells and surface chemistries on ensemble and single particle level, thereby focusing on a correlation of ensemble PL QY and PL decay kinetics with particle brightness, PL time traces, and the On-time fraction of single SCNCs. Additionally, confocal PL images were correlated with AFM measurements in order to derive the amount of absorbing, yet non-emissive ”dark” SCNCs, the presence of which resulting in an underestimation of ensemble PL quantum yields. The results of this study can help to identify synthetic routes and surface modifications, which minimize the fraction of dark SCNCs.
The flowability of cement paste is of great importance in today’s construction industry and is influenced by additives such as superplasticizers (SP). One type of SPs are polycarboxylate ether type SPs. These additives electrostatically bind with the negatively charged carboxylic groups at the backbone to the positively charged clinker phases.
To model positively charged clinker phases with adsorbed SP, silicon Wafers are pre-coated with cationic polyethylenimine (PEI) and SP is adsorbed onto the coated surface (Si/PEI/SP). Two different polycarboxylate ether type (PCE) SP are compared – one for ready-mix concrete and one for precast concrete. In this preliminary study the interaction forces between Si/PEI/SP surface and a silica microsphere (colloidal probe) are investigated under mild physico-chemical conditions (pH *6, ion concentration <10−5 M) using Colloidal Probe Atomic Force Microscopy (CP-AFM).
The interaction force between the model surfaces is attractive for low concentration of SP. The force changes from attractive to repulsive by increasing amount of SP. The force upon approach reveals a biexponential behavior. The exponential decay at large and short surface separations are attributed to electrostatic and steric interactions, respectively. The steric forces of the SP for ready-mix concrete show a steeper onset than the SP for precast concrete.
The quantification of these interaction forces will be compared to rheological measurements of similar systems. Furthermore, the parameters will be changed to better approach the conditions in real systems, i.e. higher pH and ionic strength. This helps to understand how the forces on the nanoscale influence the macroscopic rheology.
Inorganic nanoparticles are used to improve the performance of epoxy as the matrix phase in fiber-reinforced composites used for aerospace applications. The effectiveness of nanofillers on property enhancement of thermosetting polymers depends on many factors including the interaction between the functional groups of nanofillers and the polymer reactants. In the current work, we study the effect of boehmite nanoparticles (BNPs) on properties of anhydride-cured bisphenol-A-diglycidyl ether (DGEBA). Dynamic mechanical thermal analysis (DMTA) and a high-resolution force measurement approach called intermodulation atomic force microscopy (ImAFM) were carried out to investigate the thermomechanical and nanomechanical properties of this material, respectively. It was found that BNPs lead to decrease of glass transition temperature (Tg) and crosslink density of the polymer network meanwhile significantly enhancing the Young’s modulus. Besides formation of a soft interphase near the particles, significant changes in local stiffness of polymer matrix far from the interphase was observed with ImAFM. Thus, boehmite induces long-range chemical alteration on the matrix. This effect has a higher impact on overall composite properties compared to the formation of interphase which is only a short-range effect. The local chemical evaluations on the soft interphase using an infrared-AFM method (NanoIR) revealed the accumulation of anhydride hardener near the boehmite interface. Based on these observations the effect of boehmite on the curing of epoxy is hypothesized to be governed by the strong interaction between boehmite and the anhydride. This interaction causes changes the ratio of reactants in the epoxy mixture and hence alteration of curing pathway and the network architecture. In future studies we examine this hypothesis by measuring the thermomechanical properties of cured epoxies in which the epoxy-hardener ratio is systematically altered and further comparing to those properties of nanocomposites shown in the current study.
Boehmite nanoparticles (AlOOH) were recently found to improve properties such as crack resistance, shrinkage and compressive strength in epoxy composites. Concentration and surface modification of boehmite nanoparticles are key factors for abovementioned enhancements. To understand the underlying mechanisms, more detailed research of micro- and nanoscopic mechanical properties is required. The presented study aims to investigate the influence of concentration and surface modification of boehmite on the stiffness of the bulk epoxy by means of AFM-based approaches: Force-Distance curves (FDC) on the sub- microscale and Intermodulation AFM and amplitude-dependent force spectroscopy (ADFS) on the nanoscale. For this purpose, stiffness-maps of epoxy filled with boehmite, with and without surface modification (HAc-boehmite) were obtained by FDC. These measurements showed a slight increase in overall stiffness of composite with increasing the nanoparticle content. The stiffening effect was observed to be intensified with HAc-boehmite. Since the lateral resolution of FDC is not high enough to distinguish nanoparticles, this effect was assumed to be due to the inevitable inclusion of nanoparticles in the measurement. By using Intermodulation-AFM, yielding ADFS stiffness maps with the resolution of <10 nm, we were able to calculate the average stiffness of bulk epoxy without the interference of nanoparticles. It was expected that the stiffness of regions faraway from particles would be equal to neat epoxy. In contrast, the results showed a drastic increase in stiffness of epoxy with increasing boehmite concentration (0, 1, 2.5, and 15%) especially in case of introducing 15wt% HAc-boehmite. Another important observation was formation of a spatial structure with non-homogenous stiffness distribution in bulk epoxy with HAc-boehmite. The underlying mechanisms of described observations are not fully understood yet. One hypothesis is the local increase in crosslinking density which we aim to investigate in our further studies by combining Dynamic Mechanical Thermal Analysis (DMTA) and Intermodulation-AFM.
This presentation is structured in two parts: i) Hybrid metrology by combining SEM with AFM (N. Feltin) and ii) hybridization and corelative microscopy by SEM, STEM-in-SEM, TEM, EDS, Auger Electron Microscopy, TKD and more (D. Hodoroaba).
The first part is focused on the metrological part of the hybrid measurement SEM-AFM, the second part offers some further possibilities of correlative microscopy of nanoparticles based on practical examples.
In the present paper, friction and mechanical properties of AFM-Scan-Induced ripple structures on films of polystyrene and poly-n-(butyl methacrylate) are investigated. Force volume measurements allow a quantitative analysis of the elastic moduli with nanometer resolution, showing a contrast in mechanical response between bundles and troughs. Additionally, analysis of the lateral cantilever deflection shows a clear correlation between friction and the sample topography. Those results support the theory of crack propagation and the formation of voids as a mechanism responsible for the formation of ripples. This paper also shows the limits of the presented measuring methods for soft, compliant, and small structures.
This poster presents the focused ion beam preparation methodologies developed within the framework of the EU funded EURAMET project ADVENT (Advanced Energy-Saving Technology).
It summarises the key breakthroughs achieved for various in situ investigation techniques, e.g. in situ experiments at the Synchrotron facility BESSY II (IR-SNOM and XRS), TEM and SMM instrumentation.
The created experimental devices from diverse thin-film semiconductor materials paved the way to dynamic structural studies bearing the potential to determine nanoscale correlations between strain and electric fields and, moreover, for the fundamental development of new in situ capabilities.
High spatially resolved quantitative bioimaging of CdSe/ZnS Quantum Dots uptake in two kinds of cells is investigated combining laser ablation inductively coupled plasma mass spectrometry and the spatially resolved analysis of dried pL-droplets from a solution with a known concentration of Quantum Dots. Single cells and dried pL-droplets are morphologically characterized by Atomic Force Microscopy. A number concentration of CdSe/ZnS QDs between 3.5 104 and 48 104 is estimated to be uptaken by several selected single cells, after being incubated in the presence of a QDs suspension added to a standard cell culture medium. Mono-elemental bioimaging at subcellular resolution seems to show a higher number concentration of the CdSe/ZnS QDs in the cytosol around the cell nucleus.
The optical properties of semiconductor nanocrystals (SCNC) are controlled by constituent material, particle size, and surface chemistry, specifically the number of dangling bonds favoring nonradiative deactivation, and hence also by particle synthesis. In this respect, the fluorescence properties of coreshell CdSe SCNCs with different shells and surface chemistries were studied on ensemble and single particle level, using steady state and timeresolved fluorometry and confocal microscopy with time correlated single photon counting detection. Special emphasis was dedicated to correlate ensemble photoluminescence (PL) quantum yields and decay kinetics with particle brightness, PL time traces, and the Ontime fraction of the single SCNCs. Additionally, the confocal PL images were correlated with AFM measurements in order to derive the amount of absorbing, yet nonemisssive ”dark” SCNCs, the presence of which leading to an underestimation of ensemble PL quantum yields. The results of this study can help to identify synthetic routes and surface modifications minimizing the fraction of dark SCNC, thereby closing the gap to the ultimate goal of colloidally and photochemically stable SCNCs with a PL quantum yield of close to unity.
We use a dynamic scanning electron microscope (DySEM) to map the spatial distribution of the vibration of a cantilever beam. The DySEM measurements are based on variations of the local secondary electron signal within the imaging electron beam diameter during an oscillation period of the cantilever. For this reason, the surface of a cantilever without topography or material variation does not allow any conclusions about the spatial distribution of vibration due to a lack of dynamic contrast. In order to overcome this limitation, artificial structures were added at defined positions on the cantilever surface using focused ion beam lithography patterning. The DySEM signal of such high-contrast structures is strongly improved, hence information about the surface vibration becomes accessible. Simulations of images of the vibrating cantilever have also been performed. The results of the simulation are in good agreement with the experimental images.
The main outcomes of the EMPIR project nPSize are presented and the suitability of the new capabilities, e.g. reference materials, sample preparation protocols, measurement procedures, and data analysis, to be standardized and implemented in accredited analytical laboratories is discussed. Complementation and/or filling gaps of published and ongoing standardisation projects on size, shape and number concentration measurements under ISO/TC 229/JWG 2 are offered.
The two VAMAS inter-laboratory comparisons resulted from the nSPize project and just started under TWA 34 Nanoparticle Populations (Projects #15 and #16) of bipyramidal TiO2 anatase and bimodal SiO2 nanoparticles are presented in detail.
Effect of the Anchoring Layer and Transport Type on the Adsorption Kinetics of Lambda Carrageenan
(2021)
The kinetics of lambda carrageenan (λ-car) adsorption/desorption on/from anchoring layers under diffusion- and convection-controlled transport conditions were investigated. The eighth generation of poly(amidoamine) dendrimers and branched polyethyleneimine possessing different shapes and polydispersity indexes were used for anchoring layer formation. Dynamic light scattering, electrophoresis, streaming potential measurements, optical waveguide lightmode spectroscopy, and quartz crystal microbalance were applied to characterize the formation of mono- and bilayers. The unique combination of the employed techniques enabled detailed insights into the mechanism of the λ-car adsorption mainly controlled by electrostatic interactions. The results show that the macroion adsorption efficiency is strictly correlated with the value of the final zeta potentials of the anchoring layers, the transport type, and the initial bulk concentration of the macroions. The type of the macroion forming the anchoring layer had a minor impact on the kinetics of λ-car adsorption. Besides significance to basic science, the results presented in this paper can be used for the development of biocompatible and stable macroion multilayers of well-defined electrokinetic properties and structure.
During focused ion beam microscopy (FIB) of crystalline materials imaging contrast and milling result are effected by orientation of the crystals with respect to the incident ion beam. This is due to the possibility of ion channeling along preferred crystal directions which effects the depth at which interaction between ions and specimen atoms takes place. As a result of channeling emission of ion induced secondary electrons (iiSE) and secondary ions (SI) as well as the sputter rate decreases.
Theoretical channeling orientations and critical angles can be calculated.
These effects have been studied quantitatively for polycrystalline recrystallized Cu as a typical model case.
The concept behind this Research Topic (RT) was to collect works, in which Atomic Force Microscopy (AFM) techniques are employed to study tribological phenomena and to push the resolution of measurements towards single asperity contact. Thanks to the direct determination of sample height with sub-nanometer resolution and the possibility of measuring local friction, AFM can be employed after a tribotest to detect topography and friction changes at the nanometer scale. Recently, efforts are being expended to use AFM cantilevers as tribometers, i.e., as probes altering the volume of suitable samples, thereby measuring tip and/or sample wear and friction at the nano/microscale. Thus, single asperity contact, friction, and wear can be investigated. Since friction and wear at the macroscale are the result of asperities interactions, such experiments are of great importance for better understanding of tribological processes.
Corrosion behaviour of AlCrFe2Ni2Mox (x = 0.0, 0.1, 0.15, 0.3 and 0.6) high-entropy alloys was investigated in a 0.1 M H2SO4 solution. Passive films formed upon anodic polarisation, built of Al-based inner layer and (Cr, Fe, Mo)-based outer layer, had good protective properties. In particular, they prevented corrosion of the (Al, Ni)-rich BCC-B2 phase, which was observed under open-circuit conditions. Moderate amounts of Mo, up to x = 0.3, positively affected the passivation ability of AlCrFe2Ni2. Significant changes in microstructure and phase composition of the alloy at higher Mo concentrations (x = 0.6) resulted in deterioration of its corrosion resistance.
It sounds like being a simple analytical task, it is definitely not. The way toward accurate measurement of the size distribution of nanoparticles (NPs) with complex shape, having a broad size polydispersity, with inhomogeneous chemistry, and with a high degree of agglomeration/aggregation is very challenging for all available analytical methods. Particularly for the NPs with complex shape, the access to the smallest dimension (as e.g. required for regulatory purposes) can be enabled only by using imaging techniques with spatial resolution at the nanoscale. Moreover, the full 3D-chacterisation of the NP shape can be provided either by advanced characterization techniques like 3D-TEM tomography or by correlative analysis, i. e. synergetic/complementary measurement of the same field-of-view of the sample with different probes. Examples of the latter type of analysis are: i) electron microscopy for the lateral dimensions and AFM for the height of the NPs, ii) SEM with STEM-in-SEM (also called T-SEM), iii) Electron Microscopy with TKD (Transmission Kikuchi Diffraction) for determination of the geometrical orientation of crystalline NPs, iv) Raman and SEM for e.g. thickness of graphen flakes, or v) Electron Microscopy for descriptive NP shape and SAXS for the NP concentration, the latter as a NP property able to be measured with higher and higher accuracy. For all these types of measurement, reference NPs are necessary for the validation of the measured size. Particularly non-spherical reference NPs are still missing. Examples of such new reference NPs as characterized by the correlative analyses enumerated above will be presented in detail in the contribution.
In this paper, the accurate determination of the size and size distribution of bipyramidal anatase nanoparticles (NPs) after deposition as single particles on a silicon substrate by correlative Scanning Electron Microscopy (SEM) with Atomic Force Microscopy (AFM) analysis is described as a new measurement procedure for metrological purposes. The knowledge of the exact orientation of the NPs is a crucial step in extracting the real 3D dimensions of the particles. Two approaches are proposed to determine the geometrical orientation of individual nano‐bipyramides: (i) AFM profiling along the long bipyramid axis and (ii) stage tilting followed by SEM imaging. Furthermore, a recently developed method, Transmission Kikuchi Diffraction (TKD), which needs preparation of the crystalline NPs on electron‐transparent substrates such as TEM grids, has been tested with respect to its capability of identifying the geometrical orientation of the individual NPs. With the NPs prepared homogeneously on a TEM grid, the transmission mode in a SEM, i.e., STEM‐in‐SEM (or T‐SEM), can be also applied to extract accurate projection dimensions of the nanoparticles from the same sample area as that analysed by SEM, TKD and possibly AFM. Finally, Small Angle X‐ray Scattering (SAXS) can be used as an ensemble technique able to measure the NPs in liquid suspension and, with ab‐initio knowledge of the NP shape from the descriptive imaging techniques, to provide traceable NP size distribution and particle concentration.
We have studied the anisotropic milling of Cu with respect to the milling rate and the milling topography, as well. The background is twofold: i) anisotropic milling has to be taken into account during the preparation of TEM specimens and in the manufacturing of micro parts from crystalline materials, and ii) the orientation depending milling behaviour can be used to generate topographies with specific properties with respect to, for example, adsorption, wear, and corrosion.
The accurate determination of wear volumes is a prerequisite for the study of numerous tribological phenomena. Wear volumes can be measured with different techniques or else be calculated starting from some quantities measured from the wear scar. Advantages and drawbacks of the measuring techniques are shown by means of wear scars and calottes resulting from ball-on-plane tests with 100Cr6 specimens. When measuring wear volumes, white light interferometry results to be one of the most suitable techniques. When wear volumes are calculated, errors result mainly from two sources: (1) the arbitrary choice of one or few line profiles for the determination of the width and of the planimetric wear, and (2) approximations in the calculation, which are even necessary when values of the wear volumes of the single tribological partners and not only the total volume are of interest. The effect of both error sources on the accuracy in the determination of wear volumes is characterized and elucidated by examples. It is found that errors due to approximations are negligible when compared to errors due to the arbitrary choice of one line profile.
Formation of interphases between inorganic nanofillers and thermoplastic matrices are usually correlated to short-range interactions which does not exceed more than tens of nanometers away from the surface of the filler. Nevertheless, in nanocomposites with thermosetting matrices, the effect of nanofillers on the properties of the matrix is not limited to the immediate vicinities, but a long-range property alteration of the bulk polymer may be observed. The interaction between nanofillers and the polymer can disturb the curing reaction and alters the chemical, physical and mechanical properties of the polymer network in the matrix phase. In our studies, we aim to investigate short and long-range interphases of a nanocomposite system consisting of a thermosetting matrix (DGEBA) filled with an inorganic nanoparticle (boehmite). For this purpose, a combination of atomic force microscopy (AFM)-based approaches is implemented. Scanning kelvin probe microscopy (SKPM) was used to map the compositional contrast and the interphase with different electrical properties than the bulk. The mechanical properties of the interphase were probed by high resolution intermodulation AFM. (ImAFM). Furthermore, infrared spectroscopy AFM (AFM-IR) is used to investigate the chemical structure of the matrix at different distances from the nanoparticle. SKPM and (AFM-IR) measurements both show a long-range (to 10 µm) effect of boehmite on the chemical structure and surface potential of the bulk epoxy, respectively, whereas ImAFM force measurements reveals a short-range mechanical interphase between the filler and the matrix. The AFM-IR demonstrated the existence of unreacted anhydride hardener at the interphase. This indicates the preferential absorption of anhydride on the surface of boehmite. The consequence of such a selective interaction between the inorganic filler and the epoxy components is disturbance of the epoxy-hardener stoichiometric ratio, the curing mechanism. and the alteration of bulk properties of the matrix.
A European EMPIR project, which aims to use large-scale piezoresistive microprobes for contact resonance applications, a well-established measurement mode of atomic force microscopes (AFMs), is being funded. As the probes used in this project are much larger in size than typical AFM probes some of the simplifications and assumptions made for AFM probes are not applicable. This study presents a guide on how to systematically create a model that replicates the dynamic behavior of microprobes, including air damping, nonlinear sensitivities, and frequency dependencies. The model is then verified by analyzing a series of measurements.
Atomic force microscopy based Infrared spectroscopy (AFM-IR) is a quickly evolving technique that provides chemical analysis and compositional mapping with spatial resolution far below conventional optical diffraction limits. This is possible since the detection method is based on a very sharp AFM tip which starts to oscillate when the sample starts to thermally expand (the changed is caused by the absorption of IR wavelength) where the thermal expansion is related to the IR absorption. This presentation briefly described the application of that new technique from polymer characterization and utilization of AFM-IR in material research, up to life science applications.