Work Of Adhesion Values Research Articles

Effect of fat on physicochemical, rheological, textural and sensory properties of Ricotta cheese spreads

SummaryThe effect of different fat contents of milk and cheese whey mixture (20:80) on physicochemical, rheological and sensory properties of Ricotta cheese spread (RCS) was evaluated. Four types of product such as no‐fat milk (NFM)‐RCS, low‐fat milk (LFM)‐RCS, medium‐fat milk (MFM)‐RCS and full‐fat milk (FFM)‐RCS were prepared from Ricotta cheese curd added with salt (1.5%) and guar gum (0.4%). The NFM‐RCS had higher (P < 0.05) protein, ash, acidity, dynamic modulus (G' and G"), critical stress, firmness, work of shear, stickiness, work of adhesion values and lower fat, and pH, L*, a*, b* values when compared with LFM‐, MFM‐ and FFM‐RCS. Except spreadability, highest sensory scores for all other attributes were found in MFM‐RCS when compared with other experimental samples. This study indicated that increase in fat content or decrease in protein content of RCS samples produced lower viscoelastic modulus values, firmness, stickiness, adhesiveness and higher spreadability, yield, solids recovery and highly acceptable sensory characteristics.

Computing the Work of Solid-Liquid Adhesion in Systems with Damped Coulomb Interactions via Molecular Dynamics: Approaches and Insights.

Recently, the dry-surface method [Langmuir2016, 31, 8335−8345] has been developed to compute the work of adhesion of solid–liquid and other interfaces using molecular dynamics via thermodynamic integration. Unfortunately, when long-range Coulombic interactions are present in the interface, a special treatment is required, such as solving additional Poisson equations, which is usually not implemented in generic molecular dynamics software, or as fixing some groups of atoms in place, which is undesirable most of the time. In this work, we replace the long-range Coulombic interactions with damped Coulomb interactions, and explore several thermal integration paths. We demonstrate that regardless of the integration path, the same work of adhesion values are obtained as long as the path is reversible, but the numerical efficiency differs vastly. Simple scaling of the interactions is most efficient, requiring as little as 8 sampling points, followed by changing the Coulomb damping parameter, while modifying the Coulomb interaction cutoff length performs worst. We also demonstrate that switching long-range Coulombic interactions to damped ones results in a higher work of adhesion by about 10 mJ/m2 because of slightly different liquid molecule orientation at the solid–liquid interface, and this value is mostly unchanged for surfaces with substantially different Coulombic interactions at the solid–liquid interface. Finally, even though it is possible to split the work of adhesion into van der Waals and Coulomb components, it is known that the specific per-component values are highly dependent on the integration path. We obtain an extreme case, which demonstrates that caution should be taken even when restricting to qualitative comparison.

A Method for Measuring the Surface Free Energy of Topical Semi-solid Dosage Forms.

Our aim was to determine the surface free energy (SFE) of semi-solid dosage forms (SSDFs) by establishing a reproducible method for measuring the contact angle of liquids to SSDFs. Four SSDFs were used: petrolatum, an oil/water (O/W) and a water/oil (W/O) cream, and an alcohol-based gel. The SSDFs were evenly spread on a glass slide, and the change in contact angle over time was measured by dropping water, glycerol, diiodomethane and n-hexadecane as the test liquids. Depending on the combination of test liquid and SSDF, the contact angle was either constant or decreased in an exponential manner. Contact angles may have decreased in an exponential manner because the reaction between the test liquid and the SSDF altered the interfacial tension between the two phases and changed the surface tension of the test liquid and the SFE of the SSDF. The contact angle of the test liquid to the SSDF could be determined reproducibly using the initial contact angle immediately after dropping the liquid on the SSDF as the contact angle before reaction. Using the obtained contact angles and the Owens-Wendt-Rabel-Kaelble equation, we calculated the SFE and its component for the SSDFs tested and found that the results reflect the physicochemical properties of SSDFs. Furthermore, the work of adhesion (WA) of the SSDF to Yucatan micropig skin was calculated using the SFE for the SSDFs. Interestingly, the WA values for all SSDFs tested were comparable.

Surface free energy and wettability properties of transparent conducting oxide-based films with Ag interlayer

ITO, ZTO, AZO and Ag are commonly used in transparent conducting oxide (TCO)/metal/TCO electrodes to form multilayered thin films on a suitable substrate. A detailed surface free energy (SFE) knowledge of these films is critical to design desirable TCO-based sandwich structures. In this study, TCO/Ag/TCO multilayer thin films were coated onto glass substrates using ITO, ZTO, AZO and Ag targets by magnetron sputtering. The wettability properties of TCO, Ag interlayer and TCO/Ag/TCO were evaluated by contact angle measurements of seven different liquids having various surface tension values. The dispersive and polar components of SFE were calculated using geometric and harmonic mean approaches. The acidic and basic components of SFE were calculated using van Oss-Chaudhury-Good method. Following this, the work of adhesion values between TCO films and Ag interlayer were estimated using SFE values of the films. The results show that the SFE components of the surfaces differ depending on the TCO type, the total SFE values of TCO/Ag/TCO films were lower than that of TCO films, and AZO/Ag adhesion is stronger than the other TCO/Ag structures. The reasons behind these differences were discussed by evaluating the SFE, XRD, AFM and SEM analysis simultaneously.

A Criterion for the Effective Work of Adhesion in Loading and Unloading of Adhesive Soft Solids from Rough Surfaces

Recently, Dalvi and co-authors have shown detailed experimental data of adhesion of soft spheres with rough substrates with roughness measured down to almost the atomic scale, finding that the Persson and Tosatti theory gave satisfactory predictions of the apparent work of adhesion during loading, once the increase of the surface area due to roughness is correctly computed at extremely small scales. We show that unloading data would show similar correlation with the Persson–Tosatti’s simple criterion, but for a much larger effective work of adhesion, which therefore becomes not an “intrinsic” property. This suggests either strong hysteresis even at apparently very low peeling velocities or the need to use a criterion that has different behavior during loading and unloading. We attempt this inspired by the results of Guduru for a simple case of axisymmetric waviness, and a much better fit of the experimental data by Dalvi and co-authors is obtained using the entire set of data at loading and unloading, even assuming a single work of adhesion value. However, we cannot rule out that both (viscoelastic) and (roughness-induced) enhancement effects coexist in these data.

Improvement of Post CMP Cleaning Efficiency through Surface Energy Optimization and Use of Viscoelastic Fluids

The chemical and mechanical actions of the CMP process to achieve planarization and material removal also affect the defectivity and post cleaning requirements spontaneously. The wafer surface is cleaned from the excessive chemicals and the slurry particles from the post CMP operations through utilization of the fundamentals of colloids and surface chemistry. The problem of attachment of the slurry particles on the wafer surface is becoming a more severe yield issue, as the microelectronic device dimensions keep decreasing continuously. Furthermore, in integrated circuit fabrication, over 50% of the yield losses occur because of the insufficient cleaning of the wafers [1]. To address the challenges of the post CMP cleaning, this study focuses on the correlation of the surface energy of the wafer post CMP to the particle count remaining on the wafer surface for the oxide surfaces as a model approach. To study the effects of surface nature of the substrate, measurements of surface roughness, contact angle, surface energy, and surface charge of the glass slides were measured and compared to the particle count on the wafers post CMP cleaning treatment. To study the particle retention on the surface, particle removal experiments were conducted in a rinsing flow cell and a siphoning flow cell by implementing impinging jet (rinsing) flow and siphoning flow, respectively. Consequently, better post CMP cleaning formulations were suggested for the oxide-based CMP applications with optimal surface energy conditions fulfilled. The surface free energy and the work of adhesion values were observed to correlate with the surface roughness of the substrates such that, as the surface roughness values increased, the surface free energy and work of adhesion values also increased. As the surface free energy increases, it becomes more difficult to remove particles from the surface without damaging the surface quality. Therefore, water becomes insufficient for removal of particles that remained on the surface. Therefore, a new method of post CMP cleaning is proposed that utilizes viscoelastic fluids to increase the removal of surface particles by taking advantage of the additional elastic stresses that are induced on the particles [2]. After coating the substrate surface with slurry particles, polymeric solutions with 0.7 wt% PAM and with 0.5 wt% PEO were used as the viscoelastic fluid. The optimum amount of polymeric solution was determined to be 40. The CMP-treated glass slides were fully coated and tested for the percent removal of particles. After conducting the siphoning flow experiment, multiple images were taken at 30 FPS (frames per second), and these images were analyzed to conduct particle removal analyses. The use of viscoelastic fluids was observed to increase the removal of particles due to the drag force from the elastic stresses that were applied on the particles by the viscoelastic fluids.

Cooptimization of Adhesion and Power Conversion Efficiency of Organic Solar Cells by Controlling Surface Energy of Buffer Layers

Here, we demonstrate the cooptimization of the interfacial fracture energy and power conversion efficiency (PCE) of poly[N-9'-heptadecanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)] (PCDTBT)-based organic solar cells (OSCs) by surface treatments of the buffer layer. The investigated surface treatments of the buffer layer simultaneously changed the crack path and interfacial fracture energy of OSCs under mechanical stress and the work function of the buffer layer. To investigate the effects of surface treatments, the work of adhesion values were calculated and matched with the experimental results based on the Owens-Wendt model. Subsequently, we fabricated OSCs on surface-treated buffer layers. In particular, ZnO layers treated with poly[(9,9-bis(3'-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] (PFN) simultaneously satisfied the high mechanical reliability and PCE of OSCs by achieving high work of adhesion and optimized work function.

Design and in vitro evaluation of tenofovir-loaded vaginal gels for the prevention of HIV infections

Infection with the human immunodeficiency virus (HIV) is affecting women disproportionally with increasing incidence rates over the last decades. Tenofovir is one of the most commonly used antiretroviral agents, which belongs to the nucleoside/nucleotide reverse transcriptase inhibitor family, for the prevention of HIV acquisition. In scope of this study, a thermogelling system containing tenofovir-loaded chitosan nanoparticles for the controlled release of tenofovir was developed and characterized. The in vitro release studies have shown that the burst release effect was decreased to 27% with f-TFV CS NPs-Gel. Gelation temperature of developed formulation was found as 26.6 ± 0.2 °C, which provides ease of administration while gelation occurs after the administration to the vagina. The work of adhesion values was used as parameters for comparison of mucoadhesive performance and the mucoadhesion of f-TFV CS NPs-Gel was found as 0.516 ± 0.136 N.s at 37 °C. The biocompatibility of blank formulations was evaluated by cell viability studies using L929 cells, in which Gel + CS NPs formulation was found to be safe with 82.4% and 90.2% cell viability for 1:16 and 1:32 dilutions, respectively. In conclusion, an improved tenofovir containing vaginal gel formulation was successfully developed and evaluated for preventing HIV transmission.

A Detailed Molecular Dynamics Simulation and Experimental Investigation on the Interfacial Bonding Mechanism of an Epoxy Adhesive on Carbon Steel Sheets Decorated with a Novel Cerium-Lanthanum Nanofilm.

The influences of steel surface treatment by a novel cerium-lanthanum (Ce-La) nanofilm on the adhesion mechanism of an epoxy adhesive were studied through experimental and modeling approaches. The surface morphology and microstructure of the film deposited were characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). The surface free energy and work of adhesion values were evaluated through contact angle analysis. Also, the interfacial adhesion strength between the epoxy adhesive and steel surface, together with failure forms, were examined through pull-off test, under dry and wet conditions, and Fourier transform infrared (FT-IR) spectroscopy. The results obtained from experiments revealed that depositing a Ce-La nanofilm on the steel surface increased its roughness and surface free energy, and strengthened the epoxy coating adhesion. It was also observed that the epoxy adhesion on the Ce-La treated steel was stronger, compared to the Ce-treated surface. Furthermore, the adhesion extent and surface bonding mechanism of aminoamide-cross-linked epoxy resin were computationally modeled by applying atomistic molecular dynamics (MD) and electronic density functional theory (DFT) methods. The modeling results evidenced that epoxy resin adhered more strongly to the conversion layer (represented by CeO2 and La2O3), compared to an untreated steel surface (i.e., pure and oxidized iron). The epoxy binding onto CeO2(111), La2O3(001), Fe2O3(110), and Fe3O4(100) almost occurred via electrostatic interactions, while its adhesion mechanism over FeO(100) and Fe(110) surfaces was based on van der Waals forces. The computations also demonstrated that the epoxy adsorption energy decreased in wet environments, because of solvent affinity toward the epoxy and the surface, but the rate of reduction was smaller over CeO2 and La2O3, compared to that observed with iron oxides. These modeling outcomes were consistent with our experiments and proposed the superior epoxy adhesion on modified steel sheets.

Prospects of the evaluation of adhesive interaction via chemical force microscopy

The adhesive interaction of some polymer surfaces with neutral, acidic, and basic samples formed on a cantilever specimen has been evaluated via atomic-force microscopy. The thermodynamic work of adhesion has been calculated using the Johnson–Kendall–Roberts model. The differences in the work of adhesion values obtained in the interaction of acidic, basic, and neutral samples with the same polymer surface have been found. The experimentally obtained values of work of adhesion have been carefully compared with theoretically calculated ones, which allowed the conclusion to be drawn that the area of research under consideration is promising.

Acid functionalized cellulose nanocrystals and its effect on mechanical, thermal, crystallization and surfaces properties of poly (lactic acid) bionanocomposites films: A comprehensive study

This work reports the fabrication of four varieties of cellulose nanocrystals(CNCs) through hydrolysis with different acids which leads to their tailored physical, structural, thermal and surface characteristics. The hydroxyl groups of CNCs are substituted with anionic-moieties from acid which alters its interfacial interaction with PLA matrix, as predicted from dispersion surface energy and work of adhesion values. Interestingly, tunable aspect ratios of various acid-derived CNCs have substantial effect on mechanical reinforcing-efficiency and thermal behavior of nanocomposites. CNCs with high aspect ratio improved the elastic modulus of nanocomposites whereas with low aspect ratio accelerated the crystallization rate. The different acid-derived CNCs shows heterogeneous nucleation-driven crystallization phenomenon with propagation of PLA spherulites in three dimensions. Lauritzen-Hoffmann parameters shows that growth of PLA crystals are restricted requiring higher activation-energy to initiate nucleation process. Therefore, this study provides an alternative approach of selecting the appropriate acid-hydrolyzed CNCs for fabrication of CNC-reinforced polymeric nanocomposites with desired properties.

Characterization of Nickel Aluminide Formed on Ni-Based Superalloy 690 Substrate, First-Principle Ni(Cr)/NiAl Interface Simulations and Stability of Aluminide in Aggressive Environment in Pre-oxidized State

Pack aluminization of Ni-based superalloy 690 substrates in low-Al pack at 1273 K resulted in formation of NiAl on the topmost surface and nickel aluminides as adjoining layers. Cross-sectional transmission electron microscopy of NiAl revealed formation of nanoparticles of NiAl. Adherence test conducted at 3 N load along the cross-section of aluminized substrate did not exhibit any peeling off at the interlayer. First-principle calculations performed on Cr-doped Ni(111)/NiAl(110) interface showed an ideal work of adhesion value of 3524 mJ/m2 indicating fairly strong adhesion. SEM–EDS analysis along the cross-section of aluminized and oxidized (1273 K in air) substrate revealed formation of aluminium oxide on nickel aluminide. SEM–EDS analysis of oxidized nickel aluminide layer that was exposed to borosilicate melt at 1248 K for 192 h revealed fairly good stability of aluminide but presence of some phase comprising Al, Ni, O, Cr at certain locations of aluminide/glass interface was noticed.

Surface characterization of structural and stereo isomeric amino acids using sorption techniques and Raman spectroscopy

Event Abstract Back to Event Surface characterization of structural and stereo isomeric amino acids using sorption techniques and Raman spectroscopy Daniel Burnett1, Majid Naderi1, Anett Kondor1 and Manaswini Acharya1 1 Surface Measurement Systems, Ltd., United States Introduction: Amino acids are found in proteins and enzymes, which perform essential roles in nature. Different forms of compounds are known to have different physiological and therapeutic effects and therefore various effective methods are required to provide insight in their physical properties.[1] Considering that hydration is a major factor in determining the structural and isomeric forms of amino acids, the interaction with water vapor would provide fundamental information. Materials and Methods: Alanine samples were obtained from Across Organics. A unique combination of a fiber optic Raman probe with Dynamic gravimetric Vapor Sorption (DVS) was used to monitor the real-time transformation of different forms of Alanine. The sample was exposed to a particular RH while monitoring the change in mass. In-situ Raman spectra were collected during sorption experiments. Total surface free energies of different forms of Alanine were determined using IGC-SEA (Surface Measurement Systems Ltd.). IGC-SEA provides surface energy profiles of particulate/fibrous samples unlike conventional techniques which only yield a single average valued property. Results and Discussion: The combined water sorption/Raman spectroscopy results for ß-Alanine and DL-Alanine show significant characteristics in the region 800 – 1600 cm-1 for both materials. There are no changes in the Raman bands of ß-Alanine during the sorption process up to 90% RH. However, after the 90% RH stage and during the desorption stage the Raman Spectra show irreversible changes in ß-Alanine structure. The water sorption data for DL-Alanine indicates a relatively low uptake and confirms a stable material in agreement with the Raman spectrum. The difference of 125× in moisture uptake levels is attributed to water absorption into the bulk of ß-Alanine, which causes a phase change in ß-Alanine, whereas in the case of DL-Alanine there is no phase or structural changes. The dispersive and specific surface energy profiles at 0% RH indicate ß-Alanine has the higher total surface energy, thus is the most active and have higher affinity for water. At 90% RH, the acid-base surface energy of both samples is increased while the dispersive surface energy did not change significantly. Thus, the polarity, for both alanine samples increases with the relative humidity due to an increase in the acid-base surface energy of both samples. The wettability as the measure of the intermolecular interaction between the solid sample and water can is determined by the thermodynamic work of adhesion with water molecules (Figure 1). The higher work of adhesion shows higher the wettability (more hydrophilic). It is clearly observed that the wettability of both alanine samples increases with the RH, but the increase is more significant in the case of the ß-Alanine. Figure 1. Wettability of (a) DL-Alanine and (b) -Alanine at 0% RH (blue) and 90% RH (red). The work of adhesion values were calculated at 0.005 surface coverage (n/nm). Conclusions: IGC-SEA was able to measure the significant differences in surface chemistry for the ß-Alanine and DL-Alanine at 0 and 90% RH. These results correlate directly with water sorption behavior. The combination of gravimetric vapor sorption with Raman spectroscopy and IGC-SEA allows for better understanding of vapor-induced structural changes of biologically active ingredients.

Work of adhesion between resin composite cements and PEEK as a function of etching duration with sulfuric acid and its correlation with bond strength values

ObjectiveThis study investigated the impact of sulfuric acid etching duration of PEEK on work of adhesion (WA) with resin composite cements, and compared additionally measured surface parameters to shear bond strength (SBS) results. MethodsPEEK specimens were fabricated and divided according to different etching times using 98% sulfuric acid (N=448/n=54): 0, 5, 15, 30, 60, 90, 120 or 300s, respectively. The resin composite cements RelyX ARC, Variolink II and Clearfil SA Cement (N=54/n=18) were smoothed on a glass plate. The sessile drop method was applied in all contact-angle measurements; distilled water and diiodomethane served as testing liquids. Overall 1350 single contact angle measurements were performed. Thereafter, surface free energy (SFE), WA, interfacial tension (IFT) and spreading coefficient (SC) of all combinations between etched PEEK and resin composite cements were calculated. Data were statistically analysed using Kolmogorov–Smirnov, Shapiro–Wilk tests, descriptive statistics and two-/one-way ANOVA with post-hoc Scheffé test (p<0.05). Using Pearson correlation the association between SFE values and SBS results of a previous study was investigated. ResultsVariolink II showed the lowest WA, followed by RelyX ARC and Clearfil SA Cement, respectively. Etching specimens for 60s showed the lowest WA values while etching times between 0s and 30s, and 300s showed higher results. WA values for groups etched for 90s and 120s showed no differences when compared to the 60s groups. SFE and disperse percentage showed a positive correlation with SBS. A negative correlation was observed between SBS and polar percentage for etched PEEK, WA, IFT and SC. ConclusionsThe WA values do not allow statements about the bond between two materials to be made; other parameters must be taken into account. A waiver of conventional bond test methods is not possible.

Development of Promethazine Hydrochloride Mucoadhesive Patches for Buccal Delivery: In vitro, Ex vivo and In vivo Characterization

Promethazine hydrochloride (PMZ HCl), an antiemetic, undergoes extensive first-pass metabolism (bioavailability 25%). The purpose of the present investigation was to develop mucoadhesive patches for transbuccal delivery of PMZ HCl using solvent casting technique with Hydroxy ethyl cellulose (Natrosol 250 E) and hydroxylpropyl methyl cellulose as mucoadhesive polymers and propylene glycol as the plasticizer and evaluate their physicochemical characteristics, in vitro drug release, moisture absorption, surface pH, mechanical properties, in vitro bioadhesion, in vivo residence time, and ex vivo drug permeation through porcine buccal membranes from optimized buccal patch and stability studies. The physicochemical interaction between PMZ HCl and polymers was investigated by Fourier Transform Infrared Spectroscopy. Ex vivo drug permeation through porcine buccal membrane was performed and 83.7% of the drug permeated in 6 hours with flux 0.19 mg h–1cm–2. The optimized formulation AA4 showed maximum drug release (98%) in 6 hours in the Higuchi model release profile. Moisture absorption, surface pH, tensile strength, elongation at break, peak detachment force and work of adhesion values of the optimized formulation were found to be 68.1%, pH 6.7, 12.3 kg/mm2, 69.2 % mm2, 7.5 N and 2.73 mJ respectively. Formulation AA4 showed 77.6% of the drug permeated through porcine buccal membrane in 6 hours and flux calculated to be 0.45 mg h–1cm–2. FTIR studies showed no evidence of interaction between the drug and polymers. In vivo mucoadhesive behaviour of the optimized formulation was studied in healthy human volunteers and subjective parameters were evaluated. The stability of the optimized formulation was studied and no significant changes were detected in drug content, in vitro release and ex vivo permeation after 6 months.

Work of Adhesion of Thin Spray-On Liners

The interface property known as work of adhesion incorporates both adhesion and effective bond width, which are two important design parameters in thin spray-on liner (TSL) support design. The value of this parameter is yet to be recognized by the mining industry and liner manufacturers. The importance of this parameter is introduced in this study. A new methodology using pull-out load–displacement data was developed to calculate the work of adhesion between a TSL and a substrate. Tests were performed using Tekflex as a liner material, which was applied to concrete, granite or sandstone substrate. It was found that a Tekflex liner, when sprayed onto substrates, will likely have work of adhesion values around 777–973 N/m depending on the type of substrate. In addition, for the first time in TSL literature, an effective bond width calculation is introduced in this study. It was found that Tekflex has average effective bond width of 0.7 mm on different substrates. Liner manufacturers should measure and document work of adhesion for their products on a standard substrate.

Effects of Nanoparticle Coverage on the Adhesion Properties of Emulsion Aggregation Toner Particles

Toner is a critical material in printing and copying processes. Compared to the conventional pulverized toner, polymerized emulsion aggregation (EA) toner provides more precise control over the shape and surface roughness of particles. Due to its roundness and low surface roughness, the near-spherical EA toner appears to adhere more strongly to flat substrates, which is desirable for efficient toner transfer and development. However, in the cleaning and transport processes, due to enhanced adhesion, it is difficult to remove the residual EA toner from surfaces of the photoreceptor and transport belt. To reduce the adhesion of the EA toner in a controllable manner, the surfaces of the toner particles are coated with silica nanoparticles with a diameter range of 15&#x2013;32 nm. In the current study, a technique based on the rolling resistance moment of the particle-substrate adhesion bond is utilized for quantifying the effect of nanoparticle surface coating on the adhesion of individual toner particles. With the aid of a custom-made nanomanipulation system, an increasing lateral pushing force was applied to an individual toner particle adhered to a silicon substrate while the pre-rolling and rolling motions of the particle in response to the lateral pushing force were recorded. The work of adhesion between the toner particle and silicon substrate was extracted from the corresponding lateral force-particle displacement curve. The technique was used to characterize the adhesion properties of both uncoated (bare) and nanoparticle-coated model toner particles with a specified surface area coverage of 50%. It is found that the work of adhesion values between the surface-coated experimental toner particles and the silicon substrate are almost an order of magnitude lower than those for the bare ones.

Effects of Nanoparticle Coating on the Adhesion of Emulsion Aggregation Toner Particles

Toner is a key material for the xerographic printing and copying industry. Compared to conventional pulverized toner particles, emulsion aggregation (EA) toner particles could adhere more strongly to substrates and their property distributions are narrower because of their near-perfect spherical shape and higher surface free energy. However, in general, uncoated EA toner is more difficult to transfer and clean during printing/copying processes for the same reasons. Nanoparticle additives could be used as control agents to reduce the toner particle–substrate adhesion. In order to optimize their adhesion and handling performances, an accurate adhesion characterization of the toner particles coated with different levels of additives is required. In current study, two non-contact adhesion characterization techniques based on acoustic air-coupled excitation and ultrasonic base excitation are presented. Their use for the adhesion characterization of individual bare toner particles with an average diameter of 6.0 μm on silicon substrates, and their silica nanoparticle coated variants with a surface area coverage (SAC) of 50% is demonstrated. The techniques are based on the detection of the resonance frequencies of rocking motion of micro-spheres. The out-of-plane transient displacement responses of the rocking particles are captured by a laser interferometer, and the natural frequencies of particle rocking motion obtained from transient displacements at the top of particles and the substrate are related to the strength of the adhesion bond. It is reported that the work of adhesion values of the 50% SAC-coated toner on silicon substrates are almost an order of magnitude lower than those for the bare ones.

Mucoadhesive and antioxidant activity of low-thiosulfinate Allium extracts

The purpose of this study was to evaluate the composition, antioxidant and mucoadhesive properties of extracts of onions that are used in human nutrition: onion (Allium cepa L.), garlic (Allium sativum L.), leek (Allium porrum L.) and bear garlic (Allium ursinum L.), with reduced content of thiosulfinates, important antioxidant constituents [1]. Extracts were prepared by blending fresh bulb or leaves of onions with aqueous or 20% ethanolic solution, pH=3, which inactivates allinase [2], followed by freeze-drying. Total phenols, thiosulfinates, thiols as well as sugars were determined. For investigation of antioxidant activity two tests were employed: scavenging activity for DPPH free radical and reductive power assay. Among the extracts, aqueous extracts of garlic bulbs was richest in thiosulfinates (93.7µmol/g, expressed as allicin) and thiols (48.6µmol/g, expressed as cystein). Although thiosulfinate content was greatly reduced, the extracts demonstrated notable antioxidant activity in both tests. The most active DPPH radical scavenger was the ethanolic extract of leek leaf with EC50 of 2.1mg/ml. The same extract exhibited the strongest reducing power. However, its activity was significantly lower than the activity of positive controls: butylated hydroxyanisol and ascorbic acid. In general, extracts made of leaves were stronger antioxidants than extracts made of bulbs. There was also positive correlation (r2=0,70) between antioxidant activity and thiol content in the extracts which implicates that these compounds may play an important role in overall antioxidant activity of onions. To determine mucoadhesive properties of prepared extracts tensile studies were performed and work of adhesion values were measured. The results clearly showed that all the extracts tested had mucoadhesive characteristics. The most pronounced mucoadhesive properties were determined for aqueous extract of bulbs of A. sativum and A. ursinum.

Rapid Gel Formation and Adhesion in Photocurable and Biodegradable Block Copolymers with High DOPA Content

Marine mussels anchor to a variety of surfaces in turbulent intertidal zones through the use of adhesive plaques formed from hardened mussel adhesive proteins (MAPs). It is believed that 3,4-dihydroxyphenylalanine (DOPA) imparts both water-resistant adhesive characteristics and rapid curing ability to MAPs. In this paper, DOPA-modified triblock copolymers were synthesized and used to form adhesive hydrogels. Amphiphilic block copolymers with DOPA content as high as 10 wt % were prepared, and aqueous solutions of the polymers rapidly (<1 min) formed hydrogels by photopolymerization of methacrylate end groups attached to the hydrophobic segments. Contact mechanics adhesion tests were performed on the photocured hydrogels, and it was shown that incorporating DOPA into the polymer structure significantly enhanced work of adhesion to titanium surfaces submerged in an aqueous medium. Work of adhesion values as high as 410 mJ/m2 were recorded for polymers containing 10 wt % DOPA, although the introduction of Lys...