Contains reports on two research projects.Joint Services Electronics Program (Contract DAAL03-86-K-0002

Francis, Ronald

Larson, Brent D.

Litster, James David

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Graphoepitaxy of Colloidal Crystals13. Graphoepitaxy of Colloidal CrystalsAcademic and Research StaffProf. J.D. LitsterGraduate StudentsR. Francis, B.D. Larson13.1 Studies of Micellar Liquid CrystalsJoint Services Electronics Program (Contract DAAL03-86-K-0002)Brent D. Larson, J. David LitsterIn these experiments, we used precision birefringence measurements in combination withquasielastic light scattering to study the orientational order of the micelles, the normal nodeswhich arise because of this order, and the effect of the lamellar order on these modes. The latteris closely analogous to the Meissner effect in which magnetic fields are expelled from asuperconductor. The physical effect is, of course, quite different, since it consists of certain opticaxis alignment distortions being expelled from the lamellar phase. A quantitative mathematicaldescription of these effects confirmed the applicability of the Ginsberg-Landau model to describethe main features of the process by which lamellar order is established.Our studies also established that the micellar orientational order in these systems has much incommon with that in thermotropic nematic liquid crystals; the order-disorder transition is requiredto be discontinuous by symmetry, but we found it to be very nearly continuous in one system(cesium perfluoro-octanoate in water) we studied. This system thus offers the possibility to learnmore about the nematic-isotropic transition. It also has Goldstone modes (the director modes ofthe nematic phase) which are truly hydrodynamic with zero energy at long wavelengths. Thismaterial should then show behavior analogous to that predicted theoretically for an isotropicHeisenberg ferromagnet, which inludes an infinite zero field susceptibility.The scientific questions raised by this research are important and currently interesting ones inthe field of statistical mechanics, but are not closely related to problems in the area of electronicmaterials. This research therefore is no longer being carried out with support of the JointServices Electronics Program. It will be continued with support from the National ScienceFoundation under grant DMR83-19985.RLE P.R. 128Graphoepitaxy of Colloidal Crystals13.2 Growth of Colloidal CrystalsRonald Francis, J.David LitsterIn recent years there has been much interest in crystalline order formed by aqueoussuspensions of polystyrene latex spheres. These have lattice parameters several hundred nm andhave been studied as model systems for conventional crystals, for the preparation of ceramics,and to elucidate the properties of colloids. In previous, unpublished work, we had studied"thermal diffuse" scattering of light by such crystals and determined the Lindeman ratio at themelting point to be 0.007, smaller than the typical value 0.2 in most conventional solids. We haverecently followed up on that work, learning to prepare samples in water deionised by reverseosmosis as that promises to provide better control over sample properties. Our goal is to studythe epitaxial growth of these crystals on carefully controlled surface relief structures preparedusing submicron fabrication facilities.Our recent activity efforts have been to learn how to control conditions so we can reproduciblyand reliably grow the colloidal crystals. We started with commercially available synthetic colloidsof polystyrene latex spheres. These come with electrical conductivity in the range of 50-100micro Seamans (uS). The volume fraction of suspended solids is in the 8-10 percent range. Wehave found that crystallization generally requires conductivity to be less than 20 uS. Carbonicions formed from carbon dioxide in the air causes difficulty only in the region below 3 uS. Ionexchange resins filling from 25 to 50 percent of the total volume are capable of lowering theconductivity enough to cause crystallization, given several days equilibration time. One mustminimize concentration gradients in salt and ions to have a uniform crystal.A cell to grow thin samples of colloidal crystals on a 300 nm period substrate is beingconstructed. This cell will permit the crystals grown to be studied either by light scattering or byobservation under an optical microscope.RLE P.R. 128

Graphoepitaxy of Colloidal Crystals

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Graphoepitaxy of Colloidal Crystals

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