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Force-displacement curves have been acquired with a commercial atomic force microscope on a thin film of poly(n-butyl methacrylate) on glass substrates. The film thickness is nonuniform, ranging in the measured area from 0 to 30 nm, and gives the possibility to survey the so-called "mechanical double-layer" topic, i.e., the influence of the substrate on the mechanical properties of the film in dependence of the film thickness. The stiffness and the deformation for each force-distance curve were determined and related to the film thickness. We were able to estimate the resolution of the film thickness that can be achieved by means of force-distance curves. By exploiting the data acquired in the present and in a previous experiment, a novel semiempirical approach to describe the mechanical properties of a mechanical double-layer is introduced. The mathematical model, with which deformation-force curves can be described, permits to calculate the Young's moduli of film and substrate in agreement with literature values and to determine the film thickness in agreement with the topography.
Forcedisplacement curves have been acquired with a commercial atomic force microscope on thin films of poly(n-butyl methacrylate) on glass substrates. Different film thicknesses, from 10 up to 430 nm, were chosen to examine in detail the so called mechanical double-layer topic, i.e., the influence of the substrate on the determination of the mechanical properties of thin films. Taking advantage of the Hertz theory we calculated for all films the contact radius between tip and sample as a function of the applied load. Further Young's modulus of the samples was derived from the experimental data as a function of the applied load and, alternatively, of the deformation. The results of this analysis for 10 different film thicknesses were fitted with several half empirical equations proposed by several researchers. The focus of this work is to evaluate such existing half empirical theories for mechanical double-layers and to show the need for an alternative consistent approach.
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.
Spherical lignin nanoparticles (LNPs) fabricated via nanoprecipitation of dissolved lignin are among the most attractive biomass-derived nanomaterials. Despite various studies exploring the methods to improve the uniformity of LNPs or seeking more application opportunities for LNPs, little attention has been given to the fundamental aspects of the solvent effects on the intrinsic properties of LNPs. In this study, we employed a variety of experimental techniques and molecular dynamics (MD) simulations to investigate the solvent effects on the intrinsic properties of LNPs. The LNPs were prepared from softwood Kraft lignin (SKL) using the binary solvents of aqueous acetone or aqueous tetrahydrofuran (THF) via nanoprecipitation. The internal morphology, porosity, and mechanical properties of the LNPs were analyzed with electron tomography (ET), small-angle X-ray scattering (SAXS), atomic force microscopy (AFM), and intermodulation AFM (ImAFM). We found that aqueous acetone resulted in smaller LNPs with higher uniformity compared to aqueous THF, mainly ascribing to stronger solvent−lignin interactions as suggested by MD simulation results and confirmed with aqueous 1,4-dioxane (DXN) and aqueous dimethyl sulfoxide (DMSO).
More importantly, we report that both LNPs were compact particles with relatively homogeneous density distribution and very low porosity in the internal structure. The stiffness of the particles was independent of the size, and the Young’s modulus was in the range of 0.3−4 GPa. Overall, the fundamental understandings of LNPs gained in this study are essential for the design of LNPs with optimal performance in applications.
The reinforcing effect of boehmite nanoparticles (BNP) in epoxy resins for fiber composite lightweight construction is related to the formation of a soft but bound interphase between filler and polymer. The interphase is able to dissipate crack propagation energy and consequently increases the fracture toughness of the epoxy resin. Usually, the nanoparticles are dispersed in the resin and then mixed with the hardener to form an applicable mixture to impregnate the fibers. If one wishes to locally increase the fracture toughness at particularly stressed positions of the fiber-reinforced polymer composites (FRPC), this could be done by spraying nanoparticles from a suspension. However, this would entail high costs for removing the nanoparticles from the ambient air. We propose that a fiber fleece containing bound nanoparticles be inserted at exposed locations. For the present proof-of-concept study, an electrospun polycarbonate nonwoven and taurine modified BNP are proposed. After fabrication of suitable PC/EP/BNP composites, the thermomechanical properties were tested by dynamic mechanical analysis (DMA). Comparatively, the local nanomechanical properties such as stiffness and elastic modulus were determined by atomic force microscopy (AFM). An additional investigation of the distribution of the nanoparticles in the epoxy matrix, which is a prerequisite for an effective nanocomposite, is carried out by scanning electron microscopy in transmission mode (TSEM). From the results it can be concluded that the concept of carrier fibers for nanoparticles is viable.
Chemical admixtures like superplasticisers or stabilising agents are of ever increasing importance for modern concrete technology. They liberate the workability of concrete from its dependency on water content, and thus, open the gate towards innovative and future oriented concrete technologies such as selfcompacting concrete. Meanwhile admixtures have become common practice in concrete technology, but the understanding of these highly complex polymers in the entire concrete system lags far behind their application. Due to its complex time-dependent, multi-phase and multi-scale behaviour, flowable concrete systems are highly complicated and cannot be described comprehensively by simple models. It is therefore extremely challenging to identify the relevant parameters that predominantly control flow phenomena on different size scales, since these may occur on any scale between the nano scale (e.g. superplasticizer adsorption) and macro scale (e.g. grading of the aggregates). The present study discusses fundamental mechanisms at the interface between particle or hydrate surfaces and the fluid phase at a very early stage of concrete formation, and links these effects to macroscopic flow phenomena. Methods are discussed that appear promising interdisciplinary tools for enhancement of the understanding of the relevant interactions that are responsible for the macroscopic flow of flowable concrete.
Force–displacement curves have been acquired with a commercial atomic force microscope on thin films of poly(n-butyl methacrylate) on glass substrates in order to examine the so-called 'mechanical double layer' topic, i.e. the influence of the substrate on the mechanical properties of the film in dependence of the film thickness. The hyperbolic fit, a novel semi-empirical equation introduced in previous articles, has been further corroborated. The interpretation of this equation has been deepened, yielding a quantitative and demonstrative characterization of the mechanical properties of double layers. Provided that the Young's moduli of bulk polymer and substrate are measured from the deformation curves, this mathematical model permits to fit the deformationforce curves on the double layers and to determine the thickness of the polymer films in wide range (0200 nm).
Force–distance curves have been acquired with an Atomic Force Microscope on polymethyl methacrylate with embedded glass spheres. The glass spheres provide a stiff substrate with an irregular and complex topography hidden underneath a compliant and even polymer film. This situation is a special case of a mechanical double-layer, which we examined in detail in previous experiments. Up to now uniform and non-uniform polymer films on an even substrate were examined. The film thickness on each point of the sample surface was known and force–distance curves could be averaged in groups according to the film thickness. In this way we were able to develop a semi empirical approach which allows describing the shape of averaged force–distance curves depending on the Youngs moduli of the involved materials and on the film thickness. In this experiment we reconstruct a hidden topography, i.e., we determine the polymer thickness on each point of the sample by analyzing single force–distance curves with our semi empirical equation. The accuracy reached by this approach permits to obtain a reconstruction of the shape and position of the embedded particles limited by a maximum detection depth. Single curves are also analyzed qualitatively in order to locate areas where the adhesion at the polymer/glass interface is weak or the two phases are detached.