Hubert Gojzewski

Photocurable polymethacrylate-silica nanocomposites: correlation between dispersion stability, curing kinetics, morphology and properties

A comprehensive study of model systems based on poly(ethylene glycol) dimethacrylate and two methacryloxy-modified silicas (Aerosil R7200 and R711) were investigated to find possible correlation between the stability of the monomer/silica dispersion, curing kinetics, composite morphology and physical and mechanical properties of the final hybrid material. The monomer/silica dispersions were cured photochemically. The investigated parameters: Zeta potential, polymerization rate and conversion, glass transition, surface roughness and mechanical properties were found to be synchronous; when plotted as function of silica content, they showed maxima or changes in the trend at the same filler loading. This threshold (optimum) silica content in the composition was about 5 wt.-% for the investigated systems. The results obtained are discussed in terms of the solvation cell (which influences dispersion stability) and the interphase layer formation as well as their changes below and above of the threshold filler content.

Effect of Humidity on Nanoscale Adhesion on Self-Assembled Thiol Monolayers Studied by Dynamic Force Spectroscopy

The adhesion force between silicon nitride tips of an atomic force microscope and different self-assembled thiol monolayers (SAMs) was measured at different loading rates and humidity. SAMs were formed from HS(CH(2))(n)CH(3) with n = 6, 8, 9, 10, 15 and HS(CH(2))(n)OH with n = 6, 9, 11, 16. With a special setup, the loading rate could be increased to 10(7) nN s(-1). For the interaction with two-dimensional crystalline CH(3)-terminated SAMs (n > or = 8), two regimes can be distinguished. At loading rates below 10(4)-10(5) nN s(-1), the adhesion force increased proportional to the logarithm of the loading rate. Adhesion is most likely dominated by van der Waals attraction. At higher loading rates, the adhesion forces increased steeper with the logarithm of the loading rate. The specific process limiting separation is not yet identified. On OH-terminated SAMs, the adhesion force was approximately 6 times higher than on the CH(3)-terminated SAMs, even at low humidity. This can partially, but not fully, be explained by hydrogen bridges forming between the hydroxyl groups of the monolayer and silanol groups of the tip. For relative humidity above 10%, the capillary force further increased the adhesion force, which reached a maximum at values of relative humidity between 40% and 80%. Adhesion force versus loading rate (F(ad) versus r(F)) curves increased roughly linearly over the whole range of loading rates. The slope depended on the humidity, and it is correlated with the absolute strength of the capillary force.

Quantitative characterization of nanoadhesion by dynamic force spectroscopy.

We present a method for the characterization of adhesive bonds formed in nanocontacts. Using a modified atomic force microscope, the nanoadhesion between a silicon nitride tip and a self-assembled monolayer of 1-nonanethiol on gold(111) was measured at different loading rates. Adhesion force-versus-loading rate curves could be fitted with two logarithmic terms, indicating a two step (two energy barrier) process. The application of the Bell-Evans model and classical contact mechanics allows the extraction of quantitative information about the effective adhesion potential and characterization of the different components contributing to nanoadhesion.

Hyperthermic Effect in Suspension of Magnetosomes Prepared by Various Methods

The magnetic properties and hyperthermia effect were studied in solution of magnetosomes obtained by changing conditions during biomineralization of magnetotactic bacteria Magnetospirillum sp.AMB-1. It was shown that adding a higher amount of Wolfes vitamin solution (WVS) or ferric quinate (FQ) cause increase of the mean diameter from 47 nm (normal condition) up to 52 nm and 58 nm respectively. As a consequence of this change the preparation conditions coercivity and Specific Absorption Rate (SAR) increased up to 20 Oe and 949 W/gFe for sample FQ, respectively. On the other hand the process of cultivation at the changed conditions markedly reduced the cultivation time. Also the isolated chains of magnetosome were shorter containing less amount of magnetosomes too.

On the determination of the helical structure parameters of amyloid protofilaments by small-angle neutron scattering and atomic force microscopy

The helical structure of amyloid protofilaments of hen egg white lysozyme was analyzed by small-angle neutron scattering (SANS) and atomic force microscopy (AFM). The structure of these formations in bulk solutions was adequately described by SANS in terms of a simplified model of a helix with spherical structural units. The found main helix parameters (pitch and effective diameter) are consistent with the results of AFM analysis for amyloid fibrils adsorbed on a mica surface. Both methods reveal a strong isotope effect on the structure of amyloid fibrils with respect to the substitution of heavy for light water in the solvent. Specific details responsible for the structural differences when comparing SANS and AFM data are discussed from the viewpoint of methodological aspects, the influence of different (native and adsorbed) amyloid states and sample preparation.

Visco-elastic properties of thin nylon films using multi-cycling nanoindentation

Abstract Time dependent behavior of thin nylon films is investigated by depth sensing nanoindentation. Different loading rates and holding times are applied in single indentation procedures to study the relaxation behavior of nylon resulting in a characteristic nonlinear displacement – time dependence. Several load – time functions of multi-cycling indentation are developed, such as constant load repetition and incremental load increase mode sometimes containing holding segments. Hysteresis loops in multi-cycling nanoindentation quantify the visco-elastic energy of nylon films. The loading rate does not change the loop size if the maximum and minimum load of the cycle are the same. The unloading process has to be sufficiently large to allow the performance of the visco-elastic relaxation of the material.

Influence of Temperature on the Nanoadhesion of a Methyl-Terminated Thiol Monolayer: A New Insight with High-Rate Dynamic Force Spectroscopy

Alkanethiols form stable, homogeneous, and well-organized self-assembled monolayers and can be used as lubricants in micro- and nanodevices when sufficiently hydrophobic and resistant to sudden temperature changes. In this paper, we demonstrate a new analysis method which provides a deep physical insight into adhesive interactions and their temperature dependencies at the single molecule level. We have focused on the adhesion between a silicon nitride tip and a 1-decanethiol self-assembled monolayer in the temperature range from 25 to 85 °C. We performed dynamic force spectroscopy measurements and applied theoretical models of adhesive-mechanical interactions and thermally activated unbinding to obtain detailed information on the adhesive interactions. The parameters of the interaction potential describing a single adhesive bond were calculated, and their temperature dependence was discussed. Although the changes of the adhesion force versus temperature are significant and nonmonotonic, the energy of the activation barrier of a single adhesive bond appears temperature independent. We attribute observed changes in the position of the activation barrier to the interplay between the rupture and rebinding of adhesive bonds, as well as to thermal reorganization, in particular the change of the tilt angle of thiol molecules in the self-assembled monolayer.

Pulling angle-dependent force microscopy

In this paper, we describe a method allowing one to perform three-dimensional displacement control in force spectroscopy by atomic force microscopy (AFM). Traditionally, AFM force curves are measured in the normal direction of the contacted surface. The method described can be employed to address not only the magnitude of the measured force but also its direction. We demonstrate the technique using a case study of angle-dependent desorption of a single poly(2-hydroxyethyl methacrylate) (PHEMA) chain from a planar silica surface in an aqueous solution. The chains were end-grafted from the AFM tip in high dilution, enabling single macromolecule pull experiments. Our experiments give evidence of angular dependence of the desorption force of single polymer chains and illustrate the added value of introducing force direction control in AFM.

Dataset for acrylate/silica nanoparticles formulations and photocured composites: Viscosity, filler dispersion and bulk Poisson׳s ratio

UV-curable polymer composites are of importance in industry, biomedical applications, scientific fields, and daily life. Outstanding physical properties of polymer composites were achieved with nanoparticles as filler, primarily in enhancing mechanical strength or barrier properties. Structure-property relationships of the resulting nanocomposites are dictated by the polymer-filler molecular architecture, i.e. interactions between polymer matrix and filler, and high surface area to volume ratio of the filler particles. Among monomers, acrylates and methacrylates attracted wide attention due to their ease of polymerization and excellent physicochemical and mechanical properties of the derived polymers. We prepared and photopolymerized two series of formulations containing hydrophobized silica nanofiller (Aerosil R7200) dispersed in 2-hydroxyethyl acrylate (HEA) or polyethylene glycol diacrylate (PEGDA) monomers. We compared selected physical properties of the formulations, both before and after photocuring; specifically the viscosity of formulations and dispersion of the filler in the polymer matrices. Additionally, we estimated the bulk Poisson׳s ratio of the investigated nanocomposites. This article contains data related to the research article entitled “Nanoscale Young׳s modulus and surface morphology in photocurable polyacrylate/nanosilica composites” (Gojzewski et al., 2017) [1].

Effect of the Chain Length and Temperature on the Adhesive Properties of Alkanethiol Self-Assembled Monolayers

Stable and hydrophobic self-assembled monolayers of alkanethiols are promising materials for use as lubricants in microdevices and nanodevices. We applied high-rate dynamic force spectroscopy measurements to study in detail the influence of the chain length and temperature on the adhesion between methyl-terminated thiol monolayers and a silicon nitride tip. We used the Johnson-Kendall-Roberts model to calculate the number of molecules in adhesive contact and then the Dudko-Hummer-Szabo model to extract the information about the position and the height of the activation barrier per single molecule. Both parameters were determined and analyzed in the temperature range from 25 to 65 °C for three thiols: 1-decanethiol (measured previously), 1-tetradecanethiol, and 1-hexadecanethiol. We associate the increase of the activation barrier parameters versus the chain length with lower stiffness of longer molecules and higher effectiveness of adhesive bond formation. However, we relate the thermal changes of the parameters rather to rearrangements of molecules than to the direct influence of temperature on the adhesive bonds.