Dynamics of the two-dimensional melting transition of a liquid crystal confined in Anopore membranes

Sandhya, K. L.; Nair, Geetha G.; Prasad, S. Krishna; Khandelwal, Anjuli

doi:10.1080/02678290110082374

Cited by 7 publications

(4 citation statements)

References 19 publications

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“…A number of studies on the effects of surface interactions and confinement on the isotropic-nematic phase transition have appeared previously. For example, liquid crystal in Anopore and Nucleopore membranes, [25][26][27]43,44 in polymer matrices, the so called polymer dispersed liquid crystals (PDLC), [45][46][47][48] in controlled pore glasses 29,33,36,[49][50][51][52][53][54][55][56][57] and in Aerosil. 8,16,34,[58][59][60][61][62][63][64][65] Geometrical confinement and surface anchoring effects can lead to competing changes to the phase transition behaviour.…”

Section: Discussionmentioning

confidence: 99%

Effect of suspended clay particles on isotropic–nematic phase transition of liquid crystal

Zhang

Duijneveldt

2007

Soft Matter

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Sterically stabilised nano-platelets were prepared by treating montmorillonite clay with both a surfactant and a polymeric stabiliser. These nano-platelets formed stable suspensions in a thermotropic liquid crystal, 5CB. This is in marked contrast with previous work on preparing liquid crystal suspensions of either spheres, which formed gels on cooling the solvent into the nematic phase, or clay platelets stabilised only with low molecular weight surfactant, which tended to aggregate. In the isotropic state of the liquid crystal, static light scattering showed that the clay nano-platelets were freely suspended, and no aggregation was detected even after repeated temperature cycling into and out of the nematic phase. Small-angle X-ray scattering showed that the clay was delaminated nearly completely in the liquid crystal, with some stacks of a few clay nano-platelets having formed. Differential scanning calorimetry of the liquid crystal/ clay suspensions showed a small but non-monotonic shift of the transition temperature compared to that of the pure liquid crystal. This behaviour is similar to that of liquid crystal confined in porous media, with an initial increase of the transition temperature on adding clay being ascribed to the effect of surface anchoring facilitating the formation of the nematic phase, whereas a decrease at higher clay concentrations (or equivalently, for smaller pores) is ascribed to confinement effects frustrating the formation of the nematic phase. This interpretation is supported by polarising light microscopy which showed the nematic domain size becoming smaller on increasing the clay concentration.

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Section: Discussionmentioning

confidence: 99%

Effect of suspended clay particles on isotropic–nematic phase transition of liquid crystal

Zhang

Duijneveldt

2007

Soft Matter

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“…Before the usage the membranes were thoroughly degassed for extended periods of time. The procedure adapted to fill the sample into the pores of the Anopore membrane is described elsewhere [19,21]. Calorimetry experiments were done using a Perkin Elmer DSC7 calorimeter.…”

Section: Methodsmentioning

confidence: 99%

“…Such a behavior is in agreement with that seen for the N-Iso transition [28], but is at variance with that observed in systems involving a transition to crystal-B phase. For example, in the case of the compound 4O.8 showing a Sm-A-Cr-B transition the f R value decreases by nearly 2 orders of magnitude when the material is confined in 20 nm diameter Anopore membranes [21]. For a polar compound confined in macroporous sodium borosilicate glass with a pore diameter of 86 nm, there was a slight reduction in the f R value upon confinement [20].…”

Section: Dielectric Measurementsmentioning

confidence: 99%

“…Of these, Anopore membranes are attractive as they have highly parallel cylindrical pores with narrow size distributions and smoother cavity surface. The influence of confined geometry has been reported in systems with transitions involving the nematic (N) [9][10][11][12][13], Sm-A [14,15], chiral smectic-C ͑Sm-C * ͒ [16][17][18][19], and crystal-B [20,21] phases. A common feature observed in these studies is that confinement can alter (generally diminish) the transition temperature.…”

Section: Introductionmentioning

confidence: 99%

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X-ray and dielectric measurements of the smectic-A–hexatic-Btransition in bulk and confined geometries

2004

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We report x-ray and dielectric measurements on a liquid crystal exhibiting a smectic- A -hexatic- B (Sm- A -Hex- B ) transition in bulk and confined geometries. The confined geometry experiments have been performed by filling the compound, n -butyl 4(') - n -hexyloxybiphenyl-4-carboxylate, into Anopore membranes with 20 nm pore size. The surprising result seen in the x-ray studies on both the bulk and the Anopore samples is the presence of unusually strong second harmonic reflection arising from the smectic layers in both the Sm- A and Hex- B phases. In fact, the third harmonic reflection is also observed in the entire temperature range of the Hex- B phase and close to the transition in the Sm- A phase of the bulk sample, with the ratio of I(2qo) / I(qo), and I(3qo) / I(qo) being approximately 1/40 and 1/470, respectively (here I(qo), I(2qo), and I(3qo) correspond to the peak intensities of the first, second, and third harmonic reflections). These features point to the fact that the layering is much better defined in this system, unlike the usual description of pure sinusoidal mass density wave with a typical value of 10(-4) for I(2qo) / I(qo). Another notable feature observed is that whereas the extent of positional correlations of the molecules within the smectic layer, is comparable in the Sm- A phase of the bulk and Anopore samples, the correlations are reduced in the Hex- B phase. In the bulk as well as the Anopore case, the critical behavior of the positional correlations is found to be well described by a power-law expression with the exponent alpha being slightly larger for the Anopore sample. It is also seen that the weak first order nature of the transition seen in the bulk, gets weakened further, perhaps becoming second order. Despite such significant differences between the bulk and Anopore samples, the dynamics associated with the director fluctuations is only slightly influenced by confinement.

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On the influence of cylindrical sub-micrometer confinement on heptyloxycyanobiphenyl (7OCB). A dynamic dielectric study

Díez

Pérez‐Jubindo

Fuente

et al. 2006

Chemical Physics Letters

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Dynamics of the two-dimensional melting transition of a liquid crystal confined in Anopore membranes

Cited by 7 publications

References 19 publications

Effect of suspended clay particles on isotropic–nematic phase transition of liquid crystal

Effect of suspended clay particles on isotropic–nematic phase transition of liquid crystal

X-ray and dielectric measurements of the smectic-A–hexatic-Btransition in bulk and confined geometries

On the influence of cylindrical sub-micrometer confinement on heptyloxycyanobiphenyl (7OCB). A dynamic dielectric study

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