Twisted,Luxembourg 10-12May2016

Density-functionaltheoryforcholestericphasesofrealisticflexibleparticles

M.M.C.Tortora1,J.P.K.Doye11PhysicalandTheoreticalChemistryLaboratory,DepartmentofChemistry,UniversityofOxford,

SouthParksRoad,OxfordOX13QZ,UnitedKingdom

Lyotropiccholestericphasesarecommonlyobserved inmanybio-colloidalandpolymersolutions,characterisedbyacomplexinterplaybetweenthermalfluctuations,entropic and molecular forces. The difficulty of achieving accurate microscopicdescriptions of thesemany competing factors has led to the introduction of stronglycoarse-grained theoreticalmodels, whosemicroscopic underpinnings are highly non-trivial[1].Furthermore,thewidelengthscalediscrepancybetweentypicalparticlesizesand experimental pitches has largely thwarted direct numerical investigations ofcholestericself-assemblyforallbutthesimplestmodelsystems[2].

We here introduce a comprehensive numerical framework based on densityfunctionaltheory[3]toinvestigatethecholestericbehaviourofgenericparticlesintheweak chirality limit. This approach, built upon theuseof highly-efficientMonte-Carlomethods for the computation of virial-type integrals, enables us to tackle arbitrarilycomplex mesogen models and interaction potentials. We illustrate its application tosystemsof near-persistence-lengthDNAduplexes as describedby awell-documentedmolecularmodelcoarse-grainedatthenucleotidelevel[4](Fig.1),andinvestigatetherelative roles of excluded volume, electrostatics and particle flexibility on phasebehaviour and cholesteric pitch. We finally consider potential shortcomings of thetheory in termsof symmetry assumptions and inter-particle correlations, anddiscussprospectivedirectionsforfutureimprovements.

Figure1.Modelsystemof146base-pairsDNAduplexes

References[1] Wensink,H.H.,Europhys.Lett.107,36001(2014).[2] Dussi,S.etal.,Nat.Commun.7,11175(2016).[3] Straley,J.P.,Phys.Rev.A.14,1835(1976).[4] Snodin,B.E.K.etal.,J.Chem.Phys.142,234901(2016).