Preparation and properties of thin films of photocrosslinkable hydrophilic polymers

Ivanova, Irina G; Kuckling, Dirk; Adler, Hans-Jürgen P.; Wolff, Thomas; Arndt, Karl‐Friedrich

doi:10.1163/156855500750206302

Cited by 9 publications

(9 citation statements)

References 36 publications

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“…The characteristics of responsive polymers and hydrogels have been studied extensively for applications such as chemomechanical actuators, drug delivery, and separation systems, − and a wide range of techniques have been used to make films, membranes, and responsive surfaces from these materials. − The resulting surfaces can change their contact angle, affinity for different compounds in chromatographic separations, and adhesion 14,15 and frictional properties 16 in response to an external stimulus. One of the most intensively studied polymers in this field is poly( N -isopropylacrylamide) (PNIPAAm), which exhibits a temperature-induced collapse from an extended coil to a globular structure in water upon heating above 32 °C .…”

Section: Introductionmentioning

confidence: 99%

Photo-Cross-Linkable PNIPAAm Copolymers. 4. Effects of Copolymerization and Cross-Linking on the Volume-Phase Transition in Constrained Hydrogel Layers

et al. 2003

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Photo-cross-linkable temperature and pH-responsive polymers based on N-isopropylacrylamide and 2-(dimethylmaleimido)-N-ethyl-acrylamide were synthesized and spin-coated to produce uniform thin films of cross-linked, responsive hydrogels. Surface plasmon resonance and optical waveguide spectroscopy were used to determine the effect on the volume-phase transition when these materials are confined to a thin film. The film thicknesses ranged from 10 nm to 2.5 μm, and the volume-phase transition temperature and swelling ratio of the films fell into two overlapping regimes separated by at least one critical thickness. In the thick-film regime, greater than 100−760 nm, depending on the cross-linking density, ionizable comonomer concentration, and reference state, the films exhibited two transition temperatures. This can be explained by the stress imposed on the hydrogel as it swells perpendicular to the substrate. In the thin-film regime, less than 270−440 nm, depending on cross-linking density, the presence of a fixed substrate also limited the collapse of the gel at temperatures above the volume-phase transition temperature. Nonequilibrium chain conformations resulting from the spin-coating process may explain this effect. Two different mechanisms for constraint are likely in the thin- and thick-film regimes, and existing models for the anisotropic swelling of hydrogel layers were used to explain these trends. The spin-coated hydrogel layers were also compared to dip-coated and free-radical polymerized hydrogel layers to provide additional insight to the constraint mechanism. The elastic modulus of the hydrogel layers was measured with atomic force microcopy. The modulus in the swollen state was a function of both the cross-linking density and the ionizable comonomer concentration and ranged from 4.48 to 26.6 kPa. The modulus in the collapsed state was primarily a function of the cross-linking density and ranged from 466 to 1540 kPa. The effect of the ionizable comonomer concentration on the modulus also suggests the presence of non-Gaussian chain conformations in the swollen network.

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Section: Introductionmentioning

confidence: 99%

Photo-Cross-Linkable PNIPAAm Copolymers. 4. Effects of Copolymerization and Cross-Linking on the Volume-Phase Transition in Constrained Hydrogel Layers

et al. 2003

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“…Temperature-responsive polymers and gels have gained great scientific and technological importance, and the characteristics of these materials have been studied extensively for applications such as drug delivery and separation systems. [1][2][3][4][5] Numerous techniques have been used to make films, membranes, and responsive surfaces from these materials, [6][7][8][9][10][11] and their application as chemomechanical actuators has also been proposed. 2 One of the most intensively studied polymers in this field is poly(N-isopropylacrylamide) (PNIPAAm), which exhibits a sharp phase transition in water upon heating above 32 °C.…”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

“…To reduce the response time to a usable level, it is therefore necessary to reduce the gel size dramatically. Our ultimate goal is to use these materials in microsystems (e.g., microactuators) in which the gel sizes are reduced to the micrometer range. ,, Despite recent advances in the photo-cross-linking of hydrophilic polymers, there have been few previous reports on the preparation of smart gels of this size. − To compare the kinetics of the volume phase transition and equilibrium swelling behavior of hydrogels over a wide range of length scales, the swelling ratio, defined as the ratio of the water-swollen film thickness to that in the dry state, and the transition temperature ( T c ) under various conditions are usually the parameters of interest.…”

Section: Introductionmentioning

confidence: 99%

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Photo-Cross-Linkable PNIPAAm Copolymers. 2. Effects of Constraint on Temperature and pH-Responsive Hydrogel Layers

2002

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Photo-cross-linkable co- and terpolymers of N-isopropylacrylamide, 2-(dimethylmaleimido)-N-ethyl-acrylamide as the photosensitive component, and 3-acryloylaminopropionic acid or N-(2-(dimethylamino)ethyl)acrylamide as ionizable comonomers were prepared by free radical polymerization. Aqueous solutions of the linear un-cross-linked co- and terpolymers showed lower critical solution temperature behavior. The phase transition temperature, which was detected by differential scanning calorimetry, ranged from 23.1 to 39.2 °C depending on the pH of the solution and the composition of the polymer. Surface plasmon resonance and optical waveguide spectroscopy were used to obtain information about the swelling behavior of hydrogel films of the photo-cross-linked polymers, giving a measurement of film thickness and refractive index. The transition temperatures of the cross-linked polymer gels showed similar trends to those of the corresponding linear polymers in solution, and the gels were shown to be both temperature- and pH-responsive, with the transition temperature ranging from 25.3 to 44.9 °C for films having a 200 nm dry film thickness. However, the swelling behavior of the cross-linked gels was found to vary as a function of dry film thickness, and three samples were selected for a more detailed study of how film thickness affects the transition temperature and swelling ratio of hydrogel films. Dry film thicknesses ranged from 9 nm to 2.3 μm, and the swelling behavior of the films fell into two distinct regimes separated by a critical thickness, which ranged from 280 to 500 nm. In the thin-film regime, the transition temperature of the films was independent of film thickness, but the refractive index of the films in the collapsed state decreased as film thickness decreased, indicating that these films are not able to fully collapse. In the thick-film regime, the swelling ratio of the films was independent of film thickness, but the transition temperature decreased as much as 2.6 °C as the film thickness increased. This was explained by the constraint imposed on the film by the presence of a fixed substrate, with the length scale of this constraint related to the critical thickness. In these films, the ionizable comonomers were found to have little effect on the swelling ratio, which is determined primarily by cross-linking density in the swollen state and by film thickness in the collapsed state.

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“…Another photochemical approach is based on the UV irradiation of photoresponsive polyBrought to you by | University of Georgia Libraries Authenticated Download Date | 5/30/15 2:56 PM mers. In order to pattern the smart gel NIPAAm co-and terpolymers containing photocross-linkable groups has been developed [13][14][15][16][17]. Incorporation of azobenzene and spyrobenzopyran moieties into the macromolecules will lead to photoresponsive polymers.…”

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Application of Photochemistry in Synthesis of Smart Nanocomposite Hydrogels

Arndt¹,

Ferse²,

Oelsner³

2014

Zeitschrift Für Physikalische Chemie

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Hydrogels are cross-linked, water-soluble polymers which are swollen in water or in aqueous solution. Some of these hydrogels (smart hydrogels) show a drastic change of their properties, particularly the degree of swelling and the modulus, in dependence on the properties (temperature, pH, ionic strength, and composition) of the swelling agent. The application of smart gels requires a defined and fast swell kinetic. Therefore, there is an interest in the synthesis of thin patterned films with good mechanical performance. Photolithography is a powerful method to synthesize films and pattern in the μm-range. Nanocomposite (NC) hydrogels exhibit excellent mechanical properties, even in the swollen state. The photochemical reaction may be stopped easily by switching off the light source. This allows characterizing the structure of molecules formed during the reaction. On example of synthesis of nanocomposite hydrogels the monitoring of photochemical induced network formation by dynamic light scattering is demonstrated. Application relevant properties of NC-gels and the phase diagram are reported. Gels were patterned by UV irradiation through a mask. The patterning process is visualized by FT-IR imaging.

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Preparation and properties of thin films of photocrosslinkable hydrophilic polymers

Cited by 9 publications

References 36 publications

Photo-Cross-Linkable PNIPAAm Copolymers. 4. Effects of Copolymerization and Cross-Linking on the Volume-Phase Transition in Constrained Hydrogel Layers

Photo-Cross-Linkable PNIPAAm Copolymers. 4. Effects of Copolymerization and Cross-Linking on the Volume-Phase Transition in Constrained Hydrogel Layers

Photo-Cross-Linkable PNIPAAm Copolymers. 2. Effects of Constraint on Temperature and pH-Responsive Hydrogel Layers

Application of Photochemistry in Synthesis of Smart Nanocomposite Hydrogels

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