Interaction between colloidal particles in chiral nematic liquid crystals

Transcription

1 Interaction between colloidal particles in chiral nematic liquid crystals Manoj Bhushan andey, I. Smalyukh Department of hysics, Liquid Crystal Materials Research Centre, University of Colorado at Boulder, CO 80309, US

2 Outlines 1. Introduction: 1. Defects structure around beads in Nematic Liquid Crystals. 2. Defects structure around beads in Chiral Nematic Liquid Crystals. 2. Experimental set up 1. Holographic Optical Tweezers (HOT) 2. Multi mode Fluorescence Optical Microscopy 3. Results & Discussion 1. Effect of homeotropic confinement and D/ ratio 0.5~ Investigation of defects structure around particles by TL 3. Interaction between particles decorated with defect structure. 4. ssembly of particles decorated with defect structure. 5. Creation of Defect structure around particles with LG beams. 4. Conclusions

3 Defect structures around beads in Nematics Tangential anchoring Two surface point defects (boojums) at poles n 0 Weak homeotropic surface anchoring 3

4 Defect structure around beads in Nematics Homeotropic anchoring point defect Equivalent to: n 0 Dipolar structure Disclination ring s=-1/2 around bead Quadrupolar Saturn Ring structure 4

5 What will be defect structure around beads in Cholesteric LC? 1. It will depend upon confinement and alignment Boundary condition? 2. Confinement will depend upon D/ ratio?. Ribiere, S. irkl, and. Oswald, hys. Rev. 44,

6 Twisted structure in homeotropic cell CF1, +1/2 1/2 CF3, Singular CF2, +1 1/2 CF4, Singular Cholesteric Fingers Smalyukh et al, HYSICL REVIEW E 72, , 2005

7 Twisted structure in homeotropic cell Toron structure Smalyukh et al, Nat Mat, 9, 139 (2010

8 Materials and cell parameters Chiral Nematic Liquid Crystals: MLC doped with S 811 Micro articles: Melamine Resin 3&7µm, Si 2 &4 µm Cell Boundary condition: Homeotropic cell Cell thickness: 10, 15, 25 &30 µm HT of S 811 in MLC at RT: 10.47/ µm 1 HT c pitch ch D/=

9 Colloidal particles dressed with twisted structures MLC10.6 m MR 7 m 10 m hom_20x_cross polarizer

10 articles (Si 4 m) dressed with Twisted Structures C 20X C 20X C 100X C 100X MLC10.5um Si4umhom 10um hom cell

11 articles (Si 4 m) dressed with Twisted Structures C 100X C 20X White Light MLC10.5um Si4umhom 10um hom cell

12 Integrated Set up: HOT + MNOM R.. Trivedi, T. Lee, K.. Bertness, and I. I. Smalyukh, Optics Express, 18, (2010)

13 Nonlinear Optical Imaging Techniques Excited state Single hoton Multi hoton Virtual States CRS bsorption Emission pump probe Ground State SHG THG Stokes Ground State anti Stokes vib w as 2 w p w s Out In Wavelength Ground State CRS pump probe Stokes T. Lee, B. Senyuk, R.. Trivedi, and I. I. Smalyukh,. Fernandez De Las Nieves (ed.), (Wiley VCH, 2011).

14 ssembly of colloids and Interaction between particles a b c d e f g D/=0.5 Si 4 m

15 Toron structure imaged by TL a MLC 10.6um E31 2%_7umMR_10um Hom cell

16 MR article dressed with Twisted Structure (1) a b c MLC 10.6um E31 2%_7umMR_10um Hom cell

17 MR article dressed with Twisted Structure (2) a b c MLC 10.6um E31 2%_7umMR_10um Hom cell

18 Repulsive interaction between particles with structure Distance/ m Time/s otential Energy/kT 7.E+04 6.E+04 5.E+04 4.E+04 3.E+04 2.E+04 1.E+04 0.E Distance/ m MLC 10.6um E31 2%_7umMR_10um Hom cell

19 Distance dependence interaction between particles dressed with structure 1 and 2 Distance/ m Time/s Distance/ m Time/s E Force/pN otential Energy/kT 6.00E E E Distance/ m 0.00E Distance/ m

20 Two MR dressed with Twisted structure imaged by TL a b c d e f f e g MLC 10.6um E31 2%_7umMR_10um Hom cell

21 Two MR dressed with Twisted structure imaged by TL a b c d f e f g g e MLC 10.6um E31 2%_7umMR_10um Hom cell

22 a ssembly of particles assisted by optical trap e b f MLC 10.6um E31 2%_7umMR_10um Hom cell c g d h

23 ssembly of four MR particles dressed with Twisted structure imaged by TL a b c d MLC 10.6um E31 2%_7umMR_10um Hom cell

24 Generation of Twisted structure around particle (Si) by LG beam and imaged by TL Laser MLC 32 um (E31 2%) 30um hom cell, 870nm, 150mW

25 Director profile and structure around particle in homeotropic Chiral nematic simulation results rof. Zumer and coworkers

26 Generation of Twisted structure around particle (Si) by LG beam and imaged by TL MLC 32 um (E31 2%) 30um hom cell, 870nm, 150mW

27 Conclusions 1. Interaction between colloidal particles, Nature of interaction and its range depend upon the defect structure around the particles. 2. Micro particles always trapped at the point where defects has maximum energy. 3. It is possible to control the defects between colloidal particles. 4. Specific defects structure could also be created around the particles by using LG beams with different charges. 5. Cholesteric Liquid Crystals is a promising media to create colloids dressed with twist bound structure with different topological charges.

28 cknowledgement The author (MB) thanks to ICM I2CM, 1 Shields venue, Davis, C for financial assistance under Junior Research Travel wards to attend this conference through NSF grant number DMR

29 Thank you for kind attention! Comments, suggestions and?