Assessment of adhesion and autoadhesion forces between particles and surfaces. Part II. The investigation of adhesion phenomena of Salmeterol Xinafoate and lactose monohydrate particles in particle-on-particle and particle-on-surface contact

The centrifuge technique has been used to compare particle-on-particle and particle-on-surface adhesion with Salmeterol Xinafoate particles on single lactose particles or compacted lactose surfaces. The results from particle-on-particle and particle-on-surface adhesion measurements are not equivalent in terms of median adhesion force. The assessment of adhesion using either particle-on-particle or particle-on-surface systems depends on the process on which information is required: e.g. mixing problems are better investigated by applying the particle-on-particle technique, whereas surface transport problems such as powder compaction or flow can be more appropriately studied using particle-on-surface measurements. Taking autoadhesion measurements from the previous study into account, adhesion and autoadhesion forces were found to allow the prediction and choice of mixture components for powder blends. The results suggest that the homogeneity of such a powder blend depends both on thermodynamic properties and on the adhesion and autoadhesion properties of the single components.     

A test method for determining adhesion forces and Hamaker constants of cementitious materials using atomic force microscopy

A method for determining Hamaker constant of cementitious materials is presented. The method involved sample preparation, measurement of adhesion force between the tested material and a silicon nitride probe using atomic force microscopy in dry air and in water, and calculating the Hamaker constant using appropriate contact mechanics models. The work of adhesion and Hamaker constant were computed from the pull-off forces using the Johnson–Kendall–Roberts and Derjagin–Muller–Toropov models. Reference materials with known Hamaker constants (mica, silica, calcite) and commercially available cementitious materials (Portland cement (PC), ground granulated blast furnace slag (GGBFS)) were studied. The Hamaker constants of the reference materials obtained are consistent with those published by previous researchers. The results indicate that PC has a higher Hamaker constant than GGBFS. The Hamaker constant of PC in water is close to the previously predicted value C₃S, which is attributed to short hydration time (≤ 45 min) used in this study.     

Measurement of the adhesion and removal forces of submicrometer particles on silicon substrates

In this study, the magnitude of the applied removal force and its relationship to the theoretical adhesion force is determined. The removal is done through the application of known hydrodynamic drag and lift forces on submicrometer particles. The hydrodynamic removal forces are then correlated with the removal percentage and the adhesion forces. A useful correlation that can be used to determine the adhesion force from the known applied removal force and the removal percentage is presented. Below 90% removal, the data indicate a linear relationship between the removal force and the removal percentage. The effects of time on the adhesion force and particle deformation are also presented.     

Direct evidence on reduced adhesion of Salbutamol sulphate particles due to L-leucine coating

Attractive van der Waals forces are responsible for unwanted agglomeration of fine dry powder particles which can cause problems e.g. with inhalable drugs in the treatment of asthma. In this article we report on experimental evidence of reduced adhesion of salbutamol sulphate particles when they are coated with L-leucine. Particle production and coating was performed using an aerosol flow reactor. The L-leucine-containing particles were fully covered with L-leucine as evidenced by X-Ray Photoelectron Spectroscopy and Scanning Electron Microscopy findings. With a suitable concentration of precursor solution the particles become rough and adhesion diminished to one fifth of the adhesion of uncoated particles. The main reason for this reduced adhesion was an increase in surface roughness, which reduced the contact area and the number of contact points thus increasing the effective separation between particles.     

Determination of the adhesion force between particles and a flat surface, using the centrifuge technique

By using a centrifuge technique, the influence of powdery material particle size on the adhesion force particle-surface was determined. In order to achieve this, the adhesion of phosphatic rock (ρ_p = 3.090 kg m^− 3) and of manioc starch particles (ρ_p = 1.480 kg m^− 3) on a steel surface were studied. A microcentrifuge that reached a maximum speed rotation of 14000 rpm and which contained specially designed centrifuge tubes was used. There tubes contained the flat surface where the test particles were deposited. The powder particles were dispersed on these disks and the particles detachment were performed using diverse centrifugal speeds. The graphics of particle percentages still adhering on the surface of the disks as a function of the applied detachment force showed that the profile of adhesion force followed a log-normal distribution. The adhesion force increased with particle size. The manioc starch particles presented adhesion forces greater than those for the phosphatic rock particles for all particle sizes studied. The results obtained were compared with the theory proposed by Derjaguin, Muller and Toporov whose theoretical adhesion presented values close to the experimental data for the phosphatic rock particles adhesion on the stainless steel surface. On the contrary, the theoretical values were lower than the experimental ones for the manioc starch particles maybe due to the small roughness of these particles, their physical properties (softer and deformable material) and/or specific chemical interactions since the organic composition of the manioc starch particles that can dominate the adhesion force. Finally, the separation distance among the surfaces in contact (Z₀) was estimated in approximately 1.0 × 10^− 9 m for the phosphatic rock and 5.0 × 10^− 10 m for the manioc starch. These results were weakly dependent on the particle size range.     

On the low frequency dielectric behavior of carboxymethyl cellulose and its sodium salt

A dielectric dispersion and frequency loss peak within the low frequency range 0.05–1 kc/s and at temperatures of 283–333 K was observed in the case of the sodium salt of carboxymethyl cellulose and absent in the case of its acid form. The critical frequency of the dielectric absorption was independent of molecular weight and of the presence of low moisture content. The results obtained show that the variation with temperature of the dielectric constant is exponential at low frequency only in the case of the sodium salt of carboxymethyl cellulose. The significance of the results is discussed.     

A model of fine particles deposition on smooth surfaces: II—Comparison with experimental data and simplified models

The application of a model of fine particles initial deposition from a flowing suspension on smooth surfaces is discussed by comparison with literature experimental data and simplified models (Leveque equation). The model and its original features, including an accurate account of particle-surface interactions and ad hoc solution techniques, with special emphasis on the treatment of boundaries, have been thoroughly presented in Part I. The model demonstrates that in many circumstances diffusion is the limiting mechanism so that simple models based on a continuous approach (through particles concentration) together with perfect sink assumption are accurate enough. Departures from such circumstances are identified by means of a parametric study based on our model. The comparison with the experimental data also suggests additional characterizations needed for future experimental investigations.     

The relationship between particulate properties of carrier materials and the adhesion force of drug particles in interactive powder mixtures

The influence of particle size, shape, and particle surface roughness of lactose monohydrate carrier particles on the adhesion properties of drug particles in interactive powder mixtures similar in quality of a commercial product (Serevent Diskhaler^®) has been investigated. None of the ten lactose monohydrate batches tested was found to be similar in terms of particle size. To obtain more information about particle shape and surface roughness, mathematical analysis was undertaken to structure the data. The lactose monohydrate batches could be split into four different types of particle shape. In terms of particle surface roughness, as measured by a laser profilometer, three different roughness categories were identified. Two sets of mixtures were prepared to relate the physical properties of the lactose monohydrate particles to the adhesion properties of the drug formulations: (a) constant mixing time and speed (25 min, 42 rpm), and (b) optimal mixing time (speed 42 rpm) to match the adhesion properties of the Serevent Diskhaler^®. All ten lactose monohydrate batches provided different adhesion properties under test condition (a) and the optimum mixing time [test condition (b)] was also different for each batch. Multivariate data analysis showed that the adhesion force between drug and lactose monohydrate increases with a decrease in particle size and for more irregularly shaped, elongated carrier particles. The effect of surface roughness could only be qualitatively assessed and thus no definitive conclusions can be drawn to judge whether adhesion will increase or decrease as surface roughness changes.     

Effects of cure levels on adhesion between rubber and brass in the composites made up of rubber compound and brass-plated steel cord

The adhesion between rubber compound and brass-plated steel cord of rubber-brass composites with different cure levels was investigated in relation to the formation and growth of their adhesion interphase examined with AES spectroscopy. The optimum-cured adhesion sample showed a maximum pullout force, but the pullout forces of samples under-cured and over-cured were low. The adhesion property of under-cured adhesion samples enhanced with humidity aging due to further curing of rubber and supplementary growth of the adhesion interphase. Cure level exhibiting good adhesion was discussed based on the composition and structure of the adhesion interphase and the crosslinking density of the rubber layer attached to the interphase. This paper is dedicated to Professor Hyun-Ku Rhee on the occasion of his retirement from Seoul National University (Gon Seo).     

Simultaneously improved actuated performance and mechanical strength of silicone elastomer by reduced graphene oxide encapsulated silicon dioxide

Herein, graphene oxide (GO)-encapsulated silica (SiO₂) hybrids (GO@SiO₂) were prepared via electrostatic self-assembly of the 3-aminopropyltriethoxysilane (APS)-modified SiO₂ and GO. The as-prepared GO@SiO₂ was introduced into polydimethylsiloxane (PDMS) elastomer to simultaneously increase the dielectric constant (k) and mechanical properties of PDMS. Then, the in situ thermal reduction of GO@SiO₂/PDMS composites was conducted at 180°C for 2 h to increase the interfacial polarizability of GO@SiO₂. As a result, the values of k at 1000 Hz are largely improved from 3.2 for PDMS to 13.3 for the reduced GO@SiO₂ (RGO@SiO₂)/PDMS elastomer. Meanwhile, the dielectric loss of the composites remains low (<0.2 at 1000 Hz). More importantly, the actuated strain at low electric field (5 kV/mm) obviously increases from 0.3% for pure PDMS to 2.59% for the composites with 60 phr of RGO@SiO₂, an eightfold increase in the actuated strain. In addition, both the tensile strength and elastic modulus are obviously improved by adding 60 phr of RGO@SiO₂, indicating a good reinforcing effect of RGO@SiO₂ on PDMS. Our goal is to develop a simple and effective way to improve the actuated performance and mechanical strength of the PDMS dielectric elastomer for its wider application.     

Comparison of slow sand filtration and microfiltration as pretreatments for inland desalination via reverse osmosis

A pilot study was conducted from October 2007 to November 2010 to establish the long-term feasibility of using reverse osmosis (RO) treatment to manage salt levels in Central Arizona Project water. Pretreatments consisting of microfiltration (MF) and slow sand filtration (SSF) were compared based on performance—turbidity removal, silt density index (SDI), volume treated between cleaning events and protection of downstream RO—during side-by-side operation over a yearlong period. SSF always produced feed water that was suitable for RO treatment (SDI < 5). However, MF consistently provided filtrate with SDI < 3, and long-term RO performance improved significantly with MF as pretreatment. Although the economic costs of MF and SSF pretreatments are similar; MF is preferred based on the quality of treated water and stability of downstream RO operation.