Lowest Ra Values Research Articles

Influence of Manual and Ultrasonic Scaling on Surface Roughness of Four Different Base Materials Used to Elevate Proximal Dentin–Cementum Gingival Margins: AnIn VitroStudy

To evaluate and compare the effects of both manual and ultrasonic scaling on surface roughness of four different base materials, used for elevating dentin/cementum gingival margins of proximal cavities. Eighty human upper molars with compound Class II mesial cavities, with gingival margins 1 mm below the cemento-enamel junction (CEJ), were divided into four different groups according to the type of the base material used; resin-modified glass ionomer (RMGI), glass hybrid (HV-GIC), flowable bulk-fill resin composite (Bulk Flow) and bioactive ionic resin (Activa). This was followed by completing the restorations with the same resin composite. All materials were used according to the manufacturers' instructions. All groups were further subdivided into two subgroups according to the scaling technique: manual (hand) or ultrasonic. All restorative and scaling procedures were performed after fixation of specimens with acrylic beside neighboring teeth to simulate natural contact. The mean surface roughness (Ra, μm) of all specimens was measured quantitatively and qualitatively by a three-dimensional (3D) surface analyzer system at two stages; (1) after thermal cycling for 5000 cycles without scaling and (2) after scaling. Data were statistically analyzed using analysis of variance (ANOVA), Tukey post hoc tests, and paired sample t-tests (at α=0.05). For baseline readings, the Bulk Flow group had the lowest Ra values, while HV-GIC group had the highest. RMGI and Activa groups had no statistical significant difference between their Ra values (p>0.05). For post scaling readings, hand scaling had significantly lower Ra values than ultrasonic scaling in all the material groups (p<0.05), except in the Bulk Flow group, where both scaling methods were not significantly different from each other (p>0.05). Bulk Flow had the smoothest surfaces when cured against a matrix band compared with the other tested base materials. When hand and ultrasonic scaling methods were compared, the latter technique had more detrimental effect on the surface texture of the four tested base materials.

Machining of Y2O3 reinforced magnesium rare earth alloys using wire electrical discharge turning process

Advanced machining has become one of the inevitable processes for the fabrication of miniature industrial components that demands high dimensional accuracy. Magnesium (Mg) and its composites have widespread applications in the areas of aerospace, medical, and automobile sectors. The objective of this work is to analyze the machinability of Mg—rare earth (RE) alloy (Mg3Al2.5La)-based nanocomposites using wire electrical discharge turning (WEDT), a variant of EDM process. Y2O3 (0.6 and 1.9%) reinforced magnesium composites are prepared through disintegrated melt deposition technique. SEM and XRD analyses confirmed the intermetallic phase formation, such as Al11La3, and Al2La. Machining experiments are conducted with input parameters: discharge ON time, wire feed and spindle rotational speed each varied at three levels to study surface roughness (Ra) and volume of material removed (MRR). Results showed that Ra of the machined samples increases and MRR decreases, with the increase in % reinforcement and discharge ON time. The lower Ra value of 2.985 µm and higher MRR of 34.85 mm3/min are observed for the Mg3Al2.5La sample. This result is attributed to the absence of particle pullout and increased thermal conductivity of magnesium alloy during machining. Prediction analysis based on mean values is carried out to confirm the accuracy of the experimental results at optimal parametric levels.

An experimental study on magnetic field-assisted-EDM process for Inconel-625

ABSTRACT In this experimental study, the effect of magnetic field on electrical discharge machining (EDM) performance was evaluated for Inconel-625. The magnetic-field-assisted EDM (MFA-EDM) process is defined as a combination of EDM and magnetic field environment. Permanent magnets were installed at the proper distance for the creation of a magnetic field and the experiments were conducted using the Cu tool. Magnetic field intensities of 0.396 T and 0.665 T were applied during EDM operations. Performance of the EDM under the action of different magnetic fields was evaluated based on material removal rate (MRR), tool wear rate (TWR), and average surface roughness (Ra). The experimental results showed that higher MRR, higher TWR, and lower Ra values were observed under the action of the magnetic field. The scanning electron microscope (SEM) analysis also confirmed a better surface quality under the action of the magnetic field. The SEM micrograph showed the presence of lesser cracks present on the machined surface with MFA-EDM.

Effect of combining different surface treatments on the surface characteristics of polyetheretherketone-based core materials and shear bond strength to a veneering composite resin

Statement of problemHigh-performance polyetheretherketone (PEEK) has been used in dentistry because of its excellent physical and chemical properties. However, its lack of translucency requires the use of a veneering composite resin for esthetic applications. Data on bonding a veneering composite resin to PEEK are still scarce. PurposeThe purpose of this in vitro study was to assess the effect of using and combining different surface treatments on the surface roughness and wettability of PEEK core materials and the shear bond strength (SBS) to a veneering composite resin. Material and methodsSixty square PEEK specimens were divided according to surface treatments into 6 groups: group N, no surface treatment; group A, airborne-particle abrasion; group L, ER:YAG laser treatment; group LA, laser treatment and airborne-particle abrasion; group P, plasma treatment; and group PA, plasma treatment and airborne-particle abrasion. Surface roughness (Ra) and wettability (contact angle θ) were measured followed by evaluation of the surface topography. After veneering, the SBS was measured. A 1-way analysis of variance (ANOVA) was used to assess all interactions with multiple pairwise comparisons (α=.05). ResultsThe highest mean Ra values were obtained for the combination treatment groups (LA 2.94 ±0.1 and PA 2.7 ±0.1 μm) (P<.001). While the laser (1.3 ±0.1 μm) and plasma treatment (1.4 ±0.1 μm) groups had the lowest Ra values, LA and PA had the highest wetting of PEEK surfaces (LA 6.9 ±0.7 and PA 4.9 ±0.2 degrees) (P<.001). The highest mean SBS values were demonstrated on PEEK surfaces with combination treatments (LA 22 ±1.3 and PA 21.2 ±0.8 MPa) (P<.001). ConclusionsCombining airborne-particle abrasion with laser or plasma treatments increased the surface roughness and wettability of PEEK surfaces favorably compared with applying each of the 3 treatments individually. The combinations enhanced the bond strength of PEEK to the veneering composite resin.

Evaluating Service Characteristics of Working Surfaces of Car Parts by Microgeometric Quality Parameters

The correlation between the service characteristics of the working surfaces of car parts belonging to the rotary body class, and quality parameters—in particular, the height-related roughness parameter Ra—was estimated. Low values of Ra were found to be unable to guarantee an optimal microrelief geometry and, accordingly, high-performance characteristics of the working surface. The oil-accumulation power of the parts was investigated as a primary characteristic of sliding friction using the group of Rk parameters in the Abbott–Firestone diagram, based on the profilogram of the test specimen’s surfaces. The oil-absorption power of the surfaces formed by different technological operations was compared with different microgeometric quality parameter values.

Comparative Analysis of Abrasive Materials and Polishing System on the Surface Roughness of Heat-Polymerized Acrylic Resins.

Objective The aim of this in vitro experiment was to see how the operator's manual skills, polishing equipment, and abrasive materials affected the surface roughness of denture base resins. Materials and Methods Forty polymethyl methacrylate (PMMA) specimens were created and polished by using two different polishing systems, namely hand and automatic polishing machines. Three operators hand-polished 30 of specimens with eggshell powder and pumice, while 10 were automatically polished ( n = 5). A profilometer was used to determine the average surface roughness (Ra) after polishing. The Ra values for the specimens hand-polished were analyzed by using paired sample testing. The Ra values for all polished specimens were analyzed by using a one-way ANOVA. Differences between the two abrasive materials as well as the polishing system were determined by using the Bonferonni tests ( p = 0.05). Results and Conclusion For the PMMA specimens hand-polished, there was a strong connection in the Ra values. There were also significant variations in the Ra values across the three operators ( p < 0.001). The automated technique created a substantially smoother surface than the traditional technique ( p = 0.001). The greatest Ra values (0.20 µm) were found in specimens polished traditionally by using pumice, whereas the lowest Ra values (0.04 µm) were found in specimens polished mechanically with eggshell powder. The automated polishing system was the most effective polishing method when the Ra values were connected to the level of smoothness.

Synthesis, In Vitro, and In Silico Analysis of the Antioxidative Activity of Dapsone Imine Derivatives.

Dapsone (DDS) is an antibacterial drug with well-known antioxidant properties. However, the antioxidant behavior of its derivatives has not been well explored. In the present work, the antioxidant activity of 10 dapsone derivatives 4-substituted was determined by an evaluation in two in vitro models (DPPH radical scavenging assay and ferric reducing antioxidant power). These imine derivatives 1–10 were obtained through condensation between DDS and the corresponding aromatic aldehydes 4-substuited. Three derivatives presented better results than DDS in the determination of DPPH (2, 9, and 10). Likewise, we have three compounds with better reducing activity than dapsone (4, 9, and 10). In order to be more insight, the redox process, a conceptual DFT analysis was carried out. Molecular descriptors such as electronic distribution, the total charge accepting/donating capacity (I/A), and the partial charge accepting/donating capacity (ω+/ω−) were calculated to analyze the relative donor-acceptor capacity through employing a donor acceptor map (DAM). The DFT calculation allowed us to establish a relationship between GAPHOMO-LUMO and DAM with the observed antioxidant effects. According to the results, we concluded that compounds 2 and 3 have the lowest Ra values, representing a good antioxidant behavior observed experimentally in DPPH radical capturing. On the other hand, derivatives 4, 9, and 10 display the best reducing capacity activity with the highest ω− and Rd values. Consequently, we propose these compounds as the best antireductants in our DDS imine derivative series.

An investigation of the effect of surface characterization on Saos-2 cell proliferation after coating of titanium alloy surfaces by a selective laser melting process

Pure titanium alloys are commonly employed in construction of dental implants, given their advantageous features including resistance to corrosion, mechanical strength, flexibility, and bioavailability. The purpose of this study was to evaluate the surface characteristics of Ti6Al4V alloy disks upon sand-blasted, large-grit acid-etching, and/or selective laser melting applications and to assess whether and how these surface modifications affect the attachment, viability, metabolic activity, and osteoblastic differentiation of Saos-2 osteosarcoma cells. We manufactured Ti6Al4V alloy disks and divided them into four groups (non-treated, SLA-treated, Ti6Al4V ELI alloy-coated (SLM treated), and SLM+SLA-treated). The topographic analysis was carried using AFM and SEM and chemical content was evaluated by EDX . EDS. Adherence and viability of Saos-2 cells seeded onto disks were investigated via SEM and fluorescent microscopy. To assess the metabolic activity of Saos-2 cells, MTT assay was conducted and the osteoblastic differentiation interpreted via monitoring alkaline phosphatase activity. According to data acquired using AFM and SEM, the control group had the smoothest surfaces, with a lower Ra value. The roughest surface was obtained with SLM and SLA dual-treated disks. The osteoblastic activity of Saos-2 cells on the surface of dual-treated disks was higher than the other groups. Therefore, the surface of SLM+SLA-treated disks conferred a suitable environment for Saos-2 cells to adhere, proliferate, and show higher metabolic activity. We concluded that Ti6Al4V alloy disks covered with Ti6Al4V ELI alloy and subjected to SLA surface treatment may be promising to manufacture dental implants with improved adaptability, bioavailability, and osseointegration. • Surface topographies of Ti6Al4V disks subjected to various coatings were evaluated using AFM and SEM. • MTT and ALP assays were performed to reveal osteoblastic differentiation onto Saos-2 cells planted Ti6Al4V disks. • Cell adhesion increased in direct proportion to the thickness of the Ti6Al4V disks. • SLM+SLA treatment is a preferable surface construction since the morphology of osteoblasts is positively affected. • The success of dental implant surface is related to its chemical properties along its micro-morphological nature.

Contribution to the selection of cutting fluid type and its application technique for grinding of bearing steel

The elevated heat generation in grinding can develop high temperatures at the contact zone, which can adversely affect the surface integrity of the workpiece, especially when grinding hardened steels with conventional abrasives. Thus, the correct selection of cooling-lubrication condition is essential to avoid or attenuate any possible negative effect to workpiece surface integrity. However, the literature lacks work comparing different cutting fluid application technique (e.g. flood and minimum quantity lubrication – MQL) using the same fluid on both techniques. In this context, this work aims to contribute to the selection of cutting fluid type and its application technique for the grinding of bearing steel. Experimental trials were conducted comparing the use of semisynthetic and synthetic cutting fluids, both applied via conventional (flood) and MQL techniques. Different cutting conditions were also tested. A 24 full factorial design of experiment (DOE) was carried out with the following factors: fluid application technique, type of fluid, workspeed, and radial depth of cut. An analysis of main effects and interactions was performed for surface finish (Ra parameter) results, including a prediction model based on the analysis of variance (ANOVA). The morphology of ground surface and microhardness below machined surface were also analyzed. The results showed that the ground surface finish was strongly dependent on the cutting fluid type and its application technique combination: superior finishing was observed with the combination of semisynthetic fluid delivered via flood technique and with synthetic fluid delivered via MQL technique. From the surface morphology analysis, it was observed that the inferior lubrication capacity of synthetic fluid applied via flood condition deteriorated the surface finish and morphology. The surfaces ground with semisynthetic fluid provided, in general, lower values of Ra and lower microhardness variation. The prediction model for Ra showed a maximum error of 14% in comparison to the measured values.

SURFACE ROUGHNESS ANALYSIS OF CRYO-TREATED AND TEMPERED STEELS IN CYLINDRICAL GRINDING OPERATION

Cylindrical grinding operation is an important metal cutting process used as a finish process to achieve the surface quality and dimensional stability of the products. In this context, experimental work and statistical analysis in researches contribute to improve product quality of manufactured parts. Tempered steels are widely used for automotive components and manufacturing applications. The objective of this study is to analyze the surface roughness (Ra) values of cryogenically (cryo) treated and tempered steels in cylindrical grinding operation. According to the grinding experiments created by the Taguchi method, grinding wheels (Al2O3 and SiC), heat treated steel samples (HT, CT24, and CT36) and depth of cut (50, 100, and 150[Formula: see text][Formula: see text]m) were selected to determine the optimum surface roughness values of these steels. The results showed that significant improvements in Ra values of cryo-treated and tempered steels were observed. The lowest Ra values were obtained in cryo-treated sample (CT36) with SiC grinding wheel and depth of cut (50[Formula: see text][Formula: see text]m).

Does build angle have an influence on surface roughness of anterior 3D-printed restorations? An in-vitro study.

To evaluate the effect of build direction on the surface roughness (Ra) of stereolithography (SLA) printed full-coverage anterior dental restorations before and after surface polishing. A total of 45 full-coverage dental restorations were 3D printed using the SLA additive manufacturing technique. Five groups were defined based on the build angles: 90, 120, 135, 150, and 180 degrees. The Ra was measured with the contact profilometer to evaluate the arithmetic average of the absolute Ra value on the labial surface before and after polishing procedures. Data were analyzed using two-way ANOVA, and statistical significance was set at α = .05. The highest Ra was recorded in specimens printed with the 90-degree build angle, whereas the lowest values were recorded in specimens printed with the 180-degree build angle (P = .000). In all groups, the Ra values measured after polishing were significantly lower than prepolished values (P = .000), with no difference among the different build angles. Build angle significantly influenced the Ra of the SLA-printed full-coverage restorations. Polishing minimized the effect of build angle on the Ra. The 180-degree build angle is recommended when SLA printing an anterior restoration, as it provides the lowest Ra values and also requires a minimal support area and minimal number of support structures.

Experimental investigation of the effect of machinability on surface quality and vibration in hard turning of hardened AISI 4140 steels using ceramic cutting tools

In industry, hardened steels are used in manufacturing of the products such as machine parts and components. In this context, surface quality and vibration play a significant role for control of cutting parameters and cutting conditions in turning process of hardened steel materials. In this study, it was aimed to investigate the effect of machinability on surface quality (Ra and Rz) and vibration in hard turning of conventional heat treated (CHT) and tempered (T) AISI 4140 (42CrMo4) steel samples using ceramic cutting tools under dry environment. They were selected as cutting parameters; four different cutting speeds (120, 160, 200, and 240 m/min), three different feed rates (0.05, 0.10, and 0.15 mm/rev), and depth of cut (0.2 mm). To make the turning process more efficient and to measure the occurring vibrations, the data were obtained online from the ceramic cutting tool by accelerometers in three axes (x-Ch1, y-Ch2, and z-Ch3 directions). In addition, test results of hardness, tensile, microstructure images, Ra - Rz values, and chip thickness values of the experiment samples were analyzed and compared. With the microstructure obtained after the tempering process applied to the T sample, it was seen that it is more machinable and affects the surface quality - vibration positively. The results showed that the most important cutting parameter affecting vibration and surface quality was found to be the feed rate. The lowest Ra value was found as 0.144 μm at 200 m/min of cutting speed and 0.05 mm/rev of feed rate in the T sample. The lowest vibration amplitude value (Ch3) was measured as 0.0023 gRMS (Root Mean Square) at 120 m/min of cutting speed and 0.05 mm/rev of feed rate. According to the Ra and Rz values found in the literature studies, better surface qualities were obtained in the present study.

Effect of thermomechanical densification of pine wood (Pinus sylvestris L.) on cutting forces and roughness during milling

Effect of thermomechanical densification of pine wood (Pinus sylvestris L.) on cutting forces and roughness during milling. The paper presents the results of research concerning the assessment of machinability of pine wood thermomechanically compacted. The assessment was made on the basis of the cutting forces and surface roughness after the milling process. Selected properties of native and modified wood were examined. Based on the research, it was found that compacted wood is characterized by higher cutting forces during milling. The surface quality after milling was examined and the roughness index Ra values were determined. The research shows that the modified wood is characterized by a lower Ra value both along and across the grain. Statistical analysis showed that the modification had a statistically significant effect on the values of cutting forces and the physical and mechanical properties of the tested wood.

Analysis of tool vibration and surface roughness during turning process of tempered steel samples using Taguchi method

This study analyzed the tool vibration (Vib) and surface roughness (Ra) during turning of AISI 4340 (34CrNiMo6) tempered steel samples using Taguchi Method. In this context, Taguchi design L18(21× 32) was used to analyze the experimental results. The vibration amplitude values from cutting tools were recorded for different machining parameters, control factors; two different sample hardness (46 and 53 HRc), three different cutting speeds (180, 220, 260 m.min−1), and feed rates (0.08, 0.14, 0.20 mm.rev−1) were selected. The machining parameters giving optimum Vib and Ra values were determined. Regression analysis is applied to predict values of Vib and Ra. Analysis of variance was used to determine the effects of machining parameters on the Vib and Ra values. The most important machining parameters were found to be the feed rate, sample hardness, and cutting speed for Vib and Ra, respectively. The lowest Vib and Ra values were obtained in 46 HRc sample as 0.0022 gRMS and 0.255 µm, respectively. The surface quality can be improved by reducing the sources of vibration by using appropriate machining parameters. As a result, there is a significant relationship between Ra and Vib. The lower Ra values were found during turning process of tempered steel samples according to the literature studies. It is suggested that the process can be preferred as an alternative process to grinding process due to lower cost and machining time. In application of the turning of experiment samples by ceramic cutting tool, a substantial technological and economical benefit has been observed.

Pore-scale study of miscible density-driven mixing flow in porous media

Two-dimensional density-driven convective mixing processes in synthetic porous media are simulated at pore-scale using lattice Boltzmann method with a rescaled version of the nonequilibrium extrapolation method in the present work. Numerical results demonstrate that the density-driven convective mixing process varies with the Rayleigh number (Ra). For low values of Ra, the numerical results at pore-scale are consistent with those at representative elementary volume (REV) scale. With the increase in Ra, the convective mixing process becomes different, which can be reflected by the time evolution of the dissolution flux and onset time of convection at different Rayleigh numbers. On the one hand, the flux growth regime in the time evolution of the dissolution flux can be divided into two sub-regimes, which are named early and late flux growth regimes in this study. In addition, for the shutdown regime, the dissolution flux can be scaled as J∼t−1 rather than t−2 for high Ra cases, which is consistent with our theoretical analysis. On the other hand, the existence of the early flux growth regime consumes the mass at the top diffusive layer, leading to a delay of convective onset time. Therefore, the onset time of the convection calculated at pore-scale is much higher than that predicted by the existing theory and REV scale studies. The present study shows practical implications for CO2 capture and storage.

Effect of different placement techniques on color stability and surface roughness of resin composites

Abstract Introduction Longevity and clinical success of dental restorations can be influenced by many factors during the restorative procedures. Objective This study aimed to evaluate the influence of different placement techniques on color stability and surface roughness of two resin composites. Material and method The groups of specimens (n=10) were divided according to resin composite (FiltekTM Z250 XT and FiltekTM Z350 XT) and placement technique: Mylar strip, spatula, dry brush, modeling liquid, and surface sealant. Color stability and surface roughness were accessed using a spectrophotometer (CIELab color space) and a rugosimeter (standard cutoff of 0.8 mm), respectively, after water storage. Subsequently, the specimens were immersed in coffee for 48 h and final color was measured. The data were analyzed using ANOVA and the Tukey’s post hoc test (α=5%) and the correlation between surface roughness (Ra) and color change (∆Eab) was assessed using the Pearson’s correlation coefficient. Result The different placement techniques influenced Ra and ∆Eab on both resin composites. The groups treated with surface sealant showed greater difference in ∆Eab for both resin composites. The FiltekTM Z250 XT resin showed greater color stability compared with the FiltekTM Z350 XT resin regardless of the placement technique used. Ra of each placement technique was similar among the resin composites except for the FiltekTM Z350 XT modeling liquid group, which presented lower Ra values compared with those of FiltekTM Z250 XT. A correlation between Ra and staining was identified (p=0.268). Conclusion Color stability and Ra are influenced by different placement techniques.

Effects of deep cryogenic treatment on machinability, hardness and microstructure in dry turning process of tempered steels

This study investigated the effects of Deep Cryogenic Treatment (DCT) on machinability, hardness, and microstructure in dry turning process of AISI 4140 (48-51 HRc) tempered steels with ceramic cutting tools on the surface roughness (Ra). DCT process of steels has shown significant improvement in their mechanical properties. In this context, experiments were made with Taguchi L16 method and optimum values were determined. Three different values for each control factors as: different heat treated samples, cutting speeds (160, 200, 240, 280 m/min), feed rates (0.08, 0.12, 0.16, 0.20 mm/rev) were selected. As a result, the lowest Ra value was found to be 0.159 µm for the DCTT36 sample at a cutting speed of 240 m/min, a feed rate of 0.08 mm/rev. The optimum Ra value was the lowest for the DCTT36 sample compared to the other samples as 0.206 µm. The hardness values of the micro and macro were highest for the DCTT36 sample. Microstructural point of view Scanning Electron Microscopy (SEM) point of view, the DCCT36 sample showed that best results owing to its homogeneity. It was concluded that lower Ra values can be obtained with ceramic cutting tool in dry turning experiments according to the studies in the literature review. It is thought to be preferred as an alternative to cylindrical grinding process due to lower cost.

Impact of dietary acids on the surface roughness and morphology of composite resins.

This in vitro study was performed to evaluate the surface roughness (Ra) and morphology by scanning electron microscopy (SEM) of composite resins that had been stored in acidic solutions typical of those present in the diet. Three composite resins (4 Seasons, Z250, and P90) were selected and divided into three groups (n = 7) according to the solutions tested: G1: distilled water; G2, Coca-cola, and G3: orange juice. The Ra test was repeated after immersion periods of 15, 90, and 180 days. The mean Ra values were subjected to LS means analysis and the Tukey-Kramer (P < 0.05). One test specimen of each composite resin was selected for SEM analysis after each period. The Ra data indicated that P90 had the lowest Ra values. 4 Seasons and Z250 had statistically similar roughness values for all the solutions and evaluation periods. With the exception of 180-day immersion in Coca-cola, 4 Seasons showed significantly higher values than Z250. SEM analysis showed that P90 was the composite resin most resistant to the actions of all acid solutions for the periods analyzed. Interaction between components of the solutions and the active components of other dietary items, as well as oral hygiene, may affect the chemical degradation of composite resins.

Effects of porous medium and wavy surface on heat transfer and entropy generation of Cu-water nanofluid natural convection in square cavity containing partially-heated surface

This article analyzes the natural convection of nanofluid within a porous cavity containing a partially-heated vertical wall and wavy lower and upper walls. Numerical simulations are performed to explore the effects of the Rayleigh number (Ra), Darcy number (Da), porosity (ε), volume fraction of nanoparticles (φ), amplitude of wavy surface (αw), length of partially-heated wall surface (LH∗), and irreversibility distribution ratio (χ) on the Bejan number (Be), total entropy generation (St), mean Nusselt number (Num), and energy-flux-vector distribution. The results show that for high values of Da and Ra, circulation regions are developed in the energy-flux-vector distribution and hence convection heat transfer dominates. Consequently, Num and St both increase, while Be reduces as Ra, ε and Da increase. For low values of Da and Ra, the effects of Da, Ra and ε on Num and St are insignificant, and Be approaches unity since conduction heat transfer dominates. As φ and αw increase, Num and Be increase, but St decreases. Moreover, as LH∗ increases, Num and St also increase. For a high value of Ra, St increases and Be reduces as χ is increased. Finally, for a low value of Ra, the effect of χ on St is insignificant and Be ≈ 1.

Pore expanding effect of hydrophobic agent on 100 nm-sized mesoporous silica particles estimated based on Hansen solubility parameters

Mesoporous silica particles (MSPs) are synthesized in aqueous medium by a sol-gel reaction, wherein a surfactant cetyltrimethylammonium bromide (CTAB) promotes silica growth and controls the mesoscopic structure of MSP. To estimate an essential role of hydrophobic agent, herein we synthesized the 100 nm-sized spherical MSPs in the presence of hydrophobic agents, and investigated their pore size distribution. The coexistence of cyclohexane, hexane, or 1,3,5- trimethylbenzene with CTAB micelles resulted in bimodal pore size distributions, with larger pore sizes up to 10.5 nm. In contrast, the coexistence of benzene or toluene resulted in a single peak of pore size distribution ranging from 2.8 to 3.3 nm, which was similar to control (2.3 nm, without hydrophobic agents). Because the hydrophobic core region of CTAB micelle can be considered as an assembly of hexadecane molecules, Hansen solubility parameter distance (Ra value) was calculated for hexadecane and each hydrophobic agent. A lower Ra value indicates higher affinity of CTAB micelle and hydrophobic agent, and the volume fraction of large pores increased with decreasing Ra values. No pore expansion effect of benzene could be consistent with its highest Ra value among the hydrophobic agents tested here. It is concluded that the effect of hydrophobic agent on pore expansion in 100 nm size MSPs can be estimated based on the Ra value as indicator for micelle-hydrophobic agent affinity.