Dynamic light scattering studies of ionic and nonionic polymer gels with continuous and discontinuous volume transitions

We have performed dynamic light scattering experiments on poly(acrylamide)‐poly(acrylic acid) copolymer gels with controlled crosslink density and copolymer composition, by varying the temperature, amount and valency of added salt, pH, and solvent quality. Our systematic study provides several insights. The correlation length for the monomer density fluctuations, as inferred from the measured diffusion coefficient, is too small to be identified as the mesh size of the gel. The correlation length in an ionic gel, which is found to be smaller than that for an equivalent gel without ionization. Comparison of swelling ratio with the diffusion coefficient shows that these quantities are not simply geometrically related to each other. When a discontinuous volume phase transition is induced by gradually varying the solvent quality, the diffusion coefficient exhibits a pretransitional reduction by two orders of magnitude even before the gel collapse. These findings provoke a need for new theoretical approaches for describing the elastic modes of polyelectrolyte gels. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

Long-time growth kinetics of first order phase transitions in the presence of a boundary layer

The late stage growth mechanism for a first order phase transition, either through nucleation growth or spinodal decomposition, is well understood to be an Ostwald ripening or coarsening process, in which larger domains grow at the expense of smaller ones. The growth kinetics in this regime was shown by Lifshitz and Slyozov to follow at(1/3) law. However, the kinetics is altered if there exists a barrier ahead of the growth front, irrespective of the physical origin of the boundary layer. We present an analytic calculation for the growth kinetics in the presence of a boundary layer, showing that in the limit of barrier-dominated growth, the domains grow with at(1/2) law. This result holds true in the dilute regime independent of whether the growing nuclei are spherical or cylindrical.     

Ruthenium(II) hydrazone Schiff base complexes: synthesis, spectral study and catalytic applications

Ruthenium(II) hydrazone Schiff base complexes of the type [RuCl(CO)(B)(L)] (were B=PPh(3), AsPh(3) or Py; L=hydrazone Schiff base ligands) were synthesized from the reactions of hydrazone Schiff base ligand (obtained from isonicotinoylhydrazide and different hydroxy aldehydes) with [RuHCl(CO)(EPh(3))(2)(B)] (where E=P or As; B=PPh(3), AsPh(3) or Py) in 1:1 molar ratio. All the new complexes have been characterized by analytical and spectral (FT-IR, electronic, (1)H, (13)C and (31)P NMR) data. They have been tentatively assigned an octahedral structure. The synthesized complexes have exhibited catalytic activity for oxidation of benzyl alcohol to benzaldehyde and cyclohexanol to cyclohexanone in the presence of N-methyl morpholine N-oxide (NMO) as co-oxidant. They were also found to catalyze the transfer hydrogenation of aliphatic and aromatic ketones to alcohols in KOH/Isopropanol.     

Concentration dependence of diffusion-controlled processes among stationary reactive sinks

A multiple scattering theory of competition effects in diffusion-controlled reactions are presented. We consider a random array of stationary sinks which react with a density field of another reactant. Using the radiation boundary condition to describe the reaction at the surfaces of the sinks, we treat the modification of the density field due to reaction with sinks exactly. By keeping only the most divergent terms in a given order of scattering and summing them, we obtain the rate constant as a function of the sink concentration in the steady state. We also calculate the concentration-dependent diffusion constant of the density field. Both the rate and diffusion constants have nonanalytic behavior in the sink concentration.Alfred P. Sloan Foundation Fellow 1976–1980; John Simon Guggenheim Memorial Fellow 1979–1980.     

A density functional study of Ce@C82: explanation of the Ce preferential bonding site

Ce has been found experimentally to be preferentially incorporated into the C82 isomer of C2v symmetry as have other lanthanoids in M@C82 (M = La, Pr, Nd, etc.). We have investigated the underlying reason for this preference by calculating structural and electronic properties of Ce@C82 using density functional theory. The ground-state structure of Ce@C82 is found to have the cerium atom attached to the six-membered ring on the C2 axis of the C82-C2v cage, and the encapsulated atom is found to perturb the carbon cage due to chemical bonding. We have found Ce to favor this C2v chemisorption site in C82 by 0.62 eV compared to other positions on the inside wall of the cage. The specific preference of the metal atom to this six-membered ring is explained through electronic structure analysis, which reveals strong hybridization between the d orbitals of cerium and the pi orbitals of the cage that is particularly favorable for this chemisorption site. We propose that this symmetry dictated interaction between the cage and the lanthanide d orbital plays a crucial role when C82 forms in the presence of Ce to produce Ce@C82 and is also more generally applicable for the formation of other lanthanoid M@C82 molecules. Our theoretical computations are the first to explain this well-established fact. Last, the vibrational spectrum of Ce@C82 has been simulated and analyzed to gain insight into the metal-cage vibrations.     

Interactions between antimicrobial polynorbornenes and phospholipid vesicles monitored by light scattering and microcalorimetry

Antimicrobial polynorbornenes composed of facially amphiphilic monomers have been previously reported to accurately emulate the antimicrobial activity of natural host-defense peptides (HDPs). The lethal mechanism of most HDPs involves binding to the membrane surface of bacteria leading to compromised phospholipid bilayers. In this paper, the interactions between biomimetic vesicle membranes and these cationic antimicrobial polynorbornenes are reported. Vesicle dye-leakage experiments were consistent with previous biological assays and corroborated a mode of action involving membrane disruption. Dynamic light scattering (DLS) showed that these antimicrobial polymers cause extensive aggregation of vesicles without complete bilayer disintegration as observed with surfactants that efficiently solubilize the membrane. Fluorescence microscopy on vesicles and bacterial cells also showed polymer-induced aggregation of both synthetic vesicles and bacterial cells. Isothermal titration calorimetry (ITC) afforded free energy of binding values (Delta G) and polymer to lipid binding ratios, plus revealed that the interaction is entropically favorable (Delta S>0, Delta H>0). It was observed that the strength of vesicle binding was similar between the active polymers while the binding stoichiometries were dramatically different.     

Engaging Allene‐Derived Zwitterions in an Unprecedented Mode of Asymmetric [3+2]‐Annulation Reaction

Catalytic addition of chiral phosphine, that is, (R)‐ or (S)‐SITCP, to an α‐substituted allene ester generated a zwitterionic dipole. Under optimized reaction conditions, this dipole could engage isatine‐derived N‐Boc‐ketimines in a novel mode of [3+2] annulation reaction. Pyrrolinyl spirooxindoles are thus afforded in high yields and with excellent enantioselectivities. The unprecedented annulation reaction successfully facilitated the construction of sp³‐rich and highly substituted 3,2′‐pyrrolidinyl spirooxindoles supporting many chiral centers.     

Monte Carlo simulations of single crystals from polymer solutions

A novel "anisotropic aggregation" model is proposed to simulate nucleation and growth of polymer single crystals as functions of temperature and polymer concentration in dilute solutions. Prefolded chains in a dilute solution are assumed to aggregate at a seed nucleus with an anisotropic interaction by a reversible adsorption/desorption mechanism, with temperature, concentration, and seed size being the control variables. The Monte Carlo results of this model resolve the long-standing dilemma regarding the kinetic and thermal roughenings, by producing a rough-flat-rough transition in the crystal morphology with increasing temperature. It is found that the crystal growth rate varies nonlinearly with temperature and concentration without any marked transitions among any regimes of polymer crystallization kinetics. The induction time increases with decreasing the seed nucleus size, increasing temperature, or decreasing concentration. The apparent critical nucleus size is found to increase exponentially with increasing temperature or decreasing concentration, leading to a critical nucleus diagram composed in the temperature-concentration plane with three regions of different nucleation barriers: no growth, nucleation and growth, and spontaneous growth. Melting temperatures as functions of the crystal size, heating rate, and concentration are also reported. The present model, falling in the same category of small molecular crystallization with anisotropic interactions, captures most of the phenomenology of polymer crystallization in dilute solutions.     

Approximate Controllability of Second-Order Stochastic Distributed Implicit Functional Differential Systems with Infinite Delay

In this paper, sufficient conditions for the approximate controllability of the following stochastic semilinear abstract functional differential equations with infinite delay are established $$\begin{array}{@{}l@{}}d\bigl[x^{\prime}(t)-g(t,x_{t})\bigr]=\bigl[Ax(t)+f(t,x_{t})+Bu(t)\bigr]dt+G(t,x_{t})dW(t),\\\noalign{\vskip3pt}\quad \mbox{a.e on}\ t\in J:=[0,b],\\\noalign{\vskip3pt}x_{0}=\varphi\in {\mathfrak{B}},\\\noalign{\vskip3pt}x^{\prime}(0)=\psi \in H,\end{array}$$ where the state x(t)∈H,x _t belongs to phase space ${\mathfrak{B}}$ and the control u(t)∈L ₂ ^? (J,U), in which H,U are separable Hilbert spaces and d is the stochastic differentiation. The results are worked out based on the comparison of the associated linear systems. An application to the stochastic nonlinear wave equation with infinite delay is given.     

Water-soluble inhibitor on microbiologically influenced corrosion in diesel pipeline

The effect of water-soluble corrosion inhibitor on the growth of bacteria and its corrosion inhibition efficiency were investigated. Corrosion inhibition efficiency was studied by rotating cage test and flow loop techniques. The nature of biodegradation of corrosion inhibitor was also analyzed by using Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance spectroscopy (NMR) and Gas chromatography and mass spectrometer (GC–MS). The bacterial isolates (Serratia marcescens ACE2, Bacillus cereus ACE4) have the capacity to degrade the aromatic and aliphatic hydrocarbon present in the corrosion inhibitor. The degraded products of corrosion inhibitor and bacterial activity determine the electrochemical behaviour of API 5LX steel. The influence of bacterial activity on degradation of corrosion inhibitor and its influence on corrosion of API 5LX have been evaluated by employing weight loss techniques and electrochemical studies. The main finding of this paper is that the water-soluble corrosion inhibitor is consumed by the microbial action, which contributes to the decrease in inhibitor efficiency. The present study also emphasis the importance of evaluation of water-soluble corrosion inhibitor in stagnant model (flow loop test) and discusses the demerits of the water-soluble corrosion inhibitors in petroleum product pipeline.