Drying of films formed by ordered poly(ethylene oxide)-poly(propylene oxide) block copolymer gels. 2005

Zhiyong Gu, and Paschalis Alexandridis
Department of Chemical and Biological Engineering, University at Buffalo, The State University of New York, Buffalo, New York 14260-4200, USA.

The drying of hydrogel films formed by poly(ethylene oxide)-poly(propylene oxide) (PEO-PPO) block copolymers (Pluronic P105 and Pluronic L64) is investigated at various air relative humidity (RH) conditions in the range 11-94%. These amphiphilic block copolymers self-assemble to form a variety of ordered (lyotropic liquid crystalline) structures as the water content decreases. The amount of water lost increases linearly with the drying time initially (constant rate region, stage I). After this linear region, a falling rate is observed (stage II). The drying rate increases with decreasing RH, thus greatly shortening the drying time. A decrease of the initial film thickness or a decrease in the initial water content shortens the drying time; however, the drying mechanism remains the same. Analysis of the experimental data shows that the hydration level in the Pluronic hydrogel mainly determines the drying rate, rather than the type of ordered structure formed. Two distinct regions (liquid/gel and solid/crystalline) are observed in the drying isotherm for PEO-PPO block copolymers and homopolymer poly(ethylene glycol)s. A model for one-dimensional water diffusion is used to fit the experimental drying results at different RH, initial film thickness, and initial water content conditions. The model accounts for the shrinkage of the film during drying and for a water diffusion coefficient that is a function of the water concentration in the film. For the experimental conditions considered here, the Biot number (Bi) is less than unity and the drying is mainly limited by evaporation at the film surface. The diffusion model is used to obtain information for cases where Bi > 1.

UI MeSH Term Description Entries
D011108 Polymers Compounds formed by the joining of smaller, usually repeating, units linked by covalent bonds. These compounds often form large macromolecules (e.g., BIOPOLYMERS; PLASTICS). Polymer
D011409 Propylene Glycols Derivatives of propylene glycol (1,2-propanediol). They are used as humectants and solvents in pharmaceutical preparations. Propanediols,Glycols, Propylene
D004058 Diffusion The tendency of a gas or solute to pass from a point of higher pressure or concentration to a point of lower pressure or concentration and to distribute itself throughout the available space. Diffusion, especially FACILITATED DIFFUSION, is a major mechanism of BIOLOGICAL TRANSPORT. Diffusions
D012997 Solvents Liquids that dissolve other substances (solutes), generally solids, without any change in chemical composition, as, water containing sugar. (Grant & Hackh's Chemical Dictionary, 5th ed) Solvent
D014867 Water A clear, odorless, tasteless liquid that is essential for most animal and plant life and is an excellent solvent for many substances. The chemical formula is hydrogen oxide (H2O). (McGraw-Hill Dictionary of Scientific and Technical Terms, 4th ed) Hydrogen Oxide
D020100 Hydrogels Water swollen, rigid, 3-dimensional network of cross-linked, hydrophilic macromolecules, 20-95% water. They are used in paints, printing inks, foodstuffs, pharmaceuticals, and cosmetics. (Grant & Hackh's Chemical Dictionary, 5th ed) Hydrogel,In Situ Hydrogel,In Situ Hydrogels,Patterned Hydrogel,Patterned Hydrogels,Hydrogel, In Situ,Hydrogel, Patterned
D020442 Poloxamer A nonionic polyoxyethylene-polyoxypropylene block co-polymer with the general formula HO(C2H4O)a(-C3H6O)b(C2H4O)aH. It is available in different grades which vary from liquids to solids. It is used as an emulsifying agent, solubilizing agent, surfactant, and wetting agent for antibiotics. Poloxamer is also used in ointment and suppository bases and as a tablet binder or coater. (Martindale The Extra Pharmacopoeia, 31st ed) Pluronic,Poloxamers,Pluronic F-108,Pluronic F-127,Pluronic F-68,Pluronic F68,Pluronic L-101,Pluronic L-121,Pluronic L-81,Pluronics,Poloxalkol,Poloxamer 188,Poloxamer 213,Poloxamer 2930,Poloxamer 338,Poloxamer 407,188s, Poloxamer,213s, Poloxamer,2930s, Poloxamer,338s, Poloxamer,407s, Poloxamer,F68s, Pluronic,Pluronic F 108,Pluronic F 127,Pluronic F 68,Pluronic F108,Pluronic F127,Pluronic F68s,Pluronic L 101,Pluronic L 121,Pluronic L 81,Pluronic L101,Pluronic L121,Pluronic L81,Poloxalkols,Poloxamer 188s,Poloxamer 213s,Poloxamer 2930s,Poloxamer 338s,Poloxamer 407s

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