Synthesis and characterization of polyelectrolyte hydrogels with controlled swelling behaviour

Copolymerization of sulfopropyl methacrylate potassium salt (K‐SPMA) and 2‐acrylamido‐2‐methyl propane sulfonic acid (AMPS) has been studied in the range 10–90% K‐SPMA in the feedstock. The reactivity ratios have been determined for K‐SPMA/AMPS copolymers. The copolymer compositions, utilized for determining the reactivity ratio, have been determined from nitrogen content. Crosslinked poly(AMPS) and K‐SPMA/AMPS copolymers were prepared in water in the presence of potassium persulfate as initiator and N,N‐methylene bisacrylamide (MBA) as tetrafunctional crosslinker. Irradiation of K‐SPMA and AMPS with an electron‐beam was carried out at 50 wt% aqueous solution with low pH and irradiation dose 40–120 kGy. The swelling behaviour of highly crosslinked K‐SPMA/AMPS copolymer polyelectrolyte gels in aqueous medium was studied in the presence of different types of salts. The crosslink density, the average molecular weight between the crosslinks and the dissociation constant (pK_a) of the crosslinked polymer were determined from stress–strain measurements. © 2001 Society of Chemical Industry     

Investigation of some copolymers based on acrylic salts as circulation loss control agents

In this work, six copolymers were prepared from sodium and potassium acrylate. Both salts individually were copolymerized with acrylamide, methacrylic acid and acrylic acid at different ratios. The monomer reactivity ratios for copolymerization reactions of both of acrylate salts with acrylamide, methacrylic acid and acrylic acid, in solution with azobisisobutyronitrile (AIBN) as an initiator, were estimated by atomic adsorption analyser. The chemical structure was confirmed by atomic adsorption spectroscopy and FT-IR spectroscopy.The prepared copolymers were investigated as loss circulation control materials by measuring different filtration parameters such as; spurt loss, fluid loss and permeability plugging tester value according to the American Petroleum Institute (API) standard. From the obtained data, it was found that the 0.6% from the poly[PA-co-AM]_(0.4:0.6) exhibited the best results of the filtration parameters among the other copolymers. At the same time all the studied copolymers enhanced the rheological properties of the drilling mud. These results were discussed on the light of the swelling capacity of the copolymers.     

Influence of Nonionic Rosin Surfactants on Surface Activity of Silica Particles and Stability of Oil in Water Emulsions

Rosin as a natural product has become a source for production of less toxic bio-surfactants to produce emulsions which are widely used in various agriculture and food products, cosmetic, and pharmaceutical industries. In this respect, a nonionic surfactant was prepared from reaction of rosin acids and rosin maleic anhydride adduct with poly(ethylene glycol) monomethyl ether 750 (MPEG 750) to produce a rosin ester (RMPEG 750). The surface activity parameters of the prepared surfactants, such as surface excess concentration (Γ _max), the area per molecule at interface (A _min), and the effectiveness of surface tension reduction, were measured to determine the micellization and adsorption characteristics of the prepared surfactants at the water/air interface. The adsorption of the prepared surfactants on the surface of either hydrophilic or hydrophobic silica particles was determined using a spectrophotometric method. Interfacial tension between water and toluene were measured to select the best condition to obtain toluene/water emulsion in the presence of modified solid silica particles. The effects of silica particle hydrophilicity and the surfactant concentrations on the surface, interfacial activity, and on the emulsion drop size were also investigated.     

Effect of the solvent on growth of titania nanotubes prepared by anodization of Ti in HCl

The effect of the solvent on the anodic growth of titania nanotubes in HCl dissolved in water, ethylene glycol and 2-propanol was studied. These nanotubes grow with locally rapid breakdown of the passive TiO₂ film forming a forest of nanotubes-bearing microtowers with the background of passive TiO₂ Film. These bundles of assembled-groups of titania nanotubes look like Pillars corals. The low relative permittivity of the 2-propanol led to lowering of dissociation of HCl and hence lowering the activity of H⁺ and Cl⁻ ions which in turn led to suppress of dissolution of titania and increasing the growth rate of the titania nanotubes. The X-ray diffraction pattern showed that the titania nanotubes after annealing change to the crystalline anatase phase. The anodic films showed characteristic coloration with intensity and color that changes (qualitatively) with time of anodization.     

Infrared multiphoton dissociation in quadrupole time-of-flight mass spectrometry: top-down characterization of proteins

The first implementation of infrared multiphoton dissociation (IRMPD) for a hybrid quadrupole time-of-flight (QqTOF) mass spectrometer is reported. Ions were trapped in the radio frequency-only quadrupole (q2), which normally serves as a collision cell, and irradiated by a continuous CO2 IR laser. The laser beam was introduced coaxially with the quadrupoles in order to maximize overlap with the ion path. The resolution of the TOF mass analyzer allowed direct charge state determination for fragments smaller than 7 kDa. For larger fragments, the charge state could be assigned using the multiple losses of water, characteristic for IRMPD of proteins. The analytical performance is demonstrated by top-down sequencing of several representative proteins (equine myoglobin, bovine casein, and human insulin and chaperonin 10). Various post-translational modifications such as phosphorylation, acetylation, formation of disulfide bridges, and removal of N-terminal methionine followed by acetylation are detected and characterized. The utility of IRMPD for the analysis of biological samples is demonstrated in a study of a recently identified potential marker for endometrial cancer, chaperonin 10.     

Large-scale optical-field measurements with geometric fibre constructs

Optical fields are measured using sequential arrangements of optical components such as lenses, filters, and beam splitters in conjunction with planar arrays of point detectors placed on a common axis. All such systems are constrained in terms of size, weight, durability and field of view. Here a new, geometric approach to optical-field measurements is presented that lifts some of the aforementioned limitations and, moreover, enables access to optical information on unprecedented length and volume scales. Tough polymeric photodetecting fibres drawn from a preform are woven into light-weight, low-optical-density, two- and three-dimensional constructs that measure the amplitude and phase of an electromagnetic field on very large areas. First, a three-dimensional spherical construct is used to measure the direction of illumination over 4pi steradians. Second, an intensity distribution is measured by a planar array using a tomographic algorithm. Finally, both the amplitude and phase of an optical wave front are acquired with a dual-plane construct. Hence, the problem of optical-field measurement is transformed from one involving the choice and placement of lenses and detector arrays to that of designing geometrical constructions of polymeric, light-sensitive fibres.     

Tuberculosis in end-stage renal disease patients on hemodialysis

Recent studies have shown that there is an increase in the incidence of mycobacterium tuberculosis (MBT). This is more prevalent among immune compromised patients (those on dialysis) and recipients of organ transplants. Furthermore, extra-pulmonary presentation appears to be more common and difficult to diagnose. We aimed in this study to assess and evaluate the presentation of MBT in a retrospective study conducted among 256 hemodialysis (HD) patients where 18 of them were diagnosed and managed for tuberculosis over a 10-year period between 1990 and 2000. The mean age of the patients was 38 years (21-75 years). The mean interval between the onset of HD and the time of diagnosis was about 24 months (1-120 months). The diagnosis of tuberculosis was made either by isolation of acid-fast bacilli (AFB), the typical caseating granuloma on biopsy, or by recovery of tubercle bacilli from the culture of the biopsy material. Extra-pulmonary tuberculosis was more common (77.8%) than pulmonary tuberculosis (22.2%). The various extra-pulmonary tuberculosis sites noted were cervical lymphadenitis (16.7%), gastrointestinal (16.7%), genitourinary (11.1%), peritonitis (11.1%), pleural effusion (5.6%), pericardial effusion (5.6%), miliary tuberculosis (5.6%), and pyrexia of unknown origin (5.6%). None of the patients with extra-pulmonary tuberculosis had evidence of pulmonary tuberculosis. The atypical presentation with insidious onset was quite common. Anergy to tuberculin skin test was noticed in 56% of cases. All of our patients received modified antituberculosis treatment for 1 year with adequate response, and without undue side effects. We conclude that a high index of suspicion is required especially in the diagnosis of extra-pulmonary tuberculosis, and when there is a high percentage of anergy to tuberculin skin test. Tissue biopsy both for characteristic histology and demonstration of MTB, either by staining or culture, remains the main criteria for the diagnosis of extra-pulmonary tuberculosis.     

Nanoparticles for cellular drug delivery: mechanisms and factors influencing delivery

Polymeric nanoparticles have demonstrated enormous potential as cellular drug delivery vehicles. Nanoparticles improve drug's stability as well as its availability and retention at the target intracellular site of action. Therapeutic efficacy of nanoparticles can be further enhanced by conjugating specific ligands to nanoparticle surface. Ligand conjugation can also be used to favorably modify the intracellular disposition of nanoparticles. A number of ligands are available for this purpose; use of a specific ligand depends on the target cell, the material used for nanoparticle formulation, and the chemistry available for ligand-nanoparticle conjugation. Cellular drug delivery using nanoparticles is also affected by clearance through the reticuloendothelial system. In this paper, we review the recent progress on our understanding of physicochemical factors that affect the cellular uptake of nanoparticles and the different cellular processes that could be exploited to enhance nanoparticle uptake into cells.     

Fast responsive poly(acrylic acid‐co‐N‐isopropyl acrylamide) hydrogels based on new crosslinker

Novel dual temperature‐ and pH‐sensitive poly(acrylic acid‐co‐N‐isopropylacrylamide), AA/NIPAAm, hydrogels were successfully prepared by chemical crosslinking with crosslinkers. Copolymers of AA/NIPAAm were crosslinked in the presence of different mol % of N,N‐methylene bisacrylamide (MBA) and melamine triacrylamide (MAAm) as crosslinkers by bulk radical polymerization. The resultant xerogels were characterized by extracting the soluble fractions and measuring the equilibrium water content. Lower critical solution transition temperatures (LCST) were measured by DSC. The properties of crosslinked AA/NIPAAm series are evaluated in terms of compositional drift of polymerization, heterogeneous crosslinking, and chemical structure of the relevant components. Soluble fractions of the crosslinked networks were reduced by varying the MAAm and MBA concentrations. The influence of environmental conditions such as temperature and pH on the swelling behavior of these polymeric gels was investigated. The swelling behaviors of the resulting gels show pH sensitivity. The prepared MAAm type AA/NIPAAm hydrogels exhibited a more rapid deswelling rate than MBA type AA/NIPAAm hydrogels in ultra pure water in response to abrupt changes from 20°C to 50°C. The results of this study provide valuable information regarding the development of dual stimuli‐sensitive hydrogels with fast responsiveness. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Diversity Combining and SNR Estimation for Turbo-Coded Frequency-Hopped Spread-Spectrum in Partial-Band Interference and Fading Channels

We compare different combinations of the repetition diversity order L and code rate R for turbo-coded Frequency-Hopped Spread-Spectrum (FH/SS) communication systems in the presence of fading and partial-band Gaussian interference. For a fixed overall channel code rate R/L we show that using the lowest code rate and no repetition diversity always performs better than using a higher code rate and some repetition for both coherent and non-coherent schemes. We then propose a simple maximum-likelihood-based method for signal-to-noise-ratio (SNR) estimation in Non-Coherent Binary Frequency Shift Keying (NCBFSK) without training symbols. Except for impractically small hop sizes of 8 bits or less we obtain performance virtually equal to that of perfect SNR knowledge but with much less complexity than iterative schemes previously proposed. For the case of Coherent Binary Phase Shift Keying (CBPSK) we derive the Expectation Maximization (EM) estimate of the SNR without training symbols and iteratively feed the estimator with the extrinsic information from the turbo decoder. The performance for CBPSK is near that of perfect SNR knowledge for hop sizes of 64 bits or more. Unlike previously proposed methods for CBPSK the EM estimate of SNR does not require knowledge of the noise and interference variance, received bit energy, or the fading channel model.