Influence of the Processes Parameters on the Properties of The ...

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Chapter 4. Experimental Procedures and Protocols for Analyses In <strong>the</strong> Sessile drop technique, <strong>the</strong> solid surface is wetted by single drops <strong>of</strong> <strong>the</strong> probe liquid. A high resolution camera captures <strong>the</strong> shape <strong>of</strong> <strong>the</strong> drop and processes this by image analyzing s<strong>of</strong>tware. The contact angle is linked to <strong>the</strong> surface energy and so, one can estimate <strong>the</strong> surface energy and discriminate between polar and apolar interactions. Organic liquids have surface tensions that are in a similar range as solid polymer. Advantages <strong>of</strong> this optical approach are <strong>the</strong> precision and quickness. In addition, placing drops at different positions gives <strong>the</strong> opportunity to explore <strong>the</strong> diversity <strong>of</strong> <strong>the</strong> surface. The disadvantages <strong>of</strong> this method are solid sample preparation, camera resolution, toge<strong>the</strong>r with <strong>the</strong> investigation <strong>of</strong> only two contact points. Especially <strong>the</strong> camera angle to obtain a perfect baseline image is important. Baseline inaccuracy is <strong>the</strong> primary contributor <strong>of</strong> a lower repeatability [Lander et al., 1993]. Contact angle was measured, by using a contact angle meter (GBX Digidrop) apparatus, by a liquid at six different points on <strong>the</strong> surface on both sides <strong>of</strong> polylactide or composite pellets. Contact angles were measured on <strong>the</strong> surface for 4 minutes as after 3 minutes, it was observed that measured angle remained stable. Contact angle measurements are influenced by several factors. First, <strong>the</strong> shape <strong>of</strong> <strong>the</strong> drop is an important influence. Measurement should take place immediately after <strong>the</strong> drop is placed on <strong>the</strong> solid material. This should cover <strong>the</strong> errors made due to interaction with <strong>the</strong> material which must be chemically and physically homogeneous. It is assumed that <strong>the</strong> liquid does not react with <strong>the</strong> solid and that <strong>the</strong> solid surface is perfectly smooth and rigid. Secondly, surface roughness and surface impurities are influential parameters. As a result <strong>the</strong> drop can have various metastable states, which automatically influence <strong>the</strong> contact angle. Finally, relative humidity and temperature are factors that provide contact angle variance [Rudawska and Jacniacka, 2008]. 4 Protocols for Porosity and Pore Size Measurement 4.1 Average Geometric Porosity The thickness and diameter <strong>of</strong> pellets and scaffold dimensions were measured at eight different points with an electronic vernier caliper. Mass <strong>of</strong> <strong>the</strong> pellets and foams was measured on an electronic digital balance to four decimal points. The observed dimensional data values were used to calculate radius and volume and <strong>the</strong>n utilize <strong>the</strong> mass obtained to calculate density <strong>of</strong> <strong>the</strong> pellet or foam. Then finally relative density and geometric porosity <strong>of</strong> <strong>the</strong> foam was calculated. As example, we present in Table 4.2 measured data <strong>of</strong> PLGA 50:50 pellets and foam before and after sc CO 2 foaming. Table 4.2: Dimensional data <strong>of</strong> PLGA 50:50 pellets and foams for geometric porosity. Pellet Foam Geometric S/N Diameter Thickness Mass Density Diameter Thickness Mass Density Porosity d p (mm) Ø p (mm) (mg) d f (mm) Ø f (mm) (mg) P(%) 1 12.9 0.6 85.0 1074.0 25.0 1.9 96.0 101.1 90.6 2 13.0 0.6 91.6 1103.4 23.5 2.1 84.2 93.1 91.6 3 12.9 0.6 96.0 1184.2 25.1 2.1 96.1 94.4 92.0 4 12.9 0.6 94.0 1137.6 31.6 1.9 93.5 62.7 94.5 5 12.9 0.6 83.8 1066.5 27.7 1.7 84.6 83.5 92.2 6 12.9 0.7 100.0 1171.2 24.9 2.0 100.4 101.1 91.4 7 12.9 0.6 95.8 1144.8 25.9 1.7 84.0 96.3 91.6 8 12.9 0.6 101.0 1242.1 26.3 2.3 100.1 81.2 93.5 9 13.0 0.6 84.2 1022.7 32.0 2.0 90.7 55.7 94.6 - 102 -
Chapter 4. Experimental Procedures and Protocols for Analyses The foams obtained after process are mostly in circular shape, <strong>the</strong> diameter variations in not very high, however thick varies to some extent. Porosity obtained by geometric method compared with mercury intrusion porosimetry produced results 5 to 7% higher. 4.2 2D Image Analysis The scanning electron microscope (SEM) used in our study was a, LEO 435 VP model. The sections <strong>of</strong> <strong>the</strong> foams were mounted on an aluminum stub with a carbon adhesive and <strong>the</strong>n coated with silver/gold (120 sec, Argon atmosphere). The SEM micrographs were digitized on a matrix <strong>of</strong> 10241024 pixels with 256 gray levels. In order to study <strong>the</strong> foams porosity, image analysis was performed using <strong>the</strong> SCION ® image s<strong>of</strong>tware. The first stage is to obtain conductive materials by using a device called a "sputter coater." 4.2.1 Sputter Coater If powder particles were to be analyzed, <strong>the</strong>y were dispersed on double-sided carbon conductive adhesive tape attached to <strong>the</strong> studs. Double sided adhesive tape permits quick mounting <strong>of</strong> samples without using liquid or colloidal adhesives. These studs are fixed on <strong>the</strong> sample holder. For foams after being frozen in liquid nitrogen for 2 min, <strong>the</strong> specimens were fractured using a razor blade and tweezers in <strong>the</strong> directions parallel and perpendicular to <strong>the</strong> surface, <strong>the</strong>n placed on <strong>the</strong> holder with <strong>the</strong> help <strong>of</strong> isopropanol base graphite paint. The resulting transverse and longitudinal sections were sputter-coated with platinum/gold. The holder mounted with samples is placed in <strong>the</strong> chamber. Sputter coater uses an electric field and argon gas. The metalizing chamber is closed and placed under vacuum. A stream <strong>of</strong> argon eliminates <strong>the</strong> oxygen in <strong>the</strong> chamber. Gold or gold-palladium is preferred if <strong>the</strong> sample has a very irregular surface. Carbon conductive adhesive tapes Particle image Particulate Sample Particle sample on holder Coated particle sample Polymer foams Sputter Coater SEM LEO 435 VP Foam Coated foam sample Dipping foam in liquid nitrogen Tweezers to break foam Sample Holders Isopropanol Base conductive adhesive (Graphite paint) Foam pore Image Figure 4.22: Sputter coating and SEM processing flow diagram. - 103 -
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Institut National Polytechnique de
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pleased I was to work with all memb
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Publications and Conferences The wo
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Nomenclature and Abbreviations Abbr
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ρ p Pellet density Splitting (Bra
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Chapter 2 .........................
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