Influence of conducting polymers based on carboxylated polyaniline on in vitro CaCO3 crystallization

Conducting polymers are interesting materials of technological applications, while the use of polymers as additives controlling crystal nucleation and growth is a fast growing research field. In the present article, we make a first step in combining both topics and report the effect of conducting polymer derivatives, which are based on carboxylated polyanilines (c-PANIs), on in vitro CaCO3 crystallization by the Kitano and gas diffusion method. This is the first example of the mineralization control of CaCO3 by a rigid carboxylated polymer. Both the concentration of c-PANI and the presence of carboxylate groups have a strong influence on the CaCO3 crystallization behavior and crystal morphology. X-ray diffraction (XRD) analysis shows crystalline calcite particles confirmed by FTIR spectra. pH and Ca2+ measurements during CaCO3 crystallization utilizing the Kitano and a constant-pH approach show a defined nucleation period of CaCO3 particles. The measurements allow for the calculation of the supersaturation time development, and the kinetic data can be combined with time-dependent light microscopy. The presence of c-PANIs delays the time of nucleation indicative of calcite nucleation inhibition. Microscopy illustrates the morphologies of CaCO3 crystals at all crystallization stages, from homogeneous spherical amorphous CaCO3 (ACC) particles corresponding to the first steps of crystallization to transition stage calcite crystals also involving a dissolution-recrystallization process in a late stage of crystallization. The data show that it is not possible to conclude the crystallization mechanism even for a very simple additive controlled crystallization process without time-resolved microscopic data supplemented by the analysis of the species present in the solution. Finally, fluorescence analysis indicates that conducting polymer derivatives can be incorporated into precipitated calcite particles. This gives rise to CaCO3 particles with novel and interesting optical properties.     

The colloidal behaviour of kraft lignin

Kraft lignin gels have been found to exhibit both macrosyneresis and hysteresis in swelling. The effects of temperature and prehistory on swelling and on the mechanical properties have been investigated. Thermal treatment of kraft lignin gels in the protonised state induces an irreversible deswelling of the gels. This irreversible deswelling can, however, be released by deprotonization of the carboxyl groups. Deswelling also occurs when partly dried protonised gels are placed in water again. Furthermore, the gels were found to exhibit pH-hysteresis.It is concluded that the above-mentioned effects are closely related to the state of dissociation of the carboxylic groups and to their ability to form intermolecular hydrogen bonds in the network structure.It is suggested that syneresis is due to a structural rearrangement induced by breaking and formation of hydrogen bonds and promoted by the long-range van der Waal's interaction between the colloidal units in the gel. Swelling hysteresis is assumed to be related to repeptization phenomena commonly encountered in lyophobic colloids.     

A shape-persistent polymeric crystallization template for CaCO3

Alanyl-alanine-derived poly(isocyanide)s possess a helical structure that persists even in aqueous media. These rigid macromolecules possess a regular distribution of carboxylic acid-terminated side chains which for the first time allows the study of the templating process involved in biomineralization using a shape-persistent polymeric template. It is demonstrated that in the case where the polymer derived from l-Ala-d-Ala is used the formation of apple core-type calcite crystals is controlled both by nucleation of the (01.1) face and subsequent adsorption of the polymer to the {hk.0} faces of the growing crystal. A small change in the secondary structure of the template that is introduced by using the polymer derived from l-Ala-l-Ala is directly reflected in the lower degree of control over the crystallization process.     

The colloidal behaviour of kraft lignin III. Swelling behaviour and mechanical properties of kraft lignin gels

Summary Kraft lignin gels have been synthesized by cross-linking kraft lignin (Indulin ATR) in water with varying amounts of epichlorohydrin under alkaline conditions. The effects of pH and salt concentration on the swelling behaviour and on the mechanical properties of these gels have been investigated.Swelling was determined gravimetrically and the mechanical properties of the gels were tested under uni-axial compressive creep in the time interval 1–900 s. The gels show a linear viscoelastic behaviour without viscous flow.The kraft lignin gels exhibit a swelling behaviour typical for polyelectrolytic networks, i. e. the degree of swelling increases with an increasing number of ionized groups and decreases with increasing salt concentration. The swelling behaviour and ion exchange capacity were found to be nonspecific towards type of alkaline solution (LiOH, NaOH, and KOH).The ability of the carboxylic groups to form intermolecular hydrogen bonds has a strong influence on the mechanical properties of the gels. Creep compliance and creep rate increase greatly when the carboxyl groups are dissociated. It is therefore concluded that the effective number of crosslinks in the networks in addition to chemical cross-linking is also dependent on the state of dissociation of the carboxylic groups.With 11 figures and 1 table     

Bioinspired crystallization of CaCO3 coatings on electrospun cellulose acetate fiber scaffolds and corresponding CaCO3 microtube networks

This article describes the mineralization behavior of CaCO(3) crystals on electrospun cellulose acetate (CA) fibers by using poly(acrylic acid) (PAA) as a crystal growth modifier and further templating synthesis of CaCO(3) microtubes. Calcite film coatings composed of nanoneedles can form on the surfaces of CA fibers while maintaining the fibrous and macroporous structures if the concentration of PAA is in a suitable range. In the presence of a suitable concentration of PAA, the acidic PAA molecules will first adsorb onto the surface of CA fibers by the interaction between the OH moieties of CA and the carboxylic groups of PAA, and then the redundant carboxylic groups of PAA can ionically bind Ca(2+) ions on the surfaces of CA fibers, resulting in the local supersaturation of Ca(2+) ions on and near the fiber surface, which can induce the nucleation of CaCO(3) on the CA fibers instead of in bulk solution. Calcite microtube networks on the macroscale can be prepared by the removal of CA fibers after the CA@CaCO(3) composite is treated with acetone. When the CA fiber scaffold is immersed in CaCl(2) solution with an extended incubation time, the first deposited calcite coatings can act as secondary substrate, leading to the formation of smaller calcite mesocrystal fibers. The present work proves that inorganic crystal growth can occur even at an organic interface without the need for commensurability between the lattices of the organic and inorganic counterparts.     

Control of CaCO3 crystallization by demixing of monolayers

In this paper we describe how to template a demixed monolayer into a spatially patterned inorganic replica. For this purpose a new amphiphilic monomer was synthesized which can be polymerized both in solution and in the monolayer of a Langmuir-Blodgett (LB) trough. Since it inhibits the crystallization of CaCO3, it can be used--in combination with stearic acid (nucleation-promotor)--to control CaCO3 crystals formed under the monolayer. Investigations of the two-component monolayer (Langmuir isotherms and AFM measurements of transferred films) show--in the biphasic region--demixing in solid analogue stearic acid domains and the liquid analogue phase of the monomer. Crystallization of CaCO3 starts under the stearic acid domains whose size varies from less than 100 nm to several tens of micrometers. The addition of poly(acrylic acid) into the subphase hinders the three-dimensional growth of CaCO3 crystals from the monolayer into the solution. Thus, it becomes possible to transfer the pattern of the demixed domains into an inorganic replica of CaCO3.     

Template adaptability is key in the oriented crystallization of CaCO3

In CaCO3, biomineralization nucleation and growth of the crystals are related to the presence of carboxylate-rich proteins within a macromolecular matrix, often with organized beta-sheet domains. To understand the interplay between the organic template and the mineral crystal it is important to explicitly address the issue of structural adaptation of the template during mineralization. To this end we have developed a series of self-organizing surfactants (1-4) consisting of a dodecyl chain connected via a bisureido-heptylene unit to an amino acid head group. In Langmuir monolayers the spacing of these molecules in one direction is predetermined by the hydrogen-bonding distances between the bis-urea units. In the other direction, the intermolecular distance is determined by steric interactions introduced by the side groups (-R) of the amino acid moiety. Thus, by the choice of the amino acid we can systematically alter the density of the surfactant molecules in a monolayer and their ability to respond to the presence of calcium ions. The monolayer films are characterized by surface pressure-surface area (pi-A) isotherms, Brewster angle microscopy, in-situ synchrotron X-ray scattering at fixed surface area, and also infrared reflection absorption spectroscopy (IRRAS) of films transferred to solid substrates. The developing crystals are studied with scanning and transmission electron microscopy (SEM, TEM), selected area electron diffraction (SAED), and crystal modeling. The results demonstrate that although all compounds are active in the nucleation of calcium carbonate, habit modification is only observed when the size of the side group allows the molecules to rearrange and adapt their organization in response to the mineral phase.     

Effects of macromolecules on the crystallization of CaCO3 the Formation of Organic/Inorganic Composites

The effects of macromolecules as soluble additives and solid matrices have been examined for the crystallization of CaCO₃. A vaterite form grows on a glass substrate in the presence of poly(glutamic acid) (PGA) containing a carboxylic acid group as a soluble additive. In contrast, no crystal growth has been observed when poly(acrylic acid) (PAA) exists as an additive though it has the same functional group. The conformation or the backbone structure of the polymers may have an influence on the crystal polymorph of CaCO₃. Thin film states of CaCO₃ crystals have been obtained as organic/inorganic composites with chitosan that acts as a solid matrix in the presence of PAA or PGA as a soluble additive.     

Non-isothermal crystallization kinetics of UHMWPE composites filled by oligomer-modified CaCO3

The processability of ultrahigh molecular weight polyethylene (UHMWPE) improved by oligomer-modified calcium carbonate (CaCO₃) was observed in our previous work. In order to understand the effect of oligomer-modified CaCO₃ on the crystallization of UHMWPE, the non-isothermal crystallization behavior and crystallization kinetics of UHMWPE composites filled by oligomer-modified CaCO₃ was studied by differential scanning calorimetry in this work. Jeziorny and Mo methods were used to describe the non-isothermal crystallization kinetics of UHMWPE composites. The effect of modified filler content and cooling rate on the crystallization temperature and crystallization rate was discussed. The heterogeneous nucleation of modified CaCO₃ slightly increases the crystallization temperature of UHMWPE. The crystallization enthalpy of UHMWPE composites is significantly higher than that of UHMWPE. The crystallization rate of UHMWPE composites depends on the filler contents and cooling rate.

     

Controlled crystallization of CaCO(3) on hyperbranched polyglycerol adsorbed to self-assembled monolayers

The formation of biominerals by living organisms is governed by the cooperation of soluble and insoluble macromolecules with peculiar interfacial properties. To date, most of the studies on mineralization processes involve model systems that only account for the existence of one organic matrix and thus disregard the interaction between the soluble and insoluble organic components that is crucial for a better understanding of the processes taking place at the inorganic-organic interface. We have set up a model system composed of a matrix surface, namely, a self-assembled monolayer (SAM), and a soluble component, hyperbranched polyglycerol. The model mineral calcium carbonate displays diverse polymorphism. It could be demonstrated that the phase selection of calcium carbonate is controlled by the cooperative interaction of the SAM and hyperbranched polyglycerol of different molecular weights (M(n) = 500-6000 g/mol) adsorbed to the SAM. Our studies showed that hyperbranched polyglycerol is adsorbed to polar as well as to nonpolar SAMs. This effect can be related to its highly flexible structure and its amphiphilic character. The adsorption of hyperbranched polyglycerol to the SAMs with different surface polarities resulted in the formation of aragonite for alkyl-terminated SAMs and no phase selection for carboxylate-terminated SAMs.     

PVP-b-PMAA对CaCO3结晶形态的影响

可逆加成-断裂链转移;双亲水嵌段共聚物;碳酸钙;晶体生长;晶体形貌     

Effect of fatty and resin acids on properties of the surface of kraft lignin

The effect of oleic and abietic acids on the properties of the surface of alkali lignins and the capability of lignins to stabilize water-oil emulsions was examined with kraft spruce and birch lignins as examples. The kinetics of the breakdown of oleic acid-water and abietic acid-water emulsions stabilized by kraft lignins was studied.     

Analysis of precipitated lignin on kraft pulp fibers using atomic force microscopy

A method is presented which enables analysis of lignin precipitated on the surface of kraft pulp fibers. As experimental input, high-resolution atomic force microscopy phase images of the fiber surfaces have been recorded in tapping mode. A digital image analysis procedure—based on the watershed algorithm—is applied to distinguish between cellulose fibrils and the precipitated lignin. In this way, size distributions for the diameter of lignin precipitates on pulp fiber surfaces can be obtained. In an initial application of the method, three softwood kraft pulps were analyzed: a black liquor cook with a very high content of precipitated lignin, a bleached pulp where nearly no precipitated lignin is visible and an unbleached industrial pulp. The proposed method is suggested as an appropriate tool to investigate the kinetics of lignin precipitation and the structure of lignin precipitates in pulping and bleaching.     

Reactions of lignin in chlorine dioxide bleaching of kraft pulps

The reactions between chlorine dioxide and the residual lignin in oxygen-bleached softwood kraft pulps have been studied. In a first series, isolated lignin samples have been subjected to chlorine dioxide oxidation at different pH values and subsequently analysed by oxidative degradation and elemental analysis. Different analytical techniques have also been employed to follow the gradual chemical changes in lignins isolated from kraft pulps after each of the bleaching stages in the OD(EOP)DD sequence. The results demonstrate that, in order to minimize chlorination of the lignin, the first chlorine dioxide stage should be carried out at a pH around or above three. At this pH level, a high degree of lignin oxidation is also achieved. A certain (mono)-chlorination of the lignin in the first D stage cannot be avoided, but this chlorine is to a large extent removed in the later bleaching stages. The efficient and non-selective oxidation of the various phenolic lignin end groups by chlorine dioxide is clearly illustrated by the analytical data. Moreover,¹³C NMR reveals that reduced lignin structures formed during the kraft cook survive the oxidative bleaching stages to a large extent.     

Influence of demethylated lignin on the alkaline hydrolysis of cottonplant lignin

This paper gives information about the influence of demethylated lignin on the alkaline hydrolysis of the natural lignin of the cotton plant under various conditions. Institute of the Chemistry of Plant Substances, Academy of Sciences of the Republic of Uzbekistan, Tashkent, FAX (3712) 89-14-75. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 537–541, July–August, 1994.     

Influence of Surfactant-polymer Complexes on Crystallization and Aggregation of CaCO3

Hollow calcium carbonate(CaCO₃) microspheres with different morphologies were synthesized via the precipitation reaction of calcium chloride with sodium carbonate in the presence of different surfactant-polymer complexes. The selected anionic surfactants were sodium dodecyl sulfonate(SDS) and sodium dodecyl benzenesulfonate(SDBS), respectively. The selected water-soluble polymers were polyacrylic acid(PAA) and polyvinyl pyrrolidone(PVP). In this work, SDS-PVP “pearl-necklace model” micellar complex was formed via hydrophobic effectiveness between SDS and PVP and it served as the spherical template to generate spherical CaCO₃ aggregates with hollow microspheres composed of about 500 nm irregular shaped particles. SDS-PAA complexes and SDBS-PAA complexes formed “core-shell model” aggregates with calcium ions serving as the medium to link the anionic surfactant and the polymer. SDS-PAA “core-shell model” aggregates would act as templates for hollow CaCO₃ microspheres consisting of 30-50 nm irregular shaped crystallites. SDBS-PAA “core-shell model” aggregates served as the spherical aggregate templates to generate spherical CaCO₃ aggregates consisted of many small spherical particles which had grown together. All the obtained CaCO₃ hollow microspheres are calcite particles. This research may provide new insight into the control of morphologies of hollow CaCO₃ microspheres in the presence of surfactant- polymer complexes.     

Influence of demethylated lignin on the alkaline hydrolysis of cottonplant lignin

This paper gives information about the influence of demethylated lignin on the alkaline hydrolysis of the natural lignin of the cotton plant under various conditions.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Republic of Uzbekistan, Tashkent, FAX (3712) 89-14-75. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 537–541, July–August, 1994.