Abstract
Concentrated solutions of blunt-ended DNA oligomer duplexes self-assemble in living polymers and order into lyotropic nematic liquid crystal phase. Using the optical torque provided by three distinct illumination geometries, we induce independent splay, twist, and bend deformations of the DNA nematic and measure the corresponding elastic coefficients K1, K2, and K3, and viscosities ηsplay, ηtwist, and ηbend. We find the viscoelasticity of the system to be remarkably soft, as the viscoelastic coefficients are smaller than in other lyotropic liquid crystals. We find K1 > K3 > K2, in agreement with the elasticity of the nematic phase of flexible polymers, and ηbend > ηsplay > ηtwist a behavior that is nonconventional in the context of chromonic, polymeric, and thermotropic liquid crystals, indicating a possible role of the weakness and reversibility of the DNA aggregates.
Highlights
Oligomer duplexes self-assemble in living polymers and order into lyotropic nematic liquid crystal phase
To chromonic liquid crystals (LC), ordering in oligo-DNA is based on the columnar stacking of monomers, which in the case of chromonics are flat polycyclic molecules, while in oligo-DNA are cylindrical-like duplexes
Standard strategy to investigate LC, is too weak. We overcome these difficulties and measure the three elastic coefficients and related viscosities by exploiting the combination of (i) an achiral oligo-DNA system; (ii) recently developed photoaligned surfaces; and (iii) the use of optical fields whose effectiveness in the context of oligo-DNA LCs was recently shown,[11] to couple to the nematic director in selected areas of a few tens of microns, which enables circumventing issues related to defects and impurities
Summary
Where β is the angle of the optical field E with the rubbing direction (x) and c is the speed of light. As the twist deformation is induced, n is tilted away from the rubbing direction, producing an increase or decrease in the transmitted intensity IT, depending on α This is shown in Figure 2B3, where we plot IT versus time for rDNA for α = 35° and α = 55° and different values of IP (colored lines). Geometry B leads to a situation a bit more complex because of the modification in the pump polarization as it propagates in the cell In this case, the relaxation of the director deformation is given by the sum of two exponentials since it involves a significant contribution from the spatial mode, the two characteristic times being τ21 = ηtwistL2/π2K2 and τ22 = τ21/4. The elastic coefficients and viscosities that we obtain for rDNA and thermotropic LCs are reported in Table 1 that
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