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Surfactant-Free Thermochromic Hydrogel System: PVA/Borax Gel Networks Containing pH-Sensitive Dyes
Abstract
The well-known pH-indicators, phenolphthalein and bromothymol blue, exhibit an outstanding thermochromism, when they are embedded in aqueous polyvinyl alcohol/borax gel networks. The color of phenolphthalein in hydrogels changes gradually from colorless at 20°C to dark red at 70°C. The pH change in a hydrogel system was from 8.0 to 8.9 with increasing temperature. In the case of bromothymol blue, the color was optically clear green at room temperature and changed to clear blue with increasing temperature. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 890–893, 2004
... Moreover, poly(vinyl alcohol) (PVA) in the forms of both aqueous solutions and hydrogels, formed due to the crosslinking of PVA macromolecules with tetrahydroxyborate anions, was examined with respect to fragrance profile modification [10,11]. Hydrogel systems based on crosslinked poly(vinyl alcohol) are biodegradable which is a desirable feature [12,13] worthy of further research [14][15][16][17][18][19]. ...
... The total surface areas of the peaks registered in the chromatograms were taken as the measure of the analyte content in the gas phase. Determining the total peaks surface areas, only the peaks of the earlier identified substances were considered (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19). The obtained results can point out to the two tendencies. ...
... The parameter indicating the content of the substance in the gas phase was established as the surface area of its peak in the chromatogram. The total surface area of registered peaks included only the peaks of earlier identified substances (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19). ...
The chemical composition of two commercially available lavender fragrance oils was determined and compared. The process of concentration by partial evaporation was carried out and its influence on changes in the content of individual components in the analysed mixtures was examined. The effect of poly(vinyl alcohol)-based polymer matrix on the release of volatile substances from oils was tested as well. The presence and chemical composition of the polymer matrix affects the relative content of volatile substances released from the liquid phase containing the tested fragrance composition.
It is still challenging to prepare high strength hydrogels which can self-heal in both alkali and acid solutions. In this work, 6-acrylamidohexanoic acid (AACA) and [2-(methacryloyloxy)ethyl]trimethylammonium chloride solution (DMC) monomers were copolymerized in a mixture solution of polyvinyl alcohol (PVA) and borax to prepare high strength and pH responsive hydrogel. Compared with borax cross-linked PVA gel, this hydrogel exhibits better mechanical properties owing to multi-physical interactions like electrostatic interactions and hydrogen bonds. Due to the presence of noncovalent interactions the hydrogel exhibits different degrees of self-healing ability in acid and alkali at the same time. Furthermore, the conductivity of the hydrogel can be significantly change with slight deformation, which can be used to monitor the body movement like swallow and finger bending.
The vortex-ring derived particles are new type of non-spherical hydrogel particles, which are prepared by imitating the process of vortex-ring in nature. However, the traditional existing vorticity ring derived hydrogel particles were prepared by dropping polyelectrolyte solution into contra-ion coagulation bath, which limited the choice of materials. In this paper, a strategy of preparation non-spherical hydrogel particles by using non-polyelectrolyte polyvinyl alcohol through the method of vortex ring was proposed. Based on the principle that the boraciated polyvinyl alcohol solution could be quickly gelled under alkaline condition, the spherical and various derivative shapes (red cell, bowl, dish, ring) of polyvinyl alcohol vortex-ring derived hydrogel particles (PVHP) were prepared. The hydrogel particles have the ability to assemble into different modules by dynamic borate bond in the hydrogel particles. Also, this dynamic borate bond endowed the PVHP decomposable and recyclable performances. In addition, two-compartments, three-compartments and magnetic PVHP were also prepared, endowing PVHP with several functions. which opens up a new environmentally friendly way for the preparation of multifunctional particles.
The mechanisms of thermochromic materials are mostly based on Bragg reflection, surface plasmon absorption, molecular structure changes, conformational stretching or aggregation. Here, a simple class of dye-solvent binary systems with clear and reversible thermochromism around ambient temperatures is reported with an alternative mechanism. This system comprises of commercially available sulfonephthaleins dissolved in liquid linear chain esters, acids or alcohols which demonstrate colour changes at different temperatures when the solvents transition from solid to liquid states. The colour changing mechanism is based on π-π stacked aggregation or disaggregation of the sulfonephthalein dyes. Cell toxicity testings confirmed the sulfonephthalein dyes are less toxic to NIH-3T3 cells than Cyanidin chloride, which is the only reported nontoxic food dye affording thermochromism, while this is based on an alternative mechanism. With the choice of nontoxic solvent, this binary system can form a nontoxic thermochromic material.
A facile environmentally-benign approach has been developed for the preparation of dynamic, multi-responsive and self-healing hydrogels from inexpensive bamboo pulp, poly(vinyl alcohol) (PVA) and borax. The microfibrillated cellulose (MFC) reinforced PVA-borax hydrogels were produced through a one-pot route in conjunction with ball milling and physical blending in tandem in aqueous medium. In this way, MFC particles could be efficiently generated and well-dispersed in polymer matrix, which have been verified by scanning electron microscopy. The rheology analysis indicated close relationship between the mechanical strength and the MFC loading and ball milling time. Due to the dynamic equilibrium of the didiol-borax linkages and the reinforcement of MFC fibres, the hydrogels showed enhanced self-healing behavior and mechanical stiffness, which was also supported by rheology analyses. In addition, the hydrogels were found to be sensitive to the pH value. The hydrogels present solvent or gel state with the change of pH value, and this sol-gel transfer can be repeated while maintaining the shape, further demonstrating the dynamic reversible behavior of the hydrogels.
Gelling behavior of PVA or its blends with other polymers such as polyvinyl pyrrolidone (PVP), polyethylene oxide (PEO), hydroxyl propyl cellulose (HPC), agar and gelatin A has been studied as a function of borax concentration from viscosity measurements. The pH of the borax cross linked hydrogels of PVA or its blends showed an interesting behavior with temperature - it initially increases with temperature up to a maximum and then decreases with further increase in the temperature. Such temperature sensitive transparent hydrogels when embedded with a suitable acid-base indicator like phenolphthalein showed reversible thermochromism. However, thermochromism was not observed in the hydrogels of polymer blends if the amount of PVA in the blend was less than 60%. The results suggest that thermochromism in dye embedded borax cross-linked hydrogels is due to the formation of didiol cross-links between hydroxyl groups in PVA and the borax, which is governed by change in temperature. The effect of the addition of an anionic (SDS), or a non ionic (TX-100) surfactant on the thermochromic behavior of the hydrogels has also been studied. © 2011 Indian Society for Surface Science and Technology, India.
The phenomenon of changing colour intensity of PVA-Borax hydrogel in presence of surfactants like sodiumdodecyl sulfate (SDS), trimethyl triammonium bromide (TTAB) has been investigated in detail. The preparation of thermochromic Borax crosslinked PVA gel was performed by embedded with a pH sensitive dye (phenolphthalein) both in absence and presence of surfactant. The phenomenon of thermochromism in presence of surfactant was studied spectrophotometrically.
Spectral and temperature characteristics of light transmission in water solutions of chemical indicators— bromophenol blue, bromothymol blue, and cresol red—were measured in the wavelength range of 500–750 nm and the temperature range from 20 to 90°С. It was demonstrated that these solutions can be applied in optical fiber thermometers with continuous reading which are not affected by strong external electromagnetic fields.
Thermochromic polymers will play an extremely important role in the next future. The physical background of thermochromism and the state of development of thermochromic polymers based on light absorption effects are reported. In detail, the interactions between the polymer matrix and the thermochromic composite - composed of leuco or indicator dyes - are discussed on a molecular level. Thermochromic hydrogels with extremely high transparency, an outstanding switching behavior from colorless to colored or between different colors is presented. Preparation of thermosetting and thermoplastic polymers, including the resulting optical, and, for the first time, the mechanical properties are discussed in relation to matrix tuned high-resistant microcapsules.
In this study, a novel vinyl polymer containing 2,4,5‐triphenylimidazole side groups was synthesized through conventional radical polymerization, which possesses the characteristic of temperature‐dependent absorbance in the near‐ultraviolet (UV) spectral region. The linear dependence of UV absorbance on temperature was confirmed for the polymer both in solid state and in solution by experiment and also supported by the results of theoretical investigation. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012
The review demonstrates how the functions of thermochromic polymers are determined by their design. The strategy to design thermochromic systems by physical or chemical interaction of their nonthermochromic components encourages this topic. Changes of the light scattering properties on temperature change do primarily not affect the color but the transparency of the material. The review uses the term thermochromism in its closer sense denoting color changes with temperature. Another way to classify thermochromic polymers is to distinguish between polymers with inherent thermochromic properties. Polymers which become thermochromic by embedding of thermochromic pigments and polymers which become thermochromic by the interaction between a polymer matrix and additives.
Thermally reversible light scattering (TRLS) films are prepared from ultraviolet (UV) curing of polyether urethane diacrylate (PEUDA) with dispersed low molecular weight 1-octadecanol (OD). Depending on the temperature, the OD domains are crystalline or amorphous and this produce opaque or transparent films in a reversible way. Stable optically transparent and light scattering states are obtained after 100 successive heating–cooling cycles. Moreover, morphologies of the OD domains could be varied significantly with the cure temperature and this led to notable discrepancy in optical properties. By using an UV-mask and curing in two steps at different temperatures, complex patterns could be recorded in the film that were encoded at high temperatures (60°C) and revealed at low temperatures (i.e., at room temperature), which makes the film a candidate for thermo-optical recording medium.
The paper presents some triarylmethane dyes and their use in thermochromic systems of donor-accepting type. Compounds are characterized by FT-IR spectra, UV-Vis reflectance spectra and color measurements in CIELAB system and thermal analysis. Some considerations are made in relationship with dyestuff structure, developing agent and solvents used to obtain thermochromic systems. The effect of the ratio between the developing agent and lactone dye on the color differences was studied from reflectance spectra and colour measurements while the influence of the solvent type on the transition temperature was analyzed using dynamic scanning calorimetry.
Nanoporous hydrogels have been prepared by freezing-thawing method. Three types of porphyrins have been encapsulated into PVA hydrogels. It was demonstrated that the PVA hydrogels represent an efficient encapsulation vehicle for porphyrins. Hydrogels prepared from high molecular mass PVA have a better sorption profile for porphyrins, and are
better suited for the preparation of controlled release vehicles.
Diffusion coefficient of oxygen penetrating into polystyrene (PS) latex/poly (N-isopropylacrylamide) (PNIPAM) microgel composite films were measured using Fluorescence technique. Three different (5, 15, and 40 wt%) PS content films were prepared from PS/PNIPAM mixtures. Diffusivity of PS/PNIPAM composite films were studied by diffusion measurements which were performed over the temperature range of 24–70°C. Pyrene was used as the fluorescent probe. The diffusion coefficients (D) of oxygen were determined using the Stern–Volmer fluorescence quenching method combined with Fickian transport and were computed as a function of temperature for each PS content film. The results showed that D values were strongly dependent on both temperature and PS content in the film. Diffusion energies were measured and found to be dependent on the composition of the composite films. Copyright © 2011 John Wiley & Sons, Ltd.
Water-dispersed thermotropic nanoparticles with core-shell structures were synthesized by the in situ polymerization of a lightly crosslinked shell of poly(N- isopropylacrylamide) [poly(NIPAM)] onto blue polystyrene cores. At room temperature, the thermal responsive outer shell is hydrophilic and is in a fully swollen gel state; but as the temperature is raised above 31°C, it becomes increasingly hydrophobic and eventually collapses as the temperature reaches the lower critical solution temperature (LCST) of the poly(NIPAM). Passing through the LCST has a drastic effect on the color of the latex solution, which exhibited an intense blue color at room temperature and gradually pales or lightens as the temperature is raised above 31°C. Analysis using spectroscopic and dynamic light scattering techniques showed that it is a reversible process. Microscopy evaluation of samples dried by the evaporation of water at temperatures above and below the LCST revealed that the swollen/collapse state of the polymer shell influenced the morphology of the dry state. Drying at room temperature resulted in thin films in which only particles of sizes corresponding to the polystyrene core are clearly seen in the microscopy images; but for samples prepared above the LCST, the images revealed a morphology made of much larger particles with diameters of 400–500 nm. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007
This article is a report about the novel fluorescence temperature sensor based on a surfactant‐free Poly (vinly alcohol)/borax/2‐naphthol hydrogel system. The well‐known fluorescence indicator, 2‐naphthol, exhibits a change of fluorescence intensity when it is embedded in aqueous PVA/borax gel networks at various temperatures. The blue color emission intensity(PL:λ max = 426 nm) of 2‐naphthol in a basic hydrogel changed gradually to strong from 30°C to 80°C when excitation wavelength was 365 nm. The pH change in the hydrogel system was in the range from 8.50 at 30°C to 9.35 at 80°C with rising temperature.
In the case of salicylic acid, the blue color emission intensity in the acidic gel decreases with rising temperature when excitation wavelength was 365 nm in all cases. The pH change in the hydrogel system was from 2.80 at 30°C to 2.40 at 80°C with rising temperature. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2114–2118, 2004
We report a multilayer film of poly(vinyl alcohol) (PVA)-borate complex and chitosan by using a layer-by-layer approach. PVA is an uncharged polymer, but hydroxyl functional groups of PVA can be cross-linked by using borax as a cross-linking agent. As a result electrostatic charges and intra- and interchain cross-links are introduced in the PVA chain and provide physically cross-linked networks. The PVA-borate was then deposited on a flat substrate as well as on colloidal particles with chitosan as an oppositely charged polyelectrolyte. Quartz crystal microbalance, scanning electron microscopy, and atomic force microscopy were used to follow the growth of thin film on flat substrate. Analogous experiments were performed on melamine formaldehyde colloidal particles (3-3.5 microm) to quantify the process for the preparation of hollow microcapsules. Removal of the core in 0.1 N HCl results in hollow microcapsules. Characterization of microcapsules by transmission electron microscopy revealed formation of stable microcapsules. Further, self-assembly of PVA-borate/chitosan was loaded with the anticancer drug doxorubicin, and release rates were determined at different pH values to highlight the drug delivery potential of this system.
The optical memory effects of the newly developed sol-gel gel-glass based thermochromic material are studied. Several fundamental material parameters, which contribute to the formation of tow stable states in this substance are quantitatively measured. Simple writing and erasing methods along with the long term stability of each memory state are demonstrated.
Two switchable, mesoscopically periodic materials were created by combining crystalline colloidal array (CCA) self-assembly with the temperature-induced volume phase transition of poly(N-isopropylacrylamide) (PNIPAM). Body-centered-cubic CCAs of hydrated, swollen PNIPAM particles Bragg-diffract infrared, visible, and ultraviolet light weakly, whereas arrays of compact shrunken particles diffract efficiently. A tunable diffracting array was also created by embedding a CCA of polystyrene spheres within a PNIPAM hydrogel that swells and contracts with temperature; thus the array lattice constant varies with temperature, and the diffracted wavelength was thermally tunable across the entire visible spectrum. These materials may find applications in many areas of optics and materials science.
Chemical sensors respond to the presence of a specific analyte in a variety of ways. One of the most convenient is a change in optical properties, and in particular a visually perceptible colour change. Here we report the preparation of a material that changes colour in response to a chemical signal by means of a change in diffraction (rather than absorption) properties. Our material is a crystalline colloidal array of polymer spheres (roughly 100 nm diameter) polymerized within a hydrogel that swells and shrinks reversibly in the presence of certain analytes (here metal ions and glucose). The crystalline colloidal array diffracts light at (visible) wavelengths determined by the lattice spacing, which gives rise to an intense colour. The hydrogel contains either a molecular-recognition group that binds the analyte selectively (crown ethers for metal ions), or a molecular-recognition agent that reacts with the analyte selectively. These recognition events cause the gel to swell owing to an increased osmotic pressure, which increases the mean separation between the colloidal spheres and so shifts the Bragg peak of the diffracted light to longer wavelengths. We anticipate that this strategy can be used to prepare 'intelligent' materials responsive to a wide range of analytes, including viruses.
Increasing concentrations of ions flowing through the xylem of plants produce rapid, substantial, and reversible decreases in hydraulic resistance. Changes in hydraulic resistance in response to solution ion concentration, pH, and nonpolar solvents are consistent with this process being mediated by hydrogels. The effect is localized to intervessel bordered pits, suggesting that microchannels in the pit membranes are altered by the swelling and deswelling of pectins, which are known hydrogels. The existence of an ion-mediated response breaks the long-held paradigm of the xylem as a system of inert pipes and suggests a mechanism by which plants may regulate their internal flow regime.
The aim of this review is to present the last 10 years of development in sun protection by use of electrochromic devices, thermotropic gels and polymer dispersed liquid crystalline systems. Furthermore, the properties of new lyotropic liquid crystalline and thermotropic hydrogels are discussed. Thermochromic hydrogels, which change their colour by changes in the temperature, also are presented. The relationship between gel composition, optical behaviour and thermodynamic properties as investigated by differential scanning calorimetry (DSC) is also demonstrated.
Dyes whose acid and base forms are differently coloured from each other have the possibility of showing thermochromism based on the temperature dependence of the acid-base equilibrium. To clarify such character of the dyes, the temperature dependence of the acid-base equilibrium and the colour change have been investigated using 1-hydroxyanthraquinones and phthaleins. 1-Hydroxyanthraquinones in solution of sodium acetate showed such a colour change, i.e. yellow at lower temperature and orange at higher temperature. This colour change was due to the larger temperature dependence of their acidity than that of the basicity of the medium. In solution of triethylamine, on the other hand, the reverse colour change was observed because the temperature dependence of their acidity is smaller than that of the basicity of the medium. Similar thermochromic character of the phthaleins was also investigated.
Novel dye containing transparent hydrogels responding to changes in temperature with reversible color changes (thermochromism) are presented. The betaine dye 2,6-diphenyl-4-(2,4,6-triphenylpyridinio)phenolate (DTPP), and the well known indicator dye Cresol Red ( Fig. 1 ) exhibit an outstanding thermochromism, if they are embedded in an aqueous polyvinyl alcohol–borax–surfactant gel network. In case of DTPP at pH = 8.5, the color changes gradually from colorless at 10°C to a deep violet at 80°C. Similarly, for Cresol Red a change from yellow to wine-red was observed. An explanation for the observed reversible color changes in the closed hydrogel systems is given by a temperature-induced shift of the proton-transfer equilibrium between the phenolate and the phenol form of the dye molecules in the micro-environment of the gel network. The new thermochromic hydrogels can be useful in a wide range of applications, such as temperature sensors, large-area displays, and so-called smart or intelligent windows.
Steady viscosity, dynamic viscoelasticity (DVE), and dynamic light scattering (DLS) measurements were made to study the effects of temperature, T, on association behaviors of poly(vinyl alcohol) (PVA) with weight-average degree of polymerization DPw = 350 in aqueous Borax solution. Intrinsic viscosity, [η], monotonically decreased by 23% with a rise in T from 10 to 65 °C. At low T, enhancement in viscosity was observed with increasing polymer concentration, C, due to formation of viscoelastic network with the didiol complex as temporal cross-links, and the time−temperature superposition principle was found to be applicable for construction of a composite curve at each C. Those composite curves were further reduced so as to give one master curve. The system tended to lose its viscoelastic nature, when raising the temperature, toward a viscous solution owing to a decrease in the number of the didiol complexes as well as the shrinkage of the PVA chains. We found from analysis of DVE and DLS data that a clear boundary line between viscoelastic and viscous behaviors can be drawn on the T−C diagram using the temperature TN defined as the inflection point in a η vs T -1 plot for each C.
We study the formation of reversible gels induced by addition of borax in aqueous solutions of galactomannans. The number of cross-links can be well controlled by polymer and borax concentrations, temperature, and ionic strength. As theoretically expected we observe that the gelation threshold strongly depends on polymer concentration. Under suitable conditions reversible demixing into concentrated polymer (gel) and dilute phases may occur. This demixing transition can be strongly shifted by the addition of small complexing molecules such as D-mannitol. The important parameter for the onset of demixing as well as for the gelation threshold turns out to be the number of induced intermolecular cross-links per chain. As a consequence, it is possible by an appropriate rescaling to superimpose phase diagrams obtained under various very different conditions. We present a qualitative interpretation of these results in terms of the complexation and the swelling equilibria of the temporary network.
Figure 1. Equilibrium swelling ratios (relative volume of gels, V/V0 )a s a function of temperature for the MR gel prepared in the presence of norephedrine (A) and for the RF gel prepared in the absence of norephedrine (B), measured in aqueous solution of a given norephedrine concentration as indicated in the insets. The equilibrium swelling ratios were measured with increasing temperature.
Six disaccharide amphiphiles were synthesized and their hydrogel-forming behavior was extensively studied. These amphiphiles were based on maltose and lactose. Since the gels formed from some of these systems showed the ability to “trap” water molecules upon gelation, these gels were described as “hydrogels”. When these gels were heated to 70 °C, the samples turned into clear, isotropic fluids, and upon gradual cooling, the hydrogels could be reproduced. Thus these systems were also “thermoreversible”. The low molecular mass (MW 565) of the gelators compared to that of a typical polymeric gelator forming substance implies pronounced aggregation of the disaccharide amphiphiles into larger microstructures during gelation. To discern the aggregate textures and morphologies, the specimen hydrogel samples were examined by high-resolution scanning electron microscopy (SEM). A possible reason for the exceptionally high water gelating capacities (>6000 molecules of water per gelator molecule) exhibited by these N-alkyl disaccharide amphiphiles is the presence of large interlamellar spaces into which the water molecules get entrapped due to surface tension. In contrast to their single-chain counterparts, the double-chain lactosyl and maltosylamine amphiphiles upon solubilization in EtOH−H2O afforded hydrogels with reduced mechanical strengths. Interestingly, the corresponding microstructures were found to be quite different from the corresponding hydrogels of their single-chain counterparts. Rheological studies provided further insights into the behavior of these hydrogels. Varying the chain length of the alcohol cosolvent could modulate the gelation capacities, melting temperatures, and the mechanical properties of these hydrogels. To explain the possible reasons of gelation, the results of molecular modeling and energy minimization studies were also included.
Highly active and stable biocatalytic materials were produced by copolymerizing enzymes with vinyl sugar monomers. These materials display very high activity in organic solvents and are active and stable in aqueous systems at elevated temperatures.
Among the many developments associated with sol−gel processing of particular relevance for information processing and optics applications is the preparation of photochromic sol−gel materials. If these materials are properly processed as thin films or attached to optical fibers, throughout the design of an adequate thermally and photochemically stable practical device, the properties of the light throughput may be modified. Hybrid organic−inorganic sol−gel matrixes ormocers (organically modified ceramics) and ormosils (organically modified silicas) opened the gateway to approach to optical memory applications by either light or temperature writing and erasing on newly developed photochromic and thermochromic materials.
Many inorganic and organic materials exhibit redox states with distinct electronic (UV-vis) absorption bands. When the switching of redox states generates new or different visible region bands, the material is electrochromic. Electrochromic materials are currently attracting much interest in academia and industry for both their fascinating spectroelectrochemical properties and their commercial applications. In this review some of the most important examples from the major classes of electrochromic materials are highlighted. Examples of their use in both prototype and commercial electrochromic devices are illustrated including car mirrors, windows and sun-roofs of cars, windows of buildings, displays (see Figure), printing, and frozen-food monitoring.
The separation of macromolecules such as polymers and DNA by means of electrophoresis, gel permeation chromatography or filtration exploits size-dependent differences in the time it takes for the molecules to migrate through a random porous network. Transport through the gel matrices, which usually consist of full swollen crosslinked polymers, depends on the relative size of the macromolecule compared with the pore radius. Sufficiently small molecules are thought to adopt an approximately spherical conformation when diffusing through the gel matrix, whereas larger ones are forced to migrate in a snake-like fashion. Molecules of intermediate size, however, can get temporarily trapped in the largest pores of the matrix, where the molecule can extend and thus maximize its conformational entropy. This 'entropic trapping' is thought to increase the dependence of diffusion rate on molecular size. Here we report the direct experimental verification of this phenomenon. Bragg diffraction from a hydrogel containing a periodic array of monodisperse water voids confirms that polymers of different weights partition between the hydrogel matrix and the water voids according to the predictions of the entropic trapping theory. Our approach might also lead to the design of improved separation media based on entropic trapping.
The applications of a wide range of hydrogels in tissue engineering were presented. The design parameters of hydrogels required for them to be useful, regardless of their origin from natural resources or synthetic creation were discussed. The use of polymers in promoting blood vessel network formation in the tissue was described. The problems encountered in the design and engineering of various sequences of polypeptides with known functions were also studied.
A class of environmentally responsive materials based on the spatial modulation of the chemical nature of gels is proposed and demonstrated here. The modulation was achieved by limiting the interpenetration of part of one gel network with another gel network. The gels so produced have an internally heterogeneous or modulated structure. Three simple applications based on the modulated gels are described here: a bigel strip, a shape memory gel, and a gel "hand." The bigel strip bends almost to a circle in response to a temperature increase or an increase in solvent concentration. The shape memory gel changes its shape from a straight line to a pentagon to a quadrangle as the temperature increases. These transitions from one shape to another are reversible. The gel "hand" in water can grasp or release an object simply by an adjustment of the temperature.
- A Seeboth
- J Kriwanek
- R Vetter
Seeboth, A.; Kriwanek, J.; Vetter, R. Adv Mater 2000, 12, 1424.
- D R Rosseinsky
- R J Mortimer
Rosseinsky, D. R.; Mortimer, R. J. Adv Mater 2001, 13, 783.
20. Levy, D. Chem Mater 1997, 9, 2666.
- T Tajima
- H Inoue
Tajima, T.; Inoue, H.; Hida, M. Dyes Pigments 1987, 8, 119.
- R Washington
- O Steinbock
Washington, R.; Steinbock, O. J Am Chem Soc 2001, 123, 7933.
- K Y Lee
- D Mooney
Lee, K. Y.; Mooney, D. Chem Rev 2002, 101, 1869.
- A Seeboth
- J Schneider
- A Patzak
Seeboth, A.; Schneider, J.; Patzak, A. Sol Energy Mater Sol Cells
2000, 60, 263.
- M Watanabe
- T Akahoshi
- Y Tabata
- D Nakayama
Watanabe, M.; Akahoshi, T.; Tabata, Y.; Nakayama, D. J Am
Chem Soc 1998, 120, 5577.
- S Novick
- J Dordick
Novick, S.; Dordick, J. Chem Mater 1998, 10, 955.
- G Fiksman
- P Datta
- J Oton
- I Matias
- M Lopez-Amo
- F Monte
Fiksman, G.; Datta, P.; Oton, J.; Matias, I.; Lopez-Amo, M.;
Monte, F.; Levy, D. Opt Eng 1997, 36, 1766.
- J Weissman
- H Sunkara
- A Tse
- S Asher
Weissman, J.; Sunkara, H.; Tse, A.; Asher, S. Science 1996, 274,
959.
- S Bhattackarya
- S N G Acharya
Bhattackarya, S.; Acharya, S. N. G. Chem Mater 1999, 11, 3504.
- H Zhibing
- Z Xiaomin
- L Yong
Zhibing, H.; Xiaomin, Z.; Yong, L. Science 1995, 269, 525.
- E Pezron
- A Leibler
- A Ricard
Pezron, E.; Leibler, A.; Ricard, A.; Audebert, R. Macromolecules
1988, 21, 1126.
- Seeboth