Temperature-Sensitive Surfaces Prepared by UV Photografting Reaction of Photosensitizer and N-Isopropylacrylamide

Abstract

A thermal-sensitive surface was prepared on the surface of a silicone wafer (substrate) by an ultraviolet photografting reaction between a photosensitizer, (N,N′-diethylamino)dithiocarbamoylpropyl(trimethoxy)silane, and N-isopropylacrylamide. Ellipsometery measurement revealed a thin grafting layer (∼44 Å) consisting of a single terminal poly(N-isopropylacrylamide) (PNIPAAm) chain on the surface of the silicone wafers. X-ray photoelectron spectroscopy confirmed that the grafting layer was composed of the PNIPAAm structure. The properties of the grafting layer can be adjusted and manipulated by varying the photopolymerization time and the concentration of the monomer. Increasing the photopolymerization time and the concentration of the monomer increases both the thickness of the grafting layer and the wettability of the surface. The characteristics of the temperature-sensitive surface were investigated by dynamic contact angle as a function of temperature. The remarkable change on advancing contact angle can be observed around 32 °C. Compared with the substrate grafted by PNIPAAm gel, the substrate with a signal-terminal PNIPAAm chain exhibited a lower transition temperature and a narrower change range of transition temperature. This can be attributed to the mobile PNIPAAm chain with a single-terminal mode, which increases the characteristics of faster response to the temperature change.

Temperature-dependent intermolecular force measurement of poly(N-isopropylacrylamide) grafted surface with protein

“…The temperature dependence of the adsorption of biomolecules onto the PNiPAM surface can largely be explained by the fact that the interfacial free energies of the PNiPAM surface in water change as a result of the phase transition [7][8][9][10][11][19][20][21]. However, the PNiPAM chain undergoes changes not only in its chemical nature (properties of the interface with water) but also in its physical properties (from a coil to a globule) during the phase transition [1,2].…”

“…It is known that the phase transition of the PNiPAM aqueous solution accompanies not only a drastic conformation change (from a coil to a globule) [1,2], but also a rapid change in interfacial properties [6][7][8][9][10]. This phenomenon makes this polymer useful in drug delivery systems [11], tissue engineering [12,13], and in many other areas [14][15][16].…”

“…Recently, there have been many reports on the grafting of PNiPAM onto solid substrates for both scientific and engineering purposes [5][6][7][8][9][10]12,13,[16][17][18][19][20][21]. These reports include studies of changes in the interfacial properties of the PNi-PAM chain during the phase transition [5][6][7][8][9][10], changes in the structure of PNiPAM during the phase transition [18], and adsorption of biomolecules onto PNiPAM below and above the LCST [12,13,[19][20][21].…”

“…These reports include studies of changes in the interfacial properties of the PNi-PAM chain during the phase transition [5][6][7][8][9][10], changes in the structure of PNiPAM during the phase transition [18], and adsorption of biomolecules onto PNiPAM below and above the LCST [12,13,[19][20][21]. However, the changes in the intermolecular force between biomolecules and PNiPAM chains during the phase transition have not received as much attention.…”

Temperature dependent activity and structure of adsorbed proteins on plasma polymerized N-isopropyl acrylamide

“…In an aqueous environment, pNIPAM is capable of transition between collapsed and swollen state depending on the solution temperature. When it is immobilized on a substrate, the chain conformational change leads to transitions in surface wettability 9,10 and chemistry. 11 Since both factors affect protein behavior on a surface, [12][13][14] it is expected that the amount of adsorbed proteins as well as the affinity, activity and conformation/orientation of the adsorbed protein layer will vary as the polymer is cycled through its lower critical solution temperature ͑LCST͒.…”