Strain‐induced compression of smectic layers in free‐standing liquid crystalline elastomer films

The deformation of oriented smectic liquid crystal elastomer films with smectic layers parallel to the film surface was studied using optical reflectometry and small angle X‐ray diffraction. Reflectometry data show that in the chosen material, in‐plane strain causes a change in the optical thickness of the free‐standing films. Small angle X‐ray scattering was used to explore the molecular origin of this effect. The X‐ray scattering data confirm that the change in optical thickness originates from the compression of the individual smectic layers. The measured Poisson ratio in the smectic A and C* phases is close to ½, in contrast to the smectic elastomers investigated earlier by Nishikawa et…

Smectic Liquid-Crystalline Colloids by Miniemulsion Techniques

Transjugular Intrahepatic Portosystemic Shunt for Refractory Ascites: A Meta-analysis of Individual Patient Data

Several randomized controlled trials have compared a transjugular intrahepatic portosystemic shunt (TIPS) with large-volume paracentesis in cirrhotic patients with refractory ascites. Although all agree that TIPS reduces the recurrence rate of ascites, survival is controversial. The aim of this study was to compare the effects of TIPS and large-volume paracentesis in cirrhotic patients with refractory ascites by means of meta-analysis of individual patient data from 4 randomized controlled trials.The study population consisted of 305 patients: 149 allocated to TIPS and 156 to paracentesis. Cumulative probabilities of transplant-free survival and of hepatic encephalopathy (HE) were estimated…

De Vries smectic A phase formed by a liquid crystal side chain copolymer? A13C NMR study

We study the orientation and order parameter of a liquid crystalline random side chain copolymer by 13C NMR. Evidence has previously been presented that this material forms a de Vries smectic A phase. The NMR data show that the molecular tilt angle in the smectic A phase is very small or zero and the smectic A–smectic C* transition is attributed predominantly to a change of the molecular tilt rather than azimuthal ordering. We discuss the NMR results in the context of earlier X‐ray and elastic characterizations of structurally similar materials.

Ferroelectric polysiloxane liquid crystals with ‘de Vries’-type smectic A*–smectic C* transitions

We report preliminary results of optical and small angle X-ray scattering (SAXS) experiments on the smectic A*−smectic C* transition in two ferroelectric liquid crystalline polysiloxanes. Although the optical tilt angle in the SmC* phases reaches values up to 30°, temperature-dependent SAXS measurements clearly reveal that the smectic layer spacing is basically conserved during the A*–C* transition as well as in the subsequent C* phase. Connected with the A*–C* transition we further observed a significant increase in birefringence, hence reflecting an increase of orientational order. The practical absence of layer shrinkage and the enhanced orientational ordering are consistent with the de …

Mechanical manipulation of molecular lattice parameters in smectic elastomers.

Smectic liquid crystalline elastomers (SLCE) represent unique materials that combine a 1-D molecular lattice arrangement and orientational order with rubber-elasticity mediated by a polymer network. Such materials may exhibit large thermo-mechanical, opto-mechanical and electro-mechanical effects, due to the coupling of macroscopic sample geometry and microscopic structural features. It is shown that the molecular layer dimensions in the smectic phases can be influenced reversibly by macroscopic strain of the material. We present a microscopic model on the basis of experimental results obtained by mechanical dilatation measurements, optical interferometry, X-ray scattering, (13)C NMR, FTIR …

Treatment Extension of Pegylated Interferon Alpha and Ribavirin Does Not Improve SVR in Patients with Genotypes 2/3 without Rapid Virological Response (OPTEX Trial): A Prospective, Randomized, Two-Arm, Multicentre Phase IV Clinical Trial

UNLABELLED Although sofosbuvir has been approved for patients with genotypes 2/3 (G2/3), many parts of the world still consider pegylated Interferon alpha (P) and ribavirin (R) as standard of care for G2/3. Patients with rapid virological response (RVR) show response rates >80%. However, SVR (sustained virological response) in non-RVR patients is not satisfactory. Longer treatment duration may be required but evidence from prospective trials are lacking. A total of 1006 chronic HCV genotype 2/3 patients treated with P/R were recruited into a German HepNet multicenter screening registry. Of those, only 226 patients were still HCV RNA positive at week 4 (non-RVR). Non-RVR patients with ongoin…

FTIR spectroscopy of smectic elastomer films under lateral strain

Polarized Fourier transform infrared (FTIR) spectroscopy is used to study the strain‐induced compression of molecular layers in oriented smectic liquid crystal elastomer films. A reversible change of the smectic layer thickness in SmA and SmC* films in response to external strain was revealed earlier by optical reflectometry and X‐ray measurements. However, these methods cannot probe the mechanism of layer compression on a molecular level. Polarized FTIR spectra show that the induced mesogenic tilt, one of the possible mechanisms, is too small to provide the dominating contribution to the layer shrinkage. The FTIR absorbance spectra of stretched samples are also evidence that there are no s…

Differences between smectic homo‐ and co‐polysiloxanes as a consequence of microphase separation

This paper compares smectic phases formed from LC‐homo‐ and LC‐co‐polysiloxanes. In the homopolysiloxane, each repeating unit of the polymer chain is substituted with a mesogen, whereas in the copolysiloxanes mesogenic repeating units are separated by dimethylsiloxane units. Despite a rather similiar phase sequence of the homo‐ and co‐polysiloxanes—higher ordered smectic, smectic C* (SmC*), smectic A (SmA) and isotropic—the nature of their phases differs strongly. For the copolymers the phase transition SmC* to SmA is second order and of the ‘de Vries’ type with a very small thickness change of the smectic layers. Inside the SmA phase, however, the smectic thickness decreases strongly on ap…

Study of smectic elastomer films under uniaxial stress

We study the mechanical properties of free-standing films of smectic liquid crystalline elastomers. Macroscopically ordered elastomer films of submicrometer thickness are prepared from freely suspended smectic A polymer films by photo crosslinking. The deformation characteristics depend criticically on the sample composition, in particular on the density of mesogenic side chains at the siloxane backbone. In materials where the siloxane backbone is only partially substituted (dilute systems), a uniaxial stretching of the films in the layer plane is accompanied by a shrinkage of the smectic layers. This layer shrinkage is to only a minor extent achieved by the induction of a molecular tilt. W…

Refining prediction of survival after TIPS with the novel Freiburg index of post-TIPS survival.

Background & Aims Transjugular intrahepatic portosystemic shunt (TIPS) implantation is an effective and safe treatment for complications of portal hypertension. Survival prediction is important in these patients as they constitute a high-risk population. Therefore, the aim of our study was to develop an alternative prognostic model for accurate survival prediction after planned TIPS implantation. Methods A total of 1,871 patients with de novo TIPS implantation for ascites or secondary prophylaxis of variceal bleeding were recruited retrospectively. The study cohort was divided into a training set (80% of study patients; n = 1,496) and a validation set (20% of study patients; n = 375). Furth…