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A disulfide polymer that is triggerable by ultrasound, UV, and redox in aqueous solution and can self-assemble with ionic probe molecules into again multitriggerable assemblies is presented. It is ...

Unlike Na+ cations, which interact with fully neutralized poly(acrylic acid) as purely electrostatic entities, cations like Ag+, Mg2+, and Ca2+ exhibit specific interactions with the COO– residues of anionic polyacrylates. The present work analyzes the interaction of all four cations with a layer of polyacrylate chains grafted onto spherical polystyrene core as an outer shell. First and foremost the analysis answers the question on how these specific interactions influence the nature of the shell and solution behavior of the spherical polyelectrolyte brushes. It could be unambiguously demonstrated that Ag+, Mg2+, and Ca2+ cations induce a drastic shrinking of the polyacrylate shells at cation concentrations lower by 2–3 orders of magnitude compared to the transition of a fully stretched osmotic brush to a shrunken salted brush accomplished with Na+ cations. Ag+ induces a particularly abrupt contraction, which comes close to the annealing of such brushes achieved with a neutralization by protons. Finally, ...

The early stages of silica polymerization in aqueous solution proceed according to a mechanism based on three steps: nucleation, particle growth, and agglomeration of the particles. Application of time-resolved static and dynamic light scattering as a powerful in situ technique in combination with spectrophotometric analysis of the monomer consumption based on the molybdenum blue method was carried out to further investigate this 3-step process. Experiments were carried out at four different initial silicic acid contents covering a range between 350 and 750 ppm in the presence of either 10 mM NaCl or 5 mM of a mixture of CaCl2 and MgCl2. The process in all cases was initiated with a drop of pH to 7. Addition of the salts made possible an analysis of the impact of an electrolyte on the process. Independent of the presence or absence of salt, particle growth in step two proceeded as a monomer-addition process without being interfered significantly by Ostwald-ripening. The growing particles were compact with...

A detailed light scattering investigation is presented on dilute solutions of two long-chain sodium polyacrylates (NaPA) in the presence of monovalent Ag+ ions in 0.01 M NaNO3 aqueous solution at a pH of 9. The relevance for the investigation is based on two features: (i) despite its monovalency, Ag+ is expected to exhibit a much more complex interaction pattern with NaPA than salts based on alkaline cations do; (ii) aqueous solutions of AgNO3 nucleate Ag–nanoparticle formation in the presence of NaPA under UV light, which may be modulated by the solution behavior. Our study revealed the following results. Addition of a low amount of Ag+ ions leads to an aggregation of PA-chains without considerable coil shrinking. At a ratio of silver ions per monomer of 0.001 ≤ [Ag+]/[COO–] ≤ 0.05, combined static and dynamic light scattering (SLS/DLS) suggests formation of homogeneous low density aggregates. Further increase of the Ag+ ion concentration results in a formation of dense unstable aggregates. At ratios of ...

In this report, we summarize our experimental and theoretical investigations in the zinc(II) imidazolate, [Zn(im)2], and zinc(II) 4,5-dichloroimidazolate, [Zn(dcim)2], systems that have been published previously. This comprises a study on the thermodynamic stabilities of the two densest phases with coi and zni framework structures in the [Zn(im)2] system including the discovery and characterization of a new [Zn(im)2·0.5py]-neb phase (py = pyridine), a study on the mechanism of formation of the [Zn(im)2]-zni phase as well as a study on the discovery and characterization of a new [Zn(dcim)2]-SOD phase. In addition, we present as yet unpublished work. This concerns the discovery and characterization of a new [Zn(im)2·0.5mor]-neb phase (mor = morpholine) and investigations of the mechanisms of crystallization of [Zn(im)2·0.5py]-neb and [Zn(im)2·0.5mor]-neb as well as an evalutation of time-resolved SAXS/WAXS data recorded in-situ during the formation of [Zn(im)2]-zni.

Silica polymerization in a supersaturated aqueous solution of sodium silicate is a fundamental mineralization process with broad relevance for technical applications as well as for biological processes. To contribute to a better understanding of the mechanism underlying the polymerization of sodium silicate under ambient conditions, a combined multiangle static and dynamic light scattering study on the evolution of particle mass and size is applied for the first time in a time-resolving manner. The light scattering experiments are complemented by a time-resolved analysis of the decay of the concentration of monomeric silicate by means of the silicomolybdate method. Particle formation was investigated at a variable concentration of silicate at pH 7 and 8. The joint experiments revealed a loss of monomers, which is parallel to the formation of compact, spherical particles growing by a monomer-addition process. An increase in the silicate content of up to 750 ppm increased the extent of nucleation and at the same time decreased the lag time observed between the start of the reaction and the actual onset of the growth of particles. Once the silica content is considerably larger than 1000 ppm, the formation of particles is succeeded by particle-particle agglomeration leading to larger fractal-like particles. By the time agglomeration becomes noticeable with light scattering, the monomer concentration has already reached its equilibrium value. An increase in the pH to 8 again revealed particle formation via a monomer-addition process. However, the extent of nucleation was increased and particle-particle agglomeration was inhibited even at an initial silica content of 2000 ppm.

The present work investigates PMMA colloids in a polymer matrix of linear chains as a simple and suitable system for complex nanocomposites. The investigation was based on SANS experiments, which were enabled by the use of deuterated colloids immersed in a matrix of linear hydrogenated chains. Cross-linked deuterated PMMA-colloids were synthesized with two different sizes (70 and 140 nm) by means of the surfactant-free emulsion polymerization method and the swelling behavior adjusted by varying the amount of added cross-linker (1.5 and 15.0 mol-%) at each size respectively. Colloid–polymer blends were prepared from colloid–polymer solutions. SANS experiments on these blends consistently revealed that colloids with a low cross-linking density could be homogeneously distributed throughout the matrix of linear chains. Fits with model form factors indicated the structure of fuzzy spheres for these molecularly dispersed microgels, which are slightly swollen with respect to their size and shape in H2O. Contrary...

Bivalent lead ions as representative main group heavy metal cations form specific interactions with the negatively charged COO– residues of sodium polyacrylate chains in dilute aqueous solution. The interactions eventually lead to aggregation and precipitation of sodium polyacrylate chains partially neutralized with Pb2+ cations. The present work outlines a small-angle X-ray (SAXS) and light scattering study of the polyacrylate chains undergoing changes in coil conformation and successive aggregation while approaching and crossing the Pb2+-induced precipitation threshold. The study reveals a coil shrinking while approaching the precipitation threshold. Anomalous SAXS (ASAXS) complemented this information with a first insight into the spatial distribution of the Pb2+ cations captured by the polyacrylate chains together with a semiquantitative estimation of the amount of Pb2+ cations located within the collapsed domains of the shrinking chains. Conformational aspects of the shrinking coils could be establis...

In this report, we summarize our theoretical and experimental investigations on the zeolitic imidazolate framework (ZIF) system [Zn(dcim)2] (dcim=4,5-dichloroimidazolate) that have been published recently. These comprise: (1) a theoretical study on hypothetical conformational [Zn(dcm)2]-SOD polymorphs with the same underlying sodalite (SOD) topology but distinct dcim linker orientations, (2) a synthetic work that resulted in the experimental realization of the most stable predicted (trigonal) SOD-type framework conformer and improved synthetic protocols for a previously discovered cubic SOD-type material, (3) a detailed structural analysis of the trigonal and cubic SOD-type materials, (4) a comparative characterization of the SOD-type materials by gas physisorption measurements, (5) a synthetic work that resulted in the discovery of a complete series of intermediate frameworks with the trigonal and cubic SOD-type materials as the end members, and (6) time-resolved in-situ light and stopped-flow synchrotron small-angle and wide-angle X-ray scattering experiments on the rapid crystallization of the RHO-type polymorph (ZIF-71). In addition, we report as yet unpublished work, concerning time-resolved in-situ angular-dispersive synchrotron X-ray diffraction experiments on RHO-/SOD-type phase selection via the coordination modulation approach during competitive formation of the RHO-type and SOD-type materials.

A detailed in situ scattering study has been carried out on the formation of amorphous calcium carbonate (ACC) particles modulated by the presence of small amounts of sodium polyacrylate chains. The work is aiming at an insight into the modulation of ACC formation by means of two polyacrylate samples differing in their molecular weight by a factor of 50. The ACC formation process was initiated by an in situ generation of CO(3)(2-) ions via hydrolysis of 10 mM dimethylcarbonate in the presence of 10 mM CaCl(2). Analysis of the formation process by means of time-resolved small-angle X-ray and light scattering in the absence of any additives provided evidence for a monomer addition mechanism for the growth of ACC particles. ACC formation under these conditions sets in after a lag-period of some 350 s. In the presence of sodium polyacrylate chains, calcium polyacrylate aggregates are formed during the lag-period, succeeded by a modulated ACC growth in a second step. The presence of anionic polyacrylate chains changed the shape of the growing particles toward loose and less homogeneous entities. In the case of low amounts (1.5-7.5 mg/L) of the long chain additive with 97 kDa, the size of the aggregates is comparable to the size of the successively formed hybrid particles. No variation of the lag-period has been observed in this case. Use of the short chain additive with 2 kDa enabled increase of the additive concentration up to 100 mg/L and resulted in a significant increase of the lag-period. This fact, together with the finding that the resulting hybrid particles remained stable in the latter case, identified short chain sodium polyacrylates as more efficient modulators than long chain polyacrylates.

Polymers showing an upper critical solution temperature (UCST) in water are rare. Recently, the nonionic homopolymer poly(N-acryloyl glycinamide) (poly(NAGA)) has been shown to exhibit a sharp uppe...

We report on a simple and straightforward method that enables the rapid room-temperature production of nanocrystals (finely tuned in size between ∼10 and 65 nm) and microcrystals (∼1 μm) of the prototypical microporous zeolitic imidazolate framework (ZIF) material ZIF-8. Control of crystal size is achieved in a novel approach by employing an excess of the bridging bidentate ligand and various simple auxiliary monodentate ligands with different chemical functionalities (carboxylate, N-heterocycle, alkylamine). The function of the monodentate ligands can be understood as a modulation of complex formation and deprotonation equilibria during crystal nucleation and growth. Using time-resolved static light scattering, the functioning of modulating ligands is monitored for the first time by in situ experiments, which offered significant insight into the crystal growth processes. Formation of nanocrystals is characterized by continuous, comparatively slow nucleation and fast crystal growth occurring on a time sca...

Long chain sodium polyacrylate polymers in dilute aqueous solution respond extremely sensitive to the addition of small, stoichiometric amounts of Ca2+ ions. Essential features of this response are a considerable shrinking of the coil dimensions and an additional sensitivity of the coil dimensions toward a change in temperature. To reveal details of this shrinking process, the conformational changes in response to the addition of alkaline earth cations at two different temperatures are investigated by means of light and neutron scattering and by AFM on the same samples, respectively. Partially collapsed coils at 15 °C were further shrunken and modified in shape by increasing the temperature to 30 °C. The scattering curves from the intermediates at 30 °C could successfully be interpreted with a pearl necklace model, which includes a low amount of pearls per polymer separated by 80 nm from each other. AFM investigations of adsorbed chains confirm the drastic conformational changes inferred to the system wit...

The bis(guanidine)-stabilised zinc complexes [N1,N2-bis(1,3-dimethylimidazolidin-2-ylidene)ethane-1,2-diamine]dichloridozinc(II), [Zn(DMEG2e)Cl2] (C1), diacetato[N1,N2-bis(1,3-dimethylimidazolidin-2-ylidene)ethane-1,2-diamine]zinc(II),[Zn(DMEG2e)(CH3COO)2] (C2), and bis[N1,N2-bis(1,3-dimethylimidazolidin-2-ylidene)ethane-1,2-diamine]zinc(II) bis(trifluoromethanesulfonate), [Zn(DMEG2e)2](CF3SO3)2 (C3), have been synthesised and completely characterised by means of X-ray structure analysis, NMR spectroscopy and mass spectrometry. These [bis(guanidine)]zinc complexes were investigated regarding their activity in the bulk polymerisation of D,L-lactide. It could be shown that these compounds are able to act as initiators for lactide polymerisation, and polylactides with molecular weights (Mw) of around 18000–59000 g/mol could be obtained. Variation of the reaction temperature revealed that the molecular weights decrease with increasing temperature. Additionally, the correlation of the intrinsic viscosity with the molecular weight demonstrates that the obtained polymers are linear and structurally homogeneous.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

A new combination of polymer chains and small colloids is presented in order to investigate the behavior of colloid−polymer mixtures in solution (CP) in the protein limit. To this end, hydroxy-functionalized silica particles (OHSil) were prepared according to a procedure [J. Am. Chem. Soc. 2003, 125, 3712], which led to colloid radii as small as 1.2 nm. Compared to this small size, the coil dimensions of the polystyrene (PS) chains used as the polymer component were larger by more than an order of magnitude. Investigation of the CP focused on the dimension of the PS chains in the presence of a varying amount of OHSil colloids. Chain size and shape were characterized by means of light scattering, viscosity experiments, and small-angle neutron scattering (SANS). Two solvents have been used. A mixture of dimethylformamide (DMF) with toluene was isorefractive to the OHSil particles, giving access to single chain behavior of PS. Pure DMF, on the other hand, allowed an efficient contrast matching of OHSil suita...

The present work investigates the structure of large polystyrene (PS) chains in two different solvents in the presence of octa-n-propylsilsesquioxane (SILS) molecules. Both solvents are good solvents for the PS chains. Viscosity measurements combined with static and dynamic light scattering revealed a significant shrinking of the PS chain dimensions, with increasing the SILS concentration. At the same time, chain-chain interactions decreased. Highly significant light scattering experiments became possible due to the fact that one of the solvents provided a refractivity which matched the scattering contrast of SILS, thus giving way to an unperturbed picture of the polymer chains. Together with the evaluation of the phase behavior of the PS-SILS mixture in toluene and in a 0-solvent, these results suggest that the PS-SILS mixture represents an interesting model system for colloid-polymer mixtures in the protein limit. Supplementing SANS experiments on SILS in solutions of perdeuterated toluene with perdeuterated PS chains clearly indicated a zone depleted of SILS. In line with this, the crystallization tendency of SILS was increased with increasing PS concentration due to a condensation of SILS in polymer-free domains.

A synthetic route is presented for the preparation of electrically charged colloidal particles with either sign from the same precursor. In the first step, methyl methacrylate was copolymerized with ω-bromoalkyl acrylate and a cross-linker, leading to monodisperse, bromo-functionalized colloids. Substitution of the bromo-functions by either trimethylamine of Na 2 SO 3 transformed the neutral precursors into positively or negatively charged particles, respectively. The charge density could be varied in two ways: (i) by varying the fraction of bromo-functionalized monomers; (ii) by increasing the degree of substitution of the bromo-functions. Derivation of the charged particles from the same precursor colloid made it easier to explain various interesting physical properties of the charged colloidal particles. Higher charge densities were achieved for the cationic colloids. If a threshold value for the charge density of 55 μC .cm -2 was surpassed, the particles showed a significant swelling in aqueous solution.

Calcium ions were used to induce a shrinking process with sodium polyacrylate coils in aqueous 0.01 M NaCl. By means of light scattering, four solutions with promising intermediates were selected for a detailed investigation by small-angle neutron scattering. All intermediates were half as large in size as the corresponding unperturbed dimensions but still had radii of gyration that were 45% larger than the hydrodynamic radius. The resulting SANS curves showed power laws typical for objects with a sharp boundary. They were compared with various model curves. From these models, a mixture of spheres and dumbbells resulted in theoretical curves that agreed best with experiments. The sphere size of single spheres and spheres in dumbbells was roughly 10 nm. Two spheres on a dumbbell had an averaged distance larger by almost an order of magnitude. The results are considered to be compatible with pearl necklace-like transition states of shrinking polyelectrolyte chains.

Since the pioneering work of Jelley and Scheibe, it has become a widely accepted fact that the cationic dyestuff pseudoisocyanine chloride (PIC) forms large, chainlike aggregates in aqueous solutio...

We report the polymer conformation and fullerene aggregation in a ternary system containing polystyrene, C60, and toluene measured by small angle neutron, static, and dynamic light scattering. We investigate polymer concentrations across the dilute and semidilute regime for five polymer molecular weights (Mw = 20 kg/mol to 1 Mg/mol), and fullerene concentrations below and above its miscibility threshold in toluene. We find that the polymer radius of gyration (Rgpoly), hydrodynamic radius (Rh), and the mixture correlation length (ξ) remain unchanged upon addition of C60. The miscibility of C60 in toluene, however, decreases upon addition of polystyrene forming aggregates with a time-dependent radius on the order of 100 nm, and this effect is amplified with increasing polymer Mw. Our findings are relevant to the solution processing of organic photovoltaics, which generally require the effective solubilization of fullerene derivatives and polymer pairs in this concentration range.

The coil contraction of sodium polymethacrylate in dilute aqueous sodium chloride solution (0.1 N, pH = 9) was monitored by static and dynamic light scattering when the Na+ ions were partly replaced by Ca2+ or Cu2+ ions. The effect was quantified as a function of polyion and bivalent metal ion concentration. The impact of Cu2+ ions on the chain conformation and the solubility of sodium polymethacrylate was observed to be larger than the corresponding effect of Ca2+ ions. This difference was ascribed to complexation of the carboxylate group with bivalent metal cations which is larger for the Cu2+ than for the Ca2+ ion. Even at the largest extent of contraction observed close to the precipitation threshold, the ratio of the radius of gyration and the hydrodynamic radius remained unchanged in contrast to the coil−globule transition observed for neutral polymer systems below the ϑ-temperature.

We report a rapid additive-free synthesis of nanocrystals (NCs) of RHO-type ZIF-71 (1) of composition [Zn(dcim)2] (dcim = 4,5-dichloroimidazolate) in 1-propanol as solvent at room temperature. NC-1 has a size of 30–60 nm and exhibits permanent microporosity with a surface area (SBET = 970 m2 g−1) comparable to that of microcrystalline material. When kept under the mother solution NC-1 undergoes transformation into a novel SOD-type polymorph (2), which in turn converts into known ZIF-72 (3) with lcs topology. It is shown that microcrystals (MCs) of 2 can be favourably synthesised using 1-methylimidazole as a coordination modulator. NC-2 with size

Conformational changes of polyacrylate chains induced by Ca 2+ ions have been studied by means of static light scattering and viscosity measurements with two different sodium polyacrylate samples. The reference system was sodium polyacrylate in an aqueous solution of 0.1 N NaCl at a pH of 9. Replacement of different amounts of the Na + ions from the added NaCl by Ca 2+ ions led to different Ca 2+ fractions at constant ionic strength of the low molecular weight salt. At each Ca 2+ ion fraction, the size of the polyelectrolyte coils was recorded as a function of polyacrylate concentration. The results were discussed in terms of a coil collapse which precedes precipitation of the calcium polyacrylate when lowering the polyacrylate concentration

A regular solution model is used to interpret the behavior of binary surfactant mixtures at the liquid/vapor and the solid/liquid interface. Two nonionic surfactants with the general formula H(CH2)n(OCH2CH2)mOH, wherem is 4 and 8, are used in three different types of binary surfactant combinations: mixtures of two nonionic surfactants, mixtures of tetradecyl sulfate sodium salt with both nonionic surfactants, and mixtures of dodecyl sulfonate sodium salt with both nonionic surfactants. Two anionic/nonionic mixtures each have the same anionic component, thus giving evidence for correlations between the structure of the nonionic surfactant and the interaction with an anionic component. It can be shown that at the solid/liquid interface, the interaction between the anionic surfactant and the nonionic surfactant with the smaller hydrophilic headgroup is always significantly lower than that between the same anionic component and the nonionic surfactant with the larger hydrophilic headgroup.

The formation of amorphous calcium carbonate particles from supersaturated aqueous solution is relevant to many processes in nature and industry. The present work introduces time-resolved static light scattering as a new tool to investigate the initial stage of this process. The process is initiated by mixing a solution of Na(2)CO(3) with a CaCl(2) solution or, alternatively, by mixing solutions of the dimethyl ester of carbonic acid and CaCl(2) with solutions of NaOH. Particle formation was analyzed by recording scattering curves as a function of time. Scattering data indicate the formation of compact spheres with diameters close to 360 nm. In the case of particle formation induced by ester hydrolysis, nucleation sets in after a certain lag time. Particle size is homogeneous, and the growth mechanism corresponds to an addition of ions or small constituent particles to a constant number of growing spheres. An increase of the NaOH concentration, which triggers ester hydrolysis, decreases the lag period prior to the onset of particle formation. An increase of the solution temperature also decreases this lag period. The temperature and NaOH dependent duration of the lag time could successfully be interpreted in terms of the kinetics of the ester hydrolysis. The work establishes time-resolved static light scattering as an efficient tool to investigate the particle formation process of amorphous calcium carbonate.

Polyacrylate anions are used to inhibit CaCO3 precipitation and may be a promising additive to control formation of inorganic nanoparticles. The origin of this applicability lies in specific interactions between the alkaline earth cations and the carboxylate functions along the polyacrylate chains. In the absence of CO32- anions, these interactions eventually cause precipitation of polyelectrolytes. Extended investigation of dilute sodium polyacrylate solutions approaching this precipitation threshold revealed a dramatic shrinking of the PA coil dimensions once the threshold is reached (Eur. Phys. J. E 2001, 5, 117). Recent isothermal calorimetric titration experiments by Antonietti et al. (Macromolecules 2004, 37, 3444) indicated that the driving force of this precipitation is entropic in nature. In the present work, we investigated the impact of temperature on the structural changes of dissolved polyacrylate chains decorated with alkaline earth cations. To this end, large polyacrylate chains were brought close to the precipitation threshold by the addition of distinct amounts of Ca2+ or Sr2+ cations. The resulting structural intermediates were then subjected to temperature variations in the range of 15 degrees C/= T/= 40 degrees C, and the accompanying structural changes of the polyacrylate coils were recorded by means of light and neutron scattering. As a major result, we could unambiguously demonstrate that the coils can reversibly be collapsed and extended by increasing and decreasing the temperature, respectively.

Mesures des coefficients de diffusion, des rayons de giration et de 2 coefficients du viriel de ce polymere

Comportement conformationnel et dynamique de polystyrene en etoile a 3, 12 et 18 bras dans le cyclohexane a 34,5°C et dans le toluene a 20°C

Etude theorique des proprietes de diffusion (rayon de giration, coefficient diffusion, facteur de structure dynamique, fonction de diffusion particule). Influence des parties cycliques sur les proprietes de diffusion

Extension des calculs de Mansfield et Stockmayer sur le rayon de giration des molecules en etoile a la variation angulaire des fonctions de diffusion P(q). Deduction d'expressions analytiques en s'appuyant sur la theorie de Koyama si les bras sont fixes librement au centre de l'etoile. Comparaison des resultats avec les calculs de Monte Carlo pour des polymethylenes en etoile a 12 bras et avec les donnees de diffusion neutronique centrale de solutions diluees de polystyrene en etoile a 12 bras dans le cyclohexane deuterie