[ACS Symposium Series] New Polymeric Materials Volume 916 || Viscometry and Light Scattering of Polymer Blend Solutions

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<ul><li><p>Chapter 21 </p><p>Viscometry and Light Scattering of Polymer Blend Solutions </p><p>M . J. K. Chee1, C. Kummerlwe2, and H. W. Kammer1,3,* </p><p>1School of Chemical Sciences, University Sains Malaysia, 11800 Minden Penang, Malaysia </p><p>2University of Applied Sciences Osnabrck, Albrechtstrasse 30, D-49076 Osnabrck, Germany </p><p>3Current address: Mansfelder Strasse 28, D-01309 Dresden, Germany </p><p>Polymer blends comprising PHB in combination with PEO and PCL, respectively, were dissolved in common good solvents. Viscometry and light scattering served studying interactions between unlike polymers in dilute solutions of the blends. Specific viscosities obey the Huggins equation to an excellent approximation in the concentration range studied. Huggins coefficients display nonlinear dependencies on blend composition. - Apparent quantities of the ternary systems, molecular mass, radius of gyration and second virial coefficient, determined by light scattering, show also nonlinear variation with blend composition. The second virial coefficients versus blend composition display positive and negative deviations from additivity those are indicative of repulsion and attractions, respectively, between the polymer constituents. </p><p>282 </p><p>Dow</p><p>nloa</p><p>ded </p><p>by O</p><p>HIO</p><p> STA</p><p>TE U</p><p>NIV</p><p> LIB</p><p>RARI</p><p>ES o</p><p>n O</p><p>ctob</p><p>er 1</p><p>4, 2</p><p>014 </p><p>| http:</p><p>//pubs</p><p>.acs.o</p><p>rg Pu</p><p>blic</p><p>atio</p><p>n D</p><p>ate:</p><p> Sep</p><p>tem</p><p>ber 2</p><p>9, 2</p><p>005 </p><p>| doi: 1</p><p>0.1021</p><p>/bk-20</p><p>05-091</p><p>6.ch02</p><p>1</p><p>In New Polymeric Materials; Korugic-Karasz, L., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2005. </p></li><li><p>283 </p><p>Introduction </p><p>We report on viscosity and light scattering studies of ternary polymer-blend solutions to reveal dominant interactions in polymer blends. Knowledge about interactions between constituents in polymer blends is important for understanding of their phase behavior. Evaluation of polymer-polymer miscibility is especially complicated in polymer blends comprising crystallizable constituents. Solution viscometry and light scattering might then be powerful tools in assessing miscibility of the components in the amorphous state. </p><p>The viscometric method utilizes the fact that polymer-polymer interactions are reflected in the viscosity of polymer-blend solutions consisting of chemically different polymers in a common solvent. In recent years, several attempts have been made using dilute-solution viscometry to predict polymer-polymer miscibility (/-/2). Starting point is the equation for the viscosity of a polymer solution proposed by Huggins (13). According to Huggins* equation, the second-order term in the viscosity as a function of polymer concentration represents interactions between constituents of the system. This equation is extended to a polymer-blend solution consisting of two polymers in a common solvent. There are polymer-solvent and polymer-polymer interactions in the system. The interactions, including polymer-polymer interactions, are reflected in Huggins' equation via hydrodynamic interactions. In a common solvent, coils have a certain hydrodynamic volume. This volume will change owing to attractions or repulsions between chemically different chains, which in turn causes alteration of the Huggins coefficient. It means, we can deduce information about polymer-polymer interactions from the Huggins coefficient. Given the two polymers are dissolved in a common good solvent, at sufficiently low concentration of polymer they form separate swollen coils that behave like hard spheres and do not interpenetrate. Hence, one expects additive behavior of intrinsic viscosities in ternary solutions. When the concentration increases, the coils will interpenetrate and the Huggins coefficient reflects not only polymer-solvent but also polymer-polymer interactions. In that way, one can determine easily parameters from measurements of viscosity that are suitable to evaluate phase behavior of a polymer blend. </p><p>There are a number of light scattering studies on ternary solutions chiefly of immiscible polymers in a common solvent (14 - 21). Light scattering data yield the second virial coefficient. In Flory-Huggins approximation, the second virial coefficient for polymer blend solutions can be represented by an additivity term and an excess term with respect to blend composition (22). The excess term is proportional to the interaction parameter of the two polymer constituents. Positive deviation from additivity is caused by a positive interaction parameter and indicates immiscibility of the two polymers. Miscibility can be inferred </p><p>Dow</p><p>nloa</p><p>ded </p><p>by O</p><p>HIO</p><p> STA</p><p>TE U</p><p>NIV</p><p> LIB</p><p>RARI</p><p>ES o</p><p>n O</p><p>ctob</p><p>er 1</p><p>4, 2</p><p>014 </p><p>| http:</p><p>//pubs</p><p>.acs.o</p><p>rg Pu</p><p>blic</p><p>atio</p><p>n D</p><p>ate:</p><p> Sep</p><p>tem</p><p>ber 2</p><p>9, 2</p><p>005 </p><p>| doi: 1</p><p>0.1021</p><p>/bk-20</p><p>05-091</p><p>6.ch02</p><p>1</p><p>In New Polymeric Materials; Korugic-Karasz, L., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2005. </p></li><li><p>284 </p><p>when the second virial coefficient as a function of composition displays negative deviation from additivity. Determination of the excess term of the second virial coefficient in ternary solutions becomes especially simple under so-called optical condition (16, 17, 23). This condition is characterized by refractive index increments of opposite sign for the two polymer components. Unfortunately, for the blends under discussion no common good solvent could be found that obeys this condition. </p><p>In this paper we present quantities provided by viscosity and light scattering measurements on polymer blend solutions comprising poly(3-hydroxy butyrate) (PHB) in combination with po!y(ethylene oxide) (PEO) and poly(f-caprolactone) (PCL), respectively, in chloroform and trifluoroethanol (TFE). We focus especially on the composition dependence of Huggins coefficient and second virial coefficient for the blend solutions. </p><p>Theoretical Background </p><p>Viscosity. We start with Huggins' equation for the viscosity of polymer solutions. Formulated for a polymer blend solution, it reads </p><p>IspecJb = Mb cb + &amp; Hb Mb cb (1 ) </p><p>where c is the mass concentration of the macromolecules in the solvent and KH is the Huggins coefficient, subscript b refers to polymer blend. Specific viscosity, j?spec, and intrinsic viscosity, [], are defined as usual. Quantity [] of eq 1 comprises dependence of the terms on molecular mass. Hence, the Huggins coefficient is independent of molecular mass to a good approximation. </p><p>Equation 1 provides a linear relationship between reduced viscosity, %pec/c, and concentration c with intercept [], and the slope yields the dimensionless Huggins coefficient KH. Quantities [^ and KH b that follow from eq 1 refer to the blend solution. These quantities might be represented by superposition of quantities of the respective binaries. With total polymer concentration cb = cj + c2, it follows for intrinsic viscosity and KH b of the blend solution </p><p>[7lb*[7]iW| + [/7]2W2 (2) </p><p>with mass fraction w, = cjcb(i = 1,2). Eq 2 is straightforward since one expects additivity of the intrinsic viscosities for dilute solutions. The Huggins coefficient </p><p>Dow</p><p>nloa</p><p>ded </p><p>by O</p><p>HIO</p><p> STA</p><p>TE U</p><p>NIV</p><p> LIB</p><p>RARI</p><p>ES o</p><p>n O</p><p>ctob</p><p>er 1</p><p>4, 2</p><p>014 </p><p>| http:</p><p>//pubs</p><p>.acs.o</p><p>rg Pu</p><p>blic</p><p>atio</p><p>n D</p><p>ate:</p><p> Sep</p><p>tem</p><p>ber 2</p><p>9, 2</p><p>005 </p><p>| doi: 1</p><p>0.1021</p><p>/bk-20</p><p>05-091</p><p>6.ch02</p><p>1</p><p>In New Polymeric Materials; Korugic-Karasz, L., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2005. </p></li><li><p>285 </p><p>can be expressed as a second order equation of the individual quantities of the constituents plus an excess term, which is ruled by parameter * defined by </p><p>* ^ [ K H I 2 - ( K H I W / 2 ] (4) </p><p>We define a solution as ideal if the excess term of eq 3 disappears, i.e., **= 0 or KH\2 = ( # # 2 ) , / 2 Parameter reveals deviations from ideal behavior that are, to a good approximation, chiefly due to thermodynamic interactions between the different macromolecular species. At sufficiently high polymer concentration, coils will interpenetrate. Then, attractions between chemically different molecules will cause swelling of the coils leading to an excess increase in viscosity as compared to perfect behavior. Hence, positive deviations from ideal behavior are indicative of attractions between the different polymer species whereas negative deviations result from repulsions. Expressing these findings in terms of coefficient , it follows, &gt; 0 reflects miscibility whereas &lt; 0 stands for immiseibility. </p><p>Light scattering. Light scattering data are organized in Zimm plots (24). Extrapolations of the reduced scattering intensity to scattering angle (9=0 and concentration c = 0 yield the quantities of interest, the molecular mass, A/w, the second virial coefficient, A2, and the form factor, (). The latter quantity depends on the mean square radius of gyration, . Moreover, the optical constant of the scattering equations depends on the refractive index increment, which is symbolized by nc. The scattering equations, applied to ternary blend solutions, yield apparent quantities of the ternary system (14, 22). These quantities can be expressed analogously to eqs 2 and 3 in terms of the corresponding binaries. It follows </p><p>where subscript t refers to the ternary system. For the apparent molecular mass and the apparent radius of gyration, eq 5, we get simply additivity relations since these quantities are coefficients of first order terms in concentration. The second virial coefficient of the ternary system can be represented by a perfect and an excess part. The excess term characterizes deviations of the real blend solution from the perfect blend solution. Parameter Xof eq 5 might be seen as an excess second virial coefficient. It is defined in a similar way as parameter *rof eq 4 </p><p>Dow</p><p>nloa</p><p>ded </p><p>by O</p><p>HIO</p><p> STA</p><p>TE U</p><p>NIV</p><p> LIB</p><p>RARI</p><p>ES o</p><p>n O</p><p>ctob</p><p>er 1</p><p>4, 2</p><p>014 </p><p>| http:</p><p>//pubs</p><p>.acs.o</p><p>rg Pu</p><p>blic</p><p>atio</p><p>n D</p><p>ate:</p><p> Sep</p><p>tem</p><p>ber 2</p><p>9, 2</p><p>005 </p><p>| doi: 1</p><p>0.1021</p><p>/bk-20</p><p>05-091</p><p>6.ch02</p><p>1</p><p>In New Polymeric Materials; Korugic-Karasz, L., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2005. </p></li><li><p>286 </p><p>(7) </p><p>Quantities Gl2 and Vs are the derivative of Gibbs free energy per NkT with respect to concentrations of polymer components 1 and 2 in the solution and the molar volume of the solvent, respectively. Experimental results of light scattering are discussed chiefly in terms of eqs 5 and 6. In Flory-Huggins approximation and for small total volume fraction of polymer in the solution, quantities in eq 7 read P\p&gt;Gxl = I + \ - Zs\ - Zsi and 2Vsp , 2 ^ 2 ( / ) = I - 2$ where j is the density of the amorphous component /, and %l} is the interaction parameter between components / and j. It follows for the interaction parameter Xi2 from eq 7 </p><p>Equation 8 demonstrates that negative excess X of the second virial coefficient leads to &lt; 0, which is indicative of miscibility of the two polymers 1 and 2. </p><p>Materials. Molecular characteristics of the polymers used in this study are given in Table I. Polymers were purified by dissolution and precipitation in chloroform and methanol, respectively, and finally dried in vacuum at 50 C for 48 h. Polymer blend solutions for viscometry and light scattering were prepared in chloroform and trifluoroethanol (TFE), respectively, as solvents. Solvents were used without further purification. </p><p>Viscosity measurement. Ternary solutions of PHB with PEO and PCL, respectively, were prepared by dissolving polymer mixtures having different weight ratios in chloroform at 50 C, The solutions were diluted to the designated volume at room temperature to adjust desired concentrations. Concentrations ranged between 1 and 4g/l. Purification of solutions was done by filtration using nylon membrane filter prior to viscosity measurement. Ubbelohde viscometers of appropriate sizes were employed to determine the relative viscosities, of the blend solutions. In any case, the flow time of pure solvent exceeded 200 seconds so as to minimize experimental errors. Values of fall within the range of 1.2 - 2.0. Under these experimental conditions the kinetic energy and shear corrections were negligible. Viscosity measurements were carried out at 298 K. Temperature control was recorded to 0.1 K. </p><p>(8) </p><p>Experimental </p><p>Dow</p><p>nloa</p><p>ded </p><p>by O</p><p>HIO</p><p> STA</p><p>TE U</p><p>NIV</p><p> LIB</p><p>RARI</p><p>ES o</p><p>n O</p><p>ctob</p><p>er 1</p><p>4, 2</p><p>014 </p><p>| http:</p><p>//pubs</p><p>.acs.o</p><p>rg Pu</p><p>blic</p><p>atio</p><p>n D</p><p>ate:</p><p> Sep</p><p>tem</p><p>ber 2</p><p>9, 2</p><p>005 </p><p>| doi: 1</p><p>0.1021</p><p>/bk-20</p><p>05-091</p><p>6.ch02</p><p>1</p><p>In New Polymeric Materials; Korugic-Karasz, L., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2005. </p></li><li><p>287 </p><p>Light scattering experiments. Ternary solutions of PHB and PEO or PCL, respectively, were prepared in TFE in the same way as described under viscosity measurement. Solutions of five different total polymer concentrations, ranging from 1 to 5 g/1, were studied. Solutions were filtered prior to the light scattering experiments. </p><p>Table L Characteristics of the polymer samples and the solvent </p><p>Sample A C ' / kgmol"' </p><p>MJMnh) p/gcm"3 e ) A/o/gmol"1 Source </p><p>PHB 102 2.32 1.15 (25) 86 Aldrich PEO 102 1.91 1.13 (26) 44 Acros PCL 130 1.95 1.08 (27) 114 Union Carbide TFE 1.373 (28) 100 Aldrich </p><p>a ) obtained from light scattering in this study h ) obtained from GPC analysis c ) amorphous density at 25 C </p><p>Refractive index increments were measured directly in a differential refractometer (Brice-Phoenix). Unfortunately, polymer blend solutions in chloroform could not be used in light scattering experiments since the refractive index increment of PHB solutions in chloroform turned out to be very small. A photometer, equipped with a Helium-Neon Laser from Spectra-Physics (0 -632.8 nm), a Thorn-Emi photo multiplier, Model 9863/100KB, which is attached to a goniometer SP-81 from ALV-Laser GmbH, Langen (Germany), allowed to monitor the scattering intensity. </p><p>Results and Discussion </p><p>Viscometry. Data of specific viscosity over blend concentration, plotted versus concentration c, for the blend solutions in chloroform fit Huggins equation 1 with high correlation; typically, correlation coefficients amount to r = 0.9998. Regression analysis shows that intrinsic viscosities have errors of around 0.2 %. Selected results for intrinsic viscosities and Huggins coefficients are compiled in Table II. We note, both PCL and PEO display higher intrinsic viscosities than that of PHB. Moreover, intrinsic viscosities, [17], vary with blend composition according to eq 2 in excellent approximation. The respective regression functions are also listed in Table II. </p><p>Dow</p><p>nloa</p><p>ded </p><p>by O</p><p>HIO</p><p> STA</p><p>TE U</p><p>NIV</p><p> LIB</p><p>RARI</p><p>ES o</p><p>n O</p><p>ctob</p><p>er 1</p><p>4, 2</p><p>014 </p><p>| http:</p><p>//pubs</p><p>.acs.o</p><p>rg Pu</p><p>blic</p><p>atio</p><p>n D</p><p>ate:</p><p> Sep</p><p>tem</p><p>ber 2</p><p>9, 2</p><p>005 </p><p>| doi: 1</p><p>0.1021</p><p>/bk-20</p><p>05-091</p><p>6.ch02</p><p>1</p><p>In New Polymeric Materials; Korugic-Karasz, L., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2005. </p></li><li><p>288 </p><p>Table II. Selected intrinsic viscosities and Huggins coefficients for blends with PHB in chloroform </p><p>Sample [/71/cmV KH PEO/PHB </p><p>100/0 173.2 0.2 0.3347 0.0035 70/30 151.1 0.2 0.3451 0.0045 0.3373 50/50 140.4 0.4 0.3529 0.0092 0.3395 30/70 112.5 0.4 0.364 0.013 0.3424 0/100 91.2 0.2 0.3487 0.0082 </p><p>7fc(PHB/PEO...</p></li></ul>

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