Wyniki wyszukiwania - BazTech

1

Controlling sol-gel transition rates in biocatalyzed silicate gels

Bailey S., Cicha-Szot R., Falkowicz S.

Prace Naukowe Instytutu Nafty i Gazu

|

2016

|

nr 209 wyd. konferencyjne

671--675

EN

Use of biocatalysts to internally activate the sol-gel transition of silicates was evaluated. Commercial sodium silicates and colloidal silicas were screened to determine effects of physicochemical parameters in the range of biocatalysts on gelant stability, gelation transition points and gel properties. Results established stable gelant formulations that were amenable to biocatalyst control of the gelling reaction. The alkalinity of the gelants required the biocatalysts to be extreme alkaliphiles with metabolic capabilities complementary to gel stabilization to drive the reaction. Ex situ measurements indicated that after initial exponential growth of 24 – 36-hours the biocatalysts maintained stable activity in stationary phase for up to 800 hours. Placing the gelling reactions under the control of alkaliphilic biocatalyst provided a direct internal mechanism with favorable reaction kinetics. The biocatalysts reliably triggered gelation of gelants with two to six days sol-gel transition time. Gelling tests indicated biocatalyzed gels are potentially suited to a broad range of applications as controllable internal activators of sodium silicate gels.

PL

W artykule opisano sposób inicjowania żelowania zolu krzemianowego w procesie biokatalizy. Przeprowadzono szereg testów mających na celu określenie czasów żelowania własności fizykochemicznych powstałych żeli, kinetyki żelowania i innych w procesie biokatalizy. W oparciu o wyniki badań opracowano formułę kontrolowanego prowadzenia procesu biokatalizy (żelowania) zoli krzemianowych. W pierwszej kolejności uzyskano efektywne szczepy bakterii zdolnych prowadzić procesy metaboliczne w warunkach wysokiego pH równego 12. Testy wykazały, że wyselekcjonowane szczepy mikroorganizmów po początkowej 24 – 36-godzinnej ekspotencjalnej fazie wzrostu przechodziły w fazę stacjonarną, która trwała ok. 800 godzin. Mikroorganizmy w sposób powtarzalny i wiarygodny inicjowały proces żelowania roztworów krzemianu, który w zależności o warunków początkowych trwał od dwu do sześciu dni. Ta unikatowa możliwość kontroli czasu żelowania w tak szerokim spektrum czasowym potencjalnie czyni proponowaną technologię bardzo przydatną w wielu dziedzinach techniki, gdzie zachodzi konieczność głębokich modyfikacji własności filtracyjnych warstw wodo- czy roponośnych.

2

Wpływ szybkości nagrzewania na proces żelowania hydrożeli chitozanowych

Ziółkowski P., Owczarz P., Dziubiński M.

Inżynieria i Aparatura Chemiczna

|

2016

|

Nr 4

164--165

PL

Wykonano pomiary zmian właściwości reologicznych w warunkach termostatowania próbki oraz pod wpływem wzrostu tempe-ratury (dla różnych szybkości nagrzewania) dla roztworów soli chitozanu z dodatkiem p-glicerofosforanu disodu. Stwierdzono, że temperatura punktu przemiany fazowej (charakterystyczna dla przemiany fizycznej) nie jest stała, lecz zależy od szybkości nagrzewania próbki, czyli od całkowitej ilości doprowadzonej energii.

EN

Measurements of rheological properties under isothermal conditions and effect of temperature increase of the chitosan salt solution with addition of sodium p-glycerophosphate were performed. It was found that temperature of phase transition is not constant (in contrast to physical gel) but depends on the heating rate of the sample, i.e. the total amount of supplied energy.

3

Simulation of Hardening Processes, in Silicate Systems

Kudryavtsev P. G., Figovsky O. L.

International Letters of Chemistry, Physics and Astronomy

|

2015

|

Vol. 44

1--49

EN

In this paper we consider the Quasi-homogeneous Approximation to Describe the Properties of Disperse Systems. We have used the statistical polymer method is based on the consideration of averaged structures of all possible macromolecules of the same weight. One has derived equations allowing evaluation of all additive parameters of macromolecules and their systems. The statistical polymer method allows modeling of branched crosslinked macromolecules and their systems in equilibrium or non-equilibrium. The fractal consideration of statistical polymer allows modeling of all kinds of random fractal and other objects studied by fractal theory. The statistical polymer method is applicable not only to polymers but also to composites, gels, associates in polar liquids and other aggregates. In this paper Description of the state of colloidal solutions of silicon oxide from the viewpoint of statistical physics is based on the idea lies in the fact that a colloidal solution of silica - silica sol consists of a very large number of interacting with each other particles that are in continuous motion. It is devoted to the study of an idealized system of colliding, but non-interacting particles of sol. Analysis was conducted of the behavior of silica sol, in terms of Maxwell-Boltzmann distribution and was calculated the mean free path of the colloidal particles. Based on these data, it was calculated the number of particles capable to overcome the potential barrier in a collision. To modeling of the sol-gel transition kinetics had considered various approaches.

4

Porównanie grubości warstw materiału uzyskanego podczas przejścia zol-żel (metodą dip-coating) na podłożach wyciąganych z wodnych roztworów spoiw koloidalnych

Wawrylak M., Leśniewski W., Szczepaniak-Lalewicz K.

Prace Instytutu Odlewnictwa

|

2014

|

T. 54, nr 4

43--50

PL

W artykule zaprezentowano metodę badania przejścia zol-żel, w której płytki odpowiedniego podłoża są wyciągane z wodnego spoiwa koloidalnego ze stałą prędkością. Grubość naniesionej warstwy jest związana z wielkością cząstek występujących w spoiwie. Przydatność technologiczna spoiw koloidalnych ograniczona agregacją cząstek jest trudna do oceny bez dostępu do specjalistycznych urządzeń pomiarowych. Opracowanie prostej metody umożliwiającej szybką ocenę parametrów użytkowych spoiwa koloidalnego może znaleźć zastosowanie w praktyce przemysłowej.

EN

This paper presents the method of investigating the sol-gel transition by constant speed removal of plates, made of suitable substrate, from an aqueous colloidal binder. The thickness of the deposited colloidal binder layer depends on the particle sizes in the binder. The processing feasibility of colloidal binders reduced by aggregation of particles is difficult to evaluate without access to special measuring equipment. Development of a simple method for prompt evaluation of performance parameters in colloidal binders may have industrial applications.

5

Thermogelling water solutions of multifunctional macromonomers based on PLGA-PEG-PLGA triblock copolymers

Michlovská L., Vojtová L., Mravcová L., Jančár J.

Challenges of Modern Technology

|

2011

|

Vol. 2, no. 1

12--15

EN

Biodegradable thermosensitive triblock copolymers based on poly(ethylene glycol) and poly[(lactic acid)-co-(glycolic acid)](PLGA-PEG-PLGA) with PLGA/PEG weight ratio in the range of 1.5–3.0 and LA/GA molar ratio equal to 2.4 or 3.0 were prepared via ring opening polymerization (ROP). Prepared copolymers were subsequently modified in “one pot” by itaconic anhydride (ITA) in order to functionalize both ends with carboxylic acid groups and reactive double bonds. Chemical structure was characterized by means of gel permeation chromatography and nuclear magnetic resonance. Aqueous solutions of both modified and unmodified copolymers are able to form free flowing sol at room temperature and clear gel at temperature around 37°C. Therefore, sol-gel transitions of PLGA-PEG-PLGA and ITA/PLGA-PEG-PLGA/ITA copolymers in aqueous solutions were investigated using test tube inverting method. No mater if copolymer is modified or not, it was found that the critical gel temperature (CGT) increased when the PLGA/PEG weight ratio dropped from 2.5 to 2.0 and that the critical gel concentration (CGC) grew up with decreasing molar ratio of LA/GA from 3.0 up to 2.4. However, in all cases the ITA functionalization improved sol-gel characteristics of original PLGA-PEG-PLGA copolymer by approaching gel phase to body temperature. As a result, aqueous solution of ITA/PLGA-PEG-PLGA/ITA having LA/GA = 3 and PLGA/PEG = 2 with concentration higher than 6 wt% might be suitable material for biomedical applications as injectable temporary implants.

6

Viscoelasticity of polydimethylsiloxane at the sol-gel threshold: structural effects

Gasparoux J., Tixier T., Tordjeman P.

International Journal of Applied Mechanics and Engineering

|

2005

|

Vol. 10, no spec

315-322

EN

Six model polydimethylsiloxane (PDMS) networks were obtained by hydrosilation of a difunctional vinyl-terminated PDMS prepolymer with a SiH containing crosslinker. Viscoelastic experiments were performed in order to study the influence of molecular parameters on the dynamic properties around the sol-gel threshold. Critical parameters were determined close to and above the sol-gel threshold. Our results show, in agreement with those of Lusignan et al. (1999), that the gel growth mechanism is function of the ratio N/Ne, where N and Ne are the numbers of Kuhn monomers between branch points and between entanglements, respectively. By considering the literature results, three universality classes are pointed out for polymer gelation: the sol-gel transition is governed by critical percolation for N/Ne < 1, by Diffusion Limited Cluster Aggregation for 1 < N/Ne < 2, and by mean field theory for N/Ne > 2.

7

EPR spectroscopic and rheological investigation during sol-gel transition in the systems TEOS/ethanol/water and sodium water-glass

Breyer T., Breitbarth F. W., Vogelsberger W.

Bulletin of the Polish Academy of Sciences. Chemistry

|

2000

|

Vol. 48, No. 4

325-336

EN

Paramagnetic ions (V4+ , Mn2+ ) are used to detect mobility changes during the sol-gel transition of sols from sodium water glass as well as from TEOS hydrolysis. The viscosity of these samples is measured in the rotational and oscillating mode to determine the steady state viscosity and the storage and loss moduli. The overall kinetic rate constant for the formation of siloxane bonds has been determined in dependence on pH of the reaction mixture. In spite of the rapid increase of the viscosity during the solgel transition by several orders of magnitude, EPR spectra of solvated VO2+ and Mn2+ probe ions do not show significant changes of the mobility. These ions move freely in the space between the agglomerating sol particles until the gels are dried. Paramagnetic V(IV) species derived from reduction of VO(iPr)3, however, are adsorbed on the growing sol particles. They, therefore, show a powder-like EPR spectrum of immobilized ions even in the region of very low sol viscosity well before the sol-gel transition.