Shear-induced long-range alignment of BCC-ordered block copolymers

Effect of large shear on an asymmetric block copolymer with nanospherical domains has been studied using rheology and small angle X-ray scattering. The material investigated was a triblock copolymer poly[styrene-b-(ethylene-co-butylene)-b-styrene] swollen in a midblock-selective solvent. When cooled below the order–disorder transition temperature (T ODT), the system forms a locally ordered structure of grains with body-centered cubic (BCC) lattice. Isothermal shearing, either at constant rate or with large amplitude oscillatory shear (LAOS) at low frequencies and strain amplitude greater than or equal to 2.0, leads to the destruction of the BCC lattice (isothermal “shear melting”). Upon cessation of the shear, the BCC structure recovers with kinetics similar to the one after thermal quench from above T ODT. Under certain experimental conditions, LAOS leads to alignment of the BCC lattice. The lattice orientation depends primarily on shearing frequency. At low frequencies, there exists an upper and lower bound on strain amplitude where monodomain textures can be obtained. Upon alignment, the modulus drops by about 30% of that of the polycrystalline structure. Measurement of rheological properties offers an indirect method for distinguishing between polycrystalline structure (grains) and monodomain texture

Ultraslow dynamics in asymmetric block copolymers with nanospherical domains

Low shear rate and low frequency measurements focused on the extremely slow dynamics of a three-dimensional body-centered cubic (BCC) structure of an asymmetric block copolymer under nanophase-separated conditions. The material studied was poly(styrene-b-ethylene-co-butylene-b-styrene) swollen in a hydrocarbon oil selective for the midblock. Transient viscosities during start-up of shear flow at extremely low shear rates are governed by very long relaxation times and by a modulus that is nearly the same as the plateau modulus obtained from oscillatory shear experiments. Only at extremely low shear rates a zero shear viscosity could be attained. Its very high value is close to the viscosity calculated from stress relaxation experiments. The steady shear viscosity decreases by several orders of magnitude when increasing the shear rate. SAXS experiments on samples sheared even at very low rates indicated loss of the BCC order that was present in the annealed samples before shearing. The SAXS profile recorded on such a sample showed a first-order maximum followed by a broad shoulder indicating a liquid-like short-range order of PS nanospheres in the swollen EB matrix

STUDY OF TOTAL CHOLESTEROL (TC), TRIACYLGLYCEROLS (TG), HIGH DENSITY LIPOPROTEIN CHOLESTEROL (HDL-C) IN TYPE II DIABETES MELLITUS.â€

Objective: There are probably 100 million people in the world with diabetes mellitus (DM), and incidences of diabetes are on the rise. Dyslipidemia is one of the common disorders which are seen in most of the diabetes patients, which causes cardiovascular disorders. The aim of this study is to investigate the total cholesterol (TC), triacylglycerols (TGs), high-density lipoprotein cholesterol (HDL-C) in Type 2 DM, and healthy controls.Methods: The study was conducted on 50 controls and 50 Type 2 diabetic subjects between age group of 30 and 60 years. Serum TC was determined by an enzymatic (cholesterol oxidase/phenol-aminophenazone [PAP]) colorimetric method and TGs were determined by an enzymatic (glycerol phosphate oxidase-PAP) method, and HDL-C was estimated by a precipitant method. Statistical analysis was done using unpaired t-test.Results: The mean value of TC, TGs, and HDL-C in normal subjects is 165.5±24.24, 118.7±41.58, 28.38±7.85 mg/dl, respectively, and the value of TC, TGs, and HDL-C in diabetic patients is 179±31.69, 164.35±27.93, 25.4±6.86 mg/dl, respectively. The observed difference in the means of TC, TGs, and HDL-C in normal and diabetic are statistically significant (p<0.05).Conclusion: From the present study, it is concluded that TC, TGs, and HDL-C levels for all persons with Type 2 DM should be done as a routine test. Furthermore, early diagnosis and treatment of dyslipidemia can be used as a preventive measure for the development of cardiovascular disease in Type 2 diabetes.Keywords: Diabetes mellitus, Dyslipidemia, Lipid profile, Total cholesterol, Triglycerides, High-density lipoprotein cholesterol

Synthesis and Characterization of a Poly (styrene-block-methylacrylate-random-octadecylacrylate-block-styrene) Shape Memory ABA Triblock Copolymer

A new shape memory polymer (SMP) was prepared from an ABA triblock copolymer with polystyrene (PS) end blocks and a random copolymer midblock of poly(methylacrylate-random-octadecylacrylate) (PMA-r-PODA). The self-assembly of the triblock copolymer generates a three-dimensional, physically cross-linked network by the bridging of the midblocks across the glassy PS domains, which is used as the permanent network in the SMP. A second reversible network is generated by the side-chain crystallization of the PODA side-chains. Shape memory testing by uniaxial deformation and recovery of molded tensile bars demonstrated that shape fixities greater than 96% and shape recoveries greater than 98% were obtained for extensional strains up to 300%. Although some loss of properties was observed with cycling, the entirely physically cross-linked nature of the polymer allowed erasing of the sample history and recovery of the initial properties by annealing the sample at elevated temperature