Linear and branched polymers of 2-(dimethylamino)ethyl methacrylate (PDMAEMA) were synthesized in flow by atom transfer radical polymerization (ATRP) and self-condensing vinyl copolymerization ...adapted to ATRP, respectively, in capillary type stainless steel coiled tube (CT) microreactors. Coil flow inversion (CFI) was introduced to achieve better mixing and narrower residence time distributions during polymerization. This strategy was adopted to improve control over macromolecular characteristics and polymer architecture. Polydispersity index (PDI), as an overall indicator of control over polymerization, was significantly lower for CFI in the case of linear PDMAEMA, 1.39 compared to 1.53 for CT. For branched polymers containing up to 10 mol % of inimer, a reduced PDI was also obtained for CFI microreactor. As for the branching efficiency, it was found to follow the following trend CFI > CT > batch reactor.
The numerical investigation of free radical polymerization (FRP) of methyl methacrylate under mixed feed condition at inlet is made for three microtubular reactor geometries, namely, straight tube, ...coiled tube, and coil flow inverter reactor. The effect of variation of fluid thermophysical properties (FTPP) (density, viscosity, and thermal conductivity) with reaction along with discrete variation of chemical species diffusion coefficient is studied. Predicted values of monomer conversion, number‐average chain length (DPn), and polydispersity index (PDI) are found to be systematically lower for variable FTPP case compared to constant FTPP case. But contrary to expectations, results are found to be independent of reactor geometry for either case. Results clearly show the importance of modeling the variation of FTPP especially with respect to conversion. One case of varying diffusion coefficient of each chemical species based on free volume theory with constant FTPP is also simulated. Here again, the results are found to be independent of reactor geometry. Constant thermal conductivity and isothermal reactor condition are found to be good assumptions. This study clearly establishes the need not only for variable FTPP, thus coupling transport processes, but also for incorporating varying diffusion coefficient along with conversion in modeling of FRP in microreactors for better predictions.
The importance of modeling polymerization with coupled transport processes in microreactor is clearly established in this work. It affects the prediction as well as the trend of various polymer characteristic parameters. Sensitive phenomena like chaotic advection in chaotic microreactor can be observed in a better way while modeling polymerization in it.
To determine benefits of conservative versus surgical treatment in patients with necrotizing pancreatitis.
Infection of pancreatic necrosis is the most important risk factor contributing to death in ...severe acute pancreatitis, and it is generally accepted that infected pancreatic necrosis should be managed surgically. In contrast, the management of sterile pancreatic necrosis accompanied by organ failure is controversial. Recent clinical experience has provided evidence that conservative management of sterile pancreatic necrosis including early antibiotic administration seems promising.
A prospective single-center trial evaluated the role of nonsurgical management including early antibiotic treatment in patients with necrotizing pancreatitis. Pancreatic infection, if confirmed by fine-needle aspiration, was considered an indication for surgery, whereas patients without signs of pancreatic infection were treated without surgery.
Between January 1994 and June 1999, 204 consecutive patients with acute pancreatitis were recruited. Eighty-six (42%) had necrotizing disease, of whom 57 (66%) had sterile and 29 (34%) infected necrosis. Patients with infected necrosis had more organ failures and a greater extent of necrosis compared with those with sterile necrosis. When early antibiotic treatment was used in all patients with necrotizing pancreatitis (imipenem/cilastatin), the characteristics of pancreatic infection changed to predominantly gram-positive and fungal infections. Fine-needle aspiration showed a sensitivity of 96% for detecting pancreatic infection. The death rate was 1.8% (1/56) in patients with sterile necrosis managed without surgery versus 24% (7/29) in patients with infected necrosis (P <.01). Two patients whose infected necrosis could not be diagnosed in a timely fashion died while receiving nonsurgical treatment. Thus, an intent-to-treat analysis (nonsurgical vs. surgical treatment) revealed a death rate of 5% (3/58) with conservative management versus 21% (6/28) with surgery.
These results support nonsurgical management, including early antibiotic treatment, in patients with sterile pancreatic necrosis. Patients with infected necrosis still represent a high-risk group in severe acute pancreatitis, and for them surgical treatment seems preferable.
Polymeric microparticles were produced following a three-step procedure involving (i) the production of an aqueous nanoemulsion of tri and monofunctional acrylate-based monomers droplets by an ...elongational-flow microemulsifier, (ii) the production of a nanosuspension upon the continuous-flow UV-initiated miniemulsion polymerization of the above nanoemulsion and (iii) the production of core-shell polymeric microparticles by means of a microfluidic capillaries-based double droplets generator; the core phase was composed of the above nanosuspension admixed with a water-soluble monomer and gold salt, the shell phase comprised a trifunctional monomer, diethylene glycol and a silver salt; both phases were photopolymerized on-the-fly upon droplet formation. Resulting microparticles were extensively analyzed by energy dispersive X-rays spectrometry and scanning electron microscopy to reveal the core-shell morphology, the presence of silver nanoparticles in the shell, organic nanoparticles in the core but failed to reveal the presence of the gold nanoparticles in the core presumably due to their too small size (c.a. 2.5 nm). Nevertheless, the reddish appearance of the as such prepared polymer microparticles emphasized that this three-step procedure allowed the easy elaboration of composite/hybrid multi-scale and multi-domain polymeric microparticles.
An elegant, simple, and exact analytical solution (AS) was obtained for a large range of elementary steps with practical importance in free radical polymerization. The AS matches excellently with the ...numerical solution for the four cases of monomer–polymer systems studied ranging from the slowest to the fastest. It works equally well for different initiators, different initiator and monomer concentrations, presence or absence of solvent, various solvent volume fractions, and different temperatures. It also matches quite well with experimental data reported in the literature. This AS is not only in line with previous published solutions but also extends their applicability in a natural way. Overall, the conceptual correctness as well as predictive capabilities of the derived AS are established beyond doubt. This AS has the potential to be used in various practical applications such as model based process control, CFD simulations, and so forth.
Large (many mm long) closed tubes from liquid crystalline (LC)-elastomers can be prepared in a microfluidic setup by photopolymerization of an LC-monomer mixture. In these tubes, the director of the ...LC-phase is oriented parallel to their long axes as proven by X-ray measurements, thus leading to shortening at the transition to the isotropic phase while their walls become thicker simultaneously. The process of tube preparation relies on an appropriate choice of 3 immiscible phases in the microfluidic setup (continuous, LC-monomer and inner phase) as well as their interfacial tensions. Water can be used as the inner phase in combination with a selective detergent (an amphiphilic block copolymer from PNIPAM and the LC-polymer) to reduce the LC/water surface tension. In this way, long actuating (up to 50%) tubes can be prepared either from a thermotropic LC-elastomer or from an azo-containing LC-elastomer with the latter being both thermo- and photo-responsive. By irradiation of individual tubes consisting of the azo-system with white ( trans – cis ) or red light ( cis – trans ), actuations of up to 29% can be achieved. The contraction (shortening) of the tubes thereby requires about 10 seconds, while the photochemical reisomerization needs about 230 seconds. This sets the time frame for the tubes’ photochemical actuation.
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