Surface Elastic Modulus Research Articles

Mechanically strong, transparent polyimide composite thin films with a low dielectric constant

Aromatic polyimide is widely used in microelectronics as dielectric packaging layers. There is a high demand to reduce its dielectric constant to meet the fast development of communication technology. Here we report a simple and eco-friendly approach to preparing polyimide films with a lowered dielectric constant by adding silica hollow nanospheres with an average size of 100 nm in an aqueous solution of poly(amic acid) salt, and subsequent film casting and thermal imidization. The silica hollow nanospheres present a uniform distribution in polyimide matrix after surface modification with 3-aminopropyltriethoxysilane. The dielectric constant of the resulting composite films decreases linearly with particle loading till 15 wt% and reaches the lowest value of 2.5. The surface hardness and elastic modulus of the films improve by adding hollow nanospheres, while maintaining high optical transparency, high flexibility and a low coefficient of thermal expansion.

Development of ANN model for predicting mechanical properties of 3D printed PEEK polymer using FDM and optimization of process parameters for better mechanical properties

Additive manufacturing (AM) has evolved from a proven technology to a rapid prototyping tool with great potential. This technology is widely used in many industries such as automotive, aerospace, and medical; fused deposition modeling (FDM) is a popular 3D printing technique for producing PEEK (polyether ether ketone) parts, including implant prosthetic teeth. In this study, artificial neural network (ANN) modeling, parametric optimization, and experimental examination of PEEK 3D printing were conducted to enhance 3D printing processes. In this study, four critical process factors (infill density, layer height, printing speed, and infill pattern) influence the surface roughness, mechanical strength, and elastic modulus of the printed samples. Utilizing a 4–12–3 network design, this study demonstrates that an ANN model with an average error of less than 5% is optimal for all three responses. Furthermore, the study employed a teaching and learning based optimization algorithm (TLBO) and a non-dominated sorting genetic algorithm (NSGA) to optimize the printing process to obtain improved mechanical properties. The findings highlight TLBO’s ability to minimize surface roughness to 6.01 μm and NSGA’s capability to maximize the elastic modulus to 1253.35 MPa and ultimate tensile strength to 65.55 MPa. Microstructural studies supported the results obtained through parametric analysis and optimization.

Effects of Time-Elapsed Bleaching on the Surface and Mechanical Properties of Dentin Substrate Using Hydrogen Peroxide-Free Nanohydroxyapatite Gel.

There is a critical need to address concerns surrounding the potential impact of bleaching gels specifically on the tooth substrate. Therefore, this laboratory investigation aimed to assess the impact of a hydrogen peroxide (HP)-free bleaching (HiSmileTM) in comparison to an HP-based bleaching (Opalescence RegularTM) on the surface and mechanical characteristics of tooth substrate. Sixty sound human premolar teeth were sectioned to produce dentin fragments and divided into two primary groups based on the bleaching agent used. Each group was subdivided into three subgroups (n = 10) per distinct bleaching regimens: (T1) fragments underwent a 7-day immersion in distilled water at 37°C without any bleaching treatment, (T2) fragments underwent a 7-day immersion in distilled water at 37°C, with the application of bleaching gel occurring on the seventh day for 10minutes, and (T3) fragments underwent a bleaching regimen for seven consecutive days, each session lasting for 10minutes. The initial and final evaluations of surface roughness, nano-hardness, and elastic modulus were performed. Following the bleaching regimens of T3, a composite stub was fabricated on the dentin fragments for the shear bond strength (SBS) test. Statistical testing was accomplished using the analysis of variance (P < 0.05). HP-based bleaching gel showed significant differences between measurement intervals in surface roughness, elastic modulus, and SBS parameters (P < 0.05). In contrast, HP-free bleaching gel showed insignificant differences within the group (P > 0.05). The SBS between dentin-composite was significantly affected with the use of HP-based bleaching gel, while HP-free bleaching gel showed insignificant difference between measurement intervals. The qualitative validation of the treatment's impact was further demonstrated using the scanning electron microscopy. The findings suggest that the bonding stability of composite restorations to dentin may be compromised after bleaching with an HP-based gel, whereas immediate bonding procedures can be safely conducted following the application of an HP-free bleaching gel.

Effect of peroxide-free and peroxide-based in-office bleaching on the surface and mechanical properties of CAD/CAM esthetic restorative materials.

The study aimed to investigate the influence of H2O2-based and H2O2-free in-office bleaching on the surface and mechanical attributes of CAD/CAM composite blocks. CAD/CAM composite blocks from five different composite materials (CC1, CC2, CC3, CC4, and CC5) were randomly divided into two groups according to bleaching application (H2O2-based and H2O2-free). The surface topography, morphology, nanohardness, elastic modulus, flexural strength, and fracture toughness were measured. A paired and unpaired sample t-tests gauged the effect of pre- and post-bleaching on the substrates. The estimated mean differences (before-after bleaching) suggested an increase in surface roughness for two materials CC2 and CC4, and a significant decrease in nanohardness for material CC4 and in elastic modulus for materials CC2 and CC4 with H2O2-based bleaching, whereas H2O2-free bleaching resulted in changes compatible with no change in these properties. Flexural strength and fracture toughness showed no evidence of changes, irrespective of the bleaching gel used. Scanning electron microscopic analysis revealed erosive effects and micropore formation due to H2O2-based bleaching. H2O2-based bleaching deteriorates the surface of CAD/CAM composite materials while H2O2-free bleaching gel had an insignificant effect on both surface and bulk properties. The clinician should carefully evaluate the potential effects of H2O2-based bleaching on the surface properties of CAD/CAM composites.

The mechanical properties of Lucaogou shale layered samples and the influence of minerals on fracture propagation

Shale oil is one of the most promising alternative unconventional energies in the world, and Lucaogou Formation shows significant exploration potential, becoming the primary target in northwestern China. This paper compared the mechanical properties of shale layered samples from oil layer and interlayer of Lucaogou Formation, using uniaxial compressive tests with real-time micro-CT scanning. After that, the mineral analysis was conducted on one cross-section of the fractured sample to analyze the influence of mineral composition and distribution on micro-crack propagation. Such research has rarely been reported before. The results showed the surface porosity and elastic modulus of oil-bearing samples is larger than that of the interlayer samples, while the uniaxial compressive strength is lower. Besides, when there is only one dominant mineral with a content greater than 60%, a main crack tends to form at this area; When there are 2∼3 major minerals with a content of 10%∼60%, a fractured zone with many fine micro-cracks is more likely to form here. Finally, the higher the Moh’s hardness of the mineral, the more difficult it is for micro-cracks to develop through it.

Evaluation of nanohardness, elastic modulus, and surface roughness of fluoride-releasing tooth colored restorative materials.

Recently, interest in tooth-colored fluoride-releasing dental materials has increased. Although physical and mechanical properties such as surface hardness, elastic modulus and surface roughness of the restorative materials have been investigated, the effect of different immersion media on these properties is still controversial. The aim of this study was to evaluate the nanohardness, elastic modulus and surface roughness of the fluoride release of tooth-colored restorative materials after immersion in acidic beverages. Prepared samples of three restorative materials (a highly viscous glass ionomer (EQUIA Forte; GC, Tokyo, Japan), a compomer (Dyract XP; Dentsply, Weybridge, UK), and a bioactive restorative material (Activa BioACTIVE; Pulpdent, MA, USA)) were randomly divided and immersed in distilled water, a cola and an orange juice for one week. The HYSITRON T1 950 TriboIndenter device (Hysitron, USA) with the Berkovich diamond indenter tip was used for all measurements. The nanohardness and elastic modulus of the samples were measured by applying a force of 6000 μN to five different points on the sample surface. Surface roughness measurements were evaluated on random samples by scanning five random 40 × 40 μm areas. The properties were measured at the initial and one week after immersion. The values of nanohardness, elastic modulus and surface roughness were tested for significant differences using a two-way analysis of variance (ANOVA) with repeated measures (p < 0.05). Tukey's honest significant difference (HSD) test was used for multiple comparisons. AB (Activa BioACTIVE) had the highest initial mean values for nanohardness. After post-immersion, the highest mean value for elastic modulus was the initial AB value. The lowest mean value for roughness of 100.36 nm was obtained for the initial DX (Dyract XP) measurement. Acidic beverages had a negative effect on the nanohardness, elastic modulus and surface roughness of the restorative materials.

On effective surface elastic moduli for microstructured strongly anisotropic coatings

The determination of surface elastic moduli is discussed in the context of a recently proposed strongly anisotropic surface elasticity model. The aim of the model was to describe deformations of solids with thin elastic coatings associated with so-called hyperbolic metasurfaces. These metasurfaces can exhibit a quite unusual behaviour and concurrently a very promising wave propagation behaviour. In the model of strongly anisotropic surface elasticity, strain energy as a function of the first and second deformation gradients has been introduced in addition to the constitutive relations in the bulk. In order to obtain values of surface elastic moduli, we compare dispersion relations for anti-plane surface waves obtained using the two-dimensional (2D) model and three-dimensional (3D) straightforward calculations for microstructured coatings of finite thickness. We show that with derived effective surface moduli, the 2D model can correctly describe the wave propagation.

Electromechanical responses of a piezoelectric semiconducting nanoplate with the Steigmann-Ogden surface

Abstract Piezoelectric semiconductors (PSCs) find widespread applications in smart electronic devices due to their unique combination of piezoelectric and semiconductive properties. With the increasing demand for smaller and more efficient electronic devices, the performance of their components needs to be carefully optimized, especially when they are scaled down to nanoscale sizes. Pioneering studies have demonstrated that the surface elastic properties play a significant role in determining the mechanical performance of nanoscale materials and structures. Therefore, it is important to comprehensively investigate the effects of surface elasticity, including surface residual stress, surface membrane stiffness and surface bending stiffness, on the electromechanical responses of a PSC nanoplate. Additionally, it is also crucial to examine the influence of flexoelectricity at the nanoscale. Our results demonstrate that surface elastic properties predominantly impact mechanical performance, while the flexoelectric effect plays a more prominent role in electric field and redistribution of charge carriers. In particular, the significance of surface bending rigidity, which was often overlooked in previous literature, becomes pronounced when the thickness of a PSC nanoplateisless than 10 nm. Furthermore, the dependence of natural vibration frequency on surface elastic moduli, flexoelectricity and size is also systematically explored. The redistributions of electric potential and charge carriers across the cross-section are also evidently affected. Our findings provide valuable insights for improving the performance of electronic devices that utilize nanoscale PSCs.

Characterizing Chemical, Environmental, and Stimulated Subcellular Physical Characteristics of Size-Fractionated PMs Down to PM0.1.

Air pollution, especially particulate matter (PM), is a significant environmental pollution worldwide. Studying the chemical, environmental, and life-related cellular physical characteristics of size-fractionated PMs is important because of their different degrees of harmful effects on human respiratory tracts and organ systems, causing severe diseases. This study evaluates the chemical components of size-fractionated PMs down to PM0.1 collected during a biomass-burning episode, including elemental/organic carbon and trace elements. Single particle sizes and distributions of PM0.1, PM0.5-0.1, PM1.0-0.5, and PM2.5-1.0 were analyzed by scanning electron microscopy and Zeta sizer. Two commonly used cell lines, e.g., HeLa and Cos7 cells, and two respiratory-related cell lines including lung cancer/normal cells were utilized for cell cytotoxicity experiments, revealing the key effects of particle sizes and concentrations. A high-speed scanning ion conductance microscope explored particle-stimulated subcellular physical characteristics for all cell lines in dynamics, including surface roughness (SR) and elastic modulus (E). The statistical results of SR showed distinct features among different particle sizes and cell types while a E reduction was universally found. This work provides a comprehensive understanding of the chemical, environmental, and cellular physical characteristics of size-fractionated PMs and sheds light on the necessity of controlling small-sized PM exposures.

Surface Engineering of the Mechanical Properties of Molecular Crystals via an Atomistic Model for Computing the Facet Stress Response of Solids.

Dynamic molecular crystals are an emerging class of crystalline materials that can respond to mechanical stress by dissipating internal strain in a number of ways. Given the serendipitous nature of the discovery of such crystals, progress in the field requires advances in computational methods for the accurate and high-throughput computation of the nanomechanical properties of crystals on specific facets which are exposed to mechanical stress. Here, we develop and apply a new atomistic model for computing the surface elastic moduli of crystals on any set of facets of interest using dispersion-corrected density functional theory (DFT-D) methods. The model was benchmarked against a total of 24 reported nanoindentation measurements from a diverse set of molecular crystals and was found to be generally reliable. Using only the experimental crystal structure of the dietary supplement, L-aspartic acid, the model was subsequently applied under blind test conditions, to correctly predict the growth morphology, facet and nanomechanical properties of L-aspartic acid to within the accuracy of the measured elastic stiffness of the crystal, 24.53±0.56 GPa. This work paves the way for the computational design and experimental realization of other functional molecular crystals with tailor-made mechanical properties.

Characterization of the interfacial structure and fracture behavior of in situ synthesized ceramics to reinforce Ni-based composite coatings

This work used the in-situ synthesis of molten-state nitride ceramic phase-reinforced Ni-based alloy coatings, aiming to improve the phase-interface bonding through the interdependent co-solidification between molten droplets. The XRD was used to analyze the physical phases of the composite coatings. The microstructure and phase-interface structure were characterized in detail by combining SEM, TEM, HRTEM, FFT, and SAED techniques. Microhardness tester and microforce microhardness tester were employed to measure the surface hardness and elastic modulus of the composite coatings. The fracture behavior of the composite coatings was characterized by observing the fracture morphology of the coatings using SEM combined with the EDS technique. It was found that the formation mechanisms of interfacial misfit dislocation assistance, lattice distortion, aggregation of stacking faults, and specific growth orientation between the γ-Ni matrix phase and each ceramic phase in NiCrBSi-TiCrN composite coatings improved the lattice matching between the two-phase interface, which resulted in the formation of atomically corresponding coherent lattice relations and stepped interfacial semi-coherent lattice relations, and enhanced the degree of phase-interface bonding. On this basis, the composite coatings with high Cr content further inhibited the expansion of interphase penetration cracks due to the existence of Cr-rich zones at the phase interface, thus exhibiting high fracture toughness. This work provides new opinions on the improvement of phase-interface bonding and composition design of Ni-based composite coatings.

Effect of basalt fiber and carbon fiber on the evolution of water evaporation and cracking characteristics of silt soil

Cultivated land is prone to cracking during the high-temperature season, resulting in accelerated water evaporation, incomplete soil structure, and waste of resources caused by pollutants entering the soil. In this study, image analysis technology was used to compare the effects of two kinds of fibers on the drying and shrinkage characteristics of silt under the same volume. The results show that during cracking process, water evaporation can be divided into three phases: constant rate stage, deceleration rate stage, and residual stage. The crack rate of 0.08% basalt fiber-treated soil and 0.06% carbon fiber-treated soil is reduced by 27.66% and 27.98%, respectively. The addition of fibers acts like a bridge, narrowing the concentration of crack width from 0.2–0.8 to 0–0.6 mm, increasing short cracks of 0–5 mm and decreasing long cracks larger than 5 mm, thus reducing the soil cracking rate. With rough surface and high elastic modulus of fibers, the addition of fibers enhances the friction between soil particles to limit the movement of soil mass, and bears part of the tensile stress when cracking. It increases the tensile strength between the soil mass and effectively reduces the crack rate. It is found that the improvement effect of basalt fiber is relatively better and the economic benefit is higher under the same volume.

On the incremental equations in surface elasticity

We derive the incremental equations for a hyperelastic solid that incorporate surface tension effect by assuming that the surface energy is a general function of the surface deformation gradient. The incremental equations take the same simple form as their purely mechanical counterparts and are valid for any geometry. In particular, for isotropic materials, the extra surface elastic moduli are expressed in terms of the surface energy function and the two surface principal stretches. The effectiveness of the resulting incremental theory is illustrated by applying it to study the Plateau–Rayleigh and Wilkes instabilities in a solid cylinder.

Molecular structure design of polybenzoxazines with low surface energy and low modulus for marine antifouling application

The antifouling mechanism of low surface energy marine antifouling coatings is fouling release, and the key to fouling release is the adhesion strength of fouling organisms on the coating surface. Herein, we report an antifouling strategy to improve the fouling release performance of antifouling coatings by control the surface free energy and elastic modulus. Natural biomass cardanol-based benzoxazine monomers with different structures were designed by molecular structure and successfully synthesized via Mannich condensation. Detailed information of the chemical structure for the benzoxazines are analyzed by nuclear magnetic resonance (NMR) and Fourier transform infrared (FT-IR) spectroscopies. In addition, the benzoxazines polymerization behavior is investigated by differential scanning calorimetry (DSC) analyses. The properties such as surface free energy and elastic modulus of polybenzoxazine were adjusted by the structure of the amine source. Notably, polybenzoxazines with octadecylamine as amine source have higher contact angle and lower surface free energy, and their elastic modulus is significantly lower than that of the octylamine benzoxazine. The elastic modulus of the octylamine benzoxazine was 732.5 MPa, while that of octadecylamine benzoxazine was only 24.0 MPa. Therefore, the polybenzoxazine coating has less fouling adhesion and exhibits better fouling release performance, and thus has better antifouling properties. This non-releasing polybenzoxazines without antifouling agent is a green, eco-friendly antifouling coating with low surface energy and low elastic modulus designed by molecular structure.

Fabricating mesoscale polymer ribbons with tunable mechanical properties via evaporative deposition and dewetting.

Synthetic replication of the precise mesoscale control found in natural systems poses substantial experimental challenges due to the need for manipulation across multiple length scales (from nano- to millimeter). We address this challenge by using a 'flow coating' method to fabricate polymer ribbons with precisely tunable dimensions and mechanical properties. Overcoming barriers that previously limited the achievable range of properties with this method, we eliminate the need for substrate patterning and post-processing etching to facilitate the production of high aspect ratio, filament-like ribbons across a range of polymers-from glassy polystyrene to elastomeric poly(butadiene), as well as poly(butadiene-block-styrene). Our method uniquely enables the preservation of chemical fidelity, composition, and dimensions of these ribbons, leveraging polymers with elastic moduli from GPa to tens of MPa to achieve multi-scale features. We demonstrate the role of the elastocapillary length (γ/E) in determining morphological outcomes, revealing the increase in curvature with lower elastic modulus. This finding underscores the intricate relationship among surface tension, elastic modulus, and resultant structural form, enabling control over the morphology of mesoscale ribbons. The soft (MPa) polybutadiene-based ribbons exemplify our method's utility, offering structures with significant extensibility, resilience, and ease of handling, thus expanding the potential for future applications. This work advances our understanding of the fundamental principles governing mesoscale structure formation and unlocks new possibilities for designing soft materials with tailored properties, mirroring the complexity and functionality observed in nature.

Nanoscale Study on Noninvasive Prevention of Dental Erosion of Enamel by Silver Diamine Fluoride.

Here, we aimed to demonstrate the efficacy of silver diamine fluoride (SDF) in halting dental erosion caused by dietary selection and offer a potential explanation for the underlying mechanism. We investigated the surface chemical and mechanical characteristics of human tooth enamel when exposed to Coca-Cola from 10 s to 1 h, with and without the topical treatment of SDF. We analyzed the mechanical properties by measuring the enamel surface roughness and elastic modulus using atomic force microscopy and the surface chemical composition through x-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy analyses, with scanning electron microscopy as a supplementary characterization method. After 1 h of immersion in Coca-Cola, the roughness changed from 83 to 287 nm for enamel without SDF treatment and 64 to 70 nm for enamel with SDF treatment. Under the same conditions, the elastic modulus changed from 125 GPa to 13 GPa for enamel without SDF treatment and 215 GPa to 205 GPa for enamel with SDF treatment. Topical coating of SDF onto enamel formed a passivation layer composed of fluorapatite and created added fluorine flux in the system, which protected the teeth from demineralization under Coca-Cola etching, as shown by morphology and chemical composition analysis as well as roughness and modulus characterization. Applying SDF to enamel minimizes changes in chemical compositions and surface roughness while improving enamel elastic modulus.

From a distance: Shuttleworth revisited.

The Shuttleworth equation: a linear stress-strain relation ubiquitously used in modeling the behavior of soft surfaces. Its validity in the realm of materials subject to large deformation is a topic of current debate. Here, we allow for large deformation by deriving the constitutive behavior of the surface from the general framework of finite kinematics. We distinguish cases of finite and infinitesimal surface relaxation preceding an infinitesimal applied deformation. The Shuttleworth equation identifies as the Cauchy stress measure in the fully linearized setting. We show that both in finite and linearized cases, measured elastic constants depend on the utilized stress measure. In addition, we discuss the physical implications of our results and analyze the impact of surface relaxation on the estimation of surface elastic moduli in the light of two different test cases.

The effect of tooth bleaching using violet LED (405–410 nm) on the properties of resin-based composites

BackgroundThe objective of this study was to evaluate the effect of bleaching techniques, including or not the use of violet light (405–410 nm), on resin-based composites' color, surface roughness, nanohardness, and elastic modulus. MethodsNinety-six disk-shaped specimens (12 mm x 2 mm; n = 12) were prepared using Filtek Z350 XT (Z350) and IPS Empress Direct (ED) resin-based composites. After 24 h, specimens were stained in red wine for 28 days. After staining, specimens were divided into four experimental groups: 40 % Hydrogen Peroxide (HP); Violet Light (VL); 40 % Hydrogen Peroxide associated with Violet Light (HP+VL), and a control group - no treatment (NT). Specimens were evaluated at six experimental times: initial (24 h after light curing); after staining and after the 1st, 2nd, 3rd, and 4th bleaching sessions regarding the color change (ΔE00, L*, a*, b*, and WID); roughness (Ra), nanohardness and elastic modulus (GPa). Two-way analysis of variance for repeated measures was performed (α=0.05 %). ResultsThere was a statistically significant difference between staining and the 1st bleaching session for all ED groups (p<0.05). After the last bleaching session, there were no differences between the experimental and the control groups of both resin-based composites. Bleaching using violet light did not change the roughness, nanohardness and elastic modulus of the tested resin-based composites (p>0.05). ConclusionsAlthough hydrogen peroxide and violet light remove pigments from resin-based composites without affecting their surface roughness, nanohardness, and elastic modulus, the color change was similar to the one obtained by immersion in distilled water.

Silicone-modified polyurea-interpenetrating polymer network fouling release coatings with excellent wear resistance property tailored to regulations

The invasion of alien species via marine organisms attaching to the surfaces of ship hulls is a growing problem. A number of countries have introduced corresponding regulations to combat ship biofouling. One effective way to solve this problem is to apply a fouling release coating with excellent wear resistance. In this study, a silicone-modified polyaspartic ester polyurea was synthesized by a simultaneous crosslinking polymerization. Polyaspartic ester polyurea is employed to form a tightly cross-linked network with excellent toughness and outstanding adhesion, while polydimethylsiloxane is used to form a relatively soft cross-linked network with low surface energy and surface elasticity modulus. Polyurea and silicone molecular chain lock onto each other to form interpenetrating polymer network (IPN) through their respective polymerization systems and cross-linking processes. The synergy between silicone and polyurea provides excellent mechanical properties as well as fouling release performance through the locking mechanism. This study provides a promising and universal strategy for the development of fouling release coatings with excellent wear resistance.

Capsaicin-based silicone antifouling coating with enhanced interlocking adhesion via SIPN

Silicone-based coatings generally exhibit excellent dynamic fouling release due to their low surface energy and elastic modulus. However, the poor adhesion of these coatings at the interface between the coating and the substrate, as well as deficient static antifouling capabilities, severely deteriorate their antifouling properties over extended periods. Herein, an epoxy-poly(dimethylsiloxane)/capsaicin (EP-PDMS/CAP) coating with highly enhanced interfacial adhesion and remarkable antifouling performances was prepared. The coating adhesion strength of the EP-PDMS/CAP has been improved by more than 5 times compared to a PDMS control coating (from 0.4 MPa to 2.04 MPa) by forming a semi-interpenetrating polymer network (SIPN) structure between the epoxy and PDMS layers. The EP-PDMS/CAP coating achieved the superior antifouling effects in both static and dynamic conditions, the anti-bacterial rate was as high as 96.8 %, and the anti-algal adhesion rate to the green algae Chlorella increased by 95.7 %, due to the synergistic effects of the fouling release performance from the PDMS coating and the fouling prevention of capsaicin. Furthermore, the EP-PDMS/CAP coating was proven to be extremely stable in different treatments such as acid/basic solutions, air oven heating test, and cyclic sand abrasion, showing great potential for anti-biofouling under aggressive conditions. This work provides a promising pathway towards the development of high-performance silicone-based composite coatings for efficient marine anti-biofouling.