Lifshitz Van Der Waals Acid Base Research Articles

Surface Properties of the Polyethylene Terephthalate (PET) Substrate Modified with the Phospholipid-Polypeptide-Antioxidant Films: Design of Functional Biocoatings.

Surface properties of polyethylene terephthalate (PET) coated with the ternary monolayers of the phospholipid 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), the immunosuppressant cyclosporine A (CsA), and the antioxidant lauryl gallate (LG) were examined. The films were deposited, by means of the Langmuir-Blodgett (LB) technique, on activated by air low temperature plasma PET plates (PETair). Their topography and surface chemistry were determined with the help of atomic force microscopy (AFM) and time-of-flight secondary ion mass spectrometry (TOF-SIMS), respectively, while wettability was evaluated by the contact angle measurements. Then, the surface free energy and its components were calculated from the Lifshitz-van der Waals/Acid-Base (LWAB) approach. The AFM imaging showed that the Langmuir monolayers were transferred effectively and yielded smoothing of the PETair surface. Mass spectrometry confirmed compatibility of the quantitative and qualitative compositions of the monolayers before and after the transfer onto the substrate. Moreover, the molecular arrangement in the LB films and possible mechanisms of DOPC-CsA-LG interactions were determined. The wettability studies provided information on the type and magnitude of the interactions that can occur between the biocoatings and the liquids imitating different environments. It was found that the changes from open to closed conformation of CsA molecules are driven by the hydrophobic environment ensured by the surrounding DOPC and LG molecules. This process is of significance to drug delivery where the CsA molecules can be released directly from the biomaterial surface by passive diffusion. The obtained results showed that the chosen techniques are complementary for the characterization of the molecular organization of multicomponent LB films at the polymer substrate as well as for designing biocompatible coatings with precisely defined wettability.

Characteristics of Polypeptide/Phospholipid Monolayers on Water and the Plasma‐Activated Polyetheretherketone Support

AbstractPolyetheretherketone (PEEK) is a highly biocompatible polymer widely used in medicine as an implant production material. In this article, the PEEK surface was characterized in terms of its wettabillity properties after the physicochemical modifications by treatment with the low‐temperature air plasma and covering with the Langmuir–Blodgett (LB) monolayers of polypeptide (cyclosporine A, CsA) and/or phospholipid (1,2‐dipalmitoyl‐sn‐glycero‐3‐phosphocholine, DPPC). The LB deposition was preceded by the analysis of miscibility and morphology of monolayers at the air/water interface by means of the Langmuir technique and Brewster angle microscopy (BAM). Then, wettability of the polymer‐supported films was evaluated by the contact angle measurements of three probe liquids of different characters (two polar—water and formamide, one apolar—diiodomethane). The measured contact angles allowed for determination of the surface free energy and its components based on the Lifshitz‐van der Waals/acid–base (LWAB) approach. Some relations between the kind and magnitude of interactions within the model membranes on the water subphase and those of the PEEK‐supported membranes with the liquids were found out. The results allowed obtaining the interesting models of biological coatings with potential applications.

Design and mechanism of the formation of spherical KCl particles using cooling crystallization without additives

Potassium chloride crystals are cubic, which often leads to caking and greatly limits their applications. This caking can be overcome by modifying the crystal shape toward sphericity. Spherical particles have a high anti-caking ability and flowability. In this work, spherical KCl particles were prepared using a simple cooling crystallization process designed to function without additives. Among the four main processes in the crystallization of spherical particles, i.e., nucleation, growth, agglomeration, and attrition, agglomeration is the greatest contributor to the formation of spherical KCl particles, which were prepared following the principle that the adhesion force must be larger than the dispersion force. The adhesion free energy between KCl particles and solvents (i.e., water, n-hexane, formamide, diazomethane, methanol, ethanol, ethyl acetate, ethylene glycol, and dimethyl sulfoxide) was calculated using the Lifshitz–van der Waals acid–base approach, and water was found to be the most appropriate solvent because of its attractive interaction with the crystals. According to the relationship between the adhesion force and dispersion forces, we found that the stirring rate should be lower than 1300 rpm. Additionally, the effects of stirring rate and cooling rate on the KCl products were investigated and optimized, and the optimal conditions were found to be 400–500 rpm and 10–15 min/°C, respectively. All of the spherical KCl products prepared under the optimal conditions show a better morphology, flowability, and anti-caking performance than the original crystals.

Characterisation of acid–base surface free energy components of urea–water solutions

The objective of this study is to determine the Lifshitz–van der Waals/Acid–Base (LW/AB) surface energy components of urea–water-solutions (UWS) for different urea mass fractions. The surface energy parameters are evaluated by ring tensiometry and contact angle measurements of sessile drops placed onto pre-determined solid substrates. Therefore, the energetic characteristics of UWS are evaluated in relation to probe liquids. The results indicate that aqueous solutions of urea become less polar with increasing urea mass fraction while their overall surface tension is also increased. This is attributed to a significant grow of the Lifshitz–van der Waals surface energy component that compensates the reduction of the polar part. In addition, aqueous solutions of urea are characterised by a significant electron donor (γl−) capacity compared to pure water while their electron acceptor parameter (γl+) is reduced. Subsequently, γl+/γl− is continuously reduced with increasing urea concentration. The enhancement of electron-donicity is also reflected to the pH of the solutions while the overall trends are independent from the selection of acid-to-base ratio for pure water. The above findings are related to physicochemical aspects based on molecular and intermolecular interactions.

Surface properties of Ti-6Al-4V alloy part III: Biostability of deposited DPPC monolayer and bilayer

Solid supported lipid layer has been of broad interest for decades. DPPC modified Ti-6Al-4V could be used as dental and orthopedic implants because of excellent mechanical property, corrosive resistance and enhanced biocompatibility. However, to be long time lasting, biostability is also a crucial property of implanted surface. In previous Part I and Part II surface properties of Ti-6Al-4V depending on the surface smoothness (AFM and Profilometry images, wettability) both of bare surface as well with the deposited monolayer and bilayer of DPPC were investigated. In this paper stability of the deposited DPPC layers on Ti-6Al-4V alloy was examined. The plates with the DPPC film were placed in water, phosphate buffer saline, or 1% Triton X-100 solution for 2h at 37°C and then dried in a vacuum desiccator at room temperature over night. Optical profilometer and atomic force microscopy (AFM) were applied to obtain surface topography. From the measured advancing and receding contact angles of water, formamide and diiodomethane, the surface free energy was calculated using Lifshitz-van der Waals/Acid Base (LWAB) and Contact Angle Hysteresis (CAH) approaches. The obtained results exhibited significant changes in the surface structure occurring during these treatments. The most drastic changes were observed for the layers treated with Triton X-100, where in the case of DPPC monolayer it might be completely removed from the surface. The changes in topography reflected also in those of the apparent surface free energy, which were the greatest after the contact with Triton where both the surface of monolayer and bilayer became highly polar. However, the contact with pure water reduced only to some extent the surface free energy of the layers, except for the hydrogen bonding interactions γs− on the bilayer surface.

Surface Properties of Ti-6Al-4V Alloy: Part II: DPPC Monolayer and Bilayer Deposition in Aspect of Wettability

Phospholipids as the principal constituents of biological cell membranes play important roles in cell communication, signal transportation and various intra- and extra-cellular processes. Therefore, they could be prospective modifier for Ti-6Al–4V alloy used as implants. In this research, 1,2-Dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) monolayer or bilayer were deposited on the titanium plate surface using Langmuir-Blodgett and Langmuir-Schaefer (LB/LS) techniques, and spreading method to investigate the change of the surface wettability caused by the deposition. Simultaneously the surface topography was investigated by optical profilometer and atomic force microscopy (AFM). The wettability was investigated by measurement of advancing and receding contact angles of water, formamide and diiodomethane on the deposited DPPC monolayer and bilayer surfaces. Then the surface free energy was calculated applying four approaches, i.e. Lifshitz-van der Waals/Acid Base (LWAB), Contact Angle Hysteresis (CAH), Owens-Wendt (O-W) and Neumann’s equation of state (Eq.State). It is obvious that the films prepared by LB/LS technique are uniform and well-packed, just opposite to those obtained by spreading. This reflects in the surface free energy, which is higher of the DPPC films produced by spreading than by LB/LS technique, which is probably caused by exposure of more DPPC hydrophilic groups outward on the Ti-6Al–4V surface. It appeared that total surface free energy of DPPC bilayer were comparable to that of monolayer. This could be explained by reorganization of DPPC molecule in contact with air atmosphere. However, the electron-donor component was larger suggesting that more polar groups were exposed outward on the bilayer than monolayer surface.

Low-temperature air plasma modification of chitosan-coated PEEK biomaterials

Novel chitosan-coated PEEK biomaterials were prepared by air plasma modification. Low-temperature plasma effect on changes of specific thermal, mechanical and adhesive properties of polyetheretherketone (PEEK) was investigated. The topography and surface roughness of the prepared materials were determined using an optical profilometer. The wetting and energetic properties of biomaterials were studied by means of advancing and receding contact angles measurements and then apparent surface free energy (and its components) were evaluated applying the LWAB (Lifshitz–van der Waals Acid Base) theory and contact angle hysteresis model. After air plasma treatment a fairly hydrophobic character of PEEK was changed to strongly hydrophilic one. Significant differences in the wettability and thermal stability of samples were observed. However, hardly any differences in excellent mechanical properties were noticed. The profilometer images showed an increase in the surface roughness of PEEK modified surface due to the change of cross-link density, elasticity and formation of additional polar groups on the surface. Plasma treated polyetheretherketone surfaces had better adhesive features and stable chitosan coating was created. Modification by chitosan improved antibacterial properties, inherent haemostatics and polymer biocompatibility. These advantages allowed to obtain new attractive biomaterials from the same polymer differing in properties for a wide spectrum of applications, mainly regenerative medicine and orthopedic surgery.

The study of composition and surface electron structure of nitrogen-doped DLC film prepared by PIII-D

Nitrogen-doped diamond-like carbon (N-DLC) films were synthesized by plasma immersion ion implantation and deposition (PIII-D) at room temperature (RT). During the process of deposition, N 2 flow was changed from 0 to 10 sccm. Lifshitz–van der Waals/acid–base (LW-AB) approach was employed to study the surface electronic state of the films, X-ray photoelectron spectroscopic (XPS) and valence band spectra (VBS) were used to study chemical bonds and electron structure information inside the films. Bandgap of the films were calculated by the data from ultraviolet spectrophotometer. The results showed that synthesized films were n-type semiconductors and doping of nitrogen element will affect the accepted–electron capability of the film. The change tendency of the bandgap coincides with that of the ratio of acidic to alkaline component of the polar acid-alkali surface energy. There was much sp hybrid electronic state existed in the films, which mainly sp2 C=C / C=N and sp3 C–C / C–N bonds.

Analysis of the Results of Surface Free Energy Measurement of Ti6Al4V by Different Methods

Surface Free Energy (SFE) of solids should be calculated using theoretical models. The contact angle (CA) measurement on a surface is considered the most practical way to obtain the SFE. The results of five methods based in the models are compared: the method of Zisman (ZI), the geometric mean (GM), the harmonic mean (HM), the Lifshitz-van der Waals/ Acid-Base (LW/AB) and the equation of state (ES). The SFE calculated with GM, HM and LW/AB methods change with the amount and type of liquid used, however, when water, glycerol and dimethyl sulfoxide are used together the SFE and its dispersive and polar components are similar in value for the three methods. In the case of the ES model the values of SFE change with the liquid used; finally using the ZI method the SFE values are 20% lower than the values of SFE obtained with the other methods.

Caking and adhesion free energy of maltitol: Studying of mechanism in adhesion process

Caking is a common phenomenon of maltitol that causes problems of separation, processing and transportation. To study the mechanism of caking, method of capillary rise was used to measure the contact angles between maltitol particles and relevant liquids. Based on the calculation of adhesion free energy of maltitol particles in different liquids by Lifshitz–van der Waals acid-base theory, the relationship between adhesion free energy and the maltitol particles size has been established. It is concluded that the adhesion free energy of maltitol with rinsing liquid plays a key role in caking. When the adhesion free energy is higher than a critical value (about 60mJ/m2), the repulsion between the particles can avoid caking. In general, the adhesion free energy depends on the rinsing liquid used and maltitol particles size. The adhesion free energy increases with increasing the particles size of maltitol and type of liquids (water, ethyl acetate, formamide, ethylene glycol, ethanol, methanol in sequence). Hence, controlling particles size distribution and screening of rinsing liquid are crucial factors to avoid caking.

Influence of metal surface preparation on its surface profile, contact angle, surface energy and adhesion with glass fibre prepreg

Surface preparation of metal plays a vital role to enhance the adhesion of polymer coatings in ensuring the desired performance of metal infrastructure for the oil and gas industry. In this study, a range of techniques for the surface preparation of mild steel were evaluated which included garnet grit blasting, disk sanding, needle gun, flap wheel, strip wheel and wire brush. The surface profile and apparent surface energy parameters such as apparent surface energy, work of adhesion, Lifshitz-van der Waals acid–base components were measured from these trials correlation made with these properties to the metal to polymer coating bond strength and bond failure mode.The dolly pull-off strength was used to quantify the bond strength while the laminate failure area (%) was used to assess the bond failure mode. Based on the testing results, it was found that irrespective of the surface preparation technique used, the dolly pull-off strength and laminate failure area increased with increasing surface profile up to a value of approximately 21µm and both of these properties followed a plateau up to 24μm and then decreased above this surface profile value. The dolly pull-off strength was also seen to increase with the increase of surface energy and work of adhesion and decrease of contact angle. It was found that the maximum adhesion could be attained with three of the four grit sizes of the garnet grit blasting technique which appeared to have achieved the most favourable properties amongst all the surface properties studied here. Wenzel model was found to be in agreement with the values of the surface profile of different surface preparation techniques.

Influence of Volume Drop on Surface Free Energy of Glass

The aim of the research was to determine how the drop size affects the contact angle values and determine its optimal size for further contact angle measurements and comparison of the contact angle values measured for three probe liquids (water, formamide, diiodomethane) on the glass surface using the: sessile drop and tilting plate methods. Next, using the measured contact angles, the total surface free energy and its components were determined from the van Oss et al. (Lifshitz-van der Waals acidbase component, LWAB), Owens-Wendt, Neumann and contact angle hysteresis (CAH) approaches. The studies showed, that drop size is very important for contact angle measurements and consequently, for surface free energy estimation.

Physico-chemical surface properties of microalgae

This study reports a comprehensive set of experimentally measured physico-chemical surface properties of 12 different microalgae including fresh and seawater species of green algae, diatoms and cyanobacteria. The surface free energy and its components including the acid-base (AB), van der Waals (LW), electron donor/acceptor parameters were quantified based on contact angle measurements along with the Lifshitz–van der Waals acid–base approach using the probe liquid surface tension parameters proposed by van Oss et al. as well as by Della Volpe and Siboni. Moreover, the zeta and surface potentials of all species were determined using electrophoretic mobility measurements along with using Smoluchowski's model. Finally, the free energy of cohesion of the microalgae was also determined based on the calculated surface energy properties. The results showed that the electron donor parameter correlated well with the free energy of cohesion in all groups of microalgae. Moreover, species known to form colonies and exhibit benthic cultures had distinctly hydrophobic surfaces compared to microalgae prefering planktonic growth. These results indicate the importance of surface hydrophobicity for causing biofouiling or flocculation of cultures. Finally, the zeta potentials did not show a distinctive trend with the types of microalgae but the surface potentials were markedly larger for the salt water species. The reported methods and data are expected to provide critical information for researchers and technology developers concerned with cell to cell and cell to substrata interactions of microalgae in algal biomass cultivation and harvesting, biofouling of membranes and surfaces, as well as cell-surface interactions in photosynthetic microbial fuel cell technologies.

In vivo measurement of the surface energy of human fingernail plates

The surface energy of the human nail plate is expected to influence the adhesion of microorganisms (and subsequent colonization and infections) as well as that of medicines (and subsequent drug permeation) and of cosmetics. The aim of the study was therefore to measure the surface energy of nail plates in vivo. The surface energy of healthy human fingernails (untreated, hydrated and abraded) and of hoof membranes (often used as a model for the nail plate) was estimated from contact angle measurements of liquids (water, formamide, diiodomethane and glycerol) on the nail plate and subsequent computation using the Lifshitz-van der Waals/acid-base (LW-AB) approach. The surface energy of untreated fingernail plates was found to be 34 mJ m(-2) . Most of this total energy was from the apolar Lifshitz-van der Waals component. When the polar component of the surface energy was analysed, the electron donor component was considerably larger than the electron acceptor one. Hydrating the nail plate had no significant influence on the surface energy. In contrast, abrasion caused a small, but statistically significant increase in the apolar surface energy component. The surface energy of bovine hoof membrane was similar to that of the fingernail plate. We conclude that the human fingernail plate is a low-energy surface and that bovine hoof membranes may be used as a substitute for the nail plate in certain experiments.

Surface Modification of Silicate Glass Using 3-(Mercaptopropyl)trimethoxysilane for Thiol–Ene Polymerization

A thiol-ene polymerization was accomplished on silicate glass slides to graft a series of homopolymers and copolymers using 3-(mercaptopropyl)trimethoxysilane (MTS) as both a silane coupling agent and initiator. MTS was initially covalently bonded to an acid cleaned glass surface via a classical sol-gel reaction. Poly(acrylic acid) (PAA), poly(acrylamide) (PAAm), poly(methyl acrylate) (PMA), poly(acrylamido-2-methyl-propanesulfonic acid) (PAMPS), and the copolymer poly(AA-co-AAm-co-MA-co-AMPS) were grafted from the thiol group of MTS. The surface chemistry of the MTS modified slides and polymer grafts was characterized with attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). Surface texture was evaluated with tapping mode atomic force microscopy (TM-AFM). The Owens-Wendt-Kaelble (OWK) and Lifshitz-van der Waals acid-base (LW-AB) methods were used to evaluate surface energies by sessile drop contact angle method. The synthetic approach demonstrated a facile, rapid method for grafting to glass surfaces.

Synergetic Effect of Grit-Blasting and Atmospheric Cold Plasma Pretreatments on the Surface Free Energy of a Fibreglass/Epoxy Vinyl Ester Composite

For the first time, the efficiency of different surface pretreatment approaches prior to adhesive bonding of a fibreglass-reinforced epoxy vinyl ester thermoset composite has been investigated. It was found that grit-blasting generally had a negligible effect on the surface free energy (SFE) calculated using the Owens, Wendt, Rabel, and Kaelble method, as well as the Lifshitz–van der Waals/acid-base (LWAB) approach. However, contrary to abrading, grit-blasting has shown its efficiency to flatten sharp surface irregularities and introduce surface roughness features suitable to adhesive bonding processes. With or without a previous grit-blasting step, argon gas atmospheric cold plasma treatment has shown a slight to moderate efficiency in increasing the SFE polar component of the composite. However, it was found that the addition of 0.07% oxygen to the argon plasma readily allows an important gain in the SFE polar component. Indeed, when processed at a speed of 30 m/min on a previously grit-blasted composite surface, the Ar/O2 atmospheric cold plasma treatment increases the surface free energy to values >73 mJ/m2, making the surface condition optimized for structural adhesive bonding. An oxidation mechanism of the composite surface exposed to atmospheric cold plasma was suggested on the basis of correlations established between the polar part of SFE obtained from the Owens et al. method, acid/base components calculated using the LWAB approach, and ATR infrared spectroscopy signatures obtained for a model polyolefin material.

Interfacial Energetics of Bacterial Silicification

Silica nanoparticle size distributions were measured from transmission electron micrographs of bacterial cells in thin-sectioned hot spring sediment samples, as well as specimens from laboratory experiments on bacterial silicification. Diameters of silica nanoparticles on bacterial cells were smaller than corresponding values of those occurring away from bacteria in the same fields of view. Regression analysis of the particle size data and application of the Lifshitz-van der Waals Acid-Base approach to evaluations of solid surface energy established that the size difference extends from a nearly 40% decrease in the mean interfacial energy of silica nanoparticles on bacteria (0.9 mJ/m 2 ) as opposed to free in aqueous suspension (1.2 mJ/m 2 ). In thermodynamic terms, the lower interfacial energy serves to reduce equilibrium solubility values, and enhance nucleation rates, of silica nanoparticles on bacteria cells. The well documented culmination of these events in hot spring sediments and experimental studies is rapid preferential silicification and structural preservation of bacterial cells.

An investigation of microbial adhesion to natural and synthetic polysaccharide-based films and its relationship with the surface energy components

In recent years, polysaccharide-based films have been developed for many applications. Some of these are in the pharmaceutical industry, where the adhesion of microorganisms to surfaces is a concern. After adhesion of a microorganism to a solid surface has taken place, the subsequent biofilm formed can act as a vehicle for spreading infections. The aim of this study is to compare the bacterial adhesion of E. coli and S. aureus from a contaminated solid model (Tryptone Soya Agar) to a range of polysaccharide-based films. These polysaccharide-based films consist of different natural starches (potato, cassava, wheat, pea and rice) and synthetic polymers hydroxyl-propyl cellulose (HPC) and carboxyl methyl cellulose (CMC)). The surface energy parameters of the films were calculated from the contact angle measurements by the sessile drop method. Apolar and polar liquids (water, formamide and hexadecane) and the Lifshitz-Van der Waals/acid-base (LW/AB) approach were used according to the method of Van Oss, Chaundhury and Good. The surface properties of the films were also correlated to the microbial adhesion. This indicated that, for both E. coli and S. aureus, the surface roughness did not affect the microbial adhesion. Only gamma(sAB) had any correlation with the microbial adhesion and gamma(sLW) was almost constant for all the various polysaccharide films tested. In addition, the electron-donor properties of the materials, exhibited via gamma(s+), were positively correlated with the adhesion of S. aureus but not with E. coli. This was in agreement with the results of the MATS (Microbial Adhesion To Solvents) test performed on the two bacteria. This revealed that only S. aureus presented an electron-acceptor characteristic.

Surface Treatment of Indium Tin Oxide Using Radio Frequency Atmospheric and Low Pressure Plasma for OLEDs

We investigated the effect of atmospheric-pressure plasma (APP) and low-pressure plasma (LPP) treatments on the performance of organic light emitting diodes (OLEDs) with an indium tin oxide (ITO) layer. The Owens–Wendt and Lifshitz–van der Waals acid-base methods revealed that the increase of surface energy was mainly attributed to polar component and Lewis base interactions, respectively, independent of either APP or LPP treatments. Unlike APP treatment, LPP treatment more plentifully produced reactive oxygen species in the plasma. Therefore, the LPP-treated ITO surfaces slowly proceeded with reorientation compared to APP-treated ITO. The carbon content in untreated ITO was approximately 0.045%, while those of Ar APP-, APP-, and LPP-treated ITO were 0.014, 0.011, and 0.010%, respectively, mostly containing incorporated reactive oxygen. The LPP-treated surface showed more uniform roughness than Ar or APP-treated surfaces. The highest work-function value was obtained from LPP-treated ITO, intermediate values from Ar and APP-treated ITOs, and the smallest value from untreated ITO . Thus, OLED fabricated on the surface of LPP-treated ITO substrate exhibited superior performance among all plasma-treated samples.

Agglomeration and adhesion free energy of paracetamol crystals in organic solvents

AbstractThe agglomeration of paracetamol during crystallization in different pure solvents has been investigated. Narrowly sieved crystals were suspended as seeds and allowed to grow and agglomerate at constant supersaturation and temperature. Particles from each experiment were examined by image analysis and multivariate data evaluation, for the number of crystals per particle. From the resulting number distribution, parameters defining the “degree of agglomeration” were extracted. The degree of agglomeration among the product particles is fairly low in water, methanol, and ethanol, while it is substantial in acetone particularly, but also in acetonitrile and methyl ethyl ketone. Surfaces of large, well‐grown paracetamol crystals have been characterized by contact angle measurements. The surface free energy components of different crystal faces have been estimated using Lifshitz–van der Waals acid–base theory. The data are used for estimation of the solid–liquid interfacial free energy of each face in the solvents of the agglomeration experiments and the corresponding crystal–crystal adhesion free energy of pairs of faces. The degree of agglomeration in different solvents does correlate to the free energies of adhesion. This supports the hypothesis that the influence of the solvent on the crystal agglomeration relates to physico‐chemical adhesion forces between crystal faces in the solution. © 2007 American Institute of Chemical Engineers AIChE J, 53, 2007