Rheological properties of hydrophobically modified alkali-soluble polymers—effects of ethylene–oxide chain length

The rheological properties of hydrophobic alkali-soluble associative polymers (HASE) were studied using controlled rate (Mettler LS40) and controlled stress (TA CSL 500) rheometers. The effects of pH and polymer concentrations on the rheological properties of three HASE model polymer systems (i.e., HASE 5141, 5134, and 5142, with a degree of ethoxylation of 2.5, 10, and 40 mol, respectively) and a reference polymer without associative hydrophobes (MAAEA) were examined. As the pH is increased by addition of ammonia to greater than 5–6, the carboxyl groups ionize to carboxylate ions and the polymers become water soluble. The HASE polymers thicken mainly by hydrophobic association. Viscosity can increase by two to three orders of magnitude as pH is raised to 9. The degree of ethoxylation in the macromonomer controls the nature of the hydrophobic association junctions by altering the flexibility and hydrophobicity of the macromonomer. Optimum thickening efficiency is observed in the system with approximately 10 mol of an ethylene–oxide spacer between the polymer backbone and the macromonomer. Viscoelastic study shows that the maximum thickening efficiency also corresponds to the dominant elastic property observed in the system with 10 mol of EO. All the model systems except the control system without hydrophobe exhibit strain thickening of the viscous and elastic components. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2275–2290, 1998     

The synthesis,characterization, and crystal structures of poly(2,6‐naphthalenebenzobisoxazole) and poly(1,5‐naphthalenebenzobisoxazole)

The rigid‐rod polymers, poly(2,6‐naphthalenebenzobisoxazole) (Naph‐2,6‐PBO) and poly(1,5‐naphthalenebenzobisoxazole) (Naph‐1,5‐PBO) were synthesized by high temperature polycondensation of isomeric naphthalene dicarboxylic acids with 4,6‐diaminoresorcinol dihydrochloride in polyphosphoric acid. Expectedly, these polymers were found to have high thermal as well as thermooxidative stabilities, similar to what has been reported for other polymers of this class. The chain conformations of Naph‐2,6‐PBO and Naph‐1,5‐PBO were trans and the crystal structures of Naph‐2,6‐PBO and Naph‐1,5‐PBO had the three‐dimensional order, although the axial disorder existed for both Naph‐2,6‐PBO and Naph‐1,5‐PBO. Naph‐2,6‐PBO exhibited a more pronounced axial disorder than Naph‐1,5‐PBO because of its more linear shape. The repeat unit distance for Naph‐2,6‐PBO (14.15 Å) was found to be larger compared with that of Naph‐1,5‐PBO (12.45 Å) because of the more kinked structure of the latter. The extents of staggering between the adjacent chains in the ac projection of the crystal structure were 0.25c and 0.23c for Naph‐2,6‐PBO and Naph‐1,5‐PBO, respectively. Naph‐1,5‐PBO has a more kinked and twisted chain structure relative to Naph‐2,6‐PBO. The kinked and twisted chain structure of Naph‐1,5‐PBO in the crystal seems to prevent slippage between adjacent chains in the crystal structure. The more perfect crystal structure of Naph‐1,5‐PBO may be due to this difficulty in the occurrence of the slippage. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1948–1957, 2006     

Intercalation of solvent and polymer in galleries of mobile clay platelets by a Monte Carlo simulation

The intercalation of solvent particles and polymer chains of concentration C_w = 0.2 and C_p = 0.2, respectively, in a layer of (4) clay platelets is studied by a Monte Carlo simulation on a cubic lattice. Polymer chains and platelets are modeled by bond fluctuations. Besides the excluded volume, a set of polymer-clay (cs) and solvent-clay (ws) interactions with (i) cs = 1, ws = −2, (ii) cs = −2, ws = 1 and (iii) cs = ws = −2 are considered. The global dynamics of platelets is constrained due to the presence of three components, i.e., solvent, polymer, and platelets, which retain their interstitial spacing with well-defined galleries. Intercalation of solvent particles and polymer chains (low molecular weight) occurs with their attractive interaction with the platelets, which further reinforces the layered clay morphology. The density profiles of the solvent particles are similar to previous studies with platelets in a mobile solvent. The density profile of polymer chains differs considerably from the platelets in a polymer matrix alone, particularly with its attractive interaction (ii). For the same attractive interaction of solvent and polymer chains with the clay platelets (iii), the solvent particles (the smallest constituents) intercalate the fastest in the clay galleries, whereas the intercalation of polymer chains decreases with their molecular weight. The polymer density profiles, both longitudinal (x) and transverse (y), show maxima peaks around outer platelets (surface) of the layer and decay sharply both in the adjacent galleries and in the bulk. The amplitude of oscillation in the transverse density profiles, a measure of the degree of intercalation, decreases with increasing molecular weight of the polymer. The intercalation of the polymer is driven by its attractive interaction at the low molecular weight, but reduces considerably at high molecular weight because of both entanglement and larger radius of gyration. Variations of the gyration radius of the diffusing polymer chains with molecular weight and interaction with the clay are consistent with the results of their corresponding density profiles. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2487–2500, 2009     

Tao Zhang,Soo‐Young Park,B. L. Farmer,Leonard V. Interrante,Synthesis of comb‐type polycarbosilanes via nucleophilic substitution reactions on the main‐chain silicon atoms,Journal of Polymer Science Part A: Polymer Chemistry (2003) 41(7) 984–997

The original article to which this erratum refers was published in Journal of Polymer Science Part A: Polymer Chemistry (2003) 41(7) 984–997 No abstract.     

Deformations of Maass forms

We describe numerical calculations which examine the Phillips-Sarnak conjecture concerning the disappearance of cusp forms on a noncompact finite volume Riemann surface under deformation of the surface. Our calculations indicate that if the Teichmüller space of is not trivial, then each cusp form has a set of deformations under which either the cusp form remains a cusp form or else it dissolves into a resonance whose constant term is uniformly a factor of smaller than a typical Fourier coefficient of the form. We give explicit examples of those deformations in several cases.

     

Differentiation evens out zero spacings

If is a polynomial with all of its roots on the real line, then the roots of the derivative are more evenly spaced than the roots of . The same holds for a real entire function of order 1 with all its zeros on a line. In particular, we show that if is entire of order 1 and has sufficient regularity in its zero spacing, then under repeated differentiation the function approaches, after normalization, the cosine function. We also study polynomials with all their zeros on a circle, and we find a close analogy between the two situations. This sheds light on the spacing between zeros of the Riemann zeta-function and its connection to random matrix polynomials.

     

Hermitian geometries in projective space

Using a Hermitian form on a vector space over GF (l), we produce a geometry on the associated projective space and prove that this geometry is characterized by its plane sections.     

Surface chemistry and electrical properties of germanium nanowires

Germanium nanowires (GeNWs) with p- and n-dopants were synthesized by chemical vapor deposition (CVD) and were used to construct complementary field-effect transistors (FETs). Electrical transport and X-ray photoelectron spectroscopy (XPS) data are correlated to glean the effects of Ge surface chemistry to the electrical characteristics of GeNWs. Large hysteresis due to water molecules strongly bound to GeO(2) on GeNWs is revealed. Different oxidation behavior and hysteresis characteristics and opposite band bending due to Fermi level pinning by interface states between Ge and surface oxides are observed for p- and n-type GeNWs. Vacuum annealing above 400 degrees C is used to remove surface oxides and eliminate hysteresis in GeNW FETs. High-kappa dielectric HfO(2) films grown on clean GeNW surfaces by atomic layer deposition (ALD) using an alkylamide precursor is effective in serving as the first layer of surface passivation. Lastly, the depletion length along the radial direction of nanowires is evaluated. The result suggests that surface effects could be dominant over the "bulk" properties of small diameter wires.     

A cyanide‐bridged bimetallic complex, [CrPr(CN)6(C3H7NO)4(H2O)3]·H2O

The crystal structure of the bimetallic cyanide‐bridged title complex, tri­aqua‐1κ³O‐μ‐cyano‐1:2κ²N:C‐penta­cyano‐2κ⁵C‐tetrakis(N,N‐di­methyl­form­amide)‐1κ⁴O‐chromium(III)­prase­odymium(III) monohydrate, was obtained by single‐crystal X‐ray diffraction. The central praseodymium(III) ion is eight‐coordinate, arranged in a square antiprism, while the chromium(III) ion is six‐coordinate, oriented octahedrally. Molecules in the crystal lattice are held together by a network of hydrogen bonds.