Surface Free Energy Characteristics Research Articles

Moisture damage resistance of pyro-oil modified bitumen with hydrated lime using surface free energy approach

Moisture damage (MD) in bituminous mixtures occurs due to the loss of cohesion in the bitumen or adhesion between the binder and aggregates. The existence of moisture may influence the bonding between aggregates and bitumen, which may affect the moisture susceptibility of the bituminous mix. Therefore, there is a need to understand the bonding-debonding properties and the moisture susceptibility of binders and mixes, at the material selection stage. Surface free energy (SFE) method is one of the proven techniques to quantify the moisture susceptibility of bituminous mixtures, by using contact angle (CA) determination of the component materials of the mix. This study aimed to evaluate the effect of hydrated lime (HL) on the moisture susceptibility of bituminous mixtures, with control (VG30) bitumen and pyro-oil modified bitumen (POMB) having different percentages of pyro oil, using the SFE approach. Also, the study compared the SFE characteristics of VG30 and POMB with and without the optimum content of HL. POMB binders were prepared by the addition of high-density polyethylene (HDPE) pyro oil in percentages of 1, 3, and 5% in a control bitumen. HL was added as 20%, 25%, and 30% by weight of bitumen in VG30 and POMB bitumen. The aggregates used in the study were limestone, basalt, gravel, and their SFE components were directly considered from the literature. The sessile drop method was used to measure the CA of bitumen and, in turn, determine the various SFE parameters using Van Oss–Chaudhury–Good theory. The moisture susceptibility of mixtures with and without HL was evaluated and compared. From the results, the MD resistance of the bituminous mixtures with modified and unmodified bitumen was found to be increased after the optimum of HL, depending upon the type of aggregates used. Basalt has a 27.41%, 23.38%, and 10.48% greater energy ratio (ER) with POMB1/25, POMB3/25, and POMB5/30, respectively, than VG30/30, the highest ER in modified base bitumen. This indicates that HDPE pyro-oil treatment improves MD resistance for basalt. Whereas for limestone and gravel, VG30/30 gives a maximum value of ER as compared to any other combination of HL modified POMB. The ER values would assist highway agencies in selecting the most compatible binder–aggregate combinations.

Coral‐tentacle‐inspired antifouling membrane spacer: A natural solution for biofouling prevention

AbstractFouling of membrane spacers leads to increased pressure drop and reduced lifespan of membrane modules. Cleaning these fouled spacers is challenging due to strong foulant‐membrane spacer interactions. To address this issue, we introduce a novel spacer, PP‐N‐F, inspired by coral's antifouling properties. This spacer features on‐demand antifouling capabilities through a sequential growth process of functional polymer brushes on its surface. It not only possesses lower surface free energy characteristics than polypropylene spacers, but also exhibits controllable morphological changes similar to swaying coral tentacles. Temperature control strengthens the interfacial hydration layer, mitigating the trade‐off between anti‐adsorption and hydrophobicity of fluorinated surface. The temperature‐responsive surface changes enhance foulant desorption efficiency. Compared to a commercial spacer, PP‐N‐F shows an 89.3% reduction in foulant adsorption and a 61.7% decrease in pressure drop increment after 48 h cross‐flow filtration experiments. This work provides valuable insights for advanced anti‐fouling membrane module design.

Evaluation of the adhesion property and moisture stability of rubber modified asphalt mixture incorporating waste steel slag

The present study was conducted to recycle waste tire rubber and steel slag (SS) in asphalt pavement and investigates the moisture stability of asphalt mixtures incorporating these solid wastes. To this end, two types of aggregates (SS and diabase), three kinds of SS content and multiple freeze–thaw cycles were considered and three kinds of adhesion assessment methods: pull-out test and surface free energy (SFE) method, and freeze–thaw splitting test were performed. Three corresponding adhesion evaluation indicators like adhesion strength, SFE characteristics, and tensile strength ratio were obtained and six energy parameters were introduced to characterize moisture susceptibility of asphalt mixture. To explore the relations between the SFE parameters and the adhesion evaluation indicators, a grey correlation analysis method was adopted. Asphalt mixtures with high consumption of SS obtained a better moisture resistance because SS has a superior adhesion strength and higher SFE components than diabase aggregate. Stripping energy increase was found to be the main failure mode of the asphalt rubber-SS aggregate system. SFE method provides a comprehensive and accurate evaluation of adhesion property of loose asphalt rubber–SS aggregate system and moisture stability of compacted asphalt mixtures.

Epoxyorganosilane Finishing Compositions for Fibrous Fillers of Thermosetting and Thermoplastic Binders.

The development of universal finishing compositions for fibers of various natures is an urgent task for polymer composite materials science. The developed finishes can be used for the fiber reinforcement of polymer matrices with a wide range of surface free energy characteristics. Epoxy systems modified with diaminesilane in a wide concentration range were examined by optical interferometry, FTIR spectroscopy, DSC and the sessile drop technique. It was shown that the partial curing of epoxy resin by diaminesilane at room temperature under an inert atmosphere, followed by contact with air, leads to a significant increase of the surface free energy of the system. Varying the concentration of diaminesilane allows us to effectively regulate the surface free energy of the composition. This makes it possible to use fibers finished with epoxyaminosilane compositions in composite materials based on a various thermosetting and thermoplastic binders with a surface tension of up to 75 mJ/m2.

Experimental analysis of dropwise condensation heat transfer on a finned tube: Impact of pitch size

Condensation is one of the essential processes in diverse industries due to its widespread use in various industrial applications such as power generation, water desalination, and air conditioning. Much research has been conducted to achieve better efficiencies and better heat transfer performances in condensers in the past decades. Condensation is divided into dropwise and filmwise based on the surface free energy, surface roughnesses, and condensate characteristics. This study investigated the influence of the 1-Octadecanethiol coating on vertically grooved copper tube’s condensation heat transfer characteristics. The hydrophobic surfaces have been created using self-assembled monolayers (SAMs) on the pure copper tubes (99.9% Cu). Moreover, four different pitch sizes of 1.5, 2, 2.5, and 3.5 mm have been implemented on the surface. Finally, the heat flux and the heat transfer coefficient as functions of logarithmic mean temperature difference are reported in the result section. For validation, the results obtained from the experiment were compared with available data in the literature, and an acceptable agreement was achieved. According to the results, it was found that the 1.5-mm pitch size has the highest heat flux, and the 3.5-mm pitch size has the lowest heat flux. Additionally, it can be inferred that the maximum heat flux of 696.71 kW/m2 was attributed to the 1.5-mm pitch size for logarithmic mean temperature differences of 64.3 K, which is approximately 1.24 times higher compared to the plain tube.

Improvement in surface properties of Si wafer by mechanical surface treatment

In the present study, a monocrystalline silicon (Si) wafer was treated by ultrasonic nanocrystal surface modification (UNSM) to enhance the efficiency and service life of Si-based devices by reducing reflectivity and improving surface properties, respectively. Microstructure, surface reflection, surface free energy and dry tribological characteristics of Si wafer before and after UNSM were systematically investigated. A silicon nitride (Si3N4) ball with a diameter of 5 mm was used as a counterface. The wear resistance was enhanced by 23% after UNSM in comparison with that of the as-received Si wafer. The reduction in reflectivity is due to roughened surface, while the improvement in tribological characteristics due to the strengthening. Thus, it is recommended that a UNSM can be potentially used as an alternative mechanical surface treatment for thin Si wafers.

Evolution of coefficient of friction between tire and pavement under wet conditions using surface free energy technique

The interaction between tire rubber and pavement surface depends upon their surface characteristics and physical properties. Presence of water on the pavement surface aggravates the interaction and decreases the skid resistance drastically. Due to the interfacial water, the real contact area between pavement and tire decreases, which leads to decreased Coefficient of Friction (CoF). It is reported that CoF in this triphasic system (tire- water – pavement) can be derived from three components: hysterical, dry adhesion (tire-pavement) and wet adhesion (tire- water – pavement). The present study analyses a mechanistic-empirical model to evaluate the CoF between pavement and tire in wet conditions considering Surface Free Energy (SFE) characteristics of materials. The present study was conducted on five distinct types of rubber samples prevalent in Indian condition with basalt rock chosen as the surface mimicking pavement. Physical properties of the rubber samples (Hardness, material yield strength and tan delta values) were determined according to the ASTM standards. SFE parameters were calculated by measuring the contact angles using Sessile drop method. Surface roughness of basalt aggregate was measured using a Zeta Profilometer. Actual friction coefficient was measured using British pendulum (BP) tester under wet conditions. Further, theoretical CoF was calculated by inputting the experimental material properties into mathematical model. The results showed that the wet adhesive friction was the main contributor to the theoretical CoF, whereas dry adhesive friction was the least. Also, the correlation between actual CoF and the material properties was tried. The actual CoF showed fairly good correlation with the hardness of the rubber samples (R2 = 0.95). The study concludes that the SFE based model to determine friction coefficient between wet pavement and road shows potential to ascertain the frictional interactions taking place between the two surfaces.

Relationship between enamel bond fatigue durability and surface free‐energy characteristics with universal adhesives

The relationship between enamel bond fatigue durability and surface free-energy characteristics with universal adhesives was investigated. The initial shear bond strengths and shear fatigue strengths of five universal adhesives to enamel were determined with and without phosphoric acid pre-etching. The surface free-energy characteristics of adhesive-treated enamel with and without pre-etching were also determined. The initial shear bond strength and shear fatigue strength of universal adhesive to pre-etched enamel were higher than those to ground enamel. The initial shear bond strength and shear fatigue strength of universal adhesive to pre-etched enamel were material dependent, unlike those to ground enamel. The surface free-energy of the solid (γS ) and the hydrogen-bonding force (γSh) of universal adhesive-treated enamel were different depending on the adhesive, regardless of the presence or absence of pre-etching. The bond fatigue durability of universal adhesives was higher to pre-etched enamel than to ground enamel. In addition, the bond fatigue durability to pre-etched enamel was material dependent, unlike that to ground enamel. The surface free-energy characteristics of universal adhesive-treated enamel were influenced by the adhesive type, regardless of the presence or absence of pre-etching. The surface free-energy characteristics of universal adhesive-treated enamel were related to the results of the bond fatigue durability.

Effects of Polymeric Coating the Aggregate Surface on Reducing Moisture Sensitivity of Asphalt Mixtures

This paper presents the theoretical and experimental concepts of predicting moisture damage in asphalt concrete mixes using the surface free energy (SFE) concept and laboratory dynamic test, respectively. The SFE characteristics of aggregates and asphalt binders have been evaluated using a Universal Sorption Device (USD) and Wilhelmy Plate (WP) methods, respectively. To validate the results of SFE tests, a dynamic modulus test was conducted on the asphalt mixtures in a controlled stress mode under dry and wet conditions. The results of this study show that the polyvinyl chloride (PVC) coating decreases significantly the total SFE and polar SFE, and leads to an increase in the non-polar SFE of the aggregates, which make aggregates be hydrophobic. This occurrence increases the coating ability of aggregates by the asphalt binder. Comparison between the results of dynamic modulus test in dry and wet conditions confirms the results obtained from the SFE method. P index, which is the percentage of the aggregate surface that experiences stripping in different cycles of loading in wet condition, is obtained by the relation between the concepts of two investigated methods in this study.

Influence of the Oxygen-inhibited Layer on Bonding Performance of Dental Adhesive Systems: Surface Free Energy Perspectives.

To examine the influence of the oxygen inhibited layer (OIL) on shear bond strength (SBS) to dentin and surface free energy (SFE) characteristics of different adhesive systems. Three adhesive systems were used: Scotchbond Multipurpose (SM), Clearfil SE Bond (CS), and Scotchbond Universal (SU). Resin composite was bonded to dentin surfaces to determine SBS with and without OIL of adhesives. The SFE, dispersion force (γSd), polarity force (γSp), and hydrogen bonding force (γSh) of cured adhesives with and without an OIL were measured. Two-way ANOVA and Tukey's honestly significant difference (HSD) test were used for analysis of SBS data, and one-way ANOVA and Tukey's HSD test were used for the SFE and contact angle data. The SBS of SM and CS showed no significant differences between specimens with and without the OIL. However, the SBS of SU with the OIL was significantly higher than without the OIL. The SFE, γSp, and γSh of cured adhesives with an OIL were significantly higher than those of cured adhesives without an OIL. The SFE, γSp, and γSh of SM and CS with an OIL were significantly higher than those of SU with an OIL. The results of this study indicate that the presence of an OIL with a single-step self-etching adhesive promotes higher SBS to dentin, unlike in the other types of adhesive systems. The SFE characteristics of the OIL of dental adhesives differed depending on the type of adhesive system.

Influence of duration of phosphoric acid pre-etching on bond durability of universal adhesives and surface free-energy characteristics of enamel.

The purpose of this study was to evaluate the influence of duration of phosphoric acid pre-etching on the bond durability of universal adhesives and the surface free-energy characteristics of enamel. Three universal adhesives and extracted human molars were used. Two no-pre-etching groups were prepared: ground enamel; and enamel after ultrasonic cleaning with distilled water for 30 s to remove the smear layer. Four pre-etching groups were prepared: enamel pre-etched with phosphoric acid for 3, 5, 10, and 15 s. Shear bond strength (SBS) values of universal adhesive after no thermal cycling and after 30,000 or 60,000 thermal cycles, and surface free-energy values of enamel surfaces, calculated from contact angle measurements, were determined. The specimens that had been pre-etched showed significantly higher SBS and surface free-energy values than the specimens that had not been pre-etched, regardless of the aging condition and adhesive type. The SBS and surface free-energy values did not increase for pre-etching times of longer than 3 s. There were no significant differences in SBS values and surface free-energy characteristics between the specimens with and without a smear layer. The results of this study suggest that phosphoric acid pre-etching of enamel improves the bond durability of universal adhesives and the surface free-energy characteristics of enamel, but these bonding properties do not increase for phosphoric acid pre-etching times of longer than 3 s.

Bonding performance and interfacial characteristics of short fiber-reinforced resin composite in comparison with other composite restoratives.

The purpose of this study was to investigate the shear bond strength (SBS) and surface free-energy (SFE) of short fiber-reinforced resin composite (SFRC), using different adhesive systems, in comparison with other composite restoratives. The resin composites used were everX Posterior (EP), Clearfil AP-X (CA), and Filtek Supreme Ultra Universal Restorative (FS). The adhesive systems used were Scotchbond Multi-Purpose (SM), Clearfil SE Bond (CS), and G-Premio Bond (GB). Resin composite was bonded to dentin, and SBS was determined after 24 h of storage in distilled water and after 10,000 thermal cycles (TCs). The SFEs of the resin composites and the adhesives were determined by measuring the contact angles of three test liquids. The SFE values and SFE characteristics were not influenced by the type of resin composite, but were influenced by the type of adhesive system. The results of this study suggest that the bonding performance and interfacial characteristics of SFRC are the same as for other composite restoratives, but that these parameters are affected by the type of adhesive system. The bonding performance of SFRC was enhanced by thermal cycling in a manner similar to that for other composite restoratives.

Evaluation of degradability of two polyurethane refinish coatings against biological materials: A case study

Abstract In this study the effect of bird droppings and tree gums on two different polyurethane refinish coatings has been investigated. To this end, Arabic gum and pancreatin were used as simulated tree gum and bird dropping, respectively. These substances were applied on coatings exposed to UV radiation and moisture for different exposure times. Various techniques were used to study the appearance of the degraded coatings. Structural analysis of samples was done by FTIR spectroscopy. Surface free energy and thermo mechanical characteristics of refinish coatings were studied by contact angle measurement and DMTA respectively. All experiments were carried out before and after degradation process. In general, it was revealed that while pancreatin degraded the coatings chemically, Arabic gum affected it mechanically and chemically, leading to wrinkle-like deformations on the coating surface. It was also concluded that the cross-linking density and surface free energy have vital roles in the degradation of automotive refinish coatings. It was demonstrated that low cross-linking density and Tg of polyurethane system created a dynamic system which can be post-cured during experiment, leading to enhanced biological resistance. According to this finding, it was also revealed that coating history before bio attack is an important factor in the biological performance of polyurethane systems.

Influence of an oxygen-inhibited layer on enamel bonding of dental adhesive systems: surface free-energy perspectives.

The influence of an oxygen-inhibited layer (OIL) on the shear bond strength (SBS) to enamel and surface free-energy (SFE) of adhesive systems was investigated. The adhesive systems tested were Scotchbond Multipurpose (SM), Clearfil SE Bond (CS), and Scotchbond Universal (SU). Resin composite was bonded to bovine enamel surfaces to determine the SBS, with and without an OIL, of adhesives. The SFE of cured adhesives with and without an OIL were determined by measuring the contact angles of three test liquids. There were no significant differences in the mean SBS of SM and CS specimens with or without an OIL; however, the mean SBS of SU specimens with an OIL was significantly higher than that of SU specimens without an OIL. For all three systems, the mean total SFE (γS), polarity force (γSp), and hydrogen bonding force (γSh) values of cured adhesives with an OIL were significantly higher than those of cured adhesives without an OIL. The results of this study indicate that the presence of an OIL promotes higher SBS of a single-step self-etch adhesive system, but not of a three-step or a two-step self-etch primer system. The SFE values of cured adhesives with an OIL were significantly higher than those without an OIL. The SFE characteristics of the OIL of adhesives differed depending on the type of adhesive.

Influence of Light Intensity on Surface Free Energy and Dentin Bond Strength of Core Build-up Resins

We examined the influence of light intensity on surface free energy characteristics and dentin bond strength of dual-cure direct core build-up resin systems. Two commercially available dual-cure direct core build-up resin systems, Clearfil DC Core Automix with Clearfil Bond SE One and UniFil Core EM with Self-Etching Bond, were studied. Bovine mandibular incisors were mounted in acrylic resin and the facial dentin surfaces were wet ground on 600-grit silicon carbide paper. Adhesives were applied to dentin surfaces and cured with light intensities of 0 (no irradiation), 200, 400, and 600 mW/cm(2). The surface free energy of the adhesives (five samples per group) was determined by measuring the contact angles of three test liquids placed on the cured adhesives. To determine the strength of the dentin bond, the core build-up resin pastes were condensed into the mold on the adhesive-treated dentin surfaces according to the methods described for the surface free energy measurement. The resin pastes were cured with the same light intensities as those used for the adhesives. Ten specimens per group were stored in water maintained at 37°C for 24 hours, after which they were shear tested at a crosshead speed of 1.0 mm/minute in a universal testing machine. Two-way analysis of variance (ANOVA) and a Tukey-Kramer test were performed, with the significance level set at 0.05. The surface free energies of the adhesive-treated dentin surfaces decreased with an increase in the light intensity of the curing unit. Two-way ANOVA revealed that the type of core build-up system and the light intensity significantly influence the bond strength, although there was no significant interaction between the two factors. The highest bond strengths were achieved when the resin pastes were cured with the strongest light intensity for all the core build-up systems. When polymerized with a light intensity of 200 mW/cm(2) or less, significantly lower bond strengths were observed. CONClUSIONS: The data suggest that the dentin bond strength of core build-up systems are still affected by the light intensity of the curing unit, which is based on the surface free energy of the adhesives. On the basis of the results and limitations of the test conditions used in this study, it appears that a light intensity of >400 mW/cm(2) may be required for achieving the optimal dentin bond strength.

Tribological characteristics of novel branched perfluoropolyether lubricant films in hard disk drives

In this study, the basic tribological characteristics of novel branched perfluoropolyether (PFPE) lubricant films such as TA-30 and QA-40 were examined. Their surface free energy characteristics and adhesive and friction forces were investigated using an atomic force microscope. The interactions between the lubricant molecules and the water molecules were also examined by monitoring the changes in the contact angle of distilled water on the test lubricant films. The interactive forces such as the adhesive and friction forces of a film that is approximately one monolayer thick were found to be strongly dependent on the conformation of the lubricant molecules on diamond-like carbon thin films. In addition, the TA-30 and QA-40 lubricant molecules appeared to interact with the water molecules more actively than conventional Ztetraol2000 molecules. These results afforded fundamental insight into the tribological performance of novel branched PFPE lubricants in the head-disk interface.

Control of Superhydrophilicity/Superhydrophobicity using Silicon Nanowires via Electroless Etching Method and Fluorine Carbon Coatings

Surface roughness is promotive of increasing their hydrophilicity or hydrophobicity to the extreme according to the intrinsic wettability determined by the surface free energy characteristics of a base substrate. Top-down etched silicon nanowires are used to create superhydrophilic surfaces based on the hemiwicking phenomenon. Using fluorine carbon coatings, surfaces are converted from superhydrophilic to superhydrophobic to maintain the Cassie-Baxter state stability by reducing the surface free energy to a quarter compared with intrinsic silicon. We present the robust criteria by controlling the height of the nanoscale structures as a design parameter and design guidelines for superhydrophilic and superhydrophobic conditions. The morphology of the silicon nanowires is used to demonstrate their critical height exceeds several hundred nanometers for superhydrophilicity, and surpasses a micrometer for superhydrophobicity. Especially, SiNWs fabricated with a height of more than a micrometer provide an effective means of maintaining superhydrophilic (<10°) long-term stability.

Using the Surface Free Energy Method to Evaluate the Effects of Polymeric Aggregate Treatment on Moisture Damage in Hot-Mix Asphalt

Moisture damage in hot-mix asphalt (HMA) occurs because of a loss of adhesion and/or cohesion, resulting in the reduced strength or stiffness of the HMA and the development of various forms of pavement distress. There are several different approaches for improving adhesion and reducing moisture sensitivity in asphalt mixtures. One convenient approach is coating the aggregate surface with a suitable agent to reverse the predominant electrical charges at the surface and reduce the surface energy of the aggregate. In this research, the effects of two types of polyethylene (PE), namely high-density polyethylene (HDPE) and low-density polyethylene (LDPE), were added to coat the aggregate, and the moisture damage to the asphalt mixtures was evaluated. Three types of aggregates representing a considerable range in mineralogy (limestone, granite, and quartzite) were evaluated during the course of this study. This paper explains the theoretical and experimental concept of predicting moisture damage in asphalt concrete mixes using the surface free energy (SFE) concept and laboratory testing analysis, respectively. It also shows the effects of polymeric aggregate treatment on moisture damage within the mixes. SFE measurements were used to compute the work of adhesion between the aggregates, asphalt, and the cohesive bond strength in the asphalt binder and aggregate. The SFE characteristics of three types of aggregate with and without PE treatment and asphalt were evaluated for moisture-damage susceptibility using a universal sorption device (USD) and dynamic Wilhelmy plate method, respectively. To validate these results, a dynamic modulus test was used to apply a repeated unconfined, compressive load to the sample in a controlled stress mode. The results of the SFE method indicate that PE increases the wettability of asphalt binder on the aggregate and the adhesion between the asphalt binder and aggregate. The same results were achieved using the values obtained by laboratory testing analysis. The aggregates treated with HDPE showed better resistance against moisture damage in both methods of study.

Surface characteristics of orthodontic adhesives and effects on streptococcal adhesion

In this study, we analyzed the surface roughness (SR) and surface free energy (SFE) characteristics of various orthodontic adhesives and their effects on the adhesion of mutans streptococci (MS). Three nonfluoride-releasing composites, 1 fluoride-releasing composite, 1 polyacid-modified composite (compomer), and 2 resin-modified glass ionomers (RMGIs) were analyzed with confocal laser scanning microscopy and the sessile drop method. Each material was incubated with whole saliva or phosphate-buffered saline solution. Adhesion assays were then performed by incubating each material with tritium-labeled cariogenic streptococci. We found that SFE and its components were significantly different among the adhesives, despite relatively uniform SR. RMGIs showed significantly higher SFE-particularly, dispersive, polar, and acidic characteristics-than did the composites. The compomer had intermediate characteristics between the composites and RMGIs. MS adhered to RMGIs significantly more than to the composites and the compomer, but there was no significant difference among the composites. The longer incubation time increased MS adhesion, whereas saliva coating did not significantly influence MS adhesion. There was a correlation between SFE and MS adhesion. SFE and its dispersive, polar, and acid components significantly influenced MS adhesion irrespective of saliva coating. This study suggests that initial MS adhesion is significantly influenced by SFE characteristics of adhesives rather than SR or saliva coating.

Analysis of surface roughness and surface free energy characteristics of various orthodontic materials

The purpose of this study was to analyze the differences in surface characteristics of various orthodontic materials; this might provide valuable information on bacterial adhesion to orthodontic materials. Surface roughness (SR) and surface free energy (SFE) characteristics of 5 orthodontic adhesives (2 composites resins, 2 resin-modified glass ionomer cements, and 1 compomer), 5 bracket materials (2 stainless steel, 1 monocrystalline sapphire, 1 polycrystalline alumina, and 1 plastic) and bovine incisors were investigated by using confocal laser scanning microscopy and the sessile drop method. There were significant differences in SR and SFE characteristics among orthodontic materials. Bovine incisors showed the roughest surface, and monocrystalline sapphire showed the smoothest surface. However, there were only small variations in SR (less than 0.3 mum) among the materials, except for bovine incisors. In contrast to SR, there were big differences in SFE characteristics among materials. Generally, bracket materials showed lower SFE--specifically, dispersive and polar components on their surfaces--than orthodontic adhesives. Resin-modified glass ionomer cements had the highest SFE, dispersive component, and polarity; these conditions are more favorable for bacterial adhesion. This study suggests that SFE characteristics can influence bacterial adhesion to orthodontic materials more than SR, and bracket materials might have less favorable SFE characteristics for bacterial adhesion than orthodontic adhesives.