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Showing papers by "Nicholas A. Peppas published in 1986"


Journal ArticleDOI
TL;DR: In this article, a mathematical model for describing diffusion of a penetrant and a solute in a swellable polymer slab was applied to the case of a hydrophilic polymer loaded with a soluble drug in which the penetrant (water) is sorbed and solute (drug) is desorbed.
Abstract: A mathematical model developed to describe diffusion of a penetrant and a solute in a swellable polymer slab was applied to the case of a hydrophilic polymer loaded with a soluble drug in which the penetrant (water) is sorbed and solute (drug) is desorbed. An exponential dependence of the penetrant and solute diffusion coefficients on penetrant concentration was chosen and shown to be adequate for description of the systems studied. Experimental verification of the model was conducted by using copolymers of 2-hydroxyethyl methacrylate (HEMA) and N-vinyl-2-pyrrolidone (NVP). The monomers were bulk polymerized with benzoyl peroxide initiator and cut into thin disks. Monomer mole fractions of HEMA in the copolymers were 0.707, 0.446, and 0.211. Swelling behavior of the samples was observed in water at 37 and 0°C. Solute-containing samples were prepared and solute release from these samples into water was followed by monitoring the UV absorption of the release medium. The concentration dependence of the diffusivity of water and two model solutes, sodium trifluoroacetate and sodium heptafluorobutyrate, in the gels was studied by using the pulsed-gradient spin-echo NMR technique. The diffusivities measured by this technique followed the concentration dependence predicted by the free-volume theory. The simple exponential dependence used in the model was an adequate approximation of this behavior in the case of a transient diffusion experiment.

249 citations


Journal ArticleDOI
TL;DR: In this article, a mathematical model was developed to describe diffusion of a penetrant and a solute in a swellable polymer slab, in which the penetrant (water) is sorbed and solute is desorbed.
Abstract: A mathematical model was developed to describe diffusion of a penetrant and a solute in a swellable polymer slab. The model was applied to the case of a hydrophilic polymer loaded with a soluble bioactive agent, in which the penetrant (water) is sorbed and solute is desorbed. The model allows the incorporation of any appropriate form of the diffusion coefficients. A Fujita-type exponential dependence on penetrant concentration was chosen and shown to be adequate for prediction of a range of transport behavior. Dimensional changes in the sample were predicted by allowing each spatial increment to expand according to the amount of penetrant sorbed. During the initial period of release, the swelling was restricted to one dimension by the glassy core of the sample. At a later point in the process, the center of the sample had sorbed enough penetrant to plasticize it, and the sample relaxed to an isotropically swollen state; thereafter swelling was three-dimensional.

240 citations


Journal ArticleDOI
TL;DR: In this paper, the porosity and the degree of crystallinity of poly(ethylene-co-vinyl alcohol) copolymer were investigated for controlled release of theophylline.

236 citations



Journal ArticleDOI
TL;DR: In this article, the relaxational behavior of poly(2-hydroxyethyl methacrylate-co-methyl methacelate) disks containing HEMA mole fractions between 0.5 and 1.0 was studied using tensile stress relaxation experiments.

136 citations


Journal ArticleDOI
TL;DR: In this paper, a theoretical framework based on the dimensionless analysis of the penetrant swelling and solute release phenomena in a swelling-controlled system was developed for use in the prediction of the release behavior of solutes from swellable polymers.

77 citations



Journal ArticleDOI
TL;DR: Copolymerisation radicalaire monomere monovinyl-divinyl. Information cinetique de l'amorcage, propagation et reticulation, terminaison et transfert de chaine.
Abstract: Copolymerisation radicalaire monomere monovinyl-divinyl. Information cinetique de l'amorcage, propagation et reticulation, terminaison et transfert de chaine. Application au systeme styrene/(p) m-divinyl-benzene

72 citations


Book ChapterDOI
01 Dec 1986
TL;DR: The theoretical study of a hydrogel network has the purpose of revealing the structure and configuration of its chains by use of appropriate theoretical models as mentioned in this paper, which is made of mainly two theories, the equilibrium swelling theory and the rubber elasticity theory.
Abstract: The theoretical study of a hydrogel network has the purpose of revealing the structure and configuration of its chains by use of appropriate theoretical models. Characterization of the hydrogel network structure is a complex procedure because of the many types of possible networks, including, regular, irregular, loosely cross-linked, highly cross-linked, and imperfect networks. In order to determine the cross-linking density of a hydrogel, use is made of mainly two theories, the equilibrium swelling theory and the rubber elasticity theory. If an uncross-linked polymer is soluble in or thermodynamically compatible with a liquid penetrant, then the same polymer when cross-linked will be swollen by this liquid. When a cross-linked network acting as an elastomer is stretched, it reaches an equilibrium strain while the stress remains constant. The analysis of the cross-linked structure of hydrogels can be done by a variety of experimental techniques, prominent among which are swelling and mechanical tests.

59 citations




Journal ArticleDOI
TL;DR: In this article, a cyclohexane uptake overshoot was observed as a function of crosslinking ratio and geometric characteristics of the samples and it was attributed to molecular changes of polystyrene during swelling.
Abstract: Transport of liquid cyclohexane through well characterized, initially glassy, crosslinked polystyrene slabs was investigated as a function of time at 20, 30, 40, and 50 ° C. The samples used were produced by bulk polymerization of styrene and divinyl benzene using benzoyl peroxide as an initiator at 90 ° C for 48 hrs. The samples tested had initial crosslinking ratios, X, between 0.005 and 0.0250 mol DVB/mol styrene, their thickness varied from 0.025 to 0.180 cm, and the aspect ratio was maintained above 10 to achieve one-dimensional transport. A cyclohexane uptake overshoot was observed as a function of time. This overshoot was analyzed as a function of crosslinking ratio and geometric characteristics of the samples and it was attributed to molecular changes of polystyrene during swelling.

Journal ArticleDOI
TL;DR: In this paper, the average particle size and the standard deviation of the distribution were derived for batch-suspension polymerization and found that both quantities scale to the stable droplet mass of the initial dispersion of the organic phase into the aqueous one, which is a function of the agitation rate and the surface tension.
Abstract: Suspension polymerization is used for the production of polymer particles with diameter in the range of 50–750 μm. The particle size distribution of the particles produced in batch-suspension polymerization is calculated using a population balance model. Power laws are derived for the average particle size and the standard deviation of the distribution. It is found that both quantities scale to the stable droplet mass of the initial dispersion of the organic phase into the aqueous one, which is a function of the agitation rate and the surface tension.

Journal ArticleDOI
TL;DR: In this paper, the pyridine transport in 600-850μm coal particles occurs by a non-Fickian mechanism which shows coupling of both diffusion and relaxation phenomena.
Abstract: Pyridine transport in 600-850μm coal particles occurs by a non-Fickian mechanism which shows coupling of both diffusion and relaxation phenomena. In lignites (with carbon content less than 75%) the phenomenological pyridine transport mechanism is predominantly Fickian, whereas in bituminous coals (above 75% carbon) it approaches Case-II transport. However, when the porous structure of the coals is taken in consideration the true pyridine transport mechanism is Case-II transport.



Journal ArticleDOI
TL;DR: The results indicate macrosyneresis of the copolymer hydrogels upon freeze-drying even at -23 degrees C and rapid collapse of the hydrogel structure is seen upon removal of the bulk and interfacial water in the frozen state.

Journal ArticleDOI
TL;DR: In this article, the Flory thermodynamic interaction parameter, X, was calculated for a range of solvents interacting with the crosslinked macromolecular structure of coals of a wide range of carbon content.
Abstract: The Flory thermodynamic interaction parameter, X, was calculated for a range of solvents interacting with the crosslinked macromolecular structure of coals of a wide range of carbon content.

Journal ArticleDOI
TL;DR: In this paper, the structure of three cross-linked polymers containing naphthalenic rings in their backbone structure was investigated by dynamic swelling and thermal analytic techniques, and it was determined that the pyridine and n-proplyamine transport in microparticles (40 μm) of these polymers was non-Fickian, often approaching case II transport and sometimes even supercase II transport.
Abstract: The structure of three cross-linked polymers containing naphthalenic rings in their backbone structure was investigated by dynamic swelling and thermal analytic techniques It was determined that the pyridine and n-proplyamine transport in microparticles (40 μm) of these polymers was non-Fickian, often approaching case II transport and sometimes even supercase II transport The thermal analysis showed relatively stable structures up to about 350°C

Journal ArticleDOI
TL;DR: In this article, phenylalanine diffusing in well-characterized poly(2-hydroxyethyl methacrylate) (PHEMA) membranes swollen in water at 37°C were conducted.
Abstract: Studies with phenylalanine diffusing in well-characterized poly(2-hydroxyethyl methacrylate) (PHEMA) membranes swollen in water at 37°C were conducted. Films were prepared by reaction of HEMA monomer with the cross-linking agent ethylene glycol dimethacrylate (EGDMA) at cross-linking ratios, X, of 0.005, 0.01, 0.0128, 0.025, and 0.050 mole EGDMA/mole HEMA in the presence of 40 weight percent water at 60°C for 12 hours. These membranes were subsequently swollen in water at 37°C and their structure analyzed using a modified Gaussian distribution equation of swelling. The calculated values of Mc varied between 1,700 and 3,425 daltons, which corresponded to a correlation length of the mesh size, egr, of 24 to 35 A. The phenylalanine solute diffusion coefficient varied from 0.17 × 10−6 to 0.97 × 10−6 cm2/s, and depended on the aforementioned structural parameters of the membranes.

Journal ArticleDOI
TL;DR: The interaction of a biomaterial with its environment occurs primarily at the material /biological fluid interface as discussed by the authors, but many interactions are specific to the surface region (wetting, adhesion, many catalytic reactions, blood compatibility, etc.).
Abstract: The interaction of a biomaterial with its environment occurs primarily at the material /biological fluid interface. The general properties of a material are normally determined by its bulk characteristics (tensile strength, heat capacity, etc.), but many interactions are specific to the surface region (wetting, adhesion, many catalytic reactions, blood compatibility, etc.).

Journal ArticleDOI
TL;DR: In this article, a 25°C transport de chlorure de methylene dans le copolymere methacrylate d'hydroxy-2 ethyle/N-vinylpyrrolidone is described.
Abstract: Etude a 25°C du transport de chlorure de methylene dans le copolymere methacrylate d'hydroxy-2 ethyle/N-vinylpyrrolidone


Journal ArticleDOI
TL;DR: In this paper, the macromolecular structure of coal networks was analyzed by depolymerizing coal samples using the Sternberg reductive alkylation and the Miyake Alkylation techniques.
Abstract: The macromolecular structure of coal networks was analyzed by depolymerizing coal samples using the Sternberg reductive alkylation and the Miyake alkylation techniques. Electron impact mass spectra showed peaks of greater abundance of 125-132, 252-260, 383-391, and 511-520 m/z ratios. Based on analysis of the patterns of the spectra, the cluster size of the cross-linked structure of bituminous coals was determined as 126-130. Various chemical species were identified.


Journal ArticleDOI
TL;DR: In this paper, a mathematical model for the simultaneous permeation of moisture and oxygen through the packaging polymeric film and subsequent adsorption on the food surface is presented for the case of competitive adaption of the two diffusing species.
Abstract: Deterioration of food products stored in flexible packaging materials can be attributed to the presence of both water and oxygen in the environment surrounding the food. Mathematical models for the simultaneous permeation of moisture and oxygen through the packaging polymeric film and subsequent adsorption on the food surface are presented for the case of competitive adsorption of the two diffusing species. These models are then used to predict internal packaging conditions over time for selected food products. Oxygen and moisture permeation are treated as independent phenomena, and the competition is regarded as occuring on a surface described by the Langmuir adsorption isotherm. It is found that for certain polymer physical properties and relative surface coverages, water and oxygen molecules can dislodge each other from the food surface and, even for situations where the initial partial pressure of oxygen is less than the external partial pressure, can cause an outward flow of the more weakly adsorbed material. This theory is then extended to incorporate varying external conditions of storage.