Free Surface Energy of Polymers

Free bob up Energy of PolymersFree go forth force of polymers. Poly(itaconate)s and poly(methacrylate)sLigia Gargallo1, Claudia Aguirre2, Angel Leiva2, Deodato RadicAbstract The salve spring up postcode (SE) for a series of mono and diesters derived from poly(itaconic) acid, was firm by wettability measurements and estimated by theoretical calculations from Sugdens Parachor. For these polymers it was ascertained a decreaseing in the cede grow cypher as the sizing of the chain of the alkyl groups in monoitaconates and diisoalkylitaconates increases. However, it did non allow to get determine of the thaw muster up talent comparable with data- ground determine, exception was for poly(2-chloroethyl diitaconate) and poly(3-chloropropyl diitaconate) where the observational and theoretical variation was comparable. It means that the Sugden method match well for these polymers. Additionally, it was determined the salvage push through get-up-and-go for some polymers from poly(methacrylic acid) derivatives, specifically poly(phenyl methacrylate)s (PPhMA). For these systems a decrease in the put down fold energy is observed, when a fluorine segment was introduced into the phenyl group. In general there was not a good correlation coefficient between observational values and those estimated through the theoretical calculations. The influence of polymeric hit weightiness and topography on the purpose of while away burthen was canvas for poly(phenylmethacrylate)s. The results show that the photographic film weightiness to determine contact tippytoe essential be over 254 A.1. IntroductionIn general it is rattling well known that cod to the lack of coat mobility, the wax tenseness of a solid phase is too different to a eloquent phase. So that, it is not possible to measure directly the surface stress of a solid phase, as it is the incase of a liquifiable phase. It had been employ several independent approximations to estimate the su rface tension on a given system surface solid, being the measurement of contact angle the most practical way1-11 .The surface of a solid, as well as of a liquid, has an additional fire energy, but due to this lack of mobility in the surface of solids this energy is not possible to measure directly. 12 It means that the free surface energy can be estimated by wettability measurements in an substantiative way, as shown in Figure 1. 13,14An approximation to estimate the surface energy of solids is based on the interpretation of contact angle of sesil dismiss.Figure 1. Sesil decline over a solid surface. The arrows represent the surface energies when they are explained homogeneous forces of surface tension.From the schematic representation on Figure1, and considering the equilibrium state, the Youngs equation is obtained. This equation establishes a relationship between the contact angle and the lead surface tensions (2)where is the contact angle, s is the surface energy of solid- vapor interface, sl is the surface energy solid-liquid interface and l the surface energy at liquid-vapor interface.The diffusion force and polar contribution to SE, d and p, respectively, can be measured by using the Owens, Wendt and Kaelble method. 15-17The aim of this work is to obtain culture well-nigh the free surface energy of several polymers with different chemical structures and conglomerate side chains. It was also interesting to clarify the inflence of the thickness and topography of the film in the determination of the SE of the polymeric systems canvass.2. ExperimentalSynthesis and characterization of poly(diisoalkylitaconate)s, poly(monoitaconate)s and poly(methacrylate)sDiisoalkylitaconates were obtained by conventional acid catalyzed esterification of itaconic acid using sulphuric acid in toluene and the corresponding acohols. 18-20 glandular feveritaconates were obtained by reaction of itaconic acid with the respective alcohols on a lower floor fairly acidic conditions according to the method described by bread maker et al., 21,22 for lower monoesters.Methacrylates were inclined(p) by reaction of methacryloyl chloride with the appropriate alcohols in toluene solutions and N.N-dimethylaniline at reflux temperature during 24 h. nicety of the monomers was achieved by distillation chthonic reduced pressure (0.5 mm Hg) as previously reported 23,24 for diitaconates and methacrylates. Purification of monoitaconates were achieved by repeated crystallization from toluene. The monomer structures and purity were confirmed by 1H-NMR and invisible spectroscopy with Fourier Transform (FT-IR). Polymerization was achieved in bulk at 340 and 350 K, depending on the monomer, using azobisisobutyronitrile (AIBN) as initiator under N2 (polymerization time 48-60 h regeneration 70%) for diitaconates, 48 h for monoitaconates yield 35% and 10-3 w/w % of AIBN in benzene solution under vacuum in the case of methacrylates (polymerization time, 48 h conversio n 65%).Preparation of Polymeric films.Films of poly(monoitaconate)s and poly(diitaconate)s were prepared by dehydration of dilute solutions (0,05 g/dL) in tetrahydrofuran (THF), over the film over and atomic topic 14 wafer plates. Poly(metacrylate)s were prepared from dilute solutions 0.05 g/dL in chloroform. arrive at angle measurements get up free energy.The total surface energies of the polymers were determined by wettability measurements with water, diiodomethane and ethyleneglycol. Polymers films were cast onto glass slides for optical microscopy and silicon wafer. The cast films were dried for 30 min at 393 K. The wettability of the polymer films was determined by contact angle measurements. striking angles were measured using a contact angle system oca by Dataphysics with a conventional goniometer and high performance video camera, controlled by SCA20 software. A syringe connected to a Teflon capillary of active 2 mm inner diameter was used to supply liquid into the ses sile drops from above. A sessile drop of about 0.4-0.5 cm r was used. The contact angles were measured carefully from the left and right side of the drop and subsequently averaged. These procedures were repeated for six drops of each liquid on three new surfaces. All reading were then averaged to give an average contact angle. All experiments were performed at room temperature.Determination of polymeric film thickness by ellipsometry.Optical Assembly.The ellipsometer used has a polarizer, a compensator, the sample, an analyser and a detector. The light source comes from He-Ne laser whose wavelength is 632.8 nm, that fall onto the sample with an angle of 60.65. The analyzer remains fixed at an angle of 24.256, and the polarizer is mechanisticly adjusted so that the detector does not record any signal. Silicon wafers (Silicon doped with bacillus crystalline plates) were used as substrates. Pieces of 12 x 12 mm were used. The most important characteristic of these substrates, are the refractive index of silicon of 3.877 + 0.019 25, 26 and the refractive index of PPhMA was 1.5706 27. Substrates were also properly cleaned and dried, being their typical polarisation angle between 43.8 and 43.9.Preparation of films of poly(phenylmethacrylate).The film of PPhMA was prepared by evaporation of the polymeric solution in chlorform over the silicon wafer. In severalise to get different films thickness of PPhMA, different concentration of the polymeric solutions were used. Concentrations were 0.05 g/dL, 0.10 g/dL, 0.20 g/dL, 0.30 g/dL and 0.40 g/dL.Estimation of film topography.Morphological analysis of surface films of poly(phenylmethacrylate) were done by Scanning electron Microscopy (SEM). A film of PPhMA of 94 10 thickness was prepared from a solution of 0.05 g/dL in chloroform and deposited over a silicon wafer as substrate.3. Results and Discussion.Polymers studied in this work were mono and diesters from poly(itaconic) acid, and to boot some polymers from poly(m ethacrylic) acid were also studied. The sixteen polymers studied are shown in scheme 1.Surface free energy was determined by metre the contact angles (CAs) of water, ethyleneglycol and diiodomethane on the polymeric surfaces. The dispersion d and polar p contributions were calculated by the Owens, Wendt and Kaelble methods. 15,16, 28,29 The results obtained by wettability measurements of polymeric systems studied are summarized in slackens 1 to 4. In the same tables are the surface energy calculated from Sudgens parachor ( =(Ps/V)4) for the same polymers.In the case of poly(diisoalkyl itaconate)s it can be seen that the number of methylene groups increases the asquint chain, the calculated surface energy values decreases. This is a normal behaviour because the hydrophobicity of the polymer must increase. However, it did not allow to get experimental values that present this behavior. As it is important to consider the possible errors on the determination of SE values due to the effects of the roughness and at the same time the thickness on adsorbed polymers. For this reason the film thickness was studied to clarify its influence on the measurement of contact angle.Mono esters of poly(itaconic) acidDiesters of poly(itaconic) acidPoly (methacrylic) acidScheme 1In array to get films with different thickness the concentration of the solution of poly(phenylmethacrylate), PPhMA, was modified. Thicknesses and topography of the films were measured by ellipsometry on silicon wafer substrates. It was found a good linear correlation between film thickness and polymer concentration. (Regression coefficient R=0.98955).Surface free energy of substrates used was also determined in order to obtain this information to perform appropriate comparison of the results dealing with this polymer. The film thickness determination for PPhMA was made on silicon wafer, and on a glass plate. The surface free energy values in both substrates were compared. flurry 5 shows surface fre e energy values found for PPhMA in these substrates.Topography of the surface of PPhMA film at a thickness of 94 A was studied by SEM micrography. It was found that the polymer is homogenously distributed on the silicon wafer substrate, showing a surface with regular porosity. This demonstrates that PPhMA film whose thickness is 94 , the surface is not whole cover and it produces in the measurement of the contact angle non reproducible values, due to the liquid will penetrate itself within the holes.Determination of surface free energy for PPhMA was performed at different film thickness. It was observed that for films thickness of PPhMA greater than 24513 A there is a better reproducibility in the values of contact angle obtained. The SE values are shown in Table 6.4. ConclusionsPoly(monoitaconate)s with large lateral chains as poly(monodecylitaconate) and poli(monododecylitaconate), it was found that the surface free energy decreases as the length of the alkyl group increases. It allows concluding that the polymer increases its hydrophobic character, as its lateral chain increases. It is in agreement with its chemical structure. The surface free energy calculated through the Parachor parameter, for the poly(monoitaconate)s studied, decrease as the lateral chain increases its size.The estimation of surface free energy for the poly(diisoalkyl)itaconates, through Parachor, allows detect a decrease in the surface free energy for polymers, as the length of lateral chain increase that is direct relation with the experimental work done. However, this work does not allow getting surface free energy values for those polymers comparable with the experimental value. The theoretical method of Sugden was not adequate to estimate those measurements.For polymers poly(2-chloroethyl diitaconate) and poli(3-chloropropyl itaconate), the variation of experimental and theoretical surface free energy was slight. It will imply that Sugden method is well fitted for those polymers. The study of surface free energy for poly(phenylmethacrylate)s shows that the introduction of a fluorine atom at phenyl group generates a decrease in its surface free energy.For poly(phenylmetacrylate), the results showed the film thickness, needed to determinate the contact angle, need to be higher than 24513 A.The difference in the measurement of surface free energy between those experimentally determined and those estimated since Parachor, are related to the complexity of the monomeric structure. It is likely that the muckle of each group or atomic unit would be influenced by interactions of neighbor atoms within the monomeric unit. 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Surface free energy for substratesTable 6.Values of the surface free energy for poly(phenylmethacrylate) at differentfilm thicknesses1