AFM Studies Research Articles

Electrochemical, surface morphological and computational evaluation on carbohydrazide Schiff bases as corrosion inhibitor for mild steel in acidic medium

Anticorrosion and adsorption behaviour of synthesized carbohydrazide Schiff bases, namely (Z)-N′-(4-hydroxy-3-methoxybenzylidene)-6-methyl-2-oxo-4-phenyl-1,2,3,4-tetrahydropyrimidine-5-carbohydrazide(MBTC) and (Z)-N′-(3,4-dichlorobenzylidene)-6-methyl-2-oxo-4-phenyl-1,2,3,4-tetrahydropyrimidine-5-carbohydrazide (CBTC) was examined for mild steel (MS) in 15% HCl medium. The corrosion inhibition study was performed by using gravimetric, thermodynamic, electrochemical and theoretical studies including density functional theory (DFT), molecular dynamic simulation (MDS) and Monte Carlo simulations (MCS). The outcomes in terms of corrosion inhibition efficiency using electrochemical impedance spectroscopy (EIS) method at 303 K and 150 ppm concentration were 96.75% for MBTC and 95.14% for CBTC. Both inhibitors adsorbed on the MS surface through physical as well as chemical adsorption and followed the Langmuir isotherm. The mixed-type nature of both inhibitors was identified by polarization results. Surface analysis was done using FESEM, EDX, AFM and XPS studies and results showed that a protective layer of inhibitor molecules was developed over the surface of MS. The results of DFT, MCS and MDS are in accordance with experimental results obtained by weight loss and electrochemical methods.

Parasitic AlxOyNz surface defects on high-temperature annealed AlN and their role in hillock formation

High quality AlN buffer layers on sapphire wafers are a prerequisite for further improving UV LEDs. In addition, AlN templates with low screw-dislocation density might be interesting for future power electronic devices. High-temperature annealing (HTA) has proven to be a viable route to improve the crystallinity of sputtered or thin metalorganic vapor-phase epitaxy (MOVPE) AlN layers. In this work, the influence of two different pretreatment conditions prior to the MOVPE regrowth on HTA AlN templates was analyzed. AFM studies found a hillock density of roughly 106 cm−2 in regrown AlN, whereby such hillocks could no longer be observed after introducing harsher bake conditions. The origin of the observed hillock defects was clarified by using different TEM-related measurement techniques. Based on the TEM and AFM findings, a double-spiral enhanced growth mode that emits concentric surface steps on top of γ-AlON islands is suggested as a underlying mechanism for hillock formation.

Enhanced performance of organic solar cells through incorporation of MoS2 nanoparticles in bulk heterojunction layer

In this work, MoS2 nanoparticles were incorporated in P3HT:PC61BM bulk heterojunction (BHJ) layers and the effect of their concertation on BHJ morphology and structure, its optical absorption spectra and photovoltaic characteristics of P3HT:PC61BM BHJ solar cells were investigated in detail. MoS2 nanoparticles were deposited by laser ablation of MoS2 powders in chlorobenzene. AFM and optical absorption study indicates that an addition of MoS2 nanoparticles in BHJ results in an improved crystallinity and a decreased defect density. The volt-ampere measurements of BHJ solar cells shows that the increase in the MoS2 concertation up to 0.5 wt% leads to the boost of photovoltaic characteristics and a champion device, based on BHJ with MoS2 nanoparticles at concertation 0.5 wt %, generated the power conversion efficiency about 3%, which 3 times higher than an efficiency of a device based on pristine BHJ. The impedance spectroscopy (IS) technique was used to understand the effect of MoS2 nanoparticles on the charge transport mechanism. IS study revealed that a resistance of the BHJ layer slightly and steadily grows by increasing the concentration of MoS2 nanoparticles, whereas a recombination resistance determining the charge recombination rate increases reaching maximum value at the MoS2 concertation of 0.5 wt %. A further growth in the MoS2 concertation results in a decrease of the recombination resistance indicating an acceleration of charge recombination rate. The influence of conductivity nature of MoS2 nanoparticles and their distribution in the BHJ layer on charge transport mechanism is also discussed.

Development of Nanosuspension of Artemisia absinthium Extract as Novel Drug Delivery System to Enhance Its Bioavailability and Hepatoprotective Potential.

A nanosuspension of Artemisia absinthium extract was formulated and characterized for the enhancement of bioavailability and better hepatoprotective efficacy. The nanosuspension of A. absinthium extract was formulated using an antisolvent precipitation technique, and various formulation parameters were optimized using response surface methodology (RSM). The optimized nanosuspension was characterized using AFM and FT-IR spectroscopy. The drug-release profile and oral bioavailability of the optimized nanosuspension were assessed with reference to coarse suspension. The DPPH radical scavenging method was used to measure the nanosuspension's antioxidant activity, and its in vivo hepatoprotective potential was assessed against CCl4-induced hepatic injury in rats. The developed optimized nanosuspension had suitable zeta potential of -11.9 mV, PDI of 0.285, and mean particle size of 253.8 nm. AFM study demonstrated a homogeneous population of nanoparticles with average size of 25 nm. The formulated nanosuspension of A. absinthium showed faster dissolution rate and 1.13-fold enhanced bioavailability as compared to the coarse suspension (plant extract). Furthermore, the nanoformulation had stronger antioxidant and hepatoprotective potential as compared to the unprocessed coarse extract. These results demonstrated that nanosuspension is a promising strategy for improving the oral bioavailability and bioactivities of A. absinthium extract.

SPR studies in PVA composite films of SiO2@NaYF4:Er3+/Yb3+ UCNPs via AuNPs concentration variation and their temperature sensing applications

The composite film of mesoporous silica coated NaYF4:Er3+/Yb3+ upconversion nanoparticles and gold nanoparticles (AuNPs) in Poly vinyl alcohol (PVA) medium were prepared. The effect of the concentrations of AuNPs with 0 µl, 50 µl, 100 µl and 150 µl on the structure and upconversion luminescence intensity were studied. The phenomenon of enhancement in upconversion luminescence intensity due to AuNPs were explained via surface plasmon resonance (SPR) phenomenon. Apart from this the XRD, FE-SEM and AFM studies were done for estimation of structure and surface morphology etc. The impurities were estimated through FTIR analysis. The optical properties of these polymer composite films were studied via UV–vis absorption spectra and upconversion luminescence spectra analysis. A low temperature sensing ability of these films have been demonstrated for the suitability of these films in bio-medical applications.

An amphiphilic near-infrared Mn,O-chelated metallo-azadipyrromethene dye: Synthesis, acid-responsive properties, and aggregation pathway control

A new amphiphilic Mn,O-chelated azadipyrromethene dye 1 bearing dodecyl chains at the 1,7-phenyls and oligo(ethylene glycol) chains at the 3,5-phenyls was synthesized and characterized. The dye 1 exhibited an absorption maximum in NIR at 823 nm, which is largely bathochromically shifted as compared with the known aza-BODIPY as well as the B,O-chelated aza-BODIPY dyes. Meanwhile, the electrochemical studies of this dye indicated a lower HOMO-LUMO gap in comparison with the boron-chelated analogues. This dye also displayed the acid-responsive properties, as indicated by the hypsochromical shift of ca. 94 nm of the absorption band as well as the occurrence of fluorescence emission at 751 nm upon adding trifluoroacetic acid (TFA) into the dye 1 solution. Moreover, in highly polar solvent MeOH the amphiphilic dye 1 self-assembled into H-type aggregates, which exhibited a fibrous morphology in AFM studies. Further temperature-dependent UV/Vis absorption spectroscopic studies revealed a cooperative aggregation mechanism of dye 1 in MeOH. Based on the acid-responsive properties of 1, a method of control of the aggregation pathway of dye 1 by using acid and base was proposed and demonstrated by UV/Vis spectroscopic studies.

A Fluorophore-Labeled Lysine Dendrimer with an Oxo-Anion-Binding Motif for Tracking Gene Transfection.

A transfection vector based on a peptide dendrimer (1) has been developed and its abilities for DNA binding and transport have been investigated. By attaching a fluorophore to the vector system (1*), several steps in the transfection process could be monitored directly. As DLS and AFM studies showed, the labeled vector 1* condensed DNA into tightly packed aggregates able to enter eukaryotic cells. Co-localization experiments revealed that the ligand/plasmid complex is taken up by the endosomal pathway followed by an endosomal escape or lysosomal degradation. Afterwards, the plasmid DNA seems to enter the nucleus due to a breakdown of the nuclear envelope during mitosis, as only cells that have recently undergone mitosis showed H2B-GFP expression.

An activatable AIEgen for imaging of endogenous H2S: Reticulation based H2S gas sensor

Novel 2,4-dinitrophenylether functionalized hydroxybenzothiazole derivative (HBT 3) has been synthesized and characterized for selective and rapid detection of H2S in aqueous medium, gas phase and live cells. The H2S induced thiolysis of 2,4-dinitrophenylether leads to morphological transformation in HBT 3 from spherical to reticulate with aggregation induced emission (AIE + ESIPT) at 550 nm (greenish yellow aggregates) as evidenced by optical, DLS, NMR and AFM studies. The HBT 3 can specifically detect H2S with limits of detection as low as 0.45 and 1.22 µM in CH3CN; 2.9 µM and 6.8 µM in 70% HEPES buffer–CH3CN solution. The HBT 3 based solution- and solid- supported point-of-care testing (POCT) kits have been explored for detection of 75–400 ppm H2S gas; 2.4 µg H2S with fluorescence color change from non-fluorescent to fluorescent yellow. HBT 3 has been successfully utilized for endogenous and exogenous detection of H2S in live L929 cells.

Binding properties of recombinant LDL receptor and LOX-1 receptor to LDL measured using bio-layer interferometry and atomic force microscopy

Oxidation of low-density lipoproteins (LDLs) triggers a recognition by scavenger receptors such as lectin-like oxidized LDL receptor-1 (LOX-1) and is related to inflammation and cardiovascular diseases. Although LDLs that are recognized by LOX-1 can be risk-related LDLs, conventional LDL detection methods using commercially available recombinant receptors remain undeveloped. Using a bio-layer interferometry (BLI), we investigated the binding of recombinant LOX-1 (reLOX-1) and LDL receptors to the oxidized LDLs. The recombinant LDL receptor preferably bound minimally modified LDLs, while the reLOX-1 recognized extensively oxidized LDLs. An inversed response of the BLI was observed during the binding in the case of reLOX-1. AFM study showed that the extensively oxidized LDLs and aggregates of LDLs were observed on the surface, supporting the results. Altogether, a combined use of these recombinant receptors and the BLI method is useful in detecting high-risk LDLs such as oxidized LDLs and modified LDLs.

Transparent and conductive thin films of cadmium doped tin oxide fabricated by pulsed laser deposition technique

Transparent conducting thin films of cadmium doped tin oxide (CTO) were successfully fabricated on glass substrates by pulsed laser deposition technique. Several analytical tools were employed to explore the causes of changes in the structural, optical and electrical properties of these films as a function of doping concentration. The 3 wt % Cd doped films showed lowest electrical sheet resistance of 300.9Ω/□ with electrical resistivity of 2.407×10−3Ωcm. The CTO films are optically transparent with more than 80% transmission in the visible and near IR region of the electromagnetic spectrum. The optical energy gap of CTO films marginally varied from 3.40 eV to 3.49 eV for different doping amount. The AFM studies showed an increase in the surface smoothness of the film with Cd doping concentration. The X-ray diffraction study revealed the tetragonal structure of the film with lattice parameters a=4.742Å and c=3.177Å. The enhanced electrical conductivity and optical transmittance characteristics in these pulsed laser deposited Cd:SnO2 thin films, are suitable, for photo anode/electrode applications in solar cells and display panels.

Folate receptor targeted NIR cleavable liposomal delivery system augment penetration and therapeutic efficacy in breast cancer

BackgroundLiposomes are predominantly used sorts of nanocarriers for active a targeted delivery through surface functionalization using targeting ligand. The folate receptors are overexpressed in various cancers including breast cancer and because of its binding aptitude specifically to folate receptors, folic acid became the attractive ligand. MethodsIn this research, we have developed a folate and Poly-l-Lysine conjugate and coated this conjugate onto the liposomes. The prepared liposomes were characterized using DLS, FTIR, NMR, SEM, TEM, XRD, AFM, stability and drug release studies. Furthermore, in vitro studies were carried out on FR overexpressed breast cancer cell line. ResultsThe FA-LUT-ABC-Lip have diameter of 183 ± 3.17 nm with positive surface charge +33.65 ± 3 mV and the drug release studies confirm the NIR responsive payload cleavage. The coated formulation (in presence of NIR light) effectively reduced the IC50 values and kills breast cancer cells through FR mediated internalization and accelerated drug release. Moreover, LUT Formulation shows anticancer effect due to significant inhibition of cell migration and proliferation by regulating VEGF expression and induced apoptosis through the caspase-3 up-regulation. ConclusionIt is evident from the in vitro studies that the formulation was found to be very effective and can be explored for triggered and targeted delivery of the substances through active targeting. General significanceCombining receptor mediated drug delivery with triggered release aid in more amounts of drug reaching the target site and achieving enhanced therapeutic activity.

Spin Solar Cell Phenomenon on a Single-Molecule Magnet (SMM) Impacted CoFeB-Based Magnetic Tunnel Junctions

The single-molecule magnet (SMM) is demonstrated here to transform conventional magnetic tunnel junctions (MTJs), a memory device used in present-day computers, into solar cells. For the first time, we demonstrated an electronic spin-dependent solar cell effect on an SMM-transformed MTJ under illumination from unpolarized white light. We patterned cross-junction-shaped devices to form a CoFeB/MgO/CoFeB-based MTJ. The MgO barrier thickness at the intersection between the two exposed junction edges was less than the SMM extent, which enabled the SMM molecules to serve as channels to conduct spin-dependent transport. The SMM channels yielded a region of long-range magnetic ordering around these engineered molecular junctions. Our SMM possessed a hexanuclear [Mn6(μ3-O)2(H2N-sao)6(6-atha)2(EtOH)6] [H2N-saoH = salicylamidoxime, 6-atha = 6-acetylthiohexanoate] complex and thioesters end groups to form bonds with metal films. SMM-doped MTJs were shown to exhibit a solar cell effect and yielded ≈80 mV open-circuit voltage and ≈10 mA/cm2 saturation current density under illumination from one sun equivalent radiation dose. A room-temperature Kelvin Probe AFM (KPAFM) study provided direct evidence that the SMM transformed the electronic properties of the MTJ’s electrodes over a lateral area in excess of several thousand times larger in extent than the area spanned by the molecular junctions themselves. The decisive factor in observing this spin-photovoltaic effect is the formation of SMM spin channels between the two different ferromagnetic electrodes, which in turn is able to catalyze the long-range transformation in each electrode around the junction area.

Surface Modification of Silicone by Dielectric Barrier Discharge Plasma.

The objective of the study was to modify the surface of the silicone rubber, using dielectric barrier discharge (DBD) to improve its hydrophilic properties. The influence of the exposure time, discharge power, and gas composition-in which the dielectric barrier discharge was generated-on the properties of the silicone surface layer were examined. After the modification, the wetting angles of the surface were measured. Then, the value of surface free energy (SFE) and changes in the polar components of the modified silicone over time were determined using the Owens-Wendt method. The surfaces and morphology of the selected samples before and after plasma modification were examined by Fourier-transform infrared spectroscopy with attenuated total reflectance (FTIR-ATR), atomic force microscopy AFM, and X-ray photoelectron spectroscopy (XPS). Based on the research, it can be concluded that the silicone surface can be modified using a dielectric barrier discharge. Surface modification, regardless of the chosen method, is not permanent. The AFM and XPS study show that the structure's ratio of oxygen to carbon increases. However, after less than four weeks, it decreases and reaches the value of the unmodified silicone. It was found that the cause of the changes in the parameters of the modified silicone rubber is the disappearance of oxygen-containing groups on the surface and a decrease in the molar ratio of oxygen to carbon, causing the RMS surface roughness and the roughness factor to return to the initial values.

Amoxapine-Loaded Solid Lipid Nanoparticles with Superior Preclinical Pharmacokinetics for Better Brain Delivery: LC-MS/MS and GC-MS Analysis.

The tricyclic antidepressant amoxapine (AMX) has been reported for a rapid onset of action compared to other cyclic antidepressants. It has very low solubility and bioavailability due to first-pass metabolism. Therefore, we planned to develop solid lipid nanoparticles (SLNs) of AMX using a single emulsification method to increase its solubility and bioavailability. HPLC and LC-MS/MS methods were developed further to quantify AMX in the formulation, plasma, and brain tissue samples. The formulation was studied for entrapment efficiency, loading, and in vitro drug release. Particle size and ζ potential analyses, AFM, SEM, TEM, DSC, and XRD were used for further characterization. In vivo oral pharmacokinetic and brain pharmacokinetic studies were performed using Wistar rats. The entrapment and loading efficiencies of AMX in SLNs were 85.8 ± 3.42 and 4.5 ± 0.45%, respectively. The developed formulation had a mean particle size of 151.5 ± 7.02 nm and a polydispersity index of 0.40 ± 0.11. DSC and XRD results indicated that AMX was incorporated into the nanocarrier system in an amorphous form. SEM, TEM, and AFM studies of AMX-SLNs confirmed the particles' spherical shape and nanoscale size. AMX solubility increased by approx. 2.67 times compared to the pure drug. The developed LC-MS/MS method was successfully applied to the oral and brain pharmacokinetic study of AMX-loaded SLNs in rats. Oral bioavailability was enhanced 1.6 times compared to the pure drug. The peak plasma concentrations of pure AMX and AMX-SLNs were 617.4 ± 137.4 and 1043.5 ± 150.2 (ng/mL), respectively. AMX-SLNs showed more than 5.8 times brain concentration compared to the pure drug. Based on the findings, it appears that utilizing a solid lipid nanoparticle carrier to transport AMX can be a highly effective delivery method with improved pharmacokinetic properties in the brain. This approach may prove valuable for future antidepressant treatment.

The SHI irradiation induced transition to negative dielectric constant phase in K2Bi4Ti4WO18

In present communication, a new Aurivillius family compound K2Bi4Ti4WO18 was synthesized, and the impact of swift heavy ion (SHI), Ni+11 irradiation on its surface and dielectric properties has been studied in detail. The phase formation in this complex oxide, and crystallization to B2cb symmetry was confirmed by the X-ray diffraction. However, post irradiation the XRD, SEM and AFM studies shows the surface amorphization, in agreement with the theoretical calculations. Furthermore, the effect of irradiation was also observed in the bulk dielectric properties as the system transform to a phase with negative dielectric constant above 350 K in the radio frequencies. This transition is in correlation with significant change in other dielectric parameters such enhancement in AC conductivity, a helical Nyquist plot and multiple dielectric relaxations. This conspicuous changes in the dielectric response post irradiation is attributed to the SHI induced defect formation, modification of energy barriers and their consequences on the electronic structure. Thus, current study suggests that the dielectric properties of Aurivillius K2Bi4Ti4WO18 could be tailored by ion irradiation and opens a new possibility of tuning functional properties.

Template-free self-assembly of mesoporous ZnO nanocluster/ polymethyl methacrylate based anisotropic nanocomposite thin films with enhanced interfacial interactions and tuneable optical properties

Nature inspired biomimetic growth of anisotropic, hierarchical nanostructures could offer insight into new and exciting crystalline properties for advanced multifunctional applications. Our study demonstrates diethanolamine-mediated mesoscopic self-assembly of semiconducting ZnO Quantum Dots (3–5 nm) into lattice-aligned, symmetrical superstructures (40–50 nm) via non-classical oriented attachment (OA) crystal growth observed in various biomineralization processes. Multifunctional nanocomposite thin films of self-assembled nanostructures and polymethyl methacrylate were spin-coated onto plasma-treated Si wafers and the surface and interfacial properties were rigorously studied. HR-TEM images depicted the OA growth process with neighboring nano-crystals having perfectly aligned lattices. Preferential orientation of the thin films along <100> direction was evident from the XRD data. Quantum confinement in ZnO QDs and surface defect originating sharp green PL emission were examined through UV–Vis absorption and Photoluminescence spectra respectively. DLS and Zeta potential studies of surface-engineered colloidal superstructures established excellent long-term physico–chemical stability with no agglomeration or transparency loss observed in ZnO mesocrystal suspension even after 6 months. Diethanolamine, due to its dual functionality radically enhanced the interaction between polar ZnO and non-polar PMMA matrix resulting in highly stable thin films (Class II hybrids) with enhanced surface and interfacial properties as evident from the extremely low surface roughness and homogenous nanofiller dispersion observed in AFM and FE-SEM studies. Chemical interactions at the interface were also established quantitatively by XPS binding energy measurements which suggested hydrogen bonds and covalent bonds between organic-inorganic phases promoted via diethanolamine surface engineering.

Biogenic Synthesis of Silver Nanoparticles Using Pantoea stewartii and Priestia aryabhattai and Their Antimicrobial, Larvicidal, Histopathological, and Biotoxicity Potential.

In recent years, green nanotechnology has gained considerable importance for the synthesis of nanoparticles due to its economic viability and biosafety. In the current study, silver nanoparticles were synthesized using two bacterial isolates, H2 and H3, which were isolated from soil samples collected from the Western Ghats, Tamil Nadu, and identified at the species level as Pantoeastewartii (H2) and Priestiaaryabhattai (H3) by sequencing their 16s rRNA genes. Intracellularly synthesized silver nanoparticles were characterized by UV-visible spectroscopy, Fourier transform infrared spectroscopy, atomic force microscopy, and particle size analysis. AFM studies show that both of the bacterial synthesized Ag NPs were circular-shaped and disaggregated, with an average size distribution of 4 nm for Pantoeastewartii and 3.6 nm for Priestiaaryabhattai. Furthermore, their larvicidal activity, antimicrobial, histopathological, and biotoxicity effects were determined. The synthesized Ag NPs exhibited potent larvicidal activity against fourth instars of Ae.aegypti, An.stephensi, and Cx.quinquefasciatus exposed to a 50 µg/mL concentration for 24 h based on their LC50 and LC90 values. Histopathological studies of the affected mosquito larvae clearly show damage to the epithelial cells, food bolus, basement membrane, muscles, and midgut parts. The maximum antimicrobial activity of Priestiaaryabhattai-synthesized Ag NPs was observed for Streptomyces varsoviensis MTCC-1537, and that of Pantoea stewartii-synthesized Ag NPs was against Escherichia coli MTCC-43. The toxicity test on non-target organisms such as Artemia nauplii and zebrafish embryos indicates no visible abnormalities or mortality after their exposure for 48h. It is concluded that silver nanoparticles can easily be synthesized using Pantoea stewartii (H2) and Priestia aryabhattai (H3) as capping and reducing agents. Silver nanoparticles showed potent larvicidal activities and could potentially be used in integrated vector control programs because they are safe for other inhabitants of the same aquatic environment as mosquito larvae.

Enhanced Performance Electrochemical Biosensor for Detection of Prostate Cancer Biomarker PCA3 Using Specific Aptamer

In the quest for the development of accurate, reliable, and cost-effective biosensing technology for early diagnostics of prostate cancer, we describe here an electrochemical biosensor combining a simple transducing method of differential pulse voltammetry (DPV) with an RNA-based aptamer labelled with a methylene blue redox group acting as a highly specific bioreceptor to the prostate cancer biomarker PCA3. A series of DPV measurements on screen-printed gold electrodes is functionalised with a redox-labelled aptamer in solutions (either buffer or synthetic urine) containing PCA3 in a wide range of concentrations from 0.1 picomolar (pM) to 10 nanomolar (nM). In these measurements, the current peak values correlate with the concentration of PCA3 and yield a low detection limit (LDL) of 0.1 pM. Furthermore, the binding kinetics study revealed the high affinity of the aptamer to the target PCA3 with the affinity constants KD of about 3.0 × 10−8 molar. In addition, the AFM study showed the increase in the molecular layer roughness caused by the binding of PCA3, which is a large RNA molecular fragment.

Effect of Polar Faces of SiC on the Epitaxial Growth of Graphene: Growth Mechanism and Its Implications for Structural and Electrical Properties

In this study, epitaxial graphene layers of cm2 sizes were grown on silicon carbide (SiC) substrates by high-temperature sublimation. The behavior of the two crystallographic SiC-polar faces and its effect on the growth mechanism of graphene layers and their properties were investigated. Crystallographic structural differences observed in AFM studies were shown to cause disparities in the electrical conductivity of the grown layers. On the silicon-polar (Si-polar) face of SiC, the graphene formation occurred in spike-like structures that originated orthogonally from atomic steps of the substrate and grew outwards in the form of 2D nucleation with a fairly good surface coverage over time. On the carbon-polar (C-polar) face, a hexagonal structure already formed at the beginning of the growth process. On both polar faces, the known process of step-bunching promoted the formation of nm-scale structural obstacles. Such a step-bunching effect was found to be more pronounced on the C-polar face. These 2D-obstacles account for a low probability of a complete nano-sheet formation, but favor 2D-structures, comparable to graphene nanoribbons. The resulting direction-dependent anisotropic behavior in electrical conductivity measured by four-point probe method mainly depends on the height and spacing between these structural-obstacles. The anisotropy becomes less prudent as and when more graphene layers are synthesized.

Modification of Polyhydroxyalkanoates Polymer Films Surface of Various Compositions by Laser Processing.

The results of surface modification of solvent casting films made from polyhydroxyalkanoates (PHAs) of various compositions are presented: homopolymer poly-3-hydroxybutyrate P(3HB) and copolymers comprising various combinations of 3-hydroxybutyrate (3HB), 3-hydroxyvalerate (3HV), 4-hydroxybutyrate(4HB), and 3-hydroxyhexanoate (3HHx) monomers treated with a CO2 laser in continuous and quasi-pulsed radiation modes. The effects of PHAs film surface modification, depending on the composition and ratio of monomers according to the results of the study of SEM and AFM, contact angles of wetting with water, adhesion and growth of fibroblasts have been revealed for the laser radiation regime used. Under continuous irradiation with vector lines, melted regions in the form of grooves are formed on the surface of the films, in which most of the samples have increased values of the contact angle and a decrease in roughness. The quasi-pulse mode by the raster method causes the formation of holes without pronounced melted zones, the total area of which is lower by 20% compared to the area of melted grooves. The number of viable fibroblasts NIH 3T3 on the films after the quasi-pulse mode is 1.5-2.0 times higher compared to the continuous mode, and depends to a greater extent on the laser treatment mode than on the PHAs' composition. The use of various modes of laser modification on the surface of PHAs with different compositions makes it possible to influence the morphology and properties of polymer films in a targeted manner. The results that have been obtained contribute to solving the critical issue of functional biodegradable polymeric materials.