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Eugene M Terentjev

Publications and source records attributed to Eugene M Terentjev.

8 recordsLinked to original sources
PubMed2006

Nematic membranes: shape instabilities of closed achiral vesicles.

We consider the coupling between the local curvature tensor of a membrane and the local two-dimensional nematic order parameter, deriving it from a quasi-microscopic argument. This coupling makes the nematic director aligned along the lowest curvature eigenvector in a local metric. Local bending of a membrane may then generate nematic ordering. Alternatively, emerging nematic order leads to shape instabilities of closed vesicles. The theory is applied to a spherical isotropic vesicle, which turns into a prolate shape with two +1 disclinations on its poles as the nematic order sets in the membrane, described within the Landau-de Gennes continuum model.

Journal Article↗
PubMed2006

Thermal and UV shape shifting of surface topography.

The confinement of LCE materials into surface monodomains via micropatterning leads to the formation of reversible, shape-shifting surface patterns. The individual features are liquid crystalline monodomains, and by switching to an isotropic state using light or heat, the features switch between imprinted circular features and anisotropic liquid crystalline features.

Journal Article↗
PubMed2005

Mechanically induced helix-coil transition in biopolymer networks.

The quasi-equilibrium evolution of the helical fraction occurring in a biopolymer network (gelatin gel) under an applied stress has been investigated by observing modulation in its optical activity. Its variation with the imposed chain extension is distinctly nonmonotonic and corresponds to the transition of initially coiled strands to induced left-handed helices. The experimental results are in qualitative agreement with theoretical predictions of helices induced on chain extension. This new effect of mechanically stimulated helix-coil transition has been studied further as a function of the elastic properties of the polymer network: crosslink density and network aging.

Amino Acid Sequence↗
PubMed2005

Optical microscopy study for director patterns around disclinations in side-chain liquid crystalline polymer films.

Polarizing optical microscopy is employed to study director fields around disclinations in side-chain liquid crystalline polymer films. Optical black brushes together with stripes around disclinations are observed. The stripes run parallel to the local director and thus decorate overall patterns of nematic director around disclinations. Three director patterns involving radial, spiral, and circular microstructures of a positive integer disclination with s = +1 and one hyperbolic pattern of a negative integer disclination with s = -1 are observed in the thin film. It is found that the specific configurations of a pair of (+1, -1) disclinations form during the late stage of annihilation. Increasing the film thickness leads to disclination instability. We observe that black four-brushes of disclinations with s = +/-1 split into black two-brushes, where two types of director patterns of disclinations with half-integer strengths of s = +/- 1/2 produce. Theoretical analysis is presented to explain this instability.

Journal Article↗
PubMed2005

Shape-memory nanoparticles from inherently non-spherical polymer colloids.

Samples of polymeric materials generally have no intrinsic shape; rather their macroscopic form is determined by external forces such as surface tension and memory of shear (for example, during extrusion, moulding or embossing). Hence, in the molten state, the thermodynamically most stable form for polymer (nano)particles is spherical. Here, we present the first example of polymer nanoparticles that have an intrinsic non-spherical shape. We observe the formation of high-aspect-ratio ellipsoidal polymer nanoparticles, of controlled diameter, made from main-chain liquid crystalline polymers using a mini-emulsion technique. The ellipsoidal shape is shown to be an equilibrium (reversible) characteristic and a direct result of the material shape memory when a liquid crystal nanoparticle is in its monodomain form.

Colloids↗
PubMed2005

Photomechanical actuation in polymer-nanotube composites.

For some systems, energy from an external source can trigger changes in the internal state of the structure, leading to a mechanical response much larger than the initial input. The ability to unlock this internal work in a solid-state structure is of key importance for many potential applications. We report a novel phenomenon of photo-induced mechanical actuation observed in a polymer-nanotube composite when exposed to infrared radiation. At small strains the sample tends to expand, when stimulated by photons, by an amount that is orders of magnitude greater than the pristine polymer. Conversely, at larger applied pre-strain, it will contract under identical infrared excitation. The behaviour is modelled as a function of orientational ordering of nanotubes induced by the uniaxial extension. It is thought that no other materials can display this continuously reversible response of so large a magnitude, making rubber nanocomposites important for actuator applications.

Dimethylpolysiloxanes↗
PubMed2005

Atomic force microscopy study for supermolecular microstructures in side-chain liquid crystalline polymer films.

Atomic force microscopy (AFM) is employed to study the supermolecular microstructures of disclinations and inversion walls in thin films of a smectic side-chain liquid crystalline polymer. Two-dimensional nanostripes are formed in thin films when the material enters the smectic phase. A possible mechanism for their formation is also suggested. The stripes run parallel to the local director and thus decorate the overall patterns of nematic director around the disclinations and inversion walls. Three patterns involving radial, spiral, and circular supermolecular microstructures of a positive disclination with s = +1 and one hyperbolic pattern of a negative disclination with s = -1 are observed. The cores of all these microstructures exhibit circular dark centers in AFM height images. It is found that the specific configurations of a pair of (+1, -1) disclinations form during the late stage of annihilation and inversion walls always separate a pair of (+1, +1) disclinations. The analysis on the director fields around disclinations and inversion walls shows that the bend and splay elastic constants are of the same order of magnitude in the side-chain liquid crystalline polymer.

Journal Article↗