Peculiar molecular dynamics behaviours in isotropic phase of some liquid crystalline systems

8/12/2019 Peculiar molecular dynamics behaviours in isotropic phase of some liquid crystalline systems

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Peculiar molecular dynamicsbehaviours in isotropic phase of

some liquid crystalline systems

D. Filip, C. Cruz, P.J. Sebastio, A.C. Ribeiro

T. Meyer, G.H. Mehl

C.F.M.C. U. Lisboa

University of Hull


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Outline

The systems:- low molecular weight LC organosiloxane compound

- organosiloxane LC tetrapodes with laterally attached mesogenic groups

- organosiloxane tetrapode with terminally attached mesogenic groups

Purpose :

- comparison between the peculiar molecular dynamics behaviour of the studied

systems in isotropic phase with those of normal calamitics and other LC

systems

- study of the influence of the molecular characteristics on molecular

dynamics in isotropic phase by proton NMR relaxation

Discussion of the NMR relaxation results

Conclusions


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Outline




Purpose :



systems




Conclusions


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Outline




Purpose :



systems




Conclusions


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Outline




Purpose :



systems




Conclusions


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Outline

The systems:

- low molecular weight LC organosiloxane compound



Purpose :



systems




Conclusions


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monomer : normal behaviour

as usually revealed by LCs in

isotropic phase


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typical contribution of CM in

nematic phase with the typical

square root frequency dependence


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Proton Spin Relaxation Study of Molecular

Motions in the Lyotropic Liquid CrystallineSystem Potassium-Laurate Water,

W.Khner, E. Rommel, F. Noack and P. Meier,

Z. Naturforsch. 42 a, 127 (1987).

Lyotropic LC Systems


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Packing model in N phase Packing model in SmC phase


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tetrapode : peculiar frequencydispersion in isotropic phase

- square root law

- no molecular self-diffusion


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nematic phase :

- square root law



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smectic C phase :

- square root law



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tetrapode : peculiar frequency

dispersion in isotropic phase

- square root law



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nematic phase :

- square root law



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Potassium laurate/6.24 % 1-decanol/68.6 % D2O

Lyotropic LC Sytems

318 K (Isotropic)

303 K (Nematic calamitic)

291 K (Nematic discotic)

A New Formalism for the Evaluation of Order-Fluctuation Modes in Liquid Crystals from

Field- Cycling NMR-Relaxometry Data,

F. Grinberg, R.Kimmich, R.-O. Seitter

and D. Pusiol, J. Magn. Reson. 135, 54 (1998)


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tetrapode : normal behaviour

as usually revealed by LCs inisotropic phase


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higher contribution of CM when

comparing with other studied LCs

which, on the contrary showedthe dominance of SD


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Model parameters obtained from the f its in nematic and isotropic phases of Ms

Phase (ToC) I(130) N(100) N(90)

Dx108(s) 0.3 - -

Dx108(s) - 0.99 1.63

ESD

= 49 kJ mol-1

Rx1010(s) 2.94 5.68 7.57

EROT= 29 kJ mol-1

ANx10-3(s-3/2) - 1.24 2.30

Model parameters obtained fr om the fi ts in isotropic, nematic and smectic Cphases of Ts

T, oC 138 134 112 104 98 78 74 70

Phase I I N N N SmC SmC SmC

Cmaxx10-8(Hz) 2.08 1.94 0.4 0.39 0.32 0.09 0.09 0.09

Rx1010(s) 2.55 2.74 4.75 6.1 7.08 16.2 19.8 22.5

EROT= 39 kJ mol-1max10

8(s) 1.02 1.99 - - - - - -

amax10-8( ) 1.79 0.81 - - - - - -

ASRx10-4(s-3/2) 0.77 1.09 3.20 3.23 3.89 5.23 5.43 5.2


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Model parameters obtained from the fi ts in isotropic and nematic

phases of Tas

Phase(ToC) I (60) I(52) I(49) N(35) N(32) N(27)

Cmaxx10-6(Hz) 7.3 5.8 6.5 5.6 5.22 5.02Rx10

9(s) 3.77 4.47 4.7 5.9 6.4 7.6

EROT= 16 kJmol-1

ASRx10-4(s-3/2) 6.75 7.97 8.79 13.78 14.18 17.42

Model fi tting parameters obtained from the fi ts in isotropic, smectic A and

smectic C phases of T-CN

Phase(ToC) I(95) I(90) SmA(70) SmA (60) SmC(43)

Cminx10-4(Hz) - - 8.69 7.06 7.06

ASx10-7(s-2) - - 2.00 2.51 3.86

Dx109(s) - - 6.47 8.16 9.98Dx10

9(s) 6.35 7.9 - - -

Rx1010(s) 2.92 3.77 4.84 5.98 9.0

ESD= 7 kJ mol-1

EROT= 19 kJ mol-1


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Model parameters obtained from the fi ts in isotropic and nematic

phases of Tas

Phase(ToC) I (60) I(52) I(49) N(35) N(32) N(27)

Cmaxx10-6(Hz) 7.3 5.8 6.5 5.6 5.22 5.02Rx10

9(s) 3.77 4.47 4.7 5.9 6.4 7.6

EROT= 16 kJmol-1

ASRx10-4(s-3/2) 6.75 7.97 8.79 13.78 14.18 17.42

Model fi tting parameters obtained from the fi ts in isotropic, smectic A and

smectic C phases of T-CN

Phase(ToC) I(95) I(90) SmA(70) SmA (60) SmC(43)

Cminx10-4(Hz) - - 8.69 7.06 7.06

ASx10-7(s-2) - - 2.00 2.51 3.86

Dx109(s) - - 6.47 8.16 9.98Dx10

9(s) 6.35 7.9 - - -

Rx1010(s) 2.92 3.77 4.84 5.98 9.0

ESD= 7 kJ mol-1

EROT= 19 kJ mol-1


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Isotropic Polymeric Systems

ex. melts and solutions of poly(dimethyl

siloxane)

Anomalous Segment Diffusion in Polymersand NMR Relaxation Spectroscopy,

H. W. Weber and R. Kimmich, Macromolecules,

26, 2597 (1993).


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Conclusions :

isotropic phase : - typical relaxation mechanisms (SD, ROT)

- no frequency dispersion

1. Low molecular weight organosiloxane compound

3. Organosiloxane tetrapodes with shorter flexible spacers and laterally attached mesogens

isotropic phase : - frequency dispersion

- similar behaviour as in LC phase

- molecular self-diffusion very much restricted possible due the

arm interdigitation characteristic for low generation dendrimers

- same square root frequency dependence law, like in nematic phase :

these slow movements possible to be explained by the existence ofaggregates formed of interdigitated molecules

2. Organosiloxane tetrapodewith long flexible spacersand terminally attached mesogens



4. The same type of peculiar behaviours were found also for some lyotropic LCs.


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Conclusions :
















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2. Organosiloxane tetrapode with long flexible spacers and terminally attached mesogens





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2. Organosiloxane tetrapode with long flexible spacers and terminally attached mesogens





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Acknowledgements

The authors acknowledge the financial support of EU network onSuper Molecular Liquid Crystal Dendrimers (RTN-LCDD)HPRN-

CT-2000-00016 and also for a fellowship, thank P. Kouwer for X-ray

measurements on aligned samples and most helpful discussions, thank

Dr. G. Feio for the experimental help with the Bruker MSL

spectrometer, thank to D. Sousa and J. Cascais for fast field cyclingNMR technical developments and support, thank to C. Costa for

preparation of the samples and X-ray diffraction facilities technical

support.

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Peculiar molecular dynamics behaviours in isotropic phase of some liquid crystalline systems