Spontaneous thermal expansion of nematic elastomers

We study the monodomain (single-crystal) nematic elastomer materials, all side-chain siloxane polymers with the same mesogenic groups and crosslinking density, but differing in the type of crosslinking. Increasing the proportion of long di-functional segments of main-chain nematic polymer, acting as network crosslinking, results in dramatic changes in the uniaxial equilibrium thermal expansion on cooling from isotropic phase. At higher concentration of main chains their behaviour dominates the elastomer properties. At low concentration of main-chain material, we detect two distinct transitions at different temperatures, one attributed to the main-chain, the other to the side-chain component. The effective uniaxial anisotropy of nematic rubber, r(T) proportional to the effective nematic order parameter Q(T), is given by the average of the two components and thus reflects the two-transition nature of thermal expansion. The experimental data is compared with the theoretical model of ideal nematic elastomers; applications in high-amplitude thermal actuators are discussed in the end

UV-isomerisation in nematic elastomers as a route to photo-mechanical transducer

The macroscopic shape of liquid crystalline elastomers strongly depends on the order parameter of the mesogenic groups. This order can be manipulated if photoisomerisable groups, e.g. containing N=N bonds, are introduced into the material. We have explored the large photo-mechanical response of such an azobenzene-containing nematic elastomer at different temperatures, using force and optical birefringence measurements, and focusing on fundamental aspects of population dynamics and the related speed and repeatability of the response. The characteristic time of ``on'' and ``off'' regimes strongly depends on temperature, but is generally found to be very long. We were able to verify that the macroscopic relaxation of the elastomer is determined by the nematic order dynamics and not, for instance, by the polymer network relaxation.Comment: Latex (EPJE class) 12 figure

Association between pruritus and serum concentrations of parathormone, calcium and phosphorus in hemodialysis patients.

Chronic renal disorders have a progressive course in most cases, and finally result in end-stage renal disease (ESRD). Hemodialysis (HD) is one of the mainstays in the treatment of these patients. Disturbance in calcium (Ca) and phosphorus (P) metabolism and alteration of serum levels of parathormone (PTH) are observed in these patients. One of the most common cutaneous manifestations in patients on HD is pruritus. The aim of this study is to evaluate the association between pruritus and serum concentrations of Ca, P and PTH in patients with chronic renal disease. This analytic, descriptive, cross-sectional study was performed on 120 patients on HD at the Fifth-Azar Hospital in Gorgan, Iran, in 2010. Information related to the patients, including age, gender, pruritus, time of pruritus and duration on dialysis, was extracted from questionnaires. Serum concentrations of intact PTH, Ca and P were measured. Data were analyzed by the chi-square test and SPSS-16 software. A P-value less than 0.05 was considered statistically significant. Among the 120 study patients, 50% were male and the mean age (±SD) was 49 ± 12.3 years. Sixty percent of the patients had pruritus, of whom 33.3% had PTH levels above the normal range. Among the 40% of the patients who did not have pruritus, 39.6% had PTH levels higher than the normal levels. The mean serum Ca and P levels were 8.44 ± 1.65 mg/dL and 5.48 ± 1.81 mg/dL, respectively. The mean (±SD) Ca-P product was 55.46 ± 47.16 and the mean PTH concentration was 274.34 ± 286.53 pg/mL. No significant association was found between pruritus and age, sex, serum PTH and P levels as well as Ca-P product. However, the association between serum Ca levels and pruritus was significant (P = 0.03). Our study showed that most patients with pruritus had serum Ca levels in the abnormal range (lower or higher), and there was no significant correlation between serum iPTH level and pruritis. Thus, good control of serum Ca levels is important to reduce pruritus in these patients

Association of serum fetuin-A and biochemical parameters in hemodialysis patients.

Fetuin-A, a hepatic glycoprotein present in the circulation, is a potential inhibitor for systemic calcification. The main aim of this study was to evaluate the association between fetuin-A and other biochemical parameters as facilitator factors for developing atherosclerosis in hemodialysis (HD) patients. This case-control study was conducted on 44 HD patients undergoing treatment in 2012. Parathormone (i-PTH) and fetuin levels were performed by the enzyme-linked immunosorbent assay method, high-sensitivity C-reactive protein (hs-CRP) by chemiluminescence, low-density lipoprotein by direct enzymatic, calcium and albumin by colorimetric and phosphorous by ultraviolet (UV) methods. Chi-square was used for evaluating the association between variables and t-test was used for comparing the mean of the quantitative variables for the two groups. SPSS-16 software was used for data analysis and P-value less than 5% was considered as significant. Mean of serum fetuin level was 23.25 ± 4.90 ng/mL in HD patients and 32.92 ± 5.21 in the control group. Median of hs-CRP was 2.45 mg/dL in the patients and 1.00 mg/dL in the control group and i-PTH was 74.3 pg/mL in the patients and 7.30 pg/mL in the control group. The calcium-phosphorous product was 46.77 ± 14.22 mg/dL in the patient and 31.73 ± 6.48 mg/dL in the control group. A reverse significant association was found between fetuin-A and hs-CRP in this study. In this study, serum fetuin-A level in HD patients was lower than controls. Therefore, a low level of fetuin-A seems to be associated with atherosclerosis, inflammation and malnutrition

Fast microwave-assisted oxidation of 1,4-dihydropyridines with FeCl 3.SiO 2

Pyridine derivatives are easily obtained in high yields by microwave-promoted rapid oxidation of the corresponding 1,4-dihydropyridines with ferric chloride hexahydrate and silica gel under solvent-free conditions

Nematic elastomers with aligned carbon nanotubes: new electromechanical actuators

We demonstrate, for the first time, the large electromechanical response in nematic liquid crystalline elastomers filled with a very low (~0.01%) concentration of carbon nanotubes, aligned along the nematic director at preparation. The nanotubes create a very large effective dielectric anisotropy of the composite. Their local field-induced torque is transmitted to the rubber-elastic network and is registered as the exerted uniaxial stress of order ~1kPa in response to a constant field of order ~1MV/m. We investigate the dependence of the effect on field strength, nanotube concentration and reproducibility under multiple field-on and -off cycles. The results indicate the potential of the nanotube-nematic elastomer composites as electrically driven actuators

Mucocutaneous manifestations and nail changes in patients with end-stage renal disease on hemodialysis.

Mucocutaneous manifestations are common among patients on hemodialysis (HD). This study was undertaken to determine the prevalence of mucocutaneous manifestations in patients with end-stage renal disease (ESRD) who are on HD. In this cross-sectional, descriptive and analytic study conducted in 2009, 100 patients on HD at the Five Azar Hospital in Gorgan city were randomly selected. All the patients underwent detailed examination by a dermatologist to look for lesions in the skin, hair, nail and mucous membranes; if felt necessary, biopsy was obtained from the lesions. The findings were statistically analyzed using SPSS-13 software. For evaluation of normality of distribution, Kolmogorov-Smirnov was used, for quantitative variables Mann-Whitney and T-test (abnormal distribution) were used and for qualitative variables, Chi-2 and Fisher were used. In this study, P-value less than 0.05 was considered significant. Fifty-one males and 49 females were enrolled. The mean age was 49 ± 12 years. Diabetes was the most common cause of ESRD. In 95% of the patients, at least one mucocutaneous manifestation was present. Xerosis (78.3%) was the most common lesion, followed by pruritus (39.1%), lentigo (34.8%), skin discoloration (32.6%), leukonychia (32%) and thinning of the nail bed (24%). Xerosis, scaling, lentigo, folliculitis, idiopathic guttate hypopigmentation, leukonychia and half and half nail were associated with age. A significant relationship was seen between duration on dialysis and skin discoloration and leukonychia. Clubbing had a significant association with calcium-phosphorus product (Ca � P). There was a significant association between serum ferritin level and pruritus and tinea versicolor lesions. Our study shows that mucocutaneous manifestations are common among patients with ESRD. Identification of these manifestations and their association with causative factors are useful for preventing the lesions

Titanium dioxide nanoparticles catalyzed synthesis of Hantzsch esters and polyhydroquinoline derivatives

1,4-Dihydropyridine and polyhydroquinoline derivatives have been prepared efficiently in a one-pot synthesis via Hantzsch condensation using nanosized titanium dioxide as a heterogeneous catalyst. The present methodology offers several advantages such as excellent yields, short reaction times (30-120 min), environmentally benign, and mild reaction conditions. The catalyst can be readily separated from the reaction products and recovered in excellent purity for direct reuse