Disk morphology and disk-to-cylinder tunability of poly(acrylic acid)-b-poly(methyl acrylate)-b-polystyrene triblock copolymer solution-state assemblies

Disk and cylindrical micellar assemblies were formed through self-organization of poly(acrylic acid)-b-poly(methyl acrylate)-b-polystyrene (PAA-b-PMA-b-PS) amphiphilic triblock copolymers with organic diamines as counterions in water/ tetrahydrofuran (THF) solvent mixtures. The system was investigated by means of transmission electron microscopy and cryogenic transmission electron microscopy. It was found that the assembled-state morphologies could be modified by alteration of the type and concentration of cationic diamine counterion undergoing interaction with the negatively charged, polyelectrolyte PAA corona block, the relative amount of water in the water/THF mixture, and the hydrophobic block chain length. Multivalency of the organic amine counterion was critical for disk formation. It was further demonstrated that a single block copolymer underwent disc-to-cylindrical micellar transitions reversibly with variation in the relative water/THF ratio. The ability to form disks beginning from either THF-rich or water-rich solutions indicated that the disk morphology was thermodynamically stable and that THF was important in keeping the micellar structure from becoming kinetically frozen. The nanoassemblies were produced having low size dispersities and were stable for at least one month. Intermediate structures between disks and cylinders were also observed, indicating two distinct kinetic pathways between the two micelle structures.     

Shell-cross-linked vesicles synthesized from block copolymers of Poly(D,L-lactide) and Poly(N-isopropyl acrylamide) as thermoresponsive nanocontainers

A polylactide (D,L-PLA) macroRAFT agent was prepared by utilizing a hydroxyl-functional trithiocarbonate as a coinitiator for the ring-opening polymerization. The length of the resultant polymer was controlled by the concentration of the coinitiator leading to the formation of two PLA polymers with M(n) = 12500 g mol(-)(1) (PDI = 1.46) and M(n) = 20500 g mol(-)(1) (PDI = 1.38) each with omega-trithiocarbonate functionality. Chain extension of PLA via the RAFT (free radical) polymerization of N-isopropyl acrylamide (NIPAAm) resulted in the formation of amphiphilic block copolymers with the PNIPAAm block increasing in size with conversion. TEM measurements of the aggregates obtained by self-organization of the block copolymers in aqueous solutions indicated the formation of vesicles. The sizes of these aggregates were influenced by the ratio of both blocks and the molecular weight of each block. The lower critical solution temperature (LCST) of the block copolymer was largely unaffected by the size of each block. UV turbidity measurements indicated a higher LCST for the block copolymers than for the corresponding PNIPAAm homopolymers. Stabilization of the vesicles was attained by a cross-linking chain extension of the PNIPAAm block using hexamethylene diacrylate. As the trithiocarbonate group was located between the PLA and PNIPAAm blocks, the chain extension resulted in a cross-linked layer between the core and corona of the vesicles.     

Self-assembled nanocages for hydrophilic guest molecules

Reverse polymeric micelles are obtained following the association of polymeric amphiphiles in apolar media. To this date, reports of pharmaceutical applications for such micelles have been scarce, mainly because these systems have been studied in solvents that are not suitable for medical use. Here, alkylated star-shaped poly(glycerol methacrylate) polymers have been proposed in the design of oil-soluble reverse polymeric micelles. Micellar behavior was studied in various apolar solvents, including ethyl oleate, a pharmaceutically acceptable vehicle. The polymers were shown to assemble into spherical nanostructures (<40 nm) as determined by cryogenic transmission electron microscopy and atomic force microscopy studies. Interestingly, the reverse micelles were able to encapsulate various peptides/proteins (vasopressin, myoglobin, and albumin) in substantial amounts and facilitate their solubilization in oil. The nature of both the polymer used in micelle formation and the guest molecules was found to influence the ability of the micelle to interact with hydrophilic compounds.     

Dynamics of activated escape and its observation in a semiconductor laser

We report a direct experimental observation and provide a theory of the distribution of trajectories along which a fluctuating system moves over a potential barrier in escape from a metastable state. The experimental results are obtained for a semiconductor laser with optical feedback. The distribution of paths displays a distinct peak, which shows how the escaping system is most likely to move. We argue that the specific features of this distribution may give an insight into the nature of dropout events in lasers.     

Optical spectroscopy of RuC: 18,000-24,000 cm(-1)

The optical spectrum of diatomic RuC has been recorded from 17 800 to 24 200 cm(-1). Three previously unidentified excited electronic states were analyzed and identified as having Omega' = 0, Omega' = 2, and Omega' = 3. The Omega' = 3 state was determined to be a 3Delta3 state that is suggested to arise from a mixture of the 10sigma(2)11sigma(2)5pi(3)2delta(3)12sigma(1)6pi(1) and 10sigma(2)11sigma(1)5pi(3)2delta(3)12sigma(2)6pi(1) electronic configurations. Three additional bands belonging to the previously observed [18.1] (1)Pi<--X (1)Sigma(+) system were analyzed to obtain B(e) (')=0.558 244(48) cm(-1), alpha(e) (')=0.004 655(27) cm(-1), omegae' = 887.201(37) cm(-1), and omega(e) 'xe' = 5.589(7) cm(-1) for the 102Ru 12C isotopomer (1sigma error limits). A Rydberg-Klein-Rees analysis was then performed using the determined spectroscopic constants of the [18.1] 1Pi state, and similar analyses were performed for the previously observed states. The resulting potential energy curves are provided for the 100Ru 12C, 101Ru 12C, 102Ru 12C, and 104Ru 12C isotopic species.     

Testing the accuracy of employee-reported data: An inexpensive alternative approach to traditional methods

Although Information Technology (IT) solutions improve the collection and validation of operational data, Operations Managers must often rely on self-reported data from workers to make decisions. The problem with this data is that they are subject to intentional manipulation, thus reducing their suitability for decision-making. A method of identifying manipulated data, digital analysis, addresses this problem at low cost. In this paper, we demonstrate how one uses this method in real-world companies to validate self-reported data from line workers. The results of our study suggest that digital analysis estimates the accuracy of employee reported data in operations management, within limited contexts. These findings lead to improved operating performance by providing a tool for practitioners to exclude inaccurate information.