Contact Angles Of Diiodomethane Research Articles

Some remarks on the solid surface tension determination from contact angle measurements

The measurements of water, formamide and diiodomethane contact angle (θ) on polytetrafluoroethylene (PTFE), polyethylene (PE), polymethyl methacrylate (PMMA), nylon 6, quartz and silica were performed. Based on the θ values of these liquids obtained on PTFE, the Lifshitz-van der Waals and acid-base and/or dispersion and polar components of their surface tension (ST) were determined. In turn, the θ values for water, formamide and diiodomethane on PMMA were applied to calculate the electron-acceptor and electron-donor parameters of the Lewis acid-base component of the formamide ST. For this calculation the same values of the electron-acceptor and electron-donor parameters for water ST were used. Taking into account the values of components and parameters of water, formamide and diiodomethane ST obtained by us, van Oss et al. and from the water(formamide)-n-alkane and water-diiodomethane interface tension, the components and parameters of studied solids ST were calculated. To this end different approaches to the interface tension were considered. The obtained values were compared with those in the literature. It was concluded that for determination of solid ST components and parameters, those of water, formamide and diiodomethane ST obtained from the θ measurements on the model solids should be used.

Chemical properties and protein adsorptions on ozone/UV-treated poly(ethylene terephthalate) film surfaces

We have studied on chemical properties of poly(ethylene terephthalate) (PET) film surfaces treated by ozone aeration under UV light irradiation (ozone/UV treatment) in distilled water and in an aqueous ammonia solution, and on adsorption behavior of bovine serum albumin (BSA), fibrinogen (FBG), and γ globulin (BGG) on the treated PET film. Attenuated total-reflection FT-IR and X-ray photoelectron spectroscopy surface analysis indicate that the ozone/UV treatment in distilled water causes ring opening of benzene rings of PET molecular chains, introducing hydroxy and carbonyl groups on the treated PET film, and that the treatment in the ammonia solution also induces benzene ring opening, followed by deposition not only of hydroxy and carbonyl groups but also of amino and amide groups. The surface free energy evaluated from the contact angle of ultrapure water and diiodomethane on the PET film is enhanced by the ozone/UV treatment, because of the increment of polar force by the polar functional group. The adsorption of BSA and FBG having negative surface charges is lower on the PET film treated in distilled water than on the untreated film, and their adsorption on the film treated in the ammonia solution reaches the maximum, as treatment time increases. On the contrary, the adsorption of BGG, of which the surface charge is almost neutral, on the PET film remains constant during the ozone/UV treatment. We therefore consider that the ozone/UV treatment is more effective for the BSA and FBG adsorption on the PET film, but not for the BGG adsorption.

Apparent Surface Free Energy of Polymer/Paper Composite Material Treated by Air Plasma

Surface plasma treatment consists in changes of surface properties without changing internal properties. In this paper composite polymer/paper material is used for production of packaging in cosmetic industry. There are problems with bonding this material at the time of packaging production due to its properties. Composite surface was treated by air plasma for 1, 10, 20, and 30 s. The advancing and receding contact angles of water, formamide, and diiodomethane were measured using both treated and untreated samples. Apparent surface free energy was estimated using the hysteresis (CAH) and Van Oss, Good, Chaudhury approaches (LWAB). Surface roughness was investigated using optical profilometry and identification of after plasma treatment emerging chemical groups was made by means of the XPS (X-ray photoelectron spectroscopy) technique. After plasma treatment the values of contact angles decreased which is particularly evident for polar liquids. Apparent surface free energy increased compared to that of untreated samples. Changes of energy value are due to the electron-donor parameter of energy. This parameter increases as a result of adding polar groups at the time of surface plasma activation. Changes of surface properties are combination of increase of polar chemical functional groups, increase on the surface, and surface roughness increase.

Properties of PEEK-supported films of biological substances prepared by the Langmuir-Blodgett technique

In our studies the low-temperature plasma obtained from oxygen, argon, nitrogen was used to enhance polyetheretherketone PEEK adhesive properties and as “pre-deposition” before the main process which was deposition of layers of biologically active substances, e.g. phospholipid 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), lauryl gallate (LG) and mixed layers (DPPC/LG) by means of the Langmuir-Blodgett technique. Thus PEEK was used for creating biointerfaces with model membrane structures. Wettability of both unmodified and modified surfaces of the polymer as well as those covered with the films of biological substances was investigated by measurements of advancing and receding contact angles of water, formamide and diiodomethane. Then the values of the measured contact angles were used for determination of surface free energy and its components of the studied surfaces based on the theoretical models. The topography and roughness parameters were also estimated by optical profilometer. The results demonstrate that the appropriate plasma choice and the deposited film composition influence on wettability and thermodynamic parameters of the studied systems. The changes in the PEEK surface properties affect the interactions between the solid support and the membrane. The molecular packing density of the deposited film can be associated with the strength of adhesion and correlates with the surface energy and its component values. It is believed that plasma treatment will be a source of new information about PEEK surface mostly in the field of biomaterial engineering, adhesion of biomolecules as well as biocompatibility.

Surface properties of Ti-6Al-4V alloy part I: Surface roughness and apparent surface free energy

Titanium (Ti) and its alloys are the most often used implants material in dental treatment and orthopedics. Topography and wettability of its surface play important role in film formation, protein adhesion, following osseointegration and even duration of inserted implant. In this paper, we prepared Ti-6Al-4V alloy samples using different smoothing and polishing materials as well the air plasma treatment, on which contact angles of water, formamide and diiodomethane were measured. Then the apparent surface free energy was calculated using four different approaches (CAH, LWAB, O-W and Neumann's Equation of State). From LWAB approach the components of surface free energy were obtained, which shed more light on the wetting properties of samples surface. The surface roughness of the prepared samples was investigated with the help of optical profilometer and AFM. It was interesting whether the surface roughness affects the apparent surface free energy. It was found that both polar interactions the electron donor parameter of the energy and the work of water adhesion increased with decreasing roughness of the surfaces. Moreover, short time plasma treatment (1min) caused decrease in the surface hydrophilic character, while longer time (10min) treatment caused significant increase in the polar interactions and the work of water adhesion. Although Ti-6Al-4V alloy has been investigated many times, to our knowledge, so far no paper has been published in which surface roughness and changes in the surface free energy of the alloy were compared in the quantitative way in such large extent. This novel approach deliver better knowledge about the surface properties of differently smoothed and polished samples which may be helpful to facilitate cell adhesion, proliferation and mineralization. Therefore the results obtained present also potentially practical meaning.

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.

Synthesis of PPG-TDI-BDO polyurethane and the influence of hard segment content on its structure and antifouling properties

Abstract Polyurethane have good anti-protein adsorption properties, could be used as an antifouling material. In this study, a type of polyurethane antifouling coating was prepared using 2,4-toluene diisocyanate and 1,4-butanediol as the hard segment and polyether polyols as the soft segment. The influence of hard segment content on the chemical structure, mechanical properties, and surface properties of the coatings was investigated. Subsequently, the antifouling performance of the polyurethane coatings was investigated by benthic diatom adhesion and panel tests. The results showed that coating H40 (polyurethane coating with a hard segment content of 40 wt.%) exhibited the best antifouling property. The antifouling performance of the coatings was further examined by evaluating the surface changes occurring in the polyurethane coatings during immersion in seawater. In situ diiodomethane contact angle measurements were performed to monitor such changes. The oil contact angle results were consistent with the results of the panel test. The oil contact angle and antifouling property are both determined by the surface roughness, which is determined by the level of microphase separation in the polyurethane coatings.

Effects on Oxygen‐barrier Properties of Pretreating Paperboard with a Starch–Poly(Vinyl Alcohol) Blend before Polyethylene Extrusion

Polyethylene (PE) extrusion coating was performed on paperboard pre‐coated with water‐borne barrier coatings based on starch–poly(vinyl) (PVOH)–plasticizer blends in order to investigate that how the addition of a plasticizer to the pre‐coating affects the oxygen‐barrier properties of the board after PE extrusion coating. The plasticizers used were glycerol, polyethylene glycol (PEG) and citric acid (CA). Photomicrographs showed that the barrier coating layers were rather smooth, but defects were observed in the starch–PVOH layers when a plasticizer was added. Starch–PVOH layers had oxygen‐barrier properties similar to those of pure PVOH without plasticizers. When a sufficient number of layers (four layers) were applied to cover defects, the starch–PVOH layers containing CA showed oxygen transmission rate (OTR) values similar to those of starch–PVOH layers without plasticizer. The adhesion of PE to pre‐coated paperboard decreased when a plasticizer was added to the pre‐coating recipes. PE extrusion coating resulted in a reduction in the OTR in the case of pre‐coating formulations containing plasticizers. A lower OTR after polyethylene extrusion was observed with PEG as plasticizer than with CA as plasticizer. This could be explained by the increase in brittleness due to cross‐linking under the high temperature load during the extrusion process. Dynamic mechanical analysis of the films showed a substantial increase in storage modulus between 100°C and 200°C for CA‐containing starch–PVOH films. The contact angle of diiodomethane on the pre‐coating layer decreased when a plasticizer was added to the coating recipe indicating an increase in wetting of the PE melt. Addition of PEG to the pre‐coating led to a greater wetting than the addition of CA, and this may have sealed some defects in the pre‐coating leading to lower OTR values.

Effect of chain length on the wetting properties of alkyltrichlorosilane coated cellulose-based paper

The effect of alkyl chain length on the wetting properties of alkyltrichlorosilane coated cellulose-based paper is reported for four different reagents: methyltrichlorosilane (MTCS; –CH3), butyltrichlorosilane (BTCS; –C4H9), dodecyltrichlorosilane (DTCS; –C12H25) and octadecyltrichlorosilane (OTCS; –C18H37). SEM analysis reveals that by systematically varying alkyl chain length, films with different surface morphologies can be generated on flat silicon wafer control samples and on cellulose-based paper samples. The variation in surface morphology leads to different wetting behavior, as determined by measuring static water and oil contact angles. Due to the nano- and micron- scale roughness on MTCS coated substrates, paper samples coated with MTCS display superhydrophobicity with a water contact angle of 152.2°, which is the highest water contact angle among these four alkyltrichlorosilanes. However, additional nano-scale roughness from MTCS coating reduces the oil resistance of coated paper samples, while paper samples coated with long-chain alkyltrichlorosilanes have lower surface energy and also lack nano-scale roughness. As a result, paper samples coated with OTCS display the highest resistance against oils (ethylene glycol contact angle 125.5°; diiodomethane contact angle 101.3°). The intrinsic porosity of paper is largely retained after coating, as indicated by the fact that low surface tension fluids like methanol can easily penetrate coated paper samples.

Thermodynamic analysis of effects of contact angle on interfacial interactions and its implications for membrane fouling control

Concept of hydrophobicity always fails to accurately assess the interfacial interaction and membrane fouling, which calls for reliable parameters for this purpose. In this study, effects of contact angle on interfacial interactions related to membrane fouling were investigated based on thermodynamic analysis. It was found that, total interaction energy between sludge foulants and membrane monotonically decreases and increases with water and glycerol contact angle, respectively, indicating that these two parameters can be reliable indicators predicting total interaction energy and membrane fouling. Membrane roughness decreases interaction strength for over 20 times, and effects of membrane roughness on membrane fouling should consider water and glycerol contact angle on membrane. It was revealed existence of a critical water and glycerol contact angle for a given membrane bioreactor. Meanwhile, diiodomethane contact angle has minor effect on the total interaction, and cannot be regarded as an effective indicator assessing interfacial interactions and membrane fouling.

Synthesis of fluorinated polyester used for hydrophobic coating: Influence of fluoroalkyl group length on enrichment behavior

The fluorinated polyesters with different fluoroalkyl groups were synthesized from phthalic anhydride, epichlorohydrin, and fluorinated glycidyl ether. The structures of the modified polyesters were well characterized by proton and fluorine nuclear magnetic resonance (1H NMR and 19F NMR). Contact angle measurement was used to investigate the surface wettability. The results showed that the introduction of an extremely low concentration of fluorine content into the coatings resulted in a significant increase in contact angle of water or diiodomethane, and decrease in the surface energy. X-ray photoelectron spectroscopy (XPS) showed that the F/C molar ratio on the surface was much higher than that in the bulk, indicating the surface enrichment of fluoroalkyl groups. It was also found that fluorinated polyester with longer fluoroalkyl groups had a higher tendency to enrich on the coating surface. In addition, the chemical composition of the inner layer in near-surface area was also investigated by XPS equipped with argon bombarding. The enrichment of fluoroalkyl groups was supposed to occur in near-surface area.

Tracking the Effect of Adatom Electronegativity on Systematically Modified AlGaN/GaN Schottky Interfaces.

The influence of surface modifications on the Schottky barrier height for gallium nitride semiconductor devices is frequently underestimated or neglected in investigations thereof. We show that a strong dependency of Schottky barrier heights for nickel/aluminum-gallium nitride (0001) contacts on the surface terminations exists: a linear correlation of increasing barrier height with increasing electronegativity of superficial adatoms is observed. The negatively charged adatoms compete with the present nitrogen over the available gallium (or aluminum) orbital to form an electrically improved surface termination. The resulting modification of the surface dipoles and hence polarization of the surface termination causes observed band bending. Our findings suggest that the greatest Schottky barrier heights are achieved by increasing the concentration of the most polarized fluorine-gallium (-aluminum) bonds at the surface. An increase in barrier height from 0.7 to 1.1 eV after a 15% fluorine termination is obtained with ideality factors of 1.10 ± 0.05. The presence of surface dipoles that are changing the surface energy is proven by the sessile drop method as the electronegativity difference and polarization influences the contact angle. The extracted decrease in the Lifshitz-van-der-Waals component from 48.8 to 40.4 mJ/m(2) with increasing electronegativity and concentration of surface adatoms confirms the presence of increasing surface dipoles: as the polarizability of equally charged anions decreases with increasing electronegativity, the diiodomethane contact angles increase significantly from 14° up to 39° after the 15% fluorine termination. Therefore, a linear correlation between increasing anion electronegativity of the (Al)GaN termination and total surface energy within a 95% confidence interval is obtained. Furthermore, our results reveal a generally strong Lewis basicity of (Al)GaN surfaces explaining the high chemical inertness of the surfaces.

Changes in Surface Properties of Heat-Treated Phyllostachys pubescens Bamboo

The wetting phenomena and surface energetic behavior in heat-treated bamboo were studied. The bamboo specimens were heat-treated at temperatures of 100, 140, and 180 °C for 4 h, and an untreated sample served as a control. The sessile drop technique was used to estimate the surface contact angles of the control and heat-treated bamboo samples. The contact angle data were then used to determine the surface free energies using the Lifshitz-van der Waals/acid-based approach. The results revealed that the heat treatment process affects surface wettability. Heat treatment at 100 to 180 °C increased the contact angle of distilled water and formamide, but heat treatment did not cause any increase in the contact angle of diiodomethane. The hydrophobic characteristics of the bamboo surfaces also increased under heat treatment, and the surface free energy and the polarity of the bamboo decreased. Surface analysis by XPS of the samples heat-treated at 180 °C showed a decreased O/C ratio and increased C1 peak, indicating that more lignin and extractives were situated on the bamboo surface. Changes in wettability can greatly impact the use of the material, particularly with respect to the adhesion of paints and coatings.

Characterization of chitosan composites with synthetic polymers and inorganic additives

In the present study, the results from thermogravimetric analysis (TGA), contact angle measurements, tensile tests, scanning electron microscopy (SEM) and atomic force microscopy (AFM) of polymer composites containing chitosan (Ch) and montmorillonite (MMT) with and without poly(vinyl alcohol) (PVA) are presented.Measurements of the contact angles for diiodomethane (D) and glycerol (G) on the surfaces of chitosan films, Ch/MMT and Ch/PVA/MMT, were made and surface free energies were calculated. It was found that the wettability of the chitosan/MMT or Ch/PVA/MMT composite films decreased relative to the wettability of chitosan. The microstructure of unmodified polymers and their composites, as observed by SEM and AFM, showed particles that are relatively well dispersed in the polymer matrix. The TGA thermograms and mass loss percentages at different decomposition temperatures showed that the thermal stability of the binary composite slightly decreases upon the addition of PVA. The film mechanical properties such as tensile strength, Young's modulus and tensile strain at break depend on the composition and varied non-uniformly. Both composites possessed a tensile strength and Young's modulus of 27.6–94.3MPa and 1.5–3.5GPa, respectively. The addition of PVA to the composite led to a reduction in tensile strength by approximately 40%.

Some physical properties of a Si-doped nano-crystalline GaAs thin film grown by thermionic vacuum arc

A 160 nm thick Si-doped nano-crystalline GaAs film was grown on a glass substrate by means of the thermionic vacuum arc in just 50 s. Tools and techniques such as an optical reflectometer, Uv–Vis–NIR spectrophotometer, XRD, FESEM, AFM, Hall effect measurement, and diiodomethane, ethylene glycol, formamide, and water contact angle measurements were employed to investigate some of the physical properties of the produced film. XRD characterization indicated that the film contained GaAs (hexagonal system in atomic ratio of 1) and SiAs (monoclinic system in atomic ratio of 1) phases. The grain size obtained from Scherrer's Formula was in the range of 30–40 nm. The AFM micrographs showed the film topography, revealing a surface root mean square roughness of 14.5 nm and average height of 48.3 nm. From the wetting experiments, it was found that the contact angle value is strongly dependent on the liquid used.

Adsorption and wetting properties of cationic, anionic and nonionic surfactants in the glass-aqueous solution of surfactant-air system

The measurements of the advancing contact angle for water, formamide, glycerol, diiodomethane and aqueous solutions of Triton X-100 (TX-100), Triton X-165 (TX-165), sodium decylsulfate (SDS), sodium dodecylsulfate (SDDS), hexadecyltrimethylammonium bromide (CTAB) and hexadecylpyridinium bromide (CPyB) on the glass surface were carried out. Using the values of the contact angle of these liquids and solutions, the glass surface free energy as well as its components and parameters were determined. This energy, its components and parameters were used for interpretation of the glass wettability by the surfactants solutions in the light of the surfactants adsorption in the three-phase systems and the adhesion of the solution to the glass surface. It appeared that the surface free energy of glass determined from the contact angle of aqueous solution of surfactants on its surface is useful for the determination of the Gibbs surface excess concentration of surfactant at the glass–air and glass–solution interfaces and consequently, the Gibbs standard free energy of surfactant adsorption at these interfaces. It also appeared that by using the Neumann et al. and van Oss et al. equations, it is possible to predict the work of adhesion of aqueous solution of surfactant to the glass surface.

Effect of surface modification on starch biopolymer wettability

The main goal of this paper was to determine wettability properties of native starch and starch modified by antibacterial solution of chitosan or lysozyme as a function of temperature and/or after plasma treatment. Contact angles for polar water (and formamide) and nonpolar diiodomethane on glass plates covered with starch film before and after gelatinization (25 °C, 37 °C and 60 °C) were measured. The surface free energy of solid (gel) was determined from the advancing and receding contact angles of these probe liquids, using the contact angle hysteresis model (CAH). The plasma treatment was immediately followed by a sharp decrease of contact angle. In the course of ageing the contact angle also decreased due to the reorientation of polar groups into the surface layer of polymer. Also a sharp decrease in negative values of WS takes place which indicates more hydrophilic character of starch after plasma treatment. The same was after lysozyme modification but to a smaller extent. The opposite trend of changes was visible after chitosan solution treatment. The surface characterization was observed by FTIR measurements and surface topography from the profilometer images and such measurements well support the contact angle results. The arrangement of temperature, plasma treatment or biological modification can lead to improvement of starch surface wettability and stability. The obtained results open up possibilities of starch application in food, paper and packaging industries as well as in pharmacy.

Effect of surface modification on starch/phospholipid wettability

Abstract The objective of this work was to determine surface properties of biopolymer film as a function of temperature and/or after plasma treatment with the aim of further wettability tests and biocompatibility. The examined biopolymers were native starch and starch modified by solution of PC (phosphatidylcholine). Contact angles for polar water (and formamide) and nonpolar diiodomethane on the glass plates covered with starch film before and after gelatinization (25 °C, 37 °C and 60 °C) were measured for the base and plasma modified film. The surface free energy of solid (gel) was determined from the advancing and receding contact angles of these probe liquids, using the contact angle hysteresis model (CAH). The plasma treatment was immediately followed by a sharp decrease of contact angle and in the course of ageing the contact angle also decreased due to the reorientation of polar groups into the polymer surface layer. To depict better changes in hydrophilic/hydrophobic character of the starch surface before and after modification the work of water spreading, W S was calculated. A sharp decrease in negative values of W S takes place which indicates more hydrophilic character of starch surface after modification. Surface morphology and roughness were studied by optical profilometer and FTIR measurements which confirm the contact angle results. It was also proved that a combination of input treatment parameters led to improvement of biopolymer wettability and provided possibilities of starch application where uniform thin films are required.

Influence of the ambient temperature on water and diiodomethane contact angle with quartz surface

AbstractWettability of solids is a key phenomenon in many processes. One should mentioned those which accompany us in our everyday life i.e. washing or cementing as well as those applied in industry e.g. flotation of minerals. Value of the contact angles are affected by many factors. One of them is temperature. In this paper monocrystaline quartz was used in the investigations which were carried out in the range 5−50°C with the step every 5°C. As follows the value of the contact angle of both water and diiodomethane changes with the increasing temperature. The change of its value for water is much larger than in case of another liquids of apolar character. Using Chibowski approach the apparent surface free energy was calculated in two ways with and without correction about temperature change of the surface tension. The calculation show difference between both results. Taking into consideration another value of the surface tension should not be neglected even if measurements is taken at a temperature close to 20°C which is the standard in one in such measurements