In this report we provide the first description of the orientation of liquid crystalline thermosets (LCT`s) in field strengths of up to 18 T, as well as the first report of tensile properties for both unoriented and oriented LCT`S. The LCT we have chosen for study is the diglycidyl ether of dihydroxy-a-methylstilbene cured with the diamine, sulfanilamide. Orientation in magnetic fields leads to an increase of almost three times the modulus compared to the unoriented material. These values are much greater than can be obtained with conventional thermosets. The strain at break is also significantly affected by the chain orientation. The coefficient of thermal expansion and x-ray diffraction of oriented samples show high degrees of anisotropy, indicating significant chain alignment in the magnetic field. We are working to further understand the field dependence of orientation and properties plus the mechanisms of the alignment process

Benicewicz, Brian C.

Douglas, Elliot P.

Earls, Jim D.

Priester, Ralph D., Jr.

Smith, Mark E.

UNT Digital Library

LA-UR-95- 4109 Title: EFFECT OF HIGH MAGNETIC FIELDS ON ORIENTATION AND PROPERTIES OF LIQUID CRYSTALLINE THERMOSETS Author@): Submitted to: L O ~  Alamos N A T I O N A L  L A B O R A T O R  Mark E. Smith, MST-7 Brian C. Benicewicz, MST-7 Elliot P. Douglas, MST-7 Jim D. Earls, The Dow Chemical Company Ralph D. Priester, Jr., The Dow Chemical Company qmerican Chemical Society Meeting \lew Orleans, LO vlarch 24 - 2 8 , 1 9 9 p  5% Los Alamos National Laboratory, an affirmative actionlequal opportunity employer, is operated by the University of California for the U.S. Department of Energy under contract W-7405-ENG-36. By acceptance of this article, the publisher recognkes that the U.S. Government retains a nonexclusive, royalty-free license to publish or reproduce the published form of this contribution, or to allow others to do so, for U S .  Government purposes. The Los Alarnos National Laboratory requests that the publisher Identify this article as work performed under the auspices of the U.S. Department of Energy. Form No. 836 RS ST2629 10191 DISTFUSUTI0N OF= THIS DOCUMENT IS UNUMKE 1 Effect of High Magnetic Fields on Orientation and Properties of Liquid Crystalline Thermosets Mark E. Smith, Brian C. Benicewicz, and Elliot P. Douglas" Polymers and Coatings Group Los Alamos National Laboratory Los Alamos, NM 87545 Jim D. Earls and Ralph D. Priester, Jr. Dow Chemical Freeport, TX 77541 In this report we provide the first description of the orientation of liquid crystalline thermosets (LCT's) in field strengths of up to 18 T, as well as the first report of tensile properties for both unoriented and oriented LCT's. The LCT we have chosen for study is the diglycidyl ether of dihydroxy-a-methylstilbene cured with the diamine, sulfanilamide. Orientation in magnetic fields leads to an increase of almost three times the modulus compared to the unoriented material. These values are much greater than can be obtained with conventional thermosets. The strain at break is also significantly affected by the chain orientation. The coefficient of thermal expansion and x-ray diffraction of oriented samples show high degrees of anisotropy, indicating significant chain alignment in the magnetic field. We are working to further understand the field dependence of orientation and properties plus the mechanisms of the alignment process. I EFFECT O F  HIGH MAGNETIC FIELDS ON ORIENTATION AND PROPERTIES OF LIQUID CRYSTALLINE THERMOSETS Mark E. Smith, Brian C. Benicewicz. and Elliot P. Douglas* Polymers and Coatings Group Los Alamos National Laboratory Los Alamos. NM 87545 Jim D. Earls and Ralph D. Priester, Jr. The Dow Chemical Company Freeport, TX 77541 Introduction Liquid crystalline thermosets (LCT's) have become recognized over the past few years as an important new class of materials. Numerous reports from our laboratory and others have described their synthesis and phase behavior.1-10 In particular, we have described important effects due to the orientation of the rodlike molecules in a liquid crystalline phase. We have found that cur- ing rates are enhanced compared to reaction in an isotropic phase? and that the glass transition of the fully cured material can be significantly higher than the final cure temperature.4 For structural applications, orientation of LCT's will allow the maximization of mechanical properties. A few studies have de- scribed use of magnetic fields to orient LCT's.899 However, the maximum reported field strength was 1 3 I T  and no measure- ments were made of the tensile properties. In this report we pro- vide the first description of the orientation of LCT's in field strengths of up to 18 T, as well as the first report of tensileproper- ties for both unoriented and oriented LCT's. The LCT we have chosen for study is the diglycidyl ether of dihydroxy-a- methylstilbene (DGE-DHAMS) cured with the diamine, sulfanil- amide (SAA). Structures for these materials are shown in Figure I .  We have cured this thermoset at field strengths of up to 18 Tesla in order to evaluate the effects of very high magnetic fields on the properties of the system. . Experimental Maonetic Field Processino,: The thermoset formulation was pre- pared by dissolving 1 equivalent of SAA and 2 milliequivalents of an organophosphonium catalyst into 1 equivalent of DGE- DHAMS at elevated temperatures. This mixture was then poured into a mold for the magnetic field experiments. This mold con- sisted of aTeflon cup into which was placed two aluminum heater blocks, with the thermoset formulation filling the space between the blocks. Temperature control was maintained with a PID con- troller. Magnetic field experiments were conducted at the Na- tional High Magnetic Field Laboratory using a 20 T variable field electromagnet. Curing was done in the field for 1 hr at 150" C. The sample was then removed from the mold by cutting theTeflon cup and separating the aluminum plates. The final cure was done in a conventional oven, and consisted of an additional 3 hrs at 150" C. I hr at 175" C, and 4 hrs at 200" C. Plaques approxi- mately 2" s 1.5" x 0.125" were obtained. Thermal Expansion: Thermal expansion measurements were per- formed parallel and perpendicular to the field direction using an Omnitherm TMA 1000 with a heating rate of 5' C/min and a mass of 10 g. Values of CTE reported are calculated by linear extnpo- lation of the displacement-temperature curve over the tempera- ture range 30 to GO" C. Tensile Properties: Tensile properties were measured on ASTM Type V specimens using an Instron 4483 testing machine and an MTS G32.26E extensometer. The results given here are the aver- age of at least three different samples for each field strength. X-rav Diffraction: X-ray diffraction was performed using a ro- tating anodz generator and a two dimensional position sensitive detector. Calculation of the orientation parameter was done us- ing the equation f = !-(3(C0S2 2 0)- 1) where the average value of cos' (I is given by X I 2  I(@)sinQcos2 @ d@ Results and Discussion The DGE-DHAMS/SAA system, which is initially isotropic, forms a smectic phase upon curing at 150' C. The formation of the smectic phase is due to an increase in aspect ratio of the rodlike molecules 83 the reaction proceeds. Under these conditions, the smectic phase forms after approximately 20 minutes of cure. and the gel point is reached in approximately 45 minutes. Curing in the magnetic field was done for 1 hour in order to ensure that any orientation induced by the field was locked into the network sttuc- ture. Tensile propzrties of the cured LCT at 0. 15, and 18 Tare shown in Table I. Sumbers in parentheses are the standard deviations. The tensile properties of the macroscopically unoriented material are similar LO those obtained with epoxies based on bisphenol A cured under the same conditions. The unique advantages of the liquid crystalline epoxy are realized when the material is oriented in magnetic fields. Particularly noteworthy is the increase in ten- sile modulus. Orientation in magnetic fields leads to an increase of almost thrze times the modulus compared to the unoriented material. The strain at break is also significantly affected by the chain orientation. The reduction in strain at break and the in- c r e w  in the modulus are due to the decreased elasticity of chemi- r:il bonds i n  the direction of orientation. ns compared to the intercliain interactions which dominate the stress-strain bellnvior in  the unoriented sample. Measurements of the coefficient of linear thermal expansion, shown in Table 11. also indicate a high degree of anisotropy in samples prepared in magnetic fields. Again, the CTE values of the unoriented sample are similar to those of conventional epoxy thermosets. Alignment in magnetic fields causes a significant decrease in the thermal expansion parallel to the field direction and a significant increase in the thermal expansion perpendicular to the field direction. This is also consistent with the molecules being aligned parallel to the direction of the field. In order to quantify the orientation, x-ray diffraction measure- ments were performed. The orientation parameter was determined by integrating the scattered intensity around the azimuthal angle @ at a given value of the scattering angle 28 according to the equa- tions given above. The orientation parameters calculated are 0.93 and 0.90 for 15 and 18 T, respectively, where a value of 1.0 indi- cates complete orientation. These two values are the same within experimental error. X-ray results confirm that the molecular axes and the smectic layer normals are aligned parallel to the field di- rection. Conclusions This report describes preliminary results on magnetic field pro- cessing of liquid crystalline thermosets. We have provided the tirsr information on the mechanical properties of liquid crystal- line thermosets. both unaligned and aligned in high magnetic fields. To our knowledge these are the highest fields used to date I'or alignment of liquid crystalline molecules, and the degree of order obtained is higher than previously reported. Mechanical properties show significant increases in tensile modulus, giving values much greater than can be obtained with conventional ther- mosets. We are working to further understand the field depen- dence of orientation and properties plus the mechanisms of the alignment process. Acknowledgments The nuthors would like to thank the Department of Energy for providing funding through the Advanced Industrial Materials Pro- gram. Experiments were performed at the National High-Mag- netic Field Laboratory(NHMFL), which is funded by the National Scirncr Foundation. Help with the magnetic field experiments nas provided by A. Lacerda and B. Brandt of the NHMFL. The authors ivould also like to thank R. E. Heffner. Jr. of The Dow Chemicd Company for synthesizing the epoxy monomer used in :his u o r k .  References I .  2. 3. 4. 5. 6. 7. 8. 9. 10. Hoyt, A. E., Beniccwicz, 13. C.J. f 'olwi .  Sci.. Parr A: Po/ylr. Cherrr.; 2s. 3403, (1990). Hoyt, A. E., Benicewicz. B. C. J. Polym. Sci., Part A: Polym. Chem., 28,3417, (1990). Douglas, E. P. Langlois. D. A., Benicewicz. B. C. Cheni. Mater., 6, 1925, (1994). Langlois, D. A., Smith, M. E., Benicewicz, B. C., Douglas, E. P. Polyirr, Matel: Sci. Ens. 74 (1996). Litt, M. H., Whang. W., Yen, K., Qian, X. J. Polym. Sci., Part A Polym. Chem.. 31, 183. (1993). Melissaris, A. P.. Litt, M. H. Macromolecules, 27,883. (1994). Melissaris, A. P., Litt, M. H. Macromolecules, 27.888. (1994). Melissaris, A. P., Litt, M. H. Macromolecules, 27, 2675, (1994). Barclay, G. G., McNamee, S. G., Ober, C. E., Papathomas, K. I., Wang, D. W. J. Polym. Sci., Part A: Polym. Chem., 30, 1845, (1992). Barclay, G. G., Ober, C. K., Papathomas, K. I., Wang, D. LV. Macromolecules, 25,2947, (1992). . -- Figure 1: Chemical structures of materials used in this study. Top: liquid crystalline epoxy. Bottom: sulfanilamide curing agent. Table I Tensile Properties - OT - 15 T - 18T modulus (ksi) 443 (32) 1081 (93) 1174 (166) strain at break (%) 8.9 (1.6) 0.8 (0.3) 1.0 (0.03) stress at break (psi) 13,010 (621) 8117 (1105) 9985 (500) Table II: Coefficients of Thermal Expansion - OT - 15 T - 18T CTE parallel to field 54 4.7 4.3 (pm/ni/'C) CTE perpendicular to field - 99.6 I 11.2 (pm/ni/"C) 

Effect of high magnetic fields on orientation and properties of liquid crystalline thermosets

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Effect of high magnetic fields on orientation and properties of liquid crystalline thermosets

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