Mobility Of Polymer Segments Research Articles

Effect of Zn Substitution on Electrical Properties of Nanocrystalline Cobalt Ferrite

Nanocrystalline cobalt ferrites substituted with Zn with formula, Co1−xZnxFe2O4 (x = 0.0-1.0) were pre- pared by the hydrothermal method. In this process, triethy- lene glycol was used both as a solvent and surfactant. The ac conductivity measurements of the samples showed a temperature-dependency at lower frequencies and indepen- dency at higher frequencies, which indicates the ionic con- ductivity. The ac conductivity depends on the temperature. This conductivity can be fitted with the well-known power law model in higher frequency. The dc conductivity is as- sumed to obey the Arrhenius equation. The dielectric be- havior in various temperatures ranges revealed frequency dependency in a reciprocal power law. The dissipation of en- ergy stored within the nanoparticle was found to act upon the reciprocal power law of the frequency dependency. Both the analysis of electrical conductivity and the dielectric permit- tivity functions suggest that the ionic and polymer segmental mobility could strongly be coupled in the nanoparticles.

Physical aging in polymers and polymer nanocomposites: recent results and open questions

Physical aging is a ubiquitous phenomenon in glassy materials and originates from the fact that they are generally out-of-equilibrium. Due to the technological and fundamental implications, this phenomenon has been deeply investigated in the last decades especially in glassy polymers. Here we provide a critical review of the latest hot debated themes in the field of physical aging in polymers and polymer nanocomposites. We first summarize the fundamental aspects of physical aging, highlighting its relationship with the polymer segmental mobility. A review of the methods employed to monitor physical aging is also provided, in particular those probing the time dependent evolution of thermodynamic variables (or related to) and those probing the (quasi)instantaneous polymer segmental mobility. We subsequently focus our attention on the two following debated topics in the field of physical aging of polymers: (i) the fate of the dynamics and thermodynamics of glassy polymers below the glass transition temperature (Tg), i.e. the temperature below which physical aging occurs; (ii) the modification of physical aging induced by the presence of inorganic nanofillers in polymer nanocomposites. With respect to the former point particular attention is devoted to recent findings concerning possible deviations from the behavior normally observed above Tg of both dynamics and thermodynamics deep in the glassy state. Regarding the effect of the presence of nanofillers on the rate of physical aging, the role of the modification of the polymer segmental mobility and that of purely geometric factors are discussed with particular emphasis on the most recent advances in the topic. The modification of the rate of physical aging in other nanostructured systems, such as polymer thin films, is discussed with particular emphasis on the analogy in terms of a large amount of interface with polymer nanocomposites.

Glass Transition and Relaxation Processes of Nanocomposite Polymer Electrolytes

This study focus on the effect of δ-Al(2)O(3) nanofillers on the dc-conductivity, glass transition, and dielectric relaxations in the polymer electrolyte (PEO)(4):LiClO(4). The results show that there are three dielectric relaxation processes, α, β, and γ, in the systems, although the structural α-relaxation is hidden in the strong conductivity contribution and could therefore not be directly observed. However, by comparing an enhanced dc-conductivity, by approximately 2 orders of magnitude with 4 wt % δ-Al(2)O(3) added, with a decrease in calorimetric glass transition temperature, we are able to conclude that the dc-conductivity is directly coupled to the hidden α-relaxation, even in the presence of nanofillers (at least in the case of δ-Al(2)O(3) nanofillers at concentrations up to 4 wt %). This filler induced speeding up of the segmental polymer dynamics, i.e., the α-relaxation, can be explained by the nonattractive nature of the polymer-filler interactions, which enhance the "free volume" and mobility of polymer segments in the vicinity of filler surfaces.

Competition of time and spatial scales in polymer glassy dynamics: Rejuvenation and confinement effects

We use molecular-dynamics (MD) simulations and an original lateral contact experiment to explore the influence of mechanical history on polymer mechanical behavior and segmental mobility. Two typical glassy polymers are considered: bulk acrylate (experiments) and atactic polystyrene (aPS) in a bulk and in thin films (simulations). Stress-strain behavior has been investigated both experimentally for sheared, 50 μm thick, acrylate films and by MD simulations of an aPS in a bulk for two different strain rates in a closed extension–recompression loops. Cyclic shear strains applied in the plastic regime were found experimentally to induce a progressive transition of the mechanical response of the polymer glass toward a steady state which is characterized by a strong reduction of the apparent – non linear – shear modulus. The dynamics of the polymer glass in this yielded state was subsequently analyzed from a measurement of the time dependent linear viscoelastic properties at various imposed frequencies. Immediately after the cyclic plastic deformation, mechanical “rejuvenation” of the polymer is evidenced by a drop in the storage modulus and an increase in the loss modulus, as compared to the initial values recorded before plastic deformation. A progressive recovery of the viscoelastic properties is also measured as a function of time as a result of the enhanced aging rate of the system. This experimentally observed mechanical rejuvenation of polymer has been for the first time connected to the drastic increase in the simulated segmental mobility. A simulated distribution of relaxation times shows a shift to shorter times of the α and β relaxation processes which is consistent with the observed experimental changes in the viscoelastic modulus after rejuvenation. Finally, we present our first findings on the thickness- and substrate-dependence of the simulated glass transition temperature for thin aPS films. We observe the decrease of the glass transition temperature with film thickness, but for extremely thin (less than 2 nm) films.

Synthesis and properties of cationic polyelectrolyte with regioregular polyalkylthiophene backbone and ionic‐liquid like side groups

AbstractHigh‐regioregular poly{3‐[6‐(1‐methylimidazolium‐3‐yl)hexyl]thiophene‐2,5‐diyl bromide}, PMHT‐Br, has been prepared by reaction of high‐regioregular (above 92%) poly[3‐(6‐bromohexyl)thiophene‐2,5‐diyl] with 1‐methylimidazole. PMHT‐Br is soluble in water and water miscible solvents such as methanol, DMSO and shows solvatochromism; λmax (nm): 423 (H2O); 435 (MeOH); 452 (DMSO). Increased absorption band broadening observed for aqueous solution as well as NMR spectra in D2O suggests a micelle‐like structure of PMHT‐Br molecules in these solutions: poly(3‐hexylthiophene) core and 1‐methylimidazolium bromide shell. Despite the disturbing effect of ionic groups, the solid‐state PMHT‐Br shows absorption maximum at 520 nm, the band edge at 660 nm (ca. 1.9 eV), and fluorescence emission with maximum at 635 nm, in a good agreement with the polymer regioregularity. Fluorescence emission maxima: λem (nm): 598 (H2O); 562 (MeOH); 574 (DMSO), occur in a vicinity of corresponding adsorption band edges. Plot of electrical conductivity of PMHT‐Br (measured under the dynamic vacuum conditions, 5 × 10−5 Pa) versus 1/T shows a break at about 70 °C same as the temperature dependence of λmax of the solid PMHT‐Br. These breaks indicate an increase in the mobility of polymer segments and ions within PMHT‐Br; however, a thermal analysis did not provide solid evidence for it. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3073–3081, 2010

1H NMR study of temperature-induced phase separation in solutions of poly(N-isopropylmethacrylamide-co-acrylamide) copolymers

1H NMR spectroscopy was applied to investigate temperature-induced phase separation in solutions of poly(N-isopropylmethacrylamide-co-acrylamide) [P(IPMAm/AAm)] random copolymers in D2O, D2O/ethanol and D2O/acetone. The NMR relaxation behaviour of water (HDO) was also examined. The effects of P(IPMAm/AAm) composition and the ethanol or acetone content in the mixed solvents on the temperature, width and extent of the phase transition as well as on the mobility of polymer segments and water molecules were characterized. For D2O solutions of the copolymers prepared with the AAm fraction in the polymerization mixture not exceeding 25 mol% 1H NMR spectra show dynamic heterogeneity of copolymer chains in mesoglobules where AAm sequences and surrounding short IPMAm sequences are hydrated and mobile, while sufficiently long IPMAm sequences are dehydrated and their mobility is strongly reduced. The obtained results are consistent with the idea that P(IPMAm/AAm) copolymer mesoglobules are rather porous and disordered.

Polyamide/layered silicate nanocomposites: A correlation between fracture toughness and molecular mobility

AbstractThis study correlates toughness of polyamide nanocomposites with the molecular mobility of polymer segments in the amorphous phase. Two nanocomposite systems prepared by melt-compounding of polyamide-6 with sodium montmorillonite or organophilized montmorillonite were compared. They differed in the extent of silicate dispersion. While sodium montmorillonite formed intercalated nanocomposites, the organophilization promoted full exfoliation of the silicate layers in the matrix. The different morphology was imprinted in fracture behaviour, toughness of exfoliated nanocomposites was markedly lower that that of their intercalated counterparts. To explain this difference, a solid-state NMR was used as a selective tool for providing information about nanocomposites structure and, primarily, about dynamics of polymer segments. Comparison of NMR spinrelaxation behavior with fracture mechanics experiments revealed a close correlation between fracture toughness and the intensity of rapidly relaxing component of the amorphous phase.

Origin of Dynamical Properties in PMMA−C60Nanocomposites

Poly(methyl methacrylate) (PMMA)−C60 nanocomposites, with compositions in the range 0 ≤ φC60wt ≤ 0.05, are shown to exhibit systematic increases in dynamic shear moduli, in glass transition temperature (Tg), and in the longest relaxation time of the polymer (τR) with increasing fullerene concentration. We show that while the φC60wt dependence of the plateau modulus can be reconciled with a conventional “filler” effect, the systematic increases in Tg and in τR are associated with specific interactions between the C60 and the polymer segments. In the melt, these segment−C60 interactions are proposed to reduce polymer segmental mobility in the vicinity of the particle surface and ultimately suppress polymer dynamics, as measured mechanically, in a manner consistent with an increase in the polymer segmental friction coefficient.

Effect of Confinement on Polymer Segmental Motion and Ion Mobility in PEO/Layered Silicate Nanocomposites

ADVERTISEMENT RETURN TO ISSUEPREVCommunication to the...Communication to the EditorNEXTEffect of Confinement on Polymer Segmental Motion and Ion Mobility in PEO/Layered Silicate NanocompositesM. M. Elmahdy, K. Chrissopoulou, A. Afratis, G. Floudas, and S. H. AnastasiadisView Author Information Department of Physics, University of Ioannina, 451 10 Ioannina, Greece; Biomedical Research Institute, Foundation for Research and Technology-Hellas, P.O. Box 1186, 451 10 Ioannina, Greece; Institute of Electronic Structure and Laser, Foundation for Research and Technology-Hellas, P.O. Box 1527, 711 10 Heraklion Crete, Greece; Department of Physics, University of Crete, 710 03 Heraklion Crete, Greece; and Department of Chemical Engineering, Aristotle University of Thessaloniki, 541 24 Thessaloniki, Greece Cite this: Macromolecules 2006, 39, 16, 5170–5173Publication Date (Web):July 6, 2006Publication History Received13 April 2006Revised21 June 2006Published online6 July 2006Published inissue 1 August 2006https://doi.org/10.1021/ma0608368Copyright © 2006 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views1498Altmetric-Citations152LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit Read OnlinePDF (104 KB) Get e-AlertsSUBJECTS:Insulators,Layers,Nanocomposites,Polymers,Quantum confinement Get e-Alerts

Gamma radiation induced effects on silica and on silica–polymer interfacial interactions in filled polysiloxane rubber

We report in our studies to assess the impact of gamma radiation on silica and on the silica–polymer interface in filled polysiloxane rubber. Electron spin resonance (ESR) and solid-state nuclear magnetic resonance (NMR) studies have been performed on samples exposed to gamma radiation. In an effort to probe directly the effect of gamma radiation on the silica surface, we employed 1H and 29Si NMR. Our ESR studies show trapped paramagnetic species (positive holes and/or trapped electrons) within the host silica matrix for all samples exposed to gamma radiation. A sample of pure cab-o-sil irradiated to a dose of 50 kGy also shows an ESR signal. Our studies on real-time aged samples (derived from field trials) also show ESR signatures indicative of silica based trapped paramagnetic species. The growth of trapped paramagnetic species as a function of gamma dose was investigated. This shows that the build up of trapped species occurs rapidly at low gamma dose before reaching saturation at about 20–30 kGy. Radiation induced band gap excitation is the likely process leading to the creation of these paramagnetic species which may be trapped in regions of local charge deficit within the silica matrix. Species that are not trapped may take part in silica surface reactions leading to changes in filler–polymer interfacial interactions. NMR studies combined with ammonia modified swell studies have shown increased polymer segmental chain mobility (softening) at low gamma dose indicative of a possible reduction in filler–polymer interfacial interactions. For those samples exposed to high gamma dose, our ammonia modified swell studies suggest increased polymer–filler interactions presumably through silica–polymer crosslinking effects. Our 1H and 29Si NMR studies on irradiated silica suggest that the silica surface is sensitive to gamma radiation. Our observations are important as they highlight the need to better control the quality (size, purity, etc.) of the silica constituent in filled polymer components used in gamma radiation environments.

Intrinsically Proton-Conducting Benzimidazole Units Tethered to Polysiloxanes

Polysiloxanes with pendant benzimidazole units have been prepared by free radical thiol−ene coupling reactions of 2-(2-benzimidazolyl)ethanethiol and vinyl-functional polysiloxanes. The latter polymers were prepared by anionic ring opening copolymerization of 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclosiloxane and 1,3,5-hexamethylcyclosiloxane. Copolymers with different degrees of benzimidazole functionality were conveniently obtained by varying the monomer ratios. The coupling reaction was found to be very efficient, and the vinyl groups were completely consumed, as confirmed by NMR and FTIR spectroscopy. The glass transition temperature (Tg) of the benzimidazole functional copolymers increased dramatically with the benzimidazole content at low contents to reach a plateau value just above 50 °C at a content of approximately 33 mol % benzimidazole functional siloxane residues in the copolymer. Conductivity measurements carried out at 60 and 140 °C indicated that the level of polymer segmental mobility, an...

Ionic conductivity of composite electrolytes based on oligo(ethylene oxide) and fumed oxides

The effects of fumed oxide fillers (SiO 2, Al 2O 3, TiO 2) and binary mixtures of oxide fillers (SiO 2/Al 2O 3) on ionic conductivity of composite electrolytes based on poly(ethylene oxide) (PEO) oligomers ( M w=250, 500, 1000, and 2000)+lithium bis(trifluromethylsulfonyl)imide [LiN(CF 3SO 2) 2] (LiTFSI) (Li/O=1:20) are studied using electrochemical impedance spectroscopy (EIS), differential scanning calorimeter (DSC), and Fourier transform infrared spectroscopy in the attenuated total reflectance mode (FTIR-ATR). Fillers show similar effect on conductivity in all systems: no distinguishable effect is found with filler type, and addition of filler decreases conductivity at temperatures above the melting point but increases conductivity at temperatures below. The addition of fillers stiffens polymer segments, as evidenced by enhancement in Li +–polymer interactions above the melting point seen in the IR spectra and an increase in T g found from the DSC analysis. No reduction in ion-pairing upon addition of filler is observed from the IR spectra. The increase in conductivity at temperatures below the melting point is believed to be due to faster ion transport along the filler surface rather than through enhanced mobility of polymer segments. The insulating nature of fillers and stiffening of the polymer solvent in the presence of fillers cause a decrease in conductivity at temperatures above the melting point and is correlated solely with volume fraction of the filler.

Polymer gel electrolytes based on thermoplastic polyurethane

AbstractSeries of gel electrolytes based on thermoplastic polyurethane (PU) with different organic additives were prepared and studied. Structural characterization was carried out by differential scanning calorimetry (DSC), dynamic mechanical analyzer (DMA), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The results showed that propylene carbonate (PC), N,N‐dimethylformamide (DMF), polyethyleneglycol 400 (PEG400), and glycerol played roles of plasticizers and were miscible with soft‐segment in PU matrix, which led to increase of the polymer segmental mobility, which in turn led to decrease of glass transition temperature (Tg), while, diethyl carbonate (DEC) and diethylene glycol dimethyl ether (DGDE) showed no effectiveness of plasticizers. Ionic conductive properties of the electrolytes, examined by complex impedance analyzer, showed that ionic conductivities of the samples increased with the increase of organic additive content, and the sample with PEG400 as organic additive showed an ionic conductivity of 1.8 × 10−5 S cm−1 at room temperature. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2310–2315, 2003

Electrochemical and solid state NMR characterization of composite PEO-based polymer electrolytes

A comprehensive matrix of composite poly(ethyleneoxide) (PEO)-based solid-state electrolytes was developed in order to systematically study a number of variables and their impact upon the electrochemical properties of the resulting materials. The different parameters studied in the fabrication of these materials include: (i) the lithium electrolyte salt type, (ii) the ether oxygen to lithium ratio, (iii) the molecular weight of PEO, (iv) the type of ceramic additive used, either aluminum oxide (Al 2O 3), silicon oxide (SiO 2), or titanium oxide (TiO 2), (v) the particle size of the additives used, and (vi) the concentration of additive (wt.%). The standard lithium salt used for the preparation of these electrolytes was lithium trifluoromethanesulfonate (lithium triflate or LiSO 3CF 3), which served as the baseline electrolyte salt. Other lithium salts investigated include: lithium perchlorate (LiClO 4) and lithium bis-trifluoromethanesulfonimide (LiN(SO 2CF 3) 2). Conductivity measurements were performed for each electrolyte membrane over a wide temperature range (23–100 °C). In addition, cyclic voltammetry measurements were performed on selected PEO membranes as a function of temperature to determine the impact of various parameters upon the electrochemical stability. It was observed that the parameter that displayed the most significant effect upon the PEO-base polymer conductivity was the lithium salt type employed. The lithium triflate salt-containing PEO polymers demonstrated the best mechanical properties before and after heat treatment. Ceramic fillers also appear to enhance the mechanical properties of PEO polymer electrolytes at temperatures above the melting point of PEO (60–70 °C). In addition to investigating the electrochemical characteristics of the composite membrane, solid state 7Li NMR characterization was performed to study ionic mobility by measuring spectral line widths and lithium self-diffusion coefficients. It was determined that ceramic nanoparticle additives can enhance the Li + diffusivity without a corresponding increase in polymer segmental mobility.

Prediction and estimation of solvent diffusivities in polyacrylate and polymethacrylates

AbstractThe relationship between polymer side‐chain length and the hole free volume that is effective for solvent diffusion was investigated for polyacrylates and polymethacrylates on the basis of free‐volume theory. Measurements of a polymer's viscoelasticity and solvent diffusivity provided experimental evidence for polymer segment mobility, and the results indicated that hole free volume in a linear polymer increases with hydrocarbon side‐chain length. Because the molecular mechanisms of polymer viscoelasticity and diffusivity are identical, the free‐volume parameters obtained for polyacrylates and polymethacrylates by measuring the polymer viscoelastic‐temperature dependence can reliably be used in predicting the solvent diffusion coefficient. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1393–1400, 2003

Catalyst for solid polymer electrolyte fuel cells

Nuclear magnetic resonance spectroscopy (n.m.r.), dynamic mechanical thermal analysis (d.m.t.a.) and AC impedance techniques have been used in combination to probe the effect of electrolyte composition in an archetypal solid polymer electrolyte (SPE). A series of solid polymer electrolytes (SPEs) based on a urethane-crosslinked trifunctional poly(ethylene glycol) polymer host containing dissolved ionic species (LiClO4 and LiCF3SO3) have been studied. D.m.t.a. has established that increasing LiClO4 concentration causes a decrease in the polymer segmental mobility, owing to the formation of transient crosslinks via cation–polymer interaction. Investigation of the distribution of mechanical/structural relaxation times for the LiClO4/polymer complex with d.m.t.a. reveals that increasing LiClO4 concentration causes a slight broadening of the distribution, indicating a more heterogeneous environment. Results of n.m.r. 7Li T1 and T2 relaxation experiments support the idea that higher salt concentrations encourage ionic aggregation. This is of critical importance in determining the conductivity of the material since it affects the number of charge carriers available. Introduction of the plasticiser tetraglyme into the LiClO4-based SPEs suppresses the glass transition temperature of the SPE, and causes a significant broadening of the relaxation time distribution (as measured by d.m.t.a.).

Nuclear magnetic resonance studies ofnanocomposite polymer electrolytes

The origin of the ionic conductivity enhancement in polymerelectrolytes that occurs on adding inorganic oxide powders wasexplored by 1H and 7Li nuclear magnetic resonance. Ionicand molecular self-diffusion coefficients determined by pulsed fieldgradient spin-echo measurements demonstrate that lithium ionicdiffusivity is enhanced in the composites, but this enhancement isnot attributed to polymer segmental mobility. Two different systemswere investigated: a high-molecular-mass poly(ethyleneoxide)-LiClO4 complex with nanoscale TiO2; and alow-molecular-mass poly(ethylene glycol)-LiClO4 solution withAl2O3. In the latter case the effect of varying thealumina surface acidity or basicity was considered.

Time-Resolved Emission Anisotropy of Anthracene Fluorophore in the Backbone of Stereoregular Poly(methyl methacrylate)

Syndiotactic fluorescent poly(methyl methacrylate) labeled with anthracene in the middle of the polymer chain was prepared by living anionic polymerization (s-PMMA-A). Absorption and emission transition moments of the label are oriented in the direction of the polymer backbone, therefore the fluorophore really reflects the mobility of polymer segments. Stereocomplex formation between isotactic poly(methyl methacrylate) (i-PMMA) and s-PMMA-A was studied by time-resolved fluorescence depolarization method in solvents with different complexing ability and at different i-PMMA/s-PMMA-A ratios. The stoichiometry of the stereocomplex i-PMMA/s-PMMA-A was 1/2 and 1/1.5 in N,N-dimehtylformamide and 1,4 dioxane, respectively. The stereocomplex was not formed in chloroform. Determination of the rotational correlation times at different temperatures enabled us to evaluate the height of the potential barrier to rotational motion of the anthracene fluorophore (ΔU r ) or activation enthalpy and entropy (ΔH ¬= , ΔS ¬= ) of this process in the presence and absence of the stereocomplex. Time-resolved emission anisotropy data, r(t), were analyzed by intermediate zone formula of the torsion dynamics theory for stiff macromolecules. The torsional rigidity of the stereocomplex i-PMMA/s-PMMA-A, a = 1.9 w 10 -18 N.m in N,N-dimethylformamide at 30°C, is larger than that obtained for DNA (a = 3.8 x 10 -19 N.m). Self-aggregation of s-PMMA takes place probably in N,N-dimethylformamide.

Molecular dynamics and mechanical properties correlations of PA6/PPO blends compatibilized with SMA

The effects of the compatibilizer, styrene maleic anhydride (SMA-8% MA) upon the change of morphology and molecular dynamics of polyamide-6 (PA6) and poly (2,6-dimethyl-1,4-phenylene oxide) (PPO) blends were investigated by means of solid-state NMR techniques. With increasing amounts of SMA, the domains correspond to PA6 and PPO are reduced and the polymer segmental mobility increased. The correlation between NMR relaxation time, T, and the bulk mechanical properties provide a molecular level understanding of the modification of molecular dynamics by the compatibilizer (SMA). The correlation shows that the tensile strength is governed mainly by the morphology, but modulated by the PA6 crystallinity, while the tensile elongation and impact strength are closely affected by both the molecular mobility and morphology. The annealing process improved only the tensile strength, but deteriorated tensile elongation and impact strength due to the increase of PA6 crystallinity, which induced phase separation after annealing. This study raised an important point that the polymer mechanical properties are most sensitive to the molecular structure and dynamics take place within the range of 20 Å to few hundred Å. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1155–1163, 1999

EPR spin probe and spin label studies of some low molecular and polymer micelles

The rotational mobility of spin probes of different shape and size in low molecular and polymer micelles has been studied. Several probes having nitroxide fragment localized either in the vicinity of micelle interface or in the hydrocarbon core have been used. Upon increasing the number of carbon atoms in hydrocarbon chain of detergent from 7 to 13 (sodium alkyl sulfate micelles) or from 12 to 16 (alkyltrimethylammonium bromide micelles) the rotational mobility of spin probes is decreased by the factor 1.5–2.0. The spin probe rotational mobility in polymer micelles (the complexes of alkyltrimethylammonium bromides and polymethacrylic or polyacrylic acids) is less than mobility in free micelles of the same surfactants. The study of EPR-spectra of spin labeled polymethacrylic acid (PMA) indicated that formation of water soluble complexes of polymer and alkyltrimethylammonium bromides in alkaline solutions (pH 9) does not affect the polymer segmental mobility. On the other hand, the polymer complexes formation in slightly acidic water solution (pH 6) breaks down the compact PMA conformation, thus increasing the polymer segmental mobility. Possible structures of polymer micelles are discussed.