Colloid and Polymer Science: Kolloid-Zeitschrift und Zeitschrift für Polymere. (v.281, #5)
Controlling silica surfaces using responsive coupling agents
by Frank J. LaRonde; Amro M. Ragheb; Michael A. Brook (pp. 391-400).
The surface chemistry of silica was modified using coupling agents capable of participating in oxidation or in the Diels–Alder (and retro Diels–Alder) reactions. The synthesis of the latter coupling agents, using trialkoxysilane groups linked to a cyclopentadiene structure, was achieved by the condensation of sodium cyclopentadienolide with 1-chlorodimethylsilyl-3-triethoxysilylpropane to give 1-cyclopentadienyldimethylsilyl-3-trialkoxysilylpropane. The cyclopentadiene ring in this structure was shown to undergo normal Diels–Alder chemistry with maleimides or maleic anhydride to give 7-(dimethylsilylpropyltrialkoxysilane)-5-norbornene-2,3-dicarboxylic acid anhydride. The retro Diels–Alder reaction of 7-(dimethylsilylpropyltrialkoxysilane)-5-norbornene-2,3-dicarboxylic acid anhydride in solution was not very efficient: the adduct is very stable and only undergoes the retro Diels–Alder reaction at temperatures in excess of 200 °C. Once grafted to the surface, however, the retro Diels–Alder reaction was achieved at a level greater than 90% by use of thermolysis in the presence of free cyclopentadiene. In addition, a polyene-based coupling agent derived from squalene was prepared by hydrosilylation using HMe2SiOSiMe2CH2CH2Si(OEt)3. Once grafted to the surface, oxidation by ozone led to ozonides that could be reduced to ketone/aldehyde groups. These in turn could be trapped by functional groups such as hydrazines to make surface-bound hydrazones. With both types of coupling agents, the surface energy and nature of the functional groups bound to the surface could be changed on demand in response to an external stimulus.
Keywords: Silane coupling agent Silica Thermal modification Oxidative cleavage Surface functional group modification
The extended Langmuir's method and its application to double-layer interaction
by Yixiang Zhang; Jun Jin; Genxiang Luo; Haoping Wang (pp. 401-406).
On the basis of Langmuir's suggestion we simplified Poisson-Boltzmann equation and derived the relation of surface potential, potential midway and the plate distance. Thus we used the force equation derived by Langmuir to calculate the interaction energy. This method may apply to the cases of high potential, low potential, constant potential, and constant charge.
Keywords: Double layer interaction PB equation Langmuir's method
Curing and pyrolysis of epoxy resins containing 2-(6-oxido-6H-dibenz(c,e)(1,2)oxaphosphorin-6-yl)-1,4-naphthalenediol or bisphenol S
by S.-P. Rwei; S.-C. Kao; G.-S. Liou; K.-C. Cheng; W. Guo (pp. 407-415).
This work examines the curing kinetics, thermal properties, and decomposition kinetics of diglycidyl ether of bisphenol A (DGEBA) epoxies with three different curing agents, 2-(6-oxido-6H-dibenz(c,e)(1,2)oxaphosphorin-6-yl)-1,4-naphthalenediol (ODOPN), bisphenol A (BPA), and bisphenol S (BPS). The differential scanning calorimetry curing study reveals that the curing kinetics of the DGEBA/ODOPN epoxy is first order, independent of the scan rate. The ODOPN-containing epoxy, unlike the conventional BPA one, includes a phosphorus-containing bulky pendant aromatic group and results in an increase in the glass-transition temperature of 83 K, the char yield increases by a factor of 3, and the limiting oxygen index values increase from 23 to 27. For the BPS system, the glass-transition temperature increased slightly, and both the char yield and the limiting oxygen index value increased insignificantly when the test was conducted in air. Finally, the thermogravimetric analysis decomposition study in N2 from Ozawa's analysis demonstrates that the DGEBA/BPS epoxy has the highest activation energy, followed by the regular DGEBA/BPA system, and lastly the DGEBA/ODOPN has the lowest activation energy. The low activation energy for the ODOPN system is attributed to the initial decomposition of the phosphorus compound in the formation of an insulating layer.
Keywords: Curing kinetics Flame retardancy Thermal degradation 2-(6-Oxido-6H-dibenz(c,e)(1,2)oxaphosphorin-6-yl)-1,4-naphthalenediol Bisphenol A and bisphenol S
Effect of the molecular weight of poly(vinyl alcohol) on the water stability of a syndiotactic poly(vinyl alcohol)/iodine complex film
by W. Lyoo; J. Yeum; H. Ghim; J. Park; S. Lee; J. Kim; D. Shin; J. Lee (pp. 416-422).
To precisely identify the effect of the molecular weight of syndiotactic poly(vinyl alcohol) (s-PVA) on the water stability of a s-PVA/iodine complex film, we prepared four s-PVAs with similar syndiotactic diad (s-diad) contents of about 63% and with different number-average degrees of polymerization, P n, of 900, 6,000, 10,000, and 17,000, respectively. The desorption behavior of iodine in the s-PVA/iodine complex film in water was investigated in relation to the solubility of s-PVA in water. The degree of solubility of a s-PVA film having different P n in water at 80 °C was limited to about 0.3–10%, whereas the degrees of solubility of atactic PVA films with P n of 6,000 and 10,000 were 100% at the same conditions. The degree of iodine desorption of the complex film decreased with increasing P n of s-PVA. Especially, the degree of iodine desorption of a PVA drawn film having P n of 17,000 was limited to 2%, regardless of soaking temperature from 40 to 80 °C. The desorption of iodine in water was strongly affected by the dissolution of PVA. In addition, the degree of iodine desorption of the drawn s-PVA/iodine film was larger than that of the undrawn one.
Keywords: Molecular weight Syndiotactic poly(vinyl alcohol) Water stability Complex film Iodine desorption
Influence of flocculant charge on the dewaterability of flocculated clay suspensions
by D.-O. Krentz; G. Oelmeyer; J. Laudan; W.-M. Kulicke (pp. 423-430).
The influence of charged components of cationic polyelectrolytes on the dewatering of clay-containing suspensions was investigated with a view to better predicting the efficiency of flocculating agents. In flocculation and dewatering experiments on suspensions of harbour sediment and gravel washings, flocculating agents of the polyacrylamide-co-(trimethylammoniumpropyl chloride) (PTCA) type exhibited different dewatering efficiencies depending on the degree of cationicity, τ. For harbour sediment, a dewatering index, I D, of 80 was achieved with the highly charged PTCA 3 (τ=40%) at 30% lower flocculant dose than with the weakly cationic PTCA 1 (τ=3%). However, for gravel washings PTCA 1 proved to be more effective: for comparable degrees of dewatering (I D=80) approximately 40% less flocculant was required than for PTCA 3. In shear experiments on gravel washings and model suspensions with particles of differing size (d 50=0.5 und 5.7 µm) weakly cationic PTCA 1 exhibited an increased floc stability at lower concentrations than is necessary to achieve maximum I D values. For harbour sediments and model suspensions with unimodal particle size distributions this stability did not occur until the doses used were higher than the concentrations needed to achieve maximum I D values.
Keywords: Dewatering Clay Polyelectrolyte Cationicity Particle size distribution
Complexes of octadecyltrimethylammonium polyacrylate: properties in solution, gel and solid forms
by Paolo Michiotti; Maria Bonicelli; Patrizia Cafarelli; Gianfranco Ceccaroni; Carla Ferragina; Camillo La Mesa (pp. 431-438).
A polymer–surfactant complex (OTAPA) was prepared by titration of aqueous poly(sodium acrylate) with stoichiometric amounts of octadecyltrimethylammonium chloride. The resulting product is not water-soluble and does not dissolve in most polar and nonpolar, liquids. OTAPA has peculiar thermal behaviour and interesting structural properties. It has a high melting temperature and decomposes around 350 °C. According to preliminary X-ray findings, the complex is formed by an arrangement of alkyl chains around the polymer skeleton, packed into a layered structure. The complex forms an elastic gel in ethylene glycol, and, to a much lesser extent, in glycerol or tetrahydrofuran, but is hardly water-soluble. Indeed, the occurrence of micelle-assisted dissolution and the precipitation of OTAPA from such mixtures, upon dilution with water, have been observed. Applications of OTAPA as a hydrophobic modifier of surfaces can be considered.
Keywords: Polymers Surfactants Polymer–surfactant complexes Material preparation Thermal stability
Shear-induced structural transformation of pentaethylene glycol n-dodecyl ether and lithium perfluorooctane sulfonate mixed-surfactant lamellar solution
by Syuji Fujii; Tatsushi Isojima; Naoki Sasaki; Kenji Kubota; Mitsuo Nakata (pp. 439-446).
The viscoelastic behavior of the shear-induced structural transformation from the lamellar phase to multilamellar vesicles (MLVs) of a mixed-surfactant system was investigated. The transformation was divided into two processes on the basis of the strain dependence of the apparent viscosity. The first stage is a lamellar-to-intermediate structure transformation. It was found that a strain, not an applied shear rate, governed this process. The second stage is an intermediate-to-MLV phase transformation, which was not controlled by the strain. These structure developments were found in the shear-thickening viscosity regime. The MLV phase formed by applying shear flow exhibited shear-thinning viscosity behavior and reversible response to shear flow. The viscoelastic properties of the MLV phase were investigated by dynamic viscoelastic measurements. Under oscillating shear deformation, the amplitude dependence of the dynamic modulus indicated that the viscoelasticity of the MLV depended on the initial structure, such as the number of vesicle shells and the size of the MLV, which is governed by the preshear rate.
Keywords: Lamellar Multilamellar vesicle Shear effect Mixed-surfactant solution Viscoelasticity
Viscoelastic behavior of aqueous threadlike micellar solutions of oleyldimethylamineoxide
by Toshiyuki Shikata; Shyuji Itatani (pp. 447-454).
The viscoelastic behavior of aqueous oleyldimethylamineoxide (ODAO) solutions was examined by varying the concentration of ODAO, c D, and the average degree of protonation, <α>, by adding hydrogen bromide to the system. ODAO forms long threadlike micelles in aqueous solution in spite of the absence of any additives. Therefore, the aqueous ODAO system shows pronounced viscoelastic behavior caused by entanglement between threadlike micelles as highly entangled polymer systems do. The frequency dependence of the storage and loss moduli for the system is perfectly described by that of a Maxwell model possessing only one set of relaxation time, τ, and strength, G N. G N is proportional to the square of c D as observed in concentrated liner polymer solutions, while τ decreases with increasing c D. On the other hand, the addition of HBr to control <α> remarkably increases τ when G N is constant. This suggest that <α> alters the inner structure of the threadlike micelles; association of head groups, dimers or trimers of ODAO are formed in the micelles owing to hydrogen bonding between protonated ODAO or between protonated and unprotonated ODAO. An increase in the number density of the associated head groups in the threadlike micelles increases τ. Moreover, the flexibility of the threadlike micelles in the system is not affected so much by a change in the number density of the associated head groups, since G N corresponding to the number density of entanglements in the system is kept constant.
Keywords: Viscoelasticity Surfactant Dielectric relaxation Oleyldimethylamineoxide Hydrogen bond
Mixed micelles of cationic–nonionic surfactants: NMR self-diffusion studies of Triton X-100 and cetyltrimethylammonium bromide in aqueous solution
by X. Fang; S. Zhao; S. Mao; J. Yu; Y. Du (pp. 455-460).
The Fourier transform pulsed-field-gradient NMR technique has been used to measure the self-diffusion coefficients of the two surfactants cetyltrimethylammonium bromide (CTAB) and Triton X-100 (TX-100) in their mixed aqueous solutions with various molar ratios of CTAB to TX-100. Through simulating these experimental values of the self-diffusion coefficients by the two-state exchange model, some important dynamical micellization parameters, such as the critical micellar concentration of each soltute, the critical mixed micellar concentration and the self-diffusion coefficient of the mixed micelles at various molar ratios have been obtained. The composition of the mixed micelles and the interaction parameters between the two surfactants have also been evaluated. The mixed-micellization processes were discussed on the basis of these parameters. The results demonstrate the advantages of using NMR self-diffusion measurements to study binary cationic–nonionic mixed systems.
Keywords: Self-diffusion coefficient Composition of mixed micelle Cetyltrimethylammonium bromide Triton X-100 Interaction parameter
Waterborne polyurethanes containing ionic groups in soft segments
by Byung Kim; Jae Yang; Sang Yoo; Jeong Lee (pp. 461-468).
Polyurethane ionomer dispersions were prepared with ionic groups in soft segments (called ionic soft segments) as well as in hard segments (ionic hard segments). Ionic soft segments gave significantly lower solution viscosity, smaller particle size and greater dispersion viscosity, larger contact angle with water and greater water compared with ionic hard segments. These properties were interpreted in terms of delocalization of hydrophilic groups among soft segments and hard segments leading to increased soft segment–hard segment phase mixing, evidenced from IR, thermal and dynamic mechanical measurements which proved a higher glass-transition temperature, T g, and greater phase mixing with ionic soft segments. The increase in the hard segment length as well as the cross-linking density also gave a higher T g, modulus, and yield strength for the ionic soft segments.
Keywords: Segmented polyurethane Ionic soft segment Ionic hard segment Polyuretane dispersions Dynamic mechanical properties
Solvent induced polymorphism of quenched syndiotactic polypropylene in different liquids
by Giuliana Gorrasi; Liberata Guadagno; Vittoria Vittoria (pp. 469-475).
The solvent induced crystallization phenomenon (SINC) was studied for syndiotactic polypropylene quenched from the melt at 0 °C and kept at this temperature a for long time. In these conditions a mesophase having the chains in trans-planar conformation was formed. The interaction polymer-solvent with liquids having different solubility parameters, derived by both the swelling and the weight uptake, considerably varies among the different liquids, showing a maximum corresponding to carbon tetrachloride (δ=8.6). A smaller maximum was found for chloroform (δ=9.3). These two maxima were attributed to interaction either with the amorphous phase or with the trans-planar mesophase.Infrared analysis showed that all the liquids induce a conformational transition from trans-planar to helix, and only a small residual fraction of chains in trans-planar conformation was detected for the samples immersed in the liquids and vacuum dried for many hours.The X-ray analysis showed that the quenched sample undergoes in the solvents a complex transformation, partially crystallizing into the helical form I and partially into the helical form II. All the liquids induced the same transformation, in spite of very different levels of interaction.
Keywords: Syndiotactic polypropylene Polymorphism Solvent induced crystallization
Production of micron-sized polystyrene particles containing PEG near the particles surface
by H. Ahmad; K. Tauer (pp. 476-484).
Polystyrene (PS) particles in the size range of 1–7 µm, containing poly(ethylene glycol) or PEG on the particles surface, were prepared by multi-step seeded polymerizations. Micron-sized PS particles were first prepared by dispersion polymerization using 2,2′-azobisisobutyronitrile as initiator and polyvinyl pyrrolidone as stabilizer. Conventional swelling method was then used to increase the size of the PS particles with a large amount of styrene in presence of oil soluble initiator, benzoyl peroxide. In the final step, the PS particles have been used to carry out seeded polymerization with small amount of styrene in presence of poly(ethylene glycol)-azo or PEGA initiator with average molecular weights of the PEG chains of 200 and 3000 g mol–1 , respectively. The average size, size distribution, and surface morphology indicate that seeded polymerization in the final step with small amount of styrene in presence of PEGA is the best way to produce monodisperse polystyrene particles containing PEG near the particles surface.
Keywords: Polystyrene particles PEGA – initiator Swelling Seeded polymerization Morphology
Second harmonic generation and polar order in thin films of polyesters
by Biju Philip; Krishnapillai Sreekumar (pp. 485-489).
A series of optically active main chain polyesters were synthesized by high temperature polycondensation from biphenolic azo chromophores with azobenzene-4,4′-dicarbonylchloride and 1,4:3,6-dianhydro-D-sorbitol ([α]D 25=+42.5°). The second harmonic generation of the polyesters is studied in thin films. The polar order in films is determined from the UV-visible absorption spectra. The variation in SHG intensity with chiral monomer concentration is explained as a function of polar order. The polymers with chiral units showed good second harmonic efficiency. The intensity of second harmonic light (532 nm) increased with angle of incidence and indicated the polar order in the plane of the film. The SH signal also showed good temporal stability.
Keywords: Nonlinear optics Second harmonic generation Chiral polymers Polymer thin film Polar order