Petr Kadlec’s research while affiliated with Czech Academy of Sciences, Institute of Macromolecular Chemistry and other places

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Publications (14)


Collective polyelectrolyte diffusion as a function of counterion size and dielectric constant
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September 2013

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49 Reads

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10 Citations

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Jaroslav Kříž

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We report studies of the effect of counterions on the properties of solutions of a strong polyelectrolyte for a wide range of solvent dielectric constant. For this purpose we investigated the dynamic properties of polystyrene sulfonate in N-methylformamide whose dielectric constant changes significantly with temperature. By means of dynamic light scattering and NMR spectroscopy, polymers of different molecular weights and various counterions were investigated, including large phosphazene counterions P 1 , P 2 and P 4 measured for the first time. It was found that the order of counterion binding of ionomers in the solvent changed with an increase of dielectric constant. The order for low dielectric constant (high temperature) was Na < Rb < Cs < P 1 < P 2 < P 4 , whereas for a solvent with high dielectric constant no influence of counterion nature was observed. The solvation–desolvation effect together with electrostatic interactions are responsible for the observed phenomenon.


Figure 3. Structure factor S(q) experimentally obtained for a solution of the PS-PEP diblock copolymer with polymer concentration 5% (w/w) and solvent composition CX/12% DMF (filled symbols), and calculated structure factor (solid line) obtained by isotropically averaging scattering from a finite-size crystal with BCC structure and 6 scattering centers per principal axis. 
Figure 4. Two-dimensional structure factor S eff (q,φ) obtained by dividing the measured 2-dimensional SAXS diffractogram I(q,φ) with the calculated form factor F(q). The intensity scale is identical to that of Figure 3, i.e., linear and goes from 0 to 6. The full and dotted lines represent the reciprocal lattice for a twinned BCC structure with common < _ 111> axis parallel to the flow direction → V and the < _ 112> axis parallel to the neutral direction → e. The indexing is given for the grid marked by full lines and refers to lattice points to the left of the index. 
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Structure of self-organized diblock copolymer solutions in partially miscible solvents
  • Article
  • Full-text available

March 2010

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114 Reads

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2 Citations

Physical Chemistry Chemical Physics

A diblock copolymer dissolved in a mixture of partially miscible solvents creates a self-organized microemulsion with a morphology that depends on the numerous parameters of the system. We discuss one particular case of spherical particles (containing the minority solvent) forming a hard gel with cubic structure and demonstrate using high-resolution synchrotron scattering experiments that the self-organized solution has a BCC structure. After fitting one- and two-dimensional form factors we extract from the data the one- and two-dimensional structure factors, S(q) and S(q,phi). The experimental S(q) corresponds almost quantitatively, up to the 9th order Bragg peak, to that calculated numerically for a randomly-oriented, finite-size BCC crystal. S(q,phi) contains a large number of reflections that allow the structure to be identified more exactly as a twin BCC morphology with some imperfections. Examination of the dependence of the structural parameters on polymer concentration reveals that the dilution law predicted theoretically for the center-to-center distance of the spheres is confirmed experimentally while the size of the spherical objects does not follow theoretical predictions due to chain extension with increasing concentration.

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Effect of structure of HEMA–DEGMA hydrogel matrix on diffusion coefficients of PEG tracers. Variation of hydrogel crosslink density by change of polymer concentration

September 2009

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71 Reads

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13 Citations

Polymer

Dependence of diffusion coefficients of spin-labeled poly(ethylene glycol)s (PEGs, Mw = 1500, 3000, and 6000) determined by One-Dimensional Electron Spin Resonance Imaging (1D ESRI) on the properties of hydrogel matrices prepared by photopolymerization of 2-hydroxyethyl methacrylate (HEMA) and 2-(2′-hydroxyethoxy)ethyl methacrylate (DEGMA) was studied. The hydrogels were characterized by degree of crosslinking, νgel, by hydrodynamic correlation length, ξgel, and by self-diffusion coefficient of water, DH2O. The tracer diffusion coefficients were analyzed in the frame of scaling reptation and hydrodynamic models. Molecular weight dependence of the tracer diffusion coefficients follow expression D ∼ Mwx with exponent x = −1.2 ± 0.1 which excludes contribution of reptation to the diffusion. Steep decrease of the tracer diffusion coefficients with increasing polymer concentration was observed. Decrease of the tracer diffusion coefficients with increasing ratio of the hydrodynamic radius of the tracer to the hydrodynamic correlation length of the hydrogel matrix, RH/ξgel, was well fitted with predicted stretched exponential expression. Dependence of the tracer diffusion coefficients on the degree of crosslinking νgel suggested as a new scaling variable was found to closely follow empiric stretched exponential dependence in the whole νgel range studied.Graphical abstract


Hydration Modes of an Amphiphilic Molecule: NMR, FTIR, and Theoretical Study of the Interactions in the Water-Lutidine System

September 2009

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45 Reads

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10 Citations

The Journal of Physical Chemistry B

Using (1)H and (13)C NMR spectra and relaxations, PFG NMR diffusion measurements, FTIR spectra, and quantum-chemical structure predictions and optimizations on the MP2/6-31G(d) level, we have studied interactions between water (W) and lutidine (2,6-dimethylpyridine, L) in a wide range of ratios. At low W content up to 35%, W was found to bind to L by an O-H***N hydrogen bond and form transient L-W aggregates containing two to four L molecules in cooperation with two to three other W molecules. At higher W content, these aggregates are gradually cleaved to single L molecules enwrapped by a hydration shell anchored in an O-H***N hydrogen bond. At all compositions of the mixture, the various hydrate forms are in fast mutual exchange with a correlation time on the order of 1 x 10(-5) s.


Micelles of a Diblock Copolymer of Styrene and Ethylene Oxide in Mixtures of 2,6-Lutidine and Water

January 2009

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30 Reads

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5 Citations

Langmuir

We studied the micelle formation of a diblock copolymer of styrene and ethylene oxide in mixtures of 2,6-dimethylpyridine (2,6-lutidine) and water. Micelles are formed in a broad solvent composition range with a volume fraction of water ranging from 0.05 to 0.85, where neither polystyrene nor polyethylene oxide homopolymers are soluble. The diffusion behavior of pure solvent mixtures and in solutions of copolymer micelles is reported. In LTD/water mixtures, two diffusive processes corresponding to self-difusion and two modes belonging to mutual diffusion and diffusion of solvent clusters have been found. In copolymer solutions, the mode of copolymer micelle diffusion replaces the mode of solvent cluster diffusion. Quasielastic light scattering, small-angle neutron scattering, and pulsed-field gradient NMR have been employed in our study.


Complex Structure and Dynamics of Diblock Copolymers in a Mixture of Partially Miscible Solvents

February 2008

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9 Reads

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1 Citation

We have investigated the structure of self‐organized microemulsions made of two partially miscible solvents emulsified by a diblock copolymer. We have found that above the phase separation temperature Tc the solution is almost homogeneous while at temperatures below Tc the solution is microphase separated into a periodic lattice generally with body centered morphology. The lattice points are occupied by micelles that contain the minority solvent. Transmission electron microscopy shows that the micelles are first formed at random positions in the sample in the vicinity of Tc and on further cooling they self‐organize into the three‐dimensional network. The dynamical properties of this system were investigated by dynamic light scattering and pulsed‐field gradient NMR. Seven processes could be identified that correspond to (in order of increasing relaxation time) thermal diffusion, self‐diffusion of solvent molecules, cooperative diffusion, self‐diffusion of polymer chains, self‐diffusion of micelles, cluster diffusion and diffusion of grains.


A Dynamic Light Scattering Study of Fast Relaxations in Polymer Solutions

February 2007

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21 Reads

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27 Citations

Macromolecules

We have analyzed the fine structure of the distribution of relaxation times obtained from dynamic light scattering on solutions of homopolymers and diblock copolymers. We have shown that in a carefully designed experiment two additional fast modes can be identified in the distribution of relaxation times, besides the usual cooperative mode, heterogeneity mode, and cluster mode. We have shown that the faster of these two modes, well observable only at small angles, is due to the thermal diffusion coefficient of the solvent. For the slower of these two modes, several experimental findings lead to the conclusion that this mode is representative of the motion of the solvent molecules in the solution.


Three-Dimensional Analysis of Dynamic Light Scattering Data: Application to Self-Organized Polymer Solutions

January 2007

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10 Reads

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6 Citations

International Journal of Polymer Analysis and Characterization

Semi-dilute solutions of diblock copolymers in selective partially miscible solvent mixtures have been studied by dynamic light scattering and pulsed-field gradient NMR. Several dynamic modes have been identified as cooperative diffusion, polymer self-diffusion, and cluster diffusion. Their temperature dependences changed dramatically at a certain temperature, below which solutions underwent self-organization. Interpretation of the complex behavior of the dynamic processes observed has been made. The importance of a 3-D representation of the distributions of relaxation times is demonstrated.


SANS Study of Coated Block Copolymer Micelles

June 2005

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19 Reads

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2 Citations

Macromolecular Chemistry and Physics

Multishell particles were prepared by gamma-radiation-induced polymerization of methyl methacrylate (MMA) in polystyrene-block-poly(methacrylic acid) (PS-b-PMA) aqueous micellar solution and their structure was studied by small-angle neutron scattering (SANS). Before polymerization, almost all MMA molecules are distributed in aqueous phase and only 1% of MMA is accumulated inside the micelles. The newly formed polymer (PMMA) is deposited on the surface of PS cores of the original micelles. The effect of the MMA concentration, micelle concentration, absorbed radiation dose, and absorbed dose rate on the characteristics of the resulting particles was examined. The thickness of the PMMA shell (20-218 angstrom for the presented series of samples) can be easily controlled by variation of monomer and/or micelle concentration. Universal plots of the core volume (PS+PMMA) and SANS curve were presented. These plots facilitate choosing proper monomer and micelle concentrations and detecting possible irregularities in the parameters of the resulting particles.


1 H NMR and Small-Angle Neutron Scattering Investigation of the Structure and Solubilization Behavior of Three-Layer Nanoparticles

January 2005

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61 Reads

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6 Citations

Langmuir

Three-layer nanoparticles were prepared by radiation-induced polymerization of 1-10 g/L of methyl methacrylate dissolved in a 0.1 wt % D(2)O solution of polystyrene-poly(methacrylic acid) (PS-PMA) micelles. According to NMR and small-angle neutron scattering (SANS), most of the poly(methyl methacrylate) (PMMA) is adsorbed at the core-shell interface of the particles. A small fraction of shorter PMMA probably sticks to outer parts of the PMA chains. The absorption kinetics and equilibria of benzene and chloroform were studied by NMR and SANS time-resolved experiments. The diffusion front in the PS core is very narrow but quite broad in the PMMA sheet suggesting, thus, a less compact state of PMMA. According to SANS, the diffusion kinetics is almost independent of the PMMA sheet thickness. In contrast to it, the absorption capacity, reflected by both SANS and NMR, increases markedly with the PMMA content in the particle. The maximum amount of solubilized compound depends on its positive interaction with PMMA (expressed by the chi parameter) but is restricted by the growing interface tension between swollen PMMA and D(2)O. In accordance with this conclusion, a particle saturated with benzene can absorb chloroform only at the expense of a part of benzene expelled into the surrounding medium and vice versa. Starting with 10 g PMMA/L (10 times the weight of the original micelles), the particles become unstable when being swollen with a good solvent.


Citations (8)


... 87 Alternatively, dynamic light scattering is another tool to determine the presence of aggregates in solution. [93][94][95][96][97][98] Finally, HMAO starts be insoluble in water at high amount of hydrophobic units in the polymer structure. Solubility can also be tuned by temperature. ...

Reference:

Future and the past of polymeric antioxidants
Collective polyelectrolyte diffusion as a function of counterion size and dielectric constant
  • Citing Article
  • September 2013

... In the experiments performed using the ALV goniometer system, the experimental normalized time-correlation functions of the scattered intensity g (2) (t) À 1 (in the present case pseudocross correlated) were analyzed using two types of analysis: cumulant analysis (see below) and the constrained regularization REPES (Regularized Positive Exponential Sum) algorithm. [46][47][48][49] It performs an inverse Laplace transformation according to eqn (1): ...

Three-Dimensional Analysis of Dynamic Light Scattering Data: Application to Self-Organized Polymer Solutions
  • Citing Article
  • January 2007

International Journal of Polymer Analysis and Characterization

... Polysaccharide-based hydrogels have also applications as wound dressings or for the regeneration of various tissues such as bone, cartilage, and muscle (Das & Pal, 2015;Li & Mooney, 2016;Maire du Poset, Börjesson, et al., 2020;Matricardi, Di Meo, Coviello, Hennink, & Alhaique, 2013). They are made up of chemically or physically crosslinked networks of polymers, which can be characterized in various ways (degree of crosslinking, hydrodynamic correlation length, diffusion coefficient of water, etc.) (Pilař, Kříž, Meissner, Kadlec, & Přádný, 2009). A deep knowledge of the network structure of these hydrogels is necessary for the design and the control of their mechanical properties and functionalities such as their drug release profile, adsorption of undesirable molecules, swelling, etc. ...

Effect of structure of HEMA–DEGMA hydrogel matrix on diffusion coefficients of PEG tracers. Variation of hydrogel crosslink density by change of polymer concentration
  • Citing Article
  • September 2009

Polymer

... In this experiment wave vector q is defined as, q = (4пn/λ) sin (ϴ/2) where λ is the wavelength of laser light, n is the refractive index of the medium and ϴ is the scattering angle. During the experiment, a suitable equilibration time (~ 10 min) is given to equilibrate the solution at a temperature 25° C. Each correlation data for samples was taken for Many studies on dynamic light scattering on the various kinds of complex polymer solutions have revealed the appearance of two different relaxation modes [44,[48][49][50][51][52][53], where, the form of g 1 (t) is described in the form, Here, the autocorrelation data have been collected at different scattering angles, and the extracted data is fitted by standard double stretched exponential function as given below [44,45,53]: ...

A Dynamic Light Scattering Study of Fast Relaxations in Polymer Solutions
  • Citing Article
  • February 2007

Macromolecules

... [ 41 ] The reaction mixture was fi ltered and the solvent was removed at reduced pressure. The solid residue was dissolved in water, dialyzed (MWCO = 1000) and 29 OH] P2 : According to the procedure described above, 2-heptyl-2-oxazoline (409 μL, 10 eq.), 2-(pent4-ynyl)-2-oxazoline (332 μL, 10 eq.), methyl trifl ate (28 μL, 1 eq.), and 5 mL acetonitrile were mixed under inert conditions (argon). The reaction mixture was stirred at 110 °C for 4 h. ...

Characterization of Nanoparticles Based on Block Copolymer Micelles
  • Citing Article
  • September 2001

Langmuir

... 1. using a silane-based compatibilizer (triethoxysilane and aminosilane) 3,6,23-25 ; 2. copolymerizing dimethyl siloxane with diphenyl siloxane 16,18,19,26,27 ; 3. introducing reactive groups into polydimethylsiloxane (PDMS) chains to bond with ERs 17,22,28,29 ; hyperbranched polymers 30,31 ; and polyhedral oligomeric silsesquioxanes 32 ; 4. using peroxides. 33,34 Usually, these modifiers are used within a concentration interval 5-35 wt %. ...

Crosslinking of epoxy-polysiloxane system by reactive blending
  • Citing Article
  • July 2004

Polymer

... Particles were not yet fully described as such in Ref. [77], but taking into account the property S iso (q) ≈ 1 allowed to extract information about chain statistics in the "corona" of the solvent-swollen, self-assembled block copolymer building blocks of the 2D or 3D long-range-ordered structures investigated and to show later that chain statistics is not strongly affected by applying an electric field to the system [73]. It had thus taken half a decade to reach a nearly complete description of the whole scattering curve, with both intraparticle and interparticle structural contributions fully and quantitatively accounted for in terms of a body-centred structure of spheres (with some dispersity Ð) [78]. ...

Structure of self-organized diblock copolymer solutions in partially miscible solvents

Physical Chemistry Chemical Physics

... Applying DLS to block copolymer micelles, i.e. in the presence of a low molecular weight solvent, is presumably easier, generally speaking, but also rewarding in association with fluorescence correlation spectroscopy, in particular for accurately determining the (usually very low) critical micellar concentration (CMC) of such systems, as well as the hydrodynamic size of the emerging micelles close to the CMC, and P. Štěpánek contributed to such studies [44]. Besides, even if block copolymer micelles may appear as very "simple" objects, from a geometrical point of view, being therefore quite routinely characterised using DLS, their detailed structures may occasionally be difficult to describe in intuitive terms, as in the conspicuous case of a diblock copolymer of styrene and ethylene oxide forming micelles in mixtures of 2,6-dimethylpyridine and water over a broad solvent composition range, although neither polystyrene nor polyethylene oxide homopolymers are soluble in such mixtures [45]. Resorting to small-angle neutron or x-ray scattering techniques ("Small-angle neutron and x-ray scattering" section) as tools complementary to dynamic light scattering then cannot be avoided, as already illustrated in Ref. [45] or other relevant contributions by P. ŠTĚPÁNEK such as, for instance, Ref. [46][47][48][49][50][51]. ...

Micelles of a Diblock Copolymer of Styrene and Ethylene Oxide in Mixtures of 2,6-Lutidine and Water
  • Citing Article
  • January 2009

Langmuir