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The translational motion of polymers is a complex process and has a big impact on polymer structure and chemical reactivity. The process can be described by the segment velocity autocorrelation function or its diffusion spectrum, which exhibit several characteristic features depending on the observational time scale&mdash, from the Brownian delta function on a large time scale, to complex details in a very short range. Several stepwise, more-complex models of translational dynamics thus exist&mdash, from the Rouse regime over reptation motion to a combination of reptation and tube-Rouse motion. Accordingly, different methods of measurement are applicable, from neutron scattering for very short times to optical methods for very long times. In the intermediate regime, nuclear magnetic resonance (NMR) is applicable&mdash, for microseconds, relaxometry, and for milliseconds, diffusometry. We used a variation of the established diffusometric method of pulsed gradient spin-echo NMR to measure the diffusion spectrum of a linear polyethylene melt by varying the gradient pulse width. We were able to determine the characteristic relaxation time of the first mode of the tube-Rouse motion. This result is a deviation from a Rouse model of polymer chain displacement at the crossover from a square-root to linear time dependence, indicating a new long-term diffusion regime in which the dynamics of the tube are also described by the Rouse model.

1H NMR spin–lattice (T1) and spin–spin (T2) relaxation times have been measured for the residual CHCl3 component of deuterochloroform (99.8 atom% D) in neat solvent samples and in a series of isotropic solutions of the ionic surfactant n-octylammonium-n-octadecanoate and also in degassed/dried and aerated solvent systems at 298 K. Analysis of the proton relaxation times as composite values from various relaxation mechanisms suggests that the spin–lattice process is predominantly via spin–rotation while spin–spin relaxation principally involves 1H–Cl scalar coupling. Rotational correlation times from relaxation rates via the dipolar and spin–rotation mechanisms reveal similar fast picosecond molecular rotation of chloroform in the different samples. The presence of surfactant in the solution appreciably affects the 1H NMR spin–lattice relaxation time of CHCl3 and the chemical shift, which is concentration dependent owing to weak intermolecular interactions. Effects of sample condition and solvent degassing, drying, and aeration treatments on the NMR relaxation times and line shape properties of the residual CHCl3 isotopomers are also examined.

We study the impact of anisotropic nanoparticles (NPs) on the nematic liquid crystal (LC) order. Within a mesoscopic Flory–Huggins-type approach we have estimated regimes where LC–NP mixtures are essentially homogenous. Using a lattice Lebwohl–Lasher type approach we have also studied the impact of anisotropic NPs on LC ordering. We analysed the cases where the orientations of NPs are either frozen-in or could be varied, to which we refer as random field mixtures and annealed mixtures, respectively. In the latter case we have demonstrated the existence of qualitatively different regimes. In particular, we determined the concentration regime, where LC configurations resembling a transparent nematic phase could be observed. Such domain patterns are stabilised by NPs hindering the annihilation of topological defects in LC order.

1H NMR chemical shift, line width, indirect nuclear splitting value, peak area integration value, and spin–lattice and spin–spin relaxation times at 298 K are compared for low-concentration isotropic solutions of n-octylammonium n-octadecanoate prepared via different techniques and conditions using dried, distilled, and degassed deuterochloroform and the nontreated solvent containing tetramethylsilane. The nature of the variation of observed spectral parameters and relaxation/rotational behavior with chemical composition (presence of oxygen and other paramagnetic species, stabilizer, impurities, and degradation products) of the solvent, history of the solution, and sample containment are analyzed. Relaxation times are interpreted in terms of monomer structure and reorientation and internal rotation modes as a function of atomic position along the n-alkyl chains. Collectively, the relaxation behavior of the surfactant complies with the two-step model of fast picosecond internal rotations of different size segments containing methylene groups separated in timescale from slower large segment and overall molecular tumbling modes of the monomer. Fast motional phenomena do not appear to be appreciably influenced by the chemistry of the solvent in contrast to spectral parameters such as chemical shift and line width of the labile ammonium protons. A model is also presented to explain anomalous variation of the peak area integration value with chemical shift of the ammonium resonance peak.

Pulsed gradient spin echo is a method of measuring molecular translation. Changing Δ makes it sensitive to diffusion spectrum. Spin translation effects the buildup of phase structure during the application of gradient pulses as well. The time scale of the self-diffusion measurement shortens if this is taken into account. The method of diffusion spectrometry with variable δ is also less sensitive to artifacts caused by spin relaxation and internal gradient fields. Here the method is demonstrated in the case of diffusion spectrometry of molten polyethylene. The results confirm a model of constraint release in a system of entangled polymer chains as a sort of tube Rouse motion.

NMR modulated gradient spin echo method, which allows the quantification of polymer segmental displacement via the measurement of the velocity autocorrelation, requires the formulation of theoretical predictions in the frequency domain in order to test their validity. We worked out the velocity autocorrelation spectrum of the segmental motion according to the Rouse and the tube/reptation model to compare it to the experimental results obtained by the new NMR technique. The analysis of polybutadiene shows the segmental velocity autocorrelation spectrum typical for the reptation-like motion of polymer in a “tube”. The measurement of bulk water indicates a kind of Rouse motion in a network of hydrogen bonds.

We have studied the ferroelectric SmC* phase of SCE9 ferroelectric liquid crystal (LC) mixtures with magnetic nanoparticles (NPs). The impact of the NPs on the Goldstone and soft mode dielectric response has been determined by the dielectric spectroscopy measurements. The possible indirect coupling between the magnetic moments and the electrical polarization has been verified by measuring the impact of the electrical field on the magnetic susceptibility via SQUID susceptometer measurements. The disordering effects on the ferroelectric phase transition have been studied by the high resolution calorimetry. Similar disordering effects have been found as in the case of the aerosil particles [1, 2].

We have employed high-resolution calorimetric techniques in order to investigate the unresolved issue of the existence of a nematic phase for the liquid crystal dodecylcyanobiphenyl. Various heating and cooling runs were performed on dodecylcyanobiphenyl samples of different origin and their analysis did not reveal any signature of a nematic phase. The calorimetric results are presented in detail and they are additionally supported by optical polarising microscopy observations.

Many pharmaceutical tablets are based on hydrophilic polymers, which, after exposure to water, form a gel layer around the tablet that limits the dissolution and diffusion of the drug and provides a mechanism for controlled drug release. Our aim was to determine the thickness of the swollen gel layer of matrix tablets and to develop a method for calculating the polymer concentration profile across the gel layer. MR imaging has been used to investigate the in situ swelling behaviour of cellulose ether matrix tablets and NMR spectroscopy experiments were performed on homogeneous hydrogels with known polymer concentration. The MRI results show that the thickest gel layer was observed for hydroxyethylcellulose tablets, followed by definitely thinner but almost equal gel layer for hydroxypropylcellulose and hydroxypropylmethylcellulose of both molecular weights. The water proton NMR relaxation parameters were combined with the MRI data to obtain a quantitative description of the swelling process on the basis of the concentrations and mobilities of water and polymer as functions of time and distance. The different concentration profiles observed after the same swelling time are the consequence of the different polymer characteristics. The procedure developed here could be used as a general method for calculating polymer concentration profiles on other similar polymeric systems.

We study the phase behavior of octylcyanobiphenyl (8CB) liquid crystal confined to control porous glass (CPG) using high-resolution calorimetry. We used silanized and nonsilanized CPG matrices with characteristic void diameters ranging from 400 to 20 nm. With decreasing diameter the first-order isotropic to nematic (I–N) and second-order nematic to smectic A (N–SmA) phase transition temperatures monotonously decrease. The weakly first-order features of the I–N transition approaches the smeared tricritical behavior. The effective N–SmA critical exponent apparently decreases toward the 3D XY value for diameters above 100 nm, however, the N–SmA transition progressively broadens and becomes strongly suppressed for diameters below 100 nm. A simple phenomenological model is used for a qualitative explanation of results.

We present results of the deuteron nuclear magnetic resonance (NMR) and small-angle X-ray scattering (SAXS) study of ordering and phase transition behavior of octylcyanobiphenyl (8CB) liquid crystal confined to a controlled-pore glass (CPG) with nontreated and silanes-treated pore surfaces. The deuteron NMR spectra allowed to determine the degree of nematic liquid crystal ordering and also provided an indirect information on the confined 8CB smectic ordering via its influence on the nematic ordering. For the smectic phase these data are supplemented with measurements of the temperature dependence of the first-order SAXS diffraction pattern. The NMR results indicate that the average nematic and smectic order parameters of 8CB in the nontreated CPG are only weakly perturbed by the confinement. The SAXS data further suggest that in confined 8CB for both nontreated and silane-treated CPG a domainlike pattern appears in accordance with the Imry-Ma theorem.

Using proton NMR relaxometry in the kilohertz frequency range, we study dynamics of 5CB liquid crystal molecules dispersed in the form of spherical microdroplets in a PDLC material. The focus of the study is the spin-lattice relaxation in the rotating frame, T 1ρ −1 , measured above the nematic-isotropic transition T NI . We show that the relaxation rate T 1ρ −1 - when induced by uniform molecular translational diffusion in a spherical cavity - depends on the strength of the rotating magnetic field as T 1ρ −1 ∝ ω 1 −α where α varies between 0.7 and 1, depending on the thickness of the ordered surface layer. This relaxation mechanism governs mainly the transverse spin relaxation, whereas the measurements of the frequency and temperature dependence of T 1ρ −1 indicate a strong effect of slowing-down of molecular translational diffusion in contact with the polymer surface and yield the average dwell-time of molecules at the surface of the order 10 −5 s.

Proton spin–lattice relaxation, compressive strength, and water tightness measurements have been undertaken in order to study the hydration process and the mechanical properties of Portland cement modified with a calcium sulfoaluminate-based expansive additive (EXPAD). The compression strength of the modified cement was more than 70% higher while water permeability was about 60% smaller than in the unmodified cement. Magnetization–recovery curves analysis allowed for a time-resolved monitoring of both the increase of the internal surface as well as the formation of solid products during the hydration. A significant difference between the hydration kinetics of modified and unmodified cement was observed.

The inhibitory effect of a series of neutral lipophilic solutes (methanol, ethanol, n -propanol, iso -propanol, n -butanol, iso -amylalcohol, n -hexanol, diethylether, nitrobenzene, and pyridine) on the diffusional water permeability ( P d, tot ) of bovine erythrocyte membrane at 25°C was studied in comparison to that of p -chloromercuri benzoate (pCMB). Permeability data were obtained by measuring the transmembrane diffusional water exchange time τ exch using an 1 H- T 2 NMR technique. Maximal inhibition by ∼50% of P d, tot was produced by 2 mM pCMB which completely blocked the membrane water channels in 20 min, hence suggesting the channel-to-lipid diffusional water permeability ratio of about 1:1. Furthermore, the maximal inhibitory effect of pCMB in combination with the lipophilic solutes was lower than that of pCMB alone. As pCMB does not interfere with the lipid bilayer, and provided that it blocks the water channels in solute presence as well, this confirms that the solutes induce an increase in the lipid-mediated background water permeability contribution ( P d, lipid ) by the formation of aqueous leaks in the membrane hydrophobic barrier. However, faster but less efficient in permeability inhibition than pCMB (either alone or combined with solutes) were the lipophilic solutes alone. Taken together, the results indicate that the lipophilic solutes suppress the membrane total permeability P d, tot by two opposing effects: a reduction of its channel-mediated part ( P d, channel ) to the extent exceeding that of a simultaneous P d, lipid increase. The inhibitory potency of the solutes tested appears to be correlated with their solubility in the membrane medium.

We performed an x-ray scattering study of the smectic A (SmA) ordering of the liquid crystal 8CB (octylcyanobiphenyl) confined to a control porous glass with a typical void radius R = 0.2 µm. The voids were either nontreated or covered with silane. The results reveal a strong influence of spatial restriction and surface treatment on the temperature evolution of smectic ordering. The observations are qualitatively reproduced using the Landau-Ginsburg approach.

Frequency-dependent lactose uptake via the H+/lactose symporter in an externally applied low-intensity alternating electric field was demonstrated, using tracer flux experiments. The uptake of radiolabeled lactose was significantly inhibited with the electric field-strength of 30 V/cm and at frequencies below 10 Hz.

Muon spin rotation (µSR) and relaxation has been used to study the local magnetic structure of K3Fe5F15. A collinear F-µ+-F "hydrogen bond-like" symmetric double minimum type complex with a F...F distance of 2.8 Å and a separation between the two minima of 0.8 Å has been found in the paramagnetic phase. The apparent central position of the muon seems to be the result of fast muon tunneling between two equivalent minima in the F-µ+-F bond.

The effect of 0–3% (v/v) ethanol and acetonitrile on water diffusional permeability of bovine and chicken red blood cells (RBCs) was studied using a pulse 1 H- T 2 NMR technique. Transmembrane water diffusional exchange times, τ exch , of 9.2 ± 0.46 ms and 18.3 ± 1.0 ms were determined for bovine and chicken erythrocytes at 27.5° C, respectively. Arrhenius activation energies E a of water diffusion were 20.4 and 35.8 kJ mol −1 . Ethanol, and acetonitrile being 2-fold more effective, markedly increased both τ exch and E a in bovine RBC as compared to the well-known mercurial inhibitor of water channels, p -chloromercuribenzene sulfonate. Chicken RBCs that have no protein water channels, were found to be completely insensitive for either agent. It was suggested that ethanol and acetonitrile partitioning into the lipid phase of bovine RBC membrane affects the permeability of CHIP28 water channel but not the lipid confined water diffusion. The results suggest that the inhibition of transmembrane movement of water via CHIP28 channels might be involved in the anti-hemolytic action of anaesthetics such as ethanol.

We have studied the coupling interaction between liquid crystal (LC) molecules and nanoparticles (NPs) in LC=NPs mixtures. Using a simple phenomenological approach, possible structures of the coupling term are derived for strongly anisotropic NPs. The coupling terms include (i) an interaction term promoting the mutual ordering of the LC molecules and the NPs, and (ii) the Flory-Huggins-type term enforcing the phase separation. Both contributions exhibit the same scaling dependence on the diameter of the NPs. However, these terms only exist for a finite degree of nematic LC ordering. The magnetic response due to the LC-NPs coupling is probed experimentally for a mixture of weakly anisotropic magnetic NPs and a ferroelectric LC. A finite coupling effect was observed in the ferroelectric LC phase, suggesting such systems can be used as soft magnetoelectrics.

(1)H NMR spin-lattice and spin-spin relaxation times of isotropic solutions of n-octylammonium n-octadecanoate in deuterochloroform containing ca. 0.1-0.2% tetramethylsilane (v/v) at ca. 292 K are observed to vary with position of the functional group in the amphiphile ion-pair, and with solute concentration. The latter dependence can be satisfactorily described using either single or multiple equilibria models of association complex formation of the reverse micelle type above a critical concentration (ca. 0.13 mol kg(-1)). Transverse relaxation is accounted for predominantly via reorientation/rotational diffusion of monomers and micellar aggregates, and is analyzed in terms of two component times, while longitudinal relaxation principally involves motions of different size segments around covalent bonds. Picosecond correlation times are attributed to intramolecular and monomer rotations, whereas multimer reorientation/tumbling processes are an order of magnitude longer. Results are analyzed for size of the reorienting species in terms of theoretical calculations for rotational diffusion of model cylindrical and ellipsoidal volumes of revolution, which above the critical micelle concentration correspond to association complexes of 2-4 monomers. Dilution shifts of the proton NMR peak positions also comply with the model of reverse micelle formation. The use of nonspinning liquid samples for the characterization of micellization phenomena via a nuclear magnetic resonance imaging spectrometer is investigated.

A detailed x-ray scattering study has been performed in the temperature range of the smectic- A phase for the liquid crystal compounds dodecylcyanobiphenyl (12CB) and octylcyanobiphenyl (8CB) confined in different controlled-pore glasses (CPGs) characterized by their average void radius R . On decreasing the temperature in bulk samples the layer thickness is increasing for 12CB and decreasing for 8CB, respectively. In nontreated CPG samples the layers dilate significantly with respect to the bulk liquid crystal. In order to explain the layer thickness behavior on varying temperature and R , one has to take into account molecular details of the liquid crystalline samples as well as memory effects.

We present the measurements of the proton spin-lattice relaxation time ${T}_{1}$ of liquid crystal 4-$n$-octyl-${4}^{\ensuremath{'}}$-cyanobiphenyl (8CB) confined into randomly oriented $\ensuremath{\sim}15\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ pores of untreated porous glass. In the low kilohertz range the spin-lattice relaxation rate in the nanoconfined 8CB is about ten times larger than in the bulk. We show that the increase is mainly due to molecular reorientations mediated by translational displacements (RMTD). In the paranematic phase the power law describing the RMTD dispersion, ${({T}_{1}^{\ensuremath{-}1})}_{\mathit{RMTD}}\ensuremath{\propto}{\ensuremath{\omega}}^{\ensuremath{-}p}$, is well characterized by the exponent $p=0.5\ifmmode\pm\else\textpm\fi{}0.06$ and suggests an equipartition of diffusion modes with different wavelengths. The largest distance related to the decay of the orientational correlation function is about twice the diameter of the cavity. The situation is different in the nematic phase, where the orientational correlation is eventually lost at $\ensuremath{\sim}60\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ in the direction along the pore, a distance corresponding roughly to the length of a pore segment in the glassy matrix. The exponent $p$ is between 0.65 and 0.9, depending on the temperature, which implies that in the nematic phase long wavelength modes are relatively more important---a consequence of the uniform director field along the pore. These observations are in agreement with the model of mutually independent pores with nematic director parallel to the pore axis in each segment. We point out that in strongly confined liquid crystals the proton NMR relaxometry does not provide the evidence of director fluctuations correlated over micrometer distances as was suggested earlier. The local translational diffusion of molecules within the cavities is found about as fast as in bulk.

We study theoretically the combined effect of confinement and randomness on LC phase transitions in orientational (isotropic-nematic) and translational (nematic-smectic A) degrees of ordering. We focus to cases where these transitions are of (very) weakly 1st order. An adequate experimental realisation is, e.g., 8CB liquid crystal confined to a Controlled-Pore Glass matrix. Based on universal responses of “hard” and “soft” continuum fields to distortions we derive how different mechanisms influence qualitative and quantitative characteristics of phase transitions under consideration.

The passage of water through the aquaporin-1 (AQP1) transmembrane channel protein of the human erythrocyte is known to be inhibited by organic mercurials such as p -chloromercuribenzoate (pCMB), which react with the free SH-group of the critical cysteine (Cys189) located near the constriction of the AQP1 water-specific channel. Sodium nitroprusside (SNP), which is known as a nitric oxide (NO) donor in interactions with SH-containing molecules, is shown here to suppress the diffusional water permeability ( P d ) of the erythrocyte membrane, presumably as a result of reaction with the Cys189 of the human erythrocyte AQP1 water channels. Further, treatment of erythrocytes with HgCl 2 is found to result in a cell volume decrease that can be related to activation of membrane K + -selective Gardos channels and subsequent loss of intracellular K + and cell shrinkage. The variations in P d and volume of the erythrocyte were deduced from induced variations in the measured proton ( 1 H) nuclear magnetic resonance (NMR) transverse ( T 2 ) relaxation functions of water exchanging between diamagnetic intracellular and paramagnetic extracellular compartments of the 20–25% hematocrit samples. The extracellular solvent contained 10 mM membrane-impermeable paramagnetic Mn 2+ ions. The 1 H- T 2 NMR technique allows determination of the time constant τ exch (for exchange of the erythrocyte intracellular water) that is inversely proportional to the permeability coefficient P d when the intracellular water volume is left unmodified, as in the case of SNP-treated erythrocytes. However, for HgCl 2 -treated erythrocytes, this technique showed simultaneous variation of both τ exch and the volume ratio V in / V out of intracellular and extracellular water in proportions suggesting that P d was left unmodified. The HgCl 2 effect has been found to be partly reversible by the reducing activity of added mercaptoethanol.

We measured the proton spin-lattice relaxation times in the isotropic phase of liquid crystal ${4}^{\ensuremath{'}}\text{\ensuremath{-}}n\text{-pentyl-}4\text{-cyanobiphenyl}$ (5CB) confined into porous glass (CPG) with the average pore diameter $\ensuremath{\sim}72\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$. The analysis of ${T}_{1}^{\ensuremath{-}1}$ frequency dispersions, spanning over four decades, shows that the main relaxation mechanism induced by the ordered surface layer are molecular reorientations mediated by translational displacements (RMTD). The RMTD contribution to ${T}_{1}^{\ensuremath{-}1}$ is proportional to the inverse square root of Larmor frequency, a consequence of the equipartition of diffusion modes along the surface. Low and high frequency cutoffs of the RMTD mechanism clearly reveal that the surface alignment of liquid crystal is random planar with the size of uniformly oriented patches $\ensuremath{\sim}5\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$, depending on the treatment of the CPG matrix. According to the size of the uniformly oriented patches varies also the thickness of the ordered surface layer and its temperature behavior. The surface-induced order parameter is found to be temperature independent and determined by the local short range surface interactions.

Measurements of the quasistatic and frequency dependent electrical conductivity below 1 MHz were carried out on wet-spun, macroscopically oriented, calf thymus deoxyribonucleic (DNA) and umbilical cord hyaluronic acid (HA) bulk samples. The frequency dependence of the electrical conductivity in the frequency range of approximately 10(-3) - 10(6) Hz of both materials is surprisingly rather similar. Temperature dependence of the quasistatic electrical conductivity above the low temperature saturation plateau can be well described by the activated Arrhenius law with the activation energy of approximately 0.8 eV for both DNA and HA. We discuss the meaning of these findings for the possible conduction mechanism in these particular charged polyelectrolytes.

The high-resolution calorimetric study was carried out on octylcyanobiphenyl liquid crystal (LC) confined to various controlled-pore glass (CPG) matrices with silane-treated surface. The diameter of the voids cross section ranged between 23.7 and 395 nm. The results are compared to those obtained previously on CPG voids nontreated with silane. We found a striking similarity between the shifts in the isotropic to nematic and nematic to smectic-A phase transition temperatures as a function of the void radius in which order parameter variations at the LC-void interface play the dominant role. Weaker temperature shifts are observed in silane-treated samples, where surface ordering tendency is larger. In nontreated samples, a finite-size scaling law in the maximum value of the heat capacity at the nematic to smectic-A transition was observed for void diameters larger than 20 nm. In silane-treated samples, this behavior is considerably changed by surface wetting interactions.

Many pharmaceutical tablets are based on hydrophilic polymers, which, after exposure to water, form a gel layer around the tablet that limits the dissolution and diffusion of the drug and provides a mechanism for controlled drug release. Our aim was to determine the thickness of the swollen gel layer of matrix tablets and to develop a method for calculating the polymer concentration profile across the gel layer. MR imaging has been used to investigate the in situ swelling behaviour of cellulose ether matrix tablets and NMR spectroscopy experiments were performed on homogeneous hydrogels with known polymer concentration. The MRI results show that the thickest gel layer was observed for hydroxyethylcellulose tablets, followed by definitely thinner but almost equal gel layer for hydroxypropylcellulose and hydroxypropylmethylcellulose of both molecular weights. The water proton NMR relaxation parameters were combined with the MRI data to obtain a quantitative description of the swelling process on the basis of the concentrations and mobilities of water and polymer as functions of time and distance. The different concentration profiles observed after the same swelling time are the consequence of the different polymer characteristics. The procedure developed here could be used as a general method for calculating polymer concentration profiles on other similar polymeric systems.

The appearance of a “liquid-like” proton T 2 component and the relatively high value of the proton self-diffusion coefficient D = (2−6) × 10 -7 cm 2 s -1 in the high temperature phase of (NH 4 ) 4 LiH 3 (SeO 4 ) 4 and (NH 4 ) 4 LiH 3 (SO 4 ) 4 demonstrate the onset of super-ionic like fast protonic conduction in these crystals. The linear Larmor frequency dependence of the proton spin-lattice relaxation time at low fields further demonstrates that we deal with low-dimensional acid proton translational diffusion already below room temperature.

External alternating electric fields of low intensity stimulated membrane bound ATP synthesis in starving Escherichia coli cells with electric field amplitudes of 2.5-50 V/cm and a frequency optimum at 100 Hz. The model of electrocon-formational coupling was used to analyze the frequency and amplitude responses of ATP synthesis. Two relaxation frequencies of the system were obtained at 44 Hz and 220 Hz, and an estimate of roughly 12 was obtained as the effective charge displacement for the catalytic cycle of ATP synthesis.

Layers of hydrogel represent a diffusional barrier that retards the process of drug release. For better prediction of drug release, a method for evaluating the polymer concentration profile was developed.

The aim of this work was to study the effect of the type of substituent of the cellulose ethers and the molecular mass on the state and dynamics of water in the respective hydrogels to specify the quantity of adsorbed water on the polymers or, more explicitly, to calculate the average number of water molecules bound to a polymer repeating unit (PRU). 1H NMR relaxation experiments were performed on equilibrated systems of cellulose ether polymers (HEC, HPC, HPMC K4M, and HPMC K100M) with water. In particular, the water proton spin-lattice (T1) and spin-spin (T2) relaxation times were measured in these systems at room temperature. The observed proton NMR T1 and T2 of water in hydrogels at different cellulose ether concentrations at room temperature were shown to decrease with increasing polymer concentration. The relaxation rate 1/T1 is sensitive to the type of polymer substituent but insensitive to the polymer molecular mass. The rate 1/T2 appears much less influenced by the polymer substitution. The procedure developed for calculating the amount of water bound per PRU, based on the analysis of the T1 and T2 data, shows that this amount is the largest for HPC followed by HEC, HPMC K4M, and HPMC K100M. The results correlate well with the degree of hydrophilic substitution of the polymer chains. This NMR analysis deals with a single molecular layer of adsorbed water for the investigated cellulose ether polymers at all concentrations, while the rest of the water in the hydrogel is bulk-like. Therefore, the mesh size of polymer network in the view of a single molecular layer is not effectively changed.

Liquid crystals confined into small cavities are known to have a weak orientational order even above the nematic-isotropic transition temperature. The surface-induced order and molecular dynamics in this temperature range are studied with the aid of deuteron NMR spectra, spin relaxation times T(1) and T(2,) proton dipolar-correlation effect, and direct measurements of the effective diffusion coefficient for the liquid crystal 5CB confined to controlled-pore glasses. Our results show that an arrangement of molecules parallel to the wall is induced by local molecular interactions between the liquid crystal and solid, resulting in a weak and temperature independent surface order parameter, S(0) approximately 0.02 +/- 0.01. There is no indication of a significant slowing-down of molecular diffusion at the wall, neither rotational nor translational. In cavities of nanometer size, where the nematic order evolves gradually upon cooling, a broadening of the NMR linewidths due to dynamic effects should be taken into account.

Bioactive 3-alkylpyridinium polymers (poly-APS) have recently been isolated from the marine sponge Reniera sarai. Previous results have shown that these molecules in aqueous solutions form supramolecular aggregates with an average hydrodynamic radius of 2392 nm. To obtain additional evidences about the shape and the dimensions of poly-APS aggregates, we used atomic force microscopy (AFM) operating in tapping mode. The images clearly showed adsorbed aggregates with a lateral dimension of :40 nm and a thickness of the order of :1 nm. The distribution of volumes of the adsorbed aggregates is very similar to the distribution of hydrodynamic radii as obtained from the dynamic light scattering experiments. The volume distribution of these aggregates shows a maximum at 1750 nm 3 , which corresponds to a sphere with a radius of 7.5 nm. © 1999 Elsevier Science B.V. All rights reserved.

A deuteron NMR study of the 8CB liquid crystal confined to the controlled pore glass matrix is presented. The theoretical analysis based on the phenomenological Landau - de Gennes type description predicts a strong influence of the pore curvature on the confined 8CB smectic ordering and almost none on its nematic ordering, in good agreement with experiment.

The structural and thermodynamic phase behavior of the thermotropic liquid crystal dodecylcyanobiphenyl (12CB) confined in controlled-pore glasses (CPGs) has been studied by means of high-resolution calorimetry and small-angle X-ray scattering. Non-treated CPG matrices have been used with a characteristic pore size R ranging from nanometre to micrometre scale. Even in the case of the strongest confinement the isotropic-to-smectic-A (I-SmA) transition was pronounced. Both the smectic pretransitional ordering and the broadening of the specific heat capacity anomaly were relatively weak. This signals the secondary importance of the surface interaction potential and of the disorder upon phase behavior. We claim that the surface interaction is dominated by the coupling between surface-frozen and volume liquid crystal molecules. This coupling is weak due to the flexible long alkyl chains which dominantly influence the phase behavior of 12CB. The depression of the phase transition temperature Tc is dominated by smectic elastic compressibility distortions. The observed anomalous Tc(R) dependence is explained by allowing surface rearrangement processes. In severely-confined samples the 1st order I-SmA phase transition tends to be replaced by a 2nd order one. This phenomenon is attributed to a dimensional-crossover which, in 12CB samples, is not masked by surface interactions as it is in case of similar liquid crystals with shorter alkyl chains. The observed behavior is explained using scaling and dimensional analysis within the Landau–Ginzburg–de Gennes mesoscopic approach.

The temperature dependence of the deuterium NMR line shape was studied in a pentylcyanobiphenyl (5CB) nematic liquid crystal embedded into lecithin-treated and nontreated continuous-pore silica aerogel matrices. In the lecithin-treated matrix the temperature dependence of the NMR absorption spectra of 5CB exhibits a pronounced first-order nematic-isotropic transition, while in the nontreated matrix only a weak discontinuity was found. The observed almost continuous onset of nematic ordering in the latter case appears to be due to the spread of nematic-isotropic-transition temperatures T NI , in different aerogel cavities

A pulse nuclear magnetic resonance (NMR) technique is employed to study the temperature dependence of the diffusional water exchange time texch for normal and p-hydroxymercuribenzoate (p-MB) treated bovine erythrocytes. The method is based on measurements of the proton NMR transverse relaxation function of water exchange between the diamagnetic intracellular space and the paramagnetically doped extracellular solution of the erythrocyte suspension. The semi-log plots of Xcxch versus inverse absolute temperature for both normal and mercurial treated erythrocytes are straight lines, implying that one activation energy (Fa) determines the rate of transmembrane diffusional water transport in the whole temperature range studied (5-40 °C). For normal erythrocytes, the value Fa of 20.4 kJ/mol is similar to that for selfdiffusion of water (Fa = 19.3-20.1 kJ/mol). The value Xcxch = 12.5 ms, obtained for normal bovine erythrocytes at 20 °C, corresponds to the cell membrane diffusional water permeability coefficient Pd of 3.6x 10-3 cm/s. This is similar to the range of room temperature Pd between 3.3 and 4.7x 10-3 cm/s, deduced recently for fresh normal human erythrocytes. The data for p-MB treated erythrocytes display a lengthening of Texch and increased Fa of 29.0 kJ/mol. This Fa value and a permeability coefficient Pd of 2.6xl0~3 cm/s at 20 °C, if compared to the corresponding permeability data for artificial lipid bilayer membranes, indicate either only partial inhibition of the mercurial sensitive part of the membrane diffusional water permeability, possibly as a result of poor accessibility of the functionally important transmembrane protein SH-groups to p-MB, or »complete« inhibition plus new leaks.

Effects of fractal structure on the magnetic resonance phenomena are discussed. Fractal theory is a mathematical tool used to describe geometrically complex disordered systems. In principle, one can get characteristic information about a fractal system via measurements of the relevant spectroscopic parameters, which are related to the fractal structure and fractal dynamics. Here, it is demonstrated that the surface fractal dimension, frac- ton dimension and the random walk dimension can be measured by means of nuclear magnetic resonance and electron paramagnetic resonance spectroscopy. It is further shown that nuclear magnetic resonance relaxation data allow determination of the non-exponential correlation functions, which reveal the fractal structure of the potential and of the corresponding free energy. The concept of the time fractal sequences of events, leading to the stretched exponential correlation functions, is also discussed.

The influence of controlled-pore glass (CPG) confinement on the phase behavior of octylcyanobiphenyl liquid crystal (LC) is studied by means of x-ray scattering and high precision calorimetry. For CPG samples with pore diameter 2R24 nm, the smectic order parameter temperature dependence eta(T) reveals apparent presmectic ordering far above the bulk smectic A-nematic (SmA-N) phase transition for both nontreated and silane-treated CPG matrices. The behavior of eta(T) is qualitatively similar in all samples, well obeying the mean field approach (MFA) in which the surface wetting tendency plays the dominant role. In contrast, the critical fluctuations remain important in the specific heat data, which cannot be described within the MFA. We show experimentally that randomness and surface wetting become dominant over finite-size effects for 2R approximately10 nm, in agreement with theoretical analysis. In nontreated samples, the noncritical character of the static disorder and the interfacial LC-CPG coupling almost completely suppress the quasi-SmA-N and nematic-isotropic phase transitions at 2R approximately 15.1 and approximately 7.5 nm, respectively.

We study the temperature evolution of smectic ordering of 8CB liquid crystal confined to various CPG matrices. The characteristic diameters of matrices ranged from 24 nm to 128 nm. The CPG voids were either left non-treated or were treated with silane. A weakly 1st order N-SmA transition in bulk 8CB, which could be attributed to the Halperin-Lubensky-Ma (HLM) effect, is broadened in confined samples. In confined samples substantial pretransitional anchoring was also observed, particularly in the silane-treated samples.

Measurements of the temperature dependence of the phosphorus Zeeman and dipolar spin-lattice relaxation times in CsH2PO4 show in the temperature range dominated by one-dimensional correlations an extremely strong dynamic central peak which decreases by four orders of magnitude on going to the range dominated by three dimensional correlations. The order fluctuation spectrum is qualitatively different in the case of CsD2PO4.