Liquid crystal self-assembly of random-sequence DNA oligomers

In biological systems and nanoscale assemblies, the self-association of DNA is typically studied and applied in the context of the evolved or directed design of base sequences that give complementary pairing, duplex formation, and specific structural motifs. Here we consider the collective behavior of DNA solutions in the distinctly different regime where DNA base sequences are chosen at random or with varying degrees of randomness. We show that in solutions of completely random sequences, corresponding to a remarkably large number of different molecules, e.g., approximately 1012 for random 20-mers, complementary still emerges and, for a narrowrange of oligomer lengths, produces a subtle hierarchical sequence of structured self-assembly and organization into liquid crystal (LC) phases. This ordering follows from the kinetic arrest of oligomer association into long-lived partially paired double helices, followed by reversible association of these pairs into linear aggregates that in turn condense into LC domains

Force-Extension Relations for Polymers with Sliding Links

Topological entanglements in polymers are mimicked by sliding rings (slip-links) which enforce pair contacts between monomers. We study the force-extension curve for linear polymers in which slip-links create additional loops of variable size. For a single loop in a phantom chain, we obtain exact expressions for the average end-to-end separation: The linear response to a small force is related to the properties of the unstressed chain, while for a large force the polymer backbone can be treated as a sequence of Pincus--de Gennes blobs, the constraint effecting only a single blob. Generalizing this picture, scaling arguments are used to include self-avoiding effects.Comment: 4 pages, 5 figures; accepted to Phys. Rev. E (Brief Report

Physical properties and alignment of a polymer-monomer ferroelectric liquid crystal mixture

We present a new Ferroelectric Liquid Crystal (FLC) siloxane-based polymer which exhibits complete miscibility with the low molecular weight FLC (4'[(S)-(4-methylhexyl)oxy]phenyl-4-(decyloxy)benzoate). The mixture exhibits an alignment transition, orienting with the smectic layers along the rubbing direction at high polymer concentrations and, typical of low molecular weight liquid crystals, normal to the rubbing direction at low polymer concentrations. The aligned mixture exhibits high contrast electro-optic switching and has been physically characterized with respect to the sign and magnitude of the ferroelectric polarization and its temperature dependence, temperature variation of optical tilt angle and the optical response to an applied electric field.Nous décrivons un nouveau polymère mésomorphe en peigne ferroélectrique appartenant à la famille des polysiloxanes qui est miscible en toutes proportions avec un composé ferroélectrique classique, le 4-décyloxybenzoate de 4'-(s)(4-méthylhexyl)oxyphényl. Le mélange présente une transition d'alignement : pour les concentrations élevées en polymère, les plans smectiques s'orientent parallèlement à la direction de frottement alors que pour des concentrations faibles en polymère, les plans smectiques s'orientent perpendiculairement à cette direction (cette dernière situation est typique des petites molécules ferroélectriques). Les échantillons orientés présentent une commutation électro-optique avec un contraste élevé, ce qui a permis d'étudier le signe et l'amplitude de la polarisation ferroélectrique et sa variation avec la température, ainsi que l'évolution de l'angle d'inclinaison des molécules avec la température et la réponse optique en fonction du champ appliqué

Alignment of the columnar liquid crystal phase of nano-DNA by confinement in channels

We demonstrate that topographic confinement in micro-channels can produce aligned domains of the columnar liquid crystal phase of complementary duplex short deoxyribonucleic acid (DNA) oligomers. Optical microscopy probing birefringence and fluorescence polarisation showed that the columnar liquid crystal phase of a 1:1 mixture of the complementary dodecamers 5\u2032\u2013CCTCAAAACTCC\u20133\u2032 and 5\u2032\u2013GGAGTTTTGAGG\u20133\u2032 in aqueous solution was aligned with the duplex DNA chains oriented normal to the channel axis