Contact Angles Of Diiodomethane Research Articles

Poliuretanowe lakiery proszkowe modyfikowane zwiazkami fluoru

Polyisocyanates, used as crosslinking agents in powder lacquers, were synthesized in the reaction of diisocyanates, formic acid, fluorinated alcohols and imidazole. The structure of polyisocyanates was confirmed using IR, 1H NMR, 13C NMR and 19F NMR spectroscopy and the molecular weight distribution (MWD) was determined by gel permeation chromatography (GPC). The course of the unblocking and curing reactions was investigated by differential scanning calorimetry (DSC) and thermal analysis (DTA and TG). The prepared lacquer coatings containing fluorine exhibit higher values of contact angle for water, formamide and diiodomethane as well as lower surface free energy parameters compared to unmodified coatings. They also show improved application properties such as impact resistance, hardness, adhesion to steel surface and abrasion resistance.

Surface Tension of Polytetrafluoroethylene and Polymethyl Methacrylate under the Influence of the Fluorocarbon Surfactant Film

Measurements of the contact angle for water, formamide, and diiodomethane on polytetrafluoroethylene (PTFE) and polymethyl methacrylate (PMMA) covered by Zonyl FSN-100 (FSN100) and Zonyl FSO-100 (FSO100) films were made. On the basis of the obtained values, the Lifshitz–van der Waals component and electron-acceptor and electron-donor parameters of the acid–base component of PTFE and PMMA covered by the surfactant film surface tension were determined by the use of van Oss et al. approach to the interfacial tension and Young’s equation. The components and parameters of surface tension were discussed in the light of the sorption of fluorocarbon surfactants at the polymer/solution interface and proper orientation of the surfactant molecules to this interface. Taking into account the changes of determined values of the components and parameters of PTFE and PMMA surface tension under influence of the surfactant films, the relationship between the adhesion tension and the surface tension, as well as between the cosine of contact angle and the surface tension of aqueous solution of fluorocarbon surfactants, was explained.

Comparison of contact angle hysteresis of different probe liquids on the same solid surface.

Advancing and receding contact angles of water, formamide and diiodomethane were measured on 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) layers deposited on three different solid supports—glass, mica and poly(methyl methacrylate). Up to five statistical monolayers were deposited on the surfaces by spreading DPPC solution. It was found that even on five statistical DPPC monolayers, the hysteresis of a given liquid depends on the kind of solid support. Also on the same solid support the contact angle hysteresis is different for each probe liquid used. The AFM images show that the heights of roughness of the DPPC films cannot be the primary cause of the observed hysteresis because the heights are too small to cause the observed hystereses. It is believed that the hysteresis is due to the liquid film present right behind the three-phase solid surface/liquid drop/gas (vapour) contact line and the presence of Derjaguin pressure. The value of contact angle hysteresis depends on both the solid surface and liquid properties as well as on intermolecular interactions between them.

Activation of poly(ethylene terephthalate) surfaces by atmospheric pressure plasma

We report a study on effects of atmospheric pressure plasma treatment of poly(ethylene terephthalate) PET surfaces. The atmospheric pressure plasma was generated using Diffuse Coplanar Surface Barrier Discharge (DCSBD) in ambient air. The changes in wettability of PET surfaces were studied by water contact angle measurement. The surface energy was calculated using van Oss–Chaudhury–Good model from contact angles of water, ethylene and diiodomethane. The changes in surface chemistry after the plasma treatment were studied by X-ray photoelectron spectroscopy (XPS). We also observed changes in surface roughness investigated by Atomic force microscopy (AFM). We found that DCSBD plasma treatment for 1 s led to decrease of water contact angle from 78.4° to 40.1°. The surface energy analysis showed that water contact angle decrease is related to increase of polar part of surface energy. XPS measurement confirmed that the plasma treatment led to increase of polar groups on PET surface which explained the changes in surface energy. AFM investigation showed that plasma treatment led to an increase of surface roughness, which could be a benefit for further processing of PET, because higher roughness increases surface area, which can result into higher adhesion between PET and coatings.

Multifunctional surface modification of an aramid fabric via direct fluorination

This study investigated the potential of direct fluorination as a multifunctional surface modification method for an aramid fabric. The aramid fabric was fluorinated at temperatures of 30, 90, and 150°C. As the fluorination temperature increased, the fluorinated aramid fabric became more hydrophobic and oleophobic, with a water contact angle of 129.3° and a diiodomethane contact angle of 108.6° when the fluorination temperature was 150°C. Thus, the fluorinated fabric could be defined as an omniphobic surface. Both the phenol resin wettability and the impregnation of the fluorinated aramid fabric improved as the fluorination temperature increased, suggesting better interfacial adhesion between the fabric and the polymer matrix. Direct fluorination of an aramid fabric can be an efficient multifunctional surface modification method to achieve omniphobicity in the aramid fabric for the protection, self-cleaning, and improved interfacial adhesion between the fabric and resin for fiber-reinforced polymer composites.

Thermodynamic characteristics of surface densified solid Scots pine wood

Wetting phenomena of surface densified solid wood and its surface energetic behavior were investigated. The specimens of three different initial thicknesses (22 mm, 20 mm, and 18 mm) were surface densified to a target thickness of 15 mm in order to obtain three different degrees of surface densification. After surface densification one third of the specimens was heat treated at 200 °C in the presence of steam, and one third of the specimens was oil treated with linseed oil. The sessile drop technique was used to estimate the apparent contact angle of water, diiodomethane, and formamide on control and surface densified wood. The contact angle data were used to determine the surface free energies of the control and surface densified wood by the Owens Wendt Rabel and Kaelble (OWRK) method. The results of contact angle measurements revealed that surface densification process affects surface wettability. The apparent contact angles of test liquids were higher in the case of surface densified wood compared to the control undensified wood. Heat treatment and oil treatment of the surface densified wood additionally increased the contact angle of tested liquids. Furthermore, a larger reduction in the void spaces of the wood due to higher degree of densification did not affect the apparent contact angles of tested liquids and consequently the surface free energy. The surface densification process lowered the surface energetics and the polarity of wood. Furthermore, heat treatment and oil treatment additionally increased the hydrophobic character of the examined surfaces and lowered the dispersive and polar components of surface free energy.

Synthesis and characterization of fluorine‐containing polyester based on phthalic anhydride and tetrafluoropropyl glycidyl ether

AbstractFluorine‐containing polyester (FPE) was synthesized by the reaction of phthalic anhydride, epichlorohydrin, and 2,2,3,3‐tetrafluoropropyl glycidyl ether (TFGE) at the catalysis of tetraethylammonium bromide using 1,4‐butanediol as the initiator. The structure of FPE was characterized by 1H NMR and 19F NMR, and the result showed that the fluorine in TFGE was introduced into FPE. Fluorine content in FPE was determined by oxygen‐flask combustion and fluoride selective electrode. It was found that fluorine content in FPEs increased with the increase of TFGE content. The wettability of water and oil on the cured coating based on FPE was investigated by contact angle meter. Contact angles of water and diiodomethane on the cured coatings first increased with the increase of the fluorine content in FPEs and then remained constant. The X‐ray photoelectron spectroscopic analysis showed that the F/C molar ratio on the coatings surface was much higher than the overall F/C molar ratio, which indicated that fluoroalkyl groups in FPEs had enriched on the coatings surface. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Comparative Properties of Hydrophilic and Hydrophobic Fumed Silica Filled Two-Component Polyurethane Adhesives

Two fumed silicas, one hydrophilic and another hydrophobic, were added to a two-component polyurethane (PU) adhesive and their properties compared. The filled polyurethanes were characterized by thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), transmission electron microscopy (TEM), and water and diiodomethane contact angle measurements. The adhesive strength was evaluated from single lap-shear tests of solvent wiped stainless steel/polyurethane adhesive joints. The fumed silicas were well-dispersed in the polyurethane matrix as bundles of nanometric spherical silica particles. However, some micron size agglomerates of fumed silica appeared in the filled polyurethane. The addition of fumed silica favoured the degree of phase separation between the hard and the soft segments in the polyurethane. The polyurethanes were not fully cured under the conditions used in this study and the addition of fumed silica inhibited the curing reaction; the extent of the curing reaction was not affected by the hydrophilic or hydrophobic nature of the fumed silica. The filled polyurethanes were further cured during DSC experiments and this was noticed by the appearance of the melting of the hard segments and the displacement of the second glass transition to a higher temperature. On the other hand, the addition of fumed silica increased the wettability and the surface energy of the polyurethane; this increase was mainly due to an increase in the polar component of the surface energy. The increase in surface energy is somewhat more marked in the case of the hydrophilic silica filled polyurethane, indicating that the polarity of the fumed silica affected the surface properties of the polyurethane. Finally, the addition of the hydrophilic fumed silica increased the adhesion of the filled polyurethane adhesive to stainless steel which was in agreement with the higher surface energy of the hydrophilic fumed silica filled polyurethane.

Preparation of micro- and nanospheres with superamphiphobic surfaces by dispersion polymerization

Micro- and nanospheres with superamphiphobic surfaces were prepared by a simple method that employed the conventional dispersion polymerization of perfluoroalkyl methacrylates in methanol. The polymerizations of 2,2,2-trifluoroethyl methacrylate (TFMA) produced microspheres with an average 4.12-μm diameter, while that of 2-(perfluorooctyl)ethyl methacrylate (POMA) provided nanospheres with a 679-nm diameter. An X-ray photoelectron spectroscopy analysis revealed that the fluorine atoms were highly concentrated on the top of the sphere surfaces. It was found that the surface coated with the spheres had a superamphiphobicity. The water contact angles were 150° for the PTFMA microspheres and 173° for the PPOMA nanospheres, while the diiodomethane contact angles were 159° for the microspheres and 160° for the nanospheres. The synergistic effect of the spherical structure and the high concentration of fluorine on the top of the surface produced the superamphiphobicity.

Preparation of porous super-hydrophobic and super-oleophilic polyvinyl chloride surface with corrosion resistance property

Porous super-hydrophobic polyvinyl chloride (PVC) surfaces were obtained via a facile solvent/non-solvent coating process without introducing compounds with low surface energy. The microstructure, wetting behavior, and corrosion resistance of resultant super-hydrophobic PVC coatings were investigated in relation to the effects of dosage of glacial acetic acid and the temperature of drying the mixed PVC solution spread over glass slide substrate. As-prepared PVC coatings had porous microstructure, and the one obtained at a glacial acetic acid to tetrahydrofuran volume ratio of 2.5:10.0 and under a drying temperature of 17°C had a water contact angle of 150±1.5°, showing super-hydrophobicity. In the meantime, it possessed very small contact angles for liquid paraffin and diiodomethane and good corrosion resistance against acid and alkali corrosive mediums, showing promising applications in self-cleaning, waterproof for outer wall of building, seawater resistant coating, and efficient separation of oil and water.

Copolymerization of ethylene with a vinyl ether bearing a fluorinated group

The copolymerization of ethylene (E) with 1 H,1 H,2 H,2 H-perfluorodecyl vinyl ether (FAVE8) by oxidative addition of salicylaldimine ligand to bis(1,5-cyclooctadiene)nickel(0)/methylaluminoxane (MAO) at room temperature and at different ethylene pressures is reported. The homopolymerization of ethylene is known to be highly active with this catalyst in contrast to the fluorinated vinyl ether which does not homopolymerize. The copolymerization of E with FAVE8 led to linear poly(E- co-FAVE8) statistic copolymers that were characterized by means of various techniques. The obtained copolymers, analyzed by FT-IR and solid state NMR spectroscopy, showed a small incorporation of the fluorinated vinyl ether. Three copolymerization reactions were investigated with different ethylene pressures (5, 10 and 50 bar) and the copolymer compositions indicated that the content of FAVE8 units depends on the ethylene pressure. The lower this pressure, the higher the content of such a fluorinated comonomer and for a 50 bar-pressure, no FAVE8 was incorporated. Thermogravimetric and differential scanning calorimetry analyses of these resulting copolymers exhibited high thermal stability, the thermal degradation starting from ca. 300 °C whereas high melting point ( T m = 129 °C) were achieved with these copolymers. Original films processed from these poly(E- co-FAVE8) copolymers illustrated hydrophobic and oleophilic characters as evidenced by water and diiodomethane contact angles of 104° and 49°, respectively.

Improvement of surface wettability and interfacial adhesion of poly-(p-phenylene terephthalamide) by incorporation of the polyamide benzimidazole segment

In order to investigate the effect of the polyamide benzimidazole group on the surface wettability and interfacial adhesion of fiber/matrix composites, surface features of two kinds of aramid fibers, poly (p-phenylene terephthalamide) fiber (Kevlar-49) and poly-(polyamide benzimidazole-co-p-phenylene terephthalamide) (DAFIII), have been analyzed by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and contact angle analysis (CAA) system, respectively. The results show that with the incorporation of the polyamide benzimidazole segment, more polar functional groups exist on DAFIII surface. The contact angles of water and diiodomethane on DAFIII surface get smaller. The surface free energy of DAFIII increases to 36.5 mJ/m 2, which is 2.3% higher than that of Kevlar-49. In addition, DAFIII has a larger rough surface compared with that of Kevlar-49 due to different spinning processes. The interfacial shear strength (IFSS) of DAFIII/matrix composite is 25.7% higher than that of Kevlar-49/matrix composite, in agreement with the observed results from surface feature tests. SEM micrographs of failed micro-droplet specimens reveal a strong correlation between the fracture features and the observed test data.

Interaction energy of model lipid membranes with water and diiodomethane

The Langmuir–Blodgett/Schaefer (LB/LS) method and contact angle measurements were applied to study interaction energy of lipid films with water and diiodomethane. The membranes were formed on mica and constituted of single-component saturated phospholipids 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) or unsaturated 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and cholesterol (Chol), or they constituted binary systems of DPPC/DOPC or DPPC/Chol with varying DOPC and Chol molar ratio. The surface free energy of single and binary lipid mono- and bilayers was evaluated from the advancing and receding contact angles of water and diiodomethane using the contact angle hysteresis (CAH) model. Taking into account the areas occupied by one molecule in the packed monolayers determined from π– A isotherms and the calculated surface free energy of the layers, the molar interaction energies of one lipid mole with water or diiodomethane were evaluated. Thus obtained values of molar interaction energy of DPPC and DOPC agree well with some literature data available. It is believed that this procedure of the energy evaluation provided a framework for better understanding of the interactions occurring in the biological lipid systems and their wettability.

Fabrication of a transparent superamphiphobic coating with improved stability

We herein provide an effective method to fabricate a transparent superamphiphobic coating with superhydrophobicity and near-superoleophobicity, the finished coating also shows improved stability under various measurements. To do this, a transparent superhydrophobic coating was first prepared with polydimethylsiloxane (PDMS) and hydrophobic silicon dioxide (SiO2) nanoparticles. Then the coating was sintered to degrade the PDMS into SiO2 before it was further oxidized into silanol (Si–OH). Finally, the coating was treated with 1H, 1H, 2H, 2H-Perfluorooctyl-trichlorosilane (PFTS). The PFTS treated coating shows transparency, superhydrophobicity with a water contact angle of 152.7 ± 2.1° and near-superoleophobicity with a diiodomethane contact angle of 140.7 ± 3.2°. The droplets of water and diiodomethane can simultaneously slide off the surface with a sliding angle of less than 6°. Moreover, the PFTS treated coating shows a higher stability than the PDMS/SiO2 coating fabricated by spin coating under various environmental conditions. The PFTS treated coating also shows quite good stability under high temperature environment. The superamphiphobic properties, transparency and improved stability of the PFTS treated coating are systemically discussed and the results show that the finished coating may be appropriate for many outdoor applications.

Effect of different solid matrixes on surface free energy of EGDMA and TRIM polymers

Advancing and receding contact angles of water, formamide, glycerol and diiodometane were measured on the two polymers; EGDMA (dimethacrylate of ethylene glycol) and TRIM (trimethacrylate-1,1,1-trihydroksymethylopropane) which were polymerized next to glass, silanized glass, stainless steel, mica and silicon surfaces as the matrices. Then from the contact angle hystereses (CAH) and van Oss, Good, Chaudhury (LWAB) approaches the apparent surface free energies were evaluated. The measured contact angles not only depend solely on the polymer chemical structure but also, to some extent, on the solid matrix next to whose surface the sample has polymerized. Surface free energy of the polymer samples calculated from the LWAB approach shows that they interact mainly by dispersive forces. The apparent surface free energy of the polymers calculated from the diiodomethane contact angles hysteresis is practically the same irrespective of the kind of the matrix used. Therefore it can be concluded that the observed weak polar interactions in the surface free energy of the samples depend on the polymer surface preparation. The AFM images show that the obtained surfaces are of different roughness. The RMS values of roughness range between 3.7–90.2 nm for EDGMA, and 5.3–124.5 nm for TRIM. However, as reported in literature, rather protrusions bigger than 1 μm may significantly affect the contact angles, especially the receding ones.

The effect of polyhedral oligomeric silsesquioxane dispersant and low surface energy additives on spectrally selective paint coatings with self-cleaning properties

Thickness-Insensitive Spectrally Selective (TISS) paint coatings were made of fluoropolymer resin binder (Lumiflon (LF), Asahi Glass Co., Ltd., Japan) and their water- and oil-repellent properties were obtained (contact angle: θ water~150°, θ n−hexadecane~55°) by the addition of Polyhedral Oligomeric Silsesquioxane (POSS) characterized by amino (AP), isooctyl (IO) and perfluoro (PF) groups (i.e. AP 2IO 4PF 2) attached on the silsesquioxane cube (–SiO 3/2) 8. Paint dispersions were made by modifying of black spinel pigment with trisilanol isobutyl (IB 7T 7(OH) 3) POSS dispersant and with a single-capped silane isobutyltrimethoxysilane (IBTMS). Infrared and 29Si NMR spectra measurements were used for the identification of the structural characteristic of the corresponding POSS compounds. Surface free energy values of the pure cross-linked (no pigment added) LF binder which was determined from the measured contact angles for water, diiodomethane and formamide revealed the γ tot value of the LF unpigmented resin with added AP 2IO 4PF 2 T 8 POSS was about 16.4 mN/m, which led to the θ water~110°, indicating enhancement of the hydrophobicity of the pure LF resin binder ( θ water~89°). SEM micrographs, which were used for the assessment of the TISS paint coating surface morphology confirmed the beneficial dispersive effect of IB 7 T 7(OH) 3 dispersant as compared to the IBTMS silane. The presence of large Aluminium flake pigment and finely ground black pigment led to the formation of TISS paint coating surface, which exhibited bi-hierarchical roughness, resulting in water sliding angles of less than 10°, indicating the possible self-cleaning effect ( θ water>150° and θ n−hexadecane~55°). The use of POSS dispersant and POSS low surface energy additive also enhanced spectral selectivity, which became the highest known so far for the black TISS paint coatings ( e T~0.24 and a s~0.93). The use of simple silane IBTMS dispersant even in the presence of the AP 2IO 4PF 2 T 8 POSS did not lead to the oil-repellent effect confirmed by spreading of n-hexadecane on the surface of the corresponding TISS paint coating.

Surface free energy of polypropylene and polycarbonate solidifying at different solid surfaces

Advancing and receding contact angles of water, formamide, glycerol and diiodomethane were measured on polypropylene (PP) and polycarbonate (PC) sample surfaces which solidified at Teflon, glass or stainless steel as matrix surfaces. Then from the contact angle hystereses (CAH) the apparent free energies γ s tot of the surfaces were evaluated. The original PP surface is practically nonpolar, possessing small electron donor interaction ( γ s − = 1.91 mJ/ m 2 ), as determined from the advancing contact angles of these liquids. It may result from impurities of the polymerization process. However, it increases up to 8–10 mJ/m 2 for PP surfaces contacted with the solids. The PC surfaces both original and modified show practically the same γ s − = 6.5 6.7 mJ/ m 2 . No electron acceptor interaction is found on the surfaces. The γ s tot of modified PP and PC surfaces depend on the kind of probe liquid and contacted solid surface. The modified PP γ s tot values determined from CAH of polar liquids are greater than that of original surface and they increase in the sequence: Teflon, glass, stainless steel surface, at which they solidified. No clear dependence is observed between γ s tot and dielectric constant or dipole moment of the polar probe liquids. The changes in γ s tot of the polymer surfaces are due to the polymer nature and changes in its surface structure caused by the structure and force field of the contacting solid. It has been confirmed by AFM images.

Correlation between surface free energy of quartz and its wettability by aqueous solutions of nonionic, anionic and cationic surfactants

The measurements of the advancing contact angle for water, glycerol, diiodomethane and aqueous solutions of Triton X-100 (TX-100), Triton X-165 (TX-165), sodium dodecyl sulfate (SDDS), sodium hexadecyl sulfonate (SHDS), cetyltrimethylammonium bromide (CTAB) and cetylpyridinium bromide (CPyB) on quartz surface were carried out. On the basis of the contact angles values obtained for water, glycerol and diiodomethane the values of the Lifshitz–van der Waals component and electron-acceptor and electron-donor parameters of the acid–base component of the surface free energy of quartz were determined. The determined components and parameters of the quartz surface free energy were used for interpretation of the influence of nonionic, anionic and cationic surfactants on the wettability of the quartz. From obtained results it was appeared that the wettability of quartz by nonionic and anionic surfactants practically does not depend on the surfactants concentration in the range corresponding to their unsaturated monolayer at water–air interface and that there is linear dependence between adhesional and surface tension of aqueous solution of these surfactants. This dependence for TX-100, TX-165, SDDS and SHDS can be expressed by lines which slopes are positive. This slope and components of quartz surface free energy indicate that the interaction between the water molecules and quartz surface might be stronger than those between the quartz and surfactants molecules. So, the surface excess of surfactants concentration at the quartz–water interface is probably negative, and the possibility of surfactants to adsorb at the quartz/water film–water interface is higher than at the quartz–water interface. This conclusion is confirmed by the values of the adhesion work of “pure” surfactants, aqueous solutions of surfactants and water to quartz surface. In the case of the cationic surfactants the relationship between adhesional and surface tension is more complicated than that for nonionic and anionic surfactants and indicates that the relationship between the adsorption of the cationic surfactant at water–air and quartz–water interface depends on the concentration of the surfactants in the bulk phase.

Surface free energy and topography of mixed lipid layers on mica

The Langmuir–Blodgett/Schaefer (LB/LS) method, AFM technique and contact angle measurements were used to investigate the formation, structure and energetic properties of lipid films, which were constituted of single-component or binary systems formed by phospholipids: saturated 1,2-dipalmitoyl- sn-glycero-3-phosphocholine (DPPC), unsaturated 1,2-dioleoyl- sn-glycero-3-phosphocholine (DOPC) and triglyceride: glyceryl trioleate (GTO) or their mixture DPPC/DOPC and DPPC/GTO with a different DOPC or GTO molar ratio. The surface free energy and its components (apolar and polar interaction) for single and binary lipid mono- and bilayer systems were evaluated from the advancing and receding contact angles of water, formamide and diiodomethane, using two different models of interfacial interactions, namely, van Oss et al. (LWAB) and the contact angle hysteresis (CAH). The molecular structure of these layers was studied by means of atomic force microscopy (AFM). The thermodynamic analysis of the excess area and excess free energy of DPPC/DOPC mixture indicated that lateral phase separation took place for these two components. The AFM images also confirmed the phase separation, which was visualized as condensed DPPC-rich domains and a fluid DOPC matrix. Saturated DPPC mono- and bilayers exhibited much lower surface free energy than unsaturated DOPC ones, probably due to the differences in the packing of molecules. In the DPPC/DOPC mixed layers the energy increased with increasing mole fraction of DOPC in the layer. For DPPC/GTO layers a similar trend in the energy changes as a function of GTO amount was observed. These studies provided a fundamental framework for better understanding of the interactions occurring in the used lipid systems.

Some Effects of Corona Plasma Treatment of Polylactide/Montmorillonite Nanocomposite Films

AbstractInfluence of the unit energy (Eu) of corona discharge used for modification of pure polylactide (PLA) and polylactide nanocomposite (PLAC) containing 5 wt% of an aluminosilicate nanofiller (Cloisite 30B) on water (ΘW) and diiodomethane (ΘD) contact angles as well as on surface free energy (γs) of these polymers was studied. ΘW and ΘD as advancing contact angles were measured with use of a goniometer while γs was calculated by the Owens–Wendt method. It was found that ΘW increased with the rising Eu while ΘD remained approximately constant. Assuming Eu = const, it could be stated that the increase in γs was much more evident for PLA than for PLAC. This increase resulted practically from the change in the polar component of γs because the dispersive component for the two materials only slightly decreased with increase in Eu.