View
217
Download
0
Category
Preview:
Citation preview
8/12/2019 Peculiar molecular dynamics behaviours in isotropic phase of some liquid crystalline systems
1/42
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
8/12/2019 Peculiar molecular dynamics behaviours in isotropic phase of some liquid crystalline systems
2/42
8/12/2019 Peculiar molecular dynamics behaviours in isotropic phase of some liquid crystalline systems
3/42
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
8/12/2019 Peculiar molecular dynamics behaviours in isotropic phase of some liquid crystalline systems
4/42
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
8/12/2019 Peculiar molecular dynamics behaviours in isotropic phase of some liquid crystalline systems
5/42
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
8/12/2019 Peculiar molecular dynamics behaviours in isotropic phase of some liquid crystalline systems
6/42
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
8/12/2019 Peculiar molecular dynamics behaviours in isotropic phase of some liquid crystalline systems
7/42
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
8/12/2019 Peculiar molecular dynamics behaviours in isotropic phase of some liquid crystalline systems
8/42
8/12/2019 Peculiar molecular dynamics behaviours in isotropic phase of some liquid crystalline systems
9/42
8/12/2019 Peculiar molecular dynamics behaviours in isotropic phase of some liquid crystalline systems
10/42
8/12/2019 Peculiar molecular dynamics behaviours in isotropic phase of some liquid crystalline systems
11/42
8/12/2019 Peculiar molecular dynamics behaviours in isotropic phase of some liquid crystalline systems
12/42
8/12/2019 Peculiar molecular dynamics behaviours in isotropic phase of some liquid crystalline systems
13/42
monomer : normal behaviour
as usually revealed by LCs in
isotropic phase
8/12/2019 Peculiar molecular dynamics behaviours in isotropic phase of some liquid crystalline systems
14/42
typical contribution of CM in
nematic phase with the typical
square root frequency dependence
8/12/2019 Peculiar molecular dynamics behaviours in isotropic phase of some liquid crystalline systems
15/42
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
8/12/2019 Peculiar molecular dynamics behaviours in isotropic phase of some liquid crystalline systems
16/42
Packing model in N phase Packing model in SmC phase
8/12/2019 Peculiar molecular dynamics behaviours in isotropic phase of some liquid crystalline systems
17/42
tetrapode : peculiar frequencydispersion in isotropic phase
- square root law
- no molecular self-diffusion
8/12/2019 Peculiar molecular dynamics behaviours in isotropic phase of some liquid crystalline systems
18/42
nematic phase :
- square root law
- no molecular self-diffusion
8/12/2019 Peculiar molecular dynamics behaviours in isotropic phase of some liquid crystalline systems
19/42
smectic C phase :
- square root law
- no molecular self-diffusion
8/12/2019 Peculiar molecular dynamics behaviours in isotropic phase of some liquid crystalline systems
20/42
tetrapode : peculiar frequency
dispersion in isotropic phase
- square root law
- no molecular self-diffusion
8/12/2019 Peculiar molecular dynamics behaviours in isotropic phase of some liquid crystalline systems
21/42
nematic phase :
- square root law
- no molecular self-diffusion
8/12/2019 Peculiar molecular dynamics behaviours in isotropic phase of some liquid crystalline systems
22/42
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)
8/12/2019 Peculiar molecular dynamics behaviours in isotropic phase of some liquid crystalline systems
23/42
tetrapode : normal behaviour
as usually revealed by LCs inisotropic phase
8/12/2019 Peculiar molecular dynamics behaviours in isotropic phase of some liquid crystalline systems
24/42
higher contribution of CM when
comparing with other studied LCs
which, on the contrary showedthe dominance of SD
8/12/2019 Peculiar molecular dynamics behaviours in isotropic phase of some liquid crystalline systems
25/42
8/12/2019 Peculiar molecular dynamics behaviours in isotropic phase of some liquid crystalline systems
26/42
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
8/12/2019 Peculiar molecular dynamics behaviours in isotropic phase of some liquid crystalline systems
27/42
8/12/2019 Peculiar molecular dynamics behaviours in isotropic phase of some liquid crystalline systems
28/42
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
8/12/2019 Peculiar molecular dynamics behaviours in isotropic phase of some liquid crystalline systems
29/42
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
8/12/2019 Peculiar molecular dynamics behaviours in isotropic phase of some liquid crystalline systems
30/42
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).
8/12/2019 Peculiar molecular dynamics behaviours in isotropic phase of some liquid crystalline systems
31/42
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
isotropic phase : - typical relaxation mechanisms (SD, ROT)
- no frequency dispersion
4. The same type of peculiar behaviours were found also for some lyotropic LCs.
8/12/2019 Peculiar molecular dynamics behaviours in isotropic phase of some liquid crystalline systems
32/42
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
isotropic phase : - typical relaxation mechanisms (SD, ROT)
- no frequency dispersion
4. The same type of peculiar behaviours were found also for some lyotropic LCs.
8/12/2019 Peculiar molecular dynamics behaviours in isotropic phase of some liquid crystalline systems
33/42
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
isotropic phase : - typical relaxation mechanisms (SD, ROT)
- no frequency dispersion
4. The same type of peculiar behaviours were found also for some lyotropic LCs.
8/12/2019 Peculiar molecular dynamics behaviours in isotropic phase of some liquid crystalline systems
34/42
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 tetrapode with long flexible spacers and terminally attached mesogens
isotropic phase : - typical relaxation mechanisms (SD, ROT)
- no frequency dispersion
4. The same type of peculiar behaviours were found also for some lyotropic LCs.
8/12/2019 Peculiar molecular dynamics behaviours in isotropic phase of some liquid crystalline systems
35/42
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 tetrapode with long flexible spacers and terminally attached mesogens
isotropic phase : - typical relaxation mechanisms (SD, ROT)
- no frequency dispersion
4. The same type of peculiar behaviours were found also for some lyotropic LCs.
8/12/2019 Peculiar molecular dynamics behaviours in isotropic phase of some liquid crystalline systems
36/42
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
isotropic phase : - typical relaxation mechanisms (SD, ROT)
- no frequency dispersion
4. The same type of peculiar behaviours were found also for some lyotropic LCs.
8/12/2019 Peculiar molecular dynamics behaviours in isotropic phase of some liquid crystalline systems
37/42
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
isotropic phase : - typical relaxation mechanisms (SD, ROT)
- no frequency dispersion
4. The same type of peculiar behaviours were found also for some lyotropic LCs.
8/12/2019 Peculiar molecular dynamics behaviours in isotropic phase of some liquid crystalline systems
38/42
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
isotropic phase : - typical relaxation mechanisms (SD, ROT)
- no frequency dispersion
4. The same type of peculiar behaviours were found also for some lyotropic LCs.
8/12/2019 Peculiar molecular dynamics behaviours in isotropic phase of some liquid crystalline systems
39/42
8/12/2019 Peculiar molecular dynamics behaviours in isotropic phase of some liquid crystalline systems
40/42
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
isotropic phase : - typical relaxation mechanisms (SD, ROT)
- no frequency dispersion
4. The same type of peculiar behaviours were found also for some lyotropic LCs.
8/12/2019 Peculiar molecular dynamics behaviours in isotropic phase of some liquid crystalline systems
41/42
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
isotropic phase : - typical relaxation mechanisms (SD, ROT)
- no frequency dispersion
4. The same type of peculiar behaviours were found also for some lyotropic LCs.
8/12/2019 Peculiar molecular dynamics behaviours in isotropic phase of some liquid crystalline systems
42/42
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.
Recommended