The Influence of the Material Structure on the Mechanical Properties of Geopolymer Composites Reinforced with Short Fibers Obtained with Additive Technologies.

Additive manufacturing technologies have a lot of potential advantages for construction application, including increasing geometrical construction flexibility, reducing labor costs, and improving efficiency and safety, and they are in line with the sustainable development policy. However, the full exploitation of additive manufacturing technology for ceramic materials is currently limited. A promising solution in these ranges seems to be geopolymers reinforced by short fibers, but their application requires a better understanding of the behavior of this group of materials. The main objective of the article is to investigate the influence of the microstructure of the material on the mechanical properties of the two types of geopolymer composites (flax and carbon-reinforced) and to compare two methods of production of geopolymer composites (casting and 3D printing). As raw material for the matrix, fly ash from the Skawina coal power plant (located at: Skawina, Lesser Poland, Poland) was used. The provided research includes mechanical properties, microstructure investigations with the use of scanning electron microscope (SEM), confocal microscopy, and atomic force microscope (AFM), chemical and mineralogical (XRD-X-ray diffraction, and XRF-X-ray fluorescence), analysis of bonding in the materials (FT-IR), and nuclear magnetic resonance spectroscopy analysis (NMR). The best mechanical properties were reached for the sample made by simulating 3D printing process for the composite reinforced by flax fibers (48.7 MPa for the compressive strength and 9.4 MPa for flexural strength). The FT-IR, XRF and XRD results show similar composition of all investigated materials. NMR confirms the presence of SiO4 and AlO4 tetrahedrons in a three-dimensional structure that is crucial for geopolymer structure. The microscopy observations show a better coherence of the geopolymer made in additive technology to the reinforcement and equal fiber distribution for all investigated materials. The results show the samples made by the additive technology had comparable, or better, properties with those made by a traditional casting method.

Influence of Fiber Diameter of Polycaprolactone Nanofibrous Materials on Biofilm Formation and Retention of Bacterial Cells.

To develop microbiologically safe nanofibrous materials, it is crucial to understand their interactions with microbial cells. Current research indicates that the morphology of nanofibers, particularly the diameter of the fibers, may play a significant role in biofilm formation and retention. However, it has not yet been determined how the fiber diameter of poly-ε-caprolactone (PCL), one of the most widely used biopolymers, affects these microbial interactions. In this study, two nanofibrous materials electrospun from PCL (PCL45 and PCL80) with different fiber diameter and characteristic distance δ between fibers were compared in terms of their ability to support or inhibit bacterial biofilm formation and retain bacterial cells. Strains of Escherichia coli (ATCC 25922 and ATCC 8739) and Staphylococcus aureus (ATCC 25923 and ATCC 6538) were used as model bacteria. Biofilm formation rate and retention varied significantly between the E. coli and S. aureus strains (p < 0.05) for the tested nanomaterials. In general, PCL showed a lower tendency to be colonized by the tested bacteria compared to the control material (polystyrene). Fiber diameter did not influence the biofilm formation rate of S. aureus strains and E. coli 25922 (p > 0.05), but it did significantly impact the biofilm formation rate of E. coli 8739 and biofilm morphology formed by all of the tested bacterial strains. In PCL45, thick uniform biofilm layers were formed preferably on the surface, while in PCL80 smaller clusters formed preferably inside the structure. Further, fiber diameter significantly influenced the retention of bacterial cells of all the tested strains (p < 0.001). PCL45, with thin fibers (average fiber diameter of 376 nm), retained up to 7 log (CFU mL-1) of staphylococcal cells (100% retention). The overall results indicate PCL45's potential for further research and highlight the nanofibers' morphology influence on bacterial interactions and differences in bacterial strains' behavior in the presence of nanomaterials.

Measurement of the rate of transformation induced plasticity in TRIP steel by the use of Barkhausen noise emission as a function of plastic straining.

This paper investigates the rate of transformation induced plasticity in TRIP steel (TRansformation-Induced Plasticity) after plastic straining by the use of Barkhausen noise emission. The samples were subjected to a variable degree of plastic straining and analysed by the use of conventional techniques such SEM, XRD, as well as microhardness in order to investigate residual stress and microstructural alterations initiated by the uniaxial tensile test. Barkhausen noise emission is analysed as a function of plastic straining as well as in the direction of the exerted load and interpreted with respect to the aforementioned microstructure and stress alterations. It was found that Barkhausen noise markedly decreases along with increasing plastic straining, up to 20%, followed by a strain region in which the evolution of Barkhausen noise reaches saturation. Samples after the tensile test exhibited marked magnetic anisotropy since the Barkhausen noise emission in the direction perpendicular to the tensile stress remained less affected. Apart from the effective value of Barkhausen noise, the Barkhausen noise envelopes were also analysed.

The stiffness variability of a silk fibroin scaffold during bone cell proliferation.

Complex assessment of gradual changes in scaffold morphology and stiffness is an essential step in bone filler development. Current approach, however, does not reflect long term cell proliferation effect as the mechanical tests are usually conducted on pristine materials without cells or cell influence on material stiffness is evaluated after one time period only. Here, biocompatible silk fibroin (SF) porous scaffolds envisioned for bone defect filling were prepared by dissolving of fibroin fibers, followed by dialysis, freeze-drying and final stabilization. Particular attention was devoted to the influence of bone cell proliferation up to 2 months on the stiffness of the material. The morphology of the material was studied in terms of its inner structure and the overall changes in the surface characteristics due to proliferation of MG 63 bone cell line. The SF scaffold stiffness significantly increased during first month followed by its decline during second month due to bone cell seeding. After 2 months, the SF scaffold was completely colonized, which resulted in a gradual decay of its structure. The length of degradation due to bone cell proliferation and mechanical behavior corresponded to the requirements set for reasonable filler material indicating that porous SF scaffolds comprise a promising biomaterial for bone regeneration.

Effects of ultrasonic-assisted nickel pretreatment method on electroless copper plating over graphene.

In this paper, copper deposited graphene was fabricated through electroless plating. A novel and facile pretreatment method is introduced based on ultrasonic treatment with nickel nano-particles as the catalytic core. This method abandons the sensitization and activation process in the traditional pretreatment that reduces the time and economic cost dramatically. The static contact angle was determined by an Olympus BX51M optical microscope. The surface morphology and plating composition were characterized via scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS), the infrared radiation (IR) transmittance spectra of the copper plated graphene were measured by Fourier transform infrared spectroscopy (FTIR), the layer structure was measured by Raman spectrum, the phase identification was identified by X-ray diffraction (XRD), the thermogravimetric analysis (TGA) (Q5000 TA instruments, USA) was carried out to detect the thermal characteristics. The electrical resistivity of copper-plated graphene was performed in an especially designed apparatus. The results show that the surface of graphene is coarsened, and the size is reduced after ultrasonic treatment, which can facilitate the nucleation and fine particle distribution of metal. The electroless plated efficiency of copper of the nickel pretreatment copper-plated graphene is 64.27 wt%, higher than that of generic copper-plated graphene at 58.62 wt%. The resistivity decreases rapidly from 1.69 × 10-2 Ω cm of the original Gr to 0.79 × 10-2 Ω cm of Cu/Ni@Gr due to the large number of fine copper particles scattered around the graphene.

Photocatalytic Behaviour of Zinc Oxide Nanostructures on Surface Activation of Polymeric Fibres.

Zinc oxide (ZnO) in various nano forms (nanoparticles, nanorods, nanosheets, nanowires and nanoflowers) has received remarkable attention worldwide for its functional diversity in different fields i.e., paints, cosmetics, coatings, rubber and composites. The purpose of this article is to investigate the role of photocatalytic activity (role of photogenerated radical scavengers) of nano ZnO (nZnO) for the surface activation of polymeric natural fibres especially cotton and their combined effect in photocatalytic applications. Photocatalytic behaviour is a crucial property that enables nZnO as a potential and competitive candidate for commercial applications. The confirmed features of nZnO were characterised by different analytical tools, i.e., scanning electron microscopy (SEM), field emission SEM (FESEM) and elemental detection spectroscopy (EDX). These techniques confirm the size, morphology, structure, crystallinity, shape and dimensions of nZnO. The morphology and size play a crucial role in surface activation of polymeric fibres. In addition, synthesis methods, variables and some of the critical aspects of nZnO that significantly affect the photocatalytic activity are also discussed in detail. This paper delineates a vivid picture to new comers about the significance of nZnO in photocatalytic applications.

Asymmetrical Barkhausen Noise of a Hard Milled Surface.

This study is focused on the asymmetrical Barkhausen noise emission of a hard milled surface during cyclic magnetisation. The Barkhausen noise is studied as a function of the magnetising voltage and the hard milled surface is compared with a surface after heat treatment. The asymmetry in the Barkhausen noise emission after hard milling occurs due to the typical "sandwich" structure and the different magnetic hardnesses of the different layers beneath the free surface. Furthermore, this asymmetry is also due to the preferential orientation of the matrix in the direction of the cutting speed and magnetostatic fields, which hinder or favour the premagnetising process.

Barkhausen Noise Emission in Hard-Milled Surfaces.

This paper reports on an investigation treating a hard-milled surface as a surface undergoing severe plastic deformation at elevated temperatures. This surface exhibits remarkable magnetic anisotropy (expressed in term of Barkhausen noise). This paper also shows that Barkhausen noise emission in a hard-milled surface is a function of tool wear and the corresponding microstructure transformations initiated in the tool/machined surface interface. The paper discusses the specific character of Barkhausen noise bursts and the unusually high magnitude of Barkhausen noise pulses, especially at a low degree of tool wear. The main causes can be seen in specific structures and the corresponding domain configurations formed during rapid cooling following surface heating. Domains are not randomly but preferentially oriented in the direction of the cutting speed. Barkhausen noise signals (measured in two perpendicular directions such as cutting speed and feed direction) indicate that the mechanism of Bloch wall motion during cyclic magnetization in hard-milled surfaces differs from surfaces produced by grinding cycles or the raw surface after heat treatment.

In-situ development of highly photocatalytic multifunctional nanocomposites by ultrasonic acoustic method.

Cotton-titania nanocomposites with multifunctional properties were synthesized through ultrasonic acoustic method (UAM). Ultrasonic irradiations were used as a potential tool to develop cotton-titania (CT) nanocomposites at low temperature in the presence of titanium tetrachloride and isopropanol. The synthesized samples were characterized by XRD, SEM, EDX and ICP-OES methods. Functional properties i.e. Ultraviolet protection factor (UPF), self-cleaning, washing durability, antimicrobial and tensile strength of the CT nanocomposites were evaluated by different methods. Central composite design and response surface methodology were employed to evaluate the effects of selected variables on responses. The results confirm the simultaneous formation and incorporation of anatase TiO2 with average crystallite size of 4nm on cotton fabric with excellent photocatalytic properties. The sustained self-cleaning efficiency of CT nanocomposites even after 30 home launderings indicates their excellent washing durability. Significant effects were obtained during statistical analysis for selected variables on the formation and incorporation of TiO2 nanoparticles (NPs) on cotton and photocatalytic properties of the CT nanocomposites.

The Influence of Suspension Containing Nanodiamonds on the Morphology of the Tooth Tissue Surface in Atomic Force Microscope Observations.

Reduced friction and wear of materials after the use of the carbon nanomaterials including nanodiamonds (NDs) have been confirmed by several studies in material engineering. Mechanical cleaning of the tooth surface by brush bristles should leave as little tissue roughened as possible. Higher surface roughness increases the tissue's wear and encourages the redeposition of the bacteria and the colouring agents present in the diet. Therefore, we evaluated the tooth tissues' surface's morphological changes after brushing them with the NDs suspension. Ten human teeth were brushed with the NDs aqueous suspension. The surfaces were observed using an Atomic Force Microscope (AFM). We found that the nature of the tissue surface became milder and smoother. A number of selected profilometric parameters were compared before and after brushing. We observed that brushing with the suspension of NDs resulted in a significant reduction in the enamel and dentine's surface roughness both in the range of the average parameters (Ra; p-0,0019) and in the detailed parameters (Rsk; p-0,048 and Rku; p-0,036). We concluded that the NDs used in the oral hygiene applications have a potentially protective effect on the enamel and the dentine's surfaces.

Magnetic Poly(N-isopropylacrylamide) Nanocomposites: Effect of Preparation Method on Antibacterial Properties.

The most challenging task in the preparation of magnetic poly(N-isopropylacrylamide) (Fe3O4-PNIPAAm) nanocomposites for bio-applications is to maximise their reactivity and stability. Emulsion polymerisation, in situ precipitation and physical addition were used to produce Fe3O4-PNIPAAm-1, Fe3O4-PNIPAAm-2 and Fe3O4-PNIPAAm-3, respectively. Their properties were characterised using scanning electron microscopy (morphology), zeta-potential (surface charge), thermogravimetric analysis (stability), vibrating sample magnetometry (magnetisation) and dynamic light scattering. Moreover, we investigated the antibacterial effect of each nanocomposite against Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus. Both Fe3O4-PNIPAAm-1 and Fe3O4-PNIPAAm-2 nanocomposites displayed high thermal stability, zeta potential and magnetisation values, suggesting stable colloidal systems. Overall, the presence of Fe3O4-PNIPAAm nanocomposites, even at lower concentrations, caused significant damage to both E. coli and S. aureus DNA and led to a decrease in cell viability. Fe3O4-PNIPAAm-1 displayed a stronger antimicrobial effect against both bacterial strains than Fe3O4-PNIPAAm-2 and Fe3O4-PNIPAAm-3. Staphylococcus aureus was more sensitive than E. coli to all three magnetic PNIPAAm nanocomposites.