Pore size distributions in polyelectrolyte multilayers determined by nuclear magnetic resonance cryoporometry (original) (raw)
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NMR Studies of the Effect of Adsorbed Water on Polyelectrolyte Multilayer Films in the Solid State
Macromolecules, 2003
Fast-MAS 1 H NMR is used to probe the structure and dynamics of the adsorbed water and polymer components in polyelectrolyte multilayer (PEM) films and the bulk polyelectrolyte complex (PEC). The films, ranging in size from a single layer to 5 bilayers, consist of poly(diallyl dimethylammonium chloride), PDADMAC, and poly(sodium-4-styrenesulfonate), PSS, adsorbed onto colloidal silica. Relaxation and line width measurements show that the adsorbed water is less mobile in the films than in the analogous PEC. The environment of the water throughout the film is found to be affected by the nature of the outer layer with the water displaying a higher mobility and chemical shift when PDADMAC forms the outer layer. Relaxation measurements, together with 1 H double-quantum (DQ) NMR experiments, reveal that polymer dynamics in the PEMs are strongly influenced by the layer number and water content. 2D spin diffusion and DQ NMR are used to detect polymer-polymer and water-polymer association. The results support the diffuse interpenetrating model of the different layers and a partitioning of the water to the PSS component and to the surface layer.
13 C Solid-State NMR Study of Polyelectrolyte Multilayers
Macromolecules, 2003
Polyelectrolyte multilayers have been prepared by consecutively adsorbing poly(diallyldimethylammonium chloride) (PDADMAC) and poly(sodium 4-styrenesulfonate) (PSS) from aqueous solution onto colloidal silica (70-100 nm in diameter), with a total of five bilayers being prepared. The multilayer growth was followed by electrophoretic mobility as well as solid-state NMR spectroscopy. The electophoretic mobility measurements show the expected reversal in the -potential with the alternate adsorption of the polycation and polyanion. The alternation in the relative intensities observed in the 13 C solid-state NMR spectra was used to qualitatively follow the layer-by-layer growth. Relaxation measurements show that the mobility of the polyanion is found to remain constant throughout the layer-by-layer assembly, while the mobility of polycation decreases with increasing numbers of layers.
NMR Studies of PAH/PSS Polyelectrolyte Multilayers Adsorbed onto Silica
Macromolecules, 2004
Solid-state NMR spectroscopy is used to monitor the layer-by-layer (L-B-L) growth of polyelectrolyte multilayers on colloidal silica. The dynamics and conformation of polyelectrolyte multilayers comprised of the weak polycation, poly(allylamine) hydrochloride, and the strong polyanion, poly(sodium-4-styrene sulfonate), assembled at pH 7 and pH 10 were studied by a combination of 1 H and 13 C NMR measurements. NOESY spectra detect the association of water to the polyanion, while relaxation measurements show that the outermost layer and the water content influence the mobility of the polyelectrolytes and the adsorbed water. Differences in mobility for films assembled at high and neutral pH are explained by the conformation of the polycation during the assembly process. Finally, the strongweak polyelectrolyte multilayers are compared to a previous NMR study of strong-strong polyelectrolyte multilayers.
Pore Morphology of Porous Polymer Particles Probed by NMR Relaxometry and NMR Cryoporometry
The Journal of Physical …, 2005
The pore size distribution (PSD) and pore connectivity (PC) within porous polymer particles are probed by combining NMR cryoporometry and NMR relaxometry (spin-spin relaxation). With water as a probe molecule, the constant K in the so-called Gibbs-Thompson equation and the surface relaxivity (F 2 ) were determined to be K ) (420 ( 50) KÅ and F 2 ) (0.44 ( 0.01) × 10 -6 ms -1 , respectively. Also, the thickness of the interface layer was estimated to be of the order of one monolayer of water molecules. A detailed analysis of the complete set of NMR data enabled the morphology or pore structure to be probed, and is thoroughly discussed in the text.
Hydration and internal properties of polyelectrolyte multilayers
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2007
In this review we summarize novel aspects of the hydration and internal properties of polyelectrolyte multilayers formed by layer-by-layer assembly. Reflectivity techniques monitor the water content and swelling behavior, while spin relaxation monitors water mobility. Odd-even effects in dependence on the number of layers are discussed in terms of an influence of the terminating layer. Other novel methodological approaches like X-ray microscopy or NMR cryoporometry address the water content in hollow capsules, and the water pore size distribution, respectively. Multilayer material properties are relevant for different applications. As a novel concept, dielectric properties are monitored in a field effect transistor device. Ion mobility and redox processes in multilayers are revealed by the electrochemical properties. Mechanical properties of multilayers, studied by colloidal probe atomic force microscopy depend on the conformation of the polymers involved.
Molecular mobility and transport in polymer membranes and polyelectrolyte multilayers
Magnetic Resonance Imaging, 2007
Polyelectrolyte multilayers prepared by the layer-by-layer technique provide an efficient way to generate planar structures of tailored surface charge and hydrophobicity, which are used as membranes for pervaporation. The use of polyelectrolyte multilayers to form the membrane permits tailoring the surface charge of the membrane and, thus, selectivity; at the same time, it reduces fouling of the membrane by adsorption of organic matter. Pulsed field gradient (PFG) nuclear magnetic resonance has been used to investigate the diffusion of probe molecules into polymer systems. Evaluation of the apparent diffusion coefficient in porous poly(amide) results in a pore size of 4 Am, as found in electron micrographs. For the pore size obtained for polyelectrolyte multilayers, no equivalent pores could be found in microscopy. Propagators for the diffusion of propanol and propanol-water mixture into multilayers reveal that there might be selective interaction of probe molecules with the polyelectrolyte system. D
NMR Cryoporometry of Polymers: Cross-linking, Porosity and the Importance of Probe Liquid
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2019
The morphology of cross-linked polymers plays an important role in their physical and chemical properties. NMR cryoporometry allows for the investigation of these structures over different length scales, through appropriate choice of probe liquid. The different structures of two different polymeric samples, one a cross-linked polymer hydrogel, the other a pore-expanded ion-exchange polymer, are analysed here. The ability for NMR cryoporometry to analyse both polymeric materials in the swollen state is successfully demonstrated, as is the importance of probe-liquid choice for the analysis of different regions of the pore structure. In both cases, water is used to identify populations of pores smaller than ca. 5 nm. The use of t-butanol and menthol reveals the presence of additional mesoporous structures in the ionexchange resin as well as the responsiveness of the pore structure to the liquid used to swell it.
Langmuir, 2009
We studied the swelling of polyelectrolyte (PE) multilayers (PEM) in water (H 2 O) vapors. The PEM were made from polyanion poly(styrene sulfonate) (PSS) and polycation poly(diallyldimethylammonium chloride)-N-methyl-N-vinylacetamide (pDADMAC-NMVA). While PSS is a fully charged polyanion, pDADMAC-NMVA is a random copolymer made of charged pDADMAC and uncharged NMVA monomer units. Variation of the relative amount of these two units allows for controlling the charge density of pDADMAC-NMVA. The degree ofswelling was studied as a function of the relative humidity in the experimental chamber (respectively water concentration in the gas phase) for PEM prepared from PSS and pDADMAC-NMVA with their different charge densities -100%, 89% and 75%. The films were prepared by means of spraying technique and consisted of six PE couples-PSS/pDADMAC-NMVA. Neutron reflectometry was applied as main tool to observe the swelling process. The technique allows to obtain in a single experiment information about film thickness and amount of water in the film. The experiments were complemented with AFM measurements to obtain the thickness of the films. It was found that the film thickness increases when the charge density of the polycation decreases. The swelling of the PEM increases with the relative humidity and it depends on the charge density of pDADMAC-NMVA. The swelling behavior is 2-fold, splitting up in a charge dependent mode with relatively little volume increase, and a second mode with high volume expansion, which is independent from charge density of PEM. The "swelling transition" occurs for all samples at a relative humidity about 60% and a volume increase of ca. 20%. The results were interpreted according to the Flory-Huggins theory which assumes a phase separation in PEM network at higher water contents.
Macromolecules, 1998
Using neutron reflectometry we have resolvedsto high resolutionsthe internal structure of self-assembled polyelectrolyte multilayer films and have developed a detailed molecular picture of such systems by analyzing the data with a composition-space refinement technique. We show that such surface films consist of stratified structures in which polyanions and polycations of individual layers interdigitate one another intimately. Nevertheless, the deposition technique leads to results that are predictable, if well-defined and constant environmental conditions are maintained during the preparation. For alternating layers of poly(styrenesulfonate) (PSS) and poly(allylamine hydrochloride) (PAH), adsorbed onto atomically flat surfaces, a roughening of successively deposited layers leads to a progressively larger number of adsorption sites for consecutive generations of adsorbed polymer, and thus to an increase in layer thicknesses with an increasing number of deposited layers. Because of the interpenetration of adjacent polyelectrolyte species, however, this increase settles quickly into an equilibrium thickness. In fully hydrated films (100% relative humidity), water occupies g40% of the volume within the films. About twice as much water (by volume) is associated with PSS as with PAH. Incorporated inorganic salt plays a minor role only, if any. The equilibrium thickness of the deposited layer structure may be fine-tuned via the ionic strength, I, of the solutions used for the preparation. We show that the dependence of the thickness d lp per layer pair on I is linear, with a sensitivity, ∆dlp/∆I ) 16 Å × L/mol. Concurrently with the layer thickness the interface roughness σ between adjacent layers increases: σ ∼ 0.4 × dlp. In contrast to the ionic strength of the deposition solutions, the degree of polymerization of the polyanions used in the preparation plays a minor role only in determining the overall structure of the deposited films. The results reported here are quantitatively consistent with those of a recent study (Tarabia et al. J. Appl. Phys. 1998, 83, 725-732), if one assumes that the hydration of the polyelectrolyte molecules in the sample films investigated in the two studies is similar.
Polyelectrolyte Multilayers Studied by Electron Paramagnetic Resonance (EPR) Spin-Label Technique
Applied Magnetic Resonance, 2013
A nitroxide spin label has been covalently attached to the polyelectrolyte poly(ethylene-alt-maleic acid) (P(E-alt-MA)) to study the interaction between this weak polyanion, the oppositely charged strong polycation poly(diallyldimethylammonium chloride) (PDADMAC) and water in swollen polyelectrolyte multilayers (PEM) by electron paramagnetic resonance (EPR) spectroscopy. If the spin-labeled polyanion has been used for the preparation of every double layer, the growth of the PEM film can be monitored by quantitative EPR. On the other hand, if the spin-labeled polyanion has been selectively placed in different layers in the PEM film the influence of the environment such as pH of the swelling medium of the mobility of the polyelectrolyte molecules positioned in the selected layer can be investigated.